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A 3D wing cannot achieve the same high lift/drag ratio (more than a hundred sometimes) displayed by a 2D profile (airfoil section). This is due to 3D effects like spanwise flow, wingtip losses(vortices) etc.

What is the lift-to-drag ratio on a wing between endplates? Can you achieve the same ratios as a 2D section?

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  • $\begingroup$ I dimly remember reading years ago that to get close to that kind of effect from an end plate it has to extend about for about a chord length beyond the profile all the way around. In other words, it would be 2 chords +wing thickess high, and 3 chords long. It would make a nice billboard. $\endgroup$ – John K Jul 11 '19 at 19:12
  • $\begingroup$ thx. under those circumstances(and assuming small enough tip clearances) the wing would behave as "extrusion" of the 2D profile, correct? in other words, no wingtip losses, minimal spanwise flow etc. $\endgroup$ – toshi ba Jul 11 '19 at 19:54
  • $\begingroup$ @JohnK But then you'll have an increased interference drag and skin friction drag. Maybe you will recover the 2D lift slope, however? $\endgroup$ – JZYL Jul 11 '19 at 20:20
  • $\begingroup$ Yes I recall that you get close to it theoretically but the drag of this giant sheet on each wing tip negated any benefit... which is why, as usual with these types of devices that only have a theoretical benefit, end plates are just about never used, and when you do see them they are usually too small to really do any good. $\endgroup$ – John K Jul 11 '19 at 20:30

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