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 propeller disc generates greater thrust, which yaws the nose to the left.
Plain English
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.
Context Anchor
Seen in discussions of propeller turning tendencies, especially during takeoff, climb, and slow flight at high power.
Derivation
Asymmetric comes from the Greek 'a-' (not) and 'symmetria' (same measure on both sides). So 'asymmetric loading' literally means an uneven load — in this case, the load on the propeller blades is uneven, with one side working harder than the other.
Why Pilots Care
It is one of the four left-turning tendencies that pilots must counteract with rudder to maintain straight flight, especially critical at low speeds during takeoff.
Grounding Statement
Picture the nose held high in a climb: the downward-moving propeller blade meets the air more aggressively, so it produces more pull than the blade moving upward.
Intuition Check
Asymmetric loading does not mean the airplane is loaded unevenly with passengers or baggage. Here it means the propeller blades are producing uneven thrust because of how they meet the air.
Example Sentence 1
On the takeoff roll, the student added right rudder to counter the asymmetric loading pulling the nose left.
Example Sentence 2
In a steep climb, asymmetric loading increases, requiring more rudder correction.