If you want to make a small fortune out of aviation, the saying goes, you must start with a large fortune. Such stoical wit seems indispensable in an industry long on glamour but short on financial security. Even as British jet propulsion approaches its 50th anniversary next week, it does so at a time of falling share values and declining profits.
Rolls-Royce, one of the three world leaders in jet engine design and production, shocked the stock market in March when it announced a 24 per cent drop in profits, which it blamed partly on unexpectedly high spending on research and development. Though Rolls-Royce says it has a £5.7 billion order book, that is not enough and 3000 jobs must go. Rolls-Royce needs to earn £5 million per day just to tick over.
And yet the British aerospace industry deserves to celebrate the half century of the jet. It is justified in turning away, for a moment, from its insecurity and looking back with some pride on a record that has kept Rolls-Royce competing with the American giants, Pratt and Whitney and General Electric.
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The beginning, on 15 May 1941, did not seem particularly auspicious. The inventor, a 34-year-old RAF officer named Frank Whittle, decided in the morning that the weather was much too poor to allow his prototype jet off the ground from the RAF base at Cranwell, Lincolnshire. The nation was at war with Germany, a war which seemed impossible to win. The jet engine was on the Cabinet’s secret list of devices that might tip the balance in Britain’s favour.
Later in the day the weather lifted and Whittle watched the jet (now hanging in the Science Museum, London) carry out a perfect take-off, circle and landing. The E28/39 had been designed around Whittle’s engine by the Gloster aircraft company. ‘It flies!’ cried a spectator. ‘That’s what it was bloody well designed to do,’ responded Whittle.
The prototype was a single-engine, single-seat monoplane and in the series of test flights after the first flight it reached a top speed of 370 miles per hour at 25 000 feet. In one bound it exceeded the top speed of the RAF’s most glamourous aeroplane, the Spitfire fighter, which used external propellors, or airscrews, driven by piston engines. Two prototype jets were built: the second one reached 400 miles per hour.
What none of the British knew was that Germany had flown a jet 20 months before, on 27th August 1939. The aircraft was the Heinkel 178 and its test pilot, Eric Warsitz, was the first to describe the quietness and the lack of vibration of jet flight. The inventor, Hans von Ohain, only 28 years old, had got the idea in the early 1930s while he was still a student at the University of Gottingen. He had persuaded the German plane-maker Ernst Heinkel to finance him.
Whittle, however, had thought of jet propulsion first. The idea came to him in 1928 when, aged 22, he was a cadet at the RAF College at Cranwell. His first patents are dated 1930. Thus the jet engine was almost a case of simultaneous invention: both inventors now live in the US and are good friends. Each accepts that the other worked entirely independently.
Von Ohain benefitted greatly from having the rich, eccentric Heinkel as patron. Whittle’s story was far different. The Air Ministry scientific branch, now part of the Ministry of Defence, rejected his idea as impractical in 1929. Whittle went back to his squadron where he flew elderly biplanes capable of only 150 miles per hour-his dreams of flying at 500 miles per hour rudely deflated.
But not for good. The RAF recognised it had a gifted recruit and, in 1934, sent Whittle to the University of Cambridge to study engineering. While there he formed a small company, Power Jets, with two ex-RAF officers. Whittle had let his patents lapse because he could not afford the £5 needed to renew them: he got new ones by revising his earlier designs. By 1937, he was testing a rudimentary jet engine at the company’s Rugby workshops.
Whittle’s first jet engine was tiny: it weighed 623 pounds and generated a thrust of 860 pounds, giving it a power to weight ratio of less than 1.5 to 1. Modern fighters, with ratios of around 20 to 1, generate thrusts of more than 30,000 pounds; big passenger jets, with ratios of 5 or 6 to 1, are expected to be generating thrusts of up to 100,000 by 1995.
Although given a handsome lead by Whittle at the beginning of the war, Britain’s jet industry was two to five years behind Germany’s by the end of the war. Germany had the best jet fighter in service and was developing formidable jet bombers (see Box, for more details on the principles and development of jet propulsion). In 1945, the US imported this enormous fund of experience and knowledge, including the services of von Ohain, for the benefit of its own burgeoning industry.
In Britain, Whittle’s company was nationalised; the government had already forced him, in 1943, to hand over the results of his work on jet propulsion to Rolls-Royce. Such largesse helped the company to secure its postwar position in world aviation. Other, smaller aero engine companies were also let in on Whittle’s secrets, but Rolls-Royce was best able to exploit them, and one by one the other companies would fail or merge with it down the years. Whittle was compensated with a knighthood and £100,000 and, from the age of 39, he had little involvement in the development of the jet engine.
