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Wingtip vortices are created by, well, wingtips. These vortices create drag. One of the approaches to reducing this drag is taper the wing,

enter image description here source

enter image description here source

Will eliminating the wingtip, as on the lower left, eliminate these vortices, and thus eliminate induced drag? Why or why not?

Abdullah is not an Amalekite
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idonotknowmuchaboutaviationa
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  • What did this question get a downvote for.........? – Abdullah is not an Amalekite Nov 05 '20 at 04:42
  • @Abdullah I would guess the fact that it is not really clear. – Federico Nov 05 '20 at 06:53
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    This question doesn't make sense to me. Taper from where? 'All the way' from what? You can't prevent a wing stall. – GdD Nov 05 '20 at 08:30
  • Do you mean taper to a point so that the tip chord is zero? Could be stated a bit more clearly-- – quiet flyer Nov 05 '20 at 09:36
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    I think the fact the OP is called idonotknowmuchaboutaviation means that we should cut them some slack – Dave Gremlin Nov 05 '20 at 11:20
  • all the way from the ending portion of the wings. – idonotknowmuchaboutaviationa Nov 05 '20 at 11:42
  • yes, I mean taper to a point so that the tip chord is zero or near zero but the taper is not uniform. the taper increases a lot at the ending portions of the wings. kind of like a elipse wing. – idonotknowmuchaboutaviationa Nov 05 '20 at 11:54
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    Post a picture of a wing "ending portion" and then sketch onto it (MS Paint or similar is just fine) a rough approximation of what you're thinking. As they say, a picture is worth 1000 words, and, at the moment, your words are failing to accurately convey to others what you're thinking. (Doesn't mean you're thinking wrong, just that you're not explaining yourself well enough.) – FreeMan Nov 05 '20 at 11:55
  • @DaveGremlin we don't have a problem with not knowing, or we would not be here, but we need to understand what the question is about to answer it. and if it is not clear we can't answer it, that's why comments and the edit functionality exist. if the question is ambiguous, there is no slack to cut. – Federico Nov 05 '20 at 12:09
  • @Federico sorry just edited the post but still I guess it looks crappy – idonotknowmuchaboutaviationa Nov 05 '20 at 12:12
  • @idonotknowmuchaboutaviationa the "crappyness" is not a problem, but it would help if you could highlight (maybe with another color) what you want to look at specifically. – Federico Nov 05 '20 at 12:18
  • Pretty sure he is asking about the difference between a straight "Hershey bar" wing, and one shaped more like a Spitfire, that ends in a point. Why are we not getting that? – Michael Hall Nov 05 '20 at 16:43
  • @MichaelHall Possible, but I doubt that. If you're right, then of course, the answer would be "It has been done, it reduced vortex drag, but we don't like doing that because it's too hard to build wings that rounded" – Abdullah is not an Amalekite Nov 05 '20 at 17:04
  • @Abdullah, well the person asking the question is mixing up wing stall, tip stall, and vortices, but from the title question alone it should be clear that he/she is fishing for pros and cons of a wing tapering to a point versus one that has a "clipped" end. I have seen more poorly worded questions decoded adequately by experts who state any presumptions and clarify the question in the answer. – Michael Hall Nov 05 '20 at 17:24
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    Does this answer your question? How does an aircraft form wake turbulence? – Jan Hudec Nov 05 '20 at 20:31
  • I believe https://aviation.stackexchange.com/questions/8877/ explains all that needs to be explained already. – Jan Hudec Nov 05 '20 at 20:32
  • @Abdullah that is not exactly what I am asking. I think the wing on the lower left would be prone to tip stall because of the high taper. what I want to know is why can't the wing have moderate taper and the ending portion of the wings be like that of elliptical wing or pointed tip wing? from what I understand complete elliptical wings are not formed in large numbers because they are difficult to manufacture. doing what I am saying should solve the problem of cost right? – idonotknowmuchaboutaviationa Nov 06 '20 at 03:32
  • @idonotknowmuchaboutaviationa a trapezoid with a circular tip? In that case, the answer is definitely yes, it does reduce induced drag, probably a liiiiiiittle less than the ellipse. As for manufacturing, I cannot say, though it probably would be easier. – Abdullah is not an Amalekite Nov 06 '20 at 16:03
  • @Abdullah then why are planes not made that way. if commercial airliners were made that way the size of the wingtips can be reduced or there need can be completely eliminated which would decrease drag. – idonotknowmuchaboutaviationa Nov 07 '20 at 06:52

