Thanks a lot Henning, this might help. Btw, how to calculate the weight (the gravity force) in 3dgs. W = mg, in 3dgs g=-386, because it uses quants, not meters. So, according to the theory, the weight of an object with mass of 23 kg is W = 23 * -386 = -8878, though I put the value for the lift force 8200, which is less then gravity force, but the plane still manages to take off (O_o). Why? How does the 3dgs work with forces? I tried to calculate the exact lift force which would be the same as the gravity force, but I couldn't.