Science: Will the new, improved Concorde take off?: With Japan, Russia and Italy joining the original partners of supersonic passenger flight, the next generation could have 300 seats and a trans-Pacific range, says Susan Watts

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EVEN today, almost a quarter of a century after the supersonic aircraft made its maiden flight, people's heads still turn in excitement when Concorde passes overhead. A cross between a child's paper dart and a pterodactyl recreated in aluminium, its appearance is a breathtakingly perfect marriage of form and high- technology function.

Last month, British Airways set about a pounds 7m revamp of the airliner, likely to be its last before Concorde quietly slips from our skies. Those now dreaming of a successor talk of bringing supersonic travel to the masses, with four-hour flights to Australia. An international design team working on 'Son of Concorde' expanded last year to bring Japan, Russia and Italy alongside the original British/French accord and their partners from Deutsche Aerospace in Germany, Boeing and McDonnell- Douglas.

At the Paris air show there was much upbeat talk of an aircraft, provisionally named Alliance, with room for up to 300 seats, half reserved for economy passengers.

According to Robert McKinlay, chairman of the Airbus division at British Aerospace and one of the original Concorde design team, this latest concept for a supersonic aircraft to succeed Concorde would allow non-stop, 5,500-mile flights over the Pacific. This compares with Concorde's 3,500-mile range with only 100 passengers. He hopes that Europe, the US and Japan will be sufficiently confident to sign a development deal by late next summer.

'We have to have a big enough market, and we have to know what people are prepared to pay for speed. This can only be a global programme and there can only be one aircraft,' Mr McKinlay adds. He anticipates a market that will require between 500 and 1,000 aeroplanes, but warns this could be the total production run right up to the year 2050.

Existing Concordes are now in their 17th year, and are expected to reach their operational limit by 1998 or 1999. But nobody can be certain how long Concorde will soldier on.

When the aircraft went into service, it had its own unique test rig at British Aerospace's Farnborough site which was always running ahead - having simulated more flights than those clocked up by any Concorde in service. The rig put a complete fuselage, with wings and tail, through cycles that simulated every stage of a flight, including turbulence and gusting. Most importantly, the rig ran thermal tests. Concorde flies less often than subsonic aircraft, but undergoes additional stresses since it heats and cools through huge swings in temperature as it switches between subsonic to supersonic flight.

Ken Owen, author of Concorde, New Shape in the Sky, says he understood the Concorde test rig was dismantled in the early Eighties, but that by then the company had accumulated sufficient data to approve the integrity of Concorde well into the next century.

British Airways may have had to revise Concorde's life expectancy down with the rise in the number of charter flights the airliner now flies in addition to its scheduled flights. Nevertheless, its engineers do not expect to ask for major maintenance overhauls until around 2005.

By then, the Alliance project will be seeking funds at a time when industrial financiers and politicians will be under pressure to give the nod to the next generation of subsonic aeroplanes, mega-body carriers with a 600-800 seating capacity. 'The large commercial aircraft will be coming up for sensitive discussion in more or less the same time scale as supersonic planes. You have to remember we haven't designed an aeroplane yet. We will just have to put our case and hope,' Mr McKinlay says.

British Aerospace is also acutely aware that its target date of second- generation aircraft in flight by 2005 depends on environmental regulations that will not even be finalised before 1996. The team is resigned to restrictions limiting Concorde's successor to the same rules that ban its supersonic flight over land.

Although it is possible to alter the character of the famous sonic boom of a supersonic aircraft (by adjusting its weight, height and cruising altitude), it is impossible to cut the boom out altogether, or even to reduce it to a level that legislators would regard as acceptable.

The new aircraft would fly only a little faster than Concorde. 'There is probably no value in changing the signature of the boom. It's better to accept it, and focus on making the most aerodynamically streamlined aircraft we can,' Mr McKinlay says.

According to Mike Ramsden, editor of the Royal Aeronautical Society's magazine, Aerospace: 'There will be a Concorde II, without a doubt, if the history of aircraft development is any guide. But the very earliest it could be in service is 2005.'

Concorde benefited from a burgeoning military market. Its engines are based on those used in V-bombers. A military spur of this kind no longer exists for Concorde II.

The second-generation design requires no great technological breakthroughs. The main pacing factor is the development of a new engine to succeed Concorde's Rolls-Royce Olympus 593 turbojets. These depend on a process called reheat, or afterburn, in which fuel is sent into the back end of the engine to utilise unburnt air that has passed through the turbine. This provides extra thrust at take off and when the aircraft passes from subsonic to supersonic speeds.

These engines use huge amounts of fuel and are very noisy compared with modern designs. The aim is to use a dual-purpose engine that exploits the best of modern ideas for both subsonic and supersonic flights. Modern jets use high-bypass engines. But these require large diameter intakes and big fans at the front that push vast swathes of air over the casing of the engine, where it acts as a soundproof coating. Simply dragging such engines through the air would require impossible amounts of power.

Engineers are therefore looking to 'variable-cycle' engines with two sets of fans - one with a high-bypass ratio for take off, subsonic cruising and landing, and the other with a low-bypass design that would suck in and compress the largest possible amount of air to give extra thrust.

Materials scientists are very positive about the possibility of building a far lighter, quieter aircraft. The more efficient engines should cut emissions as well. Nasa's High-Speed Research Programme claims its designs will mean there will only be 10 per cent of the destructive nitrogen oxide emissions that have led environmentalists to brand Concorde an enemy of the ozone layer.

Concorde was a commercial disaster. It cost more than pounds 1bn to develop, and has failed to pay back a penny. Yet it remains one of Europe's few technological marvels. Perhaps the chief justification for that is that it prompted a raft of technical developments (Concorde was the first fly-by- wire aircraft) that have since found their way into subsonic aircraft, such as the Airbus. The same would almost certainly be true of a second generation of supersonic jets.

The US is ploughing many hundreds of millions of dollars into supersonic development - a great deal more than Europe can ever hope to spend. 'It would be very unfortunate if Europe did not have at least an equal place in future developments,' Mr McKinlay says. 'By all means, have a collaboration, but it has to be on an equal basis.'

Harsh commercial realities will decide the future of supersonic travel. They have already put paid to the notion of hypersonic flight, at least until the middle of the next century. The most famous 'spaceplane', the abandoned Hotol design from Britain's Alan Bond, has spawned designs for a successor, but this is even more ambitious a goal than hopes for a baby Concorde.

'The most important lesson of Concorde is that we must be more certain of the markets. Concorde was a case of technology before market, and its successor ought not to be launched until there is pretty convincing evidence of a continued demand, not simply a vehicle to provide it,' Mr Ramsden says.

(Photograph omitted)