Novel flying machines
Dr. Slack, Fri May 02 2014, 08:10AMI've been following Patrick's anguish over duration for hovering machines, and the fact that it seems it's difficult to break the laws of physics. Short of Tony Stark's mobile-phone-sized fusion reactor (or whatever it was), it seems it's not going to change radically any time soon.
I did have this idea,
which I now realise has two fatal balance flaws as drawn, and while the centre of mass one can be fixed, the centre of lift one cannot. The idea was to have longer, more efficient wings counter-rotating in the hover, and a more conventional fixed-wing configuration for getting to and from the loiter site, both of which should contribute to better fuel economy. It turns out that this is too far out of the box to work. But, it might stimulate others to new ideas.
This is one I posted a long while ago, in a similar effort
It's a quad with a wing in the middle. It doesn't improve the hover at all, but for getting to and from the working site, it can rotate to fly more conventionally. As the quad rotors can now provide all the pitch, yaw and roll required, the wing can be rigid. As drawn, the very short wing won't be very efficient, however any improvement might be worth having. A longer wing would compromise gust stability further.
Energy storage and energy conversion is key. Kjoules per kg - batteries are rubbish, hydrogen in tanks is rubbish, hydrocarbon fuel in a light tank is brilliant. Fuel cells are very expensive, generator/electric motors are heavy, so is it possible just to use a petrol engined fan, and tame its performance without the mechanical complexty of a helicopter?
What about these two ideas? A weedwhacker motor drives a simple prop, to generate nominally all of the downforce. In the first idea, the two downwards facing fans basically support their own weight, and provide fast pitch and roll control as a quad copter would. They both rotate opposite to the main fan, to provide some of the counter rotation, the bulk of which is supplied by the sideways blowing fan.
In the second idea, only two fans are used for control, with vectored thrust.
The second might be slightly lighter, but the first would be simpler mechanically.
The IC engine speed is servoed for vertical speed and position, which might result in fairly crude vertical stability. For a surveillance platform with downwards or slant facing cameras, this would probably not matter. If the number of control fans increased to 4 in a quad arrangement, then fine control is available vertically as well, and it's basically a small quad with a big fan in the middle.
Control power could be from batteries, which would be simpler initially, or from a small generator, which would allow the whole vehicle to be refuelled in seconds. A smaller generator with high C LiFePo4s for handling bursts may be a useful hybrid. The electrical consumption ought to be a tiny fraction of the consumption of a similar weight all electric vehicle.
So, what duration could you get from a gas driven fan?
The challenge is to come up with something that stands a chance of having the manouvrability of a multi-rotor, without the mechanical complexity of a helicopter, and a duration of an hour or more
Re: Novel flying machines
Ash Small, Fri May 02 2014, 09:27AM
Ok, I'll throw one in too. It's not really novel, it uses technology that's over a century old, but if the trend is towards hydrogen power, why not store the hydrogen as a gas, and use it for lift?
This gets you airborne without using any power. You can carry additional fuel, either as compressed H2, or whatever is convenient. As you use up the 'heavier than air' fuel/batteries/whatever, you can also burn H2 from the 'envelope' to maintain height, etc. You could even have an 'on board' H2 powered compressor for reducing lift when landing.
Only disadvantages are size and not too good in high winds. (and possible risk of fire).
Ash Small, Fri May 02 2014, 09:27AM
Ok, I'll throw one in too. It's not really novel, it uses technology that's over a century old, but if the trend is towards hydrogen power, why not store the hydrogen as a gas, and use it for lift?
This gets you airborne without using any power. You can carry additional fuel, either as compressed H2, or whatever is convenient. As you use up the 'heavier than air' fuel/batteries/whatever, you can also burn H2 from the 'envelope' to maintain height, etc. You could even have an 'on board' H2 powered compressor for reducing lift when landing.
Only disadvantages are size and not too good in high winds. (and possible risk of fire).
Re: Novel flying machines
BigBad, Fri May 02 2014, 03:43PM
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
BigBad, Fri May 02 2014, 03:43PM
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
Re: Novel flying machines
Patrick, Fri May 02 2014, 05:15PM
yep fusion reactor, thats what i need, should have sobered up and thought of this first.
Patrick, Fri May 02 2014, 05:15PM
yep fusion reactor, thats what i need, should have sobered up and thought of this first.
Re: Novel flying machines
Dr. Slack, Fri May 02 2014, 07:55PM
well I figure long blades have less induced drag, so helis ought to beat multirotors for efficiency, so why are there so many of the latter about? Is it just the cool factor, or is it that you can replace all that nasty mechanics at the heli hub with a microcontroller and multiple purchased fans? So taking the enterprise from the professional to the amateur space?
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
Dr. Slack, Fri May 02 2014, 07:55PM
BigBad wrote ...
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
well I figure long blades have less induced drag, so helis ought to beat multirotors for efficiency, so why are there so many of the latter about? Is it just the cool factor, or is it that you can replace all that nasty mechanics at the heli hub with a microcontroller and multiple purchased fans? So taking the enterprise from the professional to the amateur space?
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
Re: Novel flying machines
BigBad, Fri May 02 2014, 09:17PM
I think the quad/single doesn't make a huge difference to a first approximation, it's mostly the disc loading that matters.
There might be some Reynolds number thing, but mostly you just want a large total disc area and a nice even downdraft speed through the rotors.
The second order stuff is a different story though; you have to worry about the tip vortexes; there's going to be recirculation around the outside of the vehicle; I'm thinking a single rotor can be designed to better to control those kinds of losses, although ducting the fans might help a lot, but this adds mass.
BigBad, Fri May 02 2014, 09:17PM
I think the quad/single doesn't make a huge difference to a first approximation, it's mostly the disc loading that matters.
There might be some Reynolds number thing, but mostly you just want a large total disc area and a nice even downdraft speed through the rotors.
The second order stuff is a different story though; you have to worry about the tip vortexes; there's going to be recirculation around the outside of the vehicle; I'm thinking a single rotor can be designed to better to control those kinds of losses, although ducting the fans might help a lot, but this adds mass.
Re: Novel flying machines
Ash Small, Fri May 02 2014, 09:23PM
Well, the larger the prop, the more efficient it is, the trade-off is increased mass, although a slower turning prop may have a thinner section if less forces are involved, etc.....
Ash Small, Fri May 02 2014, 09:23PM
Dr. Slack wrote ...
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
Well, the larger the prop, the more efficient it is, the trade-off is increased mass, although a slower turning prop may have a thinner section if less forces are involved, etc.....
Re: Novel flying machines
Patrick, Fri May 02 2014, 10:05PM
Ive been reading and re-reading the above comments and previous threads.
first there are those on kickstarter persuing the wing with quad idea, and that idea may work well. The real advantage it has is the forward speed allows greater distance covered hence area possibly within reach goes up as the area of a circle.
next weed-whacker/chainsaws are disasters to mod for this purpose, the evolution 0.91NX
is nearly 2hp for 180$ and 1lb, (better than a fuel cell in cost, mass and output) there is an ace helicopter RC pilot who's already got a quad with a single engine driving variable pitch props by belts.
As per previous comments, yes the multrotor reduces the cost of the same capable helo. those RC helos have enormously complicated parts, many of them, and all precision machined, as soon as you crash you obliterate 2000$ of a 3000$ machine. So avoiding the little expensive parts is the real attraction to multirotors. but we seem to eat the loss when compared to disc loading.
i may be outsmarting myself witht the power source, perhaps the prop s what should be looking at. the convetional props for multirotors look like minor-ly modified fixed wing props for forward high speed flight. as sulaiman and others have said, perhaps a wide chord, undercambered prop would do better using the power i do have on the machine.
as for electric flight time of 1+ hour, BigBad. ive researched these thoruoghly, there basically 10% machine, 90% lithium ion. which at shallow draw rates appear more dense than Li-poly battereis, i think. but need long duration, with a useful instrument payload.
so theres the balance... total mass of machine, power source/density onboard, and how power is coupled to the air....right?
im planning a differnt propeller, given my skill with composites. a three blade, undercambered, wide chord, hopefully not lethal eperimental prop. then graph against conventional props.
pics of the AR drone version 1.0 (commercial product)
the above pics show a radical deviation from common mulltirotor and fixed wing props.
note the wide chord toward the hub/root, as Sulaiman advocates for, note the extreme undercamber too.
Patrick, Fri May 02 2014, 10:05PM
Ive been reading and re-reading the above comments and previous threads.
first there are those on kickstarter persuing the wing with quad idea, and that idea may work well. The real advantage it has is the forward speed allows greater distance covered hence area possibly within reach goes up as the area of a circle.
next weed-whacker/chainsaws are disasters to mod for this purpose, the evolution 0.91NX
is nearly 2hp for 180$ and 1lb, (better than a fuel cell in cost, mass and output) there is an ace helicopter RC pilot who's already got a quad with a single engine driving variable pitch props by belts. As per previous comments, yes the multrotor reduces the cost of the same capable helo. those RC helos have enormously complicated parts, many of them, and all precision machined, as soon as you crash you obliterate 2000$ of a 3000$ machine. So avoiding the little expensive parts is the real attraction to multirotors. but we seem to eat the loss when compared to disc loading.
i may be outsmarting myself witht the power source, perhaps the prop s what should be looking at. the convetional props for multirotors look like minor-ly modified fixed wing props for forward high speed flight. as sulaiman and others have said, perhaps a wide chord, undercambered prop would do better using the power i do have on the machine.
as for electric flight time of 1+ hour, BigBad. ive researched these thoruoghly, there basically 10% machine, 90% lithium ion. which at shallow draw rates appear more dense than Li-poly battereis, i think. but need long duration, with a useful instrument payload.
so theres the balance... total mass of machine, power source/density onboard, and how power is coupled to the air....right?
im planning a differnt propeller, given my skill with composites. a three blade, undercambered, wide chord, hopefully not lethal eperimental prop. then graph against conventional props.
pics of the AR drone version 1.0 (commercial product)
the above pics show a radical deviation from common mulltirotor and fixed wing props.
note the wide chord toward the hub/root, as Sulaiman advocates for, note the extreme undercamber too.
Re: Novel flying machines
Ash Small, Sat May 03 2014, 12:38PM
I think Patrick's assymetrical tri-copter is the simplest alternative to the 'swash plate' used in conventional helicopters.
Fewer blades will always be more efficient.
There comes a point, due to increased payload or range requirements where IC engines do become more efficient than batteries as the mass of fuel compared to mass of battery pack predominates, although, as Patrick has demonstrated, the weight of ancillaries is greater for IC engines (tank, but the maths improve as size increases) IC engine compared to electric motor, etc.
As I suggested in the other thread, without inputting all of these parameters into a graph it's difficult to say precisely where this transition occurs. You first need to define payload and range (flight time), and then work from there.
Ash Small, Sat May 03 2014, 12:38PM
Dr. Slack wrote ...
well I figure long blades have less induced drag, so helis ought to beat multirotors for efficiency, so why are there so many of the latter about? Is it just the cool factor, or is it that you can replace all that nasty mechanics at the heli hub with a microcontroller and multiple purchased fans? So taking the enterprise from the professional to the amateur space?
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
BigBad wrote ...
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
I'm not quite sure why this is such a big issue; the world record for conventional electric helicopters is over an hour using lithium ion batteries.
well I figure long blades have less induced drag, so helis ought to beat multirotors for efficiency, so why are there so many of the latter about? Is it just the cool factor, or is it that you can replace all that nasty mechanics at the heli hub with a microcontroller and multiple purchased fans? So taking the enterprise from the professional to the amateur space?
So would a heli-sized top fan without any mechanics (for amateur simplicity) coupled with 2 or 3 stabilising fans on booms like I've drawn above achieve a big improvement in mission time?
I think Patrick's assymetrical tri-copter is the simplest alternative to the 'swash plate' used in conventional helicopters.
Fewer blades will always be more efficient.
There comes a point, due to increased payload or range requirements where IC engines do become more efficient than batteries as the mass of fuel compared to mass of battery pack predominates, although, as Patrick has demonstrated, the weight of ancillaries is greater for IC engines (tank, but the maths improve as size increases) IC engine compared to electric motor, etc.
As I suggested in the other thread, without inputting all of these parameters into a graph it's difficult to say precisely where this transition occurs. You first need to define payload and range (flight time), and then work from there.
Re: Novel flying machines
Patrick, Sat May 03 2014, 05:01PM
Yep agree, but graphs are only as good as there input data, so that's the real hand up.
I am in a furious re-build of my thrust stand, to get that data. And conduct comparative testing. While I normally fly with 511g of battery, I'll probably drop that to 200g lipo, plus the IC engine 500g, plus minor tankage.
Many of the ultra light and micro heli's and multis have gears to slow the prop. I presume there matching the motors best speed and toque band to power usage for the force needed in a static hover?
Yet the larger drones don't seem to do this.
As previously stated, the swash plate is the real boogie man that comes for engineers in the night. Curtis Youngblood uses belts on his IC quad, and the tail rotor from a large heli. So he holds constant rpm on the IC, then varies the pitch, but has no real swash plate, to separate roll and pitch from a single rotor, as it's not needed.
Propeller link :
Patrick, Sat May 03 2014, 05:01PM
Yep agree, but graphs are only as good as there input data, so that's the real hand up.
I am in a furious re-build of my thrust stand, to get that data. And conduct comparative testing. While I normally fly with 511g of battery, I'll probably drop that to 200g lipo, plus the IC engine 500g, plus minor tankage.
Many of the ultra light and micro heli's and multis have gears to slow the prop. I presume there matching the motors best speed and toque band to power usage for the force needed in a static hover?
Yet the larger drones don't seem to do this.
As previously stated, the swash plate is the real boogie man that comes for engineers in the night. Curtis Youngblood uses belts on his IC quad, and the tail rotor from a large heli. So he holds constant rpm on the IC, then varies the pitch, but has no real swash plate, to separate roll and pitch from a single rotor, as it's not needed.
Propeller link :
Re: Novel flying machines
Conundrum, Sat May 03 2014, 06:42PM
Are we allowed to mention LENR on here, given that NASA have had verifiable positive results with the terahertz driven nickel lattice?
Albeit very low (3* heat gain) and needing hundreds of Watts input as both heat and THz radiation generated by a highly inefficient third harmonic process.
EDIT:- Also adding idea about using a hybrid of supercapacitor and low rate Li-Po as these can handle much more power.
Slow charge the supercap via Li-Pos and discharge through a feedback driven ZVS into the motor to ensure constant current
and have an array of these charging and discharging to allow constant motor drive.
-A
Conundrum, Sat May 03 2014, 06:42PM
Are we allowed to mention LENR on here, given that NASA have had verifiable positive results with the terahertz driven nickel lattice?
Albeit very low (3* heat gain) and needing hundreds of Watts input as both heat and THz radiation generated by a highly inefficient third harmonic process.
EDIT:- Also adding idea about using a hybrid of supercapacitor and low rate Li-Po as these can handle much more power.
Slow charge the supercap via Li-Pos and discharge through a feedback driven ZVS into the motor to ensure constant current
and have an array of these charging and discharging to allow constant motor drive.
-A
Re: Novel flying machines
Patrick, Sat May 03 2014, 07:33PM
Note : the evolution .91nx is 570g. 1400 watts/2Hp extract-able power.
But that fuel cell still ticks me off, with all there dam graphs , showing it better than lipo.
Patrick, Sat May 03 2014, 07:33PM
Conundrum wrote ...
Are we allowed to mention LENR on here, given that NASA have had verifiable positive results with the terahertz driven nickel lattice?
Albeit very low (3* heat gain) and needing hundreds of Watts input as both heat and THz radiation generated by a highly inefficient third harmonic process.
EDIT:- Also adding idea about using a hybrid of supercapacitor and low rate Li-Po as these can handle much more power.
Slow charge the supercap via Li-Pos and discharge through a feedback driven ZVS into the motor to ensure constant current
and have an array of these charging and discharging to allow constant motor drive.
-A
it would all have to fit on a 1.5kg machine, with those parts adding 500g or less, (2kg AUW). Otherwise I think IC engines win.Are we allowed to mention LENR on here, given that NASA have had verifiable positive results with the terahertz driven nickel lattice?
Albeit very low (3* heat gain) and needing hundreds of Watts input as both heat and THz radiation generated by a highly inefficient third harmonic process.
EDIT:- Also adding idea about using a hybrid of supercapacitor and low rate Li-Po as these can handle much more power.
Slow charge the supercap via Li-Pos and discharge through a feedback driven ZVS into the motor to ensure constant current
and have an array of these charging and discharging to allow constant motor drive.
-A
Note : the evolution .91nx is 570g. 1400 watts/2Hp extract-able power.
But that fuel cell still ticks me off, with all there dam graphs , showing it better than lipo.
Re: Novel flying machines
Conundrum, Sat May 03 2014, 08:50PM
I always wondered why fuel cells are so inefficient, do they recombine non electrically like LEDs?
ie produce heat instead of EMF?
It occurs to me that if I was to scratch build an ultra lightweight SOFC and run it at pulsed high temperature, for the short times it was cooling down the efficiency gain would offset the thermal cycling effects.
Conundrum, Sat May 03 2014, 08:50PM
I always wondered why fuel cells are so inefficient, do they recombine non electrically like LEDs?
ie produce heat instead of EMF?
It occurs to me that if I was to scratch build an ultra lightweight SOFC and run it at pulsed high temperature, for the short times it was cooling down the efficiency gain would offset the thermal cycling effects.
Re: Novel flying machines
Ash Small, Sat May 03 2014, 08:53PM
As previously mentioned, a larger, slower turning prop is 'always' more efficient, so decide on maximum permissible diameter, and work from there.
I think you only need two servo's to drive a swash plate. I'll try and find time to sketch something.
Ash Small, Sat May 03 2014, 08:53PM
As previously mentioned, a larger, slower turning prop is 'always' more efficient, so decide on maximum permissible diameter, and work from there.
I think you only need two servo's to drive a swash plate. I'll try and find time to sketch something.
Re: Novel flying machines
Patrick, Sat May 03 2014, 08:57PM
10 to 12 inches seems to be the max rotating diameter for a practical machine you can get in and out of a car. This is why a tend to favor 3 blades over 2.
Patrick, Sat May 03 2014, 08:57PM
Conundrum wrote ...
I always wondered why fuel cells are so inefficient, do they recombine non electrically like LEDs?
ie produce heat instead of EMF?
It occurs to me that if I was to scratch build an ultra lightweight SOFC and run it at pulsed high temperature, for the short times it was cooling down the efficiency gain would offset the thermal cycling effects.
Not sure if pulsing is the solution, but in 10 to 20 years PEMs will be useless in high power applications. Rendered obsolete by Chinese domination of precious and rare-earth metals, SOFC however have been and will continue to improve faster then the PEMs.I always wondered why fuel cells are so inefficient, do they recombine non electrically like LEDs?
ie produce heat instead of EMF?
It occurs to me that if I was to scratch build an ultra lightweight SOFC and run it at pulsed high temperature, for the short times it was cooling down the efficiency gain would offset the thermal cycling effects.
10 to 12 inches seems to be the max rotating diameter for a practical machine you can get in and out of a car. This is why a tend to favor 3 blades over 2.
Re: Novel flying machines
Carbon_Rod, Sun May 04 2014, 01:47AM
@Ash Small
In theory the fuel is quite viable:
@Conundrum
Solid chemical fuel cells have been used in military equipment for decades, as in their inert form have a practically indefinite shelf life. There were civilian transport applications proposed, but were unsuccessful for numerous reasons.
@BigBad
However, FAA regulations limit electric motor driven craft to under 6kW IIRC, but Policy 8130(H) may simply make them illegal altogether. Private UAVs must now be under 26 lbs due to federal laws.
The air cooled 2 cycle gas powered engines are usually illegal to fly in municipal areas.
However, these have the added benefit of getting lighter as the fuel is consumed.
Carbon_Rod, Sun May 04 2014, 01:47AM
@Ash Small
In theory the fuel is quite viable:
@Conundrum
Solid chemical fuel cells have been used in military equipment for decades, as in their inert form have a practically indefinite shelf life. There were civilian transport applications proposed, but were unsuccessful for numerous reasons.
@BigBad
However, FAA regulations limit electric motor driven craft to under 6kW IIRC, but Policy 8130(H) may simply make them illegal altogether. Private UAVs must now be under 26 lbs due to federal laws.
The air cooled 2 cycle gas powered engines are usually illegal to fly in municipal areas.
However, these have the added benefit of getting lighter as the fuel is consumed.
Re: Novel flying machines
Patrick, Sun May 04 2014, 04:11AM
i need about 100g of Russian plutonium to dangle 600 feet above my town. customs need not be alerted as Im a college student. The FBI need not be worried, im trust worthy.
once you have a fission or fusion reactor light enough to fly, propulsion efficiency really turns into a trivial matter.
(maybe i just need an RTG.) mental note: rob NASA at next inter-planetary launch opportunity.
More prop pics...
AR Drone V1
AR Drone V1
Conventional propellers
pics
note the curve.
note the curvature and width
light electric heli blades.
Patrick, Sun May 04 2014, 04:11AM
i need about 100g of Russian plutonium to dangle 600 feet above my town. customs need not be alerted as Im a college student. The FBI need not be worried, im trust worthy.
once you have a fission or fusion reactor light enough to fly, propulsion efficiency really turns into a trivial matter.
(maybe i just need an RTG.) mental note: rob NASA at next inter-planetary launch opportunity.
More prop pics...
AR Drone V1
AR Drone V1
Conventional propellers
pics
note the curve.
note the curvature and width
light electric heli blades.
Re: Novel flying machines
Dr. Slack, Sun May 04 2014, 06:06AM
Right, let's have somebody come up with some numbers here.
Go back to this machine. A 2-blade fixed-geometry gas power heli stabilised with small electric rotors.
Now, according to this website, a 30" long 2 blade prop 15" pitch will generate 13lbs lift at 2500rpm consuming < 1kW. It's obviously a very niave equation, as thrust is independent of pitch, and power directly proportional to, all the way down to zero pitch, which is wrong. So I'm not expecting accuracy, just trying to find a reasonable ball-park by staying away from the extremes. A 2 blade can be turned to fit through a car door, a lower pitch should consume less power for similar thrust, and the power is significantly less than the max output of a 0.91, though it would need a drive belt to get its high rpm down to 2500. I spent max 3 minutes there, so didn't investigate more than a couple of combinations, but I feel I've at least got a handle on the sorts of things that might be possible.
Now the question, how fast does a 0.91 use fuel when generating 1.2kW. How long will it run on say 500g, or even 1kg of fuel for a 16% initial mass fraction? Searches for fuel consumption come up much leaner than searches for prop thrust, though they do hint that this is the right ballpark, and that there's a significant difference between 2 and 4 stroke.
Dr. Slack, Sun May 04 2014, 06:06AM
Right, let's have somebody come up with some numbers here.
Go back to this machine. A 2-blade fixed-geometry gas power heli stabilised with small electric rotors.
Now, according to this website
, a 30" long 2 blade prop 15" pitch will generate 13lbs lift at 2500rpm consuming < 1kW. It's obviously a very niave equation, as thrust is independent of pitch, and power directly proportional to, all the way down to zero pitch, which is wrong. So I'm not expecting accuracy, just trying to find a reasonable ball-park by staying away from the extremes. A 2 blade can be turned to fit through a car door, a lower pitch should consume less power for similar thrust, and the power is significantly less than the max output of a 0.91, though it would need a drive belt to get its high rpm down to 2500. I spent max 3 minutes there, so didn't investigate more than a couple of combinations, but I feel I've at least got a handle on the sorts of things that might be possible.Now the question, how fast does a 0.91 use fuel when generating 1.2kW. How long will it run on say 500g, or even 1kg of fuel for a 16% initial mass fraction? Searches for fuel consumption come up much leaner than searches for prop thrust, though they do hint that this is the right ballpark, and that there's a significant difference between 2 and 4 stroke.
Re: Novel flying machines
Conundrum, Sun May 04 2014, 06:41AM
Interesting re. SOFCs.
Probably a stupid question, but could lasers be used to superheat something like a SOFC to avoid the need for a continuous heat source?
Also feasible, using lasers to do direct conversion ie internal combustion but using this method means novel engine designs can be used without needing to design out troublesome knocking and other problems.
My colleagues at work being impressed with my knowledge of engines did express a little disbelief at my suggestion of making a rotary engine using multiple smaller 2 stroke engines kludged together
but in theory a Wankel engine like arrangement if mechanically stable could work even though the combustion chambers are not directly linked.
Many of the small engines used in lawnmowers and hedge trimmers are basically identical and often they are discarded for reasons such as non terminal gearbox failure or some trivial electrical problem.
"As the rotor's apex seals pass over the spark plug hole, compressed charge can be lost from the charge chamber to the exhaust chamber, entailing fuel in the exhaust, reducing efficiency, and giving high emissions. This may be overcome by using laser ignition, eliminating traditional spark plugs, which may give a narrow slit in the motor housing the rotor apex seals can fully cover with no loss of compression from one chamber to another. The laser plug can fire its spark through the narrow slit. "
(wikipedia)
-A
Conundrum, Sun May 04 2014, 06:41AM
Interesting re. SOFCs.
Probably a stupid question, but could lasers be used to superheat something like a SOFC to avoid the need for a continuous heat source?
Also feasible, using lasers to do direct conversion ie internal combustion but using this method means novel engine designs can be used without needing to design out troublesome knocking and other problems.
My colleagues at work being impressed with my knowledge of engines did express a little disbelief at my suggestion of making a rotary engine using multiple smaller 2 stroke engines kludged together
but in theory a Wankel engine like arrangement if mechanically stable could work even though the combustion chambers are not directly linked.Many of the small engines used in lawnmowers and hedge trimmers are basically identical and often they are discarded for reasons such as non terminal gearbox failure or some trivial electrical problem.
"As the rotor's apex seals pass over the spark plug hole, compressed charge can be lost from the charge chamber to the exhaust chamber, entailing fuel in the exhaust, reducing efficiency, and giving high emissions. This may be overcome by using laser ignition, eliminating traditional spark plugs, which may give a narrow slit in the motor housing the rotor apex seals can fully cover with no loss of compression from one chamber to another. The laser plug can fire its spark through the narrow slit. "
(wikipedia)
-A
Re: Novel flying machines
Ash Small, Sun May 04 2014, 12:35PM
Well, it's a reasonable assumption, at least when looking for somewhere to start, that the IC engine is most efficient at the same RPM as maximum torque is produced (if looking for a ballpark).
Now, two strokes are generally less efficient, but four strokes are invariably heavier, and any lighter, tuned engine will be less efficient than a larger (read heavier) engine in a lower state of tune.
It's beginning to become clear why swash plates enabling variable pitch control are the favoured method of controlling thrust.
Ash Small, Sun May 04 2014, 12:35PM
Dr. Slack wrote ...
Now the question, how fast does a 0.91 use fuel when generating 1.2kW. How long will it run on say 500g, or even 1kg of fuel for a 16% initial mass fraction? Searches for fuel consumption come up much leaner than searches for prop thrust, though they do hint that this is the right ballpark, and that there's a significant difference between 2 and 4 stroke.
Now the question, how fast does a 0.91 use fuel when generating 1.2kW. How long will it run on say 500g, or even 1kg of fuel for a 16% initial mass fraction? Searches for fuel consumption come up much leaner than searches for prop thrust, though they do hint that this is the right ballpark, and that there's a significant difference between 2 and 4 stroke.
Well, it's a reasonable assumption, at least when looking for somewhere to start, that the IC engine is most efficient at the same RPM as maximum torque is produced (if looking for a ballpark).
Now, two strokes are generally less efficient, but four strokes are invariably heavier, and any lighter, tuned engine will be less efficient than a larger (read heavier) engine in a lower state of tune.
It's beginning to become clear why swash plates enabling variable pitch control are the favoured method of controlling thrust.
Re: Novel flying machines
Patrick, Sun May 04 2014, 04:09PM
Dr. Slack,
first, i menat to post this earlier the .91nx will produce 80% power for a little more than 1minute with 1 fl oz of nitro-alcohol.
Second, i do include ducts to break the tip vortex, and improve human safety. so turning the props isnt enough.
third, im getting my thrust stand up today or tomarrow so i can get us real numbers.
Patrick, Sun May 04 2014, 04:09PM
Dr. Slack,
first, i menat to post this earlier the .91nx will produce 80% power for a little more than 1minute with 1 fl oz of nitro-alcohol.
Second, i do include ducts to break the tip vortex, and improve human safety. so turning the props isnt enough.
third, im getting my thrust stand up today or tomarrow so i can get us real numbers.
Re: Novel flying machines
Carbon_Rod, Mon May 05 2014, 05:02AM
“Weed eater†2-cycle engines usually have a diaphragm carburetor.
And are therefore the easiest 1.3 hp motor you can buy used for under $50 that will work for flying.
Indeed, the drag losses from more rotors make them less efficient, but the lift is ultimately limited by the sectional area the blades cover. Thus 2 blades may generally improve flight times, but has the same limitation of the mass it can actually lift off the ground. Therefore a quad can lift slightly more than a tri-copter with the same diameter props, but a quad with 3 blade props will not necessarily improve lift depending on the machine.
Typically we also buy the plastic 1045/1045R (10â€x4.5†Props) in bulk, as they work well for inexpensive quads. Note, while a $2k 1.5kg ATJ-120Ti RC turbine can produce over 12kg thrust, it is not really useful for VTOL craft.
Carbon_Rod, Mon May 05 2014, 05:02AM
“Weed eater†2-cycle engines usually have a diaphragm carburetor.
And are therefore the easiest 1.3 hp motor you can buy used for under $50 that will work for flying.
Indeed, the drag losses from more rotors make them less efficient, but the lift is ultimately limited by the sectional area the blades cover. Thus 2 blades may generally improve flight times, but has the same limitation of the mass it can actually lift off the ground. Therefore a quad can lift slightly more than a tri-copter with the same diameter props, but a quad with 3 blade props will not necessarily improve lift depending on the machine.
Typically we also buy the plastic 1045/1045R (10â€x4.5†Props) in bulk, as they work well for inexpensive quads. Note, while a $2k 1.5kg ATJ-120Ti RC turbine can produce over 12kg thrust, it is not really useful for VTOL craft.
Re: Novel flying machines
Patrick, Mon May 05 2014, 05:12AM
but carbon rod, those engines are enormous blocks of milled aluminum...
yeah the RC turbines are expensive. Ive crashed electrics many times, but recovered almost everything of value but the airframe. with jet turbines in a crash you tend to have kerosene fires that destroy everything as circuit boards seem to burn well above 1200F. (crashing into the dirt at 220mph contributes to the destruction too.)
and as with fuel cells they are crap for VTOL.
PICS!
Patrick, Mon May 05 2014, 05:12AM
but carbon rod, those engines are enormous blocks of milled aluminum...
yeah the RC turbines are expensive. Ive crashed electrics many times, but recovered almost everything of value but the airframe. with jet turbines in a crash you tend to have kerosene fires that destroy everything as circuit boards seem to burn well above 1200F. (crashing into the dirt at 220mph contributes to the destruction too.)
and as with fuel cells they are crap for VTOL.
PICS!
Re: Novel flying machines
Dr. Slack, Mon May 05 2014, 05:51AM
ooh, ouch, an ounce a minute? That's 2kg and hour, give or take. Which is not the order-of-magnitude better than small electric props I had hoped.
But maybe, if you use a 4 stroke, and use less power through lower pitch heli blades rather than power through a known flaky propulsion blade calculator ...
I was kind of assuming not to use ducts, to just let it all hang out and look more like a copter. A 30" duct would weigh a lot. However, the difference between accidentally flying too close to an object and nudging it with a duct, and nudging it with the tip of a 30" diameter heli rotor, would be spectacular.
Dr. Slack, Mon May 05 2014, 05:51AM
Patrick wrote ...
first, i menat to post this earlier the .91nx will produce 80% power for a little more than 1minute with 1 fl oz of nitro-alcohol.
first, i menat to post this earlier the .91nx will produce 80% power for a little more than 1minute with 1 fl oz of nitro-alcohol.
ooh, ouch, an ounce a minute? That's 2kg and hour, give or take. Which is not the order-of-magnitude better than small electric props I had hoped.
But maybe, if you use a 4 stroke, and use less power through lower pitch heli blades rather than power through a known flaky propulsion blade calculator ...
I was kind of assuming not to use ducts, to just let it all hang out and look more like a copter. A 30" duct would weigh a lot. However, the difference between accidentally flying too close to an object and nudging it with a duct, and nudging it with the tip of a 30" diameter heli rotor, would be spectacular.
Re: Novel flying machines
Patrick, Mon May 05 2014, 05:57AM
i came up with 1.8kg per hour. not great, so im thinking the variable collective pitch tri-prop maybe the next step/
my most recent machine (Gen 3), destroyed in scientific action. watch at least the last 14 seconds.
Dr. Slack and others,
would finding an effcient "power band" of RPM and torque and holding constant RPM while torque and power out vary be useful? (for a specific motor and prop.) In so using a variable pitch propeller. most of the power i think we lose is from rapid acceleration/decelerations from the PID loops. (steve connor and i discussed conservation of momentum in a related thread.) it just seems like at the least id gain faster response, with less overshoot, if not more lift for the same size battery.
i say this, because commercial companies seem to put a lot of thought into the drive train, but we home tinker'ers seem to just randomly pick a motor, then randomly pick a prop and throw it in the air, hoping for the best.
i also think:
a first step is power storage or conversion. (battery or chemistry)
a second step is coupling so as to be useful. (drive train ending with a prop)
Patrick, Mon May 05 2014, 05:57AM
i came up with 1.8kg per hour. not great, so im thinking the variable collective pitch tri-prop maybe the next step/
Dr. Slack wrote ...
However, the difference between accidentally flying too close to an object and nudging it with a duct, and nudging it with the tip of a 30" diameter heli rotor, would be spectacular.
I watched the following machine descend into the tree and it tumbled and threw blades like you wouldnt believe. However, the difference between accidentally flying too close to an object and nudging it with a duct, and nudging it with the tip of a 30" diameter heli rotor, would be spectacular.
my most recent machine (Gen 3), destroyed in scientific action. watch at least the last 14 seconds.
Dr. Slack and others,
would finding an effcient "power band" of RPM and torque and holding constant RPM while torque and power out vary be useful? (for a specific motor and prop.) In so using a variable pitch propeller. most of the power i think we lose is from rapid acceleration/decelerations from the PID loops. (steve connor and i discussed conservation of momentum in a related thread.) it just seems like at the least id gain faster response, with less overshoot, if not more lift for the same size battery.
i say this, because commercial companies seem to put a lot of thought into the drive train, but we home tinker'ers seem to just randomly pick a motor, then randomly pick a prop and throw it in the air, hoping for the best.
i also think:
a first step is power storage or conversion. (battery or chemistry)
a second step is coupling so as to be useful. (drive train ending with a prop)
Re: Novel flying machines
BigBad, Mon May 05 2014, 01:09PM
It might be theoretically a good idea to do a hybrid; you drive the motor with an electric motor, which spins the main rotors at virtually constant speed, and then have a gas turbine which has more power than you need to fly, and then there's a small battery to buffer it.
So the gas turbine would turn on and charge the battery, and then shut down and the vehicle would fly on the battery for a while, and then turn back on again.
The reason it might make sense is that the energy density of the fuel is so much higher than a lithium ion battery, and provided the gas turbine/generator isn't too heavy it will still weigh less.
BigBad, Mon May 05 2014, 01:09PM
It might be theoretically a good idea to do a hybrid; you drive the motor with an electric motor, which spins the main rotors at virtually constant speed, and then have a gas turbine which has more power than you need to fly, and then there's a small battery to buffer it.
So the gas turbine would turn on and charge the battery, and then shut down and the vehicle would fly on the battery for a while, and then turn back on again.
The reason it might make sense is that the energy density of the fuel is so much higher than a lithium ion battery, and provided the gas turbine/generator isn't too heavy it will still weigh less.
Re: Novel flying machines
Patrick, Mon May 05 2014, 08:34PM
This is worth researching, but if it requires 34 mosfets and diodes, and adds 200g to a 2kg machine were still screwed.
Patrick, Mon May 05 2014, 08:34PM
BigBad wrote ...
It might be theoretically a good idea to do a hybrid; you drive the motor with an electric motor, which spins the main rotors at virtually constant speed, and then have a gas turbine which has more power than you need to fly, and then there's a small battery to buffer it.
So the gas turbine would turn on and charge the battery, and then shut down and the vehicle would fly on the battery for a while, and then turn back on again.
The reason it might make sense is that the energy density of the fuel is so much higher than a lithium ion battery, and provided the gas turbine/generator isn't too heavy it will still weigh less.
It might be theoretically a good idea to do a hybrid; you drive the motor with an electric motor, which spins the main rotors at virtually constant speed, and then have a gas turbine which has more power than you need to fly, and then there's a small battery to buffer it.
So the gas turbine would turn on and charge the battery, and then shut down and the vehicle would fly on the battery for a while, and then turn back on again.
The reason it might make sense is that the energy density of the fuel is so much higher than a lithium ion battery, and provided the gas turbine/generator isn't too heavy it will still weigh less.
