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Turboprop

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image:Turboprop operation.png thumb|right|320px|A schematic diagram showing the operation of a turboprop engine. A '''Turboprop''' (''Turbo-propeller'') or turboshaft engine is a type of Gas turbine gas turbine engine. It differs from a Turbojet in that the design is optimized to produce rotating shaft power to drive a propeller, instead of thrust from the exhaust gas. Basically, a turbojet consists of an intake, compressor, combustor, turbine and a propelling nozzle. Air drawn into the intake is compressed by the compressor. Fuel is burnt with the compressed air in the combustor. The hot combustion gases expand through the turbine, to provide power to the compressor. Further expansion of the gases occurs in the propelling nozzle; the high velocity jet produced providing forward thrust. In a turboprop much of the jet thrust is sacrificed in favor of shaftpower, which is obtained by extracting additional power (to that necessary to drive the compressor) from the turbine expansion process. Whilst the power turbine may be integral with the gas generator section, many turboprops today feature a Free Power Turbine, on a separate coaxial shaft. This enables the propeller to rotate freely, independent of compressor speed. Owing to the additional expansion in the turbine system, the residual energy in the jet is fairly low (<10% of total thrust, including that of the propeller). Because the propeller is very much larger in diameter than the power turbine, the tip speed of the propeller can become supersonic. Consequently, to prevent this, a speed reduction gearbox is inserted between the power turbine and propeller shafts. The gearbox is part of the engine, whereas in a turboshaft the (helicopter) rotor reduction gearbox is remote from the engine. Residual thrust on a turboshaft is avoided by further expansion in the turbine system and/or truncating and turning the exhaust through 90 degrees, to produce two opposing jets. Apart from the above, there is very little difference between a turboprop and a turboshaft. Turboprops are very efficient at modest flight speeds (below 724 km/h or 450mph), because the jet velocity of the propeller (and exhaust) is relatively low. Consequently, small commuter aircraft and military transports tend to feature turboprop engines. Although turboprops are used in some General Aviation applications, their high price deters more widespread acceptance. While most modern turbojet and turbofan engines use axial-flow compressors, turboprop engines usually contain at least one stage of centrifugal compressor centrifugal compression, because of the small size of the engines. Image:Rolls-Royce RB50 Trent Turboprop On Test Rig At Hucknall.jpg thumb|240px|right|A Rolls-Royce RB.50 ''Trent'' on a test rig at Hucknall, in March 1945 Propellers lose efficiency as aircraft speed increases, which is why turboprops are not used on higher-speed aircraft. However, turboprops are far more efficient than piston-driven propeller engines.

History
The world's first Turboprop was the 'Jendrassik Cs-1' designed by the Hungary Hungarian engineer György Jendrassik. It was produced and flown briefly in Czecho-Slovakia between 1939 and 1942. The aircraft it was fitted to was the Varga XG/XH twin-engined Recconaisance bomber. Not surprisingly the engines proved very unreliable. Jendrassik had also produced a small-scale 75 kW turboprop in 1937. The first British turboprop engine was the Rolls-Royce plc Rolls-Royce RB.50 Rolls-Royce Trent Trent, a converted Rolls-Royce Derwent Derwent II fitted with reduction gear and a Rotol 7' 11" five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 — the sole "Trent-Meteor" — which became the first relatively reliable turboprop powered aircraft. From their experience with the Trent, Rolls-Royce developed the Dart, which became one of the most reliable turbprop engines ever built. Dart production continued for more than fifty years. The first American turboprop was the General-Electric T-31. A European consortium is currently developing the 11,000 shp TP400-D6 turboprop for the Airbus A400M military transport. The engine is all-axial and has a two shaft core, with a free power turbine mounted on a third coaxial shaft. The most popular turboprop engine ever built is the legendary Pratt & Whitney Canada PT6 The first low cost 255 shp turboprop engine is now being developed by [http://www.Innodyn.com Innodyn] for the homebuilt aircraft market.

See also
*Jet Engine Performance *Jet aircraft *Jetboat *Turbofan *Turbojet *Jet Engine *Turboshaft *Ramjet *Spacecraft propulsion *Supercharger *Turbocharger *Gas turbine *Kurt Schreckling who built practical jet engines for model aircraft *[[Wikibooks:Jet_Propulsion|Wikibooks: Jet propulsion]] {{airlistbox}} Category:Gas turbines Category:Turboprop engines Turboprop engines Category:Aircraft engines Category:Jet engines de:Turboprop fa:توربوپراپ fr:Turbopropulseur ko:터보프롭 it:Turboelica nl:Turboprop no:Turboprop sv:Turbopropmotor

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