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Holy Grail: Hypersonic Flight

The future of passenger flight promises ultrafast trips to any point on the globe

2 min read

Imagine boarding a plane in New York City and stepping off three hours later in Sydney, Australia--a trip that would normally have you cooped up in a pressurized cabin for an entire day. With the recent demise of the Concorde, the supersonic passenger airliner that was retired in October 2003 after more than 25 years of service, supersonic passenger flight faces enormous technical and financial challenges and is many decades away. Nonetheless, a few groups of engineers worldwide are working on the propulsion technologies that will one day power passenger planes to several times the speed of sound.

"The ultimate objective of making the world a smaller place and being able to fly to any point in just a couple of hours is a worthy goal," says David Van Wie, supervisor of the aeronautical science and technology group at the Johns Hopkins University Applied Physics Laboratory, in Laurel, Md. An aircraft flying at, say, Mach 10, or 10 times the speed of sound, could make the three-hour New York­Sydney flight possible, and it would reduce a trip from New York to London to a mere half an hour--three hours less than the Concorde's travel time. In this world of hypersonic transportation, rich executives would be able to commute to other countries, express packages could be delivered globally in hours rather than days, and a living organ could reach a patient waiting for a transplant in minutes rather than hours.

Since Boeing introduced the 707­120, the first commercially successful passenger jet aircraft, in 1957, average air travel speed has not really changed at all. We have been flying at around 1000 km per hour for about half a century. Current turbojet engines can't propel an aircraft to hypersonic speeds--their spinning shafts and compressors would simply collapse.

To solve this problem, groups in the United States, Japan, Australia, and other countries are working on a propulsion system that burns fuel combined with air flowing at supersonic speeds through the engine, which is essentially a metallic funnel, with no moving parts. These so-called supersonic combustion ramjet (scramjet) engines could in theory propel an aircraft to Mach 10 and eventually even more, says Lowell Keel, a project manager at Allied Aerospace, in Newport News, Va. The company is working with NASA, the U.S. Air Force, Boeing, and others to develop and test scramjet engines.

Scramjet-powered aircraft would take off like conventional jets but fly three to eight times higher, says Tetsuo Hiraiwa, a propulsion researcher at the Japanese Aerospace Exploration Agency, in Kakuda. But before then, huge technical problems will have to be solved, like reducing the noise created by the infamous sonic boom and preventing the heat from the engines and from air friction from melting the whole plane.

Sorry to say, you probably won't live long enough to enjoy a quick and painless New York­Sydney flight. The first scramjet engines will appear in military craft, such as ultrafast cruise missiles, and in space vehicles that consume oxygen in the atmosphere instead of carrying big oxygen tanks, says Mark Lewis, an aerospace engineering professor at the University of Maryland in College Park. After that, economics will determine what happens next. As the Concorde demonstrated, the main challenge won't be breaking the sound barrier, but containing the cost of tickets.*

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