This is worth researching, but if it requires 34 mosfets and diodes, and adds 200g to a 2kg machine were still screwed.
Re: Novel flying machines
BigBad, Tue May 06 2014, 12:00PM
It's theoretically good, but I don't think it works nearly as well in practice. Gas turbines don't scale down very well, they lose efficiency and gain weight.
It might work better with a piston engine though.
BigBad, Tue May 06 2014, 12:00PM
It's theoretically good, but I don't think it works nearly as well in practice. Gas turbines don't scale down very well, they lose efficiency and gain weight.
It might work better with a piston engine though.
Re: Novel flying machines
Dr. Slack, Tue May 06 2014, 02:03PM
I'd be interested to see a bunch of graphs, if anybody has the bench facilities, or the data, of ...
a) the drive power requirements and weight of a system giving say 100N thrust, for where the lifting element is 3 or 4 ducted fans, or one open heli rotor
b) the weight of an energy store to rotary shaft system versus running time, for say 1kw shaft power, for energy stores of different battery chemistries, gas, nitro alcohol, and various 2 stroke, 4 stroke, series hybrid, in/outrunner motors. I would expect that for minutes, LiFePo would dominate, and for 10s of minutes, 4 stroke, but the graphs would tell.
Then with all of those curves, some usable machines ought to lie at the intersections of the highest curves.
Dr. Slack, Tue May 06 2014, 02:03PM
I'd be interested to see a bunch of graphs, if anybody has the bench facilities, or the data, of ...
a) the drive power requirements and weight of a system giving say 100N thrust, for where the lifting element is 3 or 4 ducted fans, or one open heli rotor
b) the weight of an energy store to rotary shaft system versus running time, for say 1kw shaft power, for energy stores of different battery chemistries, gas, nitro alcohol, and various 2 stroke, 4 stroke, series hybrid, in/outrunner motors. I would expect that for minutes, LiFePo would dominate, and for 10s of minutes, 4 stroke, but the graphs would tell.
Then with all of those curves, some usable machines ought to lie at the intersections of the highest curves.
Re: Novel flying machines
Steve Conner, Tue May 06 2014, 03:46PM
The beauty of the direct drive multirotor is its simplicity
Steve Conner, Tue May 06 2014, 03:46PM
The beauty of the direct drive multirotor is its simplicity
Re: Novel flying machines
Patrick, Tue May 06 2014, 06:02PM
look here... tri-copter with wings.
Patrick, Tue May 06 2014, 06:02PM
look here... tri-copter with wings.
Re: Novel flying machines
Patrick, Fri May 09 2014, 07:53PM
whats he difference wih these types of motors: (pancake motor)
and the traditional motors like mine:
Patrick, Fri May 09 2014, 07:53PM
whats he difference wih these types of motors:
(pancake motor)and the traditional motors like mine:
Re: Novel flying machines
Steve Conner, Fri May 09 2014, 08:55PM
The pancake motor is larger diameter with lots of poles. That means it is designed for a higher torque and lower RPM than a traditional shaped motor. You would use it with a large diameter, slow turning prop to get lots of thrust at low speed, for efficient hovering.
Steve Conner, Fri May 09 2014, 08:55PM
The pancake motor is larger diameter with lots of poles. That means it is designed for a higher torque and lower RPM than a traditional shaped motor. You would use it with a large diameter, slow turning prop to get lots of thrust at low speed, for efficient hovering.
Re: Novel flying machines
Patrick, Fri May 09 2014, 09:29PM
this means im outside the effciancy curve im trying to aim for.
so now steve the question, harkening back to that previous thread from several months ago, i realise the calculus of mass acceleration and force trade offs, and the momentum conservation.
but now im using 430 watt motors, traditional can-type, brushless. so can i use a reducion gear train? ( and so approximate the pancake motor) or is this botching the non-ideal system even further?
the problem is the pancake form factor motors are heavy and poor in overall power output. so i see some users making a tricopter with 6 motors, 3 pairs contra-rotating, six props. All this just to get the total lift value up.
The problem is you need 6 ESCs, 6 props, 6 copper wire bundles, 6 motors, and the aditional garbage starts piling up.
Patrick, Fri May 09 2014, 09:29PM
Steve Conner wrote ...
The pancake motor is larger diameter with lots of poles. That means it is designed for a higher torque and lower RPM than a traditional shaped motor. You would use it with a large diameter, slow turning prop to get lots of thrust at low speed, for efficient hovering.
ive not heard it so concisely stated, though ive heard what you say Steve, in drips and drabs from other sources, but i always like more opinions to avoid marketing propaganda.The pancake motor is larger diameter with lots of poles. That means it is designed for a higher torque and lower RPM than a traditional shaped motor. You would use it with a large diameter, slow turning prop to get lots of thrust at low speed, for efficient hovering.
this means im outside the effciancy curve im trying to aim for.
so now steve the question, harkening back to that previous thread from several months ago, i realise the calculus of mass acceleration and force trade offs, and the momentum conservation.
but now im using 430 watt motors, traditional can-type, brushless. so can i use a reducion gear train? ( and so approximate the pancake motor) or is this botching the non-ideal system even further?
the problem is the pancake form factor motors are heavy and poor in overall power output. so i see some users making a tricopter with 6 motors, 3 pairs contra-rotating, six props. All this just to get the total lift value up.
The problem is you need 6 ESCs, 6 props, 6 copper wire bundles, 6 motors, and the aditional garbage starts piling up.
Re: Novel flying machines
Steve Conner, Fri May 09 2014, 09:53PM
Sounds like time for a dyno experiment comparing the efficiency of a pancake motor against a regular shaped motor with a reduction gear. The gear train also adds weight and wastes some power, so I wouldn't care to say which would come out on top.
Steve Conner, Fri May 09 2014, 09:53PM
Sounds like time for a dyno experiment comparing the efficiency of a pancake motor against a regular shaped motor with a reduction gear. The gear train also adds weight and wastes some power, so I wouldn't care to say which would come out on top.
Re: Novel flying machines
Patrick, Fri May 09 2014, 10:03PM
Should i make a water-brake like load for a dynometer?
Patrick, Fri May 09 2014, 10:03PM
Steve Conner wrote ...
Sounds like time for a dyno experiment comparing the efficiency of a pancake motor against a regular shaped motor with a reduction gear. The gear train also adds weight and wastes some power, so I wouldn't care to say which would come out on top.
ok, so im already building a thrust stand.Sounds like time for a dyno experiment comparing the efficiency of a pancake motor against a regular shaped motor with a reduction gear. The gear train also adds weight and wastes some power, so I wouldn't care to say which would come out on top.
Should i make a water-brake like load for a dynometer?
Re: Novel flying machines
Steve Conner, Fri May 09 2014, 10:20PM
Probably not worth the bother, you can compare motors by measuring thrust vs. electrical power input with the same prop.
Steve Conner, Fri May 09 2014, 10:20PM
Probably not worth the bother, you can compare motors by measuring thrust vs. electrical power input with the same prop.
Re: Novel flying machines
Patrick, Fri May 09 2014, 10:28PM
-Tacho
-Voltage
-Current
-Force/ thrust
-Temp via IR
-Anemometer
-White flour for thrust colunm pics.
VPP links:
Patrick, Fri May 09 2014, 10:28PM
Steve Conner wrote ...
Probably not worth the bother, you can compare motors by measuring thrust vs. electrical power input with the same prop.
excellent, ill make a really good thrust stand, then load it with instruments.Probably not worth the bother, you can compare motors by measuring thrust vs. electrical power input with the same prop.
-Tacho
-Voltage
-Current
-Force/ thrust
-Temp via IR
-Anemometer
-White flour for thrust colunm pics.
VPP links:
Re: Novel flying machines
Dr. Slack, Sat May 10 2014, 08:08AM
I'm really dubious about going doing the VPP route (which sounds rich as it's on the grounds of complexity, like my first post wasn't complex, but I' allowed to change my mind as I think through things).
A real benefit in flying machines is mechanical simplicity, less to buy, less to set up and keep in adjustment, less to replace when you crash. You know you have a good design when there's nothing left to take away.
VPP might have a small benefit over fixed pitch (like hand crafted assembler can usually be got to work faster than compiled code). But the weight of a machine will be more or less constant, or nearly so if it's consuming fuel, and as the thrust varies as the square of the prop speed, the best speed will vary over only a small range. The max efficiency band for motors, glow and electric, is not a spike but a bit of a pudding. You'd need more speed for a fast climb, and might run slightly less efficiently after dropping your Amazon parcel, but both of those are tractable costs of the simpler approach.
What I'm saying is, a VPP on a fast motor with a gearbox might be slightly more efficient than a 22 pole pancake on a fixed rotor. You can measure cost/benefit of $ and kg and minutes, but you can't measure the cost/benefit of complexity so easily. Does that mean you will ignore complexity as part of your thinking? A mantra oft repeated in the engineering circles I move in is 'a component that's not fitted is one that's guaranteed not to fail'. This affects the lifetime cost of the project, time to design, time to debug, warranty costs, unfortunately all very intangible.
Dr. Slack, Sat May 10 2014, 08:08AM
I'm really dubious about going doing the VPP route (which sounds rich as it's on the grounds of complexity, like my first post wasn't complex, but I' allowed to change my mind as I think through things).
A real benefit in flying machines is mechanical simplicity, less to buy, less to set up and keep in adjustment, less to replace when you crash. You know you have a good design when there's nothing left to take away.
VPP might have a small benefit over fixed pitch (like hand crafted assembler can usually be got to work faster than compiled code). But the weight of a machine will be more or less constant, or nearly so if it's consuming fuel, and as the thrust varies as the square of the prop speed, the best speed will vary over only a small range. The max efficiency band for motors, glow and electric, is not a spike but a bit of a pudding. You'd need more speed for a fast climb, and might run slightly less efficiently after dropping your Amazon parcel, but both of those are tractable costs of the simpler approach.
What I'm saying is, a VPP on a fast motor with a gearbox might be slightly more efficient than a 22 pole pancake on a fixed rotor. You can measure cost/benefit of $ and kg and minutes, but you can't measure the cost/benefit of complexity so easily. Does that mean you will ignore complexity as part of your thinking? A mantra oft repeated in the engineering circles I move in is 'a component that's not fitted is one that's guaranteed not to fail'. This affects the lifetime cost of the project, time to design, time to debug, warranty costs, unfortunately all very intangible.
Re: Novel flying machines
Ash Small, Sat May 10 2014, 11:21AM
The actual 'variable pitch prop' bit is easy to do. The 'swash plate' bit is the 'slightly tricky' bit. I've thought it through and you do need four servo's for a swashplate (possibly three, but tricky), you only need one for 'variable pitch'.
EDIT: I'll post a sketch or two if anyone's interested ( I'm away this weekend though)
Ash Small, Sat May 10 2014, 11:21AM
The actual 'variable pitch prop' bit is easy to do. The 'swash plate' bit is the 'slightly tricky' bit. I've thought it through and you do need four servo's for a swashplate (possibly three, but tricky), you only need one for 'variable pitch'.
EDIT: I'll post a sketch or two if anyone's interested ( I'm away this weekend though)
Re: Novel flying machines
Dr. Slack, Sat May 10 2014, 03:58PM
pic
That looks really cool, but at what cost?
Rotating the forward motors costs a control channel, the servo and rotator weight, and the fact that the prop pitch, size and power is a compromise between low pitch high power for hover and high pitch low power for forward flight.
What if he used two big low pitch fixed counter rotating lift props ahead of the wings, with the ESC programmed to stop them in the low drag fore-aft position, and a single fixed high pitch prop in the nose for forward flight? The servo channel becomes the forward channel, the weight of the rotator becomes the weight of the forward prop, so no significant change in weight or control channels. However, each prop is now more efficient as better matched to its job, and the mechanics are simpler with no rotator.
Now, additionally, what if control were completely split with forward flight motor and control surfaces on one radio, and vertical services on the other radio? Result total parallel get you home survivability so can land vertically, or like a plane, or glide in on receiver batteries only, if there's a malfunction with one set of controls. The cost at the vehicle being the weight of a second receiver and control battery. Is it worth the weight for a much more survivable plane?
Dr. Slack, Sat May 10 2014, 03:58PM
Patrick wrote ...
look here... tri-copter with wings.
look here... tri-copter with wings.
pic
That looks really cool, but at what cost?
Rotating the forward motors costs a control channel, the servo and rotator weight, and the fact that the prop pitch, size and power is a compromise between low pitch high power for hover and high pitch low power for forward flight.
What if he used two big low pitch fixed counter rotating lift props ahead of the wings, with the ESC programmed to stop them in the low drag fore-aft position, and a single fixed high pitch prop in the nose for forward flight? The servo channel becomes the forward channel, the weight of the rotator becomes the weight of the forward prop, so no significant change in weight or control channels. However, each prop is now more efficient as better matched to its job, and the mechanics are simpler with no rotator.
Now, additionally, what if control were completely split with forward flight motor and control surfaces on one radio, and vertical services on the other radio? Result total parallel get you home survivability so can land vertically, or like a plane, or glide in on receiver batteries only, if there's a malfunction with one set of controls. The cost at the vehicle being the weight of a second receiver and control battery. Is it worth the weight for a much more survivable plane?
Re: Novel flying machines
Patrick, Sat May 10 2014, 04:47PM
you make compelling points Dr. Slack. based on good engineering philosophy, rarely taught in college couses.
and ash small, id rather not have the swash plate at all, might as well go to a full heli then.
i want collective equivlent only, cyclic is uselessly complicated. (unless this tail rotor is what you menat) ->
ok then let me do some more thinking, and ty to get the machine flying today.
Patrick, Sat May 10 2014, 04:47PM
you make compelling points Dr. Slack. based on good engineering philosophy, rarely taught in college couses.
and ash small, id rather not have the swash plate at all, might as well go to a full heli then.
i want collective equivlent only, cyclic is uselessly complicated. (unless this tail rotor is what you menat) ->
ok then let me do some more thinking, and ty to get the machine flying today.
Re: Novel flying machines
Ash Small, Sun May 11 2014, 04:57PM
I don't agree. It can be accomplished easily with four servo's. The only other thing required over 'normal' variable pitch is a spherical bearing, which isn't subjected to rotational motion (EDIT: there is an element of rotational motion, depending on 'cyclical' stuff, but I'm sure this can be dealt with) and so can therefore be quite simple. You could either adapt something like a self-aligning bearing or get something machined out of nylon 66, or similar. I'd get this machined with some form of spline on the inside so it will slide on the prop shaft thus serving the variable pitch function at the same time. The only difference between the two systems is one extra spherical bearing and three servos, but they can each be much smaller than the single one required for VPP as they share the load.
EDIT: You still need a couple of taper-roller bearings, or something similar, (along with the blade carriers and pushrods) but you need all this for VPP anyway, unless I'm missing something.
EDIT: You need a bit of extra software too, but software doesn't weigh much
Ash Small, Sun May 11 2014, 04:57PM
Patrick wrote ...
cyclic is uselessly complicated.
cyclic is uselessly complicated.
I don't agree. It can be accomplished easily with four servo's. The only other thing required over 'normal' variable pitch is a spherical bearing, which isn't subjected to rotational motion (EDIT: there is an element of rotational motion, depending on 'cyclical' stuff, but I'm sure this can be dealt with) and so can therefore be quite simple. You could either adapt something like a self-aligning bearing or get something machined out of nylon 66, or similar. I'd get this machined with some form of spline on the inside so it will slide on the prop shaft thus serving the variable pitch function at the same time. The only difference between the two systems is one extra spherical bearing and three servos, but they can each be much smaller than the single one required for VPP as they share the load.
EDIT: You still need a couple of taper-roller bearings, or something similar, (along with the blade carriers and pushrods) but you need all this for VPP anyway, unless I'm missing something.
EDIT: You need a bit of extra software too, but software doesn't weigh much
Re: Novel flying machines
Chip Fixes, Mon May 12 2014, 05:38AM
Just saw this on Hack A Day today:
Although, besides being able to hover for 19 hours, it really doesn't seem that novel.
Chip Fixes, Mon May 12 2014, 05:38AM
Just saw this on Hack A Day today:
Although, besides being able to hover for 19 hours, it really doesn't seem that novel.
Re: Novel flying machines
BigBad, Tue May 13 2014, 06:55PM
I think maybe VPPs are particularly good for variable mass vehicles.
For battery powered vehicles, you just optimise the prop for one speed (the one needed to hover), and you can deal with the differences in thrust by varying the speed somewhat, hopefully not running it too much off the optimum speed.
BigBad, Tue May 13 2014, 06:55PM
I think maybe VPPs are particularly good for variable mass vehicles.
For battery powered vehicles, you just optimise the prop for one speed (the one needed to hover), and you can deal with the differences in thrust by varying the speed somewhat, hopefully not running it too much off the optimum speed.
Re: Novel flying machines
Ash Small, Tue May 13 2014, 07:08PM
i agree, but once you start considering IC engines I think you have to consider VPP and swashplate, as swashplate doesn't contribute much mass compared to VPP (and is hardly any more complicated to implement). I'm assuming that a large percentage of 'take off' weight will be fuel, and most of the fuel will be consumed during flight, I think this is where the advantages of VPP really lie. Also, I think the torque characteristics of IC compared to electric would also favour this approach. I can't really see much advantage of using VPP with electric motors if the payload is reasonably constant.
EDIT: Although I can see advantages of using swashplate with electric, as it means you only need one motor, assuming the tail rotor is driven by gears, and one large prop is more efficient than several smaller ones.
EDIT: I think you'd only need VPP for the tail rotor. I can't see any advantage of using a swashplate there.
Ash Small, Tue May 13 2014, 07:08PM
BigBad wrote ...
I think maybe VPPs are particularly good for variable mass vehicles.
For battery powered vehicles, you just optimise the prop for one speed (the one needed to hover), and you can deal with the differences in thrust by varying the speed somewhat, hopefully not running it too much off the optimum speed.
I think maybe VPPs are particularly good for variable mass vehicles.
For battery powered vehicles, you just optimise the prop for one speed (the one needed to hover), and you can deal with the differences in thrust by varying the speed somewhat, hopefully not running it too much off the optimum speed.
i agree, but once you start considering IC engines I think you have to consider VPP and swashplate, as swashplate doesn't contribute much mass compared to VPP (and is hardly any more complicated to implement). I'm assuming that a large percentage of 'take off' weight will be fuel, and most of the fuel will be consumed during flight, I think this is where the advantages of VPP really lie. Also, I think the torque characteristics of IC compared to electric would also favour this approach. I can't really see much advantage of using VPP with electric motors if the payload is reasonably constant.
EDIT: Although I can see advantages of using swashplate with electric, as it means you only need one motor, assuming the tail rotor is driven by gears, and one large prop is more efficient than several smaller ones.
EDIT: I think you'd only need VPP for the tail rotor. I can't see any advantage of using a swashplate there.
Re: Novel flying machines
Patrick, Wed May 14 2014, 12:47AM
i shoud have said this sooner, but the real problem with a traditional heli swashplate is that when you have a prop strike, youll bend all theose precision pieces. And if i want a commercial product to eventually come of this, ill need reliability and repairabilty.
Patrick, Wed May 14 2014, 12:47AM
i shoud have said this sooner, but the real problem with a traditional heli swashplate is that when you have a prop strike, youll bend all theose precision pieces. And if i want a commercial product to eventually come of this, ill need reliability and repairabilty.
Re: Novel flying machines
Steve Conner, Wed May 14 2014, 09:30AM
Hence see Dr. Slack's earlier comments about complexity.
My favourite design right now is the RCExplorer tricopter. The frame is a couple of softwood battens from the hardware store, and the motors are held on with cable ties so they will come loose in a crash before the shaft bends. I expect the average crash would cost about $7 and take 15 minutes to fix.
Steve Conner, Wed May 14 2014, 09:30AM
Hence see Dr. Slack's earlier comments about complexity.
My favourite design right now is the RCExplorer tricopter. The frame is a couple of softwood battens from the hardware store, and the motors are held on with cable ties so they will come loose in a crash before the shaft bends. I expect the average crash would cost about $7 and take 15 minutes to fix.
Re: Novel flying machines
BigBad, Wed May 14 2014, 02:19PM
If we're talking mechanical simplicity I quite like the sycamore seed type design where you spin the whole vehicle as a wing and then control it exclusively on cyclic and thrust. Maybe use an airjet at the tip and a compressor in the central hub. You could probably synchronise the rotation with a magnetic compass.
If you put a camera on it, you get 360 degree vision for free.
BigBad, Wed May 14 2014, 02:19PM
If we're talking mechanical simplicity I quite like the sycamore seed type design where you spin the whole vehicle as a wing and then control it exclusively on cyclic and thrust. Maybe use an airjet at the tip and a compressor in the central hub. You could probably synchronise the rotation with a magnetic compass.
If you put a camera on it, you get 360 degree vision for free.
Re: Novel flying machines
Patrick, Wed May 14 2014, 03:19PM
Patrick, Wed May 14 2014, 03:19PM
BigBad wrote ...
If we're talking mechanical simplicity I quite like the sycamore seed type design where you spin the whole vehicle as a wing and then control it exclusively on cyclic and thrust. Maybe use an airjet at the tip and a compressor in the central hub. You could probably synchronise the rotation with a magnetic compass.
If you put a camera on it, you get 360 degree vision for free.
i saw the embry riddel team demonstrate this at our academic competition in north dakota, it was really cool.If we're talking mechanical simplicity I quite like the sycamore seed type design where you spin the whole vehicle as a wing and then control it exclusively on cyclic and thrust. Maybe use an airjet at the tip and a compressor in the central hub. You could probably synchronise the rotation with a magnetic compass.
If you put a camera on it, you get 360 degree vision for free.
Re: Novel flying machines
Patrick, Mon May 19 2014, 08:17AM
mind blowing !!!!
RCvertt's work...
Patrick, Mon May 19 2014, 08:17AM
mind blowing !!!!
RCvertt's work...Re: Novel flying machines
Ash Small, Tue May 20 2014, 11:08PM
Ok, this is a hypothesis, and is not proven.
Following on from my comments in Dr Spark's 'big bird' thread, Here is a 'concept heptacopter'.
The image represents the ducts and framework. The props are mounted centrally in the ducts. I think it's easy to see that the central propeller doesn't suffer from the same peripheral losses that a single prop would experience, hence greatly improving efficiency. The efficiency of the surrounding props is also increased.
Assuning 13.5 inch props, length is around one metre.
Efficiency could be further increased by adding another six props, increasing length to around 1.5M, but I'm not sure how much this would weigh. There are regulations applying to these things.
I don't know if other factors are involved, most hexacopters have their props placed far apart. This improves manouverability, but is this at the cost of efficiency (read 'flight time') or are there other factors I've not considered?
EDIT: I calculate the rduction in peripheral losses with the above design to be ~43%, compared to a design with the rotors spaced further apart.
Ash Small, Tue May 20 2014, 11:08PM
Ok, this is a hypothesis, and is not proven.
Following on from my comments in Dr Spark's 'big bird' thread, Here is a 'concept heptacopter'.
The image represents the ducts and framework. The props are mounted centrally in the ducts. I think it's easy to see that the central propeller doesn't suffer from the same peripheral losses that a single prop would experience, hence greatly improving efficiency. The efficiency of the surrounding props is also increased.
Assuning 13.5 inch props, length is around one metre.
Efficiency could be further increased by adding another six props, increasing length to around 1.5M, but I'm not sure how much this would weigh. There are regulations applying to these things.
I don't know if other factors are involved, most hexacopters have their props placed far apart. This improves manouverability, but is this at the cost of efficiency (read 'flight time') or are there other factors I've not considered?
EDIT: I calculate the rduction in peripheral losses with the above design to be ~43%, compared to a design with the rotors spaced further apart.
Re: Novel flying machines
Carbon_Rod, Wed May 21 2014, 04:42PM
For those interested in a variable pitch aerial quad:
kit $800:
These are not a complicated build project.
Carbon_Rod, Wed May 21 2014, 04:42PM
For those interested in a variable pitch aerial quad:
kit $800:
These are not a complicated build project.
Re: Novel flying machines
Ash Small, Wed May 21 2014, 05:39PM
Now I'd argue that a single rotor craft with swash plate is simpler than this quad. You do need four servos for a swashplate, but he has four on this quad anyway.
The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
EDIT: you could use a similar belt drive system as used here to drive the tail rotor, though, and you will need a fifth servo for the variable pitch tail rotor.
You could also use the system depected here in the 'concept heptacopter' design I posted above, with a single motor and belt drive, but you'd need a separate servo for each prop.
Ash Small, Wed May 21 2014, 05:39PM
Carbon_Rod wrote ...
For those interested in a variable pitch aerial quad:
kit $800:
These are not a complicated build project.
For those interested in a variable pitch aerial quad:
kit $800:
These are not a complicated build project.
Now I'd argue that a single rotor craft with swash plate is simpler than this quad. You do need four servos for a swashplate, but he has four on this quad anyway.
The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
EDIT: you could use a similar belt drive system as used here to drive the tail rotor, though, and you will need a fifth servo for the variable pitch tail rotor.
You could also use the system depected here in the 'concept heptacopter' design I posted above, with a single motor and belt drive, but you'd need a separate servo for each prop.
Re: Novel flying machines
Patrick, Wed May 21 2014, 06:09PM
Patrick, Wed May 21 2014, 06:09PM
Ash Small wrote ...
The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
your starting to convince me, and to avoid a traditional tail, I'd use vanes. Like the German V2.The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
Re: Novel flying machines
Ash Small, Wed May 21 2014, 08:34PM
Ash Small, Wed May 21 2014, 08:34PM
Patrick wrote ...
I can post a sketch of what I consider to be a fairly simple swashplate design if you like, but it probably won't be for a few days at least. I imagine most of it would survive a catastophic crash, especially if the props were designed to shear off.Ash Small wrote ...
The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
your starting to convince me, and to avoid a traditional tail, I'd use vanes. Like the German V2.The efficiency gained by using a single rotor and swashplate would be considerable in this instance.
Re: Novel flying machines
Patrick, Fri May 23 2014, 05:37PM
id like to see it, please post when able Ash.
Patrick, Fri May 23 2014, 05:37PM
id like to see it, please post when able Ash.
Re: Novel flying machines
Ash Small, Fri May 23 2014, 07:59PM
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
Ash Small, Fri May 23 2014, 07:59PM
Patrick wrote ...
id like to see it, please post when able Ash.
id like to see it, please post when able Ash.
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
Re: Novel flying machines
Patrick, Fri May 23 2014, 08:50PM
reply when you can, TY
Patrick, Fri May 23 2014, 08:50PM
Ash Small wrote ...
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
im starting to come around Ash, ive seen these before, and i typically ask those who advocate for it, if the motor, shaft and prop hub are all rigid but with the shaft going through the hole? so the motor casing torque is held where? and the motor is otherwise free to move by the servo-swash action.Patrick wrote ...
id like to see it, please post when able Ash.
id like to see it, please post when able Ash.
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
reply when you can, TY
Re: Novel flying machines
Ash Small, Sat May 24 2014, 10:07AM
The motor is fixed. the swashplate mounts on the spherical bearing. You then need something like a pair of taper roller bearings on the swashplate, which allows the swashplate to spin with the shaft while being controlled by the servos. I'll try to get a sketch together later today. It's all in my head, I just need to get it into CAD.
Ash Small, Sat May 24 2014, 10:07AM
Patrick wrote ...
reply when you can, TY
Ash Small wrote ...
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
im starting to come around Ash, ive seen these before, and i typically ask those who advocate for it, if the motor, shaft and prop hub are all rigid but with the shaft going through the hole? so the motor casing torque is held where? and the motor is otherwise free to move by the servo-swash action.Patrick wrote ...
id like to see it, please post when able Ash.
id like to see it, please post when able Ash.
Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:
reply when you can, TY
The motor is fixed. the swashplate mounts on the spherical bearing. You then need something like a pair of taper roller bearings on the swashplate, which allows the swashplate to spin with the shaft while being controlled by the servos. I'll try to get a sketch together later today. It's all in my head, I just need to get it into CAD.
Re: Novel flying machines
Ash Small, Sat May 24 2014, 04:28PM
It's actually possible to do the swashplate without a spherical bearing, I think. The spherical bearing just adds some rigidity. I think it's best to leave it in for now.
Ash Small, Sat May 24 2014, 04:28PM
It's actually possible to do the swashplate without a spherical bearing, I think. The spherical bearing just adds some rigidity. I think it's best to leave it in for now.
Re: Novel flying machines
Ash Small, Sat May 24 2014, 09:09PM
Ok, here's a very rough sketch of one of the four servo rams and a section of swashplate.
When all four servo's operate together, the spherical bearing (blue) slides up and down the propshaft (grey), giving your basic VPP.
When the servo's are not operated in unison, the swashplate (red) tilts, simple.
The servo rams (yellow) are connected to the ring (green), which is connected to the swashplate by two taper roller bearings, although it's possible to use a single bearing, two taper rollers are generally a better 'engineering' solution . The servo pivots are not shown here (yet). The connecting rods (also yellow) are connected to the swashplate and operate the VPP (I've not drawn the conrod pivots yet, either).
Any other questions?
(This is a first attempt, using standard sized bearings. I'm sure this basic design can be improved considerably)
Ash Small, Sat May 24 2014, 09:09PM
Ok, here's a very rough sketch of one of the four servo rams and a section of swashplate.
When all four servo's operate together, the spherical bearing (blue) slides up and down the propshaft (grey), giving your basic VPP.
When the servo's are not operated in unison, the swashplate (red) tilts, simple.
The servo rams (yellow) are connected to the ring (green), which is connected to the swashplate by two taper roller bearings, although it's possible to use a single bearing, two taper rollers are generally a better 'engineering' solution . The servo pivots are not shown here (yet). The connecting rods (also yellow) are connected to the swashplate and operate the VPP (I've not drawn the conrod pivots yet, either).
Any other questions?
(This is a first attempt, using standard sized bearings. I'm sure this basic design can be improved considerably)
Re: Novel flying machines
Patrick, Sat May 24 2014, 10:20PM
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
Patrick, Sat May 24 2014, 10:20PM
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
Re: Novel flying machines
Ash Small, Sat May 24 2014, 10:32PM
Do you have any relevent links? This isn't really one of my subjects.
Ash Small, Sat May 24 2014, 10:32PM
Patrick wrote ...
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
Do you have any relevent links? This isn't really one of my subjects.
Re: Novel flying machines
Patrick, Sat May 24 2014, 11:12PM
pics!
the link for more here:
Patrick, Sat May 24 2014, 11:12PM
Ash Small wrote ...
Do you have any relevent links? This isn't really one of my subjects.
sorry, head is blurry with a math hang-over.Patrick wrote ...
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
your beginning to win me over. but would a taditional heli bering be better? easier and cheaper too?
Do you have any relevent links? This isn't really one of my subjects.
pics!
the link for more here:
Re: Novel flying machines
Ash Small, Sat May 24 2014, 11:18PM
That looks pretty much like what I posted. There may be some detail differences. If that suits your purpose, use it, if not, we'll design something that does.
Ash Small, Sat May 24 2014, 11:18PM
That looks pretty much like what I posted. There may be some detail differences. If that suits your purpose, use it, if not, we'll design something that does.
Re: Novel flying machines
Patrick, Sat May 24 2014, 11:21PM
id like to start with a already machined part, then use as is or mod it. but i think we add thrust vanes too right? to avoid a tail boom?
then we call it a mono-copter. my Wii board will already work with 2 servos, but not 3. we'd also need to get the physics right.
Patrick, Sat May 24 2014, 11:21PM
id like to start with a already machined part, then use as is or mod it. but i think we add thrust vanes too right? to avoid a tail boom?
then we call it a mono-copter. my Wii board will already work with 2 servos, but not 3. we'd also need to get the physics right.
Re: Novel flying machines
Carbon_Rod, Sun May 25 2014, 05:38AM
You may want to look at model Coaxial rotors a bit...
Rube Goldberg mechanical complexity...
but the air speed is better...
Carbon_Rod, Sun May 25 2014, 05:38AM
You may want to look at model Coaxial rotors a bit...
Rube Goldberg mechanical complexity...
but the air speed is better...
Re: Novel flying machines
Ash Small, Sun May 25 2014, 10:46AM
Pretty good animation here:
I think I'd be tempted to stick with a tail rotor and one lift rotor for simplicity, but this isn't my project
EDIT: just found this: "Today, on most modern aircraft the swashplate is above the transmission and the pushrods are visible outside the fuselage, but a few early designs, notably light helicopters built by Enstrom Helicopter, placed it underneath the transmission and enclosed the rotating pushrods inside the mainshaft. This reduces rotor hub drag since there are no exposed linkages."
Enstrom F-28:
Ash Small, Sun May 25 2014, 10:46AM
Pretty good animation here:
I think I'd be tempted to stick with a tail rotor and one lift rotor for simplicity, but this isn't my project
EDIT: just found this: "Today, on most modern aircraft the swashplate is above the transmission and the pushrods are visible outside the fuselage, but a few early designs, notably light helicopters built by Enstrom Helicopter, placed it underneath the transmission and enclosed the rotating pushrods inside the mainshaft. This reduces rotor hub drag since there are no exposed linkages."
Enstrom F-28:
Re: Novel flying machines
Patrick, Sun May 25 2014, 08:20PM
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
Patrick, Sun May 25 2014, 08:20PM
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
Re: Novel flying machines
Ash Small, Mon May 26 2014, 05:59PM
Well, the vane idea might work, but a belt driven tail prop only needs one servo. (and we know it works)
Also, this Enstrom design, with the conrods inside the propshaft will be pretty much indestructible if the blades are designed to shear off in a crash. All the swashplate assembly is well hidden away inside the craft. This also considerably reduces drag, and lowers the C of G.
Also, there are some very good reasons why helicopters are almost all the same..........
EDIT: How many servo's will vanes require?
Ash Small, Mon May 26 2014, 05:59PM
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
Well, the vane idea might work, but a belt driven tail prop only needs one servo. (and we know it works)
Also, this Enstrom design, with the conrods inside the propshaft will be pretty much indestructible if the blades are designed to shear off in a crash. All the swashplate assembly is well hidden away inside the craft. This also considerably reduces drag, and lowers the C of G.
Also, there are some very good reasons why helicopters are almost all the same..........
EDIT: How many servo's will vanes require?
Re: Novel flying machines
Patrick, Mon May 26 2014, 06:34PM
fast forward to 1:35, youll see a machine i may have to compete against again. Georgia Tech is always a competent group though, they really knew what they were doing on every occasion i saw them fly in North Dakota.
Patrick, Mon May 26 2014, 06:34PM
Ash Small wrote ...
EDIT: How many servo's will vanes require?
4 probly, but theyed be micro servos and all moving in the same direction for yaw. so simple and cheap. EDIT: How many servo's will vanes require?
fast forward to 1:35, youll see a machine i may have to compete against again. Georgia Tech is always a competent group though, they really knew what they were doing on every occasion i saw them fly in North Dakota. Re: Novel flying machines
Ash Small, Mon May 26 2014, 10:43PM
The way I see it, you still need a swashplate with concentric rotors, otherwise how do you fly forwards, etc?
Ash Small, Mon May 26 2014, 10:43PM
The way I see it, you still need a swashplate with concentric rotors, otherwise how do you fly forwards, etc?
Re: Novel flying machines
Dr. Slack, Mon May 26 2014, 10:58PM
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee,, with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.
If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Just sayin'
Dr. Slack, Mon May 26 2014, 10:58PM
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee,
, with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Just sayin'
Re: Novel flying machines
Patrick, Tue May 27 2014, 12:19AM
like this :
Patrick, Tue May 27 2014, 12:19AM
Dr. Slack wrote ...
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee,, with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.
If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Just sayin'
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee,
, with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Just sayin'
like this :
Re: Novel flying machines
Ash Small, Tue May 27 2014, 04:50PM
One larger internal combustion engine is ALWAYS more efficient and lighter than two small ones.
While the Chinook does have two gas turbines, they are both linked, and either can 'fly' the chinook (this is a safety feature in case one engine fails)
I still think you'll have torque related problems using an IC engine without a swashplate, as IC engines don't develop sufficient torque at low RPM to spin the prop up to speed.
The weight and efficiency gained by using a swashplate (and single rotor?) far outweigh any advantage gained by using two IC engines.
I think if you're after efficiency with an IC engine, you always end up at the 'conventional 'copter'.
Ash Small, Tue May 27 2014, 04:50PM
One larger internal combustion engine is ALWAYS more efficient and lighter than two small ones.
While the Chinook does have two gas turbines, they are both linked, and either can 'fly' the chinook (this is a safety feature in case one engine fails)
I still think you'll have torque related problems using an IC engine without a swashplate, as IC engines don't develop sufficient torque at low RPM to spin the prop up to speed.
The weight and efficiency gained by using a swashplate (and single rotor?) far outweigh any advantage gained by using two IC engines.
I think if you're after efficiency with an IC engine, you always end up at the 'conventional 'copter'.
Re: Novel flying machines
Patrick, Tue May 27 2014, 07:19PM
I need high efficiency with batteries.
but any efficiency is tolerable with a IC.
Patrick, Tue May 27 2014, 07:19PM
I need high efficiency with batteries.
but any efficiency is tolerable with a IC.
