Definition
Airplanes equipped with a propeller whose blade angle (pitch) is set by the manufacturer and cannot be changed by the pilot in flight. Engine power in these airplanes is controlled by a single throttle lever, and engine RPM rises and falls directly with throttle position, airspeed, and load on the propeller.
Plain English
Airplanes whose propeller blades are built at one fixed angle. The pilot cannot adjust the blade angle, so the engine has only one control lever -- the throttle -- and the engine speed simply responds to how much throttle is set and how hard the air is pushing on the propeller.
Context Anchor
Seen when learning how the airplane feels during power changes, climbs, descents, and airspeed changes, especially in basic training airplanes.
Derivation
Fixed' means unchanging, and 'pitch' here refers to the angle of the propeller blades as they slice through the air. So a fixed-pitch propeller is simply one with a permanently set blade angle -- in contrast to a constant-speed (variable-pitch) propeller, where the blade angle can be adjusted in flight.
Why Pilots Care
RPM rises and falls with airspeed changes, so pilots must manage throttle carefully to avoid over-speeding the engine or losing power when maneuvering.
Intuition Check
Do not confuse pitch here with the airplane’s nose attitude. In fixed-pitch propeller airplanes, pitch means the propeller blade angle, not whether the nose is up or down.
Example Sentence 1
Most primary trainers are fixed-pitch propeller airplanes, so the student only has to manage the throttle, not a separate propeller control.
Example Sentence 2
In fixed-pitch propeller airplanes, descending at constant throttle causes propeller RPM to increase because the blades meet the air at a steeper angle.