Getting aloft requires more than lift; it also takes thrust. Thrust provides the forward motion needed to sustain lift and counteract drag. It is also used to accelerate, gain altitude, and sometimes to maneuver.

Propulsion is the act of moving or pushing an object forward. The word is derived from two Latin words: pro, meaning before or forward, and pellere, meaning to drive. A propulsion system is an engine that produces thrust to push an object, such as an airplane or rocket, forward.