Re: Novel flying machines
Ash Small, Tue May 27 2014, 09:05PM
There's no reason why contra-rotating props can't be the same diameter as a single prop would be. They can also be of thinner section if you have twice as many blades, so it needn't work out much heavier..
It would require some sort of gearbox, though.
EDIT: I think the Chinook design could be more efficient than concentric props of the same diameter, as the area under the props is greater, resulting in less velocity, and therefore less peripheral losses. (larger slower turning props are always more efficient, although one large prop is always more efficient than two, all other factors being equal. Concentric props 'may' be more efficient if they are larger than two 'chinook style' props. We're going into 'grey' areas here.
Ash Small, Tue May 27 2014, 09:05PM
There's no reason why contra-rotating props can't be the same diameter as a single prop would be. They can also be of thinner section if you have twice as many blades, so it needn't work out much heavier..
It would require some sort of gearbox, though.
EDIT: I think the Chinook design could be more efficient than concentric props of the same diameter, as the area under the props is greater, resulting in less velocity, and therefore less peripheral losses. (larger slower turning props are always more efficient, although one large prop is always more efficient than two, all other factors being equal. Concentric props 'may' be more efficient if they are larger than two 'chinook style' props. We're going into 'grey' areas here.
Re: Novel flying machines
Patrick, Thu May 29 2014, 05:51AM
no more guessing!!!!!!!!!!!!!!!!!
ive got a totally re-engineered thrust stand, this will allow me to generate lists of data on motor props and ESCs... all in 1,000 RPM increments. i may put a anemometer somewhere too.
Patrick, Thu May 29 2014, 05:51AM
no more guessing!!!!!!!!!!!!!!!!!
ive got a totally re-engineered thrust stand, this will allow me to generate lists of data on motor props and ESCs... all in 1,000 RPM increments. i may put a anemometer somewhere too.
Re: Novel flying machines
Dr. Slack, Thu May 29 2014, 07:38AM
Yay for measurement.
Now for Mk2, if you mounted the motor on a bearing, and resisted the rotation with some means of measuring torque (spring, weight on a stick, another set of small scales, whatever) you could measure true torque/power at the prop, and you'd have a motor dynamometer as well.
Dr. Slack, Thu May 29 2014, 07:38AM
Yay for measurement.
Now for Mk2, if you mounted the motor on a bearing, and resisted the rotation with some means of measuring torque (spring, weight on a stick, another set of small scales, whatever) you could measure true torque/power at the prop, and you'd have a motor dynamometer as well.
Re: Novel flying machines
Patrick, Thu May 29 2014, 07:46AM
there is a super dooper important PDF, but i cant get it to save in the attachments section.
hers the link:
the velocity and pressure diamgrams are important. i may throw flour into the propeller to visualize the exhaust stream.
Patrick, Thu May 29 2014, 07:46AM
Dr. Slack wrote ...
Now for Mk2, if you mounted the motor on a bearing, and resisted the rotation with some means of measuring torque... ....you could measure true torque/power at the prop, and you'd have a motor dynamometer as well.
hell. i should have thought of that.Now for Mk2, if you mounted the motor on a bearing, and resisted the rotation with some means of measuring torque... ....you could measure true torque/power at the prop, and you'd have a motor dynamometer as well.
there is a super dooper important PDF, but i cant get it to save in the attachments section.
hers the link:
the velocity and pressure diamgrams are important. i may throw flour into the propeller to visualize the exhaust stream.
Re: Novel flying machines
Patrick, Sun Jun 01 2014, 05:46AM
If 'm dot' is a derivative, could it also be written as dm/dt ?
Patrick, Sun Jun 01 2014, 05:46AM
If 'm dot' is a derivative, could it also be written as dm/dt ?
Re: Novel flying machines
Uspring, Sun Jun 01 2014, 08:58AM
Yes.
Uspring, Sun Jun 01 2014, 08:58AM
Yes.
Re: Novel flying machines
BigBad, Sun Jun 01 2014, 02:06PM
m dot is Newton's notation; he only knew how to differentiate wrt time
dm/dt is Leibnitz's notation, it's more general.
BigBad, Sun Jun 01 2014, 02:06PM
m dot is Newton's notation; he only knew how to differentiate wrt time
dm/dt is Leibnitz's notation, it's more general.
Re: Novel flying machines
Ash Small, Mon Jun 02 2014, 09:45PM
Not only do I have helicopters flying past my windows most days (I live on a hill in a military training area), but recemtly they've been flying around my head. I think if you have a 'Chinook' configuration, but with two pairs of concentric props (four props altogether), you can do it just with VPP, without swashplates 'IF' you drive each prop from a separate motor.....still thinking....and drinking....
EDIT: It's possible to do without VPP as well, if you use electric motors.....four motors, four props, but two concentric pairs, in Chinook configuration.
Ash Small, Mon Jun 02 2014, 09:45PM
Not only do I have helicopters flying past my windows most days (I live on a hill in a military training area), but recemtly they've been flying around my head. I think if you have a 'Chinook' configuration, but with two pairs of concentric props (four props altogether), you can do it just with VPP, without swashplates 'IF' you drive each prop from a separate motor.....still thinking....and drinking....
EDIT: It's possible to do without VPP as well, if you use electric motors.....four motors, four props, but two concentric pairs, in Chinook configuration.
Re: Novel flying machines
Patrick, Sun Jun 08 2014, 07:19PM
im thinking about all these derivations, i dont think i need the square on the (Ve - Vh) part since im using the derivative of m. is this right?
Patrick, Sun Jun 08 2014, 07:19PM
im thinking about all these derivations, i dont think i need the square on the (Ve - Vh) part since im using the derivative of m. is this right?
Re: Novel flying machines
Uspring, Tue Jun 10 2014, 10:17AM
The first equation is Newtons law of motion.
The second one is wrong.
The third describes the thrust of e.g. propeller, which accelerates air at the rate dm/dt from velocity vh to ve. Think of the situation of pushing a mass m with the force F for a time t. Then the mass will have accelerated to the velocity v. The involved quantities are related by the equation
F*t = m*v
This equation describes the conservation of momentum. Divide both sides by t and you get:
F = (m/t) * v
This is basically your third equation for the special case, that the entrant air velocity vh is zero.
Uspring, Tue Jun 10 2014, 10:17AM
The first equation is Newtons law of motion.
The second one is wrong.
The third describes the thrust of e.g. propeller, which accelerates air at the rate dm/dt from velocity vh to ve. Think of the situation of pushing a mass m with the force F for a time t. Then the mass will have accelerated to the velocity v. The involved quantities are related by the equation
F*t = m*v
This equation describes the conservation of momentum. Divide both sides by t and you get:
F = (m/t) * v
This is basically your third equation for the special case, that the entrant air velocity vh is zero.
Re: Novel flying machines
Ash Small, Tue Jun 10 2014, 02:10PM
I think the second one should be something like F=m(v2-v1)/t (it's a long time since I was a student).
Ash Small, Tue Jun 10 2014, 02:10PM
I think the second one should be something like F=m(v2-v1)/t (it's a long time since I was a student).
Re: Novel flying machines
BigBad, Tue Jun 10 2014, 02:10PM
The m and the v are related, at high v_e, you are drawing more air through your rotor per second.
i.e.
m ~= rho v_e A
where rho is the air density and A is the disk area
but the reality is more complicated; some of the air is vortexing around in a circuit and not being accelerated as much, so giving less force; you could probably have some sort of fudge factor for that. However, due to viscosity you'll still get advantage from even that.
But the rho v_e A is probably a good start.
Basically:
F = m dv/dt
let's say that every second you're accelerating a mass m of air, from rest above the vehicle to V_e, as a jet of air below the vehicle:
F = m V_e
substitute for 'm'
F = (rho V_e A) V_e
rearrange:
F = rho A V_e^2
(n.b. you have to be a bit careful with those dm/dt terms, mass is conserved, so dm/dt is always technically 0!)
BigBad, Tue Jun 10 2014, 02:10PM
The m and the v are related, at high v_e, you are drawing more air through your rotor per second.
i.e.
m ~= rho v_e A
where rho is the air density and A is the disk area
but the reality is more complicated; some of the air is vortexing around in a circuit and not being accelerated as much, so giving less force; you could probably have some sort of fudge factor for that. However, due to viscosity you'll still get advantage from even that.
But the rho v_e A is probably a good start.
Basically:
F = m dv/dt
let's say that every second you're accelerating a mass m of air, from rest above the vehicle to V_e, as a jet of air below the vehicle:
F = m V_e
substitute for 'm'
F = (rho V_e A) V_e
rearrange:
F = rho A V_e^2
(n.b. you have to be a bit careful with those dm/dt terms, mass is conserved, so dm/dt is always technically 0!)
Re: Novel flying machines
Ash Small, Tue Jun 10 2014, 04:57PM
If BigBad is reffering to the peripheral vortex losses, these are much greater for a smaller, faster turning prop than they are for a larger, slower turning prop, assuming both are consuming the same power, for two reasons, firstly, the losses will be greater from the faster moving air, and secondly, the cross sectional area/circumferance ratio means that, for a larger, slower turning prop, a smaller percentage of the moving column is at the periphery, and experiencing losses.
You want to aim to accelerate the largest volume of air possible to a low velocity, as this is far more efficient than accelerating a small volume of air to a high velocity, due to these peripheral losses.
EDIT:The 'trade-off' is manouverability. Dr Spark's drone with 5" blades spinning at 25,000RPM demonstrates this exactly, very manouverable, but short flight times.
Ash Small, Tue Jun 10 2014, 04:57PM
BigBad wrote ...
but the reality is more complicated; some of the air is vortexing around in a circuit and not being accelerated as much, so giving less force; you could probably have some sort of fudge factor for that. However, due to viscosity you'll still get advantage from even that.
but the reality is more complicated; some of the air is vortexing around in a circuit and not being accelerated as much, so giving less force; you could probably have some sort of fudge factor for that. However, due to viscosity you'll still get advantage from even that.
If BigBad is reffering to the peripheral vortex losses, these are much greater for a smaller, faster turning prop than they are for a larger, slower turning prop, assuming both are consuming the same power, for two reasons, firstly, the losses will be greater from the faster moving air, and secondly, the cross sectional area/circumferance ratio means that, for a larger, slower turning prop, a smaller percentage of the moving column is at the periphery, and experiencing losses.
You want to aim to accelerate the largest volume of air possible to a low velocity, as this is far more efficient than accelerating a small volume of air to a high velocity, due to these peripheral losses.
EDIT:The 'trade-off' is manouverability. Dr Spark's drone with 5" blades spinning at 25,000RPM demonstrates this exactly, very manouverable, but short flight times.
Re: Novel flying machines
Patrick, Tue Jun 10 2014, 05:08PM
im trying to rewreite it in terms of only vwlocity
Patrick, Tue Jun 10 2014, 05:08PM
Uspring wrote ...
The second one is wrong.
The second one is wrong.
im trying to rewreite it in terms of only vwlocity
Re: Novel flying machines
Ash Small, Tue Jun 10 2014, 05:59PM
If the starting velocity is zero, then it can be written F=mv/t, where v is the velocity of the accelerated air.
Velocity is metres per second, acceleration is metres per second per second, which (I think) is metres per second squared, not velocity squared.
F=mass times metres per second squared, I think. (it's over 30 years since I did this stuff)
Ash Small, Tue Jun 10 2014, 05:59PM
Patrick wrote ...
im trying to rewreite it in terms of only vwlocity
Uspring wrote ...
The second one is wrong.
The second one is wrong.
im trying to rewreite it in terms of only vwlocity
If the starting velocity is zero, then it can be written F=mv/t, where v is the velocity of the accelerated air.
Velocity is metres per second, acceleration is metres per second per second, which (I think) is metres per second squared, not velocity squared.
F=mass times metres per second squared, I think. (it's over 30 years since I did this stuff)
Re: Novel flying machines
Patrick, Tue Jun 10 2014, 06:09PM
Patrick, Tue Jun 10 2014, 06:09PM
Ash Small wrote ...
If the starting velocity is zero, then it can be written F=mv/t, where v is the velocity of the accelerated air.
Velocity is metres per second, acceleration is metres per second per second, which (I think) is metres per second squared, not velocity squared.
F=mass times metres per second squared, I think. (it's over 30 years since I did this stuff)
dam it, that's what I did wrong... ( m/s^2 ) = aPatrick wrote ...
im trying to rewreite it in terms of only vwlocity
Uspring wrote ...
The second one is wrong.
The second one is wrong.
im trying to rewreite it in terms of only vwlocity
If the starting velocity is zero, then it can be written F=mv/t, where v is the velocity of the accelerated air.
Velocity is metres per second, acceleration is metres per second per second, which (I think) is metres per second squared, not velocity squared.
F=mass times metres per second squared, I think. (it's over 30 years since I did this stuff)
Re: Novel flying machines
Uspring, Tue Jun 10 2014, 06:10PM
@Bigbad:
Your usage of the symbol m is unconventional. The way you are using it, it denotes a mass rate or mass flow with units of e.g. grams/second. I think, calling this dm/dt is ok.
@Patrick:
Following Bigbads reasoning
dm/dt = rho * A * v, which makes
F = rho * A * v²
@Ash: Even if there would be no vortices, there is a big advantage to large propellers. Thrust is given by the equation above, power consumption by:
P = 1/2 * rho * A * v³
Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
Uspring, Tue Jun 10 2014, 06:10PM
@Bigbad:
Your usage of the symbol m is unconventional. The way you are using it, it denotes a mass rate or mass flow with units of e.g. grams/second. I think, calling this dm/dt is ok.
@Patrick:
Following Bigbads reasoning
dm/dt = rho * A * v, which makes
F = rho * A * v²
@Ash: Even if there would be no vortices, there is a big advantage to large propellers. Thrust is given by the equation above, power consumption by:
P = 1/2 * rho * A * v³
Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
Re: Novel flying machines
Patrick, Tue Jun 10 2014, 06:16PM
Patrick, Tue Jun 10 2014, 06:16PM
Uspring wrote ...
Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
USping, this was the relationship i was searching for, i want to make or modify props for "high mass induction, low velocity change" for max static thrust at lower power than a conventional prop would allow.Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
Re: Novel flying machines
Uspring, Tue Jun 10 2014, 06:51PM
"high mass induction, low velocity change" looks to me like "big props".
Anyway, one can read off, that the effective propeller area is the cross section of the tail of the slip stream, which is just half as large as the propeller area. This can be avoided by a ducted prop, which keeps the slip stream cylindrical.
Uspring, Tue Jun 10 2014, 06:51PM
"high mass induction, low velocity change" looks to me like "big props".
Anyway, one can read off
, that the effective propeller area is the cross section of the tail of the slip stream, which is just half as large as the propeller area. This can be avoided by a ducted prop, which keeps the slip stream cylindrical.Re: Novel flying machines
Patrick, Tue Jun 10 2014, 07:08PM
Uspring, i have read that PDF many times.
and im trying to break recirculation currents with ducts as seen above.
But getting the forces to not wobble the duct apart is hard, much less randomly guessing what the slipstream shape is since i dont have a FEA fluid program.
Patrick, Tue Jun 10 2014, 07:08PM
Uspring, i have read that PDF many times.
and im trying to break recirculation currents with ducts as seen above.
But getting the forces to not wobble the duct apart is hard, much less randomly guessing what the slipstream shape is since i dont have a FEA fluid program.
Re: Novel flying machines
Ash Small, Tue Jun 10 2014, 07:31PM
Correct me if I'm mistaken, but the same equation is used to calculate the 'drag' of aerodynamic vehicles, but in this case is multiplied by the 'drag coefficient' (for most cars, around 0.3). If (and I'm making an assumption here), the 'drag coefficient' here is 1, then doesn't this equation relate to the 'peripheral vortex losses' (drag) that I was referring to?
EDIT: I'm not sure I have all the terminology correct here, but what I mean is, it's the column of air being accelerated here (comparable to the vehicle), and it's the 'drag' of this column of air that results in the vast majority of losses (comparable to the drag losses of the vehicle), at least, that's what I always understood.
Ash Small, Tue Jun 10 2014, 07:31PM
Uspring wrote ...
@Ash: Even if there would be no vortices, there is a big advantage to large propellers. Thrust is given by the equation above, power consumption by:
P = 1/2 * rho * A * v³
Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
@Ash: Even if there would be no vortices, there is a big advantage to large propellers. Thrust is given by the equation above, power consumption by:
P = 1/2 * rho * A * v³
Smaller props need higher v for the same thrust, which makes them less efficient since power consumption rises faster with v than thrust does. Roughly battery lifetime would be about proportional to prop diameter.
Correct me if I'm mistaken, but the same equation is used to calculate the 'drag' of aerodynamic vehicles, but in this case is multiplied by the 'drag coefficient' (for most cars, around 0.3). If (and I'm making an assumption here), the 'drag coefficient' here is 1, then doesn't this equation relate to the 'peripheral vortex losses' (drag) that I was referring to?
EDIT: I'm not sure I have all the terminology correct here, but what I mean is, it's the column of air being accelerated here (comparable to the vehicle), and it's the 'drag' of this column of air that results in the vast majority of losses (comparable to the drag losses of the vehicle), at least, that's what I always understood.
Re: Novel flying machines
Uspring, Tue Jun 10 2014, 08:29PM
The physics for drag and propellers are similar. Both are based on acceleration of air masses.
The above equation is based on the kinetic energy of the air. P would be the minimum power which needs to be put into the propeller to accelerate the air. This equation assumes a 100% efficient prop.
Uspring, Tue Jun 10 2014, 08:29PM
The physics for drag and propellers are similar. Both are based on acceleration of air masses.
The above equation is based on the kinetic energy of the air. P would be the minimum power which needs to be put into the propeller to accelerate the air. This equation assumes a 100% efficient prop.
Re: Novel flying machines
Ash Small, Tue Jun 10 2014, 08:43PM
That's what I assumed. I edited the previous post as you replied, not sure if you noticed.
Ash Small, Tue Jun 10 2014, 08:43PM
Uspring wrote ...
This equation assumes a 100% efficient prop.
This equation assumes a 100% efficient prop.
That's what I assumed. I edited the previous post as you replied, not sure if you noticed.
Re: Novel flying machines
Patrick, Wed Jun 11 2014, 12:12AM
so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?
Patrick, Wed Jun 11 2014, 12:12AM
so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?
Re: Novel flying machines
Ash Small, Wed Jun 11 2014, 01:40AM
Udo provided the maths here, Patrick. I can't do that. All I can do is provide the basic theory. As I said in an earlier thread, my experience is with marirne propellers. I've learn't a lot this evening, thanks to Udo.
Ash Small, Wed Jun 11 2014, 01:40AM
Udo provided the maths here, Patrick. I can't do that. All I can do is provide the basic theory. As I said in an earlier thread, my experience is with marirne propellers. I've learn't a lot this evening, thanks to Udo.
Re: Novel flying machines
Patrick, Wed Jun 11 2014, 05:38AM
i have really important data captured. but i need to put it into excel or a table. but theres some important results revealed.
first below 4krpm these props are ultra low on thrust, but at 5krpm and above they really pick up fast.
second as would be expected, most of the thrust comes from the outer sector of the radius swept.
third, the electric "E" 11x5.5 prop meant for fixed wing flight generates:
6.5g/W at 5,100 rpm (458g, 71W)
5.7g/W at 6,100 rpm (646g, 114W)
4.9g/W at 7,050 rpm (884g, 179W) (<- at 16.1 Amps and 140F, this is getting close to the max.)
which is important, now i can choose the operating point for the hover more for the grams per Watt value than just hope and guess. It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
so a 3-blade prop should generate more thrust from a given diameter.
The above wide fan induction blades intrest me, is there any practical way to get higher g/W values with out the diameter getting bigger and bigger? After 10" in diameter ducts get hard to support, there prone to wobble and flutter.
3 and 5 blades per prop may be needed if its the outer circumference where the effciency and force are trying to hide from me.
Patrick, Wed Jun 11 2014, 05:38AM
i have really important data captured. but i need to put it into excel or a table. but theres some important results revealed.
first below 4krpm these props are ultra low on thrust, but at 5krpm and above they really pick up fast.
second as would be expected, most of the thrust comes from the outer sector of the radius swept.
third, the electric "E" 11x5.5 prop meant for fixed wing flight generates:
6.5g/W at 5,100 rpm (458g, 71W)
5.7g/W at 6,100 rpm (646g, 114W)
4.9g/W at 7,050 rpm (884g, 179W) (<- at 16.1 Amps and 140F, this is getting close to the max.)
which is important, now i can choose the operating point for the hover more for the grams per Watt value than just hope and guess. It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
so a 3-blade prop should generate more thrust from a given diameter.
The above wide fan induction blades intrest me, is there any practical way to get higher g/W values with out the diameter getting bigger and bigger? After 10" in diameter ducts get hard to support, there prone to wobble and flutter.
3 and 5 blades per prop may be needed if its the outer circumference where the effciency and force are trying to hide from me.
Re: Novel flying machines
Uspring, Wed Jun 11 2014, 09:21AM
The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power.
eff is the props efficiency, which turns out to be about 0.5 for your measurement.
Uspring, Wed Jun 11 2014, 09:21AM
so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?I was thinking of something like this:
The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power.
eff is the props efficiency, which turns out to be about 0.5 for your measurement.
Re: Novel flying machines
Ash Small, Wed Jun 11 2014, 12:55PM
FWIW, 50%-55% efficiency is about the best that super-cavitating, surface piercing props on offshore racing powerboats can achieve, although some large, slow turning props on ships can reach around 80% efficiency, if I remember correctly. It's a while since I was involved in this stuff. It's good to see you're making some progress, Patrick.
Several small props close together (as in my heptacopter design) should approximate to one large prop, and the efficiency should rise further (meaning you can carry more batteries), although this is unproven theory, as yet, anyway.
Ash Small, Wed Jun 11 2014, 12:55PM
FWIW, 50%-55% efficiency is about the best that super-cavitating, surface piercing props on offshore racing powerboats can achieve, although some large, slow turning props on ships can reach around 80% efficiency, if I remember correctly. It's a while since I was involved in this stuff. It's good to see you're making some progress, Patrick.
Patrick wrote ...
It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
Several small props close together (as in my heptacopter design) should approximate to one large prop, and the efficiency should rise further (meaning you can carry more batteries), although this is unproven theory, as yet, anyway.
Re: Novel flying machines
BigBad, Wed Jun 11 2014, 05:07PM
Both go, to a first approximation, as v^2 (where v is the speed of the rotor through the air, not the down-wash speed), and the two are related by the L/D ratio:
BigBad, Wed Jun 11 2014, 05:07PM
Uspring wrote ...
The physics for drag and propellers are similar. Both are based on acceleration of air masses.
More precisely, as the propeller (or any body) moves through the air, it deflects the air, and also creates drag on the air.The physics for drag and propellers are similar. Both are based on acceleration of air masses.
Both go, to a first approximation, as v^2 (where v is the speed of the rotor through the air, not the down-wash speed), and the two are related by the L/D ratio:
Re: Novel flying machines
Patrick, Wed Jun 11 2014, 06:28PM
in that pic are they using an electric turbine, Uspring? we cant really see the face.
if i could go from 0.5 to 0.7 eff id freak ouuut.... and consider this whole thing a sucess. im also wondering if i should mod the stator to carry more copper for the same number of turns.
Patrick, Wed Jun 11 2014, 06:28PM
Uspring wrote ...
The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power.
eff is the props efficiency, which turns out to be about 0.5 for your measurement.
it really looks like a tube around a prop or turbine, but those are heavy as i said, and difficult to attach. I was told by Embry-Riddel students to keep the the gap at 0.010 or so from tip the duct. but thats awful hard, in my first attempt you could hear the prop chattering the whole time. so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?I was thinking of something like this:
The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power.
eff is the props efficiency, which turns out to be about 0.5 for your measurement.
in that pic are they using an electric turbine, Uspring? we cant really see the face.
if i could go from 0.5 to 0.7 eff id freak ouuut.... and consider this whole thing a sucess. im also wondering if i should mod the stator to carry more copper for the same number of turns.
Re: Novel flying machines
Ash Small, Wed Jun 11 2014, 11:00PM
i think, but I'm not certain, that 'turbine' style 'fans' are only really of benefit for higher pressures, which is not really what is wanted here.
Maybe someone else can comment?
Ash Small, Wed Jun 11 2014, 11:00PM
i think, but I'm not certain, that 'turbine' style 'fans' are only really of benefit for higher pressures, which is not really what is wanted here.
Maybe someone else can comment?
Re: Novel flying machines
Patrick, Wed Jun 11 2014, 11:28PM
I'm wondering what effect pitch has, Does it capture more air mass for example...
Patrick, Wed Jun 11 2014, 11:28PM
I'm wondering what effect pitch has, Does it capture more air mass for example...
Re: Novel flying machines
BigBad, Thu Jun 12 2014, 12:07AM
yup, progressively increasing the pitch gives ever more thrust, right up to the point you stall the blades out.
of course, it's less efficient; the most efficient is quite a small pitch
BigBad, Thu Jun 12 2014, 12:07AM
yup, progressively increasing the pitch gives ever more thrust, right up to the point you stall the blades out.
of course, it's less efficient; the most efficient is quite a small pitch
Re: Novel flying machines
Patrick, Thu Jun 12 2014, 12:21AM
yes, so far all data has shown this to be the case. but why? is it air mass?
im still looking at paul lipps propeller explanation and conventional slippage/pitch propeller theory.
Patrick, Thu Jun 12 2014, 12:21AM
BigBad wrote ...
...it's less efficient; the most efficient is quite a small pitch
...it's less efficient; the most efficient is quite a small pitch
yes, so far all data has shown this to be the case. but why? is it air mass?
im still looking at paul lipps propeller explanation and conventional slippage/pitch propeller theory.
Re: Novel flying machines
BigBad, Thu Jun 12 2014, 12:34AM
It's just standard wing theory, propellers are mostly just wings spinning around in circles.
As you increase AOA the wing progressively turns from an edge-on thin section to a flat-ish plate with a comparatively huge cross-section, and the amount of air you're deflecting downwards, starts off being small, goes up, but eventually starts going back down again (the air doesn't stick to the rear of the wing, the flow separates.)
Meanwhile the drag is just going up.
So we say the wing has 'stalled'.
BigBad, Thu Jun 12 2014, 12:34AM
It's just standard wing theory, propellers are mostly just wings spinning around in circles.
As you increase AOA the wing progressively turns from an edge-on thin section to a flat-ish plate with a comparatively huge cross-section, and the amount of air you're deflecting downwards, starts off being small, goes up, but eventually starts going back down again (the air doesn't stick to the rear of the wing, the flow separates.)
Meanwhile the drag is just going up.
So we say the wing has 'stalled'.
Re: Novel flying machines
Ash Small, Thu Jun 12 2014, 01:12AM
For efficiency you require a much closer approximation to the 'ideal propeller'.
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap). (Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)
Ash Small, Thu Jun 12 2014, 01:12AM
BigBad wrote ...
(the air doesn't stick to the rear of the wing, the flow separates.)
With marine props this is referred to as 'cavitation'. This is generally undesirable, but so called 'supercavitating propellers' make advantage of this, as it can reduce friction (drag?) (I think that's the easiest way to explain it). I don't think it would be desirable in an 'aviation' prop, but it can be used to advantage in marine applications, although efficiency never seems to be above ~55%, but it can be used to advantage when boat speed is above ~100mph (when no prop is very efficient, and these become the most efficient)(the air doesn't stick to the rear of the wing, the flow separates.)
For efficiency you require a much closer approximation to the 'ideal propeller'.
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap).
(Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)Re: Novel flying machines
Patrick, Thu Jun 12 2014, 02:54AM
is the shallow pitch capturing more mass, but imparting less velocity change? (than a higher pitch, all else being equal)
i have seen this, there very large, slow turning, ok so all my experiments show larger diameter shallow pitch props are best, but a 12 or 13 inch prop is getting quite big, any gains would be eaten up by supporting structure of the duct. the small diameter props are clearly better at lower speeds, but only while producing low thrust, hence the octo-copters.
what about a 5 blade shallow pitch prop? would adding more blades make up for the lesser diameter and angular velcity at the circumference?
Patrick, Thu Jun 12 2014, 02:54AM
is the shallow pitch capturing more mass, but imparting less velocity change? (than a higher pitch, all else being equal)
Ash Small wrote ...
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap). (Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap).
(Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)i have seen this, there very large, slow turning, ok so all my experiments show larger diameter shallow pitch props are best, but a 12 or 13 inch prop is getting quite big, any gains would be eaten up by supporting structure of the duct. the small diameter props are clearly better at lower speeds, but only while producing low thrust, hence the octo-copters.
what about a 5 blade shallow pitch prop? would adding more blades make up for the lesser diameter and angular velcity at the circumference?
Re: Novel flying machines
Dr. Slack, Thu Jun 12 2014, 05:58AM
egads! To mix metaphors, by lettting the tail wag the dog, you're chasing your tail round and round in a circle. Concentrate on what's dog, ie the physics, acceleration, power etc, and what's tail, practical engineering things like weight of the duct, or weight of the thing you're trying to fly. Comparing like with like is important. But if I have this advantage of gettign cheap ESCs from my brother-in-law, doesn't that mean I should use more of them? Well, yes, but that's not physics.
Zoom right back out, until you have a 'thing' that has to be levitated by acclerating a fluid flow. For flow impulse equal to craft weight, a narrow jet has high energy, and in the limit, an infinitely wide down draught has zero energy. So the physics of generating lift says use as wide a down draft as possible.
However you've got to drive that down draught with blades that have profile drag (friction) and tip drag (induced, pressure difference ameliorated by a duct), which influence the length of blade chosen. Happy the designer who has to make a 15m sailplane or a 2ft wide quad, because that compromise decision is taken out of his hands.
If you have a very long blade and a very light craft, you don't need much fluid speed, so a shallow pitch is what's required. *Keeping the down-draugt size constant*, a heavier craft needs more impulse per second, so more mass flow, so a faster prop, or a higher pitch. Everything flows from the demands of the craft weight, and the choice of down-draft diameter.
Reformulate the problem so it's clear what are arbitrary choices, what's demanded from physics, what are engineering optimisarions, and keep your eye on the donut, not the hole
Dr. Slack, Thu Jun 12 2014, 05:58AM
Patrick wrote ...
is the shallow pitch capturing more mass, but imparting less velocity change? (than a higher pitch, all else being equal)
i have seen this, there very large, slow turning, ok so all my experiments show larger diameter shallow pitch props are best, but a 12 or 13 inch prop is getting quite big, any gains would be eaten up by supporting structure of the duct. the small diameter props are clearly better at lower speeds, but only while producing low thrust, hence the octo-copters.
what about a 5 blade shallow pitch prop? would adding more blades make up for the lesser diameter and angular velcity at the circumference?
is the shallow pitch capturing more mass, but imparting less velocity change? (than a higher pitch, all else being equal)
Ash Small wrote ...
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap). (Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)
Maybe look at some of the 'human powered' flying machines that look like they're made from balsa and clingfilm (ceran wrap).
(Not sure if you need a 'proxy server' to view this Stateside of 'the pond'. If so, try googling 'Canadian team's human-powered helicopter takes flight'. The machine is called 'Atlas'.)i have seen this, there very large, slow turning, ok so all my experiments show larger diameter shallow pitch props are best, but a 12 or 13 inch prop is getting quite big, any gains would be eaten up by supporting structure of the duct. the small diameter props are clearly better at lower speeds, but only while producing low thrust, hence the octo-copters.
what about a 5 blade shallow pitch prop? would adding more blades make up for the lesser diameter and angular velcity at the circumference?
egads! To mix metaphors, by lettting the tail wag the dog, you're chasing your tail round and round in a circle. Concentrate on what's dog, ie the physics, acceleration, power etc, and what's tail, practical engineering things like weight of the duct, or weight of the thing you're trying to fly. Comparing like with like is important. But if I have this advantage of gettign cheap ESCs from my brother-in-law, doesn't that mean I should use more of them? Well, yes, but that's not physics.
Zoom right back out, until you have a 'thing' that has to be levitated by acclerating a fluid flow. For flow impulse equal to craft weight, a narrow jet has high energy, and in the limit, an infinitely wide down draught has zero energy. So the physics of generating lift says use as wide a down draft as possible.
However you've got to drive that down draught with blades that have profile drag (friction) and tip drag (induced, pressure difference ameliorated by a duct), which influence the length of blade chosen. Happy the designer who has to make a 15m sailplane or a 2ft wide quad, because that compromise decision is taken out of his hands.
If you have a very long blade and a very light craft, you don't need much fluid speed, so a shallow pitch is what's required. *Keeping the down-draugt size constant*, a heavier craft needs more impulse per second, so more mass flow, so a faster prop, or a higher pitch. Everything flows from the demands of the craft weight, and the choice of down-draft diameter.
Reformulate the problem so it's clear what are arbitrary choices, what's demanded from physics, what are engineering optimisarions, and keep your eye on the donut, not the hole
Re: Novel flying machines
Patrick, Thu Jun 12 2014, 06:20AM
im still trying to figure out where the donut is... Much less keep my eye on it, so far ive really taken a kick to the head with all this.
and i havent even figured out what the profile of a duct should be. Should it flare the fluid flow out?
But im greatful for all the help ive gotten so far.
heres the motor:
1400 k sub V. 150 watts continuous, it seems.
0.051 ohms, 3 phase brushless.
120 degrees F, for ~10 amps.
150 degrees F, for ~15+amps.
Data for the "windsor" master airscrew 10x4 prop.
Tip mach number:
10x3.14 =31.4" per rev
7,000rpm = 116rps
31.4 x 116 = 3,642 in/s = 303 ft/s
mach 1 at 800 ft = 1100 ft/s
303 / 1100 = 0.275 M
Well at least i caught a break with it being 0.27M, sub-sonic.
ellippse prop, from Paul Lipps plane.
again a unique shape. There was a article that explained his reasoning and how to dimension a prop, but now i cant find it.
Patrick, Thu Jun 12 2014, 06:20AM
im still trying to figure out where the donut is... Much less keep my eye on it, so far ive really taken a kick to the head with all this.
and i havent even figured out what the profile of a duct should be. Should it flare the fluid flow out?
But im greatful for all the help ive gotten so far.
heres the motor:
1400 k sub V. 150 watts continuous, it seems.
0.051 ohms, 3 phase brushless.
120 degrees F, for ~10 amps.
150 degrees F, for ~15+amps.
Data for the "windsor" master airscrew 10x4 prop.
Tip mach number:
10x3.14 =31.4" per rev
7,000rpm = 116rps
31.4 x 116 = 3,642 in/s = 303 ft/s
mach 1 at 800 ft = 1100 ft/s
303 / 1100 = 0.275 M
Well at least i caught a break with it being 0.27M, sub-sonic.
ellippse prop, from Paul Lipps plane.
again a unique shape. There was a article that explained his reasoning and how to dimension a prop, but now i cant find it.
Re: Novel flying machines
BigBad, Thu Jun 12 2014, 02:25PM
I think that the duct should contract on the outflow side because the air sausage you sucked in each second at the top is moving faster, and so is thinner.
But you don't want to overdo it; if you bring the duct outlet in too much you're building a jet engine, the pressure in the duct will go above ambient, and the airflow speed will increase; BUT OBVIOUSLY YOU DON'T WANT THE AIRFLOW SPEED TO INCREASE!!! ;)
If you don't bring the duct in at all, you'll get vortexing within the duct, and that will waste energy.
BigBad, Thu Jun 12 2014, 02:25PM
I think that the duct should contract on the outflow side because the air sausage you sucked in each second at the top is moving faster, and so is thinner.
But you don't want to overdo it; if you bring the duct outlet in too much you're building a jet engine, the pressure in the duct will go above ambient, and the airflow speed will increase; BUT OBVIOUSLY YOU DON'T WANT THE AIRFLOW SPEED TO INCREASE!!! ;)
If you don't bring the duct in at all, you'll get vortexing within the duct, and that will waste energy.
Re: Novel flying machines
Uspring, Thu Jun 12 2014, 03:51PM
Patrick wrote:
The slip stream around the prop constricts after it leaves the prop as shown here That is (strangely) due to the effect of the pressure the prop creates behind it. The pressure will accelerate the air behind the prop. At the prop, air speed is v/2 and at the end, when the pressure has equalized to the ambient pressure, it will have accelerated to v. (I'm looking at the special case of a prop not moving relative to the ambient air). Since the volume of air going into the prop is the same as the one going out at the end of the stream, the cross section of the stream end is just half as that of the prop.
The amount of energy required is determined by the mass flow rate and its velocity at the end of the stream. It will increase with v^2 (mass rate assumed to be constant). Thrust will be proportional to v. Thus a low v will increase the thrust to energy consumption ratio.
With a e.g. cylindrical duct, the constriction of flow behind the prop is avoided. For a given mass flow that implies, that the speed of air exiting the duct is just half of that of the unducted case. For a given power input the result is 26% more thrust.
I believe that this can be even carried further by ducts which expand behind the prop. But probably, if that space is available, a bigger prop should be used.
Uspring, Thu Jun 12 2014, 03:51PM
Patrick wrote:
and i havent even figured out what the profile of a duct should beLooking around for ducts in wiki etc. the effect of reducing vortices is mentioned, but I think another effect is more important (really sticking my neck out).
