Originally Posted by SR71
My suggestion is that the simulator fidelity is questionable only outside the phase space captured by the stability derivatives.
If you have the relevant dependent variables in the multi-dimensional matrices, just because you are outside the normal operating envelope, does not necessarily mean the simulator will respond inaccurately. The test phase space should obviously be larger than the operating envelope.
Given the demands on development time, I'd have doubts over any simulator manoeuvre not EXPLICITLY validated during the sim qualification.
For example, sims are usually validated ffor OEI cases at low sideslip angles, and for AEO cases at high sideslip angles. Without evidence that there was a match, I'd take any OEI high sideslip data with a pinch of salt - even though it would appear to be simply a case of adding together two sets of known data, it never quite works out that way ...
Non-QTG manoeuvres aren't guaranteed to be wrong, of course. But nor are they necessarily right.
In actual fact it is quite easy during wind tunnel testing to acquire stability derivatives outside the normal operating envelope of the aircraft.
Well,
static derivatives aren't TOO difficult - though there are always tunnel model limitations which may restrict what you can get - but dynamic derivatives are a whole other question.