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
Airplanes need to slow down to land safely. This helps them to both slow down and remain flying at those slower speeds.
Flaps change the shape of the wing so it can provide more lift, allowing the aircraft to fly slower as it lands.
Those are called flaps. Flaps make the wing bigger which makes planes fly better at low speeds. Planes are at low speeds when taking off and landing.
At higher speeds they retract into the wing because they aren’t needed anymore.
Its takes a lot to stop a plane so the slower you can land, the better. Enter flaps. By changing the shape of the wing, the plane can fly much slowly but it becomes more unstable. You would never want to fly with flaps down unless there was some reason you needed to be so slow you needed them.
So before where the plane needed to be moving at 140mph to stay in the air, now it can do it at 105 and can slow down much easier when it touches down.
Same when you need to take off. A little bit of flaps lets you get off the ground sooner since the speed you lift off will be lower now.
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.
Those are called flaps. Flaps increase the lift produced by the plane’s wings at low speeds, which means the plane can take off and land at lower speeds (thus using less runway). Without flaps, at such low speeds, the plane might be too close to or even below its stall speed (meaning the plane stops flying and starts falling).
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.
Sometimes planes also have them at the front of the wing for the same purpose (of increasing wing surface area). If they are in the front they are called slats
Basically makes the wing generate more lift, and can keep generating lift at slower speeds than when not extended. Good if you want to land as slowly as possible which helps you stop the plane once you’re on the ground. But doing this also adds a lot of extra drag which is why they retract in normal flight.
Put your hand out the car window when your dad’s driving 55. First, make it flat, even with the ground. Then slowly turn your hand up and down. What flaps do is kind of make it so the wind pushes your hand up more. Even when your dad slows down to 45, your hand still gets pushed up. And maybe even down to 35. So what flaps do is make it so the wind pushes the plane up even when the plane is going slower like when it’s landing and lets it have more control at those speeds too.
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