The slip stream around the prop constricts after it leaves the prop as shown here
That is (strangely) due to the effect of the pressure the prop creates behind it. The pressure will accelerate the air behind the prop. At the prop, air speed is v/2 and at the end, when the pressure has equalized to the ambient pressure, it will have accelerated to v. (I'm looking at the special case of a prop not moving relative to the ambient air). Since the volume of air going into the prop is the same as the one going out at the end of the stream, the cross section of the stream end is just half as that of the prop.The amount of energy required is determined by the mass flow rate and its velocity at the end of the stream. It will increase with v^2 (mass rate assumed to be constant). Thrust will be proportional to v. Thus a low v will increase the thrust to energy consumption ratio.
With a e.g. cylindrical duct, the constriction of flow behind the prop is avoided. For a given mass flow that implies, that the speed of air exiting the duct is just half of that of the unducted case. For a given power input the result is 26% more thrust.
I believe that this can be even carried further by ducts which expand behind the prop. But probably, if that space is available, a bigger prop should be used.
Re: Novel flying machines
Ash Small, Thu Jun 12 2014, 05:32PM
I seem to remember that the duct cross-section should be (approximately) the section of a wing, with the inside of the duct being shaped like the upper side of the wing, and the outside being cylindrical.
I can sketch it later, but have to go out soon.
I think this is pretty much in accordance with Udo, post above.
EDIT: This is a very quick, rough approximation of what I mean, and is not necessarily to scale, etc:
The prop, I think, goes pretty much at the narrowest point, I think.
Ash Small, Thu Jun 12 2014, 05:32PM
I seem to remember that the duct cross-section should be (approximately) the section of a wing, with the inside of the duct being shaped like the upper side of the wing, and the outside being cylindrical.
I can sketch it later, but have to go out soon.
I think this is pretty much in accordance with Udo, post above.
EDIT: This is a very quick, rough approximation of what I mean, and is not necessarily to scale, etc:
The prop, I think, goes pretty much at the narrowest point, I think.
Re: Novel flying machines
Patrick, Thu Jun 12 2014, 08:45PM
so i want to open the downstream funnel abit. this was my goal more than a year ago, but its a hard shape to make. so i got to get the mold right in one to three attempts.
a two plug mold seems to be the solution, with an NACA cross section. The question then becomes, 10 inch in diameter at the prop circumference. what diameter do i taper out to at what distance behind the prop face? would visualizing with saw dust be useful? then graph in cad a exponential curve?
Edit: saw dust and flour are useless, I guess I'll use my Anemometer at different stations to visualize the pressure boundary.
NACA calculator:
Patrick, Thu Jun 12 2014, 08:45PM
so i want to open the downstream funnel abit. this was my goal more than a year ago, but its a hard shape to make. so i got to get the mold right in one to three attempts.
a two plug mold seems to be the solution, with an NACA cross section. The question then becomes, 10 inch in diameter at the prop circumference. what diameter do i taper out to at what distance behind the prop face? would visualizing with saw dust be useful? then graph in cad a exponential curve?
Edit: saw dust and flour are useless, I guess I'll use my Anemometer at different stations to visualize the pressure boundary.
NACA calculator:
Re: Novel flying machines
Uspring, Fri Jun 13 2014, 10:05AM
is probably good for a prop not at rest relative to ambient air. Slipstreams are less bent for props moving forward in air.
The shape of the slipstream is caused in front of the prop by the low pressure (suction), which draws air inward toward the axis of the prop. The inward component of flow doesn't change, as it goes through the prop. The higher pressure behind the prop causes the inward flow to bend outward again, but not before the slipstream has lost diameter.
A duct alters the shape of the stream and prevents its constriction behind the prop and leads to the desirable lower air velocity. It cannot do so abrubtly as e.g. with a very short duct. It has to bend the stream to parallel to the axis in a continuous way in order to avoid turbulences.
That being said, these thoughts come much more from intuition than education on my side and for sure, this is reinventing the wheel.
Uspring, Fri Jun 13 2014, 10:05AM
The question then becomes, 10 inch in diameter at the prop circumference. what diameter do i taper out to at what distance behind the prop face?A more or less cylindrical duct as shown here
is probably good for a prop not at rest relative to ambient air. Slipstreams are less bent for props moving forward in air.The shape of the slipstream is caused in front of the prop by the low pressure (suction), which draws air inward toward the axis of the prop. The inward component of flow doesn't change, as it goes through the prop. The higher pressure behind the prop causes the inward flow to bend outward again, but not before the slipstream has lost diameter.
A duct alters the shape of the stream and prevents its constriction behind the prop and leads to the desirable lower air velocity. It cannot do so abrubtly as e.g. with a very short duct. It has to bend the stream to parallel to the axis in a continuous way in order to avoid turbulences.
That being said, these thoughts come much more from intuition than education on my side and for sure, this is reinventing the wheel.
Re: Novel flying machines
Ash Small, Fri Jun 13 2014, 06:40PM
Once again, I think we're back to where we were. The larger the prop, and the lower the velocity of the accelerated air, the the smaller will be the constriction of the slipstream, and the larger will be the diameter 0f the column of air under/behind the prop, and so the shorter the duct needs to be.
There is simply no alternative to a large, slow turning prop if you are after extended flight times, ducts or no ducts, although a longer duct will help.
I'm still of the opinion (and I'm wondering if your test rig can test this), that if you use three props as close together as possible, for example, whether or not this 'approximates' to one large prop, with an associated increase in efficiency.
My reasoning is that there should only be one 'slipstream', shared between the three props, and only one 'constricted' column of air, rateher than three separate slipstreams, etc. (at least, an 'approximation' of this. This is why I believe the 'heptacopter' layout should improve efficiency considerably, but this concept will be more problematic to test with your rig, I suspect.)
Ash Small, Fri Jun 13 2014, 06:40PM
Once again, I think we're back to where we were. The larger the prop, and the lower the velocity of the accelerated air, the the smaller will be the constriction of the slipstream, and the larger will be the diameter 0f the column of air under/behind the prop, and so the shorter the duct needs to be.
There is simply no alternative to a large, slow turning prop if you are after extended flight times, ducts or no ducts, although a longer duct will help.
I'm still of the opinion (and I'm wondering if your test rig can test this), that if you use three props as close together as possible, for example, whether or not this 'approximates' to one large prop, with an associated increase in efficiency.
My reasoning is that there should only be one 'slipstream', shared between the three props, and only one 'constricted' column of air, rateher than three separate slipstreams, etc. (at least, an 'approximation' of this. This is why I believe the 'heptacopter' layout should improve efficiency considerably, but this concept will be more problematic to test with your rig, I suspect.)
Re: Novel flying machines
Patrick, Fri Jun 13 2014, 07:31PM
yep, this is looking like a dead stick.
Perhaps i should be looking at nitro-electric, like a diesel-electric train. then for sure i could get 30-45 minute flights.
Patrick, Fri Jun 13 2014, 07:31PM
yep, this is looking like a dead stick.
Perhaps i should be looking at nitro-electric, like a diesel-electric train. then for sure i could get 30-45 minute flights.
Re: Novel flying machines
BigBad, Fri Jun 13 2014, 09:02PM
I still don't buy the argument that the guy that did an hour+ long flight with an electric helicopter shouldn't be emulated.
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.
BigBad, Fri Jun 13 2014, 09:02PM
I still don't buy the argument that the guy that did an hour+ long flight with an electric helicopter shouldn't be emulated.
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.
Re: Novel flying machines
Patrick, Sat Jun 14 2014, 12:12AM
Patrick, Sat Jun 14 2014, 12:12AM
BigBad wrote ...
I still don't buy the argument that the guy that did an hour+ long flight with an electric helicopter shouldn't be emulated.
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.
i guess i should compare battery mass to payload mass vs duration of flight and all up mass. remember the whlole is to drag useful instruments through the sky. so far they're just using helis or quads with 90% battery and a keychain HD cam. I still don't buy the argument that the guy that did an hour+ long flight with an electric helicopter shouldn't be emulated.
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.
Re: Novel flying machines
Ash Small, Sat Jun 14 2014, 12:55AM
So what is the maximun weight limit?
I seem to remember reading something like 12kg, but can't find the article/link.
Can someone please confirm this, or provide the correct figure.
This is the starting point I'd use, and then work back from there. Once you've done some calculations, you may find you don't need whatever the maximun legal weight is, although this would surely give the maximun flight time possible with the best power to weight batteries available.
I suggest that if you don't use an approach something along these lines, someone else will, and they will then have the advantage over you in the 'market place'.
You could always produce cheaper versions as well, with reduced flight time, but if maximum flight time is the goal, then you have to push everything to the limit, or the competition WILL be able to do better.
Ash Small, Sat Jun 14 2014, 12:55AM
So what is the maximun weight limit?
I seem to remember reading something like 12kg, but can't find the article/link.
Can someone please confirm this, or provide the correct figure.
This is the starting point I'd use, and then work back from there. Once you've done some calculations, you may find you don't need whatever the maximun legal weight is, although this would surely give the maximun flight time possible with the best power to weight batteries available.
I suggest that if you don't use an approach something along these lines, someone else will, and they will then have the advantage over you in the 'market place'.
You could always produce cheaper versions as well, with reduced flight time, but if maximum flight time is the goal, then you have to push everything to the limit, or the competition WILL be able to do better.
Re: Novel flying machines
Patrick, Sat Jun 14 2014, 02:48AM
well around 6 to 8 lbs starts getting heavy and big for an "easy" to deploy drone.
the 12x3.8 inch prop did turn out to be the most efficient.
Patrick, Sat Jun 14 2014, 02:48AM
well around 6 to 8 lbs starts getting heavy and big for an "easy" to deploy drone.
the 12x3.8 inch prop did turn out to be the most efficient.
Re: Novel flying machines
Ash Small, Sat Jun 14 2014, 03:14AM
Just out of interest, what are the figures for the 12x3.8 prop?
What is the weight of motor plus prop, and how many watt hours (Or whatever the correct terminology is, it's late here) do you get from, say, a pound of batteries?
Ash Small, Sat Jun 14 2014, 03:14AM
Patrick wrote ...
well around 6 to 8 lbs starts getting heavy and big for an "easy" to deploy drone.
the 12x3.8 inch prop did turn out to be the most efficient.
well around 6 to 8 lbs starts getting heavy and big for an "easy" to deploy drone.
the 12x3.8 inch prop did turn out to be the most efficient.
Just out of interest, what are the figures for the 12x3.8 prop?
What is the weight of motor plus prop, and how many watt hours (Or whatever the correct terminology is, it's late here) do you get from, say, a pound of batteries?
Re: Novel flying machines
Patrick, Sat Jun 14 2014, 05:34AM
THe batteries are 3.3 Amp-hours, 3s, 11.1 Volts, 255g. (so theres two i use in parallel.)
Watts up data logger, power harness, and two lipo batteries.
these are big motors.
props with there data tables. i could only get 2 rows on the 12x3.8 prop till the motor starting overheating, i couldnt even press it 500 more RPM with ou the current trying to go past 20 amps.
About the data,
look at the 5,000 RPM row on the 12 inch prop, its 733g and 5.13 g/w
then look at the 7,100RPM on the 10 inch, its 723g and 5.15 g/w
4 blade? possibly, or am i crazy?
Patrick, Sat Jun 14 2014, 05:34AM
THe batteries are 3.3 Amp-hours, 3s, 11.1 Volts, 255g. (so theres two i use in parallel.)
Watts up data logger, power harness, and two lipo batteries.
these are big motors.
props with there data tables. i could only get 2 rows on the 12x3.8 prop till the motor starting overheating, i couldnt even press it 500 more RPM with ou the current trying to go past 20 amps.
About the data,
look at the 5,000 RPM row on the 12 inch prop, its 733g and 5.13 g/w
then look at the 7,100RPM on the 10 inch, its 723g and 5.15 g/w
4 blade? possibly, or am i crazy?
Re: Novel flying machines
Ash Small, Sat Jun 14 2014, 09:03AM
Not sure if my maths is correct (I've been up all night, couldn't sleep), but I make it four motors plus a kg of batteries equals ~twelve minutes flight time (quick 'order of magnitude' type calculation.)
Maybe someone can check this.
Ash Small, Sat Jun 14 2014, 09:03AM
Not sure if my maths is correct (I've been up all night, couldn't sleep), but I make it four motors plus a kg of batteries equals ~twelve minutes flight time (quick 'order of magnitude' type calculation.)
Maybe someone can check this.
Re: Novel flying machines
Patrick, Sun Jun 15 2014, 02:01AM
that may be right, but i know a nitro electric engine with traditional props should fly for 30-45 min and whiegh equal or less.
Patrick, Sun Jun 15 2014, 02:01AM
that may be right, but i know a nitro electric engine with traditional props should fly for 30-45 min and whiegh equal or less.
Re: Novel flying machines
Uspring, Sun Jun 15 2014, 12:08PM
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
Uspring, Sun Jun 15 2014, 12:08PM
look at the 5,000 RPM row on the 12 inch prop, its 733g and 5.13 g/wNot much difference in prop performance there. But if you look at the numbers at 6.7g/W, there is a bigger lift for the bigger prop. It seems like the bigger prop looses efficiency at higher rpms.
then look at the 7,100RPM on the 10 inch, its 723g and 5.15 g/w
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.Assuming a
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
Re: Novel flying machines
Ash Small, Sun Jun 15 2014, 10:55PM
I think this is similar to what I concluded, but didn't post (as I wanted to think about it for a bit).
I think it's a fairly linear relationship, my figure of ~12 minutes flight time for four motors and props plus 1kg of batteries will also be equal to flight time for two motors and props, and 1/2 kg of batteries.
Payload will be double with four motors and props and 1kg batteries, but it's a linear relationship.
Of course, with the same payload, you can carry a bit more in bettery weight, but efficiency isn't really related to any of this. You need to use 'other methods' to increase efficiency, although Im still of the opionion that peripheral losses will decrease with more motors/props, due to the 'combined' increase in cross section/circumferance of the 'combined' column of accelerated air.
Of course. for the same payload, I expext flight times to by increased with a configuration along the lines of a heptacopter carrying 2kg of batteries, but then total mass gets up to over 7 kg. (could probably carry maybe an extra kg of batteries here, maybe even a bit more, which. I guess should increase flight time to ~20 minutes (maybe more), but by this time I imagine IC engines/ swashplates would probably be advantageous.
EDIT: that 'initial' 12 minute figure, from which everything else has been extrapolated is based on approximate 'hover time'.
Increasing prop diameter would increase efficiency still further.
Ash Small, Sun Jun 15 2014, 10:55PM
Uspring wrote ...
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
look at the 5,000 RPM row on the 12 inch prop, its 733g and 5.13 g/wNot much difference in prop performance there. But if you look at the numbers at 6.7g/W, there is a bigger lift for the bigger prop. It seems like the bigger prop looses efficiency at higher rpms.
then look at the 7,100RPM on the 10 inch, its 723g and 5.15 g/w
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.Assuming a
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
I think this is similar to what I concluded, but didn't post (as I wanted to think about it for a bit).
I think it's a fairly linear relationship, my figure of ~12 minutes flight time for four motors and props plus 1kg of batteries will also be equal to flight time for two motors and props, and 1/2 kg of batteries.
Payload will be double with four motors and props and 1kg batteries, but it's a linear relationship.
Of course, with the same payload, you can carry a bit more in bettery weight, but efficiency isn't really related to any of this. You need to use 'other methods' to increase efficiency, although Im still of the opionion that peripheral losses will decrease with more motors/props, due to the 'combined' increase in cross section/circumferance of the 'combined' column of accelerated air.
Of course. for the same payload, I expext flight times to by increased with a configuration along the lines of a heptacopter carrying 2kg of batteries, but then total mass gets up to over 7 kg. (could probably carry maybe an extra kg of batteries here, maybe even a bit more, which. I guess should increase flight time to ~20 minutes (maybe more), but by this time I imagine IC engines/ swashplates would probably be advantageous.
EDIT: that 'initial' 12 minute figure, from which everything else has been extrapolated is based on approximate 'hover time'.
Increasing prop diameter would increase efficiency still further.
Re: Novel flying machines
BigBad, Mon Jun 16 2014, 12:24AM
This is a good point. And yet other helicopters can go for an hour or more.
Presumably the overall weight of the helicopter relative to the disk area is a critical parameter which gives the constants of proportionality for hover time.
Something is not scaling down right.
That raises the question, why is this particular helicopter heavier than the electric helis that fly for over an hour? Are the batteries heavy, is the rotor heavy, are the motors heavy, is it the avionics, is it the payload that is heavy relative to the disc area?
BigBad, Mon Jun 16 2014, 12:24AM
Uspring wrote ...
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
Yeah, sure, it's basically a freaking big pile of battery, but that just means you need to beg, borrow or steal a big pile of battery from somewhere.Assuming a
F ~ P ^ (2/3)
dependence, the additional flight of time with more batteries will be more than cancelled out by the extra power to carry them beyond some point. It turns out, that for just hovering, the mass of the batteries should be twice the mass of the copter without batteries for max flight time. I've taken battery capacity to be proportional to its mass.
This is a good point. And yet other helicopters can go for an hour or more.
Presumably the overall weight of the helicopter relative to the disk area is a critical parameter which gives the constants of proportionality for hover time.
Something is not scaling down right.
That raises the question, why is this particular helicopter heavier than the electric helis that fly for over an hour? Are the batteries heavy, is the rotor heavy, are the motors heavy, is it the avionics, is it the payload that is heavy relative to the disc area?
Re: Novel flying machines
Ash Small, Mon Jun 16 2014, 02:27AM
These are very good points, but I assume Patrick has chosen his components carefully, and that they are pretty 'state of the art'.
Personally, after seeing comparisons of a ten inch and 12 inch prop, I'd like to see some data for, say, a 30" prop, for example.
The disc loading for that human powered helicopter, 'Atlas', that I linked to above was extremely low.
I've been saying all along that the only way to substantially increase efficiency is to substantially increase prop size, which equates to a substantial decrease in disc loading. I've also explained my reasoning in considerable depth.
EDIT: also, another point I've not really pressed is the 'angle of attack' of the blades. Ideally, you want a 'wing section' with a zero degree angle of attack, as this creates minimum turbulence, with all the lift created by the reduced pressure on the upper surface of the wing. Maybe it's time to try the old 'balsa wood and tissue paper' type wings of the 'rubber band' powered models I remember building as a kid?
There is some drag associated with the increased surface area of the 'wing', but this reduces as the speed of rotation decreases.
Once again, though, this all becomes a trade-off between efficiency and manouverability.
NB: Patrick's original design was required to be small enough to fly through doorways, and be manouverable enough to fly around inside buildings, as part of a competition, with only a few minutes flight time required.
Maybe it's time for another visit to my local helicopter museum?
Ash Small, Mon Jun 16 2014, 02:27AM
BigBad wrote ...
Something is not scaling down right.
That raises the question, why is this particular helicopter heavier than the electric helis that fly for over an hour? Are the batteries heavy, is the rotor heavy, are the motors heavy, is it the avionics, is it the payload that is heavy relative to the disc area?
Something is not scaling down right.
That raises the question, why is this particular helicopter heavier than the electric helis that fly for over an hour? Are the batteries heavy, is the rotor heavy, are the motors heavy, is it the avionics, is it the payload that is heavy relative to the disc area?
These are very good points, but I assume Patrick has chosen his components carefully, and that they are pretty 'state of the art'.
Personally, after seeing comparisons of a ten inch and 12 inch prop, I'd like to see some data for, say, a 30" prop, for example.
The disc loading for that human powered helicopter, 'Atlas', that I linked to above was extremely low.
I've been saying all along that the only way to substantially increase efficiency is to substantially increase prop size, which equates to a substantial decrease in disc loading. I've also explained my reasoning in considerable depth.
EDIT: also, another point I've not really pressed is the 'angle of attack' of the blades. Ideally, you want a 'wing section' with a zero degree angle of attack, as this creates minimum turbulence, with all the lift created by the reduced pressure on the upper surface of the wing. Maybe it's time to try the old 'balsa wood and tissue paper' type wings of the 'rubber band' powered models I remember building as a kid?
There is some drag associated with the increased surface area of the 'wing', but this reduces as the speed of rotation decreases.
Once again, though, this all becomes a trade-off between efficiency and manouverability.
NB: Patrick's original design was required to be small enough to fly through doorways, and be manouverable enough to fly around inside buildings, as part of a competition, with only a few minutes flight time required.
Maybe it's time for another visit to my local helicopter museum?
Re: Novel flying machines
Patrick, Mon Jun 16 2014, 02:44AM
yes, ive chosen the components carefully, but i need to lift heavy insturments, for a long duration of flight.
Patrick, Mon Jun 16 2014, 02:44AM
Ash Small wrote ...
BigBad wrote ...
Something is not scaling down right.
That raises the question, ..... is it the payload that is heavy relative to the disc area?
Personally, after seeing comparisons of a ten inch and 12 inch prop, I'd like to see some data for, say' a 30" prop, for example.Something is not scaling down right.
That raises the question, ..... is it the payload that is heavy relative to the disc area?
yes, ive chosen the components carefully, but i need to lift heavy insturments, for a long duration of flight.
Re: Novel flying machines
Ash Small, Mon Jun 16 2014, 02:53AM
My calculations above actually ignored the 'payload' completely. I was going to 'factor this in' after getting a better grasp of the basic principles, and how they scale.
Ash Small, Mon Jun 16 2014, 02:53AM
Patrick wrote ...
yes, ive chosen the components carefully, but i need to lift heavy insturments, for a long duration of flight.
Ash Small wrote ...
BigBad wrote ...
Something is not scaling down right.
That raises the question, ..... is it the payload that is heavy relative to the disc area?
Personally, after seeing comparisons of a ten inch and 12 inch prop, I'd like to see some data for, say' a 30" prop, for example.Something is not scaling down right.
That raises the question, ..... is it the payload that is heavy relative to the disc area?
yes, ive chosen the components carefully, but i need to lift heavy insturments, for a long duration of flight.
My calculations above actually ignored the 'payload' completely. I was going to 'factor this in' after getting a better grasp of the basic principles, and how they scale.
Re: Novel flying machines
Uspring, Mon Jun 16 2014, 11:37AM
A somewhat exotic example:
A 2 m^2 prop (60" diameter) with a heli weight of 2 kg and 4 kg batteries of the type
Uspring, Mon Jun 16 2014, 11:37AM
Presumably the overall weight of the helicopter relative to the disk area is a critical parameter which gives the constants of proportionality for hover time.Exactly. If you use the equations for thrust, assume a certain mass ratio between copter and battery weight and a certain ratio between battery weight and capacity, the hovering time will be proportional to the square root of the ratio of disk area to copter mass.
A somewhat exotic example:
A 2 m^2 prop (60" diameter) with a heli weight of 2 kg and 4 kg batteries of the type
THe batteries are 3.3 Amp-hours, 3s, 11.1 Volts, 255g. (so theres two i use in parallel.)might just hover for an hour.
Re: Novel flying machines
Ash Small, Mon Jun 16 2014, 04:51PM
Thanks for providing some maths to illustrate this, Udo.
Significantly increasing the prop diameter will significantly increase the efficiency.
I think a good starting point might be, as Meil pointed out, to start with the biggest prop that will reasonably fit in the back of an average car, for example.
Ash Small, Mon Jun 16 2014, 04:51PM
Uspring wrote ...
A somewhat exotic example:
A 2 m^2 prop (60" diameter) with a heli weight of 2 kg and 4 kg batteries of the type
A somewhat exotic example:
A 2 m^2 prop (60" diameter) with a heli weight of 2 kg and 4 kg batteries of the type
THe batteries are 3.3 Amp-hours, 3s, 11.1 Volts, 255g. (so theres two i use in parallel.)might just hover for an hour.
Thanks for providing some maths to illustrate this, Udo.
Significantly increasing the prop diameter will significantly increase the efficiency.
I think a good starting point might be, as Meil pointed out, to start with the biggest prop that will reasonably fit in the back of an average car, for example.
Re: Novel flying machines
BigBad, Tue Jun 17 2014, 12:26AM
Frankly if you make it bigger, so you have to disassemble it a bit to put it in a car, you should still do that.
So far as I can tell, the maximum efficiency you can get is mostly to do with disc loading, everything else is an also-ran.
I mean, sure if you've got the wrong props on your bird, or too much or too little battery, or the motor is inefficient, then you'll get substandard hang-time, but once those are within reason in the correct proportions, the only thing that will give you more hang-time is reducing the disc loading, and it's the one thing you can always improve by making the props bigger, and rebalancing everything.
BigBad, Tue Jun 17 2014, 12:26AM
Frankly if you make it bigger, so you have to disassemble it a bit to put it in a car, you should still do that.
So far as I can tell, the maximum efficiency you can get is mostly to do with disc loading, everything else is an also-ran.
I mean, sure if you've got the wrong props on your bird, or too much or too little battery, or the motor is inefficient, then you'll get substandard hang-time, but once those are within reason in the correct proportions, the only thing that will give you more hang-time is reducing the disc loading, and it's the one thing you can always improve by making the props bigger, and rebalancing everything.
Re: Novel flying machines
Patrick, Tue Jun 17 2014, 02:55AM
at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
Patrick, Tue Jun 17 2014, 02:55AM
at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
Re: Novel flying machines
Ash Small, Tue Jun 17 2014, 09:14AM
This is exactly what I've been repeating all the way through all these related threads, although the terminology I've been using is cross section/cicumferance ratio. The losses are all at the periphery. Larger prop means lower velocity of accelerated air 'disc loading' is just 'different terminology'.
Yep.
Exactly.
Very probably.
Ash Small, Tue Jun 17 2014, 09:14AM
BigBad wrote ...
So far as I can tell, the maximum efficiency you can get is mostly to do with disc loading, everything else is an also-ran.
So far as I can tell, the maximum efficiency you can get is mostly to do with disc loading, everything else is an also-ran.
This is exactly what I've been repeating all the way through all these related threads, although the terminology I've been using is cross section/cicumferance ratio. The losses are all at the periphery. Larger prop means lower velocity of accelerated air 'disc loading' is just 'different terminology'.
BigBad wrote ...
Frankly if you make it bigger, so you have to disassemble it a bit to put it in a car, you should still do that.
Frankly if you make it bigger, so you have to disassemble it a bit to put it in a car, you should still do that.
Yep.
BigBad wrote ...
I mean, sure if you've got the wrong props on your bird, or too much or too little battery, or the motor is inefficient, then you'll get substandard hang-time, but once those are within reason in the correct proportions, the only thing that will give you more hang-time is reducing the disc loading, and it's the one thing you can always improve by making the props bigger, and rebalancing everything.
I mean, sure if you've got the wrong props on your bird, or too much or too little battery, or the motor is inefficient, then you'll get substandard hang-time, but once those are within reason in the correct proportions, the only thing that will give you more hang-time is reducing the disc loading, and it's the one thing you can always improve by making the props bigger, and rebalancing everything.
Exactly.
Patrick wrote ...
at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
Very probably.
Re: Novel flying machines
BigBad, Tue Jun 17 2014, 01:42PM
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
For example this guy gets an hour from his quadcopter:
BigBad, Tue Jun 17 2014, 01:42PM
Patrick wrote ...
at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
Yes, although you can get the same disc area with a quad in the same external dimension, but the structure to rigidly hold the rotors in their relative positions may be slightly heavier, but it's mechanically much simpler; and you'd get much the same hang-time.at this point, im wondering if a contra-rotating/coaxial is the way to go. this way i have the largest external dimension being the rotor disc.
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
For example this guy gets an hour from his quadcopter:
Re: Novel flying machines
Ash Small, Tue Jun 17 2014, 03:11PM
But, four discs of half the diameter has twice the circumferance in total, therefore the peripheral losses are twice as great as one disc with the same area, and the peripheral losses dominate virtually to the exclusion of all other losses, all other factors being equal.
(If the four rotors are close enough together, though, losses won't actually be twice, but if they are far enough apart not to 'interfere' with each other they will be.)
Se my earlier posts. Peripheral losses are the dominant factor here.
Ash Small, Tue Jun 17 2014, 03:11PM
BigBad wrote ...
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
But, four discs of half the diameter has twice the circumferance in total, therefore the peripheral losses are twice as great as one disc with the same area, and the peripheral losses dominate virtually to the exclusion of all other losses, all other factors being equal.
(If the four rotors are close enough together, though, losses won't actually be twice, but if they are far enough apart not to 'interfere' with each other they will be.)
Se my earlier posts. Peripheral losses are the dominant factor here.
Re: Novel flying machines
Patrick, Tue Jun 17 2014, 03:56PM
heres what im thinking about: and and
Patrick, Tue Jun 17 2014, 03:56PM
heres what im thinking about:
and and Re: Novel flying machines
Ash Small, Tue Jun 17 2014, 04:30PM
With conta-rotating props?
More detail, please.
Ash Small, Tue Jun 17 2014, 04:30PM
Patrick wrote ...
heres what im thinking about: and and
heres what im thinking about:
and and With conta-rotating props?
More detail, please.
Re: Novel flying machines
Patrick, Tue Jun 17 2014, 05:15PM
Patrick, Tue Jun 17 2014, 05:15PM
Ash Small wrote ...
With conta-rotating props?
More detail, please.
like the tupulev bear bomber, that would wipe the capitalist filth from the earth.Patrick wrote ...
heres what im thinking about: and and
heres what im thinking about:
and and With conta-rotating props?
More detail, please.
Re: Novel flying machines
BigBad, Tue Jun 17 2014, 06:07PM
On the topic of novel flying machines, I've got a VTOL rocket design I've been working on for a while. It's got a pumped biprop engine, vertical takeoff/landing (it hooks off/back onto a cable) and after reaching apogee it falls sideways prior to landing (aerodynamic braking greatly reduces the landing burn). I've got a basic layout diagram for it, but no detailed design as yet, so I haven't modelled the mass distribution to make it sure it will keep the correct attitude at each point in the flight. It's looking quite promising though.
BigBad, Tue Jun 17 2014, 06:07PM
Ash Small wrote ...
But, four discs of half the diameter has twice the circumferance in total, therefore the peripheral losses are twice as great as one disc with the same area, and the peripheral losses dominate virtually to the exclusion of all other losses, all other factors being equal.
(If the four rotors are close enough together, though, losses won't actually be twice, but if they are far enough apart not to 'interfere' with each other they will be.)
Se my earlier posts. Peripheral losses are the dominant factor here.
I agree that a quad won't have the same hang-time of a single main prop, but the link showed someone got over an hour, so it has decent performance.BigBad wrote ...
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
I mean 4 discs of half the diameter have the same area and width as one disk of the full diameter; so it makes no difference in area.
But, four discs of half the diameter has twice the circumferance in total, therefore the peripheral losses are twice as great as one disc with the same area, and the peripheral losses dominate virtually to the exclusion of all other losses, all other factors being equal.
(If the four rotors are close enough together, though, losses won't actually be twice, but if they are far enough apart not to 'interfere' with each other they will be.)
Se my earlier posts. Peripheral losses are the dominant factor here.
On the topic of novel flying machines, I've got a VTOL rocket design I've been working on for a while. It's got a pumped biprop engine, vertical takeoff/landing (it hooks off/back onto a cable) and after reaching apogee it falls sideways prior to landing (aerodynamic braking greatly reduces the landing burn). I've got a basic layout diagram for it, but no detailed design as yet, so I haven't modelled the mass distribution to make it sure it will keep the correct attitude at each point in the flight. It's looking quite promising though.
Re: Novel flying machines
Ash Small, Tue Jun 17 2014, 07:15PM
That's a relief, I would have really struggled with the maths trying to prove my point
I'm looking forward to seeing more details regarding the rocket.
EDIT: I did qualify my statement with 'all other factors being equal'. If you can find 'advantage' elsewhere.........
Ash Small, Tue Jun 17 2014, 07:15PM
BigBad wrote ...
I agree that a quad won't have the same hang-time of a single main prop
I agree that a quad won't have the same hang-time of a single main prop
That's a relief, I would have really struggled with the maths trying to prove my point
I'm looking forward to seeing more details regarding the rocket.
EDIT: I did qualify my statement with 'all other factors being equal'. If you can find 'advantage' elsewhere.........
Re: Novel flying machines
Ash Small, Tue Jun 17 2014, 08:16PM
Sorry, I didn't make myself clear. I meant like these:
but with contra rotating props? and 'could you please provide some more detail?
Your post didn't make it clear that you were still considering contra-rotating props or not.
It does sound like a good idea to me.
(Sorry about the double post)
EDIT:
Ash Small, Tue Jun 17 2014, 08:16PM
Patrick wrote ...
like the tupulev bear bomber, that would wipe the capitalist filth from the earth.
like the tupulev bear bomber, that would wipe the capitalist filth from the earth.
Sorry, I didn't make myself clear. I meant like these:
Patrick wrote ...
heres what im thinking about: and and
heres what im thinking about:
and and but with contra rotating props? and 'could you please provide some more detail?
Your post didn't make it clear that you were still considering contra-rotating props or not.
It does sound like a good idea to me.
(Sorry about the double post)
EDIT:
Re: Novel flying machines
Patrick, Tue Jun 17 2014, 10:05PM
Patrick, Tue Jun 17 2014, 10:05PM
Ash Small wrote ...
Sorry, I didn't make myself clear. I meant like these:
but with contra rotating props? and 'could you please provide some more detail?
Your post didn't make it clear that you were still considering contra-rotating props or not.
It does sound like a good idea to me.
(Sorry about the double post)
EDIT:
Yep, seems to give lowest loading in a surface area.Patrick wrote ...
like the tupulev bear bomber, that would wipe the capitalist filth from the earth.
like the tupulev bear bomber, that would wipe the capitalist filth from the earth.
Sorry, I didn't make myself clear. I meant like these:
Patrick wrote ...
heres what im thinking about: and and
heres what im thinking about:
and and but with contra rotating props? and 'could you please provide some more detail?
Your post didn't make it clear that you were still considering contra-rotating props or not.
It does sound like a good idea to me.
(Sorry about the double post)
EDIT:
Re: Novel flying machines
Ash Small, Wed Jun 18 2014, 12:52AM
Yep.
Ash Small, Wed Jun 18 2014, 12:52AM
Yep.
Re: Novel flying machines
BigBad, Thu Jun 19 2014, 10:25PM
This guy used a 20Ah battery with 17 inch props on a quad and got over an hour flight time:
(figures are at the end of the video)
That's about twice the prop area than 12 inch props, and three times the battery, to get an hour flight; sounds about right.
BigBad, Thu Jun 19 2014, 10:25PM
This guy used a 20Ah battery with 17 inch props on a quad and got over an hour flight time:
(figures are at the end of the video)
That's about twice the prop area than 12 inch props, and three times the battery, to get an hour flight; sounds about right.
Re: Novel flying machines
Conundrum, Sat Jun 21 2014, 02:07PM
Hmm. I can't wait for "Mythbusters: Prison Breakout Special"... Escape via drone?! Seriously, this totally needs doing on a Bond film and soon.
AAaaaand in other news,
Conundrum, Sat Jun 21 2014, 02:07PM
Hmm. I can't wait for "Mythbusters: Prison Breakout Special"... Escape via drone?! Seriously, this totally needs doing on a Bond film and soon.
AAaaaand in other news,
Re: Novel flying machines
BigBad, Sat Jun 21 2014, 06:36PM
I want to be picked up and carried around by a cloud of drones, even if I'm not escaping from a max security prison.
BigBad, Sat Jun 21 2014, 06:36PM
I want to be picked up and carried around by a cloud of drones, even if I'm not escaping from a max security prison.
Re: Novel flying machines
Patrick, Sun Jun 22 2014, 12:03AM
There is a new Ebola outbreak, monitoring the fruit bat population and their access to pig farms could be done with some more advanced instrumentation (years from now.) For example, 20,000 drones 10 cm in diameter, one time use, flown by 100 pilots for 25 medical and PhD experts could be seeded over the relevant areas. landing and taking off o a minute by minute basis.
The use of a single "bluefin 21" sub, to search for the maylasian airliner, seems like a child randomly scribbling with crayon, when Michelangelo would be using a brush. But maybe they only had one on hand.
In any case, fleets of drones are the future for practical application, not these single one off toys.
I do have concerns with landmine and AOL CD after use issues...
Patrick, Sun Jun 22 2014, 12:03AM
There is a new Ebola outbreak, monitoring the fruit bat population and their access to pig farms could be done with some more advanced instrumentation (years from now.) For example, 20,000 drones 10 cm in diameter, one time use, flown by 100 pilots for 25 medical and PhD experts could be seeded over the relevant areas. landing and taking off o a minute by minute basis.
The use of a single "bluefin 21" sub, to search for the maylasian airliner, seems like a child randomly scribbling with crayon, when Michelangelo would be using a brush. But maybe they only had one on hand.
In any case, fleets of drones are the future for practical application, not these single one off toys.
I do have concerns with landmine and AOL CD after use issues...
Re: Novel flying machines
Ash Small, Sun Jun 22 2014, 08:25PM
OK, so maybe I will try to do some maths here after all. Power consumed is P = 1/2 * rho * A * v³
which is half air density times area times velocity cubed, which shows that it's the velocity (presumably the air column velocity in this case) multiplied by half the area (disc area, presumably). I'll assume Rho to be a constant for now).
