Leaning question

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astaib
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Leaning question

Post by astaib »

Hello,

Since I’ve read the book of Mike Busch, I now mixture my Lycoming rather lean than rich. First because it helps my 4 CHT to be balanced, under 390 degrees F and also it is less fuel consumption.

As it is quite recent, I didn’t tried to determine my peak EGT at all altitude level.
For Example at 2000ft I mixture at 8 gallons per hour at 75% power cruise.

My question is: can I check once for all the peak EGT at each altitude level and then make a « table » for the future or do I have to determine the peak EGT each flight because it is very related to current condition (temp, pressure...)?

Thanks.
Arnaud.
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40flyer
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Re: Leaning question

Post by 40flyer »

My experience is that peak EGT at any altitude is not the same from flight to flight so I think a table might get complex depending on environmentals. Sometimes I am able to fly LOP no problem but other times it's difficult to get LOP without the engine beginning to run a little rough. I haven't tried to figure out what the environmental impacts are. If you have the G1000 cockpit you can quickly determine peak EGT and go from there. Stay out of the "red box"! By the way, GAMI injectors, which I don't have but am adding on my upcoming engine overhaul, help balance CHTs and EGTs.
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Re: Leaning question

Post by waynemcc999 »

Arnaud, you'll want to collect data (e.g. KTAS, Fuel Flow) versus Density Altitude (DA; not MSL). Here's data that I collect on my 2008 DA40 (PowerFlow, EIS):
https://docs.google.com/spreadsheets/d/ ... sp=sharing

See tabs on the bottom for KTAS vs DA, FF vs DA.
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Last edited by waynemcc999 on Thu Dec 13, 2018 4:20 pm, edited 1 time in total.
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Rich
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Re: Leaning question

Post by Rich »

My EGTs tend to peak around 1550 at lower DAs and around 1510 around 10K-ish ft. Ever since installing the Powerflow lo these many years ago, #4 has been the lowest EGT and lowest CHT. Not by a great deal, but consistently true, even before and after my top OH 3-1/2 years ago. Nevertheless, running the GAMI lean test shows little if anything to be gained by installing the GAMI fuel injectors. Running LOP is most effective for me when at higher altitudes (>10K ft.). Though I can only get around 20 deg LOP EGT, my CHTs absolutely plummet by about 40 deg. I wind up cruising along around ~320 deg CHTs, 128 KTAS and 7.5 GPH (I have one of the old, slow DA40s)

But could it be we're overthinking this?

1. IO360M1A manual: For best economy, run at peak EGT.
2. DA40 POH: For best economy, lean until engine becomes rough, then enrich until it becomes smooth. At this point the EGTs should be at maximum. (Note the should).
3. General process we hear and use for running LOP: Find max EGT, continue leaning until engine runs rough, then enrich until it's smooth.
4. Instructions for running best economy from my old 1972 Cherokee 140, with carburetor control Lyc O-320: Lean until engine becomes rough, then enrich until it becomes smooth.

My humble observation: 2, 3, and 4 seem like essentially the same thing to me.
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Re: Leaning question

Post by Roxi5m9 »

My experience has been exactly like all of yours....relatively balanced cylinders, able to run smoothly between peak and 30 LOP depending on the day (still haven’t figured out what exactly determines what it will run smooth at). I’ve also noticed what Rich did, regarding the manuals, and that’s how we fly it. My question that I posted in another forum, which still remains, is what EGT, if any, should we be concerned about running at if running at peak? Or can we run these EGTs as hot as they want to go, as long as the CHTs are happy?

Im assuming this is probably a question for an engineer, if there are any out there.
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Re: Leaning question

Post by Rich »

I've not really been experimenting too much with LOP over the years. But really, I am often just flying on such short trips that cruise speed really doesn't matter much so I really should be. Yesterday I tried fiddling with it on a local hole-boring expedition.

