eli5 why are flaps extended during takeoff if they slow down the plane?
In: Engineering
Because the plane is designed that way.
Whys the plane designed that way?
Because the wing shape that is efficient for high speed flight is not the same as the wing shape for low speed flight. You’d have to fly faster, and use more runway, to takeoff without the flaps.
Why not use them all the time then?
At high speed, the wing generates lift easily, and the flaps would generate additional drag, costing efficiency – and that inefficiency has a real dollars per mile cost, in the form of fuel.
Lift is proportional to the square of your airspeed, if nothing else changes. Slowing down costs lift. You can gain it back in a variety of ways – tilting the plane a bit more nose up, so the wing attacks the air a little more aggressively, or extending the flaps – modern airliner flaps both increase the wing area, and increase wing camber, and both of these things improve lift. Effectively they allow you to become airborne at lower speeds, and to remain airborne at lower speeds.
That’s good for tyres, and great for airliners, as there are plenty of short runways, and the less runway you need, the safer it is.
You can build an aircraft without flaps. Many aircraft with them, can takeoff without using them.
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