Now that the aerodynamic forces have been examined, exactly how do these forces affect flight? There are four basic forces that control flight: weight, lift, drag, and thrust. Weight is a natural force that pulls the plane toward the ground. Lift is the opposing force that pushes the plane up against weight. Lift is created by the movement of the planes wings through the air. Drag is the force created by the air against the planes forward movement. And thrust, is the force that moves the plane forward opposing drag. Thrust is created by the planes propellers or jet engines.

Lift must be greater than weight, and thrust must be greater than drag in order for a plane to fly. When the opposing forces are equal, i.e. lift=weight and thrust=drag, then the plane flies in level flight. However, if any one of these forces change, the result is a change in the flight of the plane. It goes higher, faster, turns or stalls.

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