How is engine operation controlled on an engine equipped with a constant-speed propeller?

• A. The throttle controls power output and the propeller control maintains a constant blade angle
• B. The propeller control controls RPM and the throttle controls fuel flow
• C. Mixture controls RPM and the throttle controls blade angle
• D. The throttle controls blade angle and the propeller control sets power

Answer: (A)

In a setup with a constant-speed propeller, engine operation is managed by two separate controls: the throttle and the propeller control. The throttle determines power output by regulating the amount of air entering the engine (and thus fuel usage indirectly), so moving the throttle changes how much power the engine produces. The propeller control sets the target RPM, and the propeller governor automatically adjusts blade pitch to hold that RPM as flight conditions change. When more power is needed, the throttle opens and the governor increases blade angle to absorb the extra energy and keep RPM steady; when power is reduced, the governor decreases blade angle to let RPM drop as appropriate. Mixture affects the fuel/air ratio but does not set RPM directly. So the best description is that the throttle controls power output and the propeller control maintains the selected RPM by varying blade pitch. (Note: the pitch is not held constant—the system adjusts it to maintain the chosen RPM.)