Biplane design could break the sound barrier

Posted by Kate Taylor

An MIT researcher believes he's found a way to solve many of the  problems that grounded Concorde, and make supersonic commercial flights a reality once more.

Qiqi Wang, an assistant professor of aeronautics and astronautics, says that a modified biplane can produce significantly less drag than a single-wing aircraft at supersonic cruise speeds, meaning it would need less fuel and produce less of a sonic boom.

"The sonic boom is really the shock waves created by the supersonic airplanes, propagated to the ground," says Wang. "It’s like hearing gunfire. It’s so annoying that supersonic jets were not allowed to fly over land."

In Wang’s design, a jet with two wings, one above the other, would cancel out the shock waves produced from either wing alone. Unlike a similar design created by German engineer Adolf Busemann in the 1950s, he's found a way of avoiding the very high drag that can arise.

A computer model was used to simulate the performance of Busemann’s biplane at various speeds and determined the optimal wing shape to minimize drag at different speeds.
The researchers then aggregated the results from a dozen different speeds and 700 wing configurations to come up with an optimal shape for each wing.

They found that smoothing out the inner surface of each wing slightly created a wider channel through which air could flow. And by bumping out the top edge of the higher wing, and the bottom edge of the lower wing, the model showed that the plane would be able able to fly at supersonic speeds, with half the drag of conventional supersonic jets such as Concorde.

Wang says this performance could cut the plane's fuel requirement by more than half.

"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," he says Wang . "It’s kind of a chain reaction."

The team’s next step is to refine the model to account for other factors affecting flight.

"There are many challenges in designing realistic supersonic aircraft, such as high drag, efficient engines and low sonic-boom signature," says Karthik Duraisamy, assistant professor of aeronautics and astronautics at Stanford University, who wasn't involved in the research.

"Dr Wang’s paper presents an important first step towards reducing drag, and there is also potential to address structural issues."