Well, gollee. At 6,000 ft, 22x2200, OAT 6 degC, the plane ran fine at something like 40+ deg LOP (1470-1480 deg EGT). CHT's at 320-330, 7.2 GPH. I didn't get too anal about what the max EGT was, though I did see about 1520 whilst pulling back the mixture. It was pretty gusty and turbulent so I really couldn't get a credible reading on airspeed. But indicated was mostly bouncing around 120.

As far as the highest peak EGT one should be concerned about? I'm inclined not to worry too much about it as long as CHT's are under control. Max allowed per Lycoming is 1600. I've never seen it that high. 1550 is about it.
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Re: Leaning question

Post by Charles »

Roxi5m9 wrote:My experience has been exactly like all of yours....relatively balanced cylinders, able to run smoothly between peak and 30 LOP depending on the day (still haven’t figured out what exactly determines what it will run smooth at). I’ve also noticed what Rich did, regarding the manuals, and that’s how we fly it. My question that I posted in another forum, which still remains, is what EGT, if any, should we be concerned about running at if running at peak? Or can we run these EGTs as hot as they want to go, as long as the CHTs are happy?

Im assuming this is probably a question for an engineer, if there are any out there.
I happen to be a mechanical engineer and I work for an aircraft engine company. What Deakin and Busch say about leaning and general engine management makes a lot of sense to me. And I always run at peak EGT myself unless CHTs dictate a LOP setting.

The absolute EGT reading is meaningless. Temperatures vary widely during each engine revolution and the number that is displayed is a gross average of a complex phenomenon. It is only useful as a relative measure to determine whether at peak or LOP or ROP and by how much.

CHTs are the only reading that matters for engine heat management.

A good way for an aircraft owner to spend 2 hours is to watch this: https://youtu.be/fqe9j74qMdk
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Charles
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Re: Leaning question

Post by Charles »

astaib wrote:
My question is: can I check once for all the peak EGT at each altitude level and then make a « table » for the future or do I have to determine the peak EGT each flight because it is very related to current condition (temp, pressure...)?

Thanks.
Arnaud.
Bonjour Arnaud,

The stoichiometric mixture at a given altitude is a function of density altitude, not barometric altitude, so the table should be based on density altitude.

This would correct for the increased quantity of oxygen in a given volume of air in colder temperatures. A mixture setting that is ROP at a given altitude at +20C could very well be LOP at the same altitude but -20C.
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Re: Leaning question

Post by astaib »

Hello,

Thank you all for your feedback.

That make sense, and i will work on a table soon.

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Re: Leaning question

Post by RMarkSampson »

I'm more familiar with the Continental Engine best practices - but running at Peak EGT is OK but only if you are running at 65% power or lower. I have a %power value on my EMS so I can determine if I am cruising at 65% or lower where I can somewhat ignore EGTs and focus on keeping CHTs "not too high." This power setting would equate to "economy cruising" as previously mentioned.

My Engine Management System (EMS) also has ROP and LOP setting features but I rarely use them. "Full rich" climbing does not work on my engine - that setting is simply too rich with poor performance and tends lead to plug fouling. I normally go ROP in a cruise climb by just leaning until I see EGTs that are ball park and keep an eye on CHTs. Once leveled off I go LOP by giving it lots of throttle, then pulling the mixture back until the engine RPM decreases - then tweak throttle and mixture until I have a smooth running engine that is burning the expected GPM and CHTs remain happy.

Ultimately I am not a proponent of thumbing through tables and graphs every flight seeking specific numbers. It certainly does not make sense to me if you are climbing through different flight levels and thus different rows on a table - and trying to adjust mixture based on a flight level table. I would rather keep my eyes outside the cockpit and keep engine parameters "ball park" until I can go LOP. If you do build a ROP/LOP cruise table then I recommend your levels be based on density altitude, not MSL. I see a big difference in LOP flying between summer and winter simply looking at MSL -about a 3K change in MSL between seasons and barometric pressure. So now besides looking at tables you are doing math in flight which will impact your cockpit management even more.
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