However, the design has a major limitation for a plane – it lacks lift. The two wings create a narrow channel that limits the amount of air that can flow between them. When the plane accelerates through the sound barrier it becomes “choked” with air, causing an incredible amount of drag - much larger than a traditional Concorde-like design. This effectively means that a supersonic bi-plane works beautifully on paper, it could never reach supersonic speeds in the first place. Not only that, but the sonic-boom cancellation only works at a specific speed. If you are not at that exact speed, you don’t get the desired effect.
Shape shifters
To address these problems Wang turned to computer modeling to come up with an optimum wing shape for different speeds. The researchers then crunched through the 700 different shapes to produce an optimal configuration that would work at all speeds. Amongst the design tweaks they came up with were a smoothed inner surface for each wing to help air flow. The overall result is a wing that could fly at supersonic speeds, with half the drag of Concorde; something that could significantly cut fuel use.
Whilst it sounds like Wang and his team have cracked the problem, there is still a long way to go. So far, Wang has only shown the bi-wing concept working in two dimensions. Scaling this up to a three-dimensional prototype is more of a challenge. And expanding wing design to plane design, and getting everything to work together will be harder still.
“We are experts in designing components, and we are experts in designing something for a specific condition” says Duraisamy, who was not involved in the MIT work. In a supersonic aircraft though, nothing is constant. The conditions at take-off and landing are very different to the conditions at cruising speed. The plane encounters a whole range of possibilities, from different temperatures to different air densities.
“When you think about a supersonic aircraft it has to take-off at zero velocity, and has to reach a supersonic velocity and keep flying there,” says Duraisamy. “It also operates at zero altitude to extremely high altitude.”
But a Japanese group at Tohoku University may hold the key. The group has also been working on a Busemann bi-plane called Misora (Mitigated Sonic Boom Research Airplane and the Japanese for “beautiful sky”). However, unlike the MIT project that aims to design one wing for all uses, the Japanese project has proposed movable control surfaces so that the wings could change shape at different speeds. And if that sounds far-fetched, consider Concorde’s “drooping nose” that could be raised and lowered at different stages of flight. Of course to shape and sculpt a wing will take much more sophisticated technology and materials, but these shape-shifters could hold the key to next-generation supersonic air travel.
“I think that’s very likely” says Wang.
However if you are holding off booking that dream transatlantic trip in the hope of the shorter flight time in the near future, you may have a long wait. Duraisamy believes it will be “15 to 20 years” before anything like Concorde is seen in the skies again. And even then, it probably won’t get around all of the problems Concorde encountered.
“Maybe a supersonic business jet will come first,” he says, “because people are willing to pay the money.”
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