I have built an ultralight airplane in GMAX, and am trying to create the flight parameters. I started out using Mr. Beckwith's great spreadsheet, but the result wont fly at all.

So then I started modifying the air and cfg files from the Cessna, and found real difficulty modelling a 5000 rpm, 50hp 2 cyl 30 cc 2 stroke (10.8 compression) Rotax engine with a 64" 28 degree prop. It just wont work.

So I messed around with engine parameters until I could get the engine to run, but when you select the plane, it bounces and jumps around for about a minute until it "settles down". Then if you switch views it bounces and jumps again. It flys ok...but is real jumpy on landing too.

I have one of these planes in real life, and the plane does not move when at idle.

Any thoughts on the solution?