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AirborneZed

Engine EGT question

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How's it going everyone. A quick question, please. 

 

 

 

I've been searching this in the T7 documentation but could not find the answer to my curiosity.

 

So, I've been noticing that at every normal engine start, the EGT seems to always peak at 556-557 in the EGT reading. And this doesn't seem to be affected by Outside air temperature at all.

 

Now, I am unaware if the EEC has anything to do with limiting the EGT to a certain point at every start, but I wonder if this is either just a pre-determined EGT animation or a realistic implementation.

 

 

Thanks.

 

David


David Zambrano, CPL IRA

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If the peak is always at the exact same value with a variability of 1ºC, then it must be prefixed...

 

I might be wrong, but I don't think an EEC can control something like EGT at engine start in real life automatically to that degree of precision... Controlling "mechanical" things, such as shaft rotation speeds, is relatively easy. Controlling "thermal" things is much more complex due to the nature of thermodynamics and heat transfer.


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Controlling "thermal" things is much more complex due to the nature of thermodynamics and heat transfer.

Exactly why I doubt it can be so consistent.


David Zambrano, CPL IRA

I know there's a lot of money in aviation because I put it there. 

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Exactly why I doubt it can be so consistent.

 

When it comes to 550 degrees C, a few degrees on either side doesn't quite matter.  That said, there's been an adjustment to this in the beta process, so I wouldn't get too hung up on it.


Kyle Rodgers

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When it comes to 550 degrees C, a few degrees on either side doesn't quite matter.  That said, there's been an adjustment to this in the beta process, so I wouldn't get too hung up on it.

Not really a few, but literally + or - 1 degree, which I always felt was just odd.

 

Anyways I hope the SP will have it vary a little more.


David Zambrano, CPL IRA

I know there's a lot of money in aviation because I put it there. 

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In real life the EGT on both engine can be different to a few degree Celsius. I don't normally pay close attention to it at idle as long as it's sit around the ball park, I will have a look next time. At TO THR the maximum EGT difference between the two engines I have seen so far is around 5-10 deg C. The average TO MaX EGT at 30c is about 1045c. The differences stays about the same at cruise thrust with 83-88% N1.

 

EEC only commands thrust. It also controls the turbine blades clearance as well by channeling some bleed air to the turbine casing to maximize the efficiency of the engine at different thrust settings (basically by varying the size of the turbine case through the means of thermal expansion) But it does not directly control EGT.

 

On brand new aircraft and engines I have seen the EGT on both engines matches exactly the same. And as the engines ages, the what we so call "EGT margin" reduced hence the resulting EGT at a given thrust setting rises.

 

The reason behind is after a while the turbines of the engine are subject to tears and wears. It's efficiency decreases hence for the engine to provide the same thrust output the EEC will need to put in more fuel in order for the turbine to spin at same speed as it was new. And the more fuel you put in the higher the EGT is. For this particular reason EGT is also a very good indication to the efficiency of the engine. Often the engine with a bigger EGT will have a higher fuel flow for the reason I mentioned above it will burn more fuel.

 

I am not sure if it's possible to simulate engine wears in flight sim.

 

Happy flying.


Wing Lai

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Driverab330,

 

Thanks for that info, but it doesn't answer my question at all. I'm not sure if I worded my initial question properly. I'm Referring to the initial EGT roll after fuel is introduced, and that in the PMDG 777, it always peaks at a certain temperature, regardless of atmospheric conditions. Basically, like a predetermined animation.

 

But if SP1 addresses this issue, then no worries but then again thanks for the info.


David Zambrano, CPL IRA

I know there's a lot of money in aviation because I put it there. 

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Oh I see what you mean. Based on what I see so far that EGT surge during engine start doesn't really affected by ambient temperature, however on the GE engines in real life it's more depends on the residual EGT after the previous shutdown. Usually for a short turn around, when we start the engine again the residual EGT can still be around 200 deg c, unlike the RR engines GE does not wait until EGT to drop below 100deg c before it introduces the fuel. Hence the peak EGT will be higher than a cold start.

 

To be honest, I reckon even in the full flight sim, it is sort of look like a predetermined animation unless a hot start failure is introduced. I reckon EEC does monitor the rate of increase in EGT, and cut the fuel way before it reached the start limit to prevent EGT exceedence as part of the auto start protection on the ground.

 

Hope this is can sort of answer your question. Cheers


Wing Lai

i7 6850k OC to 4.0GHz / Asus x99-Deluxe II / CORSAIR DDR4-3200 64GB

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