The Lockheed PV-1 Ventura is a World War II-era patrol bomber aircraft. It typically used radial piston engines, such as the Pratt & Whitney R-2800 Double Wasp engine. For piston engines, the propulsive efficiency is commonly measured by the thermal efficiency of the engine. The thermal efficiency is defined as the ratio of the useful work output to the heat input.
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).