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

Airplanes need to go a certain speed or they “stall” because there’s no lift- they literally start falling out of the sky.

For takeoff and landing, the flaps are extended, which has the effect of decreasing the stall speed by increasing the lift.

For cruising, the flaps are retracted because the plane is going plenty fast and havine them increases drag and reduces efficiency.

There’s been several crashes due to not having the flaps extended at takeoff. NWA 255 crashed in Detroit killing 148 out of 149 people when the pilots took off without the flaps exteneded and the plane stalled. There’s a warning that sound when if you try to takeoff with improper flaps, but the pilots most likely silenced the warning by pulling the circuit breaker, since it annoyed them going off when they were just taxiing rather than actually taking off.

It’s easier to land without flaps because you already have the necessary speed, you just have to come in much faster than normal so you don’t dip below your stall speed.