Posted on 12/14/2005 7:45:46 PM PST by Zuben Elgenubi
Dec 8th 2005
From The Economist print edition
IMAGINE being able to cross the Atlantic in less than three and a half hours. You could fly from London to New York for a meeting and still be home in time for dinner. It used to be possible, before the demise of Concorde, of course. But while Concorde has passed into history, the dream of supersonic travel is alive and well. Several firms are now racing to develop a new breed of supersonic passenger aircraft. These planes will use new technology to ensure that they are quieter, more efficient and capable of turning a profit—something Concorde struggled to do throughout its 27-year lifespan. The new aircraft will differ in another way, too. To start with, at least, they will probably not be airliners, but much smaller business jets.
That is because business-jet users are most likely to value time over money, says Preston Henne of Gulfstream Aerospace, a big business-jet manufacturer based in Savannah, Georgia. Supersonic business jets make sense from an engineering and financial point of view, too. “Historically, if you go back and look at how today's aeroplane systems evolved, it started with smaller aircraft and affluent customers,” says Mr Henne. Concorde was an exception to this rule, which may explain why it failed.
That said, those rushing to build supersonic business jets fall into two camps, taking two very different approaches. Those in the first camp, which includes Gulfstream, are aiming to overcome what was arguably Concorde's biggest drawback: the sonic boom it created during supersonic flight. The resulting noise pollution ultimately led to international regulations banning commercial aircraft from flying supersonic over land. This in turn severely restricted the flight paths Concorde could follow, since it was so inefficient at subsonic speeds that routes had to be designed to minimise the distance flown over land. Gulfstream plans to tackle this problem head on, by getting rid of the sonic boom. It sounds ambitious, but 40 years of research suggests that it should in fact be possible.
According to a theory developed by two researchers at Cornell University, Richard Seebass and Albert George, the sonic boom can be minimised by altering the shape of the plane to redistribute the shockwaves that cause it. Sonic booms actually consist of two parts, each caused by a shockwave—one at the front of the aircraft and the other at the tail. The shockwaves arise when the plane is travelling faster than the sound waves it is producing. Unable to dissipate, these sound waves build up instead and form a shockwave. Dr Seebass's theory suggested that shaping the fuselage appropriately could reduce the boom by causing the sound waves to spread out, or better still by causing them to interfere with each other, so that some sound waves cancel others out.
But it was only in 2003 that these theories were finally shown to be correct. The complex shapes required to reduce the boom proved to be very difficult to design by hand. Eventually engineers at America's space agency, NASA, used a supercomputer to simulate the airflow around an F-5 fighter jet and determined how to alter its shape to reduce the sonic boom. In flight tests, the modified F-5—often likened to a “pregnant pelican”—proved that it was indeed possible to reduce the first part of the sonic boom by 25%. Mr Henne believes that Gulfstream can reduce the second part of the boom too, and so drastically reduce the “sonic signature” of a supersonic plane passing overhead. Supersonic flight over land might then become a possibility.
Of course, it is not quite that simple. It will be necessary to persuade regulators—the Federal Aviation Administration and the International Civil Aviation Organisation (ICAO)—to reconsider the current ban. Furthermore, to make the new aircraft commercially viable, there would also have to be changes in the way that supersonic aircraft are handled when coming in to land at airports. There is little point in having a supersonic aircraft if it gets put into a holding pattern for an hour when it arrives at its destination. These are ambitious goals which might seem foolhardy if Gulfstream were the only firm pushing for them, but it is not alone. Also looking for reform is an alliance of ten large aeronautical firms—including Lockheed Martin, Boeing Phantom Works, Raytheon and Rolls-Royce—collectively known as the Supersonic Cruise Industry Alliance (SCIA). This group is working with NASA to build a prototype supersonic aircraft.
But with NASA and SCIA having only just begun their partnership earlier this year, such an aircraft still seems a long way off. Developing the technology will take time, as will lobbying to get the regulations changed. For companies such as Gulfstream or SAI (which is taking a similar approach, in conjunction with Lockheed Martin), there is a danger that other firms could take to the skies first.
That is because those in the second camp are taking a different approach, designing aircraft that fly at supersonic speeds over sea and subsonic speeds over land, but far more efficiently than Concorde once did. Leading the pack is Aerion, based in Reno, Nevada. It hopes to have its supersonic business jets airborne by 2010 or 2011, by which time SCIA is unlikely even to have made a dent in the ICAO regulations.
Aerion's approach is based on the massive improvements in engine and airframe design since Concorde, says Richard Tracy, the company's chief technology officer. Its aircraft will be powered by two Pratt & Whitney engines, normally found on far larger aircraft, that can be reconfigured to optimise their performance for both subsonic and supersonic flight. The aircraft will meet airport noise requirements—Concorde used to make a huge amount of noise on take-off and landing—and will also produce a smaller sonic boom than would normally be expected for a plane of its size. That is an unexpected benefit of putting the engines close to the fuselage and above the wings, explains Mr Tracy, which means that most of the sonic boom is directed upwards, not down.
So, which camp is right? Perhaps both. Mr Henne admits that the first camp could lose out to rivals that are not dependent on changes to the current rules. But he is adamant that deregulating supersonic flight is the way to go. According to a survey carried out by Gulfstream, only a quarter of all journeys by business jets are over water. This, says Mr Henne, severely limits Aerion's market. Aerion does not dispute that figure, but argues that the 25% of flights that are over water are still a significant market. Indeed, notes Mr Tracy, the market is big enough that Gulfstream has developed long-range subsonic aircraft to service it, so there should be room for supersonics too.
