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Could you tell me what is the Maximum Permissible Indicated Turbine Temperature (ITT) and the ambient limit temperature for sea level static thrust?

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The Maximum Permissible Indicated Turbine Temperature (ITT) is the maximal operating temperature that you can accept without reducing power or shutting down the engine. This temperature is taken at the turbine entry and the limit is there to ensure good cycle endurance of the turbine blade. Higher temperatures and you will have increased fatigue degradation due to reduced mechanical properties. Now your question is why are there 3 different ones:

The maximum continuous is the maximal operating temperature of the engine for infinite life cycle endurance. At that temperature the engine turbine should not wear for the whole life of the engine. But in certain condition it might happen that the temperature exceed this value and in specific cases it was taken into account during the design.

The take-off temperature is what is going to dictate your power input, obviously you want 100%, but high AOA, slow relative speed means that your engine is not max performing and as you are applying full power, you might end up with a richer air-fuel ration than normal condition and see a temperature above your maximum continuous quite often. But the 5 first minutes of the flight at takeoff are critical so reducing power would be not good for safety, thus you allow for slightly higher temps, for a short amount of time.

And for the Maximum starting temp is the absolute limit you should never exceed. During startup the airflow inside the combustion chamber is not perfectly installed and it might happen that the combustion flame come closer to the turbine in addition to the richer air-fuel ratio than in normal condition, thus seeing increased temperature. But this should not extend for more than a few seconds or you'll have to shut down the engine.

Concerning the sea level static thrust this is the maximum output you can ask from the engine and only up to the max temperature indicated. Above that temperature you would see a decrease in performances to prevent exceeding ITT. This would then resume in reduced takeoff performances.

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  • $\begingroup$ can we deduce the turbine exit temperature from the ITT? $\endgroup$ – user39178 Oct 2 '20 at 21:01
  • $\begingroup$ Yes and no. It mostly depends on how much work the turbine extract from the flow to drive the propeller... If you know that you can determine the exit flow properties. $\endgroup$ – MaximEck Oct 2 '20 at 21:28
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The ambient temperature limit is the highest ambient temperature at which the engine will be able to provide listed Sea Level Static Thrust. If the air temperature is higher, the engine will reduce its thrust to prevent exceeding the maximal permissible temperature in the turbine.

The ambient temperature limit is important in aircraft operation, because at temperatures above this limit there will be less thrust available and thus the take-off performance is reduced.

The Maximum Permissible Indicated Turbine Temperature (ITT) is the maximum indicated turbine temperature that is allowed. Pilots should monitor the ITT and make sure the maximum permissible is not exceeded.

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