I'm 99.999% sure that there is a list of parameters for each plane in the program.
If you have the right sort of data, I imagine you can just plug in all the parameters.
But if you don't have extensive flight test data you can look at weights and dimensions and back calculate a lot of the parameters.
In my experience (not games and not WW2 airplanes) the best results come from a combination of the two - compare the measured (flight test) performance (which is HIGHLY variable) to the predicted performance (from physics of weight, thrust, lift, etc.) and find a happy medium.
Not answering your question really I guess, but I love an opportunity to make myself sound smart.
[This message has been edited by funked (edited 09-01-1999).]