The Rolls-Royce Gnome engine is a turboshaft engine used in various helicopters, such as the Westland Sea King. The propulsive efficiency of any jet or turboshaft engine, including the Rolls-Royce Gnome, is a measure of how effectively the engine converts the thermal energy of combusted fuel into useful thrust or shaft power.
The propulsive efficiency is a crucial parameter in evaluating the performance of a rocket engine, indicating how well it converts propellant energy into useful thrust. Practical rocket engines often have propulsive efficiencies less than 100% due to factors like incomplete combustion, heat losses, and other inefficiencies in the propulsion system.
The propulsive efficiency () is defined by the following formula:
where,
- is the propulsive efficiency,
- is the thrust produced by the rocket engine,
- is the effective exhaust velocity of the rocket,
- ṁ is the mass flow rate of the propellants,
- is the specific impulse of the rocket engine,
- g0 is the acceleration due to gravity (approximately 9.81 m/s²).