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In order to have laminar flow over the wings which helps in friction drag reduction, a number of airfoil designs have been proposed from the past to the latest 737 winglets.

But if we design a laminar flow wing for supersonic aircraft, the wing should be very thin which will end up with stall and speed related problems.

So, I am curious that if we add winglets on supersonic aircraft, will it be helpful other than for its drag? If so what are all the problems we need to consider?

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    $\begingroup$ What initial research have you done, casually or formally, before asking this question? $\endgroup$ – KorvinStarmast Jul 24 '17 at 23:28
  • $\begingroup$ XB70 has a pretty big "winglet", and Mig-31D(anti-satellite variant) has a small one. But those are more for vertical stability (effectively increasing the area of vertical stabilizer). $\endgroup$ – user3528438 Jul 25 '17 at 2:37
  • $\begingroup$ @KorvinStarmast. Actually when I was doing some research on cranked delta wings for the Supersonic Business Jet, I came across the word "Boeing 737 winglets". Thats how I ended with this question. $\endgroup$ – Sathiya Nathan Jul 25 '17 at 5:42
  • $\begingroup$ Could you please summarize that and put it into your question? $\endgroup$ – KorvinStarmast Jul 25 '17 at 16:03
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This has been (and thus can be) done and there is some current research on it as well. The XB-70 Valkyrie had dropping wing tips that added stability at high Mach speeds as well as allowed the plane to ride on its own shock wave. It also effected trim drag,

The repositioned wingtips also reduced the area behind the airplane's center of gravity, which reduced trim drag. The downturned outer panels also provided more vertical surface to improve directional stability at high Mach numbers.

You can check out this podcast episode that interviews some of the people at NASA doing various research projects including wingtip control systems and other interesting applications in that space.

You may find some info in this book on supersonic wing theory.

This thread (and you know how accurate the internet is) has some interesting points on the matter.

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Research has been carried out into this area, for instance the Computed Fluid Dynamics tests that NASA carried out on highly swept wings in supersonic flow. They reached the conclusion that winglets can have positive effect on lift/drag, but it is of course highly dependent on the wing shape and profile. From the report:

  • winglets can be designed and aligned in supersonic flow such that little or no performance penalty will be incurred relative to a wing of equal projected span.
  • alteration of winglet length, sweep, and camber may not be as critical as the toe angle or the orientation of the winglet relative to the wing.
  • winglets with negative dihedral and toe in were found to typically outperform similar winglets with positive dihedral.

One of the configurations studied is below: NACA 1402 base wing with 65 deg leading edge, and the best winglet found. One of the recommendations made is to put further research into dual use of winglets, if they are useful for yaw control at supersonic speeds.

enter image description here

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The projected European spaceplane Hermes did indeed have winglets. Those were needed for drag reduction in the landing phase. So they did not help at supersonic but at subsonic speed.

Without the winglets the energy would had bled off too quickly during rotation so the descent could not be stopped in simulations. The spaceplane without winglets was in essence impossible to land. Only by lifting the subsonic L/D above 5 with the help of the outward canted winglets did the simulation result in smooth landings.

Artist impression of Hermes spaceplane

Artist impression of Hermes spaceplane (picture source)

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Even if they can, would they be practical? Many combat aircraft use the wing tips to carry short range missiles or other light weight stores. You'd lose those hardpoints. Plus you'd introduce more complexity into the wing, especially if you rely on them for stability, making the aircraft more vulnerable.

Also, I've not done the calculations but many combat aircraft have wings that have a large taper, winglets may very well be only marginally effective with such a wing design.

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  • $\begingroup$ But how about in case of Supersonic Business Jet other than fighter jets? $\endgroup$ – Sathiya Nathan Jul 25 '17 at 6:28
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    $\begingroup$ @SathiyaNathan the effectiveness of winglets depends at least in part on the wing design. A long narrow wing is what we see winglets used on most often. If your business jet had such, they might work, especially during the subsonic phase of its flight, which would probably be a lot of the flight profile as most countries prohibit supersonic overflight except over open bodies of water (sea, maybe very large lakes). $\endgroup$ – jwenting Jul 25 '17 at 6:30
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There are 3 types of drag:

  1. Friction drag
  2. Induced drag
  3. Wave drag

In low speed flights, first two are responsible for the total drag created. Wave drag is usually neglected as it is very less compared to others. Winglets are provided to reduce the induced drag.

Now, in case of the supersonic aircrafts, wave drag creates most of the total drag as the shock wave creates enormous drag. Friction drag and wave drag are proportional with the velocity, and induced drag is inversely proportional to the velocity of flight. In case of supersonic flight, due to the velocity, the induced drag is going to be very small that it is always neglected.

So yes winglets are possible on a supersonic aircraft, but are rather decoration then useful. And most supersonic aircraft are military fighter jets, and fuel efficiency in the military is not a priority

By the way, this answer is from a Quora question found with a quick Google search.

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    $\begingroup$ Are induced drag and wave drag not normal? $\endgroup$ – Koyovis Jul 25 '17 at 1:31
  • $\begingroup$ Let me change it to General dag $\endgroup$ – Hugo Woesthuis Jul 25 '17 at 1:47
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    $\begingroup$ Is he a high ranking military officer? A specific term would be more appropiate, like friction drag. $\endgroup$ – Koyovis Jul 25 '17 at 1:58
  • $\begingroup$ I will change it, thnx for the tip ;) $\endgroup$ – Hugo Woesthuis Jul 25 '17 at 2:35
  • $\begingroup$ But anti-satellite variant of Mig-31 (and XB70?) does have winglets. So what about other use cases than drag reduction? $\endgroup$ – user3528438 Jul 25 '17 at 2:39

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