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CHT fluctuations


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I was about to reach out directly to @kortopates for this... but then thought the group might benefit as well.

https://savvyanalysis.com/flight/2798708/fee85897-96ba-4acb-9988-9e584fa5af1a

Notice the CHT's for #'s 3 and 4. Once in cruise, the temps on those two cylinders are up and down like a whore's drawers. 

Any idea why that might be? Does this indicate imminent jug failure or just a loose probe?

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I am in no way qualified to answer your question, but since it’s the internet i’ll give it a shot, then vigorously defend my uninformed opinion agains all those with more knowledge than me:

Looks like #2 CHT has the same pattern. EGTs don’t seem to change that much. I wonder if it’s the baffles or something to do with the probes or harness?

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I noticed something similar on my Encore. Only the period is 5 minutes vs the 1 minute period you see. For me it is usually cyl 3 but sometimes other cylinders. Up to 15 degrees swing between high and low, but stable EGT's. I don't see it every flight either. I only noticed this recently but when I downloaded all the data since install I see the behavior since the monitor was installed. I thought I had coupling from spark plug wires into the sensor wires, but when I checked the routing everything was fine. 

Have you checked all previous flights?

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That looks like a special one for Paul K. ...

The EGTs and CHTs all seem to have a saw tooth pattern overlaid on top of the actual data...

as if the reference keeps changing.

Speaking of reference, have you seen the grounds lately? Engine and instrument panel?  Something might be loose or dirty there?

Sawtooth patterns are often an EGT symptom related to an exhaust valve not rotating... but in this case, multiple EGTs are affected, and a few CHTs as well.  As somebody already pointed out, CHTs are really slow to change compared to these graphs...

Allow me to call in the good Dr.... it’s still kind of early on the West Coast... @kortopates... request, on a saw tooth pattern,  EGT and CHT...

Best regards,

-a-

 

 

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How about this one:

https://savvyanalysis.com/flight/2686438/c1341c15-d96a-4e88-8202-7476c8638ed8

Actually never mind, that's a formation flight with Bucko and Doc. :D

But back to the problem at hand... I've looked through a random sampling of flights back to July and they're all the same #3 is the most consistent with #4 sometimes dancing to the same beat.

 

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With that in mind...

Check back a few months at a time to see if the saw tooth disappears about the time something was maintained or added, or intruded upon... zip back until the smoothness is found...

then creep forwards until the saw tooth shows up again...

Graphics make a great way of taking in a lot of data at one time...  :)

a whole lot better than reviewing tons of data, looking for the one, undefined, thing...

Best regards,

-a-

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1 hour ago, larryb said:

I noticed something similar on my Encore. Only the period is 5 minutes vs the 1 minute period you see. For me it is usually cyl 3 but sometimes other cylinders. Up to 15 degrees swing between high and low, but stable EGT's. I don't see it every flight either. I only noticed this recently but when I downloaded all the data since install I see the behavior since the monitor was installed. I thought I had coupling from spark plug wires into the sensor wires, but when I checked the routing everything was fine. 

Have you checked all previous flights?

I have exactly the same 5 minute cyl 3 CHT thing. I thought it might be a connector issue, but now I’m thinking it might be inherent in our engine. 

6F85634D-3BDB-4E66-97BF-E0DC72B54E4F.jpeg

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I was about to reach out directly to [mention=7862]kortopates[/mention] for this... but then thought the group might benefit as well.
https://savvyanalysis.com/flight/2798708/fee85897-96ba-4acb-9988-9e584fa5af1a
Notice the CHT's for #'s 3 and 4. Once in cruise, the temps on those two cylinders are up and down like a whore's drawers. 
Any idea why that might be? Does this indicate imminent jug failure or just a loose probe?
It almost looks like "AC" voltage interference. There is no possible way the temps could change that fast in a chunk of metal like the cylinder heads. Exhaust gas could if a pipe was cracked bad but not at that frequency. Any chance a wiring issue?

Sent from my E6810 using Tapatalk

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4 minutes ago, Dream to fly said:

How close are the affected cylinders to the alternator???? Possible from diode pack?

