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The Pratt & Whitney Canada PT6 is one of the most popular turboprop aircraft engines in history,〔(【引用サイトリンク】title=United Technologies History )〕 and is produced by Pratt & Whitney Canada. The PT6 family is particularly well known for its extremely high reliability, with MTBOs on the order of 9000 hours in some models. In US military use, they are designated as T74 or T101. The main variant, the PT6A, is available in a wide variety of models, covering the power range between 580 and 920 shaft horsepower in the original series, and up to in the "large" lines. The PT6B and PT6C are turboshaft variants for helicopters. ==Design and development== In 1956, PWC's President, Ronald Riley, foreseeing the need for engines with much higher power to weight ratios, ordered engineering manager Dick Guthrie to establish a development group to create a turboprop engine designed to replace piston engines. Demand for the Pratt & Whitney Wasp radial engine was still strong and its production line's output was robust and profitable. Riley gave Guthrie a modest budget of C$100,000. Guthrie recruited young engineers from the National Research Council in Ottawa and from Orenda Engines in Ontario. In 1958, the group began development of a turboprop engine intended to deliver 450 shaft horsepower. The first engine was powered up and run successfully in February 1960.〔 It first flew on 30 May 1961, mounted on a Beech 18 aircraft at de Havilland Canada's Downsview, Ontario facility. Full-scale production started in 1963, entering service the next year. By the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions. The engine is used in over 100 different applications. Design innovations included keeping the power turbine and propeller shaft sections independent, connecting them with a fluid coupling analogous to an automotive torque converter. The igniter starts only the gas generator, making the engine easy to start, particularly in cold weather.〔 The engine consists of two sections that can be easily separated for maintenance.〔 In the ''gas-generator section'' air enters through an inlet screen into the low-pressure axial compressor. This has three stages on small and medium versions of the engine and four stages on large versions. The air then flows into a single-stage centrifugal compressor, through the annular reverse-flow combustion chamber, and finally through a single-stage compressor turbine that powers the compressors at about 45,000 rpm. The hot gas from the gas generator section then flows into a separate ''power section'' of the engine, containing a single-stage power turbine driving the power take-off system at about 30,000 rpm. For turboprop use, this powers a two-stage planetary output reduction gearbox, which turns the propeller at a speed of 1,900 to 2,200 rpm. The exhaust gas then escapes through two side mounted ducts in the power turbine housing. The engine is arranged such that the power turbines are mounted inside the combustion chamber, reducing overall length. In most aircraft installations the PT6 is mounted backwards in the nacelle, so that the intake side of the engine is facing the rear of the aircraft. This places the power section at the front of the nacelle, where it can drive the propeller directly without the need for a long shaft. Intake air is usually fed to the engine via an underside mounted duct, and the two exhaust outlets are directed rearward. This arrangement also aids maintenance by allowing the entire power section to be removed along with the propeller, exposing the gas-generator section. It also allows rough-field operations with foreign objects slung outside and around the compressor intake by inertial separators in the inlet. Several other versions of the PT6 have appeared over time. The PT6A large added an additional power turbine stage and a deeper output reduction, producing almost twice the power output, between 1,090 and . The PT6B is a helicopter turboshaft model, featuring an offset reduction gearbox with a freewheeling clutch and power turbine governor, producing at 4,500 rpm. The PT6C is a helicopter model, with a single side-mounted exhaust, producing at 30,000 rpm, which is stepped down in a user-supplied gearbox. The PT6T Twin-Pac consists of two PT6 engines driving a common output reduction gearbox, producing almost at 6,000 rpm. The ST6 is a version intended for stationary applications, originally developed for the UAC TurboTrain, and now widely used as auxiliary power units on large aircraft, as well as many other roles.〔(【引用サイトリンク】title=Pratt & Whitney PT6A-42 Turboprop )〕 When de Havilland Canada asked for a much larger engine, roughly twice the power of the PT6 Large, Pratt & Whitney Canada responded with a new design initially known as the PT7. During development this was renamed to become the Pratt & Whitney Canada PW100. Turboprops such as the PT6 and PW100 may have a bypass ratio over 50,〔Ilan Kroo and Juan Alonso. "(Aircraft Design: Synthesis and Analysis, Propulsion Systems: Basic Concepts ) (Archive )" ''Stanford University School of Engineering, Department of Aeronautics and Astronautics''. Quote: "When the bypass ratio is increased to 10-20 for very efficient low speed performance, the weight and wetted area of the fan shroud (inlet) become large, and at some point it makes sense to eliminate it altogether. The fan then becomes a propeller and the engine is called a turboprop. Turboprop engines provide efficient power from low speeds up to as high as M=0.8 with bypass ratios of 50-100."〕〔(Prof. Z. S. Spakovszky ). "(11.5 Trends in thermal and propulsive efficiency ) (Archive )" ''MIT turbines'', 2002. (Thermodynamics and Propulsion )〕〔Nag, P.K. "(Basic And Applied Thermodynamics )" p550. Published by Tata McGraw-Hill Education. Quote: "If the cowl is removed from the fan the result is a turboprop engine. Turbofan and turboprop engines differ mainly in their bypass ratio 5 or 6 for turbofans and as high as 100 for turboprop."〕 although propeller airflow is slower than for turbofans.〔"(Turboprop Engine )" ''Glenn Research Center (NASA)''〕〔Philip Walsh, Paul Fletcher. "(Gas Turbine Performance )", page 36. John Wiley & Sons, 15 April 2008. Quote: "It has better fuel consumption than a turbojet or turbofan, due to a high propulsive efficiency.., achieving thrust by a high mass flow of air from the propeller at low jet velocity. Above 0.6 Mach number the turboprop in turn becomes uncompetitive, due mainly to higher weight and frontal area."〕 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「Pratt & Whitney Canada PT6」の詳細全文を読む スポンサード リンク
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