EGT temp difference

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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ShawnM
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Re: EGT temp difference

Postby ShawnM » Fri Jun 15, 2018 9:54 pm

Warmi wrote:Shawn.
Is your front EGT probe attached at the pipe bent ? Cause I am starting to think that the difference between front and back sets is related to their different shape.


Yes, it’s right on that bend. Ironically I’ve experienced just the opposite that you do. If I decrease power my EGTs split and if I increase power then join up again. Again, the same issue but the other way around.

Warmi
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Re: EGT temp difference

Postby Warmi » Fri Jun 15, 2018 11:12 pm

Just read info from Lockwood aviation/Rotax that having even a few hundred degrees split between front and back EGT blocks ( as opposed to individual cylinders ) is not considered anything out of ordinary and the real value of EGTs is in diagnosing potential carb issues ...
Anyway, I will keep watching it and I am taking the plane for routine maintenance next week ( + ADSB install etc ) and will try to confirm if this is a real issue or not ...
Flying Sting S4 ( N184WA ) out of Illinois

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ShawnM
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Re: EGT temp difference

Postby ShawnM » Sat Jun 16, 2018 8:19 am

Care to share what you just read?

Good luck with the maintenance and finally your ADS-B install. Please report back if you find any issues and also add a post in the ADS-B topic as to your install and your thoughts. Very interested to her about it.

Warmi
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Re: EGT temp difference

Postby Warmi » Sat Jun 16, 2018 5:20 pm

This was a quote from Dynon technical support staff regarding installing only 2 EGT probes with their D120 equipment ...

After consulting with the Rotax gurus over at Lockwood Aviation (and they in turn consulted with Rotax technical support), we learned that of all the things one can glean from EGTs, the one that is most useful on the 912 is the ability to detect carbs out of sync. This requires only one EGT per bank. Additionally, on the 912, you can often see quite very different EGTs between the front and the rear pairs - as much as a few hundred degrees. This is inherent in the operation of the engine, and Rotax has seen people confused by the behavior when all four are monitored. In fact, measuring EGT isn't a requirement on the 912 per Rotax spec.

I am gonna try to ping Leading Edge Air Foils folks here close by in Wisconsin and see what's their opinion on this.
Anyway, I am going off on Wednesay for various engine and other maintenance + ADSB install and some other minor avionics work to these guys :
http://www.midwestskysports.com/

I will ask them about this issue as well and will let you know ...
Flying Sting S4 ( N184WA ) out of Illinois

RV12Heal
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Re: EGT temp difference

Postby RV12Heal » Sun Jun 17, 2018 9:43 am

This was a quote from Dynon technical support staff regarding installing only 2 EGT probes with their D120 equipment ...

After consulting with the Rotax gurus over at Lockwood Aviation (and they in turn consulted with Rotax technical support), we learned that of all the things one can glean from EGTs, the one that is most useful on the 912 is the ability to detect carbs out of sync. This requires only one EGT per bank. Additionally, on the 912, you can often see quite very different EGTs between the front and the rear pairs - as much as a few hundred degrees. This is inherent in the operation of the engine, and Rotax has seen people confused by the behavior when all four are monitored. In fact, measuring EGT isn't a requirement on the 912 per Rotax spec.


I found the above quote to be very interesting. What on-ground or in-flight EGT indications should one be looking for to evaluate whether the carbs are in sync or out of sync? Linearity? Peaking??

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Re: EGT temp difference

Postby roger lee » Sun Jun 17, 2018 12:20 pm

EGT readings on the ground vs in the air may be quite different. There are only a few things you can do to influence them.
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Re: EGT temp difference

Postby ShawnM » Sun Jun 17, 2018 2:07 pm

Also, in the Dynon install manuals for the D-120 (not sure on the Skyview system) Dynon recommends you install the two EGT probes in the rear cylinder exhaust manifolds.

Quoted from the Dynon D-120 install manual:

ROTAX ENGINES
For Rotax 912 engines, only two of the four cylinders are typically monitored for EGT. Unlike the CHT probes which are mounted on diagonal cylinders, the EGT probes should be mounted on the two rear cylinders’ exhaust manifolds. It is critical that the EGT probes be mounted to parallel cylinders’ exhaust manifolds for proper temperature comparison.


I also read elsewhere that the rear cylinders can run up to 150 degrees hotter than the front two cylinders. Seems to make sense to monitor to two hottest EGT's on the hottest cylinders.

Of course as Roger stated they can all vary depending on RPM settings and whether you are on the ground or in the air. I have never seen any high readings on the ground ever and would never compare on the ground temps with in the air temps. I'm more concerned with temps while flying.

I guess another summer project will be moving the front EGT probe to the rear (so they both are in the rear and on parallel cylinders per Dynon) and welding up the hole in the front exhaust.


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