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Lean of Peak

Gutenberg

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For us piston drivers out there. A Lancair factory instructor was teaching one of my students to run aggressively lean of peak (100 degrees lean of peak at 85 percent power) with only a single needle-type gauge for CHT. I was under the impression that this can be a dangerous practice without using tuned injectors and a JPI style engine monitoring system.

At 85 percent, I would think that while passing through peak EGT, there might be some serious detonation going on.

Your thoughts...
 

Dangerkitty

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Gutenberg said:
For us piston drivers out there. A Lancair factory instructor was teaching one of my students to run aggressively lean of peak (100 degrees lean of peak at 85 percent power) with only a single needle-type gauge for CHT. I was under the impression that this can be a dangerous practice without using tuned injectors and a JPI style engine monitoring system.

At 85 percent, I would think that while passing through peak EGT, there might be some serious detonation going on.

Your thoughts...
I do know that the Cirrus folks (especially the ones with the glass cockpits) are BIG into running their engines Lean of Peak. They state that the engine actually runs much cooler and it is better for the engine. I never fully understood the concept but I didn't read into it all that much.

I do know that there is a group of Mechanics and Piston Engine Experts that run a class in Ada, Oklahoma. The Cirrus pilots highly reccommend it. Evidently these guys will change the whole way you think about and operate high perfomance piston engines.

I forgot the name of the class but I do know that they have a website. If you go to www.cirruspilots.org and ask on the public side of the site I am sure they can direct you in the right direction.
 

mtrv

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Dangerkitty said:
Evidently these guys will change the whole way you think about and operate high perfomance piston engines.
This falls into the catagory of what causes lift, and the power/pitch debates. Lycoming is NOT a fan of leaning past peak, and as previously mentioned, fuel injection is required over a carb setup for more even temps; in addition to needing EGT readings for each cylinder. You could still have just one gauge, if there is a rotory type switch to select between single cylinders.

I personally think the pro's & con's of leaning past peak will go on forever. Because that's exactly what it is, a bunch of pro's & con's.
 

GravityHater

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I believe the restriction is more like you have to be <65-70%HP; LOP and 85%HP can result in engine damage.
The other important thing you need is not individual egt, so much as individual CHT - because you also cannot do LOP if any one cylinder is going to run outside the max operating range. Many are limited by mfg at 450F but I wouldn't go LOP if any cylinder was >375F.
The thing to read is articles by a guy named Deakin on Avweb.com.
 

Gutenberg

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yea deakin, been through them all about three times.
 

mar

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Leaning and CHTs

Dangerkitty said:
They state that the engine actually runs much cooler and it is better for the engine. I never fully understood the concept but I didn't read into it all that much.
Obviously a richer mixture cools CHTs. And CHTs will rise while leaning to peak EGT. But if you continue to lean the engine will, let's say, "loose power" and actually result in lower CHTs.

It won't necessarily result in detonation but obviously enrichening the mixture before an application of power is pretty important.

I probably follow the Rep's advice, they usually know best.
 

Dangerkitty

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Like I said I really dont understand it but I have been flying piston's very very very rarely the past 10 or so years.

I prefer turbine.
 

Bryan D

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Lop Or Pol

GravityHater said:
I believe the restriction is more like you have to be <65-70%HP; LOP and 85%HP can result in engine damage.
The other important thing you need is not individual egt, so much as individual CHT - because you also cannot do LOP if any one cylinder is going to run outside the max operating range. Many are limited by mfg at 450F but I wouldn't go LOP if any cylinder was >375F.
The thing to read is articles by a guy named Deakin on Avweb.com.
Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.
 

PeteCO

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Bryan D said:
Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.
Not if you have precise enough fuel control. By definition, lean of peak EGT is also cooler than peak EGT, yes?
 

GravityHater

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Bryan D said:
Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.
That's the myth these folks have been busting for the last 5-10 years... lean of peak (LOP) in SOME circumstances, if done correctly, IS safe for your engine and will NOT result in burned valves if you follow all the caveats.
In fact they say it is a better way to run some engines.

I used to violently resist this philosophy too until I did some learning about it! It seems it is less of an opinion now.... they have developed some pretty good science to back it up.
 

Floyd R. Turbo

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Dangerkitty said:
I do know that there is a group of Mechanics and Piston Engine Experts that run a class in Ada, Oklahoma. The Cirrus pilots highly reccommend it. Evidently these guys will change the whole way you think about and operate high perfomance piston engines.

I forgot the name of the class but I do know that they have a website. If you go to www.cirruspilots.org and ask on the public side of the site I am sure they can direct you in the right direction.

Advanced Pilot Seminars www.advancedpilot.com
 

PeteCO

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Dangerkitty said:
Thats the one! Have you been to it? Is so is it is great as all the Cirrus pilots say it is?
I'd imagine it's great. Read John Deakin's articles on the subject on Avweb. He is a principal of Advanced Pilot Seminars.
 

Moonfly201

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GravityHater said:
That's the myth these folks have been busting for the last 5-10 years... lean of peak (LOP) in SOME circumstances, if done correctly, IS safe for your engine and will NOT result in burned valves if you follow all the caveats.
In fact they say it is a better way to run some engines.

