On Mar 14, 3:54*am, Markus Gayda wrote:
How about using the propeller as a generator on the way down?
Recharge the battery. (of course you cant do that with a static prop)

THAT would be a real hybrid :-)

CU
Markus

Possibly a better approach is to look carefully at propeller
efficiency in the initial acceleration. In the ground roll where the
prop efficiency unlikely to be more than 25%. Touring motorgliders
like airplanes with fixed props are optimized for cruise, not
acceleration.

Small, high RPM props are very bad at very low airspeeds. Big, low
RPM props far better as are ducted fans. Note that helicopters use
huge rotors at around 300 RPM to slowly lift the entire aircraft
straight up. Other VTOL aircraft like the F35B use ducted fans which
are at their best below 75 knots.

The tiny prop is the weak link in current motorglider tugs. It
doesn't look as if it would be hard for the designers to lengthen the
landing gear by 25cm and ask Rotax to supply greater gear reduction
for a bigger, slower prop. A bigger prop would address the slow
acceleration.