Backpacker
A superbe post that well and truly hits the nail on the head !
FlyinDutch.
The Lycoming charts are of very little practical use with this aircraft as the propellor is optimized to give full power (2700 RPM) at 70 Kts, this way all 180 hp is avalable at the best lift drag speed for the airframe and at a speed that most modern gliders will climb well.
The assumption from the Lycoming charts is that the 2700 Rpm limit will be reached at the full throttle altitude for 75% power, ths is how most aircraft light aircraft are set up to get the best cruising performance, the DR400-180R has only one mission, that is to drag a glider as efficiently up to about 3000ft.
To do this the prop is very fine and the engine will overspeed as soon as you ask it to fly any faster than about 70kts so to keep within RPM limits the power must be reduced as TAS increases.
The aircraft performs its designed task very well but as with all very specialized equipment it is not very good at anything else.
Last edited by A and C; 19th Sep 2012 at 15:18.