Originally Posted by
BackPacker
Interesting question. No, I have not done any measurements, but wanted to comment on something else.
I don't agree that "the" (P-) effect is real. I do agree that you need a bootful of right rudder on takeoff (US Lycosaurus talking here)
Takeoff is not a good example for P factor. You do have a considerable torque effect, but the angle of attack is near zero for most of the event. (the first example that popped into my head was the incorrect takeoff example as well)
The case to consider it is stable slow flight. In this case you have
1 - high power output
2 - High angle of attack (the principle reason the effect is said to exist)
3 - Should have no different torque effect as high power cruise (as the engine torque and the wing loading are the same
4 - Should have no gyroscopic effects as the aircraft is not rotating about any axis (until it stalls)
So the need for a large boot full of rudder in slow flight is either a slip stream dynamic or P factor.
an experiment to establish the relative magnitude could be
Fly an approach to stall upright and inverted. If the plane needs left rudder upside down then P effect is dominate, if it needs less right rudder then they are both material, if the right rudder pressure is not materially different then slipstream is primary and P factor is minor. I am not an aerobatic pilot so have no practical experience with this one.