By far the most dominant factor here is the 'velocity cubed' term, which shows that any increase in air velocity is going to have a 'very negative' effect on efficiency, and a 'very large' effect on power consumed.
This is also very similar to the 'drag coefficient' equation, here: P = (1/2)(rho)(V³)(A)(Cd) Where, Cd = Coefficient of Drag.
I assume in this case, because it is a column of air that is being acceleraled, that the drag coefficient of a column of air is equal to one.
These two equations then become exactly the same, which implies that the peripheral losses at the interface between the moving column of air and the surrounding, stationary, air completely dominate all of the losses from the system.
Now, decreasing the velocity of the column of air is exactly the same as reducing the disc loading. Both result in a larger, slower turning prop and an increase in efficiency due to a lower air velocity.
Ash Small, Sun Jun 22 2014, 08:25PM
OK, so maybe I will try to do some maths here after all. Power consumed is P = 1/2 * rho * A * v³
which is half air density times area times velocity cubed, which shows that it's the velocity (presumably the air column velocity in this case) multiplied by half the area (disc area, presumably). I'll assume Rho to be a constant for now).
By far the most dominant factor here is the 'velocity cubed' term, which shows that any increase in air velocity is going to have a 'very negative' effect on efficiency, and a 'very large' effect on power consumed.
This is also very similar to the 'drag coefficient' equation, here: P = (1/2)(rho)(V³)(A)(Cd) Where, Cd = Coefficient of Drag.
I assume in this case, because it is a column of air that is being acceleraled, that the drag coefficient of a column of air is equal to one.
These two equations then become exactly the same, which implies that the peripheral losses at the interface between the moving column of air and the surrounding, stationary, air completely dominate all of the losses from the system.
Now, decreasing the velocity of the column of air is exactly the same as reducing the disc loading. Both result in a larger, slower turning prop and an increase in efficiency due to a lower air velocity.
Re: Novel flying machines
BigBad, Sun Jun 22 2014, 10:21PM
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
BigBad, Sun Jun 22 2014, 10:21PM
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
Re: Novel flying machines
Ash Small, Mon Jun 23 2014, 09:22AM
Personally, I think the Chinook is a compromise for a number of reasons.
From what I remember, the blades on a Chinook overlap a bit (the rear prop is higher), so you end up with what approximates to one oval shaped column of air. Basically, if you reach the limits as far as one prop goes, you can halve the disc loading by adding another. There are other considerations. I do keep pointing out that it's a trade off between manouverability and efficiency. Counter-rotating props have other advantages too.
The maths does say that the 'propeller equation' and the 'drag equation' are identical, for all intents and purposes.
EDIT: Can't open PPT files, I boycott Microsoft software as much as I'm able to. Open Office doesn't seem to open them.
Ash Small, Mon Jun 23 2014, 09:22AM
BigBad wrote ...
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
Personally, I think the Chinook is a compromise for a number of reasons.
From what I remember, the blades on a Chinook overlap a bit (the rear prop is higher), so you end up with what approximates to one oval shaped column of air. Basically, if you reach the limits as far as one prop goes, you can halve the disc loading by adding another. There are other considerations. I do keep pointing out that it's a trade off between manouverability and efficiency. Counter-rotating props have other advantages too.
The maths does say that the 'propeller equation' and the 'drag equation' are identical, for all intents and purposes.
EDIT: Can't open PPT files, I boycott Microsoft software as much as I'm able to. Open Office doesn't seem to open them.
Re: Novel flying machines
Uspring, Mon Jun 23 2014, 10:40AM
Ash Small wrote:
In the case of air drag on a car, the idea behind the equation is, that a column of air in front of the car is accelerated to the speed of e.g. the wind shield. So the power lost by the car is the same as the power needed to give the air column its speed. From this a drag force can be calculated.
All of this has nothing to do with vortices around the prop tips. The equations quoted describe an ideal behaviour, where such effects are not taken into account. They can accounted for by adding some fudge factor to the equations.
Uspring, Mon Jun 23 2014, 10:40AM
Ash Small wrote:
These two equations then become exactly the same, which implies that the peripheral losses at the interface between the moving column of air and the surrounding, stationary, air completely dominate all of the losses from the system.These equations describe the kinetic energy that is contained in a moving cylinder of air. For a propeller, the air has to be accelerated in order to generate thrust, so it is not a "lossy" mechanism, but the intent of the prop. Not all of the power put into the prop is converted into air energy, so one usually defines a props efficiency by the ratio of air power to prop power.
In the case of air drag on a car, the idea behind the equation is, that a column of air in front of the car is accelerated to the speed of e.g. the wind shield. So the power lost by the car is the same as the power needed to give the air column its speed. From this a drag force can be calculated.
All of this has nothing to do with vortices around the prop tips. The equations quoted describe an ideal behaviour, where such effects are not taken into account. They can accounted for by adding some fudge factor to the equations.
Re: Novel flying machines
Dr. Slack, Mon Jun 23 2014, 01:16PM
Try LibreOffice, OpenOffice didn't get onging development for some reason and forked into LO. That will open it.
Dr. Slack, Mon Jun 23 2014, 01:16PM
EDIT: Can't open PPT files, I boycott Microsoft software as much as I'm able to. Open Office doesn't seem to open them
Try LibreOffice, OpenOffice didn't get onging development for some reason and forked into LO. That will open it.
Re: Novel flying machines
BigBad, Mon Jun 23 2014, 07:54PM
I didn't have any problem with OpenOffice4.1.0
BigBad, Mon Jun 23 2014, 07:54PM
I didn't have any problem with OpenOffice4.1.0
Re: Novel flying machines
Ash Small, Mon Jun 23 2014, 07:57PM
This it what one would presumably call a 'first order approximation'. I argue that all of the losses come from some form of drag, but it is just a question of semantics I think. You can probably identify several 'distinct' types of loss if you were so inclined, but it all comes down to the resistance of the air to being accelerated, or, in other words, it's viscosity.
I've drawn a quick graph. I assume the x axis (A) is m^2 and the y axis (v^3) is m/s.
I'm not mathematically minded, but I'll try and answer any further questions.
EDIT: Actually I'm still trying to work out what the graph means
(if in doubt, draw a picture!!)
(x axis is 0-10, y axis is 0-100)
I'll sort out the PPT thing later, thanks for the tips.
Ash Small, Mon Jun 23 2014, 07:57PM
Uspring wrote ...
Ash Small wrote:
In the case of air drag on a car, the idea behind the equation is, that a column of air in front of the car is accelerated to the speed of e.g. the wind shield. So the power lost by the car is the same as the power needed to give the air column its speed. From this a drag force can be calculated.
All of this has nothing to do with vortices around the prop tips. The equations quoted describe an ideal behaviour, where such effects are not taken into account. They can accounted for by adding some fudge factor to the equations.
Ash Small wrote:
These two equations then become exactly the same, which implies that the peripheral losses at the interface between the moving column of air and the surrounding, stationary, air completely dominate all of the losses from the system.These equations describe the kinetic energy that is contained in a moving cylinder of air. For a propeller, the air has to be accelerated in order to generate thrust, so it is not a "lossy" mechanism, but the intent of the prop. Not all of the power put into the prop is converted into air energy, so one usually defines a props efficiency by the ratio of air power to prop power.
In the case of air drag on a car, the idea behind the equation is, that a column of air in front of the car is accelerated to the speed of e.g. the wind shield. So the power lost by the car is the same as the power needed to give the air column its speed. From this a drag force can be calculated.
All of this has nothing to do with vortices around the prop tips. The equations quoted describe an ideal behaviour, where such effects are not taken into account. They can accounted for by adding some fudge factor to the equations.
This it what one would presumably call a 'first order approximation'. I argue that all of the losses come from some form of drag, but it is just a question of semantics I think. You can probably identify several 'distinct' types of loss if you were so inclined, but it all comes down to the resistance of the air to being accelerated, or, in other words, it's viscosity.
I've drawn a quick graph. I assume the x axis (A) is m^2 and the y axis (v^3) is m/s.
I'm not mathematically minded, but I'll try and answer any further questions.
EDIT: Actually I'm still trying to work out what the graph means
(if in doubt, draw a picture!!)
(x axis is 0-10, y axis is 0-100)
I'll sort out the PPT thing later, thanks for the tips.
Re: Novel flying machines
Patrick, Mon Jun 23 2014, 08:23PM
im in the middle of a tri-blade experiment, results to follow shortly.
Patrick, Mon Jun 23 2014, 08:23PM
im in the middle of a tri-blade experiment, results to follow shortly.
Re: Novel flying machines
Uspring, Tue Jun 24 2014, 09:19AM
Ash Small wrote:
Being picky: the resistance of air being accelerated is due to its mass, not its viscosity.
Uspring, Tue Jun 24 2014, 09:19AM
Ash Small wrote:
I argue that all of the losses come from some form of drag, but it is just a question of semantics I think. You can probably identify several 'distinct' types of loss if you were so inclined, but it all comes down to the resistance of the air to being accelerated, or, in other words, it's viscosity.All of the props energy ends up as kinetic energy of air. Some part of it is useful, i.e. the downward air velocity, which results in an upward thrust. Other energies, e.g. the swirl around the blades and a helical component of the downward stream don't contribute to the upward thrust and are therefore regarded as losses.
Being picky: the resistance of air being accelerated is due to its mass, not its viscosity.
Re: Novel flying machines
Ash Small, Tue Jun 24 2014, 10:55AM
All of these losses pretty much follow the same law, ie the 1/2A x v^3 thing, which seems to be common through all of the propeller efficiency/drag stuff.
I think it is something to do with viscosity, especially as the drag forces increase. I seem to remember getting a similar graph when dropping different sized ball bearings into a tube of oil as a student.
There is certainly more than one way to analyse any problem.
Ash Small, Tue Jun 24 2014, 10:55AM
Uspring wrote ...
Ash Small wrote:
Being picky: the resistance of air being accelerated is due to its mass, not its viscosity.
Ash Small wrote:
I argue that all of the losses come from some form of drag, but it is just a question of semantics I think. You can probably identify several 'distinct' types of loss if you were so inclined, but it all comes down to the resistance of the air to being accelerated, or, in other words, it's viscosity.All of the props energy ends up as kinetic energy of air. Some part of it is useful, i.e. the downward air velocity, which results in an upward thrust. Other energies, e.g. the swirl around the blades and a helical component of the downward stream don't contribute to the upward thrust and are therefore regarded as losses.
Being picky: the resistance of air being accelerated is due to its mass, not its viscosity.
All of these losses pretty much follow the same law, ie the 1/2A x v^3 thing, which seems to be common through all of the propeller efficiency/drag stuff.
I think it is something to do with viscosity, especially as the drag forces increase. I seem to remember getting a similar graph when dropping different sized ball bearings into a tube of oil as a student.
There is certainly more than one way to analyse any problem.
Re: Novel flying machines
Uspring, Tue Jun 24 2014, 11:34AM
Uspring, Tue Jun 24 2014, 11:34AM
All of these losses pretty much follow the same law, ie the 1/2A x v^3 thing, which seems to be common through all of the propeller efficiency/drag stuff.I think that we have a terminology problem. What in terms of the v^3 law the drag is for e.g. a car, is the thrust for a propeller. For the case of the car I would call it loss, but not for the prop.
Re: Novel flying machines
Ash Small, Tue Jun 24 2014, 11:39AM
But does it not also equal the 'drag' losses from the periphery of the accelerated column of air?
These two 'forces' are equal and opposite, surely?
Ash Small, Tue Jun 24 2014, 11:39AM
But does it not also equal the 'drag' losses from the periphery of the accelerated column of air?
These two 'forces' are equal and opposite, surely?
Re: Novel flying machines
Uspring, Tue Jun 24 2014, 01:19PM
Uspring, Tue Jun 24 2014, 01:19PM
But does it not also equal the 'drag' losses from the periphery of the accelerated column of air?The air column will eventually be slowed and stopped by the surrounding air. But that is not relevant to the thrust the prop generates.
Re: Novel flying machines
BigBad, Tue Jun 24 2014, 01:59PM
It is somewhat relevant, depending on the Reynolds number.
The Reynolds number for a small drone is going to be a lot lower than a full size helicopter.
The lower Reynolds number means that viscosity is more significant than normal; model aircraft are designed slightly differently to full size aircraft for this reason.
Well, yeah, all aircraft are a bunch of compromises flying in close proximity, but I think you're completely overstressing the tip loss thing.
BigBad, Tue Jun 24 2014, 01:59PM
It is somewhat relevant, depending on the Reynolds number.
The Reynolds number for a small drone is going to be a lot lower than a full size helicopter.
The lower Reynolds number means that viscosity is more significant than normal; model aircraft are designed slightly differently to full size aircraft for this reason.
Ash Small wrote ...
Personally, I think the Chinook is a compromise for a number of reasons.
BigBad wrote ...
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
I'm not sure the disadvantage is quite as big as you think it is, otherwise twin rotor helicopters like the Chinook wouldn't exist.
Tip losses are treated fairly well here:
Personally, I think the Chinook is a compromise for a number of reasons.
Well, yeah, all aircraft are a bunch of compromises flying in close proximity, but I think you're completely overstressing the tip loss thing.
Ash Small wrote ...
EDIT: Can't open PPT files, I boycott Microsoft software as much as I'm able to. Open Office doesn't seem to open them.
It gives the tip losses as about 3%. EDIT: Can't open PPT files, I boycott Microsoft software as much as I'm able to. Open Office doesn't seem to open them.
Re: Novel flying machines
Ash Small, Tue Jun 24 2014, 07:48PM
Ok BB, I understand now, a mis-understanding.
When I talk about 'peripheral losses' I don't mean 'tip losses'.
I'm talking about the 'drag losses' at the circumferance of the accelerated column of air. This is where the 'peripheral losses' are, in the 'eddy currents' and 'vortices' at the interface of the accelerated column and the surrounding air.
This is why I use analogies with 'drag coefficients' of cars, etc'
I've not actually got on to the 'prop design' bit yet, I'm still trying to 'identify' the losses, if you like.
I don't mean 'tip losses', I mean 'losses from the periphery of the accelerated column of air'. I believe it's important that we understand these things first, before we try to minimise them. I hope this clears up any mis-understanding.
EDIT: It's these 'drag losses' that dominate over everything else.
EDIT EDIT: I've also noticed the similarity with the 'propeller equation' and realised that it 'looks like' the 'same maths'.
EDIT EDIT EDIT: Udo provided the equations, for which I'm extremely grateful
Ash Small, Tue Jun 24 2014, 07:48PM
Ok BB, I understand now, a mis-understanding.
When I talk about 'peripheral losses' I don't mean 'tip losses'.
I'm talking about the 'drag losses' at the circumferance of the accelerated column of air. This is where the 'peripheral losses' are, in the 'eddy currents' and 'vortices' at the interface of the accelerated column and the surrounding air.
This is why I use analogies with 'drag coefficients' of cars, etc'
I've not actually got on to the 'prop design' bit yet, I'm still trying to 'identify' the losses, if you like.
I don't mean 'tip losses', I mean 'losses from the periphery of the accelerated column of air'. I believe it's important that we understand these things first, before we try to minimise them. I hope this clears up any mis-understanding.
EDIT: It's these 'drag losses' that dominate over everything else.
EDIT EDIT: I've also noticed the similarity with the 'propeller equation' and realised that it 'looks like' the 'same maths'.
EDIT EDIT EDIT: Udo provided the equations, for which I'm extremely grateful
Re: Novel flying machines
Carbon_Rod, Wed Jun 25 2014, 10:17AM
Some chainsaws offer a 2.8hp brushless motor, ESC, and battery for under $200:
Just need 4 of them.... and some really big rotor blades.
Carbon_Rod, Wed Jun 25 2014, 10:17AM
Some chainsaws offer a 2.8hp brushless motor, ESC, and battery for under $200:
Just need 4 of them.... and some really big rotor blades.
Re: Novel flying machines
Patrick, Wed Jun 25 2014, 10:12PM
i was thinking of a glow-electric engine. Evo 40NX glow engine, with a coupler to a BC3536 outrunner.
like here: (motor)
and here: (glow engine)
Patrick, Wed Jun 25 2014, 10:12PM
Carbon_Rod wrote ...
Some chainsaws offer a 2.8hp brushless motor, ESC, and battery for under $200:
Just need 4 of them.... and some really big rotor blades.
yeah but a chain saws a bit over kill. Some chainsaws offer a 2.8hp brushless motor, ESC, and battery for under $200:
Just need 4 of them.... and some really big rotor blades.
i was thinking of a glow-electric engine. Evo 40NX glow engine, with a coupler to a BC3536 outrunner.
like here:
(motor)and here:
(glow engine)
Re: Novel flying machines
Patrick, Fri Jun 27 2014, 06:18AM
Ive made a 4 minute test flight, i guess i should upload to youtube the onboard video.
so im at 3.94 V per cell after 4 minutes of flight. thats looking like a 8 minute flight, with a 6.6Ah battery.
im real tired, its 2am here, soon to bed. bt if i do the math right, 6.6Ah = 8 minutes in hover.
then, 30 / 8 = 3.75 x 6.6 = 25Ah of battery.
and, 3.75 x 510 grams = 1.9kg of battery.
this for 30 minutes or so of flight?
yikes, i could lift that (4kg), but then id lose some duration from greater all up mass too. so im thinking itd be 20mins at best, i not even going to try that with this machine, shes just to valuable.
Patrick, Fri Jun 27 2014, 06:18AM
Ive made a 4 minute test flight, i guess i should upload to youtube the onboard video.
so im at 3.94 V per cell after 4 minutes of flight. thats looking like a 8 minute flight, with a 6.6Ah battery.
im real tired, its 2am here, soon to bed. bt if i do the math right, 6.6Ah = 8 minutes in hover.
then, 30 / 8 = 3.75 x 6.6 = 25Ah of battery.
and, 3.75 x 510 grams = 1.9kg of battery.
this for 30 minutes or so of flight?
yikes, i could lift that (4kg), but then id lose some duration from greater all up mass too. so im thinking itd be 20mins at best, i not even going to try that with this machine, shes just to valuable.
Re: Novel flying machines
Ash Small, Fri Jun 27 2014, 08:18AM
Patrick, I suggest we try to do the maths for your existing assymetrical tri-copter, and then 'scale it up' (maybe without the ducts) and do the maths for the 'largest practical design', but base everything on your existing design, because it seems to be a 'reasonable compromise' in the first place.
I'm not in any rush for the figures, though
Ash Small, Fri Jun 27 2014, 08:18AM
Patrick, I suggest we try to do the maths for your existing assymetrical tri-copter, and then 'scale it up' (maybe without the ducts) and do the maths for the 'largest practical design', but base everything on your existing design, because it seems to be a 'reasonable compromise' in the first place.
I'm not in any rush for the figures, though
Re: Novel flying machines
Patrick, Fri Jun 27 2014, 08:37AM
i do have an inflight data logger, so tomorrow ill make a full duration flight down to 20% on the batteries, then well see the amp hours put through the machine.
im thinking of a brushless motor, with 3 phase schottky bridge rectified, and a glo engine, to produce 800-900 watts
(500 W electrical, after losses) with the glow carb cotrolled automatically via a PID loop and servo. This would hold 10.5V min 12.5 max the problem is there would have to be something like a battery or ultra-capacitor to slow the volt change with load, to prevent high frequency load-throttle oscillations. and im sure there would need to be a roll off frequency on the V detector... like an SMPS.
Patrick, Fri Jun 27 2014, 08:37AM
i do have an inflight data logger, so tomorrow ill make a full duration flight down to 20% on the batteries, then well see the amp hours put through the machine.
im thinking of a brushless motor, with 3 phase schottky bridge rectified, and a glo engine, to produce 800-900 watts
(500 W electrical, after losses) with the glow carb cotrolled automatically via a PID loop and servo. This would hold 10.5V min 12.5 max the problem is there would have to be something like a battery or ultra-capacitor to slow the volt change with load, to prevent high frequency load-throttle oscillations. and im sure there would need to be a roll off frequency on the V detector... like an SMPS.
Re: Novel flying machines
Ash Small, Fri Jun 27 2014, 09:28AM
I think we should see what the maths does as we scale everything up, and reduce 'downdraught velocity'. I'm expecting to get significantly longer battery life, but we'll at least get some figures and then compare 'diesel-electric' to 'battery' power.
Ash Small, Fri Jun 27 2014, 09:28AM
I think we should see what the maths does as we scale everything up, and reduce 'downdraught velocity'. I'm expecting to get significantly longer battery life, but we'll at least get some figures and then compare 'diesel-electric' to 'battery' power.
Re: Novel flying machines
Uspring, Fri Jun 27 2014, 09:48AM
TOF ~ mb / (ma+mb)^3/2
ma being the aircraft bare mass and mb the mass of the battery. This will go through a max at mb = 2*ma. What's the mass of the copter w/o Lipos?
For lots of batteries, the capacity/weight ratio of the batteries becomes increasingly important. It looks like the NCR18650s are better than yours in this respect.
Uspring, Fri Jun 27 2014, 09:48AM
this for 30 minutes or so of flight?Flight time scales up linearly with battery size only if the battery mass is an insignificant part of total aircraft mass. Generally you'll have a time of flight dependency like this:
TOF ~ mb / (ma+mb)^3/2
ma being the aircraft bare mass and mb the mass of the battery. This will go through a max at mb = 2*ma. What's the mass of the copter w/o Lipos?
For lots of batteries, the capacity/weight ratio of the batteries becomes increasingly important. It looks like the NCR18650s are better than yours in this respect.
Re: Novel flying machines
Ash Small, Fri Jun 27 2014, 10:08AM
Yes, but efficiency goes up with prop size, and there is LOADS of room for improvement.
Ideally, you want reduction boxes on those motors. (or reduction belt drives, or something)
It will increase overall mass, but it will increase efficiency more.
Ash Small, Fri Jun 27 2014, 10:08AM
Yes, but efficiency goes up with prop size, and there is LOADS of room for improvement.
Ideally, you want reduction boxes on those motors. (or reduction belt drives, or something)
It will increase overall mass, but it will increase efficiency more.
Re: Novel flying machines
Uspring, Fri Jun 27 2014, 12:16PM
Uspring, Fri Jun 27 2014, 12:16PM
Yes, but efficiency goes up with prop size, and there is LOADS of room for improvement.I didn't mean to imply that prop area doesn't matter. The equation just allows to calculate how ToF changes by just adding batteries and keeping everything else the same.
Re: Novel flying machines
Patrick, Fri Jun 27 2014, 04:26PM
made another flight, it looks like a 8+ minute machine. thats with 10x4.5 multrirotor props. So, im thinking 12 or 14 inch props maybe the practical limit as far as diameter.
All-up-mass (AUW) = 1.61 kg
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
Patrick, Fri Jun 27 2014, 04:26PM
made another flight, it looks like a 8+ minute machine. thats with 10x4.5 multrirotor props. So, im thinking 12 or 14 inch props maybe the practical limit as far as diameter.
All-up-mass (AUW) = 1.61 kg
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
Uspring wrote ...
TOF ~ mb / (ma+mb)^3/2
ma being the aircraft bare mass and mb the mass of the battery. This will go through a max at mb = 2*ma. What's the mass of the copter w/o Lipos?
where did you get the 3/2 exponent? i only get 8 minutes if i use 3/1.6 exponent... (1.875) otherwise i think you have it close to my personal experience. so if i double the battery mass, it doesnt look good.that presumes i did the math right, im awfful tired...this for 30 minutes or so of flight?Flight time scales up linearly with battery size only if the battery mass is an insignificant part of total aircraft mass. Generally you'll have a time of flight dependency like this:
TOF ~ mb / (ma+mb)^3/2
ma being the aircraft bare mass and mb the mass of the battery. This will go through a max at mb = 2*ma. What's the mass of the copter w/o Lipos?
Re: Novel flying machines
Ash Small, Fri Jun 27 2014, 05:30PM
I need to draw another graph incorporating the thrust equation (F = rho * A * v²) and the power equation (P = 1/2 * rho * A * v³).
It seems obvious to me that increasing A and decreasing v leads to significant increases in efficiency, but I want to try to quantify this with a graph. (I tried plotting A against v^3 earlier, but I don't think I had the maths correct enough to tell me much, I need to incorporate the thrust equation, too.)
I'm currently thinking that ToF can be significantly increased by mounting the three props of an assymetric tri-copter on the 'legs' of a 'Y' frame, and mounting the motors, batteries, etc. at the intersection, and using reduction belt drives to turn much larger props than Patrick is currently considering.
It will probably take me all weekend to 'get my head round' the maths, though.
I'm convinced that the losses can be reduced by at least an order of magnitude without increasing rotor size to much more than ~1 metre diameter.
Ash Small, Fri Jun 27 2014, 05:30PM
I need to draw another graph incorporating the thrust equation (F = rho * A * v²) and the power equation (P = 1/2 * rho * A * v³).
It seems obvious to me that increasing A and decreasing v leads to significant increases in efficiency, but I want to try to quantify this with a graph. (I tried plotting A against v^3 earlier, but I don't think I had the maths correct enough to tell me much, I need to incorporate the thrust equation, too.)
I'm currently thinking that ToF can be significantly increased by mounting the three props of an assymetric tri-copter on the 'legs' of a 'Y' frame, and mounting the motors, batteries, etc. at the intersection, and using reduction belt drives to turn much larger props than Patrick is currently considering.
It will probably take me all weekend to 'get my head round' the maths, though.
I'm convinced that the losses can be reduced by at least an order of magnitude without increasing rotor size to much more than ~1 metre diameter.
Re: Novel flying machines
Patrick, Fri Jun 27 2014, 09:33PM
this is what i was planing...
torsional couplers, look at the melted one (Romanovs work) i dont know where to get these...
the ebay ones for 6.35mm to 5mm look like theyed melt too.
on this one we see the all metal type of coupler, not sure if these are meant for this purpose, or for stepper motors and such.
Patrick, Fri Jun 27 2014, 09:33PM
this is what i was planing...
torsional couplers, look at the melted one (Romanovs work) i dont know where to get these...
the ebay ones for 6.35mm to 5mm look like theyed melt too.
on this one we see the all metal type of coupler, not sure if these are meant for this purpose, or for stepper motors and such.
Re: Novel flying machines
Uspring, Sat Jun 28 2014, 10:11AM
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
F = eff * (2 * rho * A * P^2)^(1/3)
so the proportionalities
F ~ P^(2/3) or
P ~ F^(3/2)
hold. Since we hover, we have
F ~ ma+mb
for the flight duration we have
TOF ~ 1/P
Put this all together and there is the to the power of 3/2 dependence.
Uspring, Sat Jun 28 2014, 10:11AM
All-up-mass (AUW) = 1.61 kgHere's a table of expected flight times for addittional battery packs:
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
where did you get the 3/2 exponent?This is from the equation relating thrust to power consumption:
F = eff * (2 * rho * A * P^2)^(1/3)
so the proportionalities
F ~ P^(2/3) or
P ~ F^(3/2)
hold. Since we hover, we have
F ~ ma+mb
for the flight duration we have
TOF ~ 1/P
Put this all together and there is the to the power of 3/2 dependence.
Re: Novel flying machines
Ash Small, Sat Jun 28 2014, 12:10PM
If I ignore Rho for the time being, F=Av^2 and P=1/2Av^3.
There's something I'm missing, I think.
Udo wrote:"F = eff * (2 * rho * A * P^2)^(1/3)
so the proportionalities
F ~ P^(2/3) or
P ~ F^(3/2)
hold."
I don't see how you can relate F and P in this way. I'm probably missing something.
Surely power is dependant on A? The smaller A is, the more power is needed to overcome additional losses in order to achieve the same force?
I'm trying to reach the point where I can plot efficiency against A, or power required to achieve required thrust for varying areas.
I don't see how the relationship between P and F can be as simple as suggested. (unless A is constant)
EDIT: I found some more equations,
Power (WATTS)=P(in.) X D(in.)^4 X RPM^3 X 5.33 X 10^-15
Thrust (oz.)=P(in.) X D(in.)^3 X RPM^2 X 10^-10
Apparently they are called the 'Abbot equations'
EDIT: Also managed to get this spreadsheet based on the Abbot equations. I don't know how accurate or reliable it is yet. I had to rename it as a 'text file' to upload it here, you need to change the file extension to .xls before you can open it. I did this using 'cmd' and copying it .
]propeller.txt[/file]
EDIT: Also managed to download another spreadsheet from the same page as above, this one was posted by Bruce Abbot a bit further down the page. I'm not sure if it's much use for what I'm trying to do, though.
EDIT: I think I might be getting somewhere with transposition,
F/A=v^2
P/A=(v^3)/2
still thinking about it.
Ash Small, Sat Jun 28 2014, 12:10PM
If I ignore Rho for the time being, F=Av^2 and P=1/2Av^3.
There's something I'm missing, I think.
Udo wrote:"F = eff * (2 * rho * A * P^2)^(1/3)
so the proportionalities
F ~ P^(2/3) or
P ~ F^(3/2)
hold."
I don't see how you can relate F and P in this way. I'm probably missing something.
Surely power is dependant on A? The smaller A is, the more power is needed to overcome additional losses in order to achieve the same force?
I'm trying to reach the point where I can plot efficiency against A, or power required to achieve required thrust for varying areas.
I don't see how the relationship between P and F can be as simple as suggested. (unless A is constant)
EDIT: I found some more equations,
Power (WATTS)=P(in.) X D(in.)^4 X RPM^3 X 5.33 X 10^-15
Thrust (oz.)=P(in.) X D(in.)^3 X RPM^2 X 10^-10
Apparently they are called the 'Abbot equations'
EDIT: Also managed to get this spreadsheet based on the Abbot equations. I don't know how accurate or reliable it is yet. I had to rename it as a 'text file' to upload it here, you need to change the file extension to .xls before you can open it. I did this using 'cmd' and copying it .
]propeller.txt[/file]
EDIT: Also managed to download another spreadsheet from the same page as above, this one was posted by Bruce Abbot a bit further down the page. I'm not sure if it's much use for what I'm trying to do, though.
EDIT: I think I might be getting somewhere with transposition,
F/A=v^2
P/A=(v^3)/2
still thinking about it.
Re: Novel flying machines
Conundrum, Sat Jun 28 2014, 12:31PM
Is there a way to use a lighter pack but with supercapacitors, ie lift-slow descent alternately?
Conundrum, Sat Jun 28 2014, 12:31PM
Is there a way to use a lighter pack but with supercapacitors, ie lift-slow descent alternately?
Re: Novel flying machines
BigBad, Sat Jun 28 2014, 01:23PM
no, not really. This is strictly an energy/energy efficiency/total weight thing, not a power thing. supercapacitors have rotten energy density by weight; but are fairly high power.
BigBad, Sat Jun 28 2014, 01:23PM
no, not really. This is strictly an energy/energy efficiency/total weight thing, not a power thing. supercapacitors have rotten energy density by weight; but are fairly high power.
Re: Novel flying machines
Uspring, Sat Jun 28 2014, 03:37PM
Uspring, Sat Jun 28 2014, 03:37PM
I don't see how you can relate F and P in this way. I'm probably missing something.The relation holds if you keep the prop area A constant. The ~ symbol is meant as "proportional to" not as "about the same". As a physicist I use the equal sign for "about the same"
Re: Novel flying machines
Ash Small, Sat Jun 28 2014, 04:39PM
Thanks
Ash Small, Sat Jun 28 2014, 04:39PM
Uspring wrote ...
I don't see how you can relate F and P in this way. I'm probably missing something.The relation holds if you keep the prop area A constant. The ~ symbol is meant as "proportional to" not as "about the same". As a physicist I use the equal sign for "about the same"
Thanks
Re: Novel flying machines
Patrick, Sat Jun 28 2014, 05:51PM
Patrick, Sat Jun 28 2014, 05:51PM
Uspring wrote ...
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
As expected, im adding more and more mass for less and less flight time.All-up-mass (AUW) = 1.61 kgHere's a table of expected flight times for addittional battery packs:
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
Re: Novel flying machines
Ash Small, Sat Jun 28 2014, 06:15PM
I think we pretty much covered this already. We need to increase prop size for increased efficiency
(or, more specifically, we need to reduce air velocity while maintaining the same thrust)
Ash Small, Sat Jun 28 2014, 06:15PM
Patrick wrote ...
Uspring wrote ...
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
As expected, im adding more and more mass for less and less flight time.All-up-mass (AUW) = 1.61 kgHere's a table of expected flight times for addittional battery packs:
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
I think we pretty much covered this already. We need to increase prop size for increased efficiency
(or, more specifically, we need to reduce air velocity while maintaining the same thrust)
Re: Novel flying machines
Patrick, Sat Jun 28 2014, 06:38PM
Patrick, Sat Jun 28 2014, 06:38PM
Ash Small wrote ...
I think we pretty much covered this already. We need to increase prop size for increased efficiency
(or, more specifically, we need to reduce air velocity while maintaining the same thrust)
yes, but we needed mre math to convince others, not just our hunch...Patrick wrote ...
Uspring wrote ...
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
As expected, im adding more and more mass for less and less flight time.All-up-mass (AUW) = 1.61 kgHere's a table of expected flight times for addittional battery packs:
battery mass = 0.51 kg
unlaiden mass = 1.1 kg
lets say this equates to 8 min of flight.
The first comes from your measurement, the others are extrapolation.
1 Pack (0.51kg) 8min
2 Packs 10.6 min
3 Packs 11.5 min
4 Packs 11.7 min
5 Packs 11.7 min
6 Packs 11.5 min
I think we pretty much covered this already. We need to increase prop size for increased efficiency
(or, more specifically, we need to reduce air velocity while maintaining the same thrust)
Re: Novel flying machines
Ash Small, Sat Jun 28 2014, 06:46PM
It's not a hunch, although my previous experience is with marine propellers.
I've never really done the maths properly before, though. Just chose the largest prop size that was practical, and worked from there.
Ideally, you want a low pitch angle as well. From what I was reading earlier, under ~12 degrees, something to do with 'stall'.. Apparently this is much more important for 'copters than for 'planes.
Ash Small, Sat Jun 28 2014, 06:46PM
Patrick wrote ...
yes, but we needed mre math to convince others, not just our hunch...
yes, but we needed mre math to convince others, not just our hunch...
It's not a hunch, although my previous experience is with marine propellers.
I've never really done the maths properly before, though. Just chose the largest prop size that was practical, and worked from there.
Ideally, you want a low pitch angle as well. From what I was reading earlier, under ~12 degrees, something to do with 'stall'.. Apparently this is much more important for 'copters than for 'planes.
Re: Novel flying machines
Patrick, Sat Jun 28 2014, 11:18PM
and for funding, which is quite hard at the moment.
Patrick, Sat Jun 28 2014, 11:18PM
Ash Small wrote ...
It's not a hunch, although my previous experience is with marine propellers.
but i got to be able to explain things to professors and such. so i can justify one direction of thought instead of another. It's not a hunch, although my previous experience is with marine propellers.
and for funding, which is quite hard at the moment.
Re: Novel flying machines
BigBad, Sun Jun 29 2014, 12:50AM
Wikipedia page on disk loading:
Efficiency effects of disk loading:
Only, with professors, don't mention wikipedia, just pull down the references, and refer to them. They get sniffy.
If you use 17 inch props, you'll get 17^2/10^2 = 2.9 times the hover time than with a 10 inch prop assuming optimal pitch and motor stuff in each case.
It's almost EXACTLY the same as gliders. You know how gliders have those long thin wings and can fly for miles and miles without using any energy. It's like that, only your wing is spinning. You want the thinnest, longest wings possible.
BigBad, Sun Jun 29 2014, 12:50AM
Wikipedia page on disk loading:
Efficiency effects of disk loading:
Only, with professors, don't mention wikipedia, just pull down the references, and refer to them. They get sniffy.
If you use 17 inch props, you'll get 17^2/10^2 = 2.9 times the hover time than with a 10 inch prop assuming optimal pitch and motor stuff in each case.
It's almost EXACTLY the same as gliders. You know how gliders have those long thin wings and can fly for miles and miles without using any energy. It's like that, only your wing is spinning. You want the thinnest, longest wings possible.
Re: Novel flying machines
Ash Small, Sun Jun 29 2014, 11:38AM
Now we're getting somewhere, that's the graph I've been trying to plot.
If you get ~3 times flight time going from a ten inch prop to a 17 inch prop, you'll get to ten times flight time long before you get to 1 metre diameter.
How did you get to the 2.9 figure for a 17 inch prop, BB?
EDIT: Although, without ducting, I'm still guessing ~1 metre for ten times flight time
I think I'm there. 32^2/10^2=10.24. my hunch appears to be correct. 32 inches gives 10 times flight time, according to this method. This gives us a 'ballpark figure' to work from.
Ash Small, Sun Jun 29 2014, 11:38AM
Now we're getting somewhere, that's the graph I've been trying to plot.
If you get ~3 times flight time going from a ten inch prop to a 17 inch prop, you'll get to ten times flight time long before you get to 1 metre diameter.
How did you get to the 2.9 figure for a 17 inch prop, BB?
