Aviation and War Machine

History

“After World War Two, piston engines continued to power civil airliners for many years, but in the field of military aircraft they were rapidly displaced by the gas turbine. Fighters and bombers switched to the turbojet, transports and maritime-patrol aircraft used turboprops, and helicopters benefited greatly from changing to turboshaft engines. The change meant more power for less weight, far greater reliability, no cooling problems and safer kerosene-type fuels.

With extraordinary reluctance, designers eventually recognized that the turbofan, offering a wide choice of bypass ratio (BPR - the mass flow of air in the bypass duct divided by that through the core), could with advantage replace the turbojet. In supersonic aircraft the need to minimize frontal area means that BPR is seldom as high as 1, and even then the installation must be done with great care. When the J79 turbojet of 79.63 kN thrust installed in the McDonnell Douglas F-4 Phantom was replaced in the British versions by the Rolls-Royce Spey turbofan of 91.25 kN the change made the aircraft slower in level flight, while giving improvements in take-off and climb performance!

Today the turbojet is almost extinct, except for some countries like China, where different criteria apply. Elsewhere, the trend has been towards achieving greater power with engines that are not only lighter but also smaller and dramatically simpler. For example, the Spey Mk 202, the engine of the RAF Phantoms, had a total of 17 stages of blading in the compressors (5+12 flow pressure+high pressure) and four stages of blading in the turbines (2+2). The next-generation RB. 199, engine of the Tornado, has 12 stages of compression (3+3+6) and again four stages of expansion through the turbines (1+1+2), whereas today’s Eurojet EJ200, engine of the Eurofighter, has only eight compressor stages (3+5) and two turbine stages (1+ 1).
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A jet engine is an engine that discharges a fast moving jet of fluid to generate thrust in accordance with Newton’s third law of motion. This broad definition of jet engines includes turbojets, turbofans, rockets and ramjets and water jets, but in common usage, the term generally refers to a gas turbine used to produce a jet of high speed exhaust gases for special propulsive purposes.

History
In the 1930s, the piston engine in its many different forms (rotary and static radial, aircooled and liquid-cooled inline) was the only type of powerplant available to aircraft designers. However, engineers were beginning to realize conceptually that the piston engine was self-limiting in terms of the maximum performance which could be attained; the limit was essentially one of propeller efficiency. This seemed to peak as blade tips approached the speed of sound. If engine, and thus aircraft, performance were ever to increase beyond such a barrier, a way would have to be found to radically improve the design of the piston engine, or a wholly new type of powerplant would have to be developed. This was the motivation behind the development of the gas turbine engine, commonly called a “jet” engine, which would become almost as revolutionary to aviation as the Wright brothers’ first flight.

The key to a practical jet engine was the gas turbine, used to extract energy to drive the compressor from the engine itself. In 1929, Aircraft apprentice Frank Whittle formally submitted his ideas for a turbo-jet to his superiors. On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932). The patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Whittle would later concentrate on the simpler centrifugal compressor only, for a variety of practical reasons. In 1935 Hans von Ohain started work on a similar design in Germany, seemingly unaware of Whittle’s work. Whittle had his first engine running in April 1937. It was liquid-fuelled, and included a self-contained fuel pump. Von Ohain’s engine, as well as being 5 months behind Whittle’s, relied on gas supplied under external pressure, so was not self-contained. Whittle unfortunately failed to secure proper backing for his project, and so fell behind Von Ohain in the race to get a jet engine into the air.
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