A minor snippet about the SR-71 (also see page 1).
On Concorde at Mach 2, the engine itself provides only about 8% of the total thrust.
On the SR-71 at Mach 3, that percentage is even less.
And in certain flight conditions, the engine itself no longer produces any thrust at all, but some drag.
Result? Instead of the engine 'pulling' the aircraft along, it's now the aircraft that 'drags' the engine along, and yes.... the engine moves rearward in the engine mountings !!
CJ