Sent from my E6810 using Tapatalk
 

It's 3 & 4 so they're right in the middle of the six total, one on either side. The 252 has two alternators but only one of them is running in cruise flight.

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It's 3 & 4 so they're right in the middle of the six total, one on either side. The 252 has two alternators but only one of them is running in cruise flight.
My two cent guess is an induced ac ripple. If engine issues one cylinder would be a concern not two especially with identical waveform. Also if mechanical the frequency would be alot slower. Don't know enough about what is under the cowl of your dragon but wire routing like@yetti suggested is very possible. Waste gate manually controlled or electric? Any electronic solenoids working at that time? Magnets spinning? Do the four sensors in question share the same connector pack to the display?

Sent from my E6810 using Tapatalk

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A few points.

First, some theory. An engine monitor reads each probe several times per second. Then it will apply some sort of filtering and/or averaging algorithm to the values, and that filtered value is what we see. The more filtering applied, the smoother the response but also the slower the response. We do not know how many times per second the probes are read, and we do not know what sort of algorithm is applied. Probably inside JPI only the person who wrote the firmware really knows this detail. It could be in their design spec, but who knows. 

Now lets address a few of the thoughts mentioned in the thread. 

A ground issue is not likely. Each of these probes runs both thermocouple wires all the way back to the JPI. The measurements do not depend on the engine being grounded. The terminal connections between the JPI and the thermocouple are suspect however. I plan to review mine.

AC coupling from the alternator is not too likely either. The alternator is several hundred cycles per second, and we are seeing 1 temperature cycle between 1 and 5 minutes. 

If the JPI reads the probe at the instant an interference event occurs, and if the filtering is not robust enough, we can see an effect in the result. If this is happening, figuring this out will be difficult. 

I find it very interesting that 3 of us have reported a similar observation. And nobody yet has posted that they have a TSIO-360 and have not seen the effect.

I plan to review the tightness of the connections on my #3 probe, and if tight I will swap it out for a spare. 

Larry

 

 

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These kind of CHT indications are not that uncommon and are typically due to baffling. CHT3 is the main cyl with larger fluctuations. Initially CHT3 starts to fluctuate after both the plane has leveled off and ground speed has come up to cruise. Then we see fluctuations of 8-10F over about a 1 min period. Over more time in cruise, they get as large as 15F over a slightly faster period of 50 sec. CHTs 1,5, & 6 are all very stable and we see a very normal typical fluctuations in the 2-4F range in cyl #2 & #4 also - which are very typical. We also see a big more fluctuation in CHT5 in climb only, yet it stabilizes in cruise. Whereas CHT3 is pretty stable in climb but fluctuates in cruise. This is typically due to the changing air flow dynamics in the cowling.

We also often see these appear right after the cowling has been R&R's with maintenance and then go away when its R&R'd again. So it could be pinched or flexible baffling that got bent the wrong way. But since this is a middle cylinder we also recommend checking the inter-cylinder baffling to make sure that's secure and not moving around. But more likely its the silicone flexible baffling and could also be a sign of its wear.

Incidentally, we would not pronounce a poor electrical connection or interference from noisy ignition wires or high current without a much faster period and typically a poor connection or chaffed wires results in much larger fluctuations. But it never hurts to check the security of the connection and wiring when the cowling is off.

Edited by kortopates
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  • 2 years later...

ha I'm only 2 years late to this party but Mooneyspace to the rescue as to what causes these fluctuations  I also have the same symptom as Paul but mine is number 5 Cylinder instead of #3.  Does anybody have pictures of what the inter-cylinder baffling installed correctly to make sure that's secure and not moving around should look like?

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  • 2 weeks later...
On 7/2/2021 at 4:57 PM, Will.iam said:

ha I'm only 2 years late to this party but Mooneyspace to the rescue as to what causes these fluctuations  I also have the same symptom as Paul but mine is number 5 Cylinder instead of #3.  Does anybody have pictures of what the inter-cylinder baffling installed correctly to make sure that's secure and not moving around should look like?

Better late than never… -Mom

when it comes to baffling…. @GEE-BEE AEROPRODUCTS may have the pics you are looking for…

Best regards,

-a-

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