I used to violently resist this philosophy too until I did some learning about it! It seems it is less of an opinion now.... they have developed some pretty good science to back it up.
Absolutely correct. Deakin is right. You need GAMI's and a four probe EGT/CHT gauge to do it properly.

I have been running my GAMI and Insight GEM equipped Mooney Lycoming IO-360 lean of peak for about 650 hours. Saving fuel, babying my cylinders, valves, valve guides and piston rings. And burning a lot less fuel and oil.

LOP allows me to manage the engine like a turbine. Since I'm already cooled down in a normal LOP cruise, I can enrichen slightly (so temps don't get too cold) for a high-speed descent into the airport environment and pull off all the cruise power at once to level off and slow down to gear speed and land.
 

Bryan D

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Moonfly201 said:
Absolutely correct. Deakin is right. You need GAMI's and a four probe EGT/CHT gauge to do it properly.

I have been running my GAMI and Insight GEM equipped Mooney Lycoming IO-360 lean of peak for about 650 hours. Saving fuel, babying my cylinders, valves, valve guides and piston rings. And burning a lot less fuel and oil.

LOP allows me to manage the engine like a turbine. Since I'm already cooled down in a normal LOP cruise, I can enrichen slightly (so temps don't get too cold) for a high-speed descent into the airport environment and pull off all the cruise power at once to level off and slow down to gear speed and land.
This is contrary to the the principals on which every internal combustion engine operates. Leaning the fuel increases combustion chamber/cylinder head/exhaust gas temperature, a rich mixture cools the same. So how do you enrichen the mixture "so the temps don't get to cold". At any altitude I lean the mixture until I see a slight increase in RPM's or slight roughness, then I richen the mixture about 1/4 turn. If I have an EGT guage, it will be at peak everytime with this procedure. Now if I did not turn the mixture 1/4 back in, it would be lean of peak. It would be very likely that I would have detonation but would not hear it because I'm wearing a headset.
 

casper1nine

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moonfly is right and it does work. cht decreases when lop, so if operating lop, enrichening the mixture towards peak heats it up. this is not contrary to anything. for what it's worth, sometimes this is useful, and sometimes not. moonfly's example is one where he was on the winning end of the equation, financially, and performance wise. when i was flying a TC piston plane w/ similar engine monitoring equipment, i found that in my situation i couldn't make lop with the ballsy power settings allowed by a host of mods i had installed, without exceeding the max TIT. so.... in order to operate LOP, i had to run some pretty weak power settings. the moral of the story is that is DOES work with out harming anything, and that the #'s all stay where they should be. in my example though, the reduced power settings were not worth the speed loss, so it was strictly academic. note: don't try it in aircraft where you can't monitor the cylinders individually. i am just supersticious like that:)

regards,
casper1nine
 

casper1nine

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1: egt an cht don't usually peak at the same time
2: peak is PEAK. the engine does not continue to get HOTTER than PEAK, so guess what that means..... LOP is COOLER than peak.

regards.

casperthe1timecfi1niner
 

GravityHater

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Bryan D said:
This is contrary to the the principals on which every internal combustion engine operates. Leaning the fuel increases combustion chamber/cylinder head/exhaust gas temperature, a rich mixture cools the same. So how do you enrichen the mixture "so the temps don't get to cold". At any altitude I lean the mixture until I see a slight increase in RPM's or slight roughness, then I richen the mixture about 1/4 turn. If I have an EGT guage, it will be at peak everytime with this procedure. Now if I did not turn the mixture 1/4 back in, it would be lean of peak. It would be very likely that I would have detonation but would not hear it because I'm wearing a headset.
Read Deaken's and ask around on the GA plane usenets. A lot has happened in the last 5 years. I was adamant at first too, but have since learned. Keep an open mind! Things really have changed.
 

ackattacker

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L.O.P. works great at low power settings where it's safe. I wouldn't try it at >65% power or on turbocharged engines... the risks are not worth the extra fuel economy. Many people have been sold on lean of peak operations only to start replacing valves and cylinders at 500 hours. I don't know of any large commercial operators out there who run lean of peak... that speaks volumes. One cylinder can offset all your fuel savings and then some.

But the economy is impressive. I once flew a Cirrus SR-22 at 55% power lean of peak MMU-DAB nonstop. Fuel burn 10gph and TAS 150kts. Landed with 20 gallons remaining.
 

GravityHater

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LI wouldn't try it at >65% power or on turbocharged engines... the risks are not worth the extra fuel economy.
Many people read just the "risks are not worth it..." and that's all they hear. To a discriminating listener, if you follow the restrictions (<65%hp, never exceed manuf. cht limits, don't forget when descending) then there are no risks. Detonation, or valve/exhaust port damage is impossible in the conditions specified.


Many people have been sold on lean of peak operations only to start replacing valves and cylinders at 500 hours.
and then it turned out what really happened is they didn't understand the restrictions or just weren't careful. To be honest it's not rocket science.

I don't know of any large commercial operators out there who run lean of peak... that speaks volumes. One cylinder can offset all your fuel savings and then some.
If I had an air taxi op or something I wouldn't do it either - the pilots have enough on their plate as it is in these circumstances.
 
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