Ming, in a vaccuum where there is only engine and prop and let's say the plane is held on course by rockets in the absence of wind... the onlytime you would have torque is when you change engine/prop speed.

In air, the constant torque is due to work of the prop.

If my gyro top is precessing and I change the spin rate, the precession will also change.

If I cut rpm's on the moving plane with fixed prop then I also cut torque as the prop will be pushing less on the air very quickly, may even become pressed *by* the air (overall, fixed props have a twist that makes different parts bite the air at different speeds/rpm combos) and that would result in reversed torque until the plane slows down enough to re-reverse the situation.

And if I can increase rpm's while doing a maneuver that uses the precession then hey, more power to it!

Yeah, it's all one, mass and inertia. And you can place force on something and not get equal force back. That is when the thing pushed either breaks or bends and the physics gets interesting. You can't cut materials unless you can overcome the strength of them to push back.