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TIT indication on aircraft


herky400M
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Bob as far as I can tell there is no TIT difference between engines. T56-A15 needs to

make 1067°C to 1083°C in auto at take off, minimum 1007°C in null, with the overriding factor

of minimum torque for the given altitude, OAT, runway length and take-off weight. D22A needs

to be 1077°C (or as close as possible) in auto, 1007°C in null.

I built a switching device for our test cell to switch the AMP and IND leads at the T-block, so

we could check the difference when we have unusual TIT indications (works really well). Haven't

yet found a bad thermocouple, though.

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Bob as far as I can tell there is no TIT difference between engines. T56-A15 needs to

make 1067°C to 1083°C in auto at take off, minimum 1007°C in null, with the overriding factor

of minimum torque for the given altitude, OAT, runway length and take-off weight. D22A needs

to be 1077°C (or as close as possible) in auto, 1007°C in null.

I built a switching device for our test cell to switch the AMP and IND leads at the T-block, so

we could check the difference when we have unusual TIT indications (works really well). Haven't

yet found a bad thermocouple, though.

pjvr99

I'm probably going to ask these questions incorrectly. My understanding of the T56 T/C system is that unless you breakout each individual T/C out of the loom you will read the average of every T/C in the system.

So I guess my question becomes a repeat of the first question; what is the max allowable split?

And I am going to ask 2 more;

1. How "large" a failure would have to occur in how many T/C's before you would get a split?

2. Is it common for either side of the T/C to fail, or is a complete failure of the T/C more common?

Thanks!

Jetcal1

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Steve, you're probably right on that. The info I have only says 1071°C, with a large group

of people saying that 1071 is a typo, and should be 1077°C..... :hands-surrender-smiley:

In all honesty i don't know whether the thermocouple system averages or totals. The TO's

only state that in the event of a suspected bad thermocouple the engine should be run, and

TIT reading taken at about 70° throttle (+-850°C), then the engine shut down, the leads

swapped over at the T-block, and the engine run again at the same throttle setting. Difference

should not be more than 6°C (10°F).

A dead thermocouple will cause a loss of 18 to 24°C at take off ..... (but for the life of me, I

can't find the reference).

I have found several broken thermocouples over the years, but only on engines that had

already been removed for burnt turbine or some other maintenance leading into a -6

inspection. Most time maintainers don't really troubleshoot TIT problems, just run a yellow

box or adjust the TD valve.

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Hello C-130 world; bright question: what's the max TIT difference between each engine staticly......

The Thermocouples are not designed to be accurate statically. Also, they have holes that airflow runs through to deliver the heat, so no airflow=who cares what they read. We have had flight crews write-up this before, and we just sign it off. There is no limitation for it, and we inspect thermocouples enough to where this shouldn't be a problem. Now if there are other indications of thermocouple failure, I'd be more than happy to investigate it, but troubleshooting static TIT is a waste of time.

Also, Military Takeoff TIT is set on the -15 TD Amp to 1077 degrees, and the limit is 1067-1083. I thought is was understood that the Military doesn't mind lowering Turbine life for the sake of better takeoff performance. It's more cost effective for the civilians to keep their 501D cooler.

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TIT is directly proportional to fuel flow and torque and should maintain relative values at all power settings. Discrepancies will be noted by comparing indications with the other engines. Also note throttle knob distances. If I'm not mistaken it should be no more then 1 knobs distance. The 18 thermocouples generate a millivoltage that is ampified by the respective receiving unit. A defective thermocouple will lower the indicating system by 3.5-22 degrees centigrade. Failures can effect both systems or one or the other depending on the severity of the damage.

Hope all this rambling helps

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What you say is true, skier, but I would like to modify your statement just a bit.

