Lean of Peak

[Gutenberg]

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]

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]

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]

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]

yea deakin, been through them all about three times.

 

[mar]

Leaning and CHTs

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]

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]

Lop Or Pol

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]

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]

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]

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

 

[Dangerkitty]

Advanced Pilot Seminars www.advancedpilot.com

Thats the one! Have you been to it? Is so is it is great as all the Cirrus pilots say it is?

 

[PeteCO]

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]

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]

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]

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]

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]

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]

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]

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.

 

[PeteCO]

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.

No. Peak means just that - peak temp. On either side of this peak, the temps decrease. Rich or lean, doesn't matter. The old radials were run lean of peak all the time. Arguably, slightly rich of peak is the worst place to run your engine, even though Lycoming and Continental recommend it. The biggest barrier to successfully running LOP is fuel distribution - that why GAMI-jectors are pretty much needed to run LOP.

This is especially safe when making less than 75% power. Since I operate from a field at 5000 feet, I lean ruthlessly. At low power levels you simply cannot do damage to the engine with this technique. I lean so ruthlessly on the ground that the engine can't exceed say 1200rpm without stuttering.

Read Deakin's excellent articles on Avweb and you too will become a convert just as I have.

 

[JimG]

This month's edition of Flying has an interesting article on the Lancair that I just read.

Even Lancair's test pilot claimed it "stumbles and splutters" at 50 lean of peak.

That's a comforting thought.

I used to fly my normally aspirated Bonanza just barely rich of peak, but with new Ram VI's in my 340....I'll pay for the extra gas and go 100 rich. Big difference in overhauls/maintenence.

 

[Bryan D]

No. Peak means just that - peak temp. On either side of this peak, the temps decrease. Read Deakin's excellent articles on Avweb and you too will become a convert just as I have.

When I lean an engine after peak all the temperatures increase. This makes no sense to me. I have an open mind though, I'll try this on my lawnmower tommorrow.

 

[TDTURBO]

Brian, you thought you leaned them all (6) or (4) cylinders LOP. If you did, I assure you, the temps drop.


The trick is to have a "compliant" engine, ie; no induction leaks, good baffaling, ect.....

What kind of engine monitor were you using? If you only had a single probe, there is no way you can fly LOP with confidence. Meaning, you could have 5 cyliders LOP and one 20 degrees rich, that is the worst place to be if you are a cylinder running higher than 65% power, hence the OWT's regarding bad dogma regarding LOP.

You can't hurt the engine with the red knob if you are flying BELOW 65% power, so it doesn't hurt to try with a normally aspirated engine or turbo, just keep it at low power setttings until you are confident that ALL cylinders are running LOP.

Read Deaken

 

[Moonfly201]

This is especially safe when making less than 75% power. Since I operate from a field at 5000 feet, I lean ruthlessly. At low power levels you simply cannot do damage to the engine with this technique. I lean so ruthlessly on the ground that the engine can't exceed say 1200rpm without stuttering.

Keep in mind, it is not hard to keep power levels under 75% ... even full throttle at sea level, when operating LOP. You are literally choking off the fuel supply to the engine, and power settings are easy to reduce below 75%. In my case, I confirm this with indicated airspeed readings. If I was fortunate enough to have a fuel flow gauge, it would even be quicker and more accurate.

 

[Moonfly201]

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.

I give up about 7 to 8 knots indicated airspeed to operate LOP, when compared to the ROP power settings I formally used.

LOP, my IO-360 is burning 7 to 8 gal/hr, and the Mooney's TAS is 140 to 148 kts., depending upon altitude and load. I can cross the entire country (in both directions) with 2 only fuel stops and IFR reserves, with 64 useable gallons.

I'm sold. No more old wives tales for me.

 

[A Squared]

I used to fly my normally aspirated Bonanza just barely rich of peak, but with new Ram VI's in my 340....I'll pay for the extra gas and go 100 rich. Big difference in overhauls/maintenence.

Uhh, yeah, just rich of peak is the absolute worst place to run it, highest danger of detonation and highest chts.

When I lean an engine after peak all the temperatures increase. This makes no sense to me.

It really does make it cooler, I was just noticing this the other day in my 180, if I lean aggressively (below 65% power) the CHTs drop noticably.

For those who are having trouble with the concept think of it this way. when you're operating very rich your cooling with extra fuel, when you're operating lean, you're cooling with extra air. this is not eactly precise, but it may be a useful way of understanding it.

A more correct way of looking at it is this: you'll get the hottest flame when the mixture of oxygen and fuel is perfect, too much fuel and it doesn't burn as hot, too much oxygen and it doesn't burn as hot.

 

[421Driver]

For those who are having trouble with the concept think of it this way. when you're operating very rich your cooling with extra fuel, when you're operating lean, you're cooling with extra air. this is not eactly precise, but it may be a useful way of understanding it.

Well said. As everyone else said, you need a good engine monitor, but don't forget GAMI-jectors, all of the cylinders need to peak close together. A piston engine is really like 4 or 6 separate engines, depending on the model. No two cylinders will perform exactly the same.

Check out the Avweb columns, they really are enlighteneing!

 

[GravityHater]

When I lean an engine after peak all the temperatures increase. This makes no sense to me. I have an open mind though, I'll try this on my lawnmower tommorrow.

The one thing that takes learning on this is you can't hamfist the mixture to do it properly. You need a vernier mixture control as well. The difference between peak and stumbling is often less than one-half turn of the mixture. I have used a JPI fuel flow guage as a measure of how much I am leaning or enrichening. A half turn might mean one GPH which is HUGE. You have to take your time and just nudge it a tiny bit during your adjustments.

 

[VNugget]

When I lean an engine after peak all the temperatures increase.

Think about what you just said....