Paul,

The Mach/True airspeed versus Indicated airspeed issue obviousely has nothing to do with our models, but is another example of how stability changes when the relationship between static and dynamic stability changes. Static stability stays the same, but as altitude and therefore TAS increases dynamic stability or damping reduces.

I'm pretty much at my limit of knowledge here, and would have to draw a diagram to explain it. I'll see if I can find anything with Google or Wiki, but that stuff isn't really my forte.

Look for roll damping as well. It varies with Mach/Tas for the same reason.

Dave