FAA Powerplant Written Practice Test

What increases the blade angle of constant speed non-feathering propellers like McCauley and Hartzell without counterweights?

1. Electric current

2. Engine torque

3. Oil pressure

4. Mechanical linkage

The correct answer is: Oil pressure

The increase in blade angle for constant speed non-feathering propellers, such as those made by McCauley and Hartzell, occurs due to the application of oil pressure. In constant speed propellers, the governor adjusts the blade angle in response to changes in engine speed. When the engine speed increases, the governor senses this increase and directs oil pressure into the propeller hub, which pushes the blades to a higher angle of attack. This adjustment helps maintain a constant engine RPM by reducing the propeller's pitch and allowing it to handle more power efficiently without having to shift to a feathered or fine pitch. Given this operation, electric current, engine torque, or mechanical linkage do not directly affect the blade angle of the propeller like oil pressure does. Electric current might be involved in operating components of the governor, but it does not perform the primary function of adjusting blade pitch. Engine torque influences the overall dynamics of flight and power output but does not directly change the blade angle. Mechanical linkages are involved in connecting the governor to the propeller system, yet they merely facilitate the motion rather than actively control the adjustment itself.