Plain English Meaning

When the airplane's nose is pitched up, one side of the spinning propeller bites into the air harder than the other side. That uneven pull tugs the nose sideways, usually to the left.

Full Definition

A left-turning tendency that occurs when a propeller-driven airplane is flown at a high angle of attack. Because the propeller disc is tilted relative to the relative wind, the descending propeller blade (on the right side, with a typical clockwise-rotating engine viewed from the cockpit) meets the oncoming air at a higher angle of attack and at a higher relative velocity than the ascending blade on the left side. The descending blade therefore produces more thrust than the ascending blade, and this uneven thrust distribution across the propeller disc yaws the airplane to the left.