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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
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.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
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.
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.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
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.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
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.
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.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
@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.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
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.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
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.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
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)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
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.
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.
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Novel flying machines
but in theory a Wankel engine like arrangement if mechanically stable could work even though the combustion chambers are not directly linked.