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The most typical Helicopter Engines used.

Nowadays is the turboshaft engine just about the most common helicopter engines applied. A new turboshaft engine is properly a jet engine along with normally runs on a gasoline based fuel. There are various variants of turboshaft engines but they all follow basic principles and principles. To keep points simple, Internet marketing referring to the engine utilized by the Bell 206 JetRanger. The Progresses Royce Allison 250/c20J. The important cycle of the turbine engine is similar to that of the cilindro engine. There is induction, data compresion, exhaust and combustion. The major difference is the fact unlike the piston engine, the turbine engines rounds are continuous. In contrast to airplane jet engines the place that the thrust be provided by often the exhaust gases, the particular exhaust gases for the helicopter turbo shaft engine usually are intercepted by a turbine in which transfers the energy from all these gases to a gearbox that delivers power for the helicopter. It's vital that you learn not to over-torque or over-temp the engine as this can have disastrous implications for someone flying it, months or even months later. Misusing the engine will not automatically cause a problem right away.

Starting the helicopter engine causes more anxiety to the components than just in relation to any other operation due to winter shock and wear. For that reason, the commencement cycles are counted in addition to recorded in the technical record after each flight. As helicopters are likely to fly for short time periods compared to airplanes, it is possible how the engine could reach it is start count limit prior to it reaches its beneficial life hour limit. Start-ups are expensive and so it is better for you to leave the engine jogging for ten minutes when waiting for a passenger rather then shutting the engine decrease and then starting up again. The actual engine relies totally about the battery or Auxiliary Electrical power Unit (APU) for startup company. The engine has to be transforming fast enough to keep ample cold air flowing from the turbine otherwise it will come to be very hot and damage the interior components. A weak battery pack could run out of strength before the combustion process turns into self sustaining and this could well be disastrous.

A "Hung Start" can happen if the engine ceases to accelerate and the RPM remains constantly low. This melts away your battery power and if the particular battery runs out of energy then the engine slows down, lesser and lesser cold air is utilized through the engine and later the temperature in the combustion chamber becomes really very hot within a few seconds causing a great deal of damage.

A "Wet Start" is the equivalent of a loaded engine and the igniter possesses failed to light the gas. Look forward to at least 5 minutes and then mélodie the engine. Considering that the battery has already been partially cleared by the failed start plus the venting, it is possibly a good idea to get an external begin to use an APU to make sure you run out of power with your next start attempt. Should you follow the check list exactly then you definately should have no problem starting the particular helicopter engine every time. The most common reason I have viewed for hot starts is usually low time pilots commencing the engine with the accelerator already partially (or fully) open. Therefore it is vital that you can double check that the throttle is actually fully closed before important the starter button. Turbine engines take time to "Spool up" or "Spool down" after you make power changes. This is why you should operate the group or throttle very easily to prevent engine "surging". Surging can happen when the airflow within the compressor blades becomes disrupted causing them to stall. This may lead to loud banging noises (similar to a shotgun going off) and a very noticeable sto? from the engine. Turn off if this happens during startup right away.

The new air Inlet

The oxygen inlet is designed to stabilize the oxygen before it enters the actual compressor. A particle separator may be fitted at this point to clear out any foreign matter including dust or sand that could cause erosion of the compressor blades.

The Compressor.

Often the compressor is made up of a series of knives and an impellor (or centrifugal) compressor. It is created to take large quantities of air and also compress it before guiding it to the combustion segment. The engine in the JetRanger has a six stage capital flow compressor and a sole impellor compressor. In the central compressor, each stage is definitely separated by stator vanes to make sure the air hits the below blades at the correct direction. Because the air flows past these kinds of blades it becomes compressed increasingly more. The pressure goes up and its velocity decreases. Often the centrifugal compressor diverts air outwards into channels that can lead to the combustion section whilst compressing the air further. While in startup there is a bleed sphincter muscle that opens and will allow some of the air to escape in the compressor. This makes it easier to find the engine up to speed and usually takes less power from the power supply. When the engine reaches a new sustainable speed the device closes automatically. Because of the great heat of the compressed air inside compressor section (up in order to 250 degrees celsius), this particular air is used to heating the cabin and for anti-icing. Anti-icing uses air in the rear of the compressor and also directs it through the compressor casing and the inlet guidebook vanes to prevent ice developing there. When anti-icing is employed there will be a small rise in Turbine Outlet Temperature (TOT).

Typically the Combustion Section.

On this section the fuel is actually mixed with the air and captivated. Air ducts are shaped so that the flame never has contact with the metal cased characters but instead is contained inside a shroud of cooler air flow. A large proportion of the air is used with regard to cooling. As the fuel is lit as well as the engine is to running increase, the combustion is self sustaining. The particular engine is turned primarily by a starter. When there is enough airflow throughout the engine to keep everything neat, the fuel is captivated by the igniter plug. The actual fuel enters the combustion chamber through a fuel nozzle that atomizes the gas. With ignition the gases grow and flow to the turbine section at an increased speed. Approximately 60 to help 80% of the air getting into the combustion chamber can be used to keep the liners awesome. The fuel nozzle is extremely polished and engineers need to handle it very carefully because the tiniest scratch will bother the spray pattern in addition to cause hot spots that may eventually damage the turbine blades. It has holes intended for delivering fuel.

