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Why we have engine monitors

douglassmt

Well Known Member
I haven't posted in a while but thought this might be of interest. I fly an RV-10 Aerosport Power IO-540 with a slick mag and a Lightspeed Plasma III ignition. Everything has worked flawlessly for 1300 hours until a recent flight. I didn't notice the behavior when it first started but on a subsequent flight I was descending into my airport, lean of peak but still plenty of throttle, 8500', when the Advanced Flight Systems EFIS gave me a visual and audible alert that the #6 EGT (blue line on the plot) was higher than the others. I downloaded the data and saw this:

49550256636_3558aa4a1c_h.jpg


It clearly shows the #6 EGT (blue) departing from the others. The only reason I noticed the slight departure was that it finally got into the range I had set for a yellow alert - at about the 25 minute mark on the above plot. On reviewing the data, the departure only occurred when I was lean and at high power settings, over 20". I then looked at previous flights and found this from a few days earlier.

49549753938_775beffd0a_h.jpg


You can clearly see the #6 EGT departure in cruise (LOP and WOT), as well as a corresponding drop in CHT. However, the EGT#6 didn't depart a lot (80-90 deg F) and never reached the temp (I think 1440) I had set for a visual and audible alert. I decided to do some diagnostic stuff, including several GAMI mixture sweeps and an inflight LOP mag check. Here is that flight:

49550256566_e401f7e36f_h.jpg


All the mixture sweeps were normal, my GAMI spread is excellent at 0.1-0.2 gph, but when I did the inflight LOP mag check at 13,500' the #6 EGT dropped out immediately and the engine ran very rough. You can see this where the blue EGT trace spikes downward at about 56 and 59 minutes. The #6 EGT and CHT are also behaving differently than the others throughout much of the flight.

I returned to base and checked the #6 plug (fine-wire Tempest). It looked fine. The spark plug leads all looked fine. The plugs resistances measured normal. I replaced the fine-wire plug in #6 with a used massive-electrode plug I had, just in case, and flew again. The LOP mag check at 9500' again showed the #6 EGT dropping off, but much more slowly than it had at 13,500'. I Repeated it at 6500' and everything ran fine.

The mag was due for a 500-hour, actually overdue, so I pulled it and found this:

49550483812_66e71365eb_c.jpg

49549754718_0d7ab2c67a_b.jpg


There was clear corrosion on the spring in the magneto cap for the #6 lead, and corrosion in the socket on the mag.

Takeaways from this are:
1. Without an engine monitor it would have taken MUCH longer to even notice this problem, much less to diagnose which cylinder was causing it.
2. The Lightspeed ignition covers a multitude of sins in the magneto, which is a good thing...unless I need the magneto. Also, the magneto is not contributing nothing, as some people think.
3. The engine monitor, and paying attention to it, allowed me to quickly isolate the problem to a specific cylinder and plug, then find the problem.
4. The absolute value of EGT means very little, so I've considered removing the EGT alerts that I have set in my Advanced EFIS. However, they are useful for just this reason, to get an audible and visual alert when "one of these is not like the other."
5. The engine appeared to be running fine, smooth, but this was a problem that would not get any better, and might have caused some damage had I not caught it when I did. The corrosion in the lead socket was weakening the spark energy for that cylinder to the point that, under the conditions when the most spark energy was required, it didn't get enough to light the fire. Most importantly, if the Lightspeed had quit working and I needed the magneto it would have been unpleasant.
6. I should be in the habit of downloading engine data every oil change or so, even if everything appears normal, to look for things like this.
7. I should also do high altitude, WOT, LOP mag checks on a more regular basis.

Hope this is of some use to somebody.
 
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I found the discussion interesting and would love to see the images ... but they just show up as grayed out "negative" symbols for me.

Clicking "view in new tab" doesn't work either.
 
Try again

Try it again. I originally used my old Photobucket account but they somehow blocked the link. I moved them to Google Photos and now they show up on my screen.
 
Well shoot. They work fine on my screen but not on my ipad. Stand by, I'll try to figure it out.

[ed. You need to set them to 'share'. v/r,dr]
 
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I switched to Flickr but now the images are too small to see very much. Standby unless someone knows how I can fix it.
 
I think one has to use the chrome browser to see the google photos.

Another option is to use postimages.org.

Nope ... I use chrome and no pics.

I know how to post my own, but don't know how to fix the different ways they don't work on the site...
 
Very interesting data point. It's common to read that the fixed timing magneto is "doing nothing" when paired with a single EI running advanced timing. The elevated EGT after mag spark failure says the belief is incorrect.
 
