Thrust Horsepower

Thrust horsepower is the portion of an engine’s output that actually becomes useful propulsive power after the propeller’s losses are taken into account. A propeller cannot convert all brake horsepower into forward thrust because some energy is lost to blade drag, slip, and moving air around the propeller disc. Multiplying BHP by propeller efficiency gives the real thrust-producing power available at that operating condition.

Use this when you need to estimate how much of an aircraft engine’s shaft power is being turned into forward thrust, especially for propeller-driven aircraft. It is useful in performance calculations, engine comparisons, and estimating takeoff or climb capability.

• Using efficiency as 78 instead of 0.78
• Confusing brake horsepower with thrust horsepower and treating them as the same value
• Assuming propeller efficiency is always constant instead of changing with airspeed and operating conditions