Carbed LOP

[OkieFlyer]

As a new owner, I have a few questions about LOP operations.

1. Do any of you folks with carbureted continentals run LOP?
In my reading, it seems like LOP is mainly used with fuel injected engines. I guess carbed engines tend to run rough on the lean side? Is it because of uneven air/fuel distribution? What is your experience?

2. Do you lean based on EGT or CHT?
Mostly, I've read about leaning based on EGT, but I read a piece from Mike Busch that explains why he thinks leaning is better done in reference to a CHT value and basically let the EGTs do whatever they do. It made a lot of sense to me, but it doesn't seem to be the commonly used method. Your thoughts.

I hope this hasn't been beat to death already. If so, point me in the right direction and I'll gladly move along.

 

[Tom-D]

Running lean of peak with a carb, presents two problems.

for years the Cessna manuals have advised to lean until you feel the vibrations then enrich until it smooths out.

That does make some cylinders run lean of peak, but leaves some cylinders in the best power range rich of peak. When you lean until all cylinders are lean of peak the leanest cylinders will go to a lean misfire condition and the engine will run rough.

the second issue is many engines will not run at best power range very long with out the max temps being exceeded. which translates to failed cylinders.

unless you have an induction system that delivers equal air and fuel flow to all cylinders, such as the GAMI nozzles you can't really run LOP.

The only exception to this rule is the old Radial engines who run a single point fuel injection such as the Stromberg Carlson pressure injection carb which delivers fuel directly to a supercharger and plenum chamber.

 

[Neal Howard]

It's pretty rare to find a carbureted lyc or cont engine that can successfully run LOP without roughness. The O-320 in my RV-6 is the first one I've encountered that can do a fairly decent job of doing it smoothly, but only at high altitudes ( e.g. above 10000 msl) and with the throttle wide open and some carb heat applied. It also would not do it until after I replaced all the rubber intake hose segments and intake flange gaskets and made sure there was not even the tiniest induction vacuum leak. Now under the aforementioned high altitude ops, I can lean it until it flames out and it does it smoothly... but I never really run it LOP that way much because whenever I'm up that high it's because I'm going somewhere and want to get max speed so I'm usually leaned for peak RPM instead.

 

[Checkout_my_Six]

keep it at 65% HP.....and lean to best power. You'll not hurt anything.

The LOP crowd likes to produce more HP when leaning.....more like 80-85% HP in many cases.

There are a few tricks that may help in leaning the NA, non-fuel injected engine at higher HPs. Lean till you get peak EGT, and check for the max airspeed. Then continue leaning about another 30deg or 3-4 kts loss in airspeed (if she's not running rough at this point....you're fine LOP). That's gonna be your most efficient power producing setting.

Now for the trick......crack the carb heat. This will slightly enrichen the mixture by adding hot air, but also aids in fuel atomization which helps even out the fuel distribution. Another trick is to be high enough to be at a full throttle power setting. Pull the throttle back a 1/2" or so....so, that the throttle plate is cocked and not parallel to the airflow. This is another trick to create turbulent flow across the throttle plate and help with fuel atomization and a more even fuel distribution. Pulling the throttle back also reduces the fuel flow.....the last 1" to 1/2" of throttle lever throw puts the carb into an enrichment circuit in the carb and is designed to reduce detonation at high power settings. Once at altitude this extra enrichment is not necessary.

If additional airspeed is lost when reducing the throttle position.....then add back more mixture allowing the engine to make more power and only lose 3-4 kts of airspeed off of peak EGT.

Again, operations above 7,000 are typically below 65% power.....so unless you are in for a max endurance flight, most folks just lean for best power and fly at max EGT then "enrichen" by 30 deg.

 

[Henning]

Yes, it's doable, sometimes you have to crack the carb heat a touch to get it to get a smooth distribution though which makes you have to lean back more, so you have to give up more power to get smooth solid LOP with a carb than FI.

But with your engine, it's irrelevant to have all the cylinders LOP because even in a cylinder's peak performance range, with your engine rated below .5hp/cuin, that performance level is not enough to cause any destructive situation. All you need do is monitor your CHT, if you aren't seeing a cylinder over 380°, your engine will be fat, dumb, and happy at the leanest setting it will run smooth at regardless what level of power you try for. Basically your engine does not mind to run full rated power full time. Over the long run, you will do more damage and cost yourself more money by running rich.

