A Return to Supersonic Speed?
How fast is fast enough? There is an innate desire to cut travel time so as to enjoy or work harder once one gets where is going. In air flight that dream was the Concorde which was retired from use a few years back due to fuel economics as well as other reasons. For 27 years, the Concorde provided its passengers with a rare luxury: time saved. For a pricey fare, the sleek supersonic jet ferried its ticketholders from New York to Paris in a mere three-and-a-half hours — just enough time for a nap and an aperitif. Over the years, expensive tickets, high fuel costs, limited seating and noise disruption from the jet’s sonic boom slowed interest and ticket sales. On Nov. 26, 2003, the Concorde — and commercial supersonic travel — retired from service. A number of groups have been working on designs for the next generation of supersonic jets. Now an MIT researcher has come up with a concept that may solve many of the problems that grounded the Concorde. Instead of flying with one wing to a side, why not two?
Wang and his colleagues Rui Hu, a postdoc in the Department of Aeronautics and Astronautics, and Antony Jameson, a professor of engineering at Stanford University, have shown through a computer model that a modified biplane can, in fact, produce significantly less drag than a conventional single-wing aircraft at supersonic cruise speeds. The group will publish their results in the Journal of Aircraft.
This decreased drag, according to Wang, means the plane would require less fuel to fly. It also means the plane would produce less of a sonic boom.
With Wang’s design, a jet with two wings — one positioned above the other — would cancel out the shock waves produced from either wing alone. Wang credits German engineer Adolf Busemann for the original concept. In the 1950s, Busemann came up with a biplane design that essentially eliminates shock waves at supersonic speeds.
Normally, as a conventional jet nears the speed of sound, air starts to compress at the front and back of the jet. As the plane reaches and surpasses the speed of sound, or Mach 1, the sudden increase in air pressure creates two huge shock waves that radiate out at both ends of the plane, producing a sonic boom.
Through calculations, Busemann found that a biplane design could essentially do away with shock waves. Each wing of the design, when seen from the side, is shaped like a flattened triangle, with the top and bottom wings pointing toward each other. The configuration, according to his calculations, cancels out shock waves produced by each wing alone.
However, the design lacks lift: The two wings create a very narrow channel through which only a limited amount of air can flow. When transitioning to supersonic speeds, the channel, Wang says, could essentially choke, creating incredible drag. While the design could work beautifully at supersonic speeds, it can’t overcome the drag to reach those speeds.
They found that smoothing out the inner surface of each wing slightly created a wider channel through which air could flow. The researchers 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 the Concorde. Wang says this kind of performance could potentially 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," Wang says.
The desire for a second-generation supersonic aircraft has remained within some elements of the aviation industry,and several concepts have emerged since the retirement of Concorde.
In November 2003, EADS announced that it was considering working with Japanese companies to develop a larger, faster replacement for Concorde. In October 2005, JAXA, the Japan Aerospace eXploration Agency, undertook aerodynamic testing of a scale model of an airliner designed to carry 300 passengers at Mach 2. If pursued to commercial deployment, it would be expected to be in service around 2020—2025. On 18 June 2011, the Zero Emission High Speed Transport or ZEHST concept aircraft was unveiled by EADS at the Paris Air Show. The ZEHST, a hypersonic aircraft to be capable of 3,000 mph (4,800 km/h), is a result of the collaboration efforts between EADS and Japan.
For further information and photo: http://web.mit.edu/newsoffice/2012/supersonic-biplane-0319.html#1981