The Turbine Section.

It creates the power. The turbine inlet is the hottest the main helicopter engine and it is far too hot for temperature detectors to survive here. Temperature is definitely therefore measured between the wind generators by thermocouples (the tellings are averaged and exhibited in the cockpit instrument display) and is called the Turbine Store Temperature (TOT). The heat is usually kept to a manageable amount by cold air removed from the compressor which is influenced through a connection by the turbine. The gases are instructed through the compressor turbine knives (N1) thus ensuring that the particular compressor is continually run. From there the gases move through a two stage "Free Turbine" (N2). As being the free turbine is not attached to the compressor, the engine is easier to turn during start-up. The free turbine is usually connected to the Accessory gearbox which will reduces the high speed from the turbine to a more possible level. When more electrical power is required, the compressor pace (N1) increases to supply much more air. At the same time more energy enters the combustion step and therefore N2 is preserved at a constant speed. Typically the turbine blades are in a very hostile environment. As being the temperatures are so high and also the blades are spinning therefore very fast, centrifugal force reasons the blades to stretch out (blade creep). This is regular, nevertheless if the engine has had a new hot start, the particular blade creep becomes a greater than normal and turns into permanent. The actual blades can make contact with the perimeters and expensive repairs will be required. Increased TOT temperatures are acceptable during startup as the turbine is spinning relatively little by little. The N1 turbine is performing more work than the N2 turbine. It truly is exposed to hotter gases in addition. Hence the N1 turbine features only half of the service life on the N2 turbine.

Typically the Accessory Gearbox.

The adornment gearbox converts the high pace of the free turbine (N2) to a more manageable stage. Very low drive-shaft powering the main one gearbox, a rear drive-shaft powering the tail one, any freewheel attachment and product points for all the accessories including fuel pump, tachometers, generator and so on

Compressor Stall.

Compressor stop moving can occur on any turbine engine if the conditions continue. In order to meet the design demands, often the engine must have a high strength output relatively, good fuel intake and fast acceleration qualities. For these reasons it is beneficial to handle as closely as possible on the stall angle of the compressor blades.

Operating close to the stop moving angle has the following rewards:
-The volume of air succeeding the engine is improved.
-The pressure ratio of the engine is increased increasing the capability output thus.
-Turbine temperatures may be increased because of the greater air flow.
-- The efficiency of the turbine and compressor sections usually are increased.

To minimize the risk of the compressor waiting during acceleration or start-up, typically the fuel flow is cautiously regulated. What exactly is compressor stall?. Quite a few pages could be devoted to describing this but the following justification should help answer the kind of question. Compressor vanes and blades are generally aerofoils.

The airflow more than an aerofoil will individual and become turbulent if both of the following occurs:
-The velocity of the air transferring over the aerofoil is too minimal.
-The angle of strike is too high.

When the airflow over an aerofoil separates the aerofoil shops then. Around 80% of the air coming into the engine is used regarding cooling. This means that much more weather has to enter the engine than is needed for cooling. Often the cooling air is used to overpower the length of the flame inside combustion chamber and prevent the idea from touching the sides from the container. The hot combustion gas are cooled by the chilling air and the cooling weather is also heated by the combustion gases. This keeps the particular gases at an acceptable heat as they mix and the turbine section. If excessive fuel is supplied to the burning, there will be more than enough air to permit proper combustion. Nevertheless as extra air is employed during this combustion, you will have less air available for chilling and the temperature inside the combustion chamber will rise for that reason. As the temperature rises, you will have more gases to be worn out. It is possible that the volume of fumes to be exhausted may go over the capacity of the turbine as well as the turbine will "choke". During these moments, the pressure inside the combustion chamber will rise speedily and may equal or go over the pressure that the compressor is producing. If the tension in the combustion chamber is usually equal to the pressure in the compressor discharge air, the particular compressor will stall subsequently. If the pressure in the combustion chamber exceeds the stress of the compressor discharge air flow, then not only will the compressor stall but also the hot fumes will flow from the combustion chamber into the compressor part.

Which will conditions shall result in a decrease of air into the combustion holding chamber. The particular flame shall not have enough o2 and will die, resulting in a super fast drop in temperature. Because the temperature drops, the development is stopped (or significantly reduced). The turbine is not choked and the combustion slot provided pressure drops to a suprisingly low value. The low pressure inside the combustion chamber means that weather can flow in the suitable direction again. The compressor is no longer stalled and a "Surge" of air flows into the combustion chamber. This particular extremely fast movement of surroundings elongates the flame downstream and through the turbine leading to another rapid expansion on the gases. The particular cycle repeats itself on 120 times per next approximately. Compressor stalls might or may not provide an audible sound but people often be a vibration. In case the stall is severe a new flame may emanate in the exhaust or a very obnoxious backfire may be heard. Smoke cigarettes may also be seen. In the event the proper corrective action is done immediately then it is impossible that any damage will probably occur.

The actions to be taken are generally:
-Reduce the throttle in order to flight idle.
-If the stall remains in that case close the throttle entirely and shut down the engine.

Quick throttle movements may encourage stalling it is a good idea to produce smooth therefore , slow throttle movements.