Definition
Thrust horsepower is the actual propulsive power delivered by the propeller to move the aircraft through the air. It is the engine's brake horsepower (BHP) reduced by the losses incurred when the propeller converts rotational power into thrust. Because no propeller is 100 percent efficient, THP is always less than the BHP produced at the crankshaft.
Plain English
The useful power that actually pushes or pulls the airplane forward, after the propeller has done its work. It is always less than the power the engine produces, because some power is lost in turning the propeller.
Context Anchor
Seen in adjustable-pitch propeller discussions when comparing engine power to the useful push the propeller produces.
Derivation
“Thrust” comes from Old Norse thrysta, meaning to push or press. Combined with “horsepower,” a unit of mechanical power, the term simply means the pushing power produced — the portion of engine power that actually moves the aircraft.
Why Pilots Care
Affects performance calculations for climb, cruise, and range since only THP produces forward motion.
Intuition Check
THP is not the same as the horsepower the engine produces. It is the horsepower that remains as useful forward push after the propeller has done its work.
Example Sentence 1
An adjustable-pitch propeller allows the pilot to maintain higher thrust horsepower across a wider range of airspeeds than a fixed-pitch design.
Example Sentence 2
Reduced air density at altitude lowered the available thrust horsepower even though engine output remained steady.