P factor

One of the “left-turning tendencies” of aircraft with a propeller, in which the loading of a propeller disc produces more thrust on one side than the other. If the nose of the aircraft points up relative to the oncoming wind, the downward-moving blade creates greater thrust than the upward-going blade, as the former is at a higher angle of attack than the latter. Assuming that the engine is turning clockwise as viewed from the rear (as is the case in the majority of single-engine propeller aircraft), the aircraft will tend to turn left. Also known as asymmetric propeller loading.

As the tail of aircraft is down, the axis of rotation is inclined. The down-going blade produces greater thrust as it is at higher angle of attack than the up-going blade. This causes asymmetric loading and aircraft making the aircraft tending to yaw.