Which propeller type automatically changes blade pitch in flight to maintain a constant RPM?

• A. Fixed Pitch Propeller
• B. Constant Speed Propeller
• C. Variable Pitch Propeller
• D. Feathered Propeller

Answer: (B)

Maintaining a steady engine RPM in flight is achieved by a propeller that automatically changes blade pitch using a governor. A constant-speed propeller uses this governor to hold the selected RPM by adjusting the blade angle as conditions change. If more load or higher airspeed would cause the RPM to drop, the governor moves the blades to a finer pitch to allow the engine to speed back up. If the RPM tends to rise, the governor increases blade pitch to add drag and slow things down. The pitch changes are driven by oil pressure in the propeller hub, guided by weights and springs that respond to the RPM reading and a pilot-set reference. This is what distinguishes it from a fixed-pitch propeller, which cannot change pitch in flight; and from a simple variable-pitch propeller, which may not automatically maintain a specific RPM without the governor mechanism. A feathered propeller, while also involving blade angle changes, is used to minimize drag in an engine-out situation and is not about maintaining constant RPM during normal operation.