X Prize Clean Aviation: $10 million

[mheslep]

Their main problem; however, is that the FAA requires at least 30 mins reserve fuel. The Puffin flies for 5 minutes - total. This is really a fundamental problem.

5 minutes is the longest prototype test flight so far. The final design spec is ~20 mins, or http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane" (c. Reserve Fuel), and may apply only in air traffic control situations, i.e. in and out of FAA controlled airports.

 

[Cyrus]

5 minutes is the longest prototype test flight so far. The final design spec is ~20 mins, or http://www.scientificamerican.com/article.cfm?id=nasa-one-man-stealth-plane" (c. Reserve Fuel), and may apply only in air traffic control situations, i.e. in and out of FAA controlled airports.

To my knowledge, there have been no test flights of this prototype. The fuel issue still stands. I am looking outside my window right now, and it is IFR weather. If this is a 'flying car' in the most general sense, it is fundamentally not going to work because it is not robust to the environment.

When I get home, I will look through my FAR/AIM and give you the exact rules on fuel reserves required by law, and how it applies (I never really fly far enough to know this off the top of my head).

 

[mheslep]

To my knowledge, there have been no test flights of this prototype.

So then where did you get 5 minutes?

The Puffin, named because it resembles the bird, has not yet flown publicly, but Moore said its longest flight lasted five minutes.

The fuel issue still stands. I am looking outside my window right now, and it is IFR weather. If this is a 'flying car' in the most general sense, it is fundamentally not going to work because it is not robust to the environment.

<shrug>

"We're not trying to replace the car or the airplane," Moore said. "Cars are great at what they do, which is go a couple of miles at relatively slow speeds. Commercial air carriers are great at going long distances at faster speeds. But what happens when we want to go 100 or 200 or 300 miles? We have to take this very long drive

http://news.discovery.com/tech/nasa-aircraft-puffin-transportation.html

When I get home, I will look through my FAR/AIM and give you the exact rules on fuel reserves required by law, and how it applies (I never really fly far enough to know this off the top of my head).

Look forward to it, though AFAICT the source I supplied above are the current FAA regs.

 

[Cyrus]

The 5 mins are based on lab tests they have done, to my knowledge. (Edit: after reading your link, it does appear they have actually flow it. I wonder, why no pictures of the actual vehicle).

<shrug> ... really? You're answer to a 'flying car' that has to work in IFR conditions (and hence have fuel reserves for 30 mins, longer than the vehicle can even fly is ...<shrug>? This is called a fundamental problem, not ...<shrug>!

Clarification: now the article says it's not a flying car..however, one has to ask. What do you use a 5 minute, 50 mile range vehicle for? Let's be real here, at best this is a flying car (but worse than a car in performance!).

Obviously, the car is meant for use of 100 -300 mile trips, and the article states that the only way to do this (currently) is by car. But, what's wrong with taking the train?

 

[mheslep]

Clarification: now the article says it's not a flying car..however, one has to ask. What do you use a 5 minute, 50 mile range vehicle for?

https://www.physicsforums.com/showpost.php?p=2682088&postcount=101"

 

[Cyrus]

https://www.physicsforums.com/showpost.php?p=2682088&postcount=101"

Okay, better, but still not enough!

Note: (I will, rather reluctantly, admit that the more I read about this I am warming up to it).

There is also the problem that you could go 20 minutes. But you would have to leave the wife, kids, dog, and luggage at home...though that may not necessarily be a bad thing!

 

[Altrepair]

Here is a simple solution for motor weight and is cheap compared to HTS motors. Use 400 Hertz 3-phase AC induction motors. Remember people that like a transformer, higher frequencies reduce size and weight. Four-hundred hertz motors have been used in the aviation industry for years for the hydraulics or anything else that needed actuation. With 400 hertz motors you also gain insanely high RPMs. A two pole, 400HZ motor turns at about 24,000 RPM.

So I would give AC propulsion a call and ask for their AC induction motor with variable frequency speed drive package. Or talk with the engineers at 400hertz.net if you want a custom horsepower motor other than 268 HP from AC propulsion.

