[Davew]

Would any 'flight model' have to be based on basic, or advanced, aerodynamic theories?

And if that is true, are there any programs available on the subject, as an application for 'modeling'?

When you have the basic performance of an ac and the physical characteristics, can these be applied to such a program to determine other performance characteristics?

For example, if we know an ac's speed at a specific altitude, and we know some other bits of information, couldn't we determine 'Lift' and 'Drag', CL and CD from that? And with that info determine other things such as, rate-of-climb, roll-rate, stall angle, best angle for maximum climb rate, turn radius and on and on....

Sure would be nice if there were such a program!

Dennis

Its not quite that easy though.
In s/l flight at equilibrium lift = weight, thrust = drag so thats easy enough.
Coefficient of lift and drag are also not difficult given air density, velocity and surface area. Formulas for those.

Rate of climb is dependant on excess thrust available, but things like roll rate are dependant on a number of factors, stall angle depends on quite a few things such as aerofoil shape airflow characteristics etc, as does the behaviour at the stall.

Not knowing about x-plane 9 i may be a little ignorant here, but it would appear that there's an assumption that the pattern of differences between an x-plane model and an Il2 model would remain constant across the aircraft types, so as to be able to extrapolate for the other types flight envelopes.
We know that that's not the case though, because the TA-183 wouldnt actually have been able to fly IRL. Also, given the discussion about the somewhat warped flight models for some aircraft, I would suggest that it wouldnt be a fixed pattern correlating an x-plane model to the equivalent IL2 one.

What could perhaps be done though is develop the model in x-plane, gather whatever performance criteria may be possible from that model and write the flight model for IL2 with reference to a range of aircraft, broadly fitting the new aircraft into an approximate category?