Airplanes have 4 forces on them. Drag (coming from all directions), lift (coming from below), weightt (pushing it down) and speed (moving it forward). When the lift (which comes from the air pushing the plane up) exceeds the weight of the plane, it flies. The greater the speed, the more air is pushed under the plane. The plane can either have a jet engine or a propeller either way it will still fly aslong as the air is keeping it up