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I was just wondering one day about because the 787 uses a wing flex to reduce wing tip vortex, but back in World War 2 they didn't know about wing tip vortex, so then why would it be curved upwards?

B-29 Bomber 3-view

You can see in the middle picture the wing is curved upwards. I see this on a lot of commercial airplanes too like the Boeing 737

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    $\begingroup$ It's not curved, it's just a dihedral angle for stability. $\endgroup$ – DeltaLima Aug 7 '15 at 15:11
  • $\begingroup$ @fooot that's about actual flex, this one is about dihedral. $\endgroup$ – Federico Aug 7 '15 at 15:53
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    $\begingroup$ @fooot I agree, but don't get thrown off course by the wrong assuptions behind the question: 787's wing flex is not there for reducing the wingtip vortex. $\endgroup$ – Federico Aug 7 '15 at 15:58
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    $\begingroup$ raked wingtip is not wingflex $\endgroup$ – Federico Aug 7 '15 at 16:21
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    $\begingroup$ and neither of those are "wing flex". $\endgroup$ – Federico Aug 7 '15 at 17:52
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You are confusing 2 concepts here, dihedral and winglets. What you are showing in the picture is dihedral, which is not a curvature but an angle positive from the horizontal. This angle helps improve lateral (roll) stability in flight. This is nothing new, almost all commercial jets have dihedral. Winglets improve efficiency. A Boeing 787 has both.

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  • $\begingroup$ The raked wingtips on the 787 aren't really winglets but they have the same function. $\endgroup$ – fooot Aug 7 '15 at 15:22
  • $\begingroup$ Yeah winglets are there to reduce wing tip vortex and the 787 has a different system than winglets to reduce wing tip vortex by having the wing curving upwards decreasing the strength of the vortex. The 787 has no winglet $\endgroup$ – Ethan Aug 7 '15 at 15:23
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    $\begingroup$ The original poster is not referencing winglets in their post, or a wing rake. They are referencing that the wings on a 787 are very flexible and bend upward noticeably during flight. That's what he's confusing with the dihedral design. It's flexibility v. structured angle. $\endgroup$ – Jay Carr Aug 7 '15 at 16:10
  • $\begingroup$ I do actually @PeterKämpf as I don't agree on your interpretation of the question. $\endgroup$ – GdD Aug 8 '15 at 12:46

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