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.
Let's investigate how the flaps and slats work by using a Java
You can deploy the flaps and slats by using the slider at the bottom.
You can download your own copy of this simulator for use off line. The program
is provided as Flaps.zip. You must save this file on your hard drive
and "Extract" the necessary files from Flaps.zip. Click on "Flapview.html"
to launch your browser and load the program.
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.