Rotorcraft Flying Menu >Helicopter Systems>Engines >Turbine Engine > Turbine

The turbine section consists of a series of turbine wheels that are used to drive the compressor section and the rotor system. The first stage, which is usually referred to as the gas producer or N1 may consist of one or more turbine wheels. This stage drives the components necessary to complete the turbine cycle making the engine self-sustaining. Common compo-nents driven by the N1 stage are the compressor, oil pump, and fuel pump. The second stage, which may also consist of one or more wheels, is dedicated to driving the main rotor system and accessories from the engine gearbox. This is referred to as the power turbine (N2 or Nr ).

If the first and second stage turbines are mechanically cou-pled to each other, the system is said to be a direct-drive engine or fixed turbine. These engines share a common shaft, which means the first and second stage turbines, and thus the compressor and output shaft, are connected.

On most turbine assemblies used in helicopters, the first stage and second stage turbines are not mechani-cally connected to each other. Rather, they are mounted on independent shafts and can turn freely with respect to each other. This is referred to as a “free turbine.” When the engine is running, the combustion gases pass through the first stage turbine to drive the compressor rotor, and then past the independent second stage tur-bine, which turns the gearbox to drive the output shaft.