 

[mheslep]

Here is a simple solution for motor weight and is cheap compared to HTS motors. Use 400 Hertz 3-phase AC induction motors. Remember people that like a transformer, higher frequencies reduce size and weight. Four-hundred hertz motors have been used in the aviation industry for years for the hydraulics or anything else that needed actuation. With 400 hertz motors you also gain insanely high RPMs. A two pole, 400HZ motor turns at about 24,000 RPM.

So I would give AC propulsion a call and ask for their AC induction motor with variable frequency speed drive package. Or talk with the engineers at 400hertz.net if you want a custom horsepower motor other than 268 HP from AC propulsion.

The main loss component in normal electric motors is resistive, ie. IR loss in the windings. Along with the advantages of increasing frequency comes the disadvantage of increased resistive losses due to the frequency dependent http://en.wikipedia.org/wiki/Skin_effect" . Skin depth is proportional to 1/sqrt(frequency), so increasing the frequency from 60Hz to 400Hz decreases the skin depth 62%.

Windage is another loss secondary to IR, but at some high enough RPM windage will become dominant.

BTW, AC propulsion's motor ( i.e. Tesla's motor) is indeed a three phase induction design, though I don't know about frequency. At ~4KW/kg, I am not aware of any non-HTS electric motor at this scale (<500KW) with a greater power density.

 

[Altrepair]

The main loss component in normal electric motors is resistive, ie. IR loss in the windings. Along with the advantages of increasing frequency comes the disadvantage of increased resistive losses due to the frequency dependent http://en.wikipedia.org/wiki/Skin_effect" . Skin depth is proportional to 1/sqrt(frequency), so increasing the frequency from 60Hz to 400Hz decreases the skin depth 62%.

Four hundred hertz 3-phase AC induction motors have been around since before a lot people where even born that are members of this forum. All the issues of going higher frequency have been solved a long time ago when the aviation industry needed a lightweight electric motor solution. That is why in the aviation industry 400 hertz is standard since the generators and motors are light weight.

Windage is another loss secondary to IR, but at some high enough RPM windage will become dominant.

Turbo fan Jet engine turbines spin at insanely high rpms and thus suffer from windage losses too. I would say it is far worse since it has so many blades inside.

BTW, AC propulsion's motor ( i.e. Tesla's motor) is indeed a three phase induction design, though I don't know about frequency. At ~4KW/kg, I am not aware of any non-HTS electric motor at this scale (<500KW) with a greater power density.

[/QUOTE]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM. A standard off the shelf 400 hertz, 200 HP induction motor only weighs around 80 pounds compared to the 60HZ version that is in the thousands.

 

[Phrak]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM. A standard off the shelf 400 hertz, 200 HP induction motor only weighs around 80 pounds compared to the 60HZ version that is in the thousands.

Now way. How does power scale with frequency?

 

[mheslep]

Four hundred hertz 3-phase AC induction motors have been around since before a lot people where even born that are members of this forum.

Before all of the forum members were born.

All the issues of going higher frequency have been solved a long time ago when the aviation industry needed a lightweight electric motor solution. That is why in the aviation industry 400 hertz is standard since the generators and motors are light weight.

I'd say the issues are now well understood, not 'solved.' Certainly 400 Hz motors are lighter weight than similarly rated 60Hz motors. I only pointed out one known disadvantage that comes along with the other advantages (as with everything else): generally speaking a 400Hz motor will be a little less efficient than a similar 60 Hz motor because of IR winding losses. Thus on the factory floor a 400Hz motor will produce a higher electric bill per unit output than the similar 60Hz motor. For the case of a battery powered aircraft so equipped, the platform would have to carry a little more battery for a given power-time profile, even if the 400Hz motor weighs less. It's a trade off <shrug>. In a normal aircraft carrying thousands of megajoules of jet fuel, that efficiency loss doesn't matter (for auxiliary motors) so the 400 Hz weight savings dominates in traditional aviation.