Thermocouples cannot give you the correct TIT if they are not at the right point of the flame. If the fuel nozzles are not putting the flame in the right place while running (or air flow/fuel mixture/etc is messing it up during start) the thermocouple cannot give you an accurate TIT. Also, a "defective" thermocouple is totally different from one which has it's temp sensing element burned off. The TIT change from a "defective" thermocouple may not be noticeable by itself. I takes several to see a TIT loss.

Throttle knob alignment requirements exist above crossover and the limit is plus/minor 1/2 knob.

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C-130 world: I repeat my question, what is the max TIT difference between each engine?

ex: #1 indicates 18°C

#2 indicates 22°C

#3 indicates 17°C

#4 indicates 13°C

OAT = 16°C, clouded wheather and a bit of sunshine and a bit of wind...

so shouldn't I have same TIT's.....as the OAT?

What I personally do is verfy with the oil temp's, and if they corresponds then 4 me personally it's ok, but the FE's need an explanation...:eek:

any sugestions??

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Ah, now that's a different game, Bob. First thing to realize is that no 2 gauges are going to

give exactly the same reading. Next thing would be that that low down, there is no

guarenteeing the thermocouple's accuracy. Also effect of air movement through the engine,

swirling around the fuselage, etc. Sunrise on the left wing?

In the test cell, GENERALLY, early morning has TIT, OAT, fuel and oil temps within 1 or 2

degrees. Later in the day, this can change by a substantial amount.

Why is the FE concerned about this? The TIT system measures measures combustion

temperature, and is set up for an individual engine.

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C-130 world: I repeat my question, what is the max TIT difference between each engine?

ex: #1 indicates 18°C

#2 indicates 22°C

#3 indicates 17°C

#4 indicates 13°C

OAT = 16°C, clouded wheather and a bit of sunshine and a bit of wind...

so shouldn't I have same TIT's.....as the OAT?

What I personally do is verfy with the oil temp's, and if they corresponds then 4 me personally it's ok, but the FE's need an explanation...:eek:

any sugestions??

Since none of our maintenance information gives us any limits on such gages at this temp range, as long as nothing is inop or reading max, I'd reserve any complaints until I have engines running.

Most often, when the crew is in the seat awaiting clearance to start, they have a lot of time to ponder such wonders. The reality of it is that none of it counts until the aircraft is operating.

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Hello everybody!.. Don't you think that if above flight Idle, you do not have a throttle split and you do torque out before reaching the max stop!.with a correct TIT....well, I think you're in business. What about FF.!!!(as a joke I feel like sayin': It's not a Dodge pickup, It's a Lockheed Hercules!!) If nobody finds anything in the books, well!! what else can we do!! Let's do it!!!

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I guess I'm missing something....

I've been following this TIT thread for a few days and some explanations have been gived to specific conditions.

Is the crew writing this 'temperature difference' up in the forms or just asking about it?

325X1

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C-130 world: I repeat my question, what is the max TIT difference between each engine?

ex: #1 indicates 18°C

#2 indicates 22°C

#3 indicates 17°C

#4 indicates 13°C

OAT = 16°C, clouded wheather and a bit of sunshine and a bit of wind...

so shouldn't I have same TIT's.....as the OAT?

What I personally do is verfy with the oil temp's, and if they corresponds then 4 me personally it's ok, but the FE's need an explanation...:eek:

any sugestions??

I am not engineer, but here goes. If there any errors here I will find someone else to blame.

You are using an RTD (Resistance Temperature Detector) for your OAT and type K Chromel ® and Alumel thermocouples in your engine. While the RTD is more linear in and accurate at normal temperatures the type K is and will remain more accurate over time at the temperatures you operate at. Being non-linear a type K has to have the length of the wires and position of the junction specifically designed to be the most linear at the design operating temperatures.

An RTD would probably be more accurate..but, due to contamination it won’t last in the hot section environment. An RTD might be a better choice in a static kiln but not in turbine case. I also think there some limitations above about 600° C, but I don’t know.

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From the "For What it's worth department", and I have no idea what this crap actually means, but as said, there is always a +/- tolerence for the indicators.

