Aircraft

Futuristic biplane design eliminates sonic boom

The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)
The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)
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The flow features of the Busemann Biplane. Red lines indicate the positive shock waves, blue the negative (Image: Mythealias)
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The flow features of the Busemann Biplane. Red lines indicate the positive shock waves, blue the negative (Image: Mythealias)
The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)
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The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)
The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)
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The Tohoku University design would change shape during flight to adapt to supersonic speeds (Image: Tohoku University)

A throwback to early 20th Century aviation may hold the key to eliminating the sonic boom - at least according to researchers at MIT and Stanford University. Strongly reminiscent of biplanes still in use today, the researcher's concept supersonic aircraft introduces a second wing which it is claimed cancels the shockwaves generated by objects near or beyond the sound barrier.

In fact the idea is not a new one. The idea of a biplane to negate the sonic boom was proposed in the 1930s by aviation pioneer Adolf Busemann, also responsible for the idea of swept-wing aircraft.

Aircraft traveling at supersonic speeds cause shockwaves in the air around them. A first boom is caused by the rapid compression of air at the front of the plane, literally pushed together by the aircraft. A second is caused by the negative pressure left in the plane's wake - or rather, the rapid return to normal pressure that follows soon after. Though the two booms separate phenomena, they occur so close together that they they are usually perceived as a single sound. An aircraft in supersonic flight creates a continual boom as it goes.

And that's a problem. Sonic booms might be all part of the drama at an air show, but if you were to live under a supersonic flightpath in regular use, the novelty would likely quickly wear off. There are also the concerns of the effect of supersonic flight upon wildlife which might include shock or injury in the short-term, and wholesale habitat abandonment over time. It's no surprise, then, that a return of commercial supersonic flight is considered a doomed enterprise in certain quarters.

The flow features of the Busemann Biplane. Red lines indicate the positive shock waves, blue the negative (Image: Mythealias)
The flow features of the Busemann Biplane. Red lines indicate the positive shock waves, blue the negative (Image: Mythealias)

Adolf Busemann's design, known as Busemann's Biplane, features two wings with a triangular length-wise cross section. The points of the wings point towards each other so that the outer face of the wings is completely flat, parallel to the air passing over and under. The wings must be sufficiently far apart that the passage of air between isn't stifled. With this design, the first positive shock wave is created and reflected between the wings, filling the space created in the plane's wake, canceling the negative shockwaves and negating the sonic boom.

What's the catch? At sub-supersonic speeds, a Busemann Biplane doesn't produce sufficient lift under acceleration, undergoing considerable drag. The design is said to work perfectly at supersonic speeds - it's getting to them that is the trouble. So though there may be no sonic boom, there's no flight either.

But the joint MIT/Stanford research at least appears to confirm that Busemann's noise-canceling concept was sound. The study, which used computer simulation, demonstrated that the biplane concept exhibited "significantly less drag." Additional research at Tohoku University in Japan claims Busemann's concept is effective in reducing the intensity of shock waves at ground level by 85 percent.

Better yet, the MIT/Stanford team think they might have cracked the problem of lift at sub-supersonic speeds. Through an iterative processes, modeling differing design variations, the team has discovered that smoothing the wing's inner surface eases the passage of air between the wings. By additionally "bumping out" the outer edges of the two wings, the team has come up with a design it claims will fly below the speed of sound, and with half the drag of Concorde.

"If you think about it, when you take off, not only do you have to carry the passengers, but also the fuel, and if you can reduce the fuel burn, you can reduce how much fuel you need to carry, which in turn reduces the size of the structure you need to carry the fuel," said Qiqi Wang, assistant professor of aeronautics and astronautics at MIT. "It's kind of a chain reaction."

The MIT/Stanford team is now pursuing a 3D model to address other practicalities in flight, with the hopes of approaching a static, optimized design. In contrast, the Japanese concept, identified by Wang, would change shape during flight to adapt to supersonic speeds.

Sources: MIT, Tohoku University, via Live Science

25 comments
Slowburn
Given that military training areas are de facto wild life sanctuaries I think that sonic booms have no lasting effect on wildlife.
Philip Hahn
You will still have termination shocks. In order to avoid a shock off the top of the top wing or the bottom of the bottom wing, the wings will have to tilt inwards so there is expanding flow around the outside (avoiding the shock). However the consequence of that design is that you will have 2 trailing shocks off the back of the vehicle as the flow re-compresses. If the plates are perfectly flat with respect to the flow streamlines, you will still have a shock as the boundary layer on the wing will trip the flow. Also as shown in the flow configuration it has zero lift: the interior gemetry is identical top and bottom so the integration of pressures over both surfaces has a net of zero. There needs to be different shock angles to generate positive pressure. Also neglects shock impingement aeroheating.
iamwho2k
Forget about SSTs already. Boeing tried to interest the airlines in a faster (though not supersonic) airplane, the Sonic Cruiser. The airlines instead wanted to save on fuel costs and we got the 787 instead. I don't blame them. Until you can combine SST speed with subsonic fuel consumption... nothing will ever get built.
Christine Karman
I know what supersonic is, and what subsonic is, but what is sub-supersonic? Is that the same as super-subsonic?
b@man
I don't believe that design will do MACH 1.
Michael Mantion
It should be clear to most that the diagram is only to explain the concept. The angles are clearly exaggerated and no representation of the final product.. I completely disagree with B@Man, this shape could easily get to mach speeds in thinner air. It can get to thinner air because of the increased lift of an all wing design and the extra wing..
mommus
When the article says that they can create lift with the Busemann wing, they mean 'some' lift. Not nearly enough to support an airliner in flight. Adding any kind of structure to the Busemann wing will also create a shockwave and hence a boom. This includes engine pods, passenger compartments and control surfaces. You could run a fleet of SSTs that were restricted to flying over water, and also in arctic airpaces in sparsely-inhabited Siberia and Canada. All this research is in a desperate attempt to speed travel across the USA, which is currently the biggest market. In 30 years (the earliest an airliner like this could fly) the market will have moved East where Supersonic travel can take place over water.
Oztechi
The claims made about wildlife are unproven and speculative. A supersonic aircraft could be flown to an airfield away from heavily populated areas and then passengers could be transported by high-speed rail to the major cities and towns. It would be nice if they end up building a unmanned demonstrator.
Suvilo
Clearly the ugliest aircraft concept in the last years. I would ran away if I see this! How will it start or land? How will passengers enter the fuse? The high complexity is a clear showstopper. It's such a nonsense. It is heavy as hell, it has a drag as hell, it is inagile as hell, it is ridiculous! There is a reason why we don't see biplanes or should i say "boxwings" in the air. Too complex, too heavy, too ... useless!
toolman65
looks less like an airplane and more like a Romulan Warbird to me.