ABSTRACT
The term propulsion refers to an engine which applies a forward force to the fuselage of an aircraft or spacecraft. The general principle by which propulsion is accomplished is Newton’s Second Law, i.e., air or other gas is set in motion by a propulsion system, and the rate of increase of fluid momentum is proportional to the force applied to it. Since the engine applies the force to the fluid, the reaction force, i.e., the force of the fluid on the engine, is what is called thrust; this is the output of a propulsion system.
