Definition
A propeller whose blade angle (pitch) can be changed by the pilot during flight, allowing the engine and propeller to operate efficiently across a wide range of airspeeds and power settings. On most modern aircraft, the propeller is governed automatically to maintain a selected RPM, and the pilot adjusts pitch indirectly through a propeller control lever.
Plain English
A propeller where the angle of the blades can be changed while flying, instead of being permanently fixed at one angle. This lets the pilot get the best performance from the engine whether climbing, cruising, or descending.
Context Anchor
Seen in engine and propeller discussions, especially when comparing fixed-pitch propellers with propellers that can be adjusted for performance.
Derivation
‘Pitch’ here refers to the angle of the propeller blades — borrowed from the same idea as the pitch of a screw, where a steeper angle pulls more material per turn. ‘Controllable’ simply means the pilot can change it in flight, as opposed to a fixed-pitch propeller where the angle is set on the ground and never moves.
Why Pilots Care
It lets the pilot match propeller blade angle to flight conditions for better takeoff power, efficient cruise, and protection against engine overspeed.
Analogy
Think of it like the gears on a bicycle. A low gear (flat blade angle) lets you accelerate quickly from a stop but you spin out at higher speeds. A high gear (steep blade angle) lets you cruise efficiently at speed but is useless for taking off. A controllable pitch propeller lets the pilot shift between these as conditions require.
Intuition Check
Do not read “pitch” here as the airplane’s nose-up or nose-down attitude, or as sound. In this term, pitch means the angle of the propeller blades.
Example Sentence 1
After takeoff, the pilot reduced the propeller control to set a lower RPM for cruise, taking advantage of the controllable pitch propeller to ease engine wear.
Example Sentence 2
In level cruise the pilot increased pitch on the controllable pitch propeller to lower engine RPM and save fuel.