Definition
In propeller aircraft, a system in which the propeller blades automatically change their pitch (blade angle) to maintain a selected engine RPM, regardless of changes in airspeed, power setting, or aircraft attitude. A governor senses RPM and adjusts blade angle through hydraulic or mechanical action to hold the chosen RPM steady.
Plain English
A propeller setup where the blades twist automatically to keep the engine spinning at the same RPM you've set, even as flight conditions change.
Context Anchor
Seen in training for airplanes equipped with constant-speed propellers, especially when learning power settings, takeoff checks, climbs, descents, and engine management.
Derivation
Constant means unchanging, and speed here refers to rotational speed (RPM), not airspeed. The name describes what the system holds steady: the engine's rotational speed, not the airplane's speed through the air.
Why Pilots Care
A constant-speed propeller lets the pilot select the most efficient RPM for each phase of flight -- high RPM for takeoff and climb, lower RPM for cruise -- improving performance, fuel economy, and engine longevity. Operating one correctly requires understanding the relationship between manifold pressure and RPM.
Intuition Check
Constant speed does not mean the airplane holds a constant airspeed. Here, speed means propeller and engine RPM, and the system changes blade angle to keep that RPM near the selected value.
Example Sentence 1
Most high-performance trainers use a constant speed propeller, so the pilot sets RPM with the propeller control and power with the throttle.
Example Sentence 2
In cruise the constant speed unit fine-tuned blade angle so engine RPM remained steady even after a small power reduction.