Definition
The range of engine RPM and flight conditions within which a constant-speed propeller's governor can automatically adjust blade pitch to maintain the RPM selected by the pilot. As long as operating conditions stay inside this range, the governor keeps engine speed constant by increasing blade pitch when load decreases and decreasing blade pitch when load increases.
Plain English
It's the band of operating conditions where the propeller's governor can keep engine RPM steady on its own. Inside this band, the pilot picks an RPM and the propeller automatically adjusts its blade angle to hold that RPM, even as airspeed, power, or attitude change.
Context Anchor
Seen when learning how an adjustable-pitch or constant-speed propeller responds to throttle changes, airspeed changes, and propeller control settings.
Derivation
"Constant-speed" describes what the governor maintains -- a steady engine RPM. "Range" here means the span of conditions over which that maintenance is possible. Outside the range, the blades hit a mechanical stop (full fine or full coarse) and RPM is no longer held constant.
Why Pilots Care
Knowing this range shows where the propeller will deliver constant RPM and best efficiency; outside it the unit behaves like a fixed-pitch propeller.
Analogy
It is like a car's cruise control on a hill: it can hold speed only while it has enough control authority. If the hill is too steep or the limits are reached, the speed changes anyway.
Grounding Statement
Within the constant-speed range, the governor still has enough blade-angle movement available to keep RPM at the selected value.
Intuition Check
“Constant-speed” does not mean the airplane keeps a constant airspeed. It means the propeller system can keep engine RPM constant, but only within its adjustment limits.
Example Sentence 1
As long as the engine and propeller are operating within the constant-speed range, the governor will hold the RPM the pilot has selected with the propeller control.
Example Sentence 2
Above the upper limit of the constant-speed range the blades reached full coarse pitch and RPM began to drop with further airspeed increase.