Definition
The actual power delivered by an aircraft engine at its output shaft, measured before any power is lost to the propeller, accessories, or other drivetrain components. It represents the usable mechanical power the engine produces under given operating conditions.
Plain English
The real power coming out of the engine at the shaft that turns the propeller. It is what the engine actually produces, not what the propeller ends up using to push the airplane.
Context Anchor
Seen in propeller and engine performance discussions when comparing engine power with the forward pull the propeller produces.
Derivation
The 'brake' part comes from an old engineering test where a mechanical brake (called a Prony brake) was clamped onto a spinning engine shaft to measure how much force the engine could produce against resistance. That measurement became known as brake horsepower. The term stuck even though modern testing uses different equipment.
Why Pilots Care
Knowing BHP lets pilots calculate available thrust, predict takeoff and climb performance, and understand how much power actually reaches the propeller.
Grounding Statement
BHP is the engine’s usable shaft power before the propeller turns it into motion through the air.
Intuition Check
Do not read “brake” as the airplane’s wheel brakes. Here it means engine power measured by loading the engine with a measuring device.
Example Sentence 1
The engine in this trainer is rated at 180 brake horsepower at 2,700 RPM.
Example Sentence 2
Propeller efficiency charts show how much of the brake horsepower is converted into thrust.