Plain English Meaning

When the nose is pitched up, one side of the propeller bites the air harder than the other. That uneven pull tugs the nose sideways, usually to the left in most American-built single-engine airplanes.

Full Definition

Asymmetric loading, commonly called P-factor, is the unequal thrust produced by a propeller when the aircraft is flown at a high angle of attack. In this condition, the descending propeller blade on one side meets the relative wind at a greater angle and at a higher relative speed than the ascending blade on the other side, so it produces more thrust. With a clockwise-rotating propeller (as viewed from the cockpit), the right side of the generates greater thrust, which yaws the nose to the left.