Biplane Could Go Supersonic Without the Boom
Supersonic passenger jet service ended with the Concorde's retirement in October, 2003, but that hasn't stopped people from trying to build a successor. At MIT an aeronautics professor turned to a design that dates to the 1950s to design a biplane that can travel faster than sound.
Qiqi Wang, an assistant professor of aeronautics and astronautics, used Busemann's Biplane, named for Adolf Busemann, as the basis for his idea. Sixty years ago, Busemann proposed that a plane moving at supersonic speeds that had two pairs of wings, almost joined at the tips to form a hollow space, would create an airflow that eliminated sonic booms.
Sonic booms happen when a jet is moving faster than the speed of sound. A slower plane generates sound waves that radiate ahead and behind it. If the plane were stationary it would look like ripples in a pond. But as it moves faster, the waves are compressed at the front, and if the plane is moving fast enough, the pattern looks like the wake of a ship, a spreading out behind it. That wave front is the sonic boom (and its conical shape is the reason you don't hear it until the plane has gone by).
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Sonic booms were one reason the Concorde wasn't allowed to fly over land in some countries — as a result, tickets stayed pricey and the only routes that stayed viable were between New York, Washington, D.C., Paris and London.
Busemann's design was innovative but it had one big hurdle: lack of lift and "choking." The hollow space between the double wings works well at supersonic speeds but once the jet slows down, the configuration generates a lot of drag. That cuts into the planes lift, and makes it hard for it to get to the speeds where the plane can fly.
When Wang revisited the idea, he was able to solve it with a computer model, something Busemann never had — computer aided design. With his colleagues Rui Hu, at MIT and Antony Jameson, a professor of engineering at Stanford University, they used computer models to look at 700 different wing configurations and a dozen speeds to come up with one that had both the lift to get to supersonic speeds and avoided sonic booms.
They found that a smooth inner edge to inner wing surfaces, as well as pushing out the top edge of the upper wing and the lower edge of the bottom wing, produced a design that the computer simulation said will work. The next step is to build a three-dimensional model, and get a better idea of such a plane's real-world characteristics.
Wang's team isn't the only one working on reviving a Concorde-like plane – European aerospace comapny EADS unveiled its own design in June of last year. Meanwhile, the dream of getting from New York to Paris in less than four hours, or cutting the marathon trans-Asia and trans-Pacific flight times to something shorter, will have to wait –- but hopefully not forever.