Propulsive efficiency
In aerospace engineering, concerning aircraft, rocket and spacecraft design, overall propulsion system efficiency η {\displaystyle \eta } is the efficiency with which the energy contained in a vehicle's fuel is converted into kinetic energy of the vehicle, to accelerate it, or to replace losses due to aerodynamic drag or gravity. Mathematically, it is represented as η = η c η p {\displaystyle \eta =\eta _{\mathrm {c} }\eta _{\mathrm {p} }} , where η c {\displaystyle \eta _{\mathrm {c} }} is the cycle efficiency and η p {\displaystyle \eta _{\mathrm {p} }} is the propulsive efficiency.