Schematic diagram showing the operation of a simplified turboshaft engine. The compressor spool is shown in green and the free / power spool is in purple.
A
turboshaft engine is a form of
gas turbine which is optimized to produce shaft
power, rather than
jet thrust. In principle, a turboshaft engine is similar to a
turbojet, except the former features additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power.
Turboshaft engines are commonly used in applications which 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.
Overview
A turboshaft engine contains a
gas generator section, consisting of the
compressor, combustion chambers with ignitors and fuel nozzles, and one or more stages of
turbine. The gas generator's function is to create the hot expanding gases to drive the
power section, which consists of more stages of turbines, a gear reduction system, and shaft output. 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 that they may each rotate at different speeds appropriate for the conditions. This is 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 forego the weight and cost of complex multi-ratio
transmissions and
clutches.
The general layout of a turboshaft is similar to that of a
turboprop. The main difference is that a turboprop is structurally designed to support the loads created by a rotating
propeller, as the propeller is not attached to anything but the engine itself. In contrast, turboshaft engines usually drive a transmission which is not structurally attached to the engine. The transmission is attached to the vehicle structure and supports the loads created instead of the engine. However, in practice many of the same engines are built in both turboprop and turboshaft versions, with only minor differences.
History
The first true turboshaft engine was built by the
French engine firm
Turbomeca, led by the founder,
Joseph Szydlowski. In 1948 they built the first French-designed turbine engine, the 100shp 782. In 1950 this work was used to develop the larger 280shp
Artouste, which was widely used on the
Aérospatiale Alouette II and other helicopters.
See also
