Why does the back of the wing on a commercial airliner extend out during landing procedures? What effect does it have on the aircraft?

Question

Why does the back of the wing on a commercial airliner extend out during landing procedures? What effect does it have on the aircraft?

In: Engineering

Answer 1

Those devices are called flaps. They do several things.

First and foremost they increase the surface area of the wings. It makes them bigger. This allows for a higher coefficient of lift for the same angle of attack. They also increase the camber of the wing which again allows for a higher coefficient of lift for the same angle of attack.

The TLDR of is it that flaps make the wing bigger which allows the plane to fly slower while maintaining a safe margin above the stall speed.

They also have a perhaps unintuitive bonus of creating drag. Airliners are designed to be very slippery which makes for less fuel burn. But that also means that slowing down when trying to land can be a bit trickier. That’s why the added drag that flaps create can also be beneficial.

To give you some numbers, a typical landing speed for most airliners is in the 120-150 knot range. Without flaps you’d be looking at 170-190ish.

Edit: On most airliners (basically everything but the CRJ-200) there are also devices on the front of the wing that extend out in conjunction with the flaps. They’re call slats and have a similar function as the flaps.