It's carbon that burns valves and guides, it's carbon that jams rings and makes them break, it's carbon that wears down valve guides. Carbon deposits are caused by partially burned fuel, especially leaded fuel where it helps glue it on. That's what happens when you run ROP, the richer the worse.

 

[Henning]

actually Henning....it's CHT heat that does all those horrible things to the engine.

Actually what causes excess CHT does that, and what causes that is ICP and latent heat, but we are talking about a different set of destructive issues here, and if the CHTs remain below 380° as I said, those factors aren't present.

As for the carbon deposits, actually high CHT is what you need to clean them out. I have done many 'tune up' runs with many engines hard and hot to burn it out. You don't want to stay there long, and you have to be careful, but, especially if you pretreat with something like GM X-66 Carbon Remover, you can make good difference.

 

[Checkout_my_Six]

Actually what causes excess CHT does that, and what causes that is ICP and latent heat, but we are talking about a different set of destructive issues here, and if the CHTs remain below 380° as I said, those factors aren't present.

As for the carbon deposits, actually high CHT is what you need to clean them out. I have done many 'tune up' runs with many engines hard and hot to burn it out. You don't want to stay there long, and you have to be careful, but, especially if you pretreat with something like GM X-66 Carbon Remover, you can make good difference.

Na....CamGuard is what cleans it out.


remember.....the highest heat will occur at a rich setting.....further leaning "cools" the cylinders.

 

[Henning]

Na....CamGuard is what cleans it out.


remember.....the highest heat will occur at a rich setting.....further leaning "cools" the cylinders.

Yep, I understand that fully. Once you already have baked on carbon though, you may not generate enough heat LOP to clear it. You typically have to go to a rich setting and create enough destructive force to erode the carbon off, then you lean back to reduce power.

The biggest problem with aircraft engines is the RPM restriction caused by the prop. Gasoline engines are much happier putting out power around 3400-4200 rpm.

 

[Clip4]

Yes, it's doable, sometimes you have to crack the carb heat a touch to get it to get a smooth distribution though which makes you have to lean back more, so you have to give up more power to get smooth solid LOP with a carb than FI.

But with your engine, it's irrelevant to have all the cylinders LOP because even in a cylinder's peak performance range, with your engine rated below .5hp/cuin, that performance level is not enough to cause any destructive situation. All you need do is monitor your CHT, if you aren't seeing a cylinder over 380°, your engine will be fat, dumb, and happy at the leanest setting it will run smooth at regardless what level of power you try for. Basically your engine does not mind to run full rated power full time. Over the long run, you will do more damage and cost yourself more money by running rich.

It's carbon that burns valves and guides, it's carbon that jams rings and makes them break, it's carbon that wears down valve guides. Carbon deposits are caused by partially burned fuel, especially leaded fuel where it helps glue it on. That's what happens when you run ROP, the richer the worse.

When you lean the engine and then apply some carb heat, you just bypassed the air filter.

 

[poadeleted20]

Kind of like what the Chief Engineer of that Soviet Alfa class sub told Captain Tupolev about pushing the reactor to 115% -- "Possible, but not recommended". As Tom said, with carbureted engines, the f/a ratio varies enough between cylinders that you'll almost certainly have the leanest leaned to the point of uncomfortable roughness before the richest gets lean of peak EGT. This has been borne out by my 20 years of flying with JPI engine analyzers on carbureted engines. So, if you can do it, great, but odds are you won't be able to do it without significant roughness.

 

[Tom-D]

Kind of like what the Chief Engineer of that Soviet Alfa class sub told Captain Tupolev about pushing the reactor to 115% -- "Possible, but not recommended". As Tom said, with carbureted engines, the f/a ratio varies enough between cylinders that you'll almost certainly have the leanest leaned to the point of uncomfortable roughness before the richest gets lean of peak EGT. This has been borne out by my 20 years of flying with JPI engine analyzers on carbureted engines. So, if you can do it, great, but odds are you won't be able to do it without significant roughness.

Do you know why Cessna was successful in doing this ?

"for years the Cessna manuals have advised to lean until you feel the vibrations then enrich until it smooths out."

And now isn't?

 

[OkieFlyer]

Thanks for all the input guys. Pardon my ignorance on the subject, but the POH simply says to use 125° ROP for best power, 75° ROP for normal lean, and 25° ROP for maximum lean. I'm afraid 25° ROP would put my CHT in the advance metal fatigue zone (above 380°) along with high ICP.

so...

Using the POH method, am I just supposed to dial in the mixