DUMB THUM,

This is a cool idea. Generally, I think there is a lot to learn from the sailplane folks, since they have had to design everything around budgeting limited energy to stay aloft. The main difference is that, early in the flight, you need a lot of lift to carry your fuel. I will take a look at Model Aircraft Aerodynamics tonight, to get some ideas. Off the top of my head I would definitely suggest:

1) high aspect ratio wing
2) flaperons or long span flaps to allow higher camber while the plane is heavy, and lower camber when the fuel load goes down
3) maybe span load the wings by putting some of the fuel in there?
4) and engine with conservative intake & exhaust timing
5) large diameter prop

banktoturn