![Picture](/uploads/3/1/1/9/31193767/5827558_orig.jpg)
To overcome drag, airplanes use a propulsion system to generate a force called thrust. The direction of the thrust forces depends on how the engines are attached to the aircraft. In the figure shown above, two of the turbine engines are always located under the wings, parallel to the body, with thrust, acting along the body centreline. On some aircraft, such as the harrier, the thrust direction can be varied to help the airplanes to take off in a very short distance. The magnitude of the thrust depends on many factors associated with the propulsion system including the type of engine, the number of engine, and the throttle setting.