In the 1950s, the British thought that they would take a firm lead over the Americans with the Comet, the world’s first passenger jetliner. But the Comet held within its beautiful form the appalling secret of metal fatigue, the failure of a material subjected to repeated stress. After two catastrophes, in which everyone on board was killed, the Comet was grounded and had to be virtually redesigned before it could take to the air again. By then the Boeing 707 and Douglas DC 8 were ready to fly the Atlantic with fare-paying passengers.
One of the great milestones in aviation history was the development of the bypass jet in the 1960s. In this design, a large proportion of the air entering the jet flows around the centre, or core, of the engine instead of through it. The innovation enabled manufacturers to build larger, quieter engines that were capable of generating more thrust. Whittle patented the idea in the early 1940s but it took Rolls-Royce two decades to pioneer the technology with the Conway engine, which was used to power the Boeing 707.
Rolls-Royce’s American competition was not far behind. The difference for the US manufacturers, Pratt and Whitney and General Electric, was that they were developing large bypass engines to power a giant military transport, the C5A Galaxy. Rolls-Royce had no such military contract to support its civilian work, but it had to begin the development of a successor to the Conway engine. So began the saga of the RB211.
Rolls-Royce signed a disastrous contract with Lockheed, the US airframe manufacturer, to use the RB211 in the Lockheed Tristar, which it was building for the airlines. The engine would use some radical new technology, including carbon fibre composite in the front fan, which pressurises air as it enters the engine housing. Rolls had no experience of this type of material, which proved unusable in the crucial role designed for it. The company had to substitute titanium, a heavier material. This change stalled the design of the RB211 and precipitated the financial collapse of Rolls-Royce on 4th February 1971. Barely 30 years after it was born, the British jet industry lay in ruins.
Nationalisation saved Rolls-Royce from going out of business and more investment in the development of the RB211 turned it into the company’s major selling civilian engine. The aviation industry is accustomed to such paradoxes.
So how does Britain’s jet engine industry fare now? While innovation is alive and kicking, the development of ideas is now governed more by economic considerations than by technological constraints. ‘We are not in the business these days of doing things because the technology says you can do them,’ says Mike Howse, head of advanced engineering at Rolls-Royce. Engine manufacturers must be confident about what the airlines will buy, he says. ‘A 25 per cent improvement in fuel consumption may have been saleable in its own right at one time, but if it doesn’t give direct operating cost advantages they won’t buy it.’
Howse points to the large, or wide-chord, fan blade as technological innovation that has paid dividends. These blades, which are fitted to the large front fan of RB211 engines, emerged from the ruins of the experiments with carbon fibre composite in the early 1970s. The alternative material, titanium, offered the blade strength and stiffness but was too dense to use in a conventional way-it would make the blade too heavy. Rolls-Royce’s designers decided to save weight by dispensing with the metal stubs, or clappers, that lock the blades together into a vibration-resistant disc when the fan spins. They were also able to make the blades hollow, except for a titanium honeycomb inside the titanium shell. (The honeycomb is now replaced with girders.)
Rolls-Royce has used wide-chord blades since 1984; now the American industry is going the same way. GE plans to introduce wide-chord blades in its GE90 engine, which promises to be civil aviation’s most powerful propulsion system when it comes into service in mid-1995 (Technology, 27 January 1990).
Long before his first jet flight, Whittle was told that his idea was impractical because he would not find metals that could withstand the enormous temperatures predicted in the centre, or core, of the engine. But the materials appeared when he demanded them. Is this likely to happen again as combustion temperatures rise towards 2000 °C, particularly in the case of military engines? Engineers at Rolls-Royce are cautiously optimistic. They foresee non-metallic engines with ceramics replacing nickel alloys and titanium.
Fibre-reinforced metals and ceramics are the answer for the designer of the future. Titanium can be reinforced by silicon carbide fibres, which give nearly twice the strength to weight ratio of titanium alloys. Glass ceramic matrices reinforced with silicon carbide fibres are alternatives with still better performances. In the hottest parts of the engine, beyond the melting points of nickel alloys, ceramics such as silicon nitride and silicon carbide look promising. Scientists are investigating ways of toughening ceramics to overcome their brittleness. Eventually, ceramic composites will be used for turbine blades, and ceramics will be capable of working in temperatures above 2000 °C, says David Alexander, head of manufacturing technology at Rolls-Royce.
