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Absolute EGT value

On my TIO540 PA31 the EDM alarms at an EGT of 1670 or above.

At RoP cruise settings I have one, sometimes two, cylinder alarming at 1680, but with TIT below red line.

It is tempting to say that absolute values of EGT don’t matter, and to adjust the alarms on the EDM, but I wonder what the panel think?

EGKB Biggin Hill

Timothy wrote:

It is tempting to say that absolute values of EGT don’t matter, and to adjust the alarms on the EDM, but I wonder what the panel think?

Performance vise I guess only the relative value is important. But a TIO540 has one, two? turbos with their own temperature limitations I would think?

Hence my keeping TIT in limits. I am asking whether I should worry about EGT as well.

EGKB Biggin Hill

One obvious Q: after a day in the hangar

  • do all the EDM values read the same (within a degree or two)
  • do they read the ambient temperature (as above)

I ask because while JPI have AFAIK always used Type K thermocouples (for both EGT and CHT sensors) the instrument (or at least some of them) can be set for Type J or Type K. You can find the voltage generated by each type here. I would think the resulting error from that misconfig would be too great but….

1690F is a LOT for ROP operation. On mine I would see about 1300F at full power. The highest I ever see is 1580F, peak EGT, 65% power, low level.

This has been done before

Also are the EGT probes fitted at the right distance from the exhaust port?

Administrator
Shoreham EGKA, United Kingdom

I just looked at the EDM manual, and that says that TIT alarms at 1650°F, but it has no mention of EGT alarms, which don’t seem to be configurable.

So I won’t be able to stop the alarm, which is irritating.

EGKB Biggin Hill

Which EDM is this?

Looking at one composite EDM 7xx 8xx etc manual (check your email Timothy) I see that the EGT and TIT limits are adjustable but both have to be the same

(the yellow bit is nothing to do with me)

I don’t know if this applies to the “classic” EDM700 but that had a similar config. I just can’t find the IM (from year 2002) as a PDF.

BTW you probably know you can cancel the alarm by holding some button for 5 seconds.

Administrator
Shoreham EGKA, United Kingdom

Thank you. I was looking at the 760 manual; that may also say that EGT and TIT limits are the same, but I certainly don’t want to raise the TIT alarm as I know that that does matter.

I do know you can clear an alarm, but it begs the question of whether exceeding the EGT alarm matters (my question). Also, the reset only works until the next drop below limits, so is unlikely to be resilient.

EGKB Biggin Hill

I think that it is strange that your EGTs are higher than your TITs. I know that does not help much.

What could help is downloading the data from the EDM and uploading it to Savvy Analysis or Cirrusreports.

LFPT, LFPN

The general wisdom is that EGTs don’t matter because the EGT value is only a proxy, and is just an average of low duty cycle gas flows from combustion events. The actual peak gas temp is a lot hotter.

Also, the reset only works until the next drop below limits, so is unlikely to be resilient.

That is specifically not what the other manual I have says; it says the alarm is cleared until the next power cycle. Maybe the 760 is different.

Here is the 760 config stuff

and this is very interesting (my yellow)

so I reckon the crappy manual just omits to say that either there is an EGT MAX config item or it tracks the TIT MAX like the other instrument does.

Do check the Type J versus K config.

Administrator
Shoreham EGKA, United Kingdom

For my (small) part of the panel, my beliefs haven’t changed since this discussion.

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