Definition
A turbine installed in the exhaust stream of a reciprocating aircraft engine that captures otherwise wasted energy from the hot, fast-moving exhaust gases and feeds that energy back to the engine crankshaft through a fluid coupling and gear train, increasing total power output without burning additional fuel.
Plain English
A small turbine wheel spun by the engine's exhaust gases. Instead of letting all that hot exhaust energy blow away, the spinning turbine sends extra power back to the engine, giving it more total horsepower.
Context Anchor
Seen in powerplant maintenance discussions for certain high-powered piston engines, especially engines designed to recover extra power from their exhaust flow.
Derivation
Power recovery describes exactly what it does — recovering power that would otherwise be lost out the exhaust. Turbine comes from the Latin turbo, meaning a spinning thing or whirlwind, which fits since exhaust gas spins the wheel.
Why Pilots Care
It increases available horsepower and fuel efficiency by recovering energy that would otherwise be lost out the exhaust.
Intuition Check
Do not confuse a PRT with a device that simply increases intake air pressure. A PRT recovers energy from exhaust flow and feeds it back into engine output.
Example Sentence 1
The Wright R-3350 turbo-compound engine uses three power recovery turbines mounted in the exhaust collector rings to add roughly 550 horsepower at takeoff.
Example Sentence 2
On the turbo-compound engine the PRT added roughly 150 horsepower from exhaust energy alone.