Academic Reading — Test 170

Reading passage

For the first three decades of powered flight, almost every aeroplane relied on the same basic arrangement: a piston engine turning a propeller. This combination served well at the modest speeds and altitudes of early aviation, but it carried hidden limits. As an aircraft climbs into thinner air, a propeller loses its grip, and as speed rises towards the speed of sound the blade tips begin to behave erratically. Engineers in the 1920s sensed that a fundamentally different source of thrust would be needed if flight were ever to become much faster or to reach much higher. The eventual answer was the gas turbine, a machine that swallows air at the front, heats it violently in the middle, and hurls it out of the back. The British officer most closely associated with turning that idea into a working engine was Frank Whittle. Whittle was a young Royal Air Force cadet when he first set out the principle in a thesis written in 1928. His reasoning was strikingly simple. A piston engine wastes effort by stopping and starting the flow of gases thousands of times a minute; a turbine, by contrast, keeps the gases moving in one continuous stream. If a compressor squeezed incoming air, fuel were burnt in that compressed air to raise its temperature, and the hot gas were then allowed to expand through a turbine, the result would be a smooth and powerful jet of exhaust. Crucially, the same turbine that extracted energy from the gas could also drive the compressor at the front, so the machine would, once started, sustain its own cycle. Whittle applied for a patent on this design in 1930, but the Air Ministry of the day showed little interest, judging the scheme impractical, and he was unable to find official money to build it. Discouraged but not defeated, Whittle allowed his patent to lapse for want of the small renewal fee. It was only in 1936, with the backing of two former RAF colleagues and a modest amount of private investment, that he was able to form a company, Power Jets, to pursue the engine seriously. The firm built its first experimental unit, and on a spring day in 1937 that engine was run for the first time on a test bench. The trial was alarming as much as it was encouraging: the machine ran faster and faster of its own accord, and onlookers feared it might tear itself apart. The early years of testing were dominated by stubborn engineering problems. The combustion chamber, where fuel met compressed air, was especially troublesome, for no one yet knew how to burn so much fuel so quickly in so small a space without the flame going out or the metal melting. The deeper difficulty lay in materials. The turbine sat directly in the path of gas that might be hotter than nine hundred degrees Celsius, and it had to spin at enormous speed without softening or stretching. Ordinary steels could not survive such conditions for long. Progress therefore depended as much on the slow work of metallurgists, who developed new heat-resisting alloys, as on the cleverness of the designers themselves. This dependence on better metals explains why the jet engine, although conceived in the 1920s, could not have been built much earlier than it was. Whittle was not working in isolation, although for many years he did not know it. In Germany, an engineer named Hans von Ohain had arrived at a similar idea independently, and his engine actually flew first, powering a Heinkel aircraft into the air in August 1939, days before the outbreak of the Second World War. Britain's first jet-powered aeroplane, the Gloster E.28/39, did not fly until May 1941. The war, which might have been expected to delay such experimental work, instead accelerated it, because both governments now grasped the military value of faster aircraft. Resources that had been refused in peacetime were suddenly made available. By the closing stages of the war, jet fighters were entering service on both sides, though too late and in too few numbers to decide the outcome. The lasting significance of Whittle's work, however, lay beyond the conflict. The gas turbine he helped to pioneer became the standard means of propelling large aircraft, and in modified forms it now drives ships, generates electricity in power stations, and pumps gas through pipelines. Whittle himself received belated honours and is remembered as one of the central figures in the history of flight. Yet his career also illustrates a recurring pattern in invention: that a sound idea may wait years for the surrounding technology, and the institutional will, to catch up with it.