Sock Munkey: When I think of sailplanes I think of Grob (or is it Groß? I can never remember.) and Schweizer sailplanes.
Gliders aren’t as light as you’d think. They need an airframe strong enough to endure a fair amount of manuevering to catch thermals and wind from slopes. They also don’t take off under their own power. It takes a fairly robust and powerful plane to tow one aloft such as a cropduster. Once it is aloft and flying in its envelope it takes less energy to stay aloft.
Planes with marginal power sources have to be built and designed to completely different parameters. They need to be light enough so the inertia isn’t too much for the engine to overcome let alone drag so they are very fragile. Wings are designed for extremely high lift at low airspeeds. Drag is a secondary consideration because of the low speed. Notice how many early aircraft up through WWII had undercambered wings, the underside is concave. Good lift at low speeds and reasonable drag at the modest speeds they flew at.
About those CO2 engines… aren’t the tanks full of LIQUID CO2? You can put a hell of a lot more matter into a tank if it tends to condense into a liquid when under pressure.
What you are describing is a perpetual motion machine: you want to use the airplane’s motion to power a generator to turn a propeller to move the airplane. Like all perpetual motion machines, it won’t work. The power you get from the EPU will be insufficient to overcome the drag generated by the EPU, no matter how efficient or lightweight you make the entire apparatus. There’s no free lunch.
A solar powered airplane is a different matter entierly, and several such have been built. They aren’t very practical - have to be huge, fly slowly, and can’t carry much payload, but they can stal aloft for a very long time.
bbeaty
Yes, tanks are often filled with liquid CO2.
However an interesting problem with such engines is that they tend to freeze; in the OP link you can see pictures of some of them, what look like cooling fins on the cylinder heads are in fact heathing fins; that´s also the reason that these engines are fed through a relatively long cooper or bronze pipe, so the CO2 can heat up before reaching the engine.
On a larger engine the problem may get a concern, frozen engines don`t work very well I´m inclined to think 
Mantra: “I must check spelling”
:rolleyes:
Actually the best athletes (cyclists like Bryan Allen who was the pilot of the Albatross) at best only manage 1/3 hp.
Flat…