Bill has one. So does Madonna. In fact, anyone who’s anyone among the super-rich these days has a personal jet parked at the local airport. Money can’t 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’s Boeings and Lockheeds, engineers and design wonks are drawing up blueprints for the next generation of luxury jets. And for “luxury”, read “speed”. If these planes fly the way they’re supposed to, they’ll make today’s 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’s more, say the most optimistic of the engineers, once subsonic travel is passé for the super-rich, it’s 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’t exactly a runaway commercial success, and every attempt to create the “son of Concorde” 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’s supersonic engineers so cocky? The short answer is they believe they’ve come up with a cost-effective way not only to make jet engines more efficient, but to solve the one problem that’s 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.
“More than 60 per cent of current air traffic is over land,” says John Morgenstern, an aeronautical engineer and sonic boom expert at Lockheed Martin Skunk Works in Palmdale, California. “To enable commercial supersonic transport, it’s pretty clear what you’ve got to do.”
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’s 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’t 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’s 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’s 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’s more, new high-performance materials and engine designs are cranking up the efficiency of jet engines, and slashing their emissions (see “Engine magic”).
And then there’s 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 “quiet supersonic platform” 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’s 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’s nose like the drop nose on Concorde. When this flap tilts upwards a few degrees, it acts just like Seebass’s 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’t a problem, it can be flicked down to its more streamlined “off” 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’s 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’t 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. “These sorts of configurations should be considered just as reasonable as some of the other configurations around,” 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’s department of aerospace engineering. “With a laser you could possibly heat up the gas in certain parts of the shock wave,” he says. Just like the blunt nose, this would raise the air pressure ahead of the craft. “It may be able to reduce the boom.” 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 (91av, 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’ 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’s capacity and more than twice its range.
The plane’s engines, however, will be designed to be as quiet as a jumbo jet’s. “Subsonic flight over continents is baseline scheme,” says Hidehiko Nakayasu, an engineer at NAL. “But we are trying to reduce or soften sonic booms by changing the shape of body and wing.” And the first departure? Around 2020, says Nakayasu.
Morgenstern says there’s no reason why larger airliners should produce unacceptable sonic booms. “It won’t be easy,” he says, “but with a few developments, you should be able to get them down to the same level as smaller aircraft.”
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. “As far as I can see there’s nothing that will make them quieter,” 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’s 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.