# If no low-speed compromises were made, what would an ideal Mach-3 wing look like?

Things like the Concorde and Tu-144 and many other supersonic craft need a wing that has good high-speed and good low-speed performance. After all, it needs to be able to take-off and land. Good low-speed performance is achieved with things like flaps, slats, and the wing shape itself.

But let's just say, hypothetically, you don't need good low-speed performance at all. So no such compromises in the wing shape. What would an ideal Mach-3 wing look like?

The goal is to have a wing with the highest lift-to-drag ratio at Mach 3.

I chose Mach-3 because that seems to be the limit on what jet aircraft have been put into production (MiG-31, SR-71) (which does not count experimental aircraft).

I'm interested in conventional designs, not things like the Blended-Wing-Body. So presumably this ideal aircraft would look similar to the Concorde or Tu-144.

Some things I've noted over the years:

• The X-15 had a "wedge" shaped vertical stabilizer with a flat back. You can see it in photos. They said it was because the flat back produces more stability for less drag at high mach. Would a mach-3 wing also have a thick, flat trailing edge?

• Ogival Delta seems very popular for large sophisticated supersonic aircraft. Never understood why that is exactly, since the pure delta triangle is easier to manufacture and bear loads easier.

• The XB-70 Valkyrie had folding wings to give it anhedral, supposedly to capture the shockwave and thus be a wave-rider, which is more efficient. I've noticed the Concorde also has slightly drooping wings near the tips.

Note: I don't need a complete 3D model of the wing shape. I'm more interested in things like what planeform it has, what anhedral/dihedral if any, etc.

• I'm not an aerodynamics engineer, but I suspect there's not a single "ideal" wing. Even if you did the airspeed, there are other parameters you need to trade off between. Do you want maneuverability, fuel efficiency, payload... – yshavit Aug 13 '17 at 15:28
• @yshavit Ah, don't need maneuverability. Was thinking simply to get the max lift-to-drag ratio. will edit. – DrZ214 Aug 13 '17 at 21:04
• I think this is a valid question; we know for subsonic flight the ideal wing is infinitely long and narrow, so how would it look for supersonic flight? – Sanchises Aug 13 '17 at 21:08
• Looking beyond aircraft design into the design of large missiles may give a good indication of what such a craft might look like. Those are after all vehicles designed for such speeds, reached after a very short boost phase after launch which is typically performed during ballistic flight rather than controlled. – jwenting Aug 14 '17 at 9:02

One Mach 3 design which did not care about low speed characteristics was the Lockheed Q-12 / D-21 reconnaissance drone, which used a Marquardt RJ-43 ram jet for propulsion and had a flight Mach number of up to 3.5. It was initially air launched from the back of an A-12 / M-21 and crashed when fuel ran out. The purpose was deep penetration of hostile airspace to perform photographic reconnaissance in pre-satellite days. When later the launch aircraft was switched to the B-52, the D-21 needed an enormous booster to bring it up to its cruising speed of Mach 3.35.

This should be closest to a uncompromising Mach 3+ design; however, it drew massively on the aerodynamic work with the A-12 / SR-71, so probably the solution space was restricted from the start.

D-21 three side view (picture source). The anhedral was needed to compensate for the rolling moment of the high tail in sideslip. An even more uncompromising design would had used a smaller vertical and an equal fin on the lower side and no anhedral. The lower side fin, however, would had made the air launch from the back of the A-12 impossible.

All surfaces had sharp trailing edges. A wedge-like cross section like the tail of the X-15 only starts to make sense at speeds in excess of Mach 5 when using drag for directional stability is more effective than adding more tail surface.

• Wow that's quite a drone. Flight ceiling 29 km, speed Mach 3.35, range 5,550 km. My only concern is that stealth shape may have necessitated some compromise in the wing shape. I read the wiki article but all it had to say was The Q-12...used key technology from the A-12 project, including...radar cross-section reduction design features. – DrZ214 Aug 14 '17 at 2:47
• heh, so this ridiculous toy from my childhood was not as ridiculous! 3djoes.com/uploads/1/3/3/9/13396852/5617750_orig.jpg – Kevin Milner Dec 6 '17 at 18:39