For the next 15 to 20 years the great focus for the future development will be in researching, designing and building the engine for the supersonic airliner to replace Concorde, which Howse sees as being ready around 2010. Rolls-Royce is doing joint studies with Snecma, the French engine company with which it built the Olympus 593 for Concorde. The Olympus is the only engine to power civilian supersonic transport (SST) and its reliability is better than that of any military jet engine. The next SST engine, however, will have to obey far more stringent environmental conditions than does the noisy and thirsty Olympus.
Development of the next supersonic transport engine is ultimately bound up with questions of economics. How many can be sold? What fuel consumption will the airlines accept? What thrust is needed for a much larger supersonic aircraft? What Mach number will it fly?
The answers to these questions are now being worked out in Western Europe and the US. Rolls-Royce and Snecma want maximum speeds no higher than Mach 2.3 to Mach 2.5, a little faster than Concorde, which has a top speed of 1350 miles per hour. Any faster and the airframe designers will have to look for new materials as well. In the US, however, plane-makers are talking of Mach 2.5 to Mach 3.
But how does Whittle see the future, after half a century in which he has seen his ideas change the world? He expects an SST to travel at 2000 miles per hour at 70,000 feet carrying between 200 and 300 passengers. He wants to see an aircraft capable of flying nonstop from London to Hong Kong in three and a half hours. Apart from routine transatlantic supersonic flights, the great prize is to bring the West Coast of America within one stop of the cities of the Pacific basin-Seoul, Tokyo, Beijing, Hong Kong, Singapore and Sydney. The next SST will do that, too.
Long before then, presumably, the present slump will be over and passengers will have flocked back to flying. Airlines will have started buying aeroplanes again and the manufacturers will be back in profit. But will it be easy? The inspectors who investigated the crash of Rolls-Royce in 1971 pointed out that a successful aero engine manufacturer must be a prophet, an inventor, a salesman and an expert wheedler of cash from governments and banks, all rolled into one. Some things don’t change.
Glyn Jones is a science writer and film maker.
Further reading: The Jet Pioneers by Glyn Jones, published by Methuen, London (1990). Whittle: The True Story by John Golley, published by Airlife, Shrewsbury (1987).
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The big breaths that led to jet flight in Britain
Frank Whittle used to demonstrate the principle of jet propulsion by blowing up a balloon, releasing his hold on its neck and allowing it to zip around the room at great speed making a lot of noise.
Jet engines force themselves forward by taking in air and pushing it backwards. The propulsion, or thrust, generated depends on the mass and the speed of the air expelled. While traditional propellors driven by piston engines gave a small acceleration to a large weight of air, the new jet engines were designed to give a large acceleration to a small weight of air.
Whittle’s engine consisted of a fixed air intake, a compressor, a combustion chamber, a turbine and an exhaust outlet. The vanes of the spinning compressor pressurised the air as it flowed into the engine, which had the same effect as blowing up a balloon. As the air sped away from the region of high pressure, its speed was further increased by igniting a mixture of it with fuel in the combustion chamber. The hot exhaust gases flew out of the back of the engine, spinning the turbine on their way. The turbine rotated the compressor, to which it was connected by a shaft.
Whittle considered his engine to be beautifully simple. He would contrast its one moving part (the compressor, shaft and turbine rotating together) with the hundreds of moving parts in a piston engine, all rocking to and fro and wearing one another out.
The first designs of both Whittle and Hans von Ohain used centrifugal compressors. These worked by taking in the flow, whirling the air round in their vanes and throwing it out against the surrounding inside shell, or nacelle, of the engine.
The German Messerschmitt 262 fighter, in service with the Luftwaffe in 1944, broke away from this design with an engine that used axial flow compressors. Instead of being thrown to the side and pressurised, the air passed through a series of sets of blades mounted along the axis, or shaft, of the engine. As the spinning blades whipped the air from one set, or stage, to the next, its pressure increased before it entered the combustion chamber.
Subsequent developments showed that there could be as many as a dozen stages to a low pressure compressor before the air passed to a high pressure compressor where smaller blades spun in a narrower part of the engine. Only then, under very great pressure, was fuel mixed with the air and ignited.
The next major development was the bypass engine, in which air flows around as well as through the centre, or core, of the engine. The core performs as an axial flow engine; around the core, the flow of air-pressurised by a large fan at the front of the engine-is slower and cooler.
General Electric claims that the front fan of its new engine, the GE90, will be more than 3 metres in diameter, almost 25 per cent bigger than the next biggest fan. The engine will generate more thrust by increasing the amount of slower moving air that it expels. This should mean that the engine will make less noise than it would do if it generated more thrust by increasing the speed of the expelled air.