Definition
The ratio of an airplane's available engine horsepower to its total weight, typically expressed as horsepower per pound or pounds per horsepower. It is a measure of how much engine power is available to move each unit of aircraft weight, and it directly influences takeoff performance, climb rate, and acceleration.
Plain English
How much engine power the airplane has for each pound it weighs. More power per pound means stronger takeoff and climb performance; less power per pound means a more sluggish airplane that needs more runway and climbs more slowly.
Context Anchor
Seen in takeoff and climb performance discussions, especially when comparing how quickly different airplanes can accelerate, lift off, and climb.
Derivation
Horsepower is an old unit for measuring power, originally based on comparing an engine’s work rate to the work a horse could do. Ratio means a comparison between two amounts. Together, the term means a comparison between engine power and airplane weight.
Why Pilots Care
A higher value produces stronger climb performance after liftoff and shorter ground rolls, improving safety margins on short fields or at high density altitude.
Analogy
Think of it like power-to-weight in a car. A small engine in a heavy vehicle accelerates slowly; the same engine in a light vehicle feels quick. Airplanes work the same way -- more power per pound of weight means more spirited performance.
Intuition Check
Do not think of horsepower alone as the whole story. The same horsepower can perform very differently depending on how much airplane weight it has to move.
Example Sentence 1
Loaded near maximum gross weight on a hot day, the trainer's horsepower-to-weight ratio dropped enough that the climb rate was noticeably weaker than usual.
Example Sentence 2
Light trainers usually have a favorable horsepower-to-weight ratio that lets them climb steeply right after liftoff.