A constant-speed propeller is defined as which of the following?

• A. A fixed-pitch propeller whose blade angle remains constant.
• B. A controllable-pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant rpm.
• C. A propeller that adjusts rpm by throttle-only control.
• D. A propeller that automatically reduces rpm to zero in emergencies.

Answer: (B)

A constant-speed propeller keeps engine rpm essentially constant by automatically varying the blade pitch with the help of a governor. The governor senses the propeller’s rpm and moves the blades to load or unload the engine as flight conditions change. If the load increases and rpm would drop, the governor reduces the blade angle (unloads the prop) to let rpm rise back to the set value. If rpm tends to overspeed, it increases blade angle (loads the prop) to slow it down back toward the setting. This automatic pitch adjustment lets the propeller operate efficiently across a wide range of airspeeds and power settings, instead of relying on a fixed blade angle or throttle alone. A fixed-pitch propeller has no automatic pitch change, and controlling rpm by throttle alone doesn’t directly manipulate propeller load. An automatic reduction to zero rpm in emergencies isn’t how a constant-speed propeller is described or intended to operate.