Propeller

A propeller is a rotary device with two or more blades that converts engine shaft rotation into thrust by accelerating a mass of air rearward (aerodynamic thrust). It is the primary means of thrust generation for piston-engine aircraft and turboprop aircraft.

Propeller Aerodynamics

Each propeller blade acts as an airfoil — producing thrust (analogous to lift) and drag, governed by the same principles as a wing. The angle of attack of each blade section is determined by the combination of blade pitch and the aircraft’s forward speed and RPM. A propeller converts the engine’s torque (rotational power) into thrust (linear force) with efficiency typically between 75–90%.

P-Factor

At high angles of attack (e.g., during take-off rotation), the descending propeller blade (on the right, for a clockwise-rotation engine) meets the air at a higher angle of attack than the ascending blade on the left. This generates more thrust on the right side, creating a yawing moment to the left. The pilot must apply right rudder to compensate.

Related Terms

See also: Pitch Setting, Feathered Propeller, Critical Engine.