That is the principle of a ram air turbine. It's a small wind turbine which can operate as a power generator while the plane is flying.

> I wonder if you could use your propeller as a "wind turbine" when landing to recapture some energy?

Helicopters do this, it's called autorotation. They spin up the rotor while descending and then trade the rotational momentum for a little bit of lift to make a safe landing. It's a tricky maneuver but a part of every heli pilot's training.

I doubt that it's a viable strategy for light aircraft, though. The loss of airspeed from extracting energy out of the wind stream is more dangerous than gliding. Thermals aren't powerful enough to keep a non-glider aircraft in flight as far as I know.

Large aircraft use a small windmill or a ram air turbine to keep hydraulics and electrics up in case of a loss of power, though.

Small aircraft can definitely thermal. It would require powerful and big thermals compared to what a glider needs, but such conditions do exist. A small Cessna probably has a minimum sink speed in the neighborhood of 700fpm, and thermals stronger than that do exist, and are pretty common in some places.

The problem, of course, is that it's just not reliable enough to count on.

I suspect that while landing you really want the engine in "neutral" so you can at any moment kick it into full power if some issue shows up. Landing is damn close to a controlled crash.

And i don't think these kinds of aircrafts have the wing surface etc to be floating around on thermals.

Usually when landing you want something like 110% of your stall speed, which means that you're not "crashing" (by which I mean stalling). This involves some sort of engine power.

I am not aware of any plane that lands without power outside of an emergency.

Staying above stall speed in a descent does not require any power. It is extremely common to perform a "power off" landing in a small plane, and these are often not in emergency cases.

Apart from all those thousands of sailplanes people fly every week. They land without power, and very few of those landings would be an emergency.

Yeah that is correct, I was more thinking of commercial flights rather than sailplanes/gliders