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  #11  
Old 07-30-2018, 11:56 AM
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Default Strange Approach

The really strange thing about Mike's approach to leaning is that he does not advocate using EGT as a reference. That's counter to practically every other source I've read. And, most engine monitors that provide a Peak Lean function, do so based on EGT. Mike has you use CHT alone and in such a way that you never enter the peak cylinder internal pressure zone. His approach seems reasonable but seems somewhat less accurate to me than the EGT base method.
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  #12  
Old 07-30-2018, 11:56 AM
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Originally Posted by 49clipper View Post
My cylinders run much cooler than 300f a lot. According to Lycoming, I am lucky and they said my cylinders should last til TBO. He said, call me when they get below 175f and we'll talk. Cool cylinders are a plus not a problem.
Jim
This is what my Lycoming contact told me also. He said cool is good for engines.

Chris
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  #13  
Old 07-30-2018, 12:54 PM
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Originally Posted by f14av8r View Post
The really strange thing about Mike's approach to leaning is that he does not advocate using EGT as a reference. That's counter to practically every other source I've read. And, most engine monitors that provide a Peak Lean function, do so based on EGT. Mike has you use CHT alone and in such a way that you never enter the peak cylinder internal pressure zone. His approach seems reasonable but seems somewhat less accurate to me than the EGT base method.
Yeah, sorta. Except that Mike would agree that running LOP is a good thing, and you cant confirm whether you are lean of peak without EGT data.

erich
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  #14  
Old 07-30-2018, 01:04 PM
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Originally Posted by f14av8r View Post
The really strange thing about Mike's approach to leaning is that he does not advocate using EGT as a reference. That's counter to practically every other source I've read. And, most engine monitors that provide a Peak Lean function, do so based on EGT. Mike has you use CHT alone and in such a way that you never enter the peak cylinder internal pressure zone. His approach seems reasonable but seems somewhat less accurate to me than the EGT base method.
EGT isn't really a reliable measure of much because the probes don't really see the exhaust gas most of the time. Plus, they are being alternately exposed to hot and cold gas many times per second. The time constant of a thermocouple just isn't capable of responding that fast. At best you are seeing an average of some set of conditions over many seconds (hundreds of cycles of the exhaust valve). I wouldn't really trust that an EGT sensor is doing much more than telling you "the combustion conditions in this particular cylinder may be running hotter (or cooler) than they were a few minutes ago." I definitely wouldn't try to compare EGTs even between cylinders on the same engine. The conditions in which they run and the geometry of mounting them differs too much.

I can't see how an EGT probe can be said to be "accurate" in anything other than a relative sense. Running Lean of Peak is just that...relative to a peak, but the peak is just an average and may change from time to time. It will change based on engine and ambient conditions.

Last edited by 1001001 : 07-30-2018 at 01:06 PM.
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  #15  
Old 07-30-2018, 02:28 PM
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Originally Posted by erich weaver View Post
Yeah, sorta. Except that Mike would agree that running LOP is a good thing, and you cant confirm whether you are lean of peak without EGT data.

erich
Well, you clearly haven't read Mike's book. He doesn't look at EGT at all when leaning his engine. He relies solely on CHT, coming at it from either an economy a performance perspective. When performance is the goal, he leans to his CHT target (380 Continential, 400 Lycoming) or, if efficiency, he leans to his fuel flow goal, desired fuel reserve being the objective. Either way, he carefully avoids entering the peak CHT / EGT area that this necessary to establish a peak EGT for leaning with regard to that set point.
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  #16  
Old 07-30-2018, 02:34 PM
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Originally Posted by 1001001 View Post
EGT isn't really a reliable measure of much because the probes don't really see the exhaust gas most of the time. Plus, they are being alternately exposed to hot and cold gas many times per second. The time constant of a thermocouple just isn't capable of responding that fast. At best you are seeing an average of some set of conditions over many seconds (hundreds of cycles of the exhaust valve). I wouldn't really trust that an EGT sensor is doing much more than telling you "the combustion conditions in this particular cylinder may be running hotter (or cooler) than they were a few minutes ago." I definitely wouldn't try to compare EGTs even between cylinders on the same engine. The conditions in which they run and the geometry of mounting them differs too much.

