Just to throw it out there, it would be a hell of a lot of work but if you wanted *real* flight dynamics logic, I've spent a lot of time messing with FlightGear (flightgear.org), which is an open source standalone flight simulator. It has multiple flight dynamics models but the one that is most tested is called JSBSim and it is licensed LGPL, so you can compile it into a closed source T3D project if you want to without breaking the GPL. You can find more info here:
http://jsbsim.sourceforge.net/