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driving propellers, rotors, ducted fans or propfans
A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power. They are even more similar to turboprops, with only minor differences, and a single engine is often sold in both forms.
Turboshaft engines are commonly used in applications that require a sustained high power output, high reliability, small size, and light weight. These include helicopters, auxiliary power units, boats and ships, tanks, hovercraft, and stationary equipment.
A turboshaft engine may be made up of two major parts assemblies: the 'gas generator' and the 'power section'. The gas generator consists of the compressor, combustion chambers with ignitors and fuel nozzles, and one or more stages of turbine. The power section consists of additional stages of turbines, a gear reduction system, and the shaft output. The gas generator creates the hot expanding gases to drive the power section. Depending on the design, the engine accessories may be driven either by the gas generator or by the power section.
In most designs, the gas generator and power section are mechanically separate so they can each rotate at different speeds appropriate for the conditions, referred to as a 'free power turbine'. A free power turbine can be an extremely useful design feature for vehicles, as it allows the design to forgo the weight and cost of complex multiple-ratio transmissions and clutches.
An unusual example of the turboshaft principle is the Pratt & Whitney F135-PW-600 turbofan engine for the STOVL F-35B – in conventional mode it operates as a turbofan, but when powering the LiftFan, it switches partially to turboshaft mode to send 29,000 horsepower forward through a shaft  and partially to turbofan mode to continue to send thrust to the main engine's fan and rear nozzle.
Large helicopters use two or three turboshaft engines. The Mil Mi-26 uses two Lotarev D-136 at 11,400 hp each,  while the Sikorsky CH-53E Super Stallion uses three General Electric T64 at 4,380 hp each. 
The first gas turbine engine considered for an armoured fighting vehicle, the GT 101 which was based on the BMW 003 turbojet, was tested in the Panther tank in mid-1944.  The first turboshaft engine for rotorcraft was built by the French engine firm Turbomeca, led by its founder Joseph Szydlowski. In 1948, they built the first French-designed turbine engine, the 100-shp 782. Originally conceived as an auxiliary power unit, it was soon adapted to aircraft propulsion, and found a niche as a powerplant for turboshaft-driven helicopters in the 1950s. In 1950, Turbomeca used its work from the 782 to develop the larger 280-shp Artouste, which was widely used on the Aérospatiale Alouette II and other helicopters.  This was following the experimental installation of a Boeing T50 turboshaft in an example of the Kaman K-225 synchropter on December 11, 1951, as the world's first-ever turboshaft-powered helicopter of any type to fly.  The T-80 tank, which entered service with the Soviet Army in 1976, was the first tank to use a gas turbine as its main engine. Since 1980 the US Army has operated the M1 Abrams tank, which also has a gas turbine engine. (Most tanks use reciprocating piston diesel engines.) The Swedish Stridsvagn 103 was the first tank to utilize a gas turbine as a secondary, high-horsepower "sprint" engine to augment its primary piston engine's performance. The turboshaft engines used in all these tanks have considerably fewer parts than the piston engines they replace or supplement, mechanically are very reliable, produce reduced exterior noise, and run on virtually any fuel: petrol (gasoline), diesel fuel, and aviation fuels. However, turboshaft engines have significantly higher fuel consumption than the diesel engines that are used in the majority of modern main battle tanks.
A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion airbreathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.
A turboprop engine is a turbine engine that drives an aircraft propeller.
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part and are, in the direction of flow:
The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion, and the fan, a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.
An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many small UAVs have used electric motors.
The turbojet is an airbreathing jet engine, typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine. The compressed air from the compressor is heated by burning 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. 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.
The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core.
Safran Helicopter Engines, previously known as Turbomeca, is a French manufacturer of low- and medium-power gas turbine turboshaft engines for helicopters. The company also produces gas turbine engines for aircraft and missiles, as well as turbines for land, industrial and marine applications.
The Rolls-Royce Turbomeca RTM322 is a turboshaft engine produced by Safran Helicopter Engines. It was originally conceived and manufactured by Rolls-Royce Turbomeca Limited, a joint venture between Rolls-Royce plc and Turbomeca. The engine was designed to suit a wide range of military and commercial helicopter designs. The RTM322 can also be employed in maritime and industrial applications.
