Definition
A reciprocating aircraft engine that recovers energy from its exhaust gases by routing them through one or more power-recovery turbines (PRTs) mechanically coupled back to the engine crankshaft, adding power without burning extra fuel.
Plain English
A piston engine that uses small turbines spun by its own exhaust to feed extra power back into the crankshaft, getting more horsepower out of the same fuel.
Context Anchor
Seen in aircraft engine design, powerplant maintenance, and discussions of high-power piston engines that use exhaust energy more efficiently.
Derivation
‘Turbo’ comes from the Latin turbo, meaning a spinning or whirling thing, referring to the exhaust-driven turbines. ‘Compound’ comes from the Latin componere, meaning ‘to put together’ — here it means combining two power sources (piston and turbine) into one engine.
Why Pilots Care
It delivers higher horsepower and better fuel economy from the same engine size, useful for long-range or high-altitude piston operations.
Grounding Statement
Picture the exhaust leaving the engine still moving fast and hot; a turbo-compound engine catches some of that leftover energy and turns it into more shaft power.
Intuition Check
Do not confuse a turbo-compound engine with a turbocharged engine. A turbocharger uses exhaust energy to force more air into the engine; a turbo-compound system uses exhaust energy to help turn the crankshaft.
Example Sentence 1
The Wright R-3350 turbo-compound engine used three power-recovery turbines to extract additional horsepower from its exhaust.
Example Sentence 2
During preflight the mechanic pointed out the power recovery turbines that help the turbo-compound engines run more efficiently.