The "For What it's Worth Department" just produced a specification that states that the indicator's accuracy is poor, at best, at or below 100 Deg C and above 1,200 Deg C.

That's pretty much what I suspected. With a +- of 15 Deg C at 100 Deg C Scale Error Reliability, don't use it for checking the temperature outside below 100 Deg C.

Oh! If the OAT is 100C plus, you're not really checking the temperature anyway. :D I'd ask the FE why he was trying to use that indicator to check the temperature outside anyway.

If you don't want to be a smart a**, tell them the +- 15 degree error for the indicator, according to Mil-SPEC used to test the indicator during manufacture/repair, doesn't take into account the allowed errors of the wiring, T-Block, thermocouple harness nor the thermocouples.

Summing it up: It's not designed to give an accurate reading until there's fire in the hole.

325X1

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I was taught to look at the TIT (and other things). For example if three of them are reading about 30 and one is on 0 make a mental note of it and see how they read when running because that’s when it really counts. There were a few occasions where the suspect engine did show signs of thermocouple decay. If it wasn’t too bad, put it in null and fly it. This was before the 720,750 cold start change came out. After that change thermocouple decay became a showstopper IAW the dash1.

We went through a lot of thermocouples in gunships for some weird reason.

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Thermocouples have always been a weak link on the Herk, when I first got to Sewart in '66 I was put in charge of a engine phase dock crew. I was amazed that the common procedure was to pull enough thermocouples to boroscope the turbine and leave the rest unchanged. We had a thermocouple test bench in the shop but these guys were taking short cuts they should not have been. I explained to my crew why it was wrong and we were only causeing engine changes if we didn't change all 18 as speced in the phased inspection guide. There used to be a 2 page chart in the front of the 1-1 that could be used to predict TIT for a given FF and torque and conditions (OAT, PA, IAS,) I wasn't a bit embarassed to write up TIT systems as reading low inA/W with the 1-1. I figured that if the crew I took over was being lazy there had to be others being lazy too. In cruise I would demostrate to the crew chief the chart and the use of it and most of them saw my point of view, even had the chance to explain it to some engine troops and they got it. I would start off by setting all the FF's to the same, that should make the torques the same, assume the highest reading TIT is the correct one, since thermocouple failures never cause a high reading. I always assumed that FF meters were the most accurate and the only one that could be verified in flight.

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On a whim today, I did a TIT calibration. Shooting TIT from the T-block, starting at 50°C and

incrementing 50°C up to 1100° all readings within 2°C. Before and after indications of OAT,

TIT and fuel temp was 30°C, 31°C and 34°C (fuel was higher because the sun had already

gotten to the pump). I hooked up my relay and ran the engine @ 900°C and only had a 1°C

change .....

Bob, you you need to tell your FE's to concentrate on the important things:-

1. Wine

2. Women

3. Song

:-)

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But did you check the thermocouples? Low TIT readings are very likely the cause of early turbine failures, especially the engines we had back in the 60's and 70's. I can remember the floor stomping by the instructor at Allison engine school when he was talking about the effects of failed thermocouples. I started out as an jet engine troop, the got into scanner and got my AFSC changed to APG before I started flying as a FM. I put in a few long nights on engine problems.

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But did you check the thermocouples? Low TIT readings are very likely the cause of early turbine failures, .....

No. But if my suspicions are correct, it will be necessary to change them out. We're just

debugging a little oil leak at the moment - then our beady eyes will be moving there.

Oil problem moved here http://herkybirds.com/forums/showthread.php?p=13985#post13985

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This particular FE has a job a to accompany new FE's. and out of the blue this question pop's up. So my answer was: if the TIT indication and the oil temp indication are the same before the 1st start of the day, then there is nothing to worry about! wheather influence is the key player to the difference in left and right wing....

but anyway:

pilots and FE without maintenance are just pedestrians with flightjackets and funny sunglasses :cool:

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