NASA Puffin Low Noise, Electric VTOL Personal Air Vehicle

Conceptual design focusing on the ability of a redundant electric propulsion system to provide new capabilities for Vertical Takeoff and Landing aircraft. Specifically utilizing electric motor variable rpm to accomplish a low tipspeed prop-rotor (400 ft/sec tip speed at hover and 200 ft/sec at cruise) to accomplish an order of magnitude reduction in community noise for close proximity operations (30-40 db reduction). The variable rpm capability also achieves a 25% improvement in prop-rotor efficiency through operation at optimal advance ratios.

• Category

  Science & Technology

[manofsan]

I've seen a number of small turbofan projects on Youtube. If you do a search for "RC turbofan" you'll find various videos.

Have you considered that a pair of small gas-powered turboprops or turbofans could work well for the Puffin concept? At least they'd have a higher power-to-weight ratio than electric motors with batteries.

[NASAPAV]

No you really don't want to attempt to apply JetCat or other small turbines - it would be a terrible match up. The fuel consumption on these small turbines is terrible, the reliability is terrible, the required gear reduction would be huge and the gear box weight would be large. The better idea, which we are looking at is the use of a small turbine to directly spin an alternator at very high rpm (so the alternator is very light), and for that electricity to then directly power the prop motor

[NASAPAV]

By doing this, the battery weight could be made very small as only a backup short duration source. Essentially the turbine/alternator becomse a very light 'battery', even when you account for the fuel weight. We are specifically looking at applying a new turbine/alternator developed for DARPA that can burn heavy fuel (bio-fuel) and use a recuperator to increase the efficiency. But small turbines have a long way to go - I'm anxious to apply them if we get them working, but in the right way

[manofsan]

I see - but isn't that 2 conversion steps instead of one? Fuel --> Electricity --> Mechanical

What about small Wankel rotary engines? Those tend to have pretty decent power-to-weight ratios.

[NASAPAV]

Yes, and going to electric has at least 5% penalties in each direction with even the best advanced electric motors. But that is still better than attempting to have these small turbines directly turn a low rpm shaft. You realize the differential in rpm is at least 40x?  What do you do to throttle - these little turbines can't perform well off the one design point. By connecting to a high speed alternator you can optimize for running at a single speed efficiently and reliably.

[NASAPAV]

Now for rotaries - ugh. Have you run one? I have for UAV projects - small rotaries are almost as much of a pain in the ass as small turbines. They drink fuel, make a crap load of noise, have a glowing red hot exhaust, and have seal maintenance problems. They spin at crazy high rpm 10 to 15K that require a gearbox. Yes,the gearbox is easier on a rotary because the gears are only being beaten up by the prop instead of both the prop and recip engine with intermittent loads.

[NASAPAV]

Really? Do you know what the Lift/Drag ratio is for a helicopter? Between 4 and 5 - incredibly inefficient devices. Do you know what the L/D of this aircraft is? At 100 mph it's 17.5, at 150 mph it's 14.5. So about 4x the aerodynamic efficiency. Do you know how complex a helicopter rotor is and why heli's are so expensive? The hub mechanism on this is incredibly simple and low cost. Sorry, not quite...

[LWJCarroll]

I suspect thatg during flight face down, holding your head up will cause a fatigue problem (sore neck) , hence a recumbent position for the pilot would be better.??...Laurie

[DeathofaGasGuzzler]

I want one of these! ;)

[vladimirpanovru]

Шея будет болеть!

[projectdelta50]

Now how the fuck do you get out of it

[bruzote]

The pilot had better hope the A/C and defogger systems don't malfunction. That flying bed with a sunroof would overheat people rather quickly on a sunny day.

[7013032]

I can imagine count Dracula flying this thing :D

[Illus Wing]

flying coffin

[galipblj06]

Deffinately a bad idea for civilian use. The crashes would be baaad

[Stefano La Commare]

That there is one hell of a claustrophobic, uncomfortable ride...

[Edjean Dorvil]

Dear Santa,