What is the relationship between thrust horsepower and shaft horsepower under normal conditions?

The correct answer indicates that thrust horsepower (THP) can never exceed shaft horsepower (SHP). This understanding is rooted in the mechanics of how these two measurements are defined.

Thrust horsepower is a measure of the power produced by the aircraft's engines that contributes directly to generating thrust. It is calculated based on the amount of thrust provided and the speed of the aircraft. On the other hand, shaft horsepower refers to the power available at the engine's output shaft before any losses. This includes the power that is transmitted through the propulsion system and is subject to losses due to factors like friction and heat within the engine and other components.

Since THP directly correlates to the effective power being utilized to propel the aircraft while SHP encompasses the total output from the engine, SHP must be equal to or greater than THP under normal operating conditions. Any conversion process, such as from mechanical energy at the shaft to useful aerodynamic thrust, invariably incurs some losses, meaning that THP cannot exceed SHP. This relationship is fundamental in understanding how power is managed and used in aviation propulsion systems.