Definition
The turning force produced by an engine and delivered to a rotating shaft, which the propeller converts into thrust. It is the spinning output of the engine — measured as torque applied at a given rotational speed — as distinct from the linear thrust that ultimately moves the aircraft through the air.
Plain English
The spinning power the engine sends to the propeller shaft. The propeller then turns that spinning power into the forward push that moves the airplane.
Context Anchor
Seen in propeller discussions when explaining how engine power is changed into forward pull by the propeller.
Derivation
‘Rotary’ comes from the Latin ‘rotare,’ meaning ‘to turn’ or ‘to spin.’ So rotary power is literally ‘spinning power’ — power delivered as rotation rather than as a straight-line push.
Why Pilots Care
Knowing the difference between rotary power and thrust power helps pilots understand propeller efficiency and performance losses.
Intuition Check
Do not read rotary power as a special kind of electricity or as power from a rotary engine only. Here it simply means power carried by something that is turning.
Example Sentence 1
The propeller converts the engine’s rotary power into the thrust that pulls the aircraft forward.
Example Sentence 2
Propeller efficiency compares thrust produced to the rotary power supplied by the engine.