Originally Posted by
Pilot DAR
Correct. C of G is a very important factor, and spin recovery characteristics will drive C of G limits. But the moment of inertia can have an effect too. If you put a small mass wayyyy back, yet remain within C of G limits overall, the spin recovery could be affected, as there was more inertia to overcome for recovery.
Indeed. M.Sc Thesis by P. Kefalas at Cranfield University, Aircraft Spin Dynamics Model Design, 2001 has some good info including this summary.
Originally Posted by
Pilot DAR
I think of a few engine change STC's which include a few pounds of lead in the tail to balance a heavier engine.
Yes. I've seen some fairly significant amounts of ballast added to fix the CG with nil consideration of moments of inertia effects on spinning etc.