Basic Propeller Principles

Kevin Jung

What is propeller?

• • • Consists of two or more blades Rotating wing Transforms the rotary power of the engine into forward thrust

The Left Turning Tendency

• • The propeller causes the airplane to turn left. Four major causes are ▫ Torque ▫ Corkscrew effect (Slipstream effect) ▫ Asymmetric loading of the propeller (P-Factor) ▫ Gyroscopic effect

Torque Reaction

• • • Newton’s Third Law of Physics ▫ For every action, there is an equal and opposite reaction When the airplane is in the air, this force is acting around the longitudinal axis, tending to make the aircraft roll to the left When the airplane is on the ground during takeoff, torque will cause the airplane to yaw to the left.

Corkscrew Effect

• • At high propeller speeds and low forward speed, this spiraling rotation is very compact and exerts a strong sideward force on the aircraft’s vertical tail surface It yaws the airplane to the left

Asymmetric Loading (P-Factor)

• • • It is caused when one side of the propeller produces more thrust than the other side At a high AOA, the downward moving blade has a higher resultant velocity, creating more lift than the upward moving blade It yaws the airplane to the left

Gyroscopic Effect

• • Less noticeable than other three Produces a left yawing motion when pitching down and a right yawing motion when pitching up

Summary

• • • • • Propeller = Rotating Wing Torque – rolls and yaws to the left Corkscrew effect – yaws to the left P-Factor – yaws to the left Gyroscopic Effect ▫ Yaws to the left when pitching down ▫ Yaws to the right when pitching up