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On a recent vlog, YouTuber CGP Grey mentioned how much the wing of the plane he was on bent. I understand that wings are designed to bend a little, but what actually causes so much deformation?

Here it's a video of it:

Why does this happen?

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    $\begingroup$ Why does this happen? Because its designed to. $\endgroup$ – Ron Beyer Jun 1 '17 at 21:26
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    $\begingroup$ @Pureferret, the weight of the aircraft it is carrying. $\endgroup$ – Jan Hudec Jun 1 '17 at 22:11
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    $\begingroup$ The wing is quite literally holding the entire weight of the aircraft. Almost every kilogram is being held in the air by those wings! $\endgroup$ – Dan Jun 1 '17 at 22:11
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    $\begingroup$ I've no idea what the superimposed blue line is. It's certainly not the position of the wing when unloaded. $\endgroup$ – David Richerby Jun 1 '17 at 23:23
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    $\begingroup$ This isn't a duplicate. The other question is asking what aspects of the design allow it to bend; this question is what causes the actual bending. $\endgroup$ – David Richerby Jun 1 '17 at 23:27
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Because that wing is a cantilevered beam which is now supporting over half the weight of the jet on it. This causes the wing to flex, much like a leaf spring, when loaded. While fascinating to watch this is benign and designed to do this. In addition, this wing flexure helps to absorb bumps, air turbulence, dampen flutter, maneuvering loadings, etc. much like the coil springs in your car's suspension do. Don't be alarmed to see this. Those wing structures have been tested to far worse loads and conditions that you will ever see on a revenue carrying flight before failure occurs. A 747's wingtips can flex by as much as 12ft up/down during flight. Newer composite wings are capable of much greater flexure.

This was video shot of Boeing's destructive testing on the 777 wing. Note the wingtip flexes by as much as 20ft upward at a loading over 150% that of its design load limits before structural failure occurred.

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