How does a huge airliner lift off from the ground and fly through the air? There are two reasons. The first is that, as a plane moves forwards, air hitting the leading (front) edge of the wing separates above and below the wing. Because of the wing's aerofoil shape—curved more on its upper side than on its lower side—air flows over the top of the wing faster than under it. This creates higher air pressure under the wing than above it. This produces an upwards force called lift. The plane will climb into the air if this lift is greater than its weight. The faster the airflow, the greater the lift, which is why the plane must travel very fast along the runway before it can take off. The second reason is that the wings are angled so that their fronts are higher than their rear edges. As they move through the air, a force acts on the undersides of the wings, pushing them, and the plane, upwards.

Maximum lift is needed at take-off and landing, when speeds are slower than when the plane is in the air. Flaps fitted to the wings are used to extend the wing surface and exaggerate its curved profile in order to provide extra lift at these times. When an airliner takes off or lands, the flaps extend outwards at the trailing (rear) edge of the wings. The airliner’s wings may have a layered “skirt” of three flaps with slots in between through which the air is channelled. Hinged flaps at the leading edges of the wings also project forwards to extend the wing surface even more.