The Bristol Siddeley Nimbus, later known as the Rolls-Royce Nimbus, was a British turboshaft engine developed under license by Blackburn Aircraft Ltd. from the Turbomeca Turmo in the late 1950s. It was used on the Westland Scout and Westland Wasp helicopters.
The Turbomeca Astazou is a highly successful series of turboprop and turboshaft engines, first run in 1957. The original version weighed 110 kg (243 lb) and developed 240 kW (320 shp) at 40,000 rpm. It was admitted for aviation service on May 29, 1961, after a 150-hour test run. The main developing engineer was G. Sporer. It was named after two summits of the Pyrenees.
The Turbomeca Arriel is a series of French turboshaft engines that first ran in 1974. Delivering 650 to 1,000 hp, over 12,000 Arriel engines have been produced from 1978 to 2018, logging more than 50 million flight hours for 40 helicopter applications. In June 2018, 1,000 Arriel 2D were in service, powering H125 and H130 single-engine helicopters, having logged one million flight hours since 2011. After endurance tests and fleet data analysis, their TBO increased by 25% to 5,000 hours and mandatory inspection rose to 15 years with no hourly limit, lowering maintenance costs.
The Turbomeca Artouste is an early French turboshaft engine, first run in 1947. Originally conceived as an auxiliary power unit (APU), it was soon adapted to aircraft propulsion, and found a niche as a powerplant for turboshaft-driven helicopters in the 1950s. Artoustes were licence-built by Bristol Siddeley in the UK, Hindustan Aeronautics Limited in India, and developed by Continental CAE in the US as the Continental T51. Two major versions of the Artouste were produced. The Artouste II family, mainly used in the Aérospatiale Alouette II helicopter, had a one-stage centrifugal compressor and a two-stage turbine, with gearbox-limited power of 300 kW (400 hp). The Artouste III family, mainly used in Aérospatiale's Alouette III and Lama helicopters, had a two-stage axial-centrifugal compressor and a three-stage turbine, with gearbox-limited power of 420–440 kW (560–590 hp).
The Turbomeca Turmo is a family of French turboshaft engines manufacturered for helicopter use. Developed from the earlier Turbomeca Artouste, later versions delivered up to 1,300 kW (1,700 shp). A turboprop version was developed for use with the Bréguet 941 transport aircraft.
The General Electric T58 is an American turboshaft engine developed for helicopter use. First run in 1955, it remained in production until 1984, by which time some 6,300 units had been built. On July 1, 1959, it became the first turbine engine to gain FAA certification for civil helicopter use. The engine was license-built and further developed by de Havilland in the UK as the Gnome, in the West Germany by Klöckner-Humboldt-Deutz, and also manufactured by Alfa Romeo and the IHI Corporation.
The Turbomeca Astafan is a single-spool, variable-pitch turbofan engine developed from the Turbomeca Astazou. Despite successful flight-testing, an efficient, quiet and clean design and some commercial interest, the Astafan never entered series production. The engines were only flown on the Fouga 90 prototype and Turbomeca's two test aircraft.
An airbreathing jet engine is a jet engine that ejects a propelling (reaction) jet of hot exhaust gases after first taking in atmospheric air, followed by compression, heating and expansion back to atmospheric pressure through a nozzle. Alternatively the reaction jet may include a cold jet of ducted bypass air which has been compressed by a fan before returning to atmospheric pressure through an additional nozzle. These engines are gas turbine engines. Engines using only ram for the compression process, and no turbomachinery, are the ramjet and pulsejet.
The Turbomeca Orédon was a small French turbo-shaft / Auxiliary Power Unit (APU) engine produced by Turbomeca in the late 1940s.
Many variations of aircraft engine starting have been used since the Wright brothers made their first powered flight in 1903. The methods used have been designed for weight saving, simplicity of operation and reliability. Early piston engines were started by hand, with geared hand starting, electrical and cartridge-operated systems for larger engines being developed between the wars.
A free-turbine turboshaft is a form of turboshaft or turboprop gas turbine engine where the power is extracted from the exhaust stream of a gas turbine by an independent turbine, downstream of the gas turbine. The power turbine is not mechanically connected to the turbines that drive the compressors, hence the term "free", referring to the independence of the power output shaft. This is opposed to the power being extracted from the turbine/compressor shaft via a gearbox.
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