 

[mheslep]

It is a 400 hertz design with copper rotor bars instead of aluminum. It is 4-pole instead of two, so it will turn at about 12,000 RPM.

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

 

[Altrepair]

Before all of the forum members were born.

I know the low frequency design of AC induction motors have been around since the 1800's, but I did not think the 400 Hertz design has been.

 

[Phrak]

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

The article says it all. The transmission is at a fixed gear ratio, so varying the frequency stands in place of shifting gears. I'm pleasantly surprised to hear about using induction motors. I'd always considered them too massive and underpowered for transportation. However, I can't say I understand the reasoning to inducing a 4 pole magnet in the rotor rather than using a 4 pole permanent magnet.

 

[mheslep]

Tesla Motors eventually included a transmission (2 gears I think) in their Roadster - still a big improvement over the transmissions used with combustion engines.

 

[Altrepair]

The article says it all. The transmission is at a fixed gear ratio, so varying the frequency stands in place of shifting gears. I'm pleasantly surprised to hear about using induction motors. I'd always considered them too massive and underpowered for transportation.

Until today when you learned of high frequency designs.

However, I can't say I understand the reasoning to inducing a 4 pole magnet in the rotor rather than using a 4 pole permanent magnet.

There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator. If instead magnets were used, it would be a synchronous motor which have no starting torque. So it would sit there buzzing with a very angry 60 HZ hum until damage occurs or some safety device trips. The large industrial synchronous motors start up as asynchronous induction motors since they also have rotor bars embedded into the rotor, till about 75% speed, at which point the DC field circuit is energized which causes the rotor to lock up in sync with the rotating magnetic field of the stator. Before they made them this way, a "pony motor" which is synonymous with a starter motor used for ICE's was used to bring up the speed of the synchronous motor.

I've never heard/seen a 400Hz spec for the Tesla. AC Propulsion http://www.acpropulsion.com/products-drivesystem.html" , I expect in the hundreds of hertz range. Do you have a reference for the 400 Hz claim?

If you look at the specs you see it says four pole, and if you know the formula to find the frequency of an ac induction motor when the poles and RPM are known then you can get a general idea of the frequency it is designed for. Another factor is also weight.

The Tesla uses AC propulsion's designs. The motor from AC propulsion weighs in at 110 pounds where as the 400 HZ, 200 HP motor from: http://www.400hertz.net/Products/ME-400-200-416.htm" weighs in at 85 pounds. The weight differences are due to more HP likely in the AC propulsion design and/or the frame the motor is in maybe weighs more, but both of them are are at least 12,000 RPM or greater and have about the same weight.

 

[Phrak]

Until today when you learned of high frequency designs.

I'm an electronics products design engineer in instrumentation, controls, and power conversion (and I don't push papers, I engineer). I know a little about DC motors and haven't done anything with AC induction motors beyond turning them on and off and advising against unreliable speed control using triacs.

There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator. If instead magnets were used, it would be a synchronous motor which have no starting torque.

Not really. An induction motor requires slip to generate a field on the rotor. No slip, no rotor field, no torque. For a permanent magnet rotor, no slip is required, and the torque is maximal at stall. DC motors that have permanent magnets are not driven by a constant AC frequency and neither is the tesla motor. DC motors are supplied with their own alternating potential mechanically or electronically.

 

[Phrak]

Tesla Motors eventually included a transmission (2 gears I think) in their Roadster - still a big improvement over the transmissions used with combustion engines.

Interesting. I was curious about how they managed one gear. The power and torque curves of an electric motor are OK, but not wonderful. I think another alternative is to vary the field winding current (where both stator and field are electromagnets), but I haven't looked into it. It could have drawbacks.

 

[Altrepair]

Not really. An induction motor requires slip to generate a field on the rotor. No slip, no rotor field, no torque. For a permanent magnet rotor, no slip is required, and the torque is maximal at stall. DC motors that have permanent magnets are not driven by a constant AC frequency and neither is the tesla motor. DC motors are supplied with their own alternating potential mechanically or electronically.

