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The turbojet is an airbreathing jet engine, usually used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet, a compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by the fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust.〔(【引用サイトリンク】 publisher = NASA Glenn Research Center )〕 Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s. Turbojets have been replaced in slower aircraft by turboprops which use less fuel. At medium speeds, where the propeller is no longer efficient, turboprops have been replaced by turbofans. The turbofan is quieter and uses less fuel than the turbojet. Turbojets are still common in medium range cruise missiles, due to their high exhaust speed, small frontal area, and relative simplicity. The jet engine is only efficient at high vehicle speeds, which limits their usefulness apart from aircraft. Turbojet engines have been used in isolated cases to power vehicles other than aircraft, typically for attempts on land speed records. Where vehicles are 'turbine powered' this is more commonly by use of a turboshaft engine, a development of the gas turbine engine where an additional turbine is used to drive a rotating output shaft. These are common in helicopters and hovercraft. Turbojets have also been used experimentally to clear snow from switches in railyards. == History == The first patent for using a gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume.〔Maxime Guillaume,"Propulseur par réaction sur l'air," French patent (filed: 3 May 1921; issued: 13 January 1922)〕 His engine was to be an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. Practical axial compressors were made possible by ideas from A.A.Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). The centrifugal-flow turbojet was first patented in 1930 by Frank Whittle of the Royal Air Force, and in Germany, Hans von Ohain patented a similar engine in 1935.〔Experimental & Prototype US Air Force Jet Fighters, Jenkins & Landis, 2008〕 The first turbojet to run was the Power Jets WU which ran on 12 April 1937. On 27 August 1939 the Heinkel He 178 became the world's first aircraft to fly under turbojet power with test-pilot Erich Warsitz at the controls,〔Warsitz, Lutz: (''THE FIRST JET PILOT - The Story of German Test Pilot Erich Warsitz'' (p. 125), Pen and Sword Books Ltd., England, 2009, ISBN 978-1-84415-818-8 )〕 thus becoming the first practical jet plane. The first two operational turbojet aircraft, the Messerschmitt Me 262 and then the Gloster Meteor entered service towards the end of World War II in 1944. Air is drawn into the rotating compressor via the intake and is compressed to a higher pressure before entering the combustion chamber. Fuel is mixed with the compressed air and burns in the combustor. The combustion products leave the combustor and expand through the turbine where power is extracted to drive the compressor. The turbine exit gases still contain considerable energy that is converted in the propelling nozzle to a high speed jet. The first jet engines were turbojets, with either a centrifugal compressor (as in the Heinkel HeS 3), or Axial compressors (as in the Junkers Jumo 004) which gave a smaller diameter, although longer, engine. By replacing the propeller used on piston engines with a high speed jet of exhaust higher aircraft speeds were attainable. One of the last applications for a turbojet engine was the Concorde which used the Olympus 593 engine. At the time of its design the turbojet was still seen as the optimum for cruising at twice the speed of sound despite the advantage of turbofans for lower speeds. For the Concorde less fuel was required to produce a given thrust for a mile at Mach 2.0 than a modern high-bypass turbofan such as General Electric CF6 at its Mach 0.86 optimum speed. Turbojet engines had a significant impact on commercial aviation. Aside from giving faster flight speeds turbojets had greater reliability than piston engines, with some models demonstrating dispatch reliability rating in excess of 99.9%. Pre-jet commercial aircraft were designed with as many as 4 engines in part because of concerns over in-flight failures. Overseas flight paths were plotted to keep planes within an hour of a landing field, lengthening flights. The increase in reliability that came with the turbojet enabled three and two-engine designs, and more direct long-distance flights. High-temperature alloys were a reverse salient, a key technology that dragged progress on jet engines. Jet engines built in the 1930s and 1940s had to be overhauled every 10 or 20 hours due to creep failure and other types of damage to blades. It was not until the 1950s that superalloy technology allowed more economically practical engines.〔Sims, C.T., Chester, A History of Superalloy Metallurgy, Proc. 5th Symp. on Superalloys, 1984.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「turbojet」の詳細全文を読む スポンサード リンク
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