When, a decade ago this month, an Air France Concorde crashed on take-off killing all 109 people on board, the dream of supersonic travel seemed to be over. Hastening an idea that was already in the wind, three years later Concorde was mothballed, and with it the prospect of a commercial traveller zipping over the Atlantic faster than a speeding bullet. But as the last Concorde flight touched down, a company in the market town of Abingdon was already part way through designing a bigger, better alternative. Reaction Engines may be a space plane developer, but now it was part of a European Space Agency (ESA) and an EU-initiated project to see if its Skylon shuttle might have a more Earthbound spin-off.
It did: the A2 was a concept for a 300-seat aircraft, capable of non-stop flight to the other side of the planet at a cruising speed of Mach 5, or five times the speed of sound, around 3,500mph. "The objective was to design an aircraft that could travel from Brussels to Sydney in just a few hours," says Reaction's technical director Richard Varvill. "Our studies showed the A2 would do it in 4.7 hours."
The A2 is now in the second phase of an EU/ESA-backed study, due for completion in two years. "The A2 shows that such an aircraft is technically feasible," says Varvill. "We calculated that the ticket price would be about the same as today's typical business class flight, which is not too bad. But the question is how to make it commercially viable and to also make it environmentally acceptable. There are still doubts about whether an aircraft flying at such an altitude would damage the ozone layer."
To provide the range that would allow it to travel non-stop such an aircraft would, he contends, need to be fuelled by liquid hydrogen too. On the downside this is expensive and would require a global supply structure. On the upside it is CO2 emissions-free and that structure might prove the launch pad for all aircraft to make the switch to liquid hydrogen. "The bottom line is that a large, long-distance supersonic passenger jet is looking very promising in terms of technical feasibility," says Varvill. "And it's just not credible that we'll be stuck at Mach 0.9 from now on. Someone will up and do it."
That someone may be a rather rich individual first. The A2 may not take to the skies before 2030, but it is possible that supersonic flight will be back on the agenda for the few within five years. At $80m a pop, Nevada-based research company Aerion Aviation's Supersonic Business Jet may not be cheap, even by private jet standards, but that has not stopped $4bn of advanced orders being placed. Then again, while much of the design is conventional, its proprietary "laminar-flow" technology means it could cross the Atlantic in just two hours. The jet could also be scaled up to create a 50-seater version, half the passenger load of Concorde. The company is now in discussions with manufacturers to build its patented design and hopes to have a deal signed by the end of next year.
"The changes in technology since Concorde are such that the economics of building and getting a meaningful return on supersonic aircraft is that much more feasible," says Aerion's CEO Brian Barents. "As an industry we already have larger and more comfortable jets but we're still providing aircraft that fly at the speed they did in the 1950s. Speed is the next frontier. And business jets are a stepping stone to the commercial jets that there is no question we'll see."
Varvill is sceptical about the contribution made by such business jets in shifting us towards genuine supersonic commercial passenger flight, arguing that the companies producing them cannot sell enough of their craft to pay for the advanced research needed to make it happen. But interest in that market is rising. Gulfstream Aerospace, one of the world's biggest manufacturers of private jets, launched one stalled design project with the Sukhoi Design Bureau of Moscow and is also now working on a new jet, and NASA has established its Supersonics Project.
The return of the Mach may come more slowly than many hope for, however. Unexpectedly perhaps, the biggest obstacle to supersonic passenger flight is not one of logistics or bureaucracy – the complex reworking of the roads of the sky, for example, one that would be required to manage the combination of today's conventional airliners travelling at perhaps Mach 0.75 with others zipping through at twice that speed. Nor is it the need to change regulations to lift the speed limit that effectively prohibits non-military supersonic flight over land, regulations that further sped the end of Concorde and a change necessary in order to make a business case for supersonic flight.
The issue of general acceptability is not standing on the supersonic runway either – that subsonic aircraft can carry more people the same distance for roughly the same expenditure of fuel, or the potential environmental damage, and this despite airliners being one of the whipping boys of global-warming awareness. This spring a US Navy fighter jet actually made the first supersonic flight powered by biofuels. Even in an age of runaway banks and bonuses, the anti-elitism that Robbie Cowart, director of Gulfstream's supersonic research programme, admits he hears talk of in his scientific circles is more widely rejected too. "A supersonic aircraft would be a stepping stone to its wider use," he reckons. "The mobile phone started as an expensive item for the minority and similarly it took a few people who could see its value early on and who could afford it to make it feasible for everyone.