EDIT: Although, without ducting, I'm still guessing ~1 metre for ten times flight time
I think I'm there. 32^2/10^2=10.24. my hunch appears to be correct. 32 inches gives 10 times flight time, according to this method. This gives us a 'ballpark figure' to work from.
Re: Novel flying machines
BigBad, Sun Jun 29 2014, 02:35PM
It's probably not 100% accurate because the longer rotor will weigh a bit more, but it's also thinner, and the motors can be lighter, because you don't need as much power.
Also adding multiple disks helps too; 4 rotors of 10 inches is ~4 times more efficient than 1 rotor of 10 inches, because they share the weight (up to the point where the weight of the rotor and motors and the structure completely dominate the mass of the vehicle, and then adding more doesn't help because the disk loading doesn't go down any further).
BigBad, Sun Jun 29 2014, 02:35PM
It's probably not 100% accurate because the longer rotor will weigh a bit more, but it's also thinner, and the motors can be lighter, because you don't need as much power.
Also adding multiple disks helps too; 4 rotors of 10 inches is ~4 times more efficient than 1 rotor of 10 inches, because they share the weight (up to the point where the weight of the rotor and motors and the structure completely dominate the mass of the vehicle, and then adding more doesn't help because the disk loading doesn't go down any further).
Re: Novel flying machines
Patrick, Sun Jun 29 2014, 02:41PM
Patrick, Sun Jun 29 2014, 02:41PM
BigBad wrote ...
Also adding multiple disks helps too; 4 rotors of 10 inches is ~4 times more efficient than 1 rotor of 10 inches, because they share the weight...
yes, from my thrust stand, a slower lower thrust prop as higher grams per watts, as that same prop accelerates, the efcicenccy number drops. Also adding multiple disks helps too; 4 rotors of 10 inches is ~4 times more efficient than 1 rotor of 10 inches, because they share the weight...
Re: Novel flying machines
Ash Small, Sun Jun 29 2014, 02:43PM
Well, the prop could still spin at the same speed, but with reduced pitch, for example, or it could be geared down.
I'm 'sort of' basing this on a direct 'scale up' of Patrick's existing assymetrical tri-copter design, as that's a design that was reached by well documented method, and for which we have some figures.
Working on a ten inch prop giving 8 minutes flying time (a figure I believe Patrick mentioned), I've arrived at the following graph:
EDIT: This also seems to fit Dr. Spark's 5 minute flight time with 5" props
Ash Small, Sun Jun 29 2014, 02:43PM
Well, the prop could still spin at the same speed, but with reduced pitch, for example, or it could be geared down.
I'm 'sort of' basing this on a direct 'scale up' of Patrick's existing assymetrical tri-copter design, as that's a design that was reached by well documented method, and for which we have some figures.
Working on a ten inch prop giving 8 minutes flying time (a figure I believe Patrick mentioned), I've arrived at the following graph:
EDIT: This also seems to fit Dr. Spark's 5 minute flight time with 5" props
Re: Novel flying machines
Uspring, Sun Jun 29 2014, 03:40PM
BigBad wrote:
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
Uspring, Sun Jun 29 2014, 03:40PM
BigBad wrote:
If you use 17 inch props, you'll get 17^2/10^2 = 2.9 times the hover time than with a 10 inch prop assuming optimal pitch and motor stuff in each case.Are you sure? I get a linear dependency of flight time on prop diameter.
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
Re: Novel flying machines
Ash Small, Sun Jun 29 2014, 03:46PM
I also have some reservations here, but I do think we're certainly on the right track.
The relationship between disc loading and efficiency is based on the 'drag losses' at the edge of the accelerated column of air. It is independant of the aircraft mass, and is dependant solely on air velocity, which is PROPORTIONAL to disc loading.
EDIT: F/A=v^2
V=SqRt(F/A)
Ash Small, Sun Jun 29 2014, 03:46PM
Uspring wrote ...
BigBad wrote:
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
BigBad wrote:
If you use 17 inch props, you'll get 17^2/10^2 = 2.9 times the hover time than with a 10 inch prop assuming optimal pitch and motor stuff in each case.Are you sure? I get a linear dependency of flight time on prop diameter.
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
I also have some reservations here, but I do think we're certainly on the right track.
The relationship between disc loading and efficiency is based on the 'drag losses' at the edge of the accelerated column of air. It is independant of the aircraft mass, and is dependant solely on air velocity, which is PROPORTIONAL to disc loading.
EDIT: F/A=v^2
V=SqRt(F/A)
Re: Novel flying machines
BigBad, Sun Jun 29 2014, 05:08PM
Wikipedia gives:
P = T sqrt(T/2pA)
where T is the thrust
BigBad, Sun Jun 29 2014, 05:08PM
Uspring wrote ...
BigBad wrote:
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
edit: yes, my bad, it's linear on rotor length.BigBad wrote:
If you use 17 inch props, you'll get 17^2/10^2 = 2.9 times the hover time than with a 10 inch prop assuming optimal pitch and motor stuff in each case.Are you sure? I get a linear dependency of flight time on prop diameter.
The graph you quoted is interesting. I can't derive a relationship between disk loading and efficiency, which does not take into account the mass of the aircraft explicitly.
Wikipedia gives:
P = T sqrt(T/2pA)
where T is the thrust
Re: Novel flying machines
Patrick, Sun Jun 29 2014, 08:30PM
im thinking 14 to 17 inches might be the right diameter. i certainly cant keep going bigger...
Patrick, Sun Jun 29 2014, 08:30PM
im thinking 14 to 17 inches might be the right diameter. i certainly cant keep going bigger...
Re: Novel flying machines
Ash Small, Sun Jun 29 2014, 09:04PM
I'm thinking twice this size for an 'order of magnitude' improvement.
We've also 'accounted' for the mass of motors and batteries. I'm assuming 'payload' will be a 'small percentage' of this.
This equation: V=SqRt(F/A) is a tramsposition of the original thrust equation provided by Udo, and illustrates the point quite clearly, I think. I've left out Rho, for simplicity. Losses are dependant on V. When V is small, losses tend to zero, when V is large, losses tend to infinity.
Ash Small, Sun Jun 29 2014, 09:04PM
Patrick wrote ...
im thinking 14 to 17 inches might be the right diameter. i certainly cant keep going bigger...
im thinking 14 to 17 inches might be the right diameter. i certainly cant keep going bigger...
I'm thinking twice this size for an 'order of magnitude' improvement.
We've also 'accounted' for the mass of motors and batteries. I'm assuming 'payload' will be a 'small percentage' of this.
This equation: V=SqRt(F/A) is a tramsposition of the original thrust equation provided by Udo, and illustrates the point quite clearly, I think. I've left out Rho, for simplicity. Losses are dependant on V. When V is small, losses tend to zero, when V is large, losses tend to infinity.
Re: Novel flying machines
Patrick, Sun Jun 29 2014, 10:24PM
for a 1.7kg machine with 14" props, i was planning on 500 grams at least of payload. (keep in mind i couldnt get fuel cells anywhere near the energy density to achieve this.) (total AUW = 2.2kg)
my PEM fuel cell maker wanted 18,000 US$ for one prototype, at 1.5kg or there abouts. thats with a sodium borohydride reactor attcahed. at this point i know i could build a lipo hex copter with 24" props to fly 30+ mins. for a lot less tha 18k$'s.
Patrick, Sun Jun 29 2014, 10:24PM
for a 1.7kg machine with 14" props, i was planning on 500 grams at least of payload. (keep in mind i couldnt get fuel cells anywhere near the energy density to achieve this.) (total AUW = 2.2kg)
my PEM fuel cell maker wanted 18,000 US$ for one prototype, at 1.5kg or there abouts. thats with a sodium borohydride reactor attcahed. at this point i know i could build a lipo hex copter with 24" props to fly 30+ mins. for a lot less tha 18k$'s.
Re: Novel flying machines
Dr. Slack, Mon Jun 30 2014, 08:04AM
Now there's general agreement that bigger props are better, what happens in the limit of an infinite length blade? I'm a bit nervous when equations seem to say 'longer is better, without limit' that some other effect has been ignored.
Obviously there are practical details, like how big your car is for transporting it, or how strong is unobtanium from which to hew an infinite length blade, or whether that geometry will be stable in flutter.
There are more physics-based real effects though, as what is being sought is best lift to drag ratio. Blade power dissipation will be a function of many variables, obviously the most important for small blades are the speed and lift dependent terms like air-column energy and tip vortices. However, as the blade gets longer, and the disc loading goes down, the viscous drag will increase in relative importance.
So what I'm asking is, at what disc loading does the drag of just hauling the blade surfaces through viscous air become a significant term in the power loss, and so at what loading is there no point in reducing it further?
Dr. Slack, Mon Jun 30 2014, 08:04AM
Now there's general agreement that bigger props are better, what happens in the limit of an infinite length blade? I'm a bit nervous when equations seem to say 'longer is better, without limit' that some other effect has been ignored.
Obviously there are practical details, like how big your car is for transporting it, or how strong is unobtanium from which to hew an infinite length blade, or whether that geometry will be stable in flutter.
There are more physics-based real effects though, as what is being sought is best lift to drag ratio. Blade power dissipation will be a function of many variables, obviously the most important for small blades are the speed and lift dependent terms like air-column energy and tip vortices. However, as the blade gets longer, and the disc loading goes down, the viscous drag will increase in relative importance.
So what I'm asking is, at what disc loading does the drag of just hauling the blade surfaces through viscous air become a significant term in the power loss, and so at what loading is there no point in reducing it further?
Re: Novel flying machines
Ash Small, Mon Jun 30 2014, 08:38AM
When prop diameter approaches infinity, losses approach zero, which means that all power put into the system goes into accelerating the aircraft.
Obviously there will be drag losses from the blade, which can be minimized.
The reason the 'thrust equation' (F=A x v^2) doesn't account for these is because, in a 'first order' approximation, these losses are negligible compared to 'drag losses', in most 'real world' scenarios.
All I've done is taken the thrust equation and re-arranged it, but the 'thrust equation', as written, does imply that an infinite length prop will have zero losses.
We need 'different maths' to answer your question, Neil.
EDIT: Obviously, all losses from other sources should be minimized, for example, a long, thin blade with little pitch won't produce 'a lot' of drag, but will still require 'optimization'.
Can I just point out that we would have 'sufficient lift, flight time, etc' long before we reach an 'infinite length' prop. We're only looking for one order of magnitude improvement.
EDIT: Actually, a larger prop has to do less work, as there are less losses to overcome, so it should be possible to design it with 'less drag'.
This graph covers nearly 5 orders of magnitude. If it's possible to identify where we are on the graph, we should be able to deduce how practical a single order of magnitude increase in efficiency actually is
Ash Small, Mon Jun 30 2014, 08:38AM
When prop diameter approaches infinity, losses approach zero, which means that all power put into the system goes into accelerating the aircraft.
Obviously there will be drag losses from the blade, which can be minimized.
The reason the 'thrust equation' (F=A x v^2) doesn't account for these is because, in a 'first order' approximation, these losses are negligible compared to 'drag losses', in most 'real world' scenarios.
All I've done is taken the thrust equation and re-arranged it, but the 'thrust equation', as written, does imply that an infinite length prop will have zero losses.
We need 'different maths' to answer your question, Neil.
EDIT: Obviously, all losses from other sources should be minimized, for example, a long, thin blade with little pitch won't produce 'a lot' of drag, but will still require 'optimization'.
Can I just point out that we would have 'sufficient lift, flight time, etc' long before we reach an 'infinite length' prop. We're only looking for one order of magnitude improvement.
EDIT: Actually, a larger prop has to do less work, as there are less losses to overcome, so it should be possible to design it with 'less drag'.
This graph covers nearly 5 orders of magnitude. If it's possible to identify where we are on the graph, we should be able to deduce how practical a single order of magnitude increase in efficiency actually is
Re: Novel flying machines
Dr. Slack, Mon Jun 30 2014, 01:45PM
What surprises me about that graph is that there are three orders of magnitude between the disc loading of the jump jet and a helicopter, but barely one order of magnitude for hover efficiency. That suggests you will need to work very hard with disc area to bring about much improvement in flight time. The disc area goes as blade length squared, so the flight time might increase as blade length ^2/3. It's a pity the graph wasn't plotted as log-log rather than semi-log, as with log-log it's very close to a straight line.
The no-lift rotor power, from which the minimum practical disc loading can be inferred, can be measured by spinning a prop/rotor of zero pitch in a dynamometer. There will be no lift related drag terms, only viscous air, friction and non-lift turbulence.
This is exactly analogous to the motor no-load condition, where a certain minimum power is required to spin it against the viscous air between the rotor and stator, and a few other miscellaneous losses. It's well known that there is no point using a big motor to provide a very small output, the efficiency will be horrible. It's better to use a motor with lower no-load losses, even if its high load efficiency is poorer.
Similarly, there will be little point using a large swept area to produce a small thrust.
Dr. Slack, Mon Jun 30 2014, 01:45PM
What surprises me about that graph is that there are three orders of magnitude between the disc loading of the jump jet and a helicopter, but barely one order of magnitude for hover efficiency. That suggests you will need to work very hard with disc area to bring about much improvement in flight time. The disc area goes as blade length squared, so the flight time might increase as blade length ^2/3. It's a pity the graph wasn't plotted as log-log rather than semi-log, as with log-log it's very close to a straight line.
The no-lift rotor power, from which the minimum practical disc loading can be inferred, can be measured by spinning a prop/rotor of zero pitch in a dynamometer. There will be no lift related drag terms, only viscous air, friction and non-lift turbulence.
This is exactly analogous to the motor no-load condition, where a certain minimum power is required to spin it against the viscous air between the rotor and stator, and a few other miscellaneous losses. It's well known that there is no point using a big motor to provide a very small output, the efficiency will be horrible. It's better to use a motor with lower no-load losses, even if its high load efficiency is poorer.
Similarly, there will be little point using a large swept area to produce a small thrust.
Re: Novel flying machines
Uspring, Mon Jun 30 2014, 02:02PM
Dr. Slack wrote:
is a table for props efficiencies in terms of motor energy utilisation. They use the equation (ζ for power conversion efficiency)
F = (2 * rho * A * (ζ*P)^2)^(1/3)
instead of the one I quoted
F = eff * (2 * rho * A * P^2)^(1/3)
They are really the same except for the definition of efficiency. For their definition here's a translation of the table:
ζ = 0.7 - 0.75 can be reached for man-carrying helis
ζ = 0.7 dream value for models
ζ = 0.65 can be reached by very good model props
ζ = 0.55 - 0.6 average to good model props
ζ = 0.5 model props shouldn't be worse than this
ζ < 0.5 sadly happens occasionally
Uspring, Mon Jun 30 2014, 02:02PM
Dr. Slack wrote:
Now there's general agreement that bigger props are better, what happens in the limit of an infinite length blade? I'm a bit nervous when equations seem to say 'longer is better, without limit' that some other effect has been ignored.The efficiency of conversion of motor power to air speed seems to be remarkably independent of the prop size. In this (german) paper
is a table for props efficiencies in terms of motor energy utilisation. They use the equation (ζ for power conversion efficiency)F = (2 * rho * A * (ζ*P)^2)^(1/3)
instead of the one I quoted
F = eff * (2 * rho * A * P^2)^(1/3)
They are really the same except for the definition of efficiency. For their definition here's a translation of the table:
ζ = 0.7 - 0.75 can be reached for man-carrying helis
ζ = 0.7 dream value for models
ζ = 0.65 can be reached by very good model props
ζ = 0.55 - 0.6 average to good model props
ζ = 0.5 model props shouldn't be worse than this
ζ < 0.5 sadly happens occasionally
Re: Novel flying machines
Ash Small, Mon Jun 30 2014, 02:03PM
But where are we in terms of Lb/Hp and Lb/ft^2?
We need some figures from Patrick.
EDIT: Udo, as I understand it, the power conversion of the prop isn't what's relevant. What's relevant is the subsequent losses due to V (air velocity).
If V is lower, then subsequent losses are lower, so the prop doesn't have to do so much work in the first place.
The way I see the losses here is analagous to current flowing in a wire of a certain cross-section.
No matter how much you increase the voltage, the losses just keep increasing. The way to reduce losses is to use a larger cross-section of wire.
Same as water down a pipe.
Ash Small, Mon Jun 30 2014, 02:03PM
But where are we in terms of Lb/Hp and Lb/ft^2?
We need some figures from Patrick.
EDIT: Udo, as I understand it, the power conversion of the prop isn't what's relevant. What's relevant is the subsequent losses due to V (air velocity).
If V is lower, then subsequent losses are lower, so the prop doesn't have to do so much work in the first place.
The way I see the losses here is analagous to current flowing in a wire of a certain cross-section.
No matter how much you increase the voltage, the losses just keep increasing. The way to reduce losses is to use a larger cross-section of wire.
Same as water down a pipe.
Re: Novel flying machines
BigBad, Mon Jun 30 2014, 02:33PM
But the rotor first has to carry its own weight, so as you add rotor eventually the vehicle tends to become pretty much all rotor and then adding extra rotor makes very little difference, because the weight and the lift go up together and the downwash speed stops changing.
So when you include rotor mass, the efficiency hits a limit with infinite rotor length. But at the moment, presumably the mass of the rotor is small relative to the battery and payload.
BigBad, Mon Jun 30 2014, 02:33PM
Dr. Slack wrote ...
Now there's general agreement that bigger props are better, what happens in the limit of an infinite length blade? I'm a bit nervous when equations seem to say 'longer is better, without limit' that some other effect has been ignored.
It makes a difference right now because the downwash speed is reducing as you increase the rotor size.Now there's general agreement that bigger props are better, what happens in the limit of an infinite length blade? I'm a bit nervous when equations seem to say 'longer is better, without limit' that some other effect has been ignored.
But the rotor first has to carry its own weight, so as you add rotor eventually the vehicle tends to become pretty much all rotor and then adding extra rotor makes very little difference, because the weight and the lift go up together and the downwash speed stops changing.
So when you include rotor mass, the efficiency hits a limit with infinite rotor length. But at the moment, presumably the mass of the rotor is small relative to the battery and payload.
Re: Novel flying machines
Uspring, Mon Jun 30 2014, 03:51PM
Ash wrote:
The only value that isn't known precisely is the ζ. From what I've seen in Patricks measurement his ζ is at the lower end of the range. That might be due to losses in his motor. The table quoted does not contain the motor efficiency.
Uspring, Mon Jun 30 2014, 03:51PM
Ash wrote:
But where are we in terms of Lb/Hp and Lb/ft^2?Just plugin the numbers
The only value that isn't known precisely is the ζ. From what I've seen in Patricks measurement his ζ is at the lower end of the range. That might be due to losses in his motor. The table quoted does not contain the motor efficiency.EDIT: Udo, as I understand it, the power conversion of the prop isn't what's relevant. What's relevant is the subsequent losses due to V (air velocity).All losses are captured in the ζ. Where they come from is interesting, but to calculate thrust from rotor power, one needn't know.
Re: Novel flying machines
Ash Small, Mon Jun 30 2014, 05:52PM
I'm hoping Patrick can provide these figures. I looked back through the thread, but couldn't find all the necessary data.
I still think we're looking at this differently. I'm looking at this by visualizing the 'equal and opposite reaction' (Newton's third law?) that opposes the 'action of the prop'. This 'reaction force' is equal to the 'action force' of the prop.
I'm still struggling to get my head round the power equation. I'll look at it again later. I'm not saying some of the maths here isn't flawed, but I do think I'm visualizing the problem reasonably well.
Ash Small, Mon Jun 30 2014, 05:52PM
Uspring wrote ...
Ash wrote:
Ash wrote:
But where are we in terms of Lb/Hp and Lb/ft^2?
I'm hoping Patrick can provide these figures. I looked back through the thread, but couldn't find all the necessary data.
Uspring wrote ...
"All losses are captured in the ζ. Where they come from is interesting, but to calculate thrust from rotor power, one needn't know."
"All losses are captured in the ζ. Where they come from is interesting, but to calculate thrust from rotor power, one needn't know."
I still think we're looking at this differently. I'm looking at this by visualizing the 'equal and opposite reaction' (Newton's third law?) that opposes the 'action of the prop'. This 'reaction force' is equal to the 'action force' of the prop.
I'm still struggling to get my head round the power equation. I'll look at it again later. I'm not saying some of the maths here isn't flawed, but I do think I'm visualizing the problem reasonably well.
Re: Novel flying machines
Patrick, Mon Jun 30 2014, 09:11PM
Patrick, Mon Jun 30 2014, 09:11PM
Ash Small wrote ...
i can get you these numbers : kg per w (thrust) and kg per m^2 (disc loading).Uspring wrote ...
Ash wrote:
I'm hoping Patrick can provide these figures. I looked back through the thread, but couldn't find all the necessary data.Ash wrote:
But where are we in terms of Lb/Hp and Lb/ft^2?
Re: Novel flying machines
Ash Small, Tue Jul 01 2014, 10:35AM
That would be ideal. I can convert Watts to Hp, etc. Then we can see where we are on that Wikipedia graph.
EDIT: With reference to comments regarding blades of infinite length, and drag losses from 'long blades', I personally expect to run into 'manouverability limitations' before these 'long propeller limitations' come into play.
For example, if we look back at 'Atlas', the 'human powered helicopter' I linked to earlier in the thread, which doesn't quite have an infinite length prop, nor quite achieves zero losses, it's pretty easy to see, I think, that manouverability has already reached zero, as near as makes no difference. The 'very large' disc area, however, obviously doesn't have anywhere near 'infinite drag'.
I have mentioned earlier that it's always a 'trade off' between efficiency and manouverability. I'm reasonably confident we can reach the efficiency figures we're after, what I'm not sure about is whether the aircraft will be manouverable enough to be of any practical use in 'real world' scenarios.
Ash Small, Tue Jul 01 2014, 10:35AM
Patrick wrote ...
Ash Small wrote ...
i can get you these numbers : kg per w (thrust) and kg per m^2 (disc loading).Uspring wrote ...
Ash wrote:
I'm hoping Patrick can provide these figures. I looked back through the thread, but couldn't find all the necessary data.Ash wrote:
But where are we in terms of Lb/Hp and Lb/ft^2?
That would be ideal. I can convert Watts to Hp, etc. Then we can see where we are on that Wikipedia graph.
EDIT: With reference to comments regarding blades of infinite length, and drag losses from 'long blades', I personally expect to run into 'manouverability limitations' before these 'long propeller limitations' come into play.
For example, if we look back at 'Atlas', the 'human powered helicopter' I linked to earlier in the thread, which doesn't quite have an infinite length prop, nor quite achieves zero losses, it's pretty easy to see, I think, that manouverability has already reached zero, as near as makes no difference. The 'very large' disc area, however, obviously doesn't have anywhere near 'infinite drag'.
I have mentioned earlier that it's always a 'trade off' between efficiency and manouverability. I'm reasonably confident we can reach the efficiency figures we're after, what I'm not sure about is whether the aircraft will be manouverable enough to be of any practical use in 'real world' scenarios.
Re: Novel flying machines
Patrick, Tue Jul 01 2014, 08:17PM
for all of the recent flights made on my you tube channel "Test Pilot Mafia", ive been using the 10 x 4.5 MR APC prop. ill post the data here in a minute.
AUW = 1.62 kg
hover time = 8 minutes
1.62 kg / 3 fans = 540 g/fan
at 6,200 RPM --> 540 g / 96 W = 5.62 g/W
disk area = PI x R^2 so 10" = 78.5 in^2
pics
Patrick, Tue Jul 01 2014, 08:17PM
for all of the recent flights made on my you tube channel "Test Pilot Mafia", ive been using the 10 x 4.5 MR APC prop. ill post the data here in a minute.
AUW = 1.62 kg
hover time = 8 minutes
1.62 kg / 3 fans = 540 g/fan
at 6,200 RPM --> 540 g / 96 W = 5.62 g/W
disk area = PI x R^2 so 10" = 78.5 in^2
pics
Re: Novel flying machines
Ash Small, Tue Jul 01 2014, 08:57PM
Thanks. Just doing the conversion.
2.18 Lbs/foot^2
9.247 Lbs/Hp
This is where we appear to be, based on those figures provided. Please feel free to check my maths, etc.
I'll try and plot a log/log graph as suggested by Neil when I get a chance. That should make extrapolation a lot simpler.
Unless anyone else beats me to it
Ash Small, Tue Jul 01 2014, 08:57PM
Thanks. Just doing the conversion.
2.18 Lbs/foot^2
9.247 Lbs/Hp
This is where we appear to be, based on those figures provided. Please feel free to check my maths, etc.
I'll try and plot a log/log graph as suggested by Neil when I get a chance. That should make extrapolation a lot simpler.
Unless anyone else beats me to it
Re: Novel flying machines
Patrick, Tue Jul 01 2014, 09:12PM
im thinking of going to 14 inch props.
pics to follow;
10 x 4.5 prop multirotor, APC
14 x 5.5 prop multirotor, APC.
Given the above thrust stand and data sheets:
0.089 Hp x 746 W = 66.4 W @ 6k RPM, (for the 10x4.5 MR prop)
7.4 A x 11.32 V = 83.7 W
83.7 W - 66.4 W = 17.3 W lost in the electric motor and ESC.
17.3 W / 83.7 W = 21% loss from battery to wind conversion.
Patrick, Tue Jul 01 2014, 09:12PM
im thinking of going to 14 inch props.
pics to follow;
10 x 4.5 prop multirotor, APC
14 x 5.5 prop multirotor, APC.
Given the above thrust stand and data sheets:
0.089 Hp x 746 W = 66.4 W @ 6k RPM, (for the 10x4.5 MR prop)
7.4 A x 11.32 V = 83.7 W
83.7 W - 66.4 W = 17.3 W lost in the electric motor and ESC.
17.3 W / 83.7 W = 21% loss from battery to wind conversion.
Re: Novel flying machines
Ash Small, Tue Jul 01 2014, 10:44PM
So if you go to 14" props and decide you still have plenty of manouverability, but still need longer flight time, will you consider going bigger still?
I think you want less pitch if you increse to 14", by the way
Ash Small, Tue Jul 01 2014, 10:44PM
So if you go to 14" props and decide you still have plenty of manouverability, but still need longer flight time, will you consider going bigger still?
I think you want less pitch if you increse to 14", by the way
Re: Novel flying machines
Patrick, Tue Jul 01 2014, 10:58PM
APC multirotor props :
i could go with foreign child-slave-labor made products though...
EDIT:
(16 inch would be the maximum, even then i dont know if i could support a duct around it.)
Patrick, Tue Jul 01 2014, 10:58PM
Ash Small wrote ...
So if you go to 14" props and decide you still have plenty of manouverability, but still need longer flight time, will you consider going bigger still?
I think you want less pitch if you increse to 14", by the way
they dont make them with less pitch. and 14 is already huge! So if you go to 14" props and decide you still have plenty of manouverability, but still need longer flight time, will you consider going bigger still?
I think you want less pitch if you increse to 14", by the way
APC multirotor props :
i could go with foreign child-slave-labor made products though...
EDIT:
(16 inch would be the maximum, even then i dont know if i could support a duct around it.)
Re: Novel flying machines
Ash Small, Tue Jul 01 2014, 11:14PM
Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.
Ash Small, Tue Jul 01 2014, 11:14PM
Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.
Re: Novel flying machines
Patrick, Tue Jul 01 2014, 11:17PM
Patrick, Tue Jul 01 2014, 11:17PM
Ash Small wrote ...
Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.
Im intrigued, what propeller shape would you propose?Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.
Re: Novel flying machines
Ash Small, Wed Jul 02 2014, 12:02AM
Probably something more close to a conventional heli blade.
Ash Small, Wed Jul 02 2014, 12:02AM
Probably something more close to a conventional heli blade.
Re: Novel flying machines
Patrick, Wed Jul 02 2014, 12:04AM
not my machine, not my work or child...
link to this machine:
how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?
Patrick, Wed Jul 02 2014, 12:04AM
not my machine, not my work or child...
link to this machine:
how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?
Re: Novel flying machines
Dr. Slack, Wed Jul 02 2014, 07:49AM
Not entirely sure what you're suggesting here, but
a) it's much the same total area as a rotor with fewer blades, so similar mass of air, similar velocities, so similar lift and lift-induced losses to a more conventional rotor
b) it's heavier
c) it has waaaaay more surface area in contact with the air, so will suffer higher viscous/friction losses, regardless of disc loading
Dr. Slack, Wed Jul 02 2014, 07:49AM
Patrick wrote ...
how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?
how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?
Not entirely sure what you're suggesting here, but
a) it's much the same total area as a rotor with fewer blades, so similar mass of air, similar velocities, so similar lift and lift-induced losses to a more conventional rotor
b) it's heavier
c) it has waaaaay more surface area in contact with the air, so will suffer higher viscous/friction losses, regardless of disc loading
Re: Novel flying machines
Ash Small, Wed Jul 02 2014, 12:24PM
I think turbines are generally used where very high disc loadings are called for, eg high pressure applications.
Completely the opposite of what we're after here.
EDIT: The assymetric tri-copter layout was arrived at in order to obtain the necessary control and manouverability required without resorting to swashplates. If anything, the current design lacks stability.
Building a lightweight 'Y' frame, and mounting long thin props at the extremities should increase stability, in an already 'inherently manouverable' design. If we lose the ducting, but retain the existing motors, batteries and control circuitry, etc, any increase in 'all up weight' can be minimized. We can improve efficiency and stability in an inherently manouverable design.
Ash Small, Wed Jul 02 2014, 12:24PM
I think turbines are generally used where very high disc loadings are called for, eg high pressure applications.
Completely the opposite of what we're after here.
EDIT: The assymetric tri-copter layout was arrived at in order to obtain the necessary control and manouverability required without resorting to swashplates. If anything, the current design lacks stability.
Building a lightweight 'Y' frame, and mounting long thin props at the extremities should increase stability, in an already 'inherently manouverable' design. If we lose the ducting, but retain the existing motors, batteries and control circuitry, etc, any increase in 'all up weight' can be minimized. We can improve efficiency and stability in an inherently manouverable design.
Re: Novel flying machines
BigBad, Wed Jul 02 2014, 01:44PM
Yes, I think theoretically a single double length blade would be more efficient than the normal double ended blade. (Single blades are used on some powered gliders, it's not completely dumb, but you'd probably need a counterweight, although that could perhaps be the motor or something.)
Using more blades only reduces the aerodynamic efficiency; but going from 1 to 2 doesn't make that much difference so far as I know, I haven't seen the numbers on it. But certainly going 3,4,5,6.. efficiency goes down because the blades interfere.
Turbines are used where you want to pump the air into a volume at positive pressure, if you don't fill the disk with blades most of the air will push past the blades in between.
Still, it might be worth trying (3 or) 4 blades, it won't be as good as two sets of double blades/motors, but it might not be that much worse, and you can spin the blades slower, and you don't need extra motors and structure and power circuitry.
BigBad, Wed Jul 02 2014, 01:44PM
Yes, I think theoretically a single double length blade would be more efficient than the normal double ended blade. (Single blades are used on some powered gliders, it's not completely dumb, but you'd probably need a counterweight, although that could perhaps be the motor or something.)
Using more blades only reduces the aerodynamic efficiency; but going from 1 to 2 doesn't make that much difference so far as I know, I haven't seen the numbers on it. But certainly going 3,4,5,6.. efficiency goes down because the blades interfere.
Turbines are used where you want to pump the air into a volume at positive pressure, if you don't fill the disk with blades most of the air will push past the blades in between.
Still, it might be worth trying (3 or) 4 blades, it won't be as good as two sets of double blades/motors, but it might not be that much worse, and you can spin the blades slower, and you don't need extra motors and structure and power circuitry.
Re: Novel flying machines
Ash Small, Wed Jul 02 2014, 06:37PM
I think the point that BB is making here is that you don't want lots of blades or lots of blade area.
While a 'one bladed helicopter' is quite novel, I imagine that by the time you've added conter-weights and whatnot, it would be simpler to have two, thinner blades. Some helicopters have four thin blades (I was reading somewhere about balancers, etc, which apparently are sometimes required with two blades).
Most helicopter blades droop somewhat at rest, and 'tilt up' (for want of a better expression) under load.
Mass is obviously a consideration here, but adding counterweights is counter-productive, in my opinion.
If the blades are thin enough and the pitch shallow enough, gearing down may not be required, but the simplest form of gearing down is probably a reduction belt drive, which might allow the motors to be placed at, or close to, the intersection of a 'Y' frame, should you choose to go that route.
Ash Small, Wed Jul 02 2014, 06:37PM
I think the point that BB is making here is that you don't want lots of blades or lots of blade area.
While a 'one bladed helicopter' is quite novel, I imagine that by the time you've added conter-weights and whatnot, it would be simpler to have two, thinner blades. Some helicopters have four thin blades (I was reading somewhere about balancers, etc, which apparently are sometimes required with two blades).
Most helicopter blades droop somewhat at rest, and 'tilt up' (for want of a better expression) under load.
Mass is obviously a consideration here, but adding counterweights is counter-productive, in my opinion.
If the blades are thin enough and the pitch shallow enough, gearing down may not be required, but the simplest form of gearing down is probably a reduction belt drive, which might allow the motors to be placed at, or close to, the intersection of a 'Y' frame, should you choose to go that route.
Re: Novel flying machines
Patrick, Wed Jul 02 2014, 07:22PM
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
Patrick, Wed Jul 02 2014, 07:22PM
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
Re: Novel flying machines
Ash Small, Wed Jul 02 2014, 07:39PM
There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.
I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.
EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.
Ash Small, Wed Jul 02 2014, 07:39PM
Patrick wrote ...
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.
I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.
EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.
Re: Novel flying machines
Patrick, Wed Jul 02 2014, 08:31PM
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
Evolution 40NX, glow engine.
glow engine wieghs half as much as the 6.6Ah battery. should be good to 1.4hp.
Patrick, Wed Jul 02 2014, 08:31PM
Ash Small wrote ...
There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.
I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.
EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.
Patrick wrote ...
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.
There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.
I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.
EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
Evolution 40NX, glow engine.
glow engine wieghs half as much as the 6.6Ah battery. should be good to 1.4hp.
Re: Novel flying machines
Ash Small, Wed Jul 02 2014, 08:40PM
Sounds good. You do have an 'inherently manouverable' design.
Ash Small, Wed Jul 02 2014, 08:40PM
Patrick wrote ...
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
Sounds good. You do have an 'inherently manouverable' design.
Re: Novel flying machines
BigBad, Wed Jul 02 2014, 10:29PM
One problem with the fuel engine idea is that you will have variable weight; that would push you towards having to have collective.
How long do you need to fly for? What weight of fuel does that equate to?
BigBad, Wed Jul 02 2014, 10:29PM
One problem with the fuel engine idea is that you will have variable weight; that would push you towards having to have collective.
How long do you need to fly for? What weight of fuel does that equate to?
Re: Novel flying machines
Patrick, Thu Jul 03 2014, 05:08AM
1.7-ish kg, plus 0.8 kg in payload, plus fuel/oil mass would be 24-ish fluid ounces of alcohol.
24fl oz x 24.2 g = 580g Alcohol
CoG is critical but ill just have to arrange the locations carefully, so as the tank empties it gets lighter but doesnt lose its CoG (as with the P-51)
Patrick, Thu Jul 03 2014, 05:08AM
BigBad wrote ...
One problem with the fuel engine idea is that you will have variable weight; that would push you towards having to have collective.
How long do you need to fly for? What weight of fuel does that equate to?
Duration should be 25 to 45 minutes, with heavy instruments. One problem with the fuel engine idea is that you will have variable weight; that would push you towards having to have collective.
How long do you need to fly for? What weight of fuel does that equate to?
1.7-ish kg, plus 0.8 kg in payload, plus fuel/oil mass would be 24-ish fluid ounces of alcohol.
24fl oz x 24.2 g = 580g Alcohol
CoG is critical but ill just have to arrange the locations carefully, so as the tank empties it gets lighter but doesnt lose its CoG (as with the P-51)
Re: Novel flying machines
Ash Small, Thu Jul 03 2014, 09:04AM
One thing that concerns me regarding the thrust measurments etc. is 'ground effect'.
I'm trying to work out if we need to make an allowance for it or not.
I'm sure we're all familiar with 'wing in ground effect', which allows seaplanes to have incredible range. I assume we have a similar 'ground effect' with 'copters. Do we need to allow for this in the thrust measurments or not?
EDIT: I'm wondering if this explains why we appear to be outside of the shaded areas on the disc loading graph, or if there is another explanation.
Where we are on that graph tends to suggest that any significant reductions in disc loading will give very significant improvements in efficiency, but I'll wait until I've plotted a log/log graph before attempting to extrapolate any 'reliable' information.
Ash Small, Thu Jul 03 2014, 09:04AM
One thing that concerns me regarding the thrust measurments etc. is 'ground effect'.
I'm trying to work out if we need to make an allowance for it or not.
I'm sure we're all familiar with 'wing in ground effect', which allows seaplanes to have incredible range. I assume we have a similar 'ground effect' with 'copters. Do we need to allow for this in the thrust measurments or not?
EDIT: I'm wondering if this explains why we appear to be outside of the shaded areas on the disc loading graph, or if there is another explanation.
