Can a supersonic aircraft have winglets?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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 (picture source)

Answer 4

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.

Answer 5

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.

Answer 6

The North American XB-70 Valkyrie was a Mach 3 bomber which had variable-geometry winglets. Their purpose was most unusual in that they turned vertically down to help reduce drag during supersonic cruise, and returned to horizontal to increase the wing area for takeoff and landing.

The wing of the Valkyrie was a waveriding delta. The engine intakes formed a central underwing body which created a strong shock wave. The wing leading edge was angled such that at cruising speed the shock front ran out along the wing just behind it. All the wing behind it was subject to an increase in air pressure, creating a substantial amount of extra lift and improving the lift/drag ratio of the wing. When the shock met the downturned winglets, it was reflected back under the rear of the wing creating even more lift and improving cruise efficiency even more.

The winglets also provided additional directional stability just when it was needed, as this normally reduces at high speeds.