Forces of Flight There are four forces involved in the flight of an airplane. They are lift, weight, thrust, and drag. Lift comes from the wings. Weight comes from the mass of the airplane, and the force of gravity pulling down on it. Thrust comes from the engines whether it is a jet engine forcing air backwards, or a propeller pulling the plane through the air. Drag comes from the air resistance as the plane moves through the air. During straight and level unaccelerated flight, thrust equals drag, and lift equals weight.                                                                                                       Up Next: How Planes Control their Direction