Nor is Aerion alone in this belief. Earlier this year an agreement was signed between the Society of Japanese Aerospace Companies (SJAC) and France's Aerospace Industries Association to develop technologies jointly that could be used to produce supersonic airliners. Like Aerion, this partnership is concentrating on adapting existing technology to produce a supersonic aircraft that can fly subsonic over land, in accordance with existing regulations. The aim is to have an airliner capable of carrying 300 passengers 6,000 nautical miles, equivalent to the distance from Tokyo to New York.
It is still early days for this joint-venture, but it seems to mean business. In October, researchers at Japan's space agency, JAXA, carried out flight tests of a prototype airframe in Woomera, Australia. It achieved speeds in excess of Mach 2.5, or two and a half times the speed of sound. That said, Akira Yanagida, general manager of engineering at SJAC, says that at speeds above Mach 1.6 the economics simply do not work. As a result, none of the runners in the new supersonic race aims to fly faster than Concorde, which used to cruise at Mach 2. Whoever wins the race, this much seems clear: supersonic aircraft are about to stage some sort of a comeback. And this time they will be here to stay.
aero ping [every once in a while I come across something of interest]
Something sees wrong with that assertion. Sonic boom has nothing to do with engines.
I can be in Europe or Asia at a keystroke. I might need to be there a couple times a year if I'm doing business but if I need to, I'll take a 747.
While I agree with you, there is some science to this.
Sonic booms are caused by high pressure/low pressure areas where the sound waves converge. By making a sleek nose and putting the engines over the wings, when the waves converge at the front of the engine the sound reflects off the wings and bounces upward. The tailing low pressure area will still have the same boom, I can't figure how that will be mitigaged.
Shrug. Might be able to cut the sound somewhat. The first boom might be small, the second will still be the same far as I can tell.
One of the big new developments in fighter craft is supercruise, i.e. the ability to fly supersonic without afterburners. Given that, you'd figure the idea of supersonic air travel would have to come back.
Well, if one suffers from cardio-vascular disease (as I do), the less time in an airplane the better. You young guys have all the fun and can enjoy the 747s
Interestingly enough, the USAF has great interest in such a plane, since it would allow for a Mach 2+ bomber to fly anywhere in the world with no pronounced sonic boom announcing its presence flying overhead. Several companies--Boeing, Lockheed, and Northrup Grumman--have been studying the idea under DARPA contracts since the late 1990's.
But even more interesting is that some aerospace analysts have said the shelved Sonic Cruiser design from Boeing could be the basis for a quiet SST. By carefully shaping the Sonic Cruiser design to drastically reduce the pressure wave buildup, that could lead to a 200 to 225-passenger SST flying at Mach 1.7 that would have the following advantages:
1. By limiting the top speed to Mach 1.7, you can apply the jet engine technology developed for the F-22A Raptor fighter for a jet engine that doesn't need to run fuel-gulping afterburning mode all the time, not to mention meeting the ICAO Stage IV criteria for jet engine noise emissions on takeoff and landing. It also means less expensive engine design, too. The result could mean the airliner could easily fly over 6,000 nautical miles easily, maybe fly as far as 7,200 nautical miles! 
2. Also, limiting top speed to Mach 1.7 means far less issues with atmospheric frictional heating, so this makes it possible to use lighter-weight aluminum-lithium alloys and carbon-fiber composite materials to drastically reduce the total structural weight of the plane.
3. Limiting the top speed to Mach 1.7 also means far easier design in terms to trying to reduce the pressure wave buildup that causes the sonic boom in the first place.
In short, Boeing might be quietly (pun intended!) working on a Mach 1.7 SST that might even have enough range to fly from Los Angeles to Sydney nonstop; imagine instead of a 15-hour flight from Los Angeles to Sydney flying nonstop on a 747-400 or A380-800, you'll fly the same distance in just over 9 hours. Because the engines will likely meet Stage IV noise standards, it also means you can use most of the world's major airports with very few noise curfew restrictions.
You are right and there's a market for it, too.
I wouldn't bank on it.
It looks like (and probably has the same glide ratio as) a lawn dart.
There's a market for business-class jets to transport businespeople internationally. I;ve recently invested in that concept and the company is cited in this article. To me, this is easy risk assessment so if you don't want to make money, don't invest. Particularly, don't bank because there's absolutely no money there.
> IMAGINE being able to cross the Atlantic in less than
> three and a half hours.
Less time than you already wasted getting to the airport
early, clearing security, then clearing customs and
security again at the other end, and that's a big
problem for selling speed in transit.
There are reasons why SST required subsidies. even
before 9-11, and why none are flying today (without
ordnance, anyway :-)
Cutting 3-4 hours on a transatlantic flight is a minor reduction in travel time, when you take into account you still have to go thru customs, security, baggage claim, and get a cab to your destination
People are more likely to pay money to reduce a 15-hour-torture-flight to something more reasonable. If it has the range for the Pacific routes, it will do well
Gosh, look at the time. It's almost midnight here and I've got to get some shuteye. I should have posted the article earlier in the evening.
Thanks for your comments.
bump.
I would think most of these supersonic business jets will be owned by chartering and fractional ownership companies.
But at what price?
Most probably.
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