I can't see how an EGT probe can be said to be "accurate" in anything other than a relative sense. Running Lean of Peak is just that...relative to a peak, but the peak is just an average and may change from time to time. It will change based on engine and ambient conditions.
I don't understand your statement at all. An EGT probe obviously doesn't display the instantaneous EGT but it should display a very accurate average which is derived over a fairly short period of time. A "few minutes" certainly isn't my experience with the reaction time of my EGT probes. They respond within a few seconds of my changing engine parameters.

I do agree that running LOP is relative to a peak. I just think it is relative to a very accurate peak derived from the very near past, not minutes, but seconds.

My point is that Mike Busch advocates avoiding every seeing LOP CHT or EGT with his method and many others advocate finding peak EGT as a necessary step in leading your engine to whatever performance point your desire.
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  #17  
Old 07-30-2018, 03:05 PM
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Originally Posted by f14av8r View Post
When performance is the goal, he leans to his CHT target (380 Continential, 400 Lycoming) or, if efficiency, he leans to his fuel flow goal, desired fuel reserve being the objective. Either way, he carefully avoids entering the peak CHT / EGT area that this necessary to establish a peak EGT for leaning with regard to that set point.
I would think peak fuel efficiencies would be obtained LOP, and I dont see how LOP can be attained without ever passing through peak EGT, although that could certainly be done relatively rapidly.

erich
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  #18  
Old 07-30-2018, 03:31 PM
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Originally Posted by erich weaver View Post
I would think peak fuel efficiencies would be obtained LOP, and I dont see how LOP can be attained without ever passing through peak EGT, although that could certainly be done relatively rapidly.

erich
You're right about that. Using EGTs and logging fuel flow when each cylinder peaks is necessary for nozzle tuning but not for every day flying. The big pull to an expected fuel flow takes you right through the peak and the dreaded red box and gets you to the LOP condition too quickly for any detonation problems to have developed. Once on the LOP side of things, you can fine tune for whatever cruise power/fuel flow you want with CHTs being primary. Don't care what EGTs read anymore. If the cylinders are not over 380-400 and rising, a dangerous level of detonation is not occurring. Maximum available LOP cruise power will be at your personal maximum continuous CHT on the hottest cylinder. If you want to go faster, set it to max CHT on the rich side of peak. My personal max continuous CHT is 380F.

Ed Holyoke
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  #19  
Old 07-30-2018, 03:42 PM
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engine efficiency is all about air fuel ratio (leaving CR, valve timing and ignition timing to the side for this discussion) Peak EGT is almost directly related to stochiometric (14.7:1 AFR) as well as being quite fast at identifying this. It is therefore a very good tool for working to a baseline AFR and operating at some point from or at that baseline. This would be quite difficult to with CHT, as it reacts very slowly to combustion temperature and is also impacted by ambient temps and cooling airflow volume. I am not even sure where combustion temps peak, though I suspect it is also at stochiometric. I am sure most have seen how CHTs can be higher or lower, based upon ambients or airspeed, at the same power setting (EGT sees very little variability from ambient or airflow). Therefore a peak must be found individually for every circumstance and this would take a long time, due to the slow reaction.

Larry
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Last edited by lr172 : 07-30-2018 at 03:50 PM.
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  #20  
Old 07-30-2018, 04:37 PM
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Originally Posted by f14av8r View Post
My point is that Mike Busch advocates avoiding every seeing LOP CHT or EGT with his method and many others advocate finding peak EGT as a necessary step in leading your engine to whatever performance point your desire.
Obviously he does pass through peak EGT, as you can't get from rich to lean and back any other way. He just doesn't look for it. I suspect he knows exactly where a particular fuel flow puts him in relation to peak.

Consider Busch is flying a twin, so setting mixture by peak EGT would be 12 probes to track. Within caveats, he can do the same with matched FF needles at some familiar power setting

Reference to peak is an accurate indicator. The need for accuracy is high at high power settings. Accuracy is not necessary at low power settings, which is where he operates.
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