Where we are on that graph tends to suggest that any significant reductions in disc loading will give very significant improvements in efficiency, but I'll wait until I've plotted a log/log graph before attempting to extrapolate any 'reliable' information.
Re: Novel flying machines
Patrick, Thu Jul 03 2014, 04:28PM
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
Patrick, Thu Jul 03 2014, 04:28PM
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
Re: Novel flying machines
Ash Small, Thu Jul 03 2014, 04:44PM
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
Ash Small, Thu Jul 03 2014, 04:44PM
Patrick wrote ...
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
Re: Novel flying machines
Patrick, Thu Jul 03 2014, 05:06PM
Patrick, Thu Jul 03 2014, 05:06PM
Ash Small wrote ...
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.Patrick wrote ...
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
Re: Novel flying machines
Ash Small, Thu Jul 03 2014, 06:17PM
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
EDIT: It could be related to scale, I suppose.
Ash Small, Thu Jul 03 2014, 06:17PM
Patrick wrote ...
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
EDIT: It could be related to scale, I suppose.
Re: Novel flying machines
Patrick, Thu Jul 03 2014, 07:06PM
this is quite complicated, and so many on the interwebs are just throwing random flying garbage together, and hoping for the best. while id like a more thorough, thoughtful, elegant solution.
(piston-electric pisses me off, but im still working on it.)
EDIT: on the graph, we see the harrier like implementation on the lower right. and the traditional heli of the upper left. but the effciency is best in the upper right side right?
Patrick, Thu Jul 03 2014, 07:06PM
Ash Small wrote ...
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
EDIT: It could be related to scale, I suppose.
yes i worry about scalability, but im still grateful for everybody's help so far, and dont kill yourself working for me. (though a Kickstarter for this stuff is looking more desirable.) Patrick wrote ...
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
EDIT: It could be related to scale, I suppose.
this is quite complicated, and so many on the interwebs are just throwing random flying garbage together, and hoping for the best. while id like a more thorough, thoughtful, elegant solution.
(piston-electric pisses me off, but im still working on it.)
EDIT: on the graph, we see the harrier like implementation on the lower right. and the traditional heli of the upper left. but the effciency is best in the upper right side right?
Re: Novel flying machines
Ash Small, Thu Jul 03 2014, 08:01PM
Disc loading is along the bottom, and efficiency is up the side. Efficiency requires low disc loading, is basically what the graph is saying.
Our disc loading is low (close to the left hand side) but you'd expect better efficiency from a full sized copter. This could be due to scale, or due to poor prop design, or maybe a combination involving other, unforseen factors.
We are in the area of the graph where a reduction of disc loading results in a big improvement in efficiency, if I'm reading it right, but I want to draw a log/log graph before I make any 'predictions'.
I am interested in this stuff, I had marine props going round and round my head 20-25 years ago. I also had an interest in hovercraft design as a kid, but in that case the improvements in efficiency are due to the 'plenum chamber'.
EDIT: I may need to 'tap' you for a loan oneday, when you've made your first million
Ash Small, Thu Jul 03 2014, 08:01PM
Patrick wrote ...
EDIT: on the graph, we see the harrier like implementation on the lower right. and the traditional heli of the upper left. but the effciency is best in the upper right side right?
EDIT: on the graph, we see the harrier like implementation on the lower right. and the traditional heli of the upper left. but the effciency is best in the upper right side right?
Disc loading is along the bottom, and efficiency is up the side. Efficiency requires low disc loading, is basically what the graph is saying.
Our disc loading is low (close to the left hand side) but you'd expect better efficiency from a full sized copter. This could be due to scale, or due to poor prop design, or maybe a combination involving other, unforseen factors.
We are in the area of the graph where a reduction of disc loading results in a big improvement in efficiency, if I'm reading it right, but I want to draw a log/log graph before I make any 'predictions'.
I am interested in this stuff, I had marine props going round and round my head 20-25 years ago. I also had an interest in hovercraft design as a kid, but in that case the improvements in efficiency are due to the 'plenum chamber'.
EDIT: I may need to 'tap' you for a loan oneday, when you've made your first million
Re: Novel flying machines
Patrick, Thu Jul 03 2014, 08:43PM
I'll be cashing a 25 million check soon... you want some?
i see the same trend here, no coincidence i think.
Patrick, Thu Jul 03 2014, 08:43PM
I'll be cashing a 25 million check soon... you want some?
i see the same trend here, no coincidence i think.
Re: Novel flying machines
Ash Small, Fri Jul 04 2014, 11:59AM
Well, the graph is the same shape for the same reasons, although it's a different graph.
It does depict that the space shuttle flys faster than a 747, but that the 747 is more efficient, I think, but I'm not familiar with the 'specific impulse' term. Sounds like 'rocket science' to me
Ash Small, Fri Jul 04 2014, 11:59AM
Well, the graph is the same shape for the same reasons, although it's a different graph.
It does depict that the space shuttle flys faster than a 747, but that the 747 is more efficient, I think, but I'm not familiar with the 'specific impulse' term. Sounds like 'rocket science' to me
Re: Novel flying machines
Ash Small, Fri Jul 04 2014, 03:01PM
Going back to the disc loading graph, I've done some quick calculations regarding disc area divided by circumferance for two props with the same disc loading but one of 1 metre diameter, and one of 20 metres diameter.
Disc area divided by circumferance for the 1 metre prop works out at 0.25
Disc area sivided by circumferance for the 20 metre prop works out at 5
I guess this illustrates how scale affects these things. These numbers will be proportional to efficiency, with 5 being more efficient than 0.25.
I guess it also implies that we can reduce the disc loading still further on a smaller prop without unduly affecting manouverability, though.
EDIT: The smaller prop has more losses per unit area of disc, even when the disc loading is the same. This will account for the shaded ares on the graph and also accounts for us being outside of the shaded areas, although it may still be possible to improve on prop design, etc., the main reason we are outside of the shaded area is due to 'scaling', as we suspected. I'll repeat it again, for a 'first order approximation', all the losses are at the periphery of the accelerated column of air. Losses increase with V^2 (this may be slightly oversimplified, but it's 'in the ballpark')
I still need to look at the propeller equation again, which I hope to do over the weekend.
Ash Small, Fri Jul 04 2014, 03:01PM
Going back to the disc loading graph, I've done some quick calculations regarding disc area divided by circumferance for two props with the same disc loading but one of 1 metre diameter, and one of 20 metres diameter.
Disc area divided by circumferance for the 1 metre prop works out at 0.25
Disc area sivided by circumferance for the 20 metre prop works out at 5
I guess this illustrates how scale affects these things. These numbers will be proportional to efficiency, with 5 being more efficient than 0.25.
I guess it also implies that we can reduce the disc loading still further on a smaller prop without unduly affecting manouverability, though.
EDIT: The smaller prop has more losses per unit area of disc, even when the disc loading is the same. This will account for the shaded ares on the graph and also accounts for us being outside of the shaded areas, although it may still be possible to improve on prop design, etc., the main reason we are outside of the shaded area is due to 'scaling', as we suspected. I'll repeat it again, for a 'first order approximation', all the losses are at the periphery of the accelerated column of air. Losses increase with V^2 (this may be slightly oversimplified, but it's 'in the ballpark')
I still need to look at the propeller equation again, which I hope to do over the weekend.
Re: Novel flying machines
Ash Small, Fri Jul 04 2014, 07:12PM
Sory about the multiple post, but new info:
Here's my first attemp at the log/log graph. Should I go for the best straight line, or try and plot a curve?
I think there probably were some discrepancies on my part, but it almost looks as if it should be a curve.
Any comments welcome.
EDIT: I'm currently thinking I should try 'best straight line', I don't think the points accurately represent a curve, but I could try both. Any suggestions?
Maybe someone else should check, or plot their own, for comparison?
I can provide a .pdf of the log/log paper if required.
Ash Small, Fri Jul 04 2014, 07:12PM
Sory about the multiple post, but new info:
Here's my first attemp at the log/log graph. Should I go for the best straight line, or try and plot a curve?
I think there probably were some discrepancies on my part, but it almost looks as if it should be a curve.
Any comments welcome.
EDIT: I'm currently thinking I should try 'best straight line', I don't think the points accurately represent a curve, but I could try both. Any suggestions?
Maybe someone else should check, or plot their own, for comparison?
I can provide a .pdf of the log/log paper if required.
Re: Novel flying machines
Patrick, Fri Jul 04 2014, 09:15PM
so what about prop shape?
Patrick, Fri Jul 04 2014, 09:15PM
so what about prop shape?
Re: Novel flying machines
Ash Small, Fri Jul 04 2014, 09:48PM
As I said before, more like conventional heli. Right now I'd prefer a second opinion on this graph.
Neil suggested it should be a straight line, no-one else has given an opinion as yet.
I'm planning to re-do the plot, and see if I get the same thing, or something that looks like a straight line or a curve.
But I'd appreciate any other input
EDIT: It does look fairly straight, but maybe I don't have enough plots to tell if it turns upwards at the left hand end?
Maybe we need some more thrust data from 14" props, Patrick?
Ash Small, Fri Jul 04 2014, 09:48PM
Patrick wrote ...
so what about prop shape?
so what about prop shape?
As I said before, more like conventional heli. Right now I'd prefer a second opinion on this graph.
Neil suggested it should be a straight line, no-one else has given an opinion as yet.
I'm planning to re-do the plot, and see if I get the same thing, or something that looks like a straight line or a curve.
But I'd appreciate any other input
EDIT: It does look fairly straight, but maybe I don't have enough plots to tell if it turns upwards at the left hand end?
Maybe we need some more thrust data from 14" props, Patrick?
Re: Novel flying machines
Patrick, Fri Jul 04 2014, 11:12PM
until i get the props in the mail heres the link. its listed in 1000's of RPM...
lnik:
Patrick, Fri Jul 04 2014, 11:12PM
Ash Small wrote ...
Maybe we need some more thrust data from 14" props, Patrick?
ill get some data on the 14's...Maybe we need some more thrust data from 14" props, Patrick?
until i get the props in the mail heres the link. its listed in 1000's of RPM...
lnik:
Re: Novel flying machines
Uspring, Sat Jul 05 2014, 10:47AM
Ash Small wrote:
F = (2 * rho * A * (ζ*P)^2)^(1/3)
Raise to the third power on both sides:
F³ = 2 * rho * A * (ζ*P)²
Divide both sides by F * P²:
(F/P)² = 2 * rho * ζ² * (A/F)
This is the equation, which relates "efficiency", i.e. F/P to disk loading, i.e. F/A. In a log-log plot it should be a straight line. The graph on helis doesn't exactly follow this description, but gets close. Prop efficiency ζ seems to be somewhat larger for heavily loaded props.
Note that the usage of the term "efficiency" is ambiguous in this discussion. I prefer using it for ζ, which is solely a property of the prop. The "efficiency" F/P also depends on the disk load or the props rpm.
According to the tables Patrick posted, the ζ for the 10" prop is 0.41, for the 14" it is 0.40. Both are quite less than sensational values. Note that the lower value for the 14" prop does not imply, that it gives less lift per power than the 10" one.
Uspring, Sat Jul 05 2014, 10:47AM
Ash Small wrote:
Here's my first attemp at the log/log graph. Should I go for the best straight line, or try and plot a curve?Have a look at the equation for thrust:
F = (2 * rho * A * (ζ*P)^2)^(1/3)
Raise to the third power on both sides:
F³ = 2 * rho * A * (ζ*P)²
Divide both sides by F * P²:
(F/P)² = 2 * rho * ζ² * (A/F)
This is the equation, which relates "efficiency", i.e. F/P to disk loading, i.e. F/A. In a log-log plot it should be a straight line. The graph on helis doesn't exactly follow this description, but gets close. Prop efficiency ζ seems to be somewhat larger for heavily loaded props.
Note that the usage of the term "efficiency" is ambiguous in this discussion. I prefer using it for ζ, which is solely a property of the prop. The "efficiency" F/P also depends on the disk load or the props rpm.
According to the tables Patrick posted, the ζ for the 10" prop is 0.41, for the 14" it is 0.40. Both are quite less than sensational values. Note that the lower value for the 14" prop does not imply, that it gives less lift per power than the 10" one.
Re: Novel flying machines
Ash Small, Sat Jul 05 2014, 11:24AM
Thanks for the input, Udo. I'll study this later.
Patrick, do you have any smaller props that we can plot as well?
As Udo points out, I also don't think the prop design you're currently using is optimal for this application. These are, after all, mass produced, relatively cheap propellers.
EDIT:
Yep. I was lumping them all in together, but treating the 'prop losses' as a 'secondary factor' which doesn't dominate at this point, and I was assuming an efficient prop.
I agree these need to be considered before finalizing a design, but I was initially concentrating on the 'disc loading' thing.
I don't think Patrick will find the improvements in flight time that he is after by just looking at prop efficiency
Ash Small, Sat Jul 05 2014, 11:24AM
Thanks for the input, Udo. I'll study this later.
Patrick, do you have any smaller props that we can plot as well?
As Udo points out, I also don't think the prop design you're currently using is optimal for this application. These are, after all, mass produced, relatively cheap propellers.
EDIT:
Uspring wrote ...
Note that the usage of the term "efficiency" is ambiguous in this discussion. I prefer using it for ζ, which is solely a property of the prop. The "efficiency" F/P also depends on the disk load or the props rpm.
Note that the usage of the term "efficiency" is ambiguous in this discussion. I prefer using it for ζ, which is solely a property of the prop. The "efficiency" F/P also depends on the disk load or the props rpm.
Yep. I was lumping them all in together, but treating the 'prop losses' as a 'secondary factor' which doesn't dominate at this point, and I was assuming an efficient prop.
I agree these need to be considered before finalizing a design, but I was initially concentrating on the 'disc loading' thing.
I don't think Patrick will find the improvements in flight time that he is after by just looking at prop efficiency
Re: Novel flying machines
Ash Small, Sat Jul 05 2014, 06:23PM
I think the conclusion I'm coming to is that we need more data to plot before we can perform any 'reliable' extrapolation.
It may even be worth designing and constructing some larger props, and plotting the data obtained from them, but this is quite a large undertaking.
Ash Small, Sat Jul 05 2014, 06:23PM
I think the conclusion I'm coming to is that we need more data to plot before we can perform any 'reliable' extrapolation.
It may even be worth designing and constructing some larger props, and plotting the data obtained from them, but this is quite a large undertaking.
Re: Novel flying machines
Patrick, Sat Jul 05 2014, 08:17PM
Let me get you some other sizes...
9x4.5 mr
10x4.5mr
11x4.5mr
12x4.5mr
14x5.5mr
There is no 13 inch MR prop...
Patrick, Sat Jul 05 2014, 08:17PM
Let me get you some other sizes...
9x4.5 mr 10x4.5mr 11x4.5mr 12x4.5mr 14x5.5mrThere is no 13 inch MR prop...
Re: Novel flying machines
Ash Small, Sat Jul 05 2014, 09:04PM
We need data that I can convert into Lbs/Foot^2 and Lbs/Hp. Data we've measured ourselves.
Unless anyone wants to try predicting from manufacturer's data sheets? I wouldn't know where to start, and certainly wouldn't rely on their info.
We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.
Ash Small, Sat Jul 05 2014, 09:04PM
We need data that I can convert into Lbs/Foot^2 and Lbs/Hp. Data we've measured ourselves.
Unless anyone wants to try predicting from manufacturer's data sheets? I wouldn't know where to start, and certainly wouldn't rely on their info.
We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.
Re: Novel flying machines
Patrick, Sat Jul 05 2014, 09:12PM
EDIT 1: So if we were to design heli like blades, what would they look like? Would we make the the root crossection different than the Tip?
EDIT 2: link this is important, as he claims to push the thrust more inboard, even if we dont copy the 'ellipse" prop, we should consider the implications on a constant chord heli blade.
EDIT 3: im going to cut 0.5 inche diamters off the 10x5.5mr props tomarrow, to see where the thrust-power is located.
Patrick, Sat Jul 05 2014, 09:12PM
Ash Small wrote ...
We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.
OK we'll have to wait for the mailman then... I have props coming.We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.
EDIT 1: So if we were to design heli like blades, what would they look like? Would we make the the root crossection different than the Tip?
EDIT 2: link
this is important, as he claims to push the thrust more inboard, even if we dont copy the 'ellipse" prop, we should consider the implications on a constant chord heli blade.EDIT 3: im going to cut 0.5 inche diamters off the 10x5.5mr props tomarrow, to see where the thrust-power is located.
Re: Novel flying machines
Ash Small, Sun Jul 06 2014, 04:24PM
It's usual to have a different section for root and tip as the tip is travelling faster than the root. I'm not that familiar with heli blades, but I think we should find some examples.
I don't think we need to copy the LIPPS prop. My opinion is that it may be advantageous in a 'tilt wing' or 'lift fan' aircraft, but we wan't low disc loading and low drag.
It may be advantageous to increase material at the root if we decide we need it for reasons of strength/rigidity, but I don't think I'd consider it for any other reasons for this application.
We want low disc loading and low drag. The LIPPS design looks like it's more suited for high disc loading applications.
Ash Small, Sun Jul 06 2014, 04:24PM
It's usual to have a different section for root and tip as the tip is travelling faster than the root. I'm not that familiar with heli blades, but I think we should find some examples.
I don't think we need to copy the LIPPS prop. My opinion is that it may be advantageous in a 'tilt wing' or 'lift fan' aircraft, but we wan't low disc loading and low drag.
It may be advantageous to increase material at the root if we decide we need it for reasons of strength/rigidity, but I don't think I'd consider it for any other reasons for this application.
We want low disc loading and low drag. The LIPPS design looks like it's more suited for high disc loading applications.
Re: Novel flying machines
Patrick, Sun Jul 06 2014, 06:44PM
should we be looking at NACA profiles then?
Patrick, Sun Jul 06 2014, 06:44PM
should we be looking at NACA profiles then?
Re: Novel flying machines
Ash Small, Mon Jul 07 2014, 02:55PM
Well, Wikipedia says they are 'airfoils'
"The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure, and steel or titanium, with abrasion shields along the leading edge."
EDIT: I also found this:
Which includes a "Rotor Blade Case Study", which I'm reading now, and which includes this:
I imagine you're experienced enough now with composites to attemp a prototype, Patrick
EDIT: Also found this:
Ash Small, Mon Jul 07 2014, 02:55PM
Patrick wrote ...
should we be looking at NACA profiles then?
should we be looking at NACA profiles then?
Well, Wikipedia says they are 'airfoils'
"The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure, and steel or titanium, with abrasion shields along the leading edge."
EDIT: I also found this:
Which includes a "Rotor Blade Case Study", which I'm reading now, and which includes this:
I imagine you're experienced enough now with composites to attemp a prototype, Patrick
EDIT: Also found this:
Re: Novel flying machines
Patrick, Mon Jul 07 2014, 07:23PM
the shape along its lenght, airfoil cross section, and hub are the parts i worry about most, i can layup the CF and GF easilly enough.
Patrick, Mon Jul 07 2014, 07:23PM
the shape along its lenght, airfoil cross section, and hub are the parts i worry about most, i can layup the CF and GF easilly enough.
Re: Novel flying machines
Ash Small, Mon Jul 07 2014, 07:29PM
Well, I'm sure we can help with the design. Udo seems quite eager to get stuck into the prop design I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.
Ash Small, Mon Jul 07 2014, 07:29PM
Patrick wrote ...
the shape along its lenght, airfoil cross section, and hub are the parts i worry about most,
the shape along its lenght, airfoil cross section, and hub are the parts i worry about most,
Well, I'm sure we can help with the design. Udo seems quite eager to get stuck into the prop design
I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.Re: Novel flying machines
Patrick, Mon Jul 07 2014, 09:09PM
Im thinking 14, 16, and 18 inch props 2-blade. Since those are the best sizes too given shipping and disc loading.
But,
Patrick, Mon Jul 07 2014, 09:09PM
Im thinking 14, 16, and 18 inch props 2-blade. Since those are the best sizes too given shipping and disc loading.
But,
Ash Small wrote ...
I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.
are you meaning your graph? or my 14 inch prop?I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.
Re: Novel flying machines
Ash Small, Mon Jul 07 2014, 11:13PM
Neither really, just pointing out you need a prop with maybe 10 times the area in order to achieve the flight times you want from the same batteries. I don't have enough data yet to say exactly how big, and I don't know how much manouverability will suffer.
Ash Small, Mon Jul 07 2014, 11:13PM
Patrick wrote ...
are you meaning your graph? or my 14 inch prop?
are you meaning your graph? or my 14 inch prop?
Neither really, just pointing out you need a prop with maybe 10 times the area in order to achieve the flight times you want from the same batteries. I don't have enough data yet to say exactly how big, and I don't know how much manouverability will suffer.
Re: Novel flying machines
BigBad, Tue Jul 08 2014, 12:34AM
Running them at lower disc loading may well not give optimal performance, although may give better performance anyway.
BigBad, Tue Jul 08 2014, 12:34AM
Uspring wrote ...
According to the tables Patrick posted, the ζ for the 10" prop is 0.41, for the 14" it is 0.40. Both are quite less than sensational values. Note that the lower value for the 14" prop does not imply, that it gives less lift per power than the 10" one.
I expect that the props are optimised for some particular disc loading (to the extent that they are optimised).According to the tables Patrick posted, the ζ for the 10" prop is 0.41, for the 14" it is 0.40. Both are quite less than sensational values. Note that the lower value for the 14" prop does not imply, that it gives less lift per power than the 10" one.
Running them at lower disc loading may well not give optimal performance, although may give better performance anyway.
Re: Novel flying machines
Patrick, Tue Jul 08 2014, 01:24AM
im looking at geometry and airfoil cross sections for now.
here: and
we'll need at 16" to reduce the RPM, or motor load problems, whiich is why we start seeing those pancake motors.
involute gear link :
Patrick, Tue Jul 08 2014, 01:24AM
im looking at geometry and airfoil cross sections for now.
here:
and we'll need at 16" to reduce the RPM, or motor load problems, whiich is why we start seeing those pancake motors.
involute gear link :
Re: Novel flying machines
Dr. Slack, Tue Jul 08 2014, 07:46AM
I think the point is that, compared to the original graph, which looks definitely curved, like it's asymptotic to both axes, the log-log looks straighter. Given that it's a collection of results from differently controlled experiments over several orders of magnitude, I'd call it 'ruler-flat', much the same way that an engineer would consider two quantities of the same order of magnitude 'equal'.
The next thing to consider, if you're building your own blades, is the distribution of the lift along the blade length. There are several arguments. One is to control the blade chord and angle of attack so that the airspeed is uniform across the disc. This means high pitch in the middle, low pitch at the tip. This would apparently give the lowest mean speed per momentum imparted, and so best efficiency. However, all sorts of sources from the elliptical spitfire wing, to tip-fences on airliners, suggest that a rapid change of velocity and pressure at the stream edge causes excessive induced drag, so reducing total efficiency. This would suggest a faster fall-off of pitch at the end of the blade. Just an idle thought, I wonder if a tip-fence is sort of half a duct? Now, a blade is not a fixed wing, the latter moves at constant speed across its width, the former is obviously fastest at the tip. This starts suggesting to me that the tip of the blade is 'expensive' in terms of viscous/wetted surface drag, and so should be made to lift a bit harder than it would be made to lift on a fixed wing. The blade has to end somewhere, so it is a problem that must be met somewhere, or ignored at the cost of best efficiency. Given that the blade tip is expensive for drag, I think this is why winglets or tip-fences may appear on fixed wings, but should be kept off rotor blades. So rather like the work-week, which should not really have a Monday, rotors should not have tips, they're just generally a bad idea. I guess this is where ducts appear from, allows the drag-expensive tip of the blade to generate a reasonable amount of lift, while mitigating the induced drag. Anyhow, figure out what distribution of lift you want along the blade, then this will drive what blade profile you end up with, not should it look like the LIPPS. What's the distribution of lift on commercial props you can buy, I'm not sure they're all idiots?
Dr. Slack, Tue Jul 08 2014, 07:46AM
I'm planning to re-do the plot, and see if I get the same thing, or something that looks like a straight line or a curve.
But I'd appreciate any other input
EDIT: It does look fairly straight, but maybe I don't have enough plots to tell if it turns upwards at the left hand end?
I think the point is that, compared to the original graph, which looks definitely curved, like it's asymptotic to both axes, the log-log looks straighter. Given that it's a collection of results from differently controlled experiments over several orders of magnitude, I'd call it 'ruler-flat', much the same way that an engineer would consider two quantities of the same order of magnitude 'equal'.
The next thing to consider, if you're building your own blades, is the distribution of the lift along the blade length. There are several arguments. One is to control the blade chord and angle of attack so that the airspeed is uniform across the disc. This means high pitch in the middle, low pitch at the tip. This would apparently give the lowest mean speed per momentum imparted, and so best efficiency. However, all sorts of sources from the elliptical spitfire wing, to tip-fences on airliners, suggest that a rapid change of velocity and pressure at the stream edge causes excessive induced drag, so reducing total efficiency. This would suggest a faster fall-off of pitch at the end of the blade. Just an idle thought, I wonder if a tip-fence is sort of half a duct? Now, a blade is not a fixed wing, the latter moves at constant speed across its width, the former is obviously fastest at the tip. This starts suggesting to me that the tip of the blade is 'expensive' in terms of viscous/wetted surface drag, and so should be made to lift a bit harder than it would be made to lift on a fixed wing. The blade has to end somewhere, so it is a problem that must be met somewhere, or ignored at the cost of best efficiency. Given that the blade tip is expensive for drag, I think this is why winglets or tip-fences may appear on fixed wings, but should be kept off rotor blades. So rather like the work-week, which should not really have a Monday, rotors should not have tips, they're just generally a bad idea. I guess this is where ducts appear from, allows the drag-expensive tip of the blade to generate a reasonable amount of lift, while mitigating the induced drag. Anyhow, figure out what distribution of lift you want along the blade, then this will drive what blade profile you end up with, not should it look like the LIPPS. What's the distribution of lift on commercial props you can buy, I'm not sure they're all idiots?
Re: Novel flying machines
Patrick, Tue Jul 08 2014, 07:50AM
as for the pitch and lift, some of the APC MR's look like they have steep pitch at the root.
Patrick, Tue Jul 08 2014, 07:50AM
Dr. Slack wrote ...
Anyhow, figure out what distribution of lift you want along the blade, then this will drive what blade profile you end up with, not should it look like the LIPPS. What's the distribution of lift on commercial props you can buy, I'm not sure they're all idiots?
fair enough, but the Paul lipps prop tapers to an unconventional tip for the reasons you state. Anyhow, figure out what distribution of lift you want along the blade, then this will drive what blade profile you end up with, not should it look like the LIPPS. What's the distribution of lift on commercial props you can buy, I'm not sure they're all idiots?
as for the pitch and lift, some of the APC MR's look like they have steep pitch at the root.
Re: Novel flying machines
Uspring, Tue Jul 08 2014, 09:19AM
Dr. Slack wrote:
Uspring, Tue Jul 08 2014, 09:19AM
Dr. Slack wrote:
Anyhow, figure out what distribution of lift you want along the blade, then this will drive what blade profile you end up with, not should it look like the LIPPS. What's the distribution of lift on commercial props you can buy, I'm not sure they're all idiots?I'd just make a survey on all the thrust and power consumption tables you can get your hands on with the biggest props you can accomodate. Look at the entries which correspond to the weight you need to lift. The shapes of the best props might give you an idea what to look for. Wrt to the weight of your craft, I'd choose battery weight about equal to the rest of the copter. Adding more batteries won't increase flight time significantly. Lowering the bare weight (and battery weight correspondingly) will, though.
Re: Novel flying machines
Ash Small, Tue Jul 08 2014, 08:02PM
I'd consider leaving out the 'blade' near the root, or have less pitch here than the maths suggests, as this would reduce drag considerably without too much detriment to lift, as there is not much lift at the root anyway. Pitch will be least at the tip anyway, and if you go for high RPM, you can get away with less pitch across the whole blade.
We've not done 'prop drag' in detail yet, and I'm aware that zero pitch props still have drag, but I suspect there may be advantages to reducing pitch and increasing RPM, rather than increasing pitch and reducing RPM. For one thing the blades presumably won't be as wide. either. I'm not certain about this, but I think it's worth considering.
What I think is required here is long thin high RPM blades, with not a lot of pitch, but we'll see
EDIT: If gearing down is still required, I'd go for a reduction belt system, as it's much easier to adjust the gearing if required, for one thing.
EDIT: I suggest designing for the thinnest section that has sufficient strength. More pitch means you need a stronger prop, I think.
EDIT: The props you are currently using are all designed for a higher 'disc loading' than what we want.
Ash Small, Tue Jul 08 2014, 08:02PM
I'd consider leaving out the 'blade' near the root, or have less pitch here than the maths suggests, as this would reduce drag considerably without too much detriment to lift, as there is not much lift at the root anyway. Pitch will be least at the tip anyway, and if you go for high RPM, you can get away with less pitch across the whole blade.
We've not done 'prop drag' in detail yet, and I'm aware that zero pitch props still have drag, but I suspect there may be advantages to reducing pitch and increasing RPM, rather than increasing pitch and reducing RPM. For one thing the blades presumably won't be as wide. either. I'm not certain about this, but I think it's worth considering.
What I think is required here is long thin high RPM blades, with not a lot of pitch, but we'll see
EDIT: If gearing down is still required, I'd go for a reduction belt system, as it's much easier to adjust the gearing if required, for one thing.
EDIT: I suggest designing for the thinnest section that has sufficient strength. More pitch means you need a stronger prop, I think.
EDIT: The props you are currently using are all designed for a higher 'disc loading' than what we want.
Re: Novel flying machines
Ash Small, Wed Jul 09 2014, 04:48PM
I did notice that the point I plotted at the extreme left hand side was to high (still getting used to log/log graphs), and I've drawn what I consider to be the best straight line.
I will give this some more thought, although at the moment I think it should be more curved.
For example, what can we deduce from the points where it crosses the X and Y axes?
Any suggestions welcome.
I do think we need to plot from 'measured values' in order to perform any meaningful extrapolation, although we can probably learn something from what we already have here.
EDIT: The units for this graph are the same as in the Wikipedia 'disc loading' graph.
EDIT: I'm expecting the point of intersection with the Y axis to be higher once we have some more relevant data to plot.
Ash Small, Wed Jul 09 2014, 04:48PM
Dr. Slack wrote ...
I think the point is that, compared to the original graph, which looks definitely curved, like it's asymptotic to both axes, the log-log looks straighter. Given that it's a collection of results from differently controlled experiments over several orders of magnitude, I'd call it 'ruler-flat', much the same way that an engineer would consider two quantities of the same order of magnitude 'equal'.
I think the point is that, compared to the original graph, which looks definitely curved, like it's asymptotic to both axes, the log-log looks straighter. Given that it's a collection of results from differently controlled experiments over several orders of magnitude, I'd call it 'ruler-flat', much the same way that an engineer would consider two quantities of the same order of magnitude 'equal'.
I did notice that the point I plotted at the extreme left hand side was to high (still getting used to log/log graphs), and I've drawn what I consider to be the best straight line.
I will give this some more thought, although at the moment I think it should be more curved.
For example, what can we deduce from the points where it crosses the X and Y axes?
Any suggestions welcome.
I do think we need to plot from 'measured values' in order to perform any meaningful extrapolation, although we can probably learn something from what we already have here.
EDIT: The units for this graph are the same as in the Wikipedia 'disc loading' graph.
EDIT: I'm expecting the point of intersection with the Y axis to be higher once we have some more relevant data to plot.
Re: Novel flying machines
Dr. Slack, Wed Jul 09 2014, 05:01PM
if you have a relationship like
y = k * x^b
and you take logs, you get
log(y) = log(k) + b*log(x)
if you now plot a log-log graph, the slope is the power b to which x is raised, so it's handy for identifying power laws. I'll let you work out what the intercepts means from that log equation
Dr. Slack, Wed Jul 09 2014, 05:01PM
if you have a relationship like
y = k * x^b
and you take logs, you get
log(y) = log(k) + b*log(x)
if you now plot a log-log graph, the slope is the power b to which x is raised, so it's handy for identifying power laws. I'll let you work out what the intercepts means from that log equation
Re: Novel flying machines
Ash Small, Wed Jul 09 2014, 05:18PM
Ok, Thanks
In the meantime, though, the 'original' Wikipedia graph obviously cross the Y axis at ~12Lbs/Hp (maybe I didn't read the log/log graph correctly), and I'm now assuming that the reason 'our' measurement on that graph (the Wiki one) that I plotted earlier in the thread is so far from the other figures is that we are using a prop designed for higher disc loading than we really need, therefore there are extra drag losses.
Now, back to looking at that 'log(y) = log(k) + b*log(x)' stuff (I did look at this stuff briefly the other day, but it's a long time since I used it as a student or whatnot.)
EDIT: Ok, I've got as far as F(x)=constant.x^m, I'll look at it again later.
Ash Small, Wed Jul 09 2014, 05:18PM
Dr. Slack wrote ...
if you have a relationship like
y = k * x^b
and you take logs, you get
log(y) = log(k) + b*log(x)
if you now plot a log-log graph, the slope is the power b to which x is raised, so it's handy for identifying power laws. I'll let you work out what the intercepts means from that log equation
if you have a relationship like
y = k * x^b
and you take logs, you get
log(y) = log(k) + b*log(x)
if you now plot a log-log graph, the slope is the power b to which x is raised, so it's handy for identifying power laws. I'll let you work out what the intercepts means from that log equation
Ok, Thanks
In the meantime, though, the 'original' Wikipedia graph obviously cross the Y axis at ~12Lbs/Hp (maybe I didn't read the log/log graph correctly), and I'm now assuming that the reason 'our' measurement on that graph (the Wiki one) that I plotted earlier in the thread is so far from the other figures is that we are using a prop designed for higher disc loading than we really need, therefore there are extra drag losses.
Now, back to looking at that 'log(y) = log(k) + b*log(x)' stuff (I did look at this stuff briefly the other day, but it's a long time since I used it as a student or whatnot.)
EDIT: Ok, I've got as far as F(x)=constant.x^m, I'll look at it again later.
Re: Novel flying machines
Ash Small, Thu Jul 10 2014, 11:23AM
Ok, so just looking at the graph, it looks like the intersection with the Y axis equates to 1Lb/foot^2 = 12Lbs/Hp, although the Wikipedia graph doesn't appear to support this, and suggests that 1Lb/foot^2 disc loading equates to significantly more than 12Lbs/Hp.
We definitely need more data to plot. I also think that if, as Udo suggested, higher disc loadings can by more efficient, this graph won't be a straight line, and will actually be a curve.
I will continue with the maths above, just to see where it goes, but I still think we need more data before performing any reliable extrapolation.
Ash Small, Thu Jul 10 2014, 11:23AM
Ok, so just looking at the graph, it looks like the intersection with the Y axis equates to 1Lb/foot^2 = 12Lbs/Hp, although the Wikipedia graph doesn't appear to support this, and suggests that 1Lb/foot^2 disc loading equates to significantly more than 12Lbs/Hp.
We definitely need more data to plot. I also think that if, as Udo suggested, higher disc loadings can by more efficient, this graph won't be a straight line, and will actually be a curve.
I will continue with the maths above, just to see where it goes, but I still think we need more data before performing any reliable extrapolation.
Re: Novel flying machines
Ash Small, Sun Jul 13 2014, 01:48PM
Well, I've got as far as y=mx+b with the graph, but when I try to put any numbers in it doesn't seem to make any sense. I'm probably making some fundamental mistakes with logs, it's been a long time.........
Ash Small, Sun Jul 13 2014, 01:48PM
Well, I've got as far as y=mx+b with the graph, but when I try to put any numbers in it doesn't seem to make any sense. I'm probably making some fundamental mistakes with logs, it's been a long time.........
Re: Novel flying machines
Dr. Slack, Sun Jul 13 2014, 06:27PM
Extrapolation is, by definition, unreliable. You don't do new measurements, new science, with the intention of extrapolating, that way lies madness, unless you're a cosmologist of course. Dig the slope out of the log log graph to see if it is somewhere near a strght line, to see if you have a power law, and if you have, whether you can understand why. Then get new measrements, preferrably beyond the extremes of your existing data, and see if the line starts to bend, as another term, neglected in the middling region, starts to become significsnt (like I expect viscous drag to be in the region of very low disc loading - but, I'm spoiling the plot!)
Dr. Slack, Sun Jul 13 2014, 06:27PM
wrote ...
I will continue with the maths above, just to see where it goes, but I still think we need more data before performing any reliable extrapolation.
I will continue with the maths above, just to see where it goes, but I still think we need more data before performing any reliable extrapolation.
Extrapolation is, by definition, unreliable. You don't do new measurements, new science, with the intention of extrapolating, that way lies madness, unless you're a cosmologist of course. Dig the slope out of the log log graph to see if it is somewhere near a strght line, to see if you have a power law, and if you have, whether you can understand why. Then get new measrements, preferrably beyond the extremes of your existing data, and see if the line starts to bend, as another term, neglected in the middling region, starts to become significsnt (like I expect viscous drag to be in the region of very low disc loading - but, I'm spoiling the plot!)
