Bill has one. So does Madonna. In fact, anyone who鈥檚 anyone among the super-rich these days has a personal jet parked at the local airport. Money can鈥檛 buy you love but it can get you a much smaller planet. A piece of advice, though, to anyone thinking of mortgaging their penthouse for one of these winged status symbols: wait a while.
In the backroom labs of the world鈥檚 Boeings and Lockheeds, engineers and design wonks are drawing up blueprints for the next generation of luxury jets. And for 鈥渓uxury鈥�, read 鈥渟peed鈥�. If these planes fly the way they鈥檙e supposed to, they鈥檒l make today鈥檚 machines seem about as cutting-edge as a white Roller and caviar.
Personal jets, you see, are about to go supersonic, whipping people from London to Rome in just 50 minutes and to Hong Kong in time for lunch after a morning start. What鈥檚 more, say the most optimistic of the engineers, once subsonic travel is pass茅 for the super-rich, it鈥檚 only a matter of time before the Ibiza-bound masses are boarding bigger, cheaper versions of the planes. Indeed, one day in the not-too-distant future virtually all airline travel could be faster than the speed of sound.
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A year after Concorde came down in flames, it sounds like a case of shameless hubris. After all, even before its crash Concorde wasn鈥檛 exactly a runaway commercial success, and every attempt to create the 鈥渟on of Concorde鈥� in the past couple of decades has either failed to win the necessary financial backing or been scrapped mid-project. In the 1990s, for example, the US government and aerospace industry poured hundreds of millions of dollars into developing a plane that by 2015 would be able to fly 300 people from LA to Tokyo at Mach 2.4. But the dream died when planners at Boeing realised it would never pass the exacting noise and pollution standards projected for 2020. Powerful jet engines of the type found on Concorde chuck out vast amounts of nitrogen oxides, which play havoc with the ozone layer at the high altitudes at which such planes must cruise.
So what makes today鈥檚 supersonic engineers so cocky? The short answer is they believe they鈥檝e come up with a cost-effective way not only to make jet engines more efficient, but to solve the one problem that鈥檚 always been the bugbear of supersonic flight-gut-thumping, ear-splitting noise.
The sonic boom that Concorde creates when it punches through the sound barrier means that it is banned from supersonic flight over land. Its sonic booms exceed almost all noise regulations-they can even shatter glass or damage buildings. Restricted to hops across the Pond, Concorde is a very expensive beast to run.
鈥淢ore than 60 per cent of current air traffic is over land,鈥� says John Morgenstern, an aeronautical engineer and sonic boom expert at Lockheed Martin Skunk Works in Palmdale, California. 鈥淭o enable commercial supersonic transport, it鈥檚 pretty clear what you鈥檝e got to do.鈥�
Sonic booms result from a sudden change in air pressure as a supersonic craft passes overhead. The aircraft is travelling so fast that the sound waves it produces pile up in front to form shock waves (see Diagram). Each aircraft forms two conical shock waves that spread out behind it: one starting at the nose and one at the tail.
These shock waves can be heard far away from the flight path. For every 300 metres of altitude, a supersonic jet鈥檚 shock waves spread to about 1 kilometre either side of the flight path at ground level. So Concorde, flying supersonic at 15,000 metres, creates a boom along an 100-kilometre-wide swathe of land beneath, and the shock can often show up on seismographs up to 5000 kilometres away.
Such dirty, noisy machines can鈥檛 fly as cheaply as their quieter, subsonic cousins, and are limited in where they can go. Yet just a few years after the US High-Speed Civil Transport programme folded, supersonic passenger planes are on the way back. But this time the designers are taking a different approach. It looks like the first son of Concorde will be an executive jet.
Boeing, for example, recently announced that it is discussing a small supersonic business jet with Russia鈥檚 Rosaviacosmos aviation agency and aircraft manufacturer Sukhoi. In France, Dassault Aviation has announced plans to build its own small supersonic aircraft, while US manufacturer Gulfstream Aerospace is also looking into a long-range business jet.
So what鈥檚 triggered the switch? A number of factors, says Preston Henne, senior vice-president of Gulfstream Aerospace. Small aircraft produce a smaller sonic boom, and supersonic executive jets make sound business sense too. Aviation industry analysts reckon more than 10,000 new business jets will be built in the next decade, and more than 200 of them could be supersonic.
At the same time, fractional ownership-in which companies or wealthy individuals share the cost of a plane-is exploding in popularity. This gives almost every large business, mail company or rock star access to long-range, high-speed transport. What鈥檚 more, new high-performance materials and engine designs are cranking up the efficiency of jet engines, and slashing their emissions (see 鈥淓ngine magic鈥�).
And then there鈥檚 politics. Last year the US government set up a programme to support research into low-noise supersonic flight-partly because the US aviation industry is worried by foreign competition, and also because of the support of companies such as NetJets, a leader in the fractional jet ownership business. Run by the US Defense Advanced Research Projects Agency, the 鈥渜uiet supersonic platform鈥� programme will distribute $35 million to researchers in universities and the aviation industry over the next two years.
