Green Flight Challenge Final Results

I am an infrequent follower, so apologies if this has been answered, but how was fuel equivalent calculated? Was it based on the total chemical energy released when burning a gallon of 100LL or was it a measure of useful energy based on an ideal thermal cycle, or some other measure?

(Editor’s Note: The methods used to measure fuel or energy use are detailed in this white paper, http://cafefoundation.org/v2/pdf_GFC/GFC.Energy.White.Paper.pdf.

“BTU: British Thermal Unit, a measure of energy based upon the amount of heat required
to raise the temperature of one pound of liquid water by one degree from 60° to
61°Fahrenheit at a constant pressure of one atmosphere. 1000 BTU equal
0.29307107 kWh, making the 115,000 BTU energy content of 1 gallon of 87
Octane unleaded auto gasoline be equivalent to: 33.7 kWh.”)

Congratulations to all contestants in the Green Flight Challenge! Thank you to NASA, Google, CAFE Foundation for making it possible. Note that the Phoenix motorglider is a stock production Rotax powered aircraft you can buy today achieving 94.3 MPG in the Efficiency competition and 55 mpg at 137.5 mph in the Speed competition!

Looking at the table above released for the NASA Green Flight Challenge, it appears as though the e-Genius went about the same distance and speed, only used approximately 1/2 the fuel and energy as the Pipistrel, but came in second. Can anyone explain why?

(Editor’s Note: The Pipistrel carried two pilots, but also enough concrete and sandbags to simulate two additional passengers. It doubled its passenger miles per gallon relative to the two-seaters by this expedient.)

Re: the solar cells and pedals:
Hah! The solar cells might provide enough energy to power small fans to help cool the occupants while they pedal. And then CAFE would have to figure out what a pedaling human is worth in equivalent gallons of 100LL. After all, humans aren’t particularly efficient, consume rather expensive fuel and put out stinky emissions.

(Editor’s Note: CAFE’s rules on solar cells, etc. can be found in the Frequently-Asked-Questions part of the GFC explication, http://cafefoundation.org/v2/gfc_2011_faq.php.

Would the reader suggest that a street filled with cyclists would be overall more costly on a passenger mile basis – which might depend on whether riders are ingesting filet mignon rather than rice and beans, or that the street filled with automobiles would have a more pleasing aroma?)

I am very excited about electric powered flight and appreciate all the hard work being done here by CAFE and the contestants. I also agree with Dave on appreciating what can be done NOW with market ready tech to reduce energy consumption while delivering great performance. I am also surprised that CAFE doesn’t factor in some PRIMARY fuel source coefficient. Calling electricity Energy seems inaccurate when totaling it with 100LL fuel to arrive at a total equivalent fuel used amount. Seems like all the energies used to power the craft should be normalized to a primary energy source, or even multiple, to address the issue of the efficiency of converting it to electricity.
I can’t wait to fly an electric powered aircraft someday, and I am grateful for the work being done by all of you. Congratulations to Pipestrel.

Even after reading the relevant pdf’s, it is far from clear to me how CAFE computed “mileage” for the electric aircraft. The right way of doing it is clear enough: base the mileage on the fossil fuel used to charge the batteries. Electric motors and batteries are not subject to Carnot efficiency limitations. They can seem to be nearly 100% efficient until one looks at the power source that charged the batteries. That objection would disappear if CAFE used solar power to charge the batteries, but the rules appear to require diesel generators.

“Would the reader suggest that a street filled with cyclists would be overall more costly on a passenger mile basis – which might depend on whether riders are ingesting filet mignon rather than rice and beans, or that the street filled with automobiles would have a more pleasing aroma?”

Well, I wasn’t trying to be too serious, but, yes, filet mignon washed down with Dom Pérignon could be quite expensive fuel considering the average male would consume between 1/2 and 1 pound per hour of steak (if my quick internet search wasn’t flawed — and ignoring the fact that you’d want a more varied diet). Also, yes, I’d rather follow behind electric automobiles than a bunch of cyclists that sustain themselves on rice and beans!

Human powered efficieny

“The Daedalus human powered planes did about 4x the ePMPG of these planes (about .25 equivalent electric kW for one passenger) but it was at 17 mph and very fragile.”

… and note the specific consumption of the engine (the pilot) : 4 liters of energyzing liquid (water, sugar, salt) in 4 hours at 250 W, that is 4 kg/kW/h : 20 times the SFC of a diesel engine (0.2 kg/kW/h).