Definition
A propeller that is driven by the engine through a system of reduction gears, so the propeller turns at a slower speed than the engine crankshaft. This arrangement allows the engine to operate at its most efficient high RPM while keeping the propeller tip speed below the point where it loses efficiency or generates excessive noise.
Plain English
A propeller connected to the engine through gears that slow it down, so the engine can run fast while the propeller turns more slowly.
Context Anchor
Seen in aircraft engine and propeller descriptions, especially when comparing direct-drive engines with engines that use reduction gearing.
Derivation
From 'gear,' a toothed wheel used to transfer rotation between shafts. A 'geared' propeller uses gears between the engine and propeller to change the speed ratio, just as gears in a car transmission change the relationship between engine speed and wheel speed.
Why Pilots Care
Permits higher engine power output without exceeding safe propeller tip speeds that would create excessive noise, vibration, or structural stress.
Analogy
It is like using the gears on a bicycle. Your legs can move at a comfortable speed while the wheel turns at the speed needed to move the bike efficiently.
Intuition Check
Geared propeller does not mean the propeller blades themselves have gears. It means gears are used between the engine and the propeller shaft.
Example Sentence 1
Because the aircraft has a geared propeller, the engine runs at a much higher RPM than the propeller itself.
Example Sentence 2
Geared propellers let the engine develop full power while keeping blade tips well below supersonic speeds.