If you read the text of mine you quoted (There would be no torque if current was not induced into the rotor bars which requires slip of the rotor relative to the rotating magnetic field of the stator.) you would see I said it required slip. No slip means no current will be induced into the rotor bars. It is that simple. If the rotor followed exactly with the rotating magnetic field, no current will be induced since no magnetic flux lines will be passed through by the rotor bar conductors meaning no current could ever flow in the conductors, thus no magnetic field will set up on the rotor, meaning NO torque.



I did not say anything of PM DC brushless motors which have a feed back loop either by hall effect sensors or by back EMF, in which case the controller knows the position of the rotor to correctly time when to energize the next set of windings (the electronic version of the commutator).

Synchronous AC motors, though, have no starting torque and have totally a different torque curve and work differently, PERIOD, compared to PM brushless DC motors. You can argue that till the cows come home, but it is a fact. Either a pony motor is needed or it must be the type that has rotor bars embedded into the rotor such that it starts up as an asynchronous induction motor till sufficient speed is reached for the rotor to lock in step with the rotating magnetic field when the DC power source is supplied to the slip rings of the rotor that powers the electromagnets.

If I am not considered a credible source by you, then have a look here that backs up my claim of pure AC synchronous motors having no starting torque at all:

http://www.engineersedge.com/motors/synchronous_motor.htm"

http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee11/bdeee11_8.aspx"

http://www.tpub.com/content/neets/14177/css/14177_92.htm"

I did make one honest mistake by saying 75% synchronous speed, when it is actually 95% of synchronous speed before the DC circuit is energized to power the rotor electromagnets to lock the motor in step with the rotating magnetic field.

Finally, the AC induction motor in the Tesla roadster works on the same principle as your typical AC induction motor which requires sinusoidal current to work. The voltage feed to it from the vector-variable-voltage/frequency drive is variable length square waveform that has the on/off ratios such that it makes the current flowing through the motor windings sinusoidal due to its inductance.

Have a look: http://oee.nrcan.gc.ca/industrial/equipment/vfd-ref/images/figure-08.jpg"

Anyways, I think we are stirring the topic off course and so I shall refrain from posting about motor characteristics.

 

[mheslep]

If you look at the specs you see it says four pole, and if you know the formula to find the frequency of an ac induction motor when the poles and RPM are known then you can get a general idea of the frequency it is designed for.

Yes for a synchronous AC motor rpm = 120 x frequency / # poles. This motor can not be synchronous. Phrac noted the design is in fact variable frequency.

 

[Altrepair]

Yes for a synchronous AC motor rpm = 120 x frequency / # poles. This motor can not be synchronous. Phrac noted the design is in fact variable frequency.

It also applies to asynchronous motors, but their will be slip obviously when a load is applied so the full load RPM will be less than synchronous. Even a 60HZ motor can have its frequency increased by a variable frequency drive. There is no "design" difference as you state. Some motor manufactures will sale "inverter duty" which the only difference is the motor's insulation is able to withstand the voltage spikes caused by the controller without insulation breakdown.

Anyways I have a feeling you only wrote this because I said I was not going to talk about motor characteristics any longer. You are causing this topic to go off course. If you wish to learn more then either PM or go to the Electrical Engineering forum to post more about electric motors. We need to get back to talking about this X-prize...

 

[mheslep]

Note I started the thread on "X Prize Clean Aviation". A discussion of the power density and / or efficiency of electric motors along with their possible energy sources is extremely relevant in my view.

 

[Altrepair]

Then the alternative would be brushless DC motors which are also cheaper than High temperature super conducting motors. Surely you want to make this clean flying airplane within practical budget. The other benefit is brushless DC motors are also more efficient than asynchronous induction motors.

 

[Phrak]

Anyways, I think we are stirring the topic off course and so I shall refrain from posting about motor characteristics.

