Aaron Crowl said:
One of the main problems with the Concorde was simply the noise. A colleague told me stories about working at La Guardia. He told me that a hangar a mile away from the takeoff of a Concorde would shake and rattle. That had to be so inefficient. I always wondered if anyone in the supersonic industry tried to design a high-bypass engine capable of running at supersonic speeds. That would be quieter and more efficient.
The engine design is much less of a problem than wing design. The problem with supersonic transport aircraft is that they must necessarily spend a large portion of time flying at subsonic speeds during takeoff and landing and, given flight rules, any time they are near or over land. Drag on a supersonic wing is governed pretty much entirely on its leading edge shape and thickness. The thinner and sharper it is, the less drag it will experience. On a subsonic wing, it is a more complicated problem, but generally, thin, sharp wings are not only not the most efficient design, but also a very
inefficient design. In essence, it means that the Concorde had supersonic wings but had to spend a lot of time at subsonic speeds, and it needed a while lot of thrust during those periods in order to maintain sufficient lift. The fact that it also used turbojets (as opposed to turbofans) compounded the issue.
At any rate, building a high-bypass turbofan that can go supersonic would be quite diffecult since the drag penalty would be enormous. Supersonic drag is determined in large part by frontal area and how blunt an object is. High-bypass turbofan essentially looks like a very large blunt object flying through the air and its extra drag would almost certainly outweigh its efficiency benefits. That's why you see the engines hidden inside of the structure in many supersonic planes so that they can be hidden behind relatively small, sharp intakes. At the very least, though, you could probably use a low-bypass turbofan that is still small enough to be integrated into the body a little bit better. That would still be an improvement. This is what most modern supersonic business jet concepts do, such as the Aerion AS2 (which, incidentally, also takes steps to try to overcome the wing issue as well).
Aaron Crowl said:
Gulf stream is working on a supersonic model. Their idea is to extend a boom from the tip of the nose during supersonic flight. The boom shapes the bowshock for better flight control and lower noise.
The quiet spike that Gulfstream patented is one approach. There are others as well, such as designing the nose tip to help shape the bow shock such that it is more spread out and therefore the boom is weaker. It's an interesting problem.
I should also note that my above statement in an earlier post about the boom generated by wings being insignificant is not necessarily true. For example, if the wings are not entirely within the shock generated by the nose, then they will be exposed to the full incoming Mach number of the free stream and likely create a stronger shock than the nose cone does. Additionally, depending on the sweep angle of the wing and the strength of the shock from the nose, the wings may still contribute significantly to the boom.
Also, it should be noted that the Busemann biplane, about which the original article posted by
@wolram was written, only results in no shocks projected away from the wing when it is at zero angle of attack. It also turns out that it produces zero lift in this configuration. In that configuration, it does indeed have very low drag and no outward-projected shock waves. However, if you wanted to actually use it to provide lift to a plane, then it will still generate a shock that would likely be experienced on the ground.
