Definition
The ratio of useful thrust power produced by an engine-propeller (or engine-jet) system to the total power the engine delivers. It measures how effectively the engine's output is converted into forward motion of the aircraft, and it varies with airspeed and the speed of the air or exhaust accelerated rearward by the propulsion system.
Plain English
How much of the engine's power actually ends up pushing the airplane forward, rather than being wasted. A higher number means more of the engine's effort is turning into useful movement.
Context Anchor
Seen in turboprop engine discussions when comparing how propellers and jet engines turn engine power into forward motion.
Derivation
From Latin propellere, 'to drive forward.' Efficiency comes from Latin efficere, 'to accomplish.' Together: how well a system accomplishes the job of driving the aircraft forward.
Why Pilots Care
Higher propulsive efficiency improves fuel economy and range at the lower speeds where turboprops operate most efficiently.
Grounding Statement
A propeller is more propulsively efficient when it gives a large amount of air a modest push, rather than wasting energy by throwing a small amount of air backward very fast.
Intuition Check
Propulsive efficiency does not mean fuel economy by itself. It means how well engine power becomes useful forward push.
Example Sentence 1
A turboprop reaches its best propulsive efficiency at moderate cruise speeds, which is why it is well suited to regional operations.
Example Sentence 2
When comparing engine types the handbook notes that propulsive efficiency drops at higher speeds for propeller-driven aircraft.