What provides forward and reverse thrust on a propeller?

• A. Geometric pitch
• B. Controllable pitch
• C. Effective pitch
• D. Fixed pitch

Answer: (B)

Controlling the blade angle is what lets a propeller push in either direction. A controllable pitch propeller can change the blade pitch, so you can set it for forward thrust or flip it to a reverse angle to produce backward thrust. This capability is what makes forward and reverse thrust possible, useful for optimizing efficiency in flight and for braking on the ground.

Geometric pitch is simply the blade angle as designed, not something you actively vary during operation. Effective pitch is the actual thrust-producing angle given current conditions, a derived result rather than a mechanism. Fixed pitch can’t change the blade angle, so it can’t provide reverse thrust.