When engine power is increased, the constant-speed propeller maintains RPM by which action?

• A. decreasing blade angle
• B. increasing oil pressure
• C. reducing thrust
• D. increasing blade angle and maintaining a low angle of attack

Answer: (D)

A constant-speed propeller uses a governor to keep engine RPM steady by changing the blade pitch to load or unload the propeller as power changes. When engine power is increased, more torque is available, which would tend to spin the prop faster if nothing else changed. The governor responds by increasing the blade angle (pitch), which increases aerodynamic drag on the blades and loads the propeller. This extra load requires more torque to maintain the same RPM, so the RPM stays at the set value.

Keeping the blade angle higher also helps the blade operate within a safe, efficient range of angle of attack at the current airspeed, avoiding stalls or excessive stress while the throttle power is up.