This mostly just to create some links to interesting sites worthy of more investigation:

JSB Open Source Flight Dynamics Modeler

JSBSim is an open source flight dynamics model (FDM) that compiles and runs under many operating systems, including Microsoft Windows, Apple Macintosh, Linux, IRIX, Cygwin (Unix on Windows), etc. The FDM is essentially the physics/math model that defines the movement of an aircraft, rocket, etc., under the forces and moments applied to it using the various control mechanisms and from the forces of nature.

Open Extensible Architecture for the Analysis and Generation of Linked Simulations