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What can cause a turbine to overheat? - 7/12/2012 2:47 PM   
Pete S-RCU



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Status: offline 		My SJ 1200-18 has started over temping at full throttle.
I'm running it on a test stand, so it has all the air it needs.
Runs up to 159k and the temp goes over 800C.
Then ecu throttles it back to 140k and it does the same thing.
I know bad bearings can cause drag and high temps.
I had new bearings put in two tears ago, it only has seven flights on since.
Brgs seem ok, it continues to spin if you spin it by hand.
Can ceramic bearings rust?
I thought they had stainless steel races, and the ceramic balls won't rust.

What else can cause high temps?



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RE: What can cause a turbine to overheat? - 7/12/2012 4:06 PM   
bluescoobydoo


 

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Status: offline 		how much oil is there in your fuel?

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RE: What can cause a turbine to overheat? - 7/12/2012 4:13 PM   
basimpsn


 

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quote:

ORIGINAL: Pete S-RCU

My SJ 1200-18 has started over temping at full throttle.
I'm running it on a test stand, so it has all the air it needs.
Runs up to 159k and the temp goes over 800C.
Then ecu throttles it back to 140k and it does the same thing.
I know bad bearings can cause drag and high temps.
I had new bearings put in two tears ago, it only has seven flights on since.
Brgs seem ok, it continues to spin if you spin it by hand.
Can ceramic bearings rust?
I thought they had stainless steel races, and the ceramic balls won't rust.

What else can cause high temps?




Could be touching at full Rpm, does the tail cone glows bright orange at full power? if not then it could be your probe too far inside the cone.


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RE: What can cause a turbine to overheat? - 7/12/2012 4:16 PM   
flyinfool1



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Status: offline 		Another possibility is the the thermocouple is too far into the exhaust giving an artificially high temp. Each turbine has a specific distance that it should be. I do not know what yours is supposed to be.


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RE: What can cause a turbine to overheat? - 7/12/2012 6:05 PM   
Pete S-RCU



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Status: offline 		Everything is as it always was, but I'll try moving it out a little and see.
Good suggestion.
I'll let you know if it helps.



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RE: What can cause a turbine to overheat? - 7/12/2012 6:46 PM   
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Status: offline 		I have (twice)  see a turbine have issues with rubbing and getting red hot at the aft.  The issue was a high sulphur kero fuel.  Sadly it did this on two seprate turbines on the same fuel.  Something in it caused it to overheat which expanded things too much and it began to rub.  Locally pumped and did not know that the fuel was sub-standard.  Yes ss races in the bearing can be bad and pitted also.  Change fuel.  Then if possible change out your temp probe also, but likely not the issue.  Hope this helps John

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RE: What can cause a turbine to overheat? - 7/12/2012 7:21 PM   
Kevin_W


 

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Status: offline 		Improper tolerances or bad bearings allowing the turbine wheel to rub the EGV could cause it, but you would most likely hear some bad noises coming from the engine, so I doubt that is the problem.

I would suspect broken or clogged fuel tubes, and/or a distorted combustion chamber.

Edit:
Could also be FOD blocking the airflow. I have had an engine ingest a bunch of grass. I was able to clean what I thought was all the grass out of the compressor and the bearings seemed fine, but when I ran it it overtemped. I pulled the front housing off to find that there was grass wrapped around almost every stator vane.

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RE: What can cause a turbine to overheat? - 7/12/2012 7:36 PM   
GSR


 

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Status: offline 		You didnt say how much time on the engine. It could just have worn out. As the tolerances get out of whack the ECU keep pumping in more fuel trying to maintain the required RPM/throttle setting. The extra fuel just makes more heat. Scotty

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RE: What can cause a turbine to overheat? - 7/12/2012 8:50 PM   
Pete S-RCU



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Status: offline 		Lots to think about.
I did move the thermocouple out till only a 1/16" was in the tailpipe.
Might have helped a little, but it still did overtemp.
I ran it up and slowly approached full rpm, was able to hold it below 800c, about 780 or so, but it was only at 158k, not the 165 it's suppoe4sed to hit.
Still must be something wrong.
Turbine doesn't have much time on it since new bearings.
Only about 8 runs in a plane, but plenty on the test stand trying to sort out various problems.
I bought it in 2005, has a total of 57 flights on it.
No noises that I can hear, seems to spool down as always.
The bearings did fail on it before, but strangely I didn't notice till I landed and shut it off and it sounded terrible.
Will check for any shiny spots on the turbine wheel.
I just thought of something, I am programming a new, un-programmed ecu from Xicoy.
Good unit, but I haven't calibrated the thermocouple for temp.
As I recall it was about 20 degrees too high.
That might help!


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RE: What can cause a turbine to overheat? - 7/13/2012 1:27 AM   
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Status: offline 		I had a similar thing happen with a turbine. It would shutdown on overtemp. But, you could see inside the tailcone a bright red to yellow band as the engine heated up. The tail cone was necked down too far for the elevation/air density I fly at. I opened the tailcone by 2 mm by trimming the end. The engine then ran dead cool at around 380 DegC. Could be your problem?

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RE: What can cause a turbine to overheat? - 7/13/2012 4:02 AM   
TimD.



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Status: online 		The injectors could be clogged , check your pump output values to see if they are within parameters at full throttle.

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RE: What can cause a turbine to overheat? - 7/13/2012 9:54 AM   
olnico



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Status: offline 		Clogged injectors, bent injectors, wrapped combustion chamber could be the problem.
If the EGT sensor has not been moved, don't move it to hide the problem.
You need to sort out the root cause or you will ruin the engine.
You can take a shoot at the back of the tailcone from a far distance ( place a camera on a tripod that you' securely fasten from at least 50 feet behind the engine and zoom into the inside of the combustion chamber) to have a look a the flame pattern. You will probably see a hot spot developing at the location of the EGT sensor.

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RE: What can cause a turbine to overheat? - 7/13/2012 2:57 PM   
Pete S-RCU



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Status: offline 		Turns out the temp cal is about right.
Indicates 32c when air temp was about 88f.
The tail cone is red on the bottom half, but I attribute that to bright light on the top half.
Will need to run it in darker conditions like evening.
I hate to spend anymore money on that thing, no parts available for it since Simjet went out of the hobby business.
Maybe time for a new one?

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RE: What can cause a turbine to overheat? - 7/13/2012 3:23 PM   
sieze2


 

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Status: offline 		I had exactly this problem recently. It turned out I was losing compressor efficiency due to losing a bit of compressor blade. Wren also changed the combustion chamber as the injectors were burnt out due to age.

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RE: What can cause a turbine to overheat? - 7/13/2012 5:08 PM   
erbroens



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Status: online 		Sorry, wrong post!

Best regards, Enrique.



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