The P factor is an effect of a rotating propeller, the aircraft in flight experiences with a high angle of attack. It leads to a shift of Schub-/Vortriebszentrums the propeller and thus an asymmetric thrust distribution. Apart from other influences, such as side wind, there is the displacement of the Schub-/Vortriebszentrums on a horizontal straight line passing through the hub of the propeller.
The P factor is partially counteracted by use of a motor train.
In the normal flight position is the running plane of the rotor blades of a propeller at right angles to the oncoming air, so the " airspeed " vector. Once the aircraft is in an attitude with (strong) increased angle of attack, the horizontal downward current sheet a higher speed relative to the air and a greater angle of attack on, as the horizontal upward -going. This is analogous to a reduced speed relative to the air and a smaller angle of attack. The leaves, just push through the vertical, show no further change with respect to its thrust generation.
In a clockwise direction as seen in the flight -rotating propeller, the thrust center of the mid migrates ( on the motor shaft away) horizontally to the right. Thus, a torque is generated to the left around the yaw axis ( yaw moment). However, this can be compensated by counter-steering with the rudder. The effect is so apparent, for example, in a rolling taildragger. Aircraft with such a suspension have in ground operation characteristic of a higher angle of attack than those with tricycle landing gear.
For two-engined airplanes whose propellers have the same sense of rotation away at the engine, the downward moving blade is turned to the wing end of the relevant page, the propulsion center of the hull away, while it shifts at the engine on the other side from the fuselage. The latter is thus the "critical " engine, because in case of failure, it requires a stronger countermeasures. In normal flight, both engines have the same lever arm about the vertical axis. So while decreases the lever arm at the critical engine increases it in the other engine. For two-engined airplanes with opposite sense of rotation of the motors to the center of thrust displacements compensate. It is then advisable to choose the direction of rotation so that the hull facing blades go down. Thus, when a failure will always remain an engine which operates with a reduced lever arm.
Due to the direct proportionality of the P- factor to engine performance, the negative influences on the landing approach when the flare ( flare english ) with a high angle of attack just before touch down are negligible. The P- factor is theoretically existent in terms of its impact strength, but in practice is subject to the stronger, generated by the twisted propeller slipstream " corkscrew " effect.