This page is intended for college, high school, or middle school students.
For younger students, a simpler explanation of the information on this page is
available on the
The amount of lift generated by a wing depends on the shape
of the airfoil, the wing area, and the
During takeoff and landing the airplane's velocity is relatively
low. To keep the lift high (to avoid objects on the ground!),
airplane designers try to increase the wing area and change the
airfoil shape by putting some moving parts on the wings' leading and
trailing edges. The part on the leading edge is called a slat,
while the part on the trailing edge is called a flap. The
flaps and slats move along metal tracks built into the wings. Moving
the flaps aft (toward the tail) and the slats forward
increases the wing area. Pivoting the leading edge of the slat and
the trailing edge of the flap downward increases the
effective camber of the airfoil, which
increases the lift. In addition, the large aft-projected area of the
flap increases the drag of the aircraft.
This helps the airplane slow down for landing.
The next time you fly in an airliner, watch the wings during
takeoff and landing. On takeoff, we want high lift and low drag, so
the flaps will be set downward at a moderate setting. During landing
we want high lift and high drag, so the flaps and slats will be fully
deployed. When the wheels touch down, we want to decrease the lift
(to keep the plane on the ground!), so you will often see spoilers
deployed on the top of the wing to kill the lift. Spoilers create
additional drag to slow down the plane.
Parts of an Airplane:
Flaps and Slats:
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