Definition
The actual power an aircraft propeller delivers to move the airplane through the air, calculated from the thrust the propeller produces and the airplane's forward speed. Thrust horsepower is always less than the engine's brake horsepower because the propeller cannot convert all of the engine's shaft power into useful thrust — some is lost to propeller inefficiency, slipstream turbulence, and friction.
Plain English
How much of the engine's power actually ends up pushing the airplane forward, after losses in the propeller.
Context Anchor
Seen in aircraft performance, propeller efficiency, and engine power discussions.
Derivation
Thrust comes from the Old Norse 'thrysta', meaning to push or force. Horsepower was coined by James Watt to compare steam engine output to the work of draft horses. Together the term means the pushing power the propeller actually delivers — distinct from the power the engine produces at its shaft.
Why Pilots Care
Knowing thrust horsepower shows how much engine power is truly available to move the airplane, which affects takeoff distance, climb rate, and propeller selection.
Grounding Statement
If the propeller is pushing the airplane forward, thrust horsepower is the rate at which that push is doing useful work.
Intuition Check
Do not read thrust horsepower as the engine’s listed horsepower. It means the useful forward-pushing power after the engine’s power has been turned into thrust.
Example Sentence 1
Even though the engine was producing its full rated brake horsepower, the thrust horsepower was lower because the propeller was only about 80 percent efficient.
Example Sentence 2
During the takeoff roll the same engine produced only 120 thrust horsepower because propeller efficiency is lower at slow speeds.