Well, the best thing I advise is to have a crack at making your own Flight Model if you have one thats no good!
http://www.mudpond.us/
All the tools you need should be here (you’ll need MS excel for the Flight Dynamics Workbook) but it’s not as hard as you might think! 😉 There is also a beta version of the excellent ‘Air Wrench’ which uses all the formulas & Coefficients that the FDWB uses but is far simpler to use and will make brand new FM’s based on the existing air & cfg files.
You’ll really get the best out of the FS Sim Engine with these. 😀
Just make sure you have the required data for your chosen machine (weights, power, dimensions, control surface areas and movement etc) and you should have a half decent FM! 🙂
Cheers
Paul