Is hypersonic flight possible with a Busemann's Biplane?

Question

The modifications to the Busemann's Biplane design reported in this article have proven that it is possible to design a modified Busemann's Biplane wing design that actually produces lift at supersonic speeds. Is it then possible to fly the same plane at hypersonic speeds of say Mach 10 (and ground speeds of above 10,000 km/h)? What are the other technical limitations?

The engines can achieve it and the air frame could be cooled, is noise once again an impediment at those speeds? Are there any effects on the human body for flying that fast given gradual acceleration? What about fuel, is it fuel efficient? Do we have a type of fuel that could power today's engine designs at those speeds given the complexities of using hydrogen?

Answer 1

Why Mach 10? Would Mach 3 or 4 not be enough? See here and here and here for the complications which arise at higher speeds.

The linked article is full of misrepresentations - of course will the Busemann biplane create lift at sub-supersonic speed (what is that, anyway? I read it as subsonic speed). Give it a proper subsonic airfoil and it will do so just like any other biplane, and even with the trapezoidal airfoil it will do so, albeit with more drag. It will also create lift and drag if operated at a proper angle of attack below its design speed (maybe that is meant by sub-supersonic speed, but the author never clarifies that).

Busemann biplane as shown in the linked article (source)

Did you note that the shock lines in the graph only occur between the two wings? That means that on the outer surfaces you will only see ambient pressure. The pressures internally cancel each other, and the result is that the Busemann biplane will not create any lift at its supersonic design speed in order to do its magic. As soon as it starts to create lift, it needs to create shock waves on the outside which will invariably be audible. That the researchers at Tohoku claim them to be 85% weaker is easy if they omit to mention to what they compare it.

Now look at the bulky passenger compartment on the top wing. This is clearly not optimised for supersonic travel (please compare it to the fuselages of the Concorde or the Tu-144 to get an idea what works).

No, this article is just utter nonsense.

Answer 2

The idea is certainly valid.

Busemann's original design could not generate lift, but modern variations can. Here are just three recent papers on how it can be done:

• Kusunose, Matsushima and Maruyama. (2011). "Supersonic biplane — A review". Progress in Aerospace Sciences 47. pp.53–87.
• Wu, Jamieson and Wang. (2012). "Adjoint based aerodynamic optimization of supersonic biplane airfoils". Journal of Aircraft, Vol.49, No.3. May-June 2012. pp.802 ff.
• Ma, Wang, Wu and Ye. (2020). "Avoiding Choked Flow and Flow Hysteresis of Busemann Biplane by Stagger Approach" (paywalled). Journal of Aircraft, Volume 57, Number 3, May 2020.

Wave drag has two causes, one due to the bulk or form of the plane and the other due to the lift generated.

The Busemann concept can eliminate form shock drag but not that due to lift. Busemann's original geometry eliminated all wave drag and hence also lift. Modern Busemann type designs can create lift, with its associated shockwave, while still eliminating much or all of the form drag, thus achieving considerable improvements in efficiency over conventional designs. They can also allow adequate performance over a range of speeds and angles of attack. The three papers linked explore different ways of achieving all this; some use variable geometry.

But Mach 10 cruise is less likely. We do not yet have the materials or airbreathing engines to achieve even half that for sustained flight. Moreover Mach 10 cruise requires extreme altitudes and it can be more economic to go for a conventionally-winged ballistic/suborbital spaceplane which maintains its cruise segment of the journey in empty space. The acceleration of any airborne vehicle can be limited to a level comfortable for the particular passengers, although varying gee levels can affect the economics.

Whichever approach is taken, to avoid overheating at hypersonic speeds above Mach 5 the fuselage nose would have to be bluff like the Space Shuttle rather than pointed like Concorde.

On engines and fuels, the only airbreathing technologies in the offing for these speeds are the scramjet and the airbreathing rocket (principally SABRE). For different technical reasons, both these are likely to be restricted to hydrogen fuel.