Roy Smith writes:

No, that's not true. If there is no prop, the engine will only exert
torque on the airframe when its rotational speed is changing.

The forces that compel the engine to rotate in one direction engender
equal and opposite forces that tend to rotate the airframe in the
opposite direction.

My mom used to have a 1960-something Buick with a big-ass V8 and a mushy
suspension. You could set the thing rocking just by revving the engine in
neutral.

That's because the amount of torque changes with the rotational speed
of the engine. However, as long as it is turning, it is exerting
torque on the rest of the car.

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