Long restatements of common knowledge aren't interesting to read. On topic interests are those you have avoided or misunderstood or don't understand: 1) How does an induction motor scale with frequency? 2) What are the advantages for electric flight, if any, in inducing a magnetic field in a rotor rather than having it supplied for free?

 

[FlexGunship]

2) What are the advantages for electric flight, if any, in inducing a magnetic field in a rotor rather than having it supplied for free?

Asynchronous induction motors traditionally weigh less than synchronous motors with the same power (torque x speed) capability since light weight windings can be made lighter than permanent magnets. Honestly, though, this is only true at very high torque and power values. Probably in excess of 150kW total motive power.

I don't plan to get involved in this discussion, though...

 

[OmCheeto]

Note I started the thread on "X Prize Clean Aviation". A discussion of the power density and / or efficiency of electric motors along with their possible energy sources is extremely relevant in my view.

Agreed.

RonL's spinning battery packs and your SC motor mated in my brain and I ran across something close to the child product:

Brunvoll presents a ”Rim driven thruster” (RDT)

Rather than having the electric motor positioned along the central axis, move it out to the periphery.

I can't imagine a bearing that size being efficient at aircraft speeds, so I would position a conventional core axial bearing support.

Basically, the electric motor and ducted fan become one integral unit.

 

[Altrepair]

OmCheeto, like the idea, and would probably reduce cost even more so.
FlexGunship, I sent that person a PM on what he wanted to know, but what you say is also true.

 

[mheslep]

Updated narrated version of the Puffin VTOL video.
https://www.youtube.com/watch?v=GV0qBU_u3tQ

Summary:

• Blades don't counter rotate, but left and right sides run in opposite directions to counter torque
• On start, trailing edge control surfaces split to deflect thrust, keeping aircraft on the ground until pilot is ready
• Carbon fiber construction for body, provides 300 lb airframe (empty)
• 14' wing span,
• 7' rotors
• cruise 150 mph, sprint 300 mph
• Much quieter than conventional craft due to e-motors
• No turbo charge at high altitude
• Ceiling 30k' feet w/ environmental auxiliaries for pilot
• 50 mile range at cruise w/ 100 lbs of batteries, NASA aiming for 175 miles in 7 years

 

[Cyrus]

50 miles, eek...why not take a car. Even 175 miles is not all that attractive a decade later.

 

[KalamMekhar]

I would prefer something a little more. . . comfortable. As a to and from work device, it seems plausible, but quite frankly traveling long distances in that thing would be absolutely horrible.

 

[mheslep]

50 miles, eek...why not take a car. Even 175 miles is not all that attractive a decade later.

Have fun:

 

[OmCheeto]

I would prefer something a little more. . . comfortable. As a to and from work device, it seems plausible, but quite frankly traveling long distances in that thing would be absolutely horrible.

I'll take a 2 minute uncomfortable flight to work vs a comfortable but maddening 45 minute snail crawl to work any day.

But then, I always was a double black diamond kind of person.

(Emphasis on "was". I'd break a hip if I tried that now.)

 

[RonL]

Have fun:

I would think that is in a foreign country, not America.

 

[Cyrus]

Have fun:

Is this suppose to constutite a valid argument? You don't even know what the average distance those cars in that picture travel and if this vehicle would even begin to address the issue in that photo.

 

[mheslep]

Is this suppose to constutite a valid argument? You don't even know what the average distance those cars in that picture travel and if this vehicle would even begin to address the issue in that photo.

Valid argument? Cyrus, please. My casual response to

50 miles, eek...why not take a car.

Was completely appropriate.

 

[mheslep]

I would think that is in a foreign country, not America.

Oh yes, it's completely different in the US. Texas:
http://www.texasfreeway.com/houston/historic/photos/images/us59_trench_traffic_jam_1962.jpg

 

[RonL]

Oh yes, it's completely different in the US. Texas:
http://www.texasfreeway.com/houston/historic/photos/images/us59_trench_traffic_jam_1962.jpg

Hmmmm, March 1962, I was 19 years old and moved to Houma, La. looks like I made a good choice.
I was living in Houston at that time.