Re: Novel flying machines
Ash Small, Sun Jul 13 2014, 06:53PM
I agree that extrapolation is, by definition, unreliable. That's why I'm not prepared to try it without some more data
I also agree that viscous drag will become a factor with very low disc loadings, but I still don't think this graph is a straight line. It does seem to curve at both ends.
Any extrapolation won't be 'spot on', but the better the data, the more accurate it will be.
I'm still trying to get my head around logs again, it's slowly coming back......
EDIT: I think we'll lose all manouverability long before viscous drag becomes a dominant factor, resulting in a completely uncontrollable, useless aircraft.
Ash Small, Sun Jul 13 2014, 06:53PM
Dr. Slack wrote ...
Extrapolation is, by definition, unreliable. You don't do new measurements, new science, with the intention of extrapolating, that way lies madness, unless you're a cosmologist of course. Dig the slope out of the log log graph to see if it is somewhere near a strght line, to see if you have a power law, and if you have, whether you can understand why. Then get new measrements, preferrably beyond the extremes of your existing data, and see if the line starts to bend, as another term, neglected in the middling region, starts to become significsnt (like I expect viscous drag to be in the region of very low disc loading - but, I'm spoiling the plot!)
Extrapolation is, by definition, unreliable. You don't do new measurements, new science, with the intention of extrapolating, that way lies madness, unless you're a cosmologist of course. Dig the slope out of the log log graph to see if it is somewhere near a strght line, to see if you have a power law, and if you have, whether you can understand why. Then get new measrements, preferrably beyond the extremes of your existing data, and see if the line starts to bend, as another term, neglected in the middling region, starts to become significsnt (like I expect viscous drag to be in the region of very low disc loading - but, I'm spoiling the plot!)
I agree that extrapolation is, by definition, unreliable. That's why I'm not prepared to try it without some more data
I also agree that viscous drag will become a factor with very low disc loadings, but I still don't think this graph is a straight line. It does seem to curve at both ends.
Any extrapolation won't be 'spot on', but the better the data, the more accurate it will be.
I'm still trying to get my head around logs again, it's slowly coming back......
EDIT: I think we'll lose all manouverability long before viscous drag becomes a dominant factor, resulting in a completely uncontrollable, useless aircraft.
Re: Novel flying machines
Patrick, Mon Jul 14 2014, 03:21AM
ive got the 12 and 14 inch props on there way, but APC can be slow. They should be here soon. Then well be able to measure from 10 to 12 to 14 inch disc loading. graph that I think well see a concave up curve.
Patrick, Mon Jul 14 2014, 03:21AM
ive got the 12 and 14 inch props on there way, but APC can be slow. They should be here soon. Then well be able to measure from 10 to 12 to 14 inch disc loading. graph that I think well see a concave up curve.
Re: Novel flying machines
Ash Small, Mon Jul 14 2014, 10:33AM
While I think those props are optimized for a higher disc loading than we need, they should provide some useful information. Props optimized for a lower disc loading will be more efficient.
The three plots should give us enough information to tell if it's a straight line or a curve.
Ash Small, Mon Jul 14 2014, 10:33AM
Patrick wrote ...
ive got the 12 and 14 inch props on there way, but APC can be slow. They should be here soon. Then well be able to measure from 10 to 12 to 14 inch disc loading. graph that I think well see a concave up curve.
ive got the 12 and 14 inch props on there way, but APC can be slow. They should be here soon. Then well be able to measure from 10 to 12 to 14 inch disc loading. graph that I think well see a concave up curve.
While I think those props are optimized for a higher disc loading than we need, they should provide some useful information. Props optimized for a lower disc loading will be more efficient.
The three plots should give us enough information to tell if it's a straight line or a curve.
Re: Novel flying machines
BigBad, Mon Jul 14 2014, 12:50PM
The confounding factor here is probably the fixed pitch of the blades; the manufacturer will have pitched them somehow, but you might want them differently, probably finer.
Probably the more or less ideal way to graph this would be to use a straight prop and then statically adjust its pitch to give the best efficiency for the same target thrust; and then do that over different lengths; keeping the target thrust the same.
Otherwise you're at the mercy of the manufacturers; whatever pitch they think their customers want.
BigBad, Mon Jul 14 2014, 12:50PM
The confounding factor here is probably the fixed pitch of the blades; the manufacturer will have pitched them somehow, but you might want them differently, probably finer.
Probably the more or less ideal way to graph this would be to use a straight prop and then statically adjust its pitch to give the best efficiency for the same target thrust; and then do that over different lengths; keeping the target thrust the same.
Otherwise you're at the mercy of the manufacturers; whatever pitch they think their customers want.
Re: Novel flying machines
Ash Small, Mon Jul 14 2014, 04:08PM
I agree that we want a prop with less pitch than the 'all rounders' that the suppliers provide, but we should still learn something from three different diameter, mass produced props. We should be able to conclude whether or not it's a straight line or a curve.
An optimized prop for our application will be more efficient than the mass produced ones, however I don't think we want a prop with the same pitch all along the length (if that's what you mean by a 'straight prop').
Once we have these figures we should be able to design a prop with a bit of 'twist' using the relevant maths, though, although I'm still expecting a bit of 'trial and error' before the optimum design is reached.
We will, pretty much, be comparing 'like with like'.
Ash Small, Mon Jul 14 2014, 04:08PM
BigBad wrote ...
The confounding factor here is probably the fixed pitch of the blades; the manufacturer will have pitched them somehow, but you might want them differently, probably finer.
Probably the more or less ideal way to graph this would be to use a straight prop and then statically adjust its pitch to give the best efficiency for the same target thrust; and then do that over different lengths; keeping the target thrust the same.
Otherwise you're at the mercy of the manufacturers; whatever pitch they think their customers want.
The confounding factor here is probably the fixed pitch of the blades; the manufacturer will have pitched them somehow, but you might want them differently, probably finer.
Probably the more or less ideal way to graph this would be to use a straight prop and then statically adjust its pitch to give the best efficiency for the same target thrust; and then do that over different lengths; keeping the target thrust the same.
Otherwise you're at the mercy of the manufacturers; whatever pitch they think their customers want.
I agree that we want a prop with less pitch than the 'all rounders' that the suppliers provide, but we should still learn something from three different diameter, mass produced props. We should be able to conclude whether or not it's a straight line or a curve.
An optimized prop for our application will be more efficient than the mass produced ones, however I don't think we want a prop with the same pitch all along the length (if that's what you mean by a 'straight prop').
Once we have these figures we should be able to design a prop with a bit of 'twist' using the relevant maths, though, although I'm still expecting a bit of 'trial and error' before the optimum design is reached.
We will, pretty much, be comparing 'like with like'.
Re: Novel flying machines
Patrick, Mon Jul 14 2014, 09:30PM
what about a prop hub that allows changing pitch with a set screw ? for multiple iterations in my thrust stand?
the problem I see either way, the heli prop or the MR prop. The inboard can produce a lot of thrust, but it will also be the first part to stall, with horrid separated flow.
if the intereior 30% of the blade, has a undercamber, but no variable pitch. The last 70% of the blade could be variable pitch if we are willing to go down that road. i dont like so many moving parts though, and variable pitch really and them on.
the advantage of variable pitch is that the head speed is held constant, and the variable pitch can take place quickly, therefore aiding the PIDs in stability. Where as in the current most popular process, the whole prop disc and motor most change inertial state, which takes time and hinders the PID stability.
Patrick, Mon Jul 14 2014, 09:30PM
what about a prop hub that allows changing pitch with a set screw ? for multiple iterations in my thrust stand?
the problem I see either way, the heli prop or the MR prop. The inboard can produce a lot of thrust, but it will also be the first part to stall, with horrid separated flow.
if the intereior 30% of the blade, has a undercamber, but no variable pitch. The last 70% of the blade could be variable pitch if we are willing to go down that road. i dont like so many moving parts though, and variable pitch really and them on.
the advantage of variable pitch is that the head speed is held constant, and the variable pitch can take place quickly, therefore aiding the PIDs in stability. Where as in the current most popular process, the whole prop disc and motor most change inertial state, which takes time and hinders the PID stability.
Re: Novel flying machines
Ash Small, Tue Jul 15 2014, 12:07AM
Personaly I think we need to calculate diameter, RPM, pitch and slip, then design the prop accordingly.
We can calculate these once we have an idea of the disc loading we require.
The info from the props on order will be useful, however these props won't be optimized, so we won't need as big a prop as the data from these props will suggest.
I'd also suggest having less pitch than the calculations suggest at the root, due to the stall and drag that you refer to.
I assume, from looking at examples, that conventional 'swashplate' copters have 'straight' blades, with no twist, so that they can be accelerated up to speed before increasing pitch for lift. I think we can improve on conventional copter efficiency (assuming we don't use swashplates, and have 'fixed pitch') by adding some carefully calculated 'twist'.
Assuming we need to manufacture some blades, though, it may be simpler to use straight blades to start with, for prototypes, until we get close to where we want to be.
It may be worth considering using a hub with adjustable blades to get some initial data, but these needn't be conventional 'variable pitch' blades.
Ash Small, Tue Jul 15 2014, 12:07AM
Personaly I think we need to calculate diameter, RPM, pitch and slip, then design the prop accordingly.
We can calculate these once we have an idea of the disc loading we require.
The info from the props on order will be useful, however these props won't be optimized, so we won't need as big a prop as the data from these props will suggest.
I'd also suggest having less pitch than the calculations suggest at the root, due to the stall and drag that you refer to.
I assume, from looking at examples, that conventional 'swashplate' copters have 'straight' blades, with no twist, so that they can be accelerated up to speed before increasing pitch for lift. I think we can improve on conventional copter efficiency (assuming we don't use swashplates, and have 'fixed pitch') by adding some carefully calculated 'twist'.
Assuming we need to manufacture some blades, though, it may be simpler to use straight blades to start with, for prototypes, until we get close to where we want to be.
It may be worth considering using a hub with adjustable blades to get some initial data, but these needn't be conventional 'variable pitch' blades.
Re: Novel flying machines
Patrick, Tue Jul 15 2014, 01:05AM
ok so for a first start, lets agree to a modded heli blade. With a twist, long length, short chord.
Ash, do you have access to and knowledge of the CAD, and its ways?
what diamerter should we start with, ill need to start thinking about fabrication.
EDIT: on multirotor props they do taper the tip greatly, i wonder if that increases disc loading.
link:
im thinking of a 0010 or 0012 airfoil.
Patrick, Tue Jul 15 2014, 01:05AM
ok so for a first start, lets agree to a modded heli blade. With a twist, long length, short chord.
Ash, do you have access to and knowledge of the CAD, and its ways?
what diamerter should we start with, ill need to start thinking about fabrication.
EDIT: on multirotor props they do taper the tip greatly, i wonder if that increases disc loading.
link:
im thinking of a 0010 or 0012 airfoil.
Re: Novel flying machines
Ash Small, Tue Jul 15 2014, 09:36AM
I think we should be aiming for a more conventional helicopter blade. These are designed for a lower disc loading than the props you are currently using, which are much closer to airplane props, which are designed for high disc loading.
Helicopter props are designed for low disc loading and low drag, which, unsurprisingly, is exactly what we want.
I'd go for the thinnest section that has sufficient strength. Something like a NACA 0010 sounds like it's 'in the ballpark'. I did link to some typical heli blade cross sections above somewhere.
Are you using a foam core and carbon for the ducts that you are currently using?
A thinner section with thinner width will have lower drag, so you can spin it faster. slower props with greater pitch may run into stall problems, I think.
EDIT: Just remembered that carbon only has tensile strength, no compressive strength. The lower surface of the blade will be in tension, the upper surface will be in compression. A bit of thought will be required here.
EDIT EDIT: Actually, I've just been googling, and apparently it is strong in both tension and compression, but weak in 'bending'. I need to read a bit more. I am aware that it does have limitations, though.
EDIT EDIT EDIT: There seems to be a lot of contradictory opinion on google.
"Carbon fiber is very strong when stretched or bent, but weak when compressed or exposed to high shock (e.g. a carbon fiber bar is extremely difficult to bend, but will crack easily if hit with a hammer)." Apparently from Wikipedia
There does seem to be some concensus that it is twice as strong in tension than in compression, though, which is pretty much what I thought in the first place.
Ash Small, Tue Jul 15 2014, 09:36AM
I think we should be aiming for a more conventional helicopter blade. These are designed for a lower disc loading than the props you are currently using, which are much closer to airplane props, which are designed for high disc loading.
Helicopter props are designed for low disc loading and low drag, which, unsurprisingly, is exactly what we want.
I'd go for the thinnest section that has sufficient strength. Something like a NACA 0010 sounds like it's 'in the ballpark'. I did link to some typical heli blade cross sections above somewhere.
Are you using a foam core and carbon for the ducts that you are currently using?
A thinner section with thinner width will have lower drag, so you can spin it faster. slower props with greater pitch may run into stall problems, I think.
EDIT: Just remembered that carbon only has tensile strength, no compressive strength. The lower surface of the blade will be in tension, the upper surface will be in compression. A bit of thought will be required here.
EDIT EDIT: Actually, I've just been googling, and apparently it is strong in both tension and compression, but weak in 'bending'. I need to read a bit more. I am aware that it does have limitations, though.
EDIT EDIT EDIT: There seems to be a lot of contradictory opinion on google.
"Carbon fiber is very strong when stretched or bent, but weak when compressed or exposed to high shock (e.g. a carbon fiber bar is extremely difficult to bend, but will crack easily if hit with a hammer)." Apparently from Wikipedia
There does seem to be some concensus that it is twice as strong in tension than in compression, though, which is pretty much what I thought in the first place.
Re: Novel flying machines
BigBad, Tue Jul 15 2014, 06:29PM
Actually for a heli blade i would have thought that along most of its length it's more or less only in tension, due to the centripetal forces.
BigBad, Tue Jul 15 2014, 06:29PM
Actually for a heli blade i would have thought that along most of its length it's more or less only in tension, due to the centripetal forces.
Re: Novel flying machines
Dr. Slack, Tue Jul 15 2014, 06:35PM
for making measurements, why not just buy a heli blade?
The root hinges on a heli blade seem to suggest that it's not designed to need to take any bending moment at all, but operates in centripetal tension
Dr. Slack, Tue Jul 15 2014, 06:35PM
for making measurements, why not just buy a heli blade?
The root hinges on a heli blade seem to suggest that it's not designed to need to take any bending moment at all, but operates in centripetal tension
Re: Novel flying machines
Patrick, Tue Jul 15 2014, 08:53PM
yes compression and striking are poor conditions for CF to survive. (a problem for the US F-22 when a 20mm russian API explosive round comes in versus titanium for example.)
to mitigate this, and improve safety, i could use balsa or PU foam core, then 5.7 osy CF, with 4 oz S2 FG. torsional straength still worries me though. (fiber glass, especially S2, is very survivable, even though its the bastard child of CF, which is high tech and glamorous.)
i was thinking of a slightly wider chord and steeper pitch in the root, then a flat-bottom narrow chord, low pitch at teh tip end.
EDIT: i just wish there was a simple freeware program or app that would given and aproximation for NACA profiles.
heres the ugly math, but its looks well expalianed :
Patrick, Tue Jul 15 2014, 08:53PM
yes compression and striking are poor conditions for CF to survive. (a problem for the US F-22 when a 20mm russian API explosive round comes in versus titanium for example.)
to mitigate this, and improve safety, i could use balsa or PU foam core, then 5.7 osy CF, with 4 oz S2 FG. torsional straength still worries me though. (fiber glass, especially S2, is very survivable, even though its the bastard child of CF, which is high tech and glamorous.)
i was thinking of a slightly wider chord and steeper pitch in the root, then a flat-bottom narrow chord, low pitch at teh tip end.
EDIT: i just wish there was a simple freeware program or app that would given and aproximation for NACA profiles.
heres the ugly math, but its looks well expalianed :
Re: Novel flying machines
Ash Small, Wed Jul 16 2014, 02:13PM
Well, yes, there are obviously centripetal forces
I was just pointing out the (possibly) less obvious forces. For every action there is an equal and opposite reaction (Newton's third law), so there is an upward force acting on the blade that is equal to the downward force acting on the accelerated air. which is equal to the mass of the craft while hovering, and is greater when ascending. This force is obviously divided by the number of blades.
This results in a 'bending moment'(?) acting on the prop that puts the underside in tension and the topside in compression, which needs to be taken into consideration when designing the prop. I assume Patrick is somewhat familiar with the directional properties of carbon, and how to best lay up carbon to achieve the required directional strength. (for example, carbon masts on yachts tend to use unidirectional carbon and utilise a 'vertical' cylinder, with unidirectional carbon running in alternating spirals around this, to deal with the bending and compressive forces acting on the mast. Various other 'weaves' are available, including diagonal and crowsfoot, to name two, depending on the various forces to which the part is subjected. As Patrick points out, a 'composite' including 'S' glass, and maybe even kevlar may be appropiate in some cases. The centripetal forces can be dealt with using longitudinal unidirectional carbon, but the other forces, bending vertically due to 'lift' and bending 'backwards' due to drag 'may' require a bit more thought.
Sounds reasonable, but I wouldn't use as much pitch near the root as the maths suggests is required, for the previously mentioned reasons of stall and drag. A wider chord at the root would add strength here, where it is most needed, but there isn't a lot of lift generated at the root anyway.
EDIT: Balsa way well prove easier to work with than foam core in this application
Ash Small, Wed Jul 16 2014, 02:13PM
Well, yes, there are obviously centripetal forces
I was just pointing out the (possibly) less obvious forces. For every action there is an equal and opposite reaction (Newton's third law), so there is an upward force acting on the blade that is equal to the downward force acting on the accelerated air. which is equal to the mass of the craft while hovering, and is greater when ascending. This force is obviously divided by the number of blades.
This results in a 'bending moment'(?) acting on the prop that puts the underside in tension and the topside in compression, which needs to be taken into consideration when designing the prop. I assume Patrick is somewhat familiar with the directional properties of carbon, and how to best lay up carbon to achieve the required directional strength. (for example, carbon masts on yachts tend to use unidirectional carbon and utilise a 'vertical' cylinder, with unidirectional carbon running in alternating spirals around this, to deal with the bending and compressive forces acting on the mast. Various other 'weaves' are available, including diagonal and crowsfoot, to name two, depending on the various forces to which the part is subjected. As Patrick points out, a 'composite' including 'S' glass, and maybe even kevlar may be appropiate in some cases. The centripetal forces can be dealt with using longitudinal unidirectional carbon, but the other forces, bending vertically due to 'lift' and bending 'backwards' due to drag 'may' require a bit more thought.
Patrick wrote ...
i was thinking of a slightly wider chord and steeper pitch in the root, then a flat-bottom narrow chord, low pitch at teh tip end.
i was thinking of a slightly wider chord and steeper pitch in the root, then a flat-bottom narrow chord, low pitch at teh tip end.
Sounds reasonable, but I wouldn't use as much pitch near the root as the maths suggests is required, for the previously mentioned reasons of stall and drag. A wider chord at the root would add strength here, where it is most needed, but there isn't a lot of lift generated at the root anyway.
EDIT: Balsa way well prove easier to work with than foam core in this application
Re: Novel flying machines
Patrick, Wed Jul 16 2014, 06:29PM
im thinking of a planform, but i dont know if the flight forces will twist from my low drag - low pitch tip to being higher pitch in rotation. I dont think any of us have a strobe light and high speed camera ?
Patrick, Wed Jul 16 2014, 06:29PM
im thinking of a planform, but i dont know if the flight forces will twist from my low drag - low pitch tip to being higher pitch in rotation. I dont think any of us have a strobe light and high speed camera ?
Re: Novel flying machines
Ash Small, Wed Jul 16 2014, 08:19PM
If we can calculate the forces involved, surely we can apply this force to the blade and see how much it twists, or even calculate how much it will twist?
This stuff is pretty basic mechanics (forces on a beam, etc. The first subject covered in most mechanics syllabi)
EDIT: We should factor in a safety margin of three, anyway.
Ash Small, Wed Jul 16 2014, 08:19PM
Patrick wrote ...
im thinking of a planform, but i dont know if the flight forces will twist from my low drag - low pitch tip to being higher pitch in rotation. I dont think any of us have a strobe light and high speed camera ?
im thinking of a planform, but i dont know if the flight forces will twist from my low drag - low pitch tip to being higher pitch in rotation. I dont think any of us have a strobe light and high speed camera ?
If we can calculate the forces involved, surely we can apply this force to the blade and see how much it twists, or even calculate how much it will twist?
This stuff is pretty basic mechanics (forces on a beam, etc. The first subject covered in most mechanics syllabi)
EDIT: We should factor in a safety margin of three, anyway.
Re: Novel flying machines
Patrick, Wed Jul 16 2014, 09:57PM
as long as you can help me through it, my integral and differential calculus is always questionalble, and in this link : if we have all the pieces we can start on some functions to apply over surfaces and lengths.
i need force diagrams, of the airfoil section, which show the forces, as i vary the length from tip to root.
Patrick, Wed Jul 16 2014, 09:57PM
as long as you can help me through it, my integral and differential calculus is always questionalble, and in this link :
if we have all the pieces we can start on some functions to apply over surfaces and lengths.i need force diagrams, of the airfoil section, which show the forces, as i vary the length from tip to root.
Re: Novel flying machines
Ash Small, Thu Jul 17 2014, 01:09PM
I'm still reading through your link, but if you look at the sections of heli blade I posted on the previous page, they are symmetrical, without the airofoil shape and rely on the pitch of the prop to accelerate the column of air downwards, much the same as ailerons on the trailing edge of a wing.
It is this pitch angle that varies from root to tip on a prop, to give the air the same velocity from root to tip even though the velocity of the prop varies from root to tip.
You are probably aware of this, but it's not clear from your comments.
While an aerofoil section may have advantages, the thickness of the section (naca profile) would need to taper from root to tip in order to maintain the same lift from root to tip, which I don't think would be practical as it would adversely affect drag.
The props you have are concave on the lower surface and convex on the upper surface so they do resemble a naca profile more than a conventional heli pfofile.
I think we need to consider which shape has the least drag, as we need to reduce drag as much as possible in order to optimise the advantages of low disc loading.
I'd assume that the conventional helicopter blade probably has the greatest strength and least drag, compared to the 'conventional' prop design that is optimised for much higher disc loading.
I think we should be aiming to copy a conventional helicopter blade section rather than going for a naca profile as it will increase strength and therefore reduce drag, by enabling the use of a thinner section, I think.
We do need to minimize drag in order to maximize the advantages of low disc loading.
I'll continue reading the link later.
Ash Small, Thu Jul 17 2014, 01:09PM
I'm still reading through your link, but if you look at the sections of heli blade I posted on the previous page, they are symmetrical, without the airofoil shape and rely on the pitch of the prop to accelerate the column of air downwards, much the same as ailerons on the trailing edge of a wing.
It is this pitch angle that varies from root to tip on a prop, to give the air the same velocity from root to tip even though the velocity of the prop varies from root to tip.
You are probably aware of this, but it's not clear from your comments.
While an aerofoil section may have advantages, the thickness of the section (naca profile) would need to taper from root to tip in order to maintain the same lift from root to tip, which I don't think would be practical as it would adversely affect drag.
The props you have are concave on the lower surface and convex on the upper surface so they do resemble a naca profile more than a conventional heli pfofile.
I think we need to consider which shape has the least drag, as we need to reduce drag as much as possible in order to optimise the advantages of low disc loading.
I'd assume that the conventional helicopter blade probably has the greatest strength and least drag, compared to the 'conventional' prop design that is optimised for much higher disc loading.
I think we should be aiming to copy a conventional helicopter blade section rather than going for a naca profile as it will increase strength and therefore reduce drag, by enabling the use of a thinner section, I think.
We do need to minimize drag in order to maximize the advantages of low disc loading.
I'll continue reading the link later.
Re: Novel flying machines
Ash Small, Fri Jul 18 2014, 05:14PM
Looks like you do want a naca profile (or something similar) after all, apparently symmetrical blades were only used due to the difficulty of making assymetrical blades strong enough
"The types of aerofoils used with a rotorblade differ (figure below). For a long time, most of them were symmetrical. However, a higher L/D ratio is possible with non-symmetrical versions. Due to the greater internal forces occurring in these types of blades, they only came into existence when the appropriate composite materials were developed. These can cope with the high internal strain, while their weight is kept low.
"
I'm still reading this, but it looks like it's got a lot of good theory in it.
EDIT: There is a rather humorous typo in it, namely when it refers to the 'sound of speed'
EDIT: The comment at the bottom looks interesting too:
"As an alternative approach, engineers may wish to consider trying the VABS software for modeling very complex composite rotor blades. Developed at Georgia Tech and Utah State University, VABS is capable of quickly and rigorously decoupling an original 3D slender solid with complex microstructure (sophisticated cross-section with or without spanwise heterogeneity) into a simple engineering beam model. VABS (Variational Asymptotical Beam Sectional Analysis), is a unique tool capable of realistic modeling of initially curved and twisted anisotropic beams with arbitrary sectional topology and materials. Evaluation licenses of VABS are available through AnalySwift."
Maybe you can obtain an evaluation license through your college, Patrick?
EDIT: This is just one page of a series that starts here: and seems to cover pretty much the whole 'helicopter design' thing, albeit fairly concisely.
EDIT: I forgot to answer this question above:
I do have a twenty year old version of TurboCad Pro V3, which I bought when I was running my own company, and I also picked up a copy of TurboCad V16 Deluxe, which is not a pro version, but does have some features that V3 doesn't have, although it doesn't have all the 'Pro' features.
I can do most things with them, and they are compatible with AutoCad .dwg and .dxf files. I believe the V16 deluxe version also produces Adobe .pdf files, etc.
Ash Small, Fri Jul 18 2014, 05:14PM
Looks like you do want a naca profile (or something similar) after all, apparently symmetrical blades were only used due to the difficulty of making assymetrical blades strong enough
"The types of aerofoils used with a rotorblade differ (figure below). For a long time, most of them were symmetrical. However, a higher L/D ratio is possible with non-symmetrical versions. Due to the greater internal forces occurring in these types of blades, they only came into existence when the appropriate composite materials were developed. These can cope with the high internal strain, while their weight is kept low.
"
I'm still reading this, but it looks like it's got a lot of good theory in it.
EDIT: There is a rather humorous typo in it, namely when it refers to the 'sound of speed'
EDIT: The comment at the bottom looks interesting too:
"As an alternative approach, engineers may wish to consider trying the VABS software for modeling very complex composite rotor blades. Developed at Georgia Tech and Utah State University, VABS is capable of quickly and rigorously decoupling an original 3D slender solid with complex microstructure (sophisticated cross-section with or without spanwise heterogeneity) into a simple engineering beam model. VABS (Variational Asymptotical Beam Sectional Analysis), is a unique tool capable of realistic modeling of initially curved and twisted anisotropic beams with arbitrary sectional topology and materials. Evaluation licenses of VABS are available through AnalySwift."
Maybe you can obtain an evaluation license through your college, Patrick?
EDIT: This is just one page of a series that starts here:
and seems to cover pretty much the whole 'helicopter design' thing, albeit fairly concisely.EDIT: I forgot to answer this question above:
Patrick wrote ...
Ash, do you have access to and knowledge of the CAD, and its ways?
Ash, do you have access to and knowledge of the CAD, and its ways?
I do have a twenty year old version of TurboCad Pro V3, which I bought when I was running my own company, and I also picked up a copy of TurboCad V16 Deluxe, which is not a pro version, but does have some features that V3 doesn't have, although it doesn't have all the 'Pro' features.
I can do most things with them, and they are compatible with AutoCad .dwg and .dxf files. I believe the V16 deluxe version also produces Adobe .pdf files, etc.
Re: Novel flying machines
Patrick, Fri Jul 18 2014, 09:12PM
ill go you one better, i have it in with Georgia tech, ive even been at the IARC Mission 6 compettion with them for 3 years in a row (Grand Forks, North Dakota) let me contact my Professor Robert Michelson at Georgia Tech. He might vouch for me since we've met and talk often.
EDIT: im trying through their website too.
Patrick, Fri Jul 18 2014, 09:12PM
ill go you one better, i have it in with Georgia tech, ive even been at the IARC Mission 6 compettion with them for 3 years in a row (Grand Forks, North Dakota) let me contact my Professor Robert Michelson at Georgia Tech. He might vouch for me since we've met and talk often.
EDIT: im trying through their website too.
Re: Novel flying machines
Patrick, Mon Jul 21 2014, 07:58PM
i got all the props, about 10 mnutes ago. Ill run the loading tests in a few hours.
Patrick, Mon Jul 21 2014, 07:58PM
i got all the props, about 10 mnutes ago. Ill run the loading tests in a few hours.
Re: Novel flying machines
Patrick, Sun Jul 27 2014, 08:19AM
Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?
Patrick, Sun Jul 27 2014, 08:19AM
Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?
Re: Novel flying machines
Ash Small, Mon Jul 28 2014, 10:25AM
That makes sense.
Any news on the VABS software yet?
Any more thoughts regarding producing some low pitch, low drag, low disc loading blades?
(I think we all agree that this is the way forward)
Ash Small, Mon Jul 28 2014, 10:25AM
Patrick wrote ...
Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?
Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?
That makes sense.
Any news on the VABS software yet?
Any more thoughts regarding producing some low pitch, low drag, low disc loading blades?
(I think we all agree that this is the way forward)
Re: Novel flying machines
Patrick, Mon Jul 28 2014, 08:01PM
yep, it looks like heli blades are the solution, endless tinkering with heavy disc loaded props wont lead any where useful.
Patrick, Mon Jul 28 2014, 08:01PM
yep, it looks like heli blades are the solution, endless tinkering with heavy disc loaded props wont lead any where useful.
Re: Novel flying machines
BigBad, Mon Jul 28 2014, 11:48PM
Makes sense.
That's why heli blades are built like that; for maximum hang-time.
BigBad, Mon Jul 28 2014, 11:48PM
Makes sense.
That's why heli blades are built like that; for maximum hang-time.
Re: Novel flying machines
Patrick, Tue Jul 29 2014, 01:23AM
ive put in a request for a academic demo, i didnt see where to download a trial copy though.
Patrick, Tue Jul 29 2014, 01:23AM
BigBad wrote ...
Makes sense.
That's why heli blades are built like that; for maximum hang-time.
but im not sure they should be symetric, they may need to be more chord width at the root too.Makes sense.
That's why heli blades are built like that; for maximum hang-time.
ive put in a request for a academic demo, i didnt see where to download a trial copy though.
Re: Novel flying machines
Ash Small, Tue Jul 29 2014, 04:57PM
I agree that assymetric blade design should be well within your capability, Patrick.
Lift/drag ratio, as I believe Udo pointed out earlier in the thread, will be the dominant factor once disc loading has been finalized.
Increasing chord at the root, in my opinion, should only be done if extra strength at the root is required, as there is less lift here anyway. (Tapering the blade towards the tip 'should' improve lift/drag ratio if done correctly, I think).
It all depends how complicated you wish to make it. A 'D' shaped blade of constant section would be easiest to produce, and may be useful for some initial disc loading modelling (make some long blades, then cut them shorter in order to plot a graph, maybe?)
Maybe others have some suggestions here as well?
Ash Small, Tue Jul 29 2014, 04:57PM
I agree that assymetric blade design should be well within your capability, Patrick.
Lift/drag ratio, as I believe Udo pointed out earlier in the thread, will be the dominant factor once disc loading has been finalized.
Increasing chord at the root, in my opinion, should only be done if extra strength at the root is required, as there is less lift here anyway. (Tapering the blade towards the tip 'should' improve lift/drag ratio if done correctly, I think).
It all depends how complicated you wish to make it. A 'D' shaped blade of constant section would be easiest to produce, and may be useful for some initial disc loading modelling (make some long blades, then cut them shorter in order to plot a graph, maybe?)
Maybe others have some suggestions here as well?
Re: Novel flying machines
Patrick, Wed Jul 30 2014, 12:54AM
ok lets try a conventional constant chord and large diameter, with a D crossection.
Patrick, Wed Jul 30 2014, 12:54AM
ok lets try a conventional constant chord and large diameter, with a D crossection.
Re: Novel flying machines
Patrick, Thu Jul 31 2014, 12:23AM
ive gotten a reply from the VABS maker, but it only runs on 64 bit systems. i guess ill have to send it to one of you or find a 64 bit machine.
Patrick, Thu Jul 31 2014, 12:23AM
ive gotten a reply from the VABS maker, but it only runs on 64 bit systems. i guess ill have to send it to one of you or find a 64 bit machine.
Re: Novel flying machines
Ash Small, Thu Jul 31 2014, 10:47AM
"To run a 64-bit version of Windows, your computer must have a 64-bit-capable processor. To find out if your processor is 64-bit-capable, do the following:
1.
Open Performance Information and Tools by clicking the Start button , clicking Control Panel, clicking System and Maintenance, and then clicking Performance Information and Tools.
2.
Click View and print details.
3.
In the System section, you can see what type of operating system you're currently running under System type. Under 64-bit capable, you can see whether you can run a 64-bit version of Windows. (If your computer is already running a 64-bit version of Windows, you won't see the 64-bit capable listing.) "
Ash Small, Thu Jul 31 2014, 10:47AM
"To run a 64-bit version of Windows, your computer must have a 64-bit-capable processor. To find out if your processor is 64-bit-capable, do the following:
1.
Open Performance Information and Tools by clicking the Start button , clicking Control Panel, clicking System and Maintenance, and then clicking Performance Information and Tools.
2.
Click View and print details.
3.
In the System section, you can see what type of operating system you're currently running under System type. Under 64-bit capable, you can see whether you can run a 64-bit version of Windows. (If your computer is already running a 64-bit version of Windows, you won't see the 64-bit capable listing.) "
Re: Novel flying machines
Patrick, Sat Aug 02 2014, 08:39PM
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
Patrick, Sat Aug 02 2014, 08:39PM
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
Re: Novel flying machines
Ash Small, Sat Aug 02 2014, 08:51PM
It's summer break, I assume?
Ash Small, Sat Aug 02 2014, 08:51PM
Patrick wrote ...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
It's summer break, I assume?
Re: Novel flying machines
Patrick, Sat Aug 02 2014, 09:28PM
Patrick, Sat Aug 02 2014, 09:28PM
Ash Small wrote ...
It's summer break, I assume?
yep, but i can still get into rooms, without committing crimes. ill be flying my current drone too just for peeps to see.Patrick wrote ...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
It's summer break, I assume?
Re: Novel flying machines
Ash Small, Sat Aug 02 2014, 10:31PM
Well, I imsgine you'd only need a mainboard and processor, and maybe some extra ram, but if you can get access to a 64 bit machine on campus, without getting arrested.........
Ash Small, Sat Aug 02 2014, 10:31PM
Patrick wrote ...
Ash Small wrote ...
It's summer break, I assume?
yep, but i can still get into rooms, without committing crimes. ill be flying my current drone too just for peeps to see.Patrick wrote ...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
i dont have any 64 bit systems at home, thats why i wanted to send the prog to others or find one on campus...
It's summer break, I assume?
Well, I imsgine you'd only need a mainboard and processor, and maybe some extra ram, but if you can get access to a 64 bit machine on campus, without getting arrested.........
Re: Novel flying machines
Patrick, Sun Aug 03 2014, 10:48PM
yep, i may recieve a 64 bit computer soon, or ill go on campus this week, there's always staff theyre who'll let me in.
im thinking of the profile though. and how its typically formed with materials. Its sort of an "I" beam near the bulge. Aerodynamic flutter worries me most.
Patrick, Sun Aug 03 2014, 10:48PM
yep, i may recieve a 64 bit computer soon, or ill go on campus this week, there's always staff theyre who'll let me in.
im thinking of the profile though. and how its typically formed with materials. Its sort of an "I" beam near the bulge. Aerodynamic flutter worries me most.
Re: Novel flying machines
Patrick, Sat Sept 13 2014, 01:33AM
Ive got a tail rotor section on the way. 21 US$, did a lot of research, 450 and 500 were too small, 600 size seems right 700 seemed excessively heavy duty, like a M1A1 battle tank.
its belt driven and ill be setting up a 3D printed gear on a electric motor to test it all.
link:
for the tail, im thinking of using tilting vanes like the V2 rocket, instead of tilting the whole prop disc.
Patrick, Sat Sept 13 2014, 01:33AM
Ive got a tail rotor section on the way. 21 US$, did a lot of research, 450 and 500 were too small, 600 size seems right 700 seemed excessively heavy duty, like a M1A1 battle tank.
its belt driven and ill be setting up a 3D printed gear on a electric motor to test it all.
link:
for the tail, im thinking of using tilting vanes like the V2 rocket, instead of tilting the whole prop disc.
Re: Novel flying machines
Ash Small, Sun Sept 14 2014, 01:39PM
Solid carbon sounds like a good starting point, if going for low disc loading and thin blade section.
Alternatively, two 'skins' and a re-inforcing beam epoxied between might be suitable.
Have you got the software tunning yet?
Ash Small, Sun Sept 14 2014, 01:39PM
Solid carbon sounds like a good starting point, if going for low disc loading and thin blade section.
Alternatively, two 'skins' and a re-inforcing beam epoxied between might be suitable.
Have you got the software tunning yet?
Print this page