Definition
The rotational speed of the propeller, expressed in revolutions per minute. On a fixed-pitch propeller, propeller rpm equals engine rpm because the propeller is bolted directly to the crankshaft. On an aircraft with a reduction gearbox or a constant-speed propeller system, propeller rpm differs from engine rpm and is controlled or limited independently.
Plain English
How many full turns the propeller makes each minute. On simple airplanes, the propeller spins at the same speed as the engine. On more complex airplanes, the propeller can spin slower than the engine or be held at a chosen speed.
Context Anchor
Seen in engine operation, takeoff checks, cruise power settings, and engine instrument monitoring.
Derivation
Rpm stands for revolutions per minute -- one revolution is one complete turn. Propeller comes from the Latin propellere, 'to drive forward,' which is what the spinning blades do to the air, and through reaction, to the airplane.
Why Pilots Care
Correct propeller rpm keeps the engine efficient, prevents overspeed damage, and delivers the intended power.
Intuition Check
Do not assume propeller rpm is the same thing as airplane speed. It only tells how fast the propeller is turning; the airplane’s speed depends on several other factors too.
Example Sentence 1
During the runup, the pilot checked that propeller rpm dropped within limits when each magneto was tested.
Example Sentence 2
During the takeoff roll, propeller rpm climbed steadily to the red line.