Definition
A propeller governor is an engine-driven device that automatically maintains a selected propeller speed (RPM) by adjusting the pitch of the propeller blades. It senses changes in engine RPM through flyweights and uses oil pressure to increase or decrease blade pitch, keeping RPM constant despite changes in airspeed, power setting, or aircraft attitude.
Plain English
It is a small device on the engine that keeps the propeller spinning at the speed the pilot has chosen. If the propeller starts to spin too fast or too slow, the governor automatically twists the blades to a different angle so the speed stays right where it was set.
Context Anchor
You encounter this term when learning how a constant-speed propeller maintains selected RPM during climbs, descents, cruise, and power changes.
Derivation
From 'govern,' meaning to control or regulate. The term is borrowed from steam-engine technology, where a governor used spinning flyweights to control engine speed. The propeller governor works on the same principle: spinning flyweights sense speed and signal a correction.
Why Pilots Care
Proper use lets the pilot choose an RPM that protects the engine, improves fuel efficiency, and gives the best combination of thrust and cooling for each phase of flight.
Analogy
Think of cruise control in a car. You set the speed you want, and the system automatically applies more or less throttle to hold it as the road goes uphill or downhill. The propeller governor does the same thing for propeller RPM, but by adjusting blade pitch instead of throttle.
Intuition Check
Do not think of “governor” as a person or outside authority here. In this context, it means an automatic device that controls propeller speed.
Example Sentence 1
When the pilot pushed the propeller control forward, the governor increased oil pressure to flatten the blades and bring RPM up to the takeoff setting.
Example Sentence 2
During a power reduction in descent, the governor decreased blade angle so the propeller would not overspeed.