If the drag force is greater than the thrust, the plane decelerates or slows down. When the thrust and drag are equal, the plane maintains an even speed, neither speeding up or slowing down. This is Newton's First Law of Motion: every motion stays in motion, until acted upon by an external force.

Other airplanes, such as jets, have additional control surfaces on the wings, e.g. flaps, to provide additional lift at slower speeds for takeoff and landing. The flaps move together rather than opposite each other, like ailerons.

To land, the pilot reduces the speed, which will reduce the lift. To keep the plane from crashing, the pilot increases the angle of attack and lowers the flap. This changes the lift-to-drag ratios, which allows the plane to slowly descend.

QUESTIONS - BACK

Please send any comments to:
Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov