Wing
Modern passenger aircraft have wings with flaps that extend when landing. This increases the surface area and curvature of the wing which causes an increase in lift at relative low speeds.
As the flaps are lowered the increase in curvature of the upper surface causes the air to flow over it at greater speeds.

 
Wind tunnel tests show how the flaps increase the speed of the air flowing over the upper surface. The flaps obstruct air flowing over the bottom surface of the wing and cause more air to flow over the upper surface increasing lift even more without increasing the speed of the plane. This is ideal for taking off and landing where the plane must be travelling at safer, slower speeds. View the video on the right (from How An Airplane Flies by Shell 1975).

 
Why are the flaps of the wing not extended when the aircraft is flying at peak altitude and maximum speed?
How do the flaps the protrude from the rear of the wing influence the curvature of hte wing? How does this change the characteristics of the wing?
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