3
$\begingroup$

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?

$\endgroup$
19
  • $\begingroup$ What did this question get a downvote for.........? $\endgroup$ – Abdullah Nov 5 '20 at 4:42
  • 1
    $\begingroup$ This question doesn't make sense to me. Taper from where? 'All the way' from what? You can't prevent a wing stall. $\endgroup$ – GdD Nov 5 '20 at 8:30
  • 2
    $\begingroup$ I think the fact the OP is called idonotknowmuchaboutaviation means that we should cut them some slack $\endgroup$ – Dave Gremlin Nov 5 '20 at 11:20
  • 2
    $\begingroup$ 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.) $\endgroup$ – FreeMan Nov 5 '20 at 11:55
  • 1
    $\begingroup$ Does this answer your question? How does an aircraft form wake turbulence? $\endgroup$ – Jan Hudec Nov 5 '20 at 20:31
2
$\begingroup$

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.

$\endgroup$
4
  • $\begingroup$ Skybrary claims, without explanation, that taper weakens tip vortices (penultimate paragraph). Maybe that says more about Skybrary than about aerodynamics. $\endgroup$ – Camille Goudeseune Nov 5 '20 at 21:06
  • 2
    $\begingroup$ @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. $\endgroup$ – Peter Kämpf Nov 5 '20 at 22:56
  • 1
    $\begingroup$ 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. $\endgroup$ – Guy Inchbald Nov 6 '20 at 10:59
  • $\begingroup$ @GuyInchbald sorry I didn't understand what you are saying. $\endgroup$ – idonotknowmuchaboutaviationa Nov 7 '20 at 17:28
2
$\begingroup$

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.

$\endgroup$
2
  • $\begingroup$ 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? $\endgroup$ – idonotknowmuchaboutaviationa Nov 7 '20 at 14:30
  • $\begingroup$ 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? $\endgroup$ – Guy Inchbald Nov 7 '20 at 16:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.