"The lack of Concorde has actually reinvigorated interest in supersonic flight. Because there's a sense in the aviation industry that if we're not going as fast as we were 10 years ago then we're not progressing."
The biggest barrier is supersonic flight's signature: the sonic boom, the bang created by the movement of pressure waves around an aircraft as it passes through the sound barrier. When John F Kennedy created the National Supersonic Transport programme to develop the supersonic Boeing 2707, it was cancelled as a consequence of noise complaints.
"That is the single largest challenge to opening up the supersonic market," explains Cowart. "There are negative perceptions of the sonic boom. There is the belief – and research suggests unfounded belief – that it harms animals and damages homes. People get very upset by it."
Limiting supersonic speeds to over the oceans is one possible solution. But muffling or even eliminating the boom is moving closer. The International Civil Aviation Organisation has established a technical group to investigate supersonic noise reduction and a joint Gulfstream/ NASA programme has completed development of its Quiet Spike, a retractable lance for the nose of an aircraft that swaps the single loud boom (actually two, at the nose and tail of the aircraft, but heard as one) for three much quieter ones.
Other attempts at boom-less flight have looked at the shape of the aircraft, even creating channels through the aircraft to cut the drag which rises with speed and which contributes to the noise. Aerion's design involves a long, slender, drag-reducing fuselage creating a boom quieter than a fighter jet's. Yet finding a design that works is no guarantee of its successful application. The v-tail design of the Quiet Supersonic Transport aircraft – tested in 2004 by the Lockheed Martin Corporation that developed the Stealth Bomber – produced a boom longer than Concorde's but only a hundredth of the volume. But the organisation behind it, Supersonic Aerospace International, is defunct.
"I can see how the booms might seem the least of the problems to be tackled, but it would be unacceptable to have them every other minute during rush hour," says Varvill. "There would be uproar. After all, to flip the debate, you can fly to Australia in a day and relatively cheaply and that is pretty good as it is. Getting there faster is not really solving a critical problem."
Yet for every person under a supersonic flight path who might object to the big bang, there are enthusiasts to whom it is music. The Save Concorde Group has completed a 25,000-signature petition, rustled up celebrity support, and has just completed tests on the airworthiness of one of the mothballed aircraft engines, all with a view to getting at least one flying again, if only for ceremonial duties and perhaps in time for the London Olympics in 2012. The enthusiasm is not only a reminder that we already have the technology, but poses the most mysterious question of the supersonic debate. Why was Concorde canned in the first place? Not for its safety record. The French incident was its only crash, caused by debris on the runway.
Ben Lord, the group's vice chairman, said: "Some say Concorde's too expensive to run but nobody involved will provide figures. Contrary to the public perception, it made money, around £500m net operating profit from BA's privatisation up to the aircraft's retirement. They couldn't sell tickets fast enough. The number of people who turned out to see its final landing shows how much it's loved. But more than that, there is a demand for supersonic flight – time is money. We went backwards the day Concorde was grounded: for the first time in the history of engineering there was nothing better to follow it."
Taking it to the limit
It's not just commercial planes that are revving up to break the sound barrier. A full-scale model of the car that a British team of experts are hoping will reach 1,000 miles per hour has been unveiled at this year's Farnborough International Air Show. Coming in at 12.8 metres long and weighing about six tonnes, they hope the Bloodhound SuperSonic Car will smash the current land speed record of 763 miles per hour, set in 1997 by the Thrust SuperSonic Car.
It has taken the team three years of aerodynamic study to be happy with their model. They plan to start building the rear of the actual car early next year before beginning runway tests at the end of the year or the beginning of 2012. Once the car passes those initial tests, it will be taken to the Northern Cape of South Africa, to a place called Hakskeen Pan where the team will attempt the world record. The huge power of its Falcon hybrid rocket and Eurofighter-Typhoon jet engine has meant the team expect this car to thrash the previous record by more than 250 miles per hour.
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