pappy-need for you to come out of retirement, and do a proper engine that sips gas/fuel instead of guzzling the stuff!
Would guess-maybe wrongly so, besides streamlining the aircraft, that an engine exists that can be worked to fill NASA's requirements.

http://news.cnet.com/8301-11386_3-10012892...tml?tag=cd.blog

well best i ever did was some 20 mpg at about 90 mpr , i still have my licence although not current.
would post pix if you want but not many want to see an old man an toys.

100mpg at 100mphr aint gonna be easy. Best bet would probably be a glider with a light light weight diesel sustainer motor. Probably will even have to put a cowl around the prop to make it more efficient.

Edit: oh and pappy...would love to see some pics
<-------- aeronautics and astronautics engineering student.

Not bad pappy! For NASA .... "the best attempt achieved 28.8 miles per gallon." Plus, these guys put a ton of money into the project-the prize is nice. But, suspect they were selling engines and planes! If you have planes and engines-please post!