ORIGINAL: MMallory
91fx isn't a high rpm engine. You will need at least a 10 pitch prop to use the power of that one. A piped Super Tiger .75 would be a better bet.
I use the 91FX on a pattern plane with a 15x8 prop with great result, but the specs says that the rpm range goes up to 16000rpm. Isn't that high rpm? How is this engine timed? For high or low rpm? I haven't tacked my engine yet, but I guess it is getting close to 16000rpm with the MA 13.5x7 3-blade. If anyone else finds a higher pitched prop for this engine let me know.
JKR
I will probably install retracts soon. I will move the retracts closer to the cg. I think that would make the take-offs better.
JKR