Very interesting data point. It's common to read that the fixed timing magneto is "doing nothing" when paired with a single EI running advanced timing. The elevated EGT after mag spark failure says the belief is incorrect.

It may be common to read, but almost always "wrong". A fixed magneto is certainly contributing to the effective timing of the PCP event. As a composite of two events the magneto or EI can drag the overall curve one way or the other.

In any case, this incident also reinforces the value of the "mag check" when stressed (high and lean), and also the near worthlessness of that same check on the EOR (under no stress).
 
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Is there more to this ?

Love the post and discussion. For sure these egine monitors are awesome tools.
But... I'm still puzzled : the 'earlier flight' graph shows a very sudden departure of nr6 from inline-with-other-cylinder-values to "out-of-whack". Can that be explained by corrosion ? I would expect a more gradual deviation developing over time. Is there anything more to this ?
 
...I'm still puzzled : the 'earlier flight' graph shows a very sudden departure of nr6 from inline-with-other-cylinder-values to "out-of-whack". Can that be explained by corrosion ?

Do you mean the excessive and sharp drop when he did the mag check in flight?
 
So how did you go about cleaning the corrosion up.

It was a bit overdue for the 500-hour inspection so I have it in to a shop. They will clean it all up and they gave me a new spring for the lead. If it had not been due for inspection I would have put in a new spring - or cleaned the corrosion from the old one - and used a wire brush to clean up the socket.
 
Love the post and discussion. For sure these egine monitors are awesome tools.
But... I'm still puzzled : the 'earlier flight' graph shows a very sudden departure of nr6 from inline-with-other-cylinder-values to "out-of-whack". Can that be explained by corrosion ? I would expect a more gradual deviation developing over time. Is there anything more to this ?

What you say seems intuitive but I've looked back several flights before that one, when I got to the same altitude, and it just wasn't there. I will repeat the inflight LOP mag check when I get the mag back and reinstalled, but I found nothing else that would explain the EGT6 departure. It's possible that the corrosion just finally reached a point where enough metal had been removed that it created the problem.
 
In any case, this incident also reinforces the value of the "mag check" when stressed (high and lean), and also the near worthlessness of that same check on the EOR (under no stress).

This is very true. As a case in point, after I replaced the fine-wire plug on #6 with a massive electrode plug and flew again, the inflight LOP mag check at 9500' or so resulted in the same loss of spark on #6. When repeated at 6500' a few minutes later it did not. So, doing the LOP mag check in flight is more diagnostic when done at a high altitude. It's not a bad idea to do one on every flight before descent. I believe the API and Mike Busch recommend this.
 
All cylinder monitoring of CHT, EGT as well as fuel flow is one of the best safety features to come along to GA, with GPS detailed map data and in-flight weather. If we pay attention we can see trends.

In commercial aviation engine parameters are monitored by computer which sends that data almost real time in-flight direct to the airline and manufacture. Trends in turbine EGT and vibration are watched closely. This is why very flew airliners have on wing engine failures.
 
vibration probe

... Trends in turbine EGT and vibration are watched closely. ...
Anyone know if there is a vibration probe that we could include with our engine monitoring? Seems like it would be an easy development. Vern?
 
why we have engine monitors

Noticed Dep, destination., Missoula -Roundup. FWIW I own a hangar in RPX, last one SW @ end of rd., or from fuel tank, leased out to 2 bldrs. Many from Billings fly up, Air Venture due to low fuel prices.
 
Thanks for sharing this! Very interesting and educational.

Thinking of getting that software for my soon to be flying (and AFS5600 equipped) 7A with a 390.

Will be too busy in the early flights, but it appears to be super valuable and having baseline data and reviewable data from the start seems like a good idea too.

Any reason not to do this?

Thanks-
 
Noticed Dep, destination., Missoula -Roundup. FWIW I own a hangar in RPX, last one SW @ end of rd., or from fuel tank, leased out to 2 bldrs. Many from Billings fly up, Air Venture due to low fuel prices.

Yes, RPX is a nice, if remote, stop that usually has cheap gas. We were there to pick up a Cessna that had lost an engine returning from OSH last year and was able to glide in to RPX and land without incident.
 
Thanks for sharing this! Very interesting and educational.

Thinking of getting that software for my soon to be flying (and AFS5600 equipped) 7A with a 390.

Will be too busy in the early flights, but it appears to be super valuable and having baseline data and reviewable data from the start seems like a good idea too.

Any reason not to do this?

Thanks-

In my opinion, it would be foolish not to install this tool and to use it frequently. I'm pretty sure it's included with the AFS EFIS or at least available as an option at a very reasonable price. Most importantly, LEARN HOW TO INTERPRET THE DATA.
 
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