It might be worth reading a bit on X-plane. It works starting with a model of the plane's shape and calculates the aerodynamic forces on the fly. There are tools for making models of new planes and a fair library of existing ones.

It is made to talk to other programs in a motion simulator environment. It has an external interface to get out the state vectors and probably put in the controls.

Does anybody know if it has a way to put in the tow rope forces?