How Airplane Flaps Work

To adequately understand how airplane flaps work, you first have to understand some airplane and aerodynamic basics. Airplane wings are curved on top and flat underneath. The distance air must travel is subsequently longer across the top of the wing than it is underneath the wing. The air flowing over the top of the wing must therefore move faster in order to keep up with the air underneath the wing. Faster moving air puts less pressure on the top of the wing than the underside, creating “lift.”

Flaps are sections of the wing that can move up, down, or both, depending on the model of plane and style of flaps. Flaps on the main wings are ailerons, while flaps on tail wings are elevators. By raising or lowering the flaps, the pilot can change the airflow over and under the wings to create lift or increase drag. To create lift at take-off, a pilot may not engage flaps at all, depending on the plane, rather allowing the natural aerodynamics of the wings to create the needed lift. However, pilots usually need to adjust the flaps to achieve and maintain the necessary angle needed for take-off.

Pilots use “full flaps” most often when landing. The flaps are used to create drag, which operates on much the same principle as car brakes. By lower flaps on the wings, air underneath the wings must move around the flaps in order to keep up with air from the top of the wing. This slows down the air and increases pressure under the wing. The result is drag, an overall slowing of the plane’s progress, just like brakes on a car. This also causes the nose of the plane to lower and the tail to rise, thus losing altitude.

During take-off, depending on the model of plane and type of flaps, the pilot will use elevators to help pull the nose of the plane up. The elevators (the flaps on rear wings) are raised, giving the air above the wing more area to move across. The air has to move faster in order to still keep up with the air under the wing. Faster air equals less pressure, less pressure on top, more lift. With elevators raised, the nose will pull up while the tail of the plane pulls down, providing the angle needed for take-off, or to increase altitude during flight.

Pilots also use ailerons (the flaps on front wings) to “steer” the plane during flight. If the pilot wants to turn to the right, he will raise the right flap while lowering the left. By raising the right aileron, lift is decreased and the wing pulls down. On the other side, by lowering the left aileron, lift is increased and the wing rises. This creates more drag on the right side and pulls the airplane towards the right. Imagine applying brakes in your car to only the right front wheel. Naturally, the car would pull towards the right side as the left side tries to continue moving forward.  

It takes a great deal of training to fully understand all of the aerodynamic principles necessary to fly a plane. Add to that training the necessary knowledge of differences in plane models and sizes, as well as types of flaps. A pilot must understand each of these principles, as well as possess extensive operating knowledge of any plane he intends to fly. Knowing how the flaps in his individual plane work can make the difference in a safe flight.    

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