Ron

 

[Cyrus]

Valid argument? Cyrus, please. My casual response to Was completely appropriate.

No, I had a legitimate gripe. 50 miles is what a car is used for, and this is what NASA said this vehicle would not compete against.

 

[Cyrus]

Oh yes, it's completely different in the US. Texas:
http://www.texasfreeway.com/houston/historic/photos/images/us59_trench_traffic_jam_1962.jpg

Again, how far are those cars traveling?

 

[OmCheeto]

Oh yes, it's completely different in the US. Texas:
http://www.texasfreeway.com/houston/historic/photos/images/us59_trench_traffic_jam_1962.jpg

I drove back home from Seattle a few years back on a Sunday afternoon.
The 60 mile stretch to Olympia took me 4 hours.

There was no construction.

There were no accidents.

Just a slew of cars out for a Sunday drive.

I will never drive to Seattle again.

Next time, I'm flying.

And back to the topic:
Those little Schubeler electric ducted fans are only $314 each.(298eur-19%vat)
Generating 20lbs of thrust each, it would only require 8 to lift me off the ground.
Another 8 to lift a smaller Puffin style vehicle.
Another 8 to lift the 160lb battery pack.
That's only $7500 bucks for motors.
100 wh/kg * 73 kg batteries = 7.3 kwh
each fan consumes 7 kw
7*24 fans = 168 kw
7.3 kwh / 168 kw = 2.6 minutes
...

hmmm...

I'll have to do some scaling.




I was coming back from a 3 day regional conference. So no, I was not out for just a Sunday drive.

 

[mheslep]

No, I had a legitimate gripe. 50 miles is what a car is used for, and this is what NASA said this vehicle would not compete against.

Why not? The range is 50 miles in 20 minutes, parking lot to parking lot just like for the car. The car takes an hour, maybe two if you are behind the traffic in one of the photos.

 

[Cyrus]

Why not? The range is 50 miles in 20 minutes, parking lot to parking lot just like for the car. The car takes an hour, maybe two if you are behind the traffic in one of the photos.

Just think about it, having people fly around in an automated highway in the sky "grid" for anything less than 50 miles is a nightmare. All you have done is take the cars and congestion and put it slightly higher in the sky. The airways are already designed for aircraft, so if you are going to suddenly introduce car like airways, they are going to have to be well defined, probably flying overhead existing roads. So you can't just reroute cars anywhere you like it some sort of an optimizer that figure out where to direct each car to minimize travel time for the entire system.

Even for something between 50-400 miles, I don't see why this vehicle works. Take a Cessna, not only is it quick, I can take 4 people along with me.

For more than 400 miles, fly commercial.

 

[mheslep]

Just think about it, having people fly around in an automated highway in the sky "grid" for anything less than 50 miles is a nightmare.

Different topic. You asked why not take a car, not what would happen if all short distance transportation moved into the air.

Even for something between 50-400 miles, I don't see why this vehicle works. Take a Cessna, not only is it quick, I can take 4 people along with me.

Because you can't fly the Cessna out of your back yard. Most people in the US will require at least 40 minutes to get their light traffic airport to reach that Cessna, in which case one might as well drive ( or helo)

 

[Cyrus]

Different topic. You asked why not take a car, not what would happen if all short distance transportation moved into the air.

Because you can't fly the Cessna out of your back yard. Most people in the US will require at least 40 minutes to get their light traffic airport to reach that Cessna, in which case one might as well drive ( or helo)

Watch the video over again, they take off from a heli-port, not peoples back yards, and for good reason. But, let's assume you do fly it from your back yard. This vehicle is a single seater, this is very different from a vehicle you can put more than one person and payload in for an extended range. At that point, you're now talking about larger levels of noise, and inherently large disk loadings. Which means this thing will be shooting rocks and dirt below it at dangerous speeds to people, houses, fences, etc.

The V-22 suffers from this problem too.

