Understanding Helicopter’s Engine | Turboshaft


a turboshaft engine acts as the powerhouse of modern helicopters they are also used for power generation and marine propulsion this video will illustrate the inner workings of turboshaft engines in a clear and logical way the main function of a turboshaft engine is to generate shaft power this is contrary to the function of the turbofan engines used in airliners where the engine function is to produce thrust force in a helicopter shaft power produced by the turbine shaft engine is used to run the rotor let’s examine how this shaft power is produced along with the other accessories needed to produce it the power shaft which turns the rotor receives power from a set of turbines the turbine absorbs energy from hot and high-pressure gas flowing over the blades airfoil technology enables the turbine blades to turn in order to properly guide the flow a set of stator blades is used these are fixed to the engine cover the stator blades also ensure that sufficient flow velocity is maintained at the turbine row Inlet now the question is how this high-energy gas is produced the answer a combustion chamber for effective combustion an atomized fuel form is to be mixed with medium temperature and high pressure air this air is produced by a set of compression stages you can see this compressor is fitted on a hollow shaft and is not connected to the power shaft the compressor requires energy for its operation this energy is provided by a new turbine set which is fitted on the same hollow shaft the only purpose of this new turbine is to supply energy to the compressor it is referred to as a gas producer turbine you can see how the gas producer turbine unit and power turbine unit rotate independently using a coaxial shaft arrangement thus the synchronized operation of the compressor combustion chamber and turbine produced necessary power output at the power shaft a centrifugal compressor is also introduced in the compressor section to effectively compress the gas these are the basic parts and workings of a turbo shaft engine still there are many excellent engineering innovations hidden in this turbine design let’s explore them you may have noticed that the power turbine and gas producer turbine rotate in opposite directions why is the so this is to reduce the gyroscopic effects associated with spinning objects a spinning object has angular momentum this angular momentum affects helicopter motion in a quite complex manner and makes controlling a helicopter quite difficult by spinning the power and gas generator units in opposite directions we almost eliminate the angular momentum of the engine thus making helicopter navigation easier another peculiar design feature is that the fire in the combustion chamber flows in the direction opposite to the major airflow in the system this kind of design is called the reverse flow combustion chamber can also note that a major portion of the compressed air is not used for the combustion process rather they simply engulf the combustion chamber and are bypassed to the combustion chamber this is all to limit the combustion chamber material temperature the combustion produces flame temperatures of up to 1700 degrees Celsius no chamber material will be able to withstand such high temperatures thus by admitting colder secondary air via holes and slots a protective shield is created and proper insulation is given against superhot flames almost 80% of the air is used for cooling purposes a counter flow heat exchanger is the most efficient in exchanging heat the colder air flow counter to the flame makes sure that maximum cooling is guaranteed for the combustion chamber this in effect helps in reducing the combustion chamber length a peculiar and disastrous problem that helicopter and airline pilots face occasionally is compressor stall this results in sudden uncontrolled explosions from the engine along with total loss of shaft power output compressor stall is basically caused by flow separation at compressor airfoil blades birdstrikes low airspeed or wear and tear are frequent reasons for this flow separation to explain the detailed compressor stall physics a dedicated video is needed we will release this soon the compressor stall can be effectively overcome by controlling the throttle and with the usage of variable pitch stator blades the flow separation can be prevented by using these techniques please support us at patreon.com so that we can sustain our video production service thank you