It can call on all kinds of design tricks to achieve its aim (see Diagram). Back in the 1970s, Richard Seebass at the University of Colorado, Boulder, calculated that simply blunting the aircraft鈥檚 nose would virtually eliminate the boom. A blunt nose would raise the air pressure ahead of the aircraft, increasing air temperature and stretching the bow shock out in front of the aircraft. Blurring the shock wave like this reduces its peak pressure and so lowers the amplitude of the sonic boom.FIG-mg23044701.JPG
Then in 1998 Morgenstern, who was working at McDonnell Douglas in St Louis at the time, found a better way to achieve this effect. It involves a flat flap that extends forwards from the aircraft鈥檚 nose like the drop nose on Concorde. When this flap tilts upwards a few degrees, it acts just like Seebass鈥檚 blunt nose, stretching the bow shock wave and reducing its peak pressure.
This design also creates lift, helping cut fuel consumption. And over the ocean, where noise isn鈥檛 a problem, it can be flicked down to its more streamlined 鈥渙ff鈥� position. The tail, too, would be equipped with a flap to soften the tail shock wave.
In 1999 Morgenstern published a patent for a more daring design to stifle sonic booms. His aircraft鈥檚 most distinguishing features are its elongated nose and a V!-shaped tail that sweeps forwards towards the wings rather than backwards. The nose is designed to increase air pressure just ahead of the craft, while the tail adds lift at the rear. It could also help damp out shock waves. By adjusting the shape of the tail and its distance from the wing, shock waves generated by the upper surface of the wing could interfere with those from the underside of the tail and cancel out. This trick was first suggested by German aerodynamicist Adolf Busemann, who drew up plans for a supersonic biplane that would be faster and quieter than conventional designs.
Supersonic biplanes aren鈥檛 as crazy as they sound, says Domenic Maglieri from Eagle Aerospace in Hampton, Virginia. Maglieri is an aeronautical engineer who has studied sonic booms for over 40 years. Back in the mid-1960s, he recalls, researchers proposed a biplane that could eliminate the sonic boom by distributing lift over a larger area. This would reduce the average pressure on the wings and so weaken the shock wave.
Heinz Gerhardt, an aeronautical engineer at Northrop Grumman in Los Angeles, has designed a new family of supersonic biplanes which he believes could outperform more familiar designs. And last year, another team at Northrop Grumman proposed a quiet supersonic land vehicle incorporating the same biplane idea. 鈥淭hese sorts of configurations should be considered just as reasonable as some of the other configurations around,鈥� says Maglieri.
One of the most radical-if speculative-proposals comes from H. K. Cheng, a retired aeronautical engineer formerly at the University of Southern California鈥檚 department of aerospace engineering. 鈥淲ith a laser you could possibly heat up the gas in certain parts of the shock wave,鈥� he says. Just like the blunt nose, this would raise the air pressure ahead of the craft. 鈥淚t may be able to reduce the boom.鈥� In fact, researchers are already looking at a similar idea-using hot plasma to heat the air around supersonic planes and control the formation of shock waves (快猫短视频, 28 October 2000, p 26).
So far, no one will say whether any of these techniques has reached the test stage. Everyone in the multimillion-dollar world of commercial airliners worries that the opposition will steal their secrets. But Henne admits that Gulfstream hopes its business jet will fly in around five or six years鈥� time. And Sukhoi, which has been working on a similar plane for some years, has announced that its craft will take to the air by 2010.
Much larger supersonic craft may not be far behind. Last year Boeing announced its brand-new aeroplane, the Sonic Cruiser. Its spokesman Craig Martin says this aeroplane will avoid sound barrier problems by flying at Mach 0.95. And Michael Bair, vice-president of Boeing Commercial Aviation Services, has revealed that the Sonic Cruiser is the first step towards a larger, faster airliner that could be flight-tested by 2007.
In Japan, the National Aerospace Laboratory has announced that it will begin full-scale development of a supersonic jet by March 2002. The proposed aircraft will be able to fly roughly 300 people a distance of 11,000 kilometres-three times Concorde鈥檚 capacity and more than twice its range.
The plane鈥檚 engines, however, will be designed to be as quiet as a jumbo jet鈥檚. 鈥淪ubsonic flight over continents is baseline scheme,鈥� says Hidehiko Nakayasu, an engineer at NAL. 鈥淏ut we are trying to reduce or soften sonic booms by changing the shape of body and wing.鈥� And the first departure? Around 2020, says Nakayasu.
Morgenstern says there鈥檚 no reason why larger airliners should produce unacceptable sonic booms. 鈥淚t won鈥檛 be easy,鈥� he says, 鈥渂ut with a few developments, you should be able to get them down to the same level as smaller aircraft.鈥�
Not everyone will see these planes as good news. Many environmentalists would rather go to their graves than let Concorde 2.0 pollute the skies. 鈥淎s far as I can see there鈥檚 nothing that will make them quieter,鈥� says John Stewart of HACAN ClearSkies, an anti-noise consortium based in London.
And while shorter journeys may help eliminate the dangers of deep vein thrombosis and even calm potential air ragers, there鈥檚 one thing to bear in mind before you head for check-in. These airliners might carry you at twice the speed of sound, but they will never outrun those interminable airport delays that keep your feet stuck firmly in the departure lounge.