-nS-C-xuH-g[/youtube]

 

[mheslep]

Economist article on burgeoning electric aircraft

High voltage
Transport: As electric cars make steady progress on land, battery- powered aircraft of various kinds are quietly taking to the air
http://www.economist.com/node/16295620

 

[mheslep]

Add to that list: Cessna along with Bye Energy are coming out with an electric Cessna Skyhawk 172. Aviation week and mfn sources say the aircraft will

o carry enough batteries on board for two hours of flight,
o have solar panels built into the wings to augment range,
o have a cost per mile flown 'several multiples' cheaper than the same distance flown with aviation fuel.
​

[URL]http://www.byeenergy.com/Pages/assets/images/banners/banner-cessna-iso.jpg[/URL]
http://www.byeenergy.com/Pages/FAQ.html
http://www.cessna.com/NewReleases/New/NewReleaseNum-1192324720455.html

 

[mheslep]

NASA just http://www.nasa.gov/topics/technology/centennial/gfc_final.html" for an (effectively) electric aircraft competition: $1.35 million.

The winning aircraft had to fly 200 miles in less than two hours and use less than one gallon of fuel per occupant, or the equivalent in electricity. The first and second place teams, which were both electric-powered, achieved twice the fuel efficiency requirement of the competition, meaning they flew 200 miles using just over a half-gallon of fuel equivalent per passenger.

Or 400 mpg effective for the winners. By comparison, according to NASA, typical general aviation aircraft achieve 5-50 mpg.Energy per gallon of gasoline is ~34 kWh, so the winners achieved 200 miles/17 kWh. At 150 Wh per kg of Li-ion battery: 113 kg of battery aboard (Edit: reserve of 30 mins required, or +25%; total minimum on board charge/wgt: 21.3 kWh/ 142kg)
More rules:
http://www.nasa.gov/pdf/590567main_NASA Green Flight Challenge_revised.pdf

Performance Required:
Range: 200 statute miles, with 30 min. reserve, day VFR at ≥ 4000’ MSL over nonmountainous, sparsely-populated coastal terrain
Efficiency: ≥ 200 Passenger-MPGe energy equivalency
Speed: ≥ 100 mph average on each of two 200 mile flights
Minimum Speed: ≤ 52 mph in level flight without stall, power and flaps allowed
Takeoff Distance: ≤ 2000 feet from brake release to clear a 50 foot obstacle
Community Noise: ≤ 78 dBA at full power takeoff, measured 250 feet sideways to takeoff brake release
Handling Qualities: Acceptable on all 7 basic handling qualities.

Features Required:
Passengers: Upright seats with adequate volume for a 6-foot tall, 200 pound (lb) adult.
Wingspan: Must fit inside 44-foot wide hangar for weighing (wingfold is acceptable). Height, length and landing gear footprint limits are defined in the Green Flight Challenge Team Agreement.
Vehicle Weights: ≤ 6500 lb. with ≤ 4500 lb. on main gear and ≤ 2000 lb. on nosewheel or tail-wheel
Field of View: Acceptable to FAA licensing authorities and FAA AC25.773-1
Control System: Must provide dual controls if two or more seats
Payload Carried: 200 lbs per seat. Dual pilots if two or more seats. 200 lbs per seat sandbag ballast in all seats not occupied by pilot/co-pilot
Seating Configuration: Tandem seating is allowed, but vehicles with 3 or more seats must place at least 2 seats directly side-by-side. Rapid exit required for all seats.
Fuel/Energy Use: Energy consumed: 1 gallon of 87 octane unleaded auto gasoline = 115,000 BTU. [...]
Fuels/Energy Allowed: Avgas 100 low-lead (LL), Jet-A, diesel, unleaded auto gasoline, bio-fuels, H2, synthetics, electricity.
ePower Measurement: Electric-powered aircraft will use a CAFE-provided power meter to accurately determine energy used during the competition
Flightworthiness: Valid US FAA Airworthiness Certificate for unrestricted day VFR flight in the Continental United States, proof of structural limit

https://www.youtube.com/watch?v=ujeJB8dlie8