What is a turboshaft engine?
A turboshaft engine, which is a version of the jet engine, powers nearly every helicopter built today. As the above image illustrates, the turboshaft utilizes many of the same components as a turbojet.
The key difference between the turboshaft and other jet engines is that the turbine not only drives the compressors, but the shaft is also connected to a gear box that drives a helicopter’s rotor blades.
Although the engine shaft rotates about the horizontal, the gear box contains a sequence of gears that transform that motion to a rotation about the vertical axis as required by a helicopter main rotor.
Helicopters also typically operate at much lower altitudes than aircraft where dust, sand, and other debris can easily be sucked into the engine. To address this problem, most turboshaft engines are equipped with a particle separator that filters out and expels the unwanted dust before the air flow reaches the compressor.
As a consequence of flying lower, these engines can be deafeningly loud hence the need for onboard headphones and speakers in most helicopters for passengers to communicate with each other.