If I want to predict the fuel consumption rate of an engine in the air before I install a tank in the plane, can I test it on the bench using the flight prop, tank, muffler and intended RPM (the engine is well broken in) or will the fact that the engine is stationary skew my results one way or the other? The tank installation is going to be tricky, with limited space, so I'd like to be confident of the fuel volume beforehand.

Thanks.

Fuel consumption on the bench verses in the air is tricky but usually you will use more fuel in the air. My moki 51 used same consumption on tha bench as well as in the air. It will vary with different engines but to estimate it is almost immpossible I would say that most engines will use at least 5% more. Only way to test it is put engine on a plane and check it out. There are ways to increase milage but that is a whole different ballgame.