Like a turboprop, a turboshaft engine is an internal combustion machine which has been fitted with an additional turbine. But instead of driving a propeller, it powers the helicopter rotor blades through a special transmission system, which is connected to the additional turbine shaft.
A special type of turboshaft engine is employed for auxiliary power units, like the Solar T-62T-27. It serves as a backup electrical power source in the air or on the ground. In power generation, this type of engine is also utilized as industrial gas turbine which drives stationary power generators.
How it works
The turboshaft engine compressor first increases the incoming air pressure, which is then directed into the combustion chamber, where it is mixed with vaporized fuel and burned. This combustion produces hot gases, which expands through the two separate turbines, with the first one driving the compressor and the second one driving the shaft horse power that propels the helicopter rotor through a transmission gear. Finally, the gas is released through an exhaust duct. This gas does not provide any thrust.
Below, a diagram of a General Electric T64 turboshaft engine, with its different parts
