I will explain assumptions I have made: All global vars, such as Alpha, Alpha_dot, Density, Altitude, so on, have correct values in the moment cherokee functions are called. Body coord system is defined as follows: X_body -> from cg to nose Y_body -> along right wing Z_body -> "down" (to make right coord system) All forces and moments act in CG. If strange behaviour is experienced, (like impossibility of level flight), it is probably misused coord system. Let me know and fix the error. All controls are in the range [-1.0, 1.0] If it is not so, values in cherokee_aero.c on lines 119-121 should be changed acordingly. If commands appear to be oposite, this is the place to change sign convention. Engine controls are in range [0.0, 1.0] (I found out later that lower bound is -0.2, so I added fabs(). I know, it is dirty and phisiclly wrong, but it was simply the fastest way to deal with it). All initialization files are *.ic: mass = 74.53 slugs Ixx = 1070 slugs Iyy = 1249 slugs Izz = 2312 slugs Ixz = 0.0 slugs above changes are writen in *.ic included in cherokee.zip. However, other data in *.ic files are not changed in any way. aditional properties: (if needed) S = 157.5 ft^2 -> wing area b = 30.0 ft -> wing span Ar = 5.71 -> aspect ratio c = 5.25 ft -> midspan chord Once more: Source are TOTALY UNCHECKED. I hope it will work, but I do not dare to claim that ewerything will work first time you compile it. Good Luck! Gordan gsikic@public.srce.hr PS Work to be done (for myself): Landing gear (it is just navion_gear.c copied for now, these are similar class of aircraft, so it should work), Alpha_max is still undone, Spin (if I find any references concerning simulating spin), Efect of ground, Flaps, .......