US researchers design biplane that could fly faster than sound

Researchers in the US have designed a biplane that they claim could fly faster than sound and reduce sonic boom.

Engineers at the Massachusetts Institute of Technology (MIT) and Stanford University have used a computer model to show that their design for an aircraft with two sets of wings can produce significantly less drag than single-wing planes at supersonic speeds.

The decreased drag means the plane would require less fuel to fly and would produce less of a sonic boom, according to the craft’s creator, Qiqi Wang, assistant professor of aeronautics and astronautics at MIT, who will publish his work in the Journal of Aircraft.

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

The plane uses a concept first developed by German engineer Adolf Busemann in the 1950s that means the two wings above one another cancel out the shock wave produced by each wing separately.

A sonic boom is produced when the sudden increase in air pressure at the front and back of a plane as it surpasses the speed of sound creates two large shock waves that radiate out from both ends of the craft.

Busemann found that the design of two flattened triangle-shaped wings pointed towards each other cancels out the shock waves. However, this also creates large amounts of drag as the two wings create a very narrow channel that limit the air flow over them.

As this would typically prevent a craft from reaching supersonic speeds, Wang, along with fellow MIT researcher Rui Hu and Prof Antony Jameson of Stanford, created a simulation that enabled them to optimise the wing shape to minimise the drag.

After testing a dozen different speeds and 700 wing configurations, they found that smoothing the inner surface of each wing slightly created a wider channel through which air could flow.

They also found that by bumping out the top edge of the higher wing, and the bottom edge of the lower wing, the conceptual plane was able to fly at supersonic speeds, with half the drag of conventional supersonic jets such as Concorde.

Wang said this could cut the amount of fuel required to fly the plane 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.’

The team is now planning to design a three-dimensional model to account for other factors affecting flight. Another group in Japan is also working on a Busemann-like biplane with wings that change shape during flight to reach supersonic speeds.

‘Now people are having more ideas on how to improve [Busemann’s] design,’ said Wang. ‘This may lead to a dramatic improvement and there may be a boom in the field in the coming years.’