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Turboshaft

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A turboshaft is a specialized type of gas turbine engine. Most jet engines are designed to produce jet thrust to push an aircraft forward. A turboshaft is optimized to produce shaft horsepower instead. This means the engine focuses on turning a mechanical shaft to provide power.

Turboshaft operation (multilanguage)
Turboshaft operation (multilanguage)

These engines are vital for machines requiring high power output and reliability. They are valued because they are small and lightweight for the energy they provide.

To understand the mechanism, you can view the engine as two main assemblies. The first assembly is the gas generator. This part contains a compressor, combustion chambers with fuel nozzles, and ignitors. It also includes one or more stages of turbine. The gas generator works to create hot, expanding gases. These gases are then sent to the second assembly, known as the power section.

Turboshaft operation (multilanguage)
Turboshaft operation (multilanguage)

The power section consists of additional turbine stages, a gear reduction system, and the shaft output. The expanding gases drive these turbines to create mechanical power.

Many modern designs use a specific setup called a free power turbine. In these engines, the gas generator and the power section are mechanically separate. This separation allows the two parts to rotate at different speeds. Each part spins at a speed that is best for its specific conditions. This design is very useful for vehicles. It allows engineers to avoid the high cost and weight of complex clutches or multiple-ratio transmissions.

Turboshaft technology has a long history of development. In 1948, the French firm Turbomeca built the 782 engine. This was the first French-designed turbine and produced 100 shaft horsepower. In 1950, they developed the larger Artouste engine. A major milestone occurred on December 11, 1951. On that date, a Boeing T50 turboshaft powered a Kaman K-225 synchropter. This was the first time a helicopter of any type flew using a turboshaft engine.

These engines are used in many heavy-duty machines. Large helicopters often require multiple engines to operate safely. For example, the Mil Mi-26 uses two Lotarev D-136 engines. Each of those engines produces 11,400 hp. The Sikorsky CH-53E Super Stallion uses three General Electric T64 engines. Each T64 engine produces 4,380 hp.

Austin gasturbine engine (cutaway) Heritage Motor Centre, Gaydon
Austin gasturbine engine (cutaway) Heritage Motor Centre, Gaydon

Such high power is necessary for lifting heavy loads in the air.

Military vehicles also utilize gas turbine technology. The Soviet T-80 tank entered service in 1976 as the first tank to use a gas turbine as its main engine. The US Army has operated the M1 Abrams tank with a gas turbine since 1980. Some tanks use them differently, like the Swedish Stridsvagn 103. That tank used a gas turbine as a secondary "sprint" engine to help its primary piston engine.

Austin gasturbine engine (cutaway) Heritage Motor Centre, Gaydon
Austin gasturbine engine (cutaway) Heritage Motor Centre, Gaydon

These engines are reliable and can run on petrol, diesel, or aviation fuels.

There are interesting connections between different types of engines. The Pratt & Whitney F135-PW-600 is a unique example. It is a turbofan engine used for the STOVL Lockheed F-35B Lightning II. In normal flight, it works as a turbofan. However, it can switch partially to turboshaft mode. In this mode, it sends 29,000 horsepower through a shaft to power the Rolls-Royce LiftSystem. This allows the jet to perform special vertical maneuvers.

Turboshaft operation (multilanguage)
Turboshaft operation (multilanguage)
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