In a constant-speed propeller, what component directly moves the pilot valve when the prop control is adjusted?

• A. Oil pressure from the engine
• B. The pilot valve
• C. The speed governor
• D. Speeder spring movement inside the governor

Answer: (D)

The prop control sets a desired engine speed by changing the preload on the speeder spring inside the governor. This adjustment directly moves the speeder spring, which is the force that shifts the governor’s internal mechanism and, in turn, positions the pilot valve. The pilot valve then modulates hydraulic oil flow to the propeller’s pitch-change actuator, altering blade angle until the engine rpm matches the commanded setting. Oil pressure from the engine provides the hydraulic power, but it is the movement of the speeder spring inside the governor that directly moves the pilot valve.