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4hv.org :: Forums :: General Science and Electronics
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Novel flying machines

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Dr. Slack
Fri May 02 2014, 08:10AM Print
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I'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,
1398931969 72 FT149110 Planeplan
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


1352673085 72 FT0 Quad Wing


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.


1399022774 72 FT149110 Whacker 3


In the second idea, only two fans are used for control, with vectored thrust.


1399022756 72 FT149110 Whacker 2


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
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Ash Small
Fri May 02 2014, 09:27AM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
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).
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BigBad
Fri May 02 2014, 03:43PM
BigBad Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
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.
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Patrick
Fri May 02 2014, 05:15PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
yep fusion reactor, thats what i need, should have sobered up and thought of this first.
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Dr. Slack
Fri May 02 2014, 07:55PM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
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.

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?
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BigBad
Fri May 02 2014, 09:17PM
BigBad Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
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.
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Ash Small
Fri May 02 2014, 09:23PM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
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?

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.....
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Patrick
Fri May 02 2014, 10:05PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
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 Link2 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)

1399076181 2431 FT1630 A

1399076181 2431 FT1630 B


1399078777 2431 FT1630 C

1399078777 2431 FT1630 D

1399078777 2431 FT1630 F


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.
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Ash Small
Sat May 03 2014, 12:38PM
Ash Small Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Dr. Slack wrote ...

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.

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.
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Patrick
Sat May 03 2014, 05:01PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
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 : Link2
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