2 Answers2

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One of the approaches to reducing this drag is taper the wing

No, not at all. The vortex strength depends on the lift at the center wing. This strength invariably tapers to zero towards the wingtip, regardless of the wing's geometric taper ratio. The taper ratio will only change the local gradient, not the absolute decline in vortex strength. In the end, what happens at the tip is insignificant for the shape and strength of the wake.

Peter Kämpf
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  • Skybrary claims, without explanation, that taper weakens tip vortices (penultimate paragraph). Maybe that says more about Skybrary than about aerodynamics. – Camille Goudeseune Nov 05 '20 at 21:06
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    @CamilleGoudeseune Nonsense like this gem: "Although there must always be at least some induced drag because wings have a finite thickness …" confirms your verdict. More nonsense: "Well designed winglets can prevent about 20% of the airflow spillage at the tip - and therefore 20% of the induced drag." Whoever wrote this had no clue. – Peter Kämpf Nov 05 '20 at 22:56
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    I suppose one can argue that the tip vortex is just a component of the overall trailing vortex; a tip can exert downforce with its local vortex reversed, but it makes no difference to the overall picture. Winglets do reduce tip vortex strength and they do reduce induced drag, so any kind of blanket statement/denial is dangerous. – Guy Inchbald Nov 06 '20 at 10:59
  • @GuyInchbald sorry I didn't understand what you are saying. – idonotknowmuchaboutaviationa Nov 07 '20 at 17:28
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The relation between tip vortex strength and induced drag is not a simple one and the suggested advantage is not realised in practice. Meanwhile, a pointed tip has other problems. Some that occur to me:

If the wing has a constant aerofoil profile then a pointed tip will tend to stall first at high angles of attack. This creates turbulence over the ailerons and reduces pilot control at a critical moment. Changing the aerofoil such as twisting downward or "washout" reduces the problem. For example the de Havilland DH.88 Comet racer of 1934 has a fairly pointed wing with no washout - and a notoriously vicious wing-drop in the stall. American replica N88XD has around 2 or 3 degrees (I forget exactly) of washout to try and ease this, with the same being included in the restoration of Comet G-ACSP Black Magic.

But reprofiling the outer section changes the lift distribution to a less efficient one. Widening the tip section can help restore efficiency, as well as further reducing the stall problem.

Structurally, a fine point is both prone to damage and difficult to fit a robust aileron hinge inside. The ailerons have to be moved inboard to a wider part of the wing, which reduces their effectiveness.

The point contributes little lift but significant moment and physical width, so removing it improves aileron and gust responses and eases ground handling, without any significant lift penalty.

Guy Inchbald
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  • someone had edited my question. I want to know is why can't the wing have a moderate taper and the ending portion of the wings be like that of elliptical wing or pointed tip wing? from what I understand complete elliptical wings are not formed in large numbers because they are difficult to manufacture. doing what I am saying would reduce the possibility of tip stall, won't it? – idonotknowmuchaboutaviationa Nov 07 '20 at 14:30
  • I see what you mean. Wing tips are often rounded, rather than cut off square. But cutting at angles with a stubbier pointed tip, as in your original drawing, still has several of the problems of the pointed tip that I mentioned. Does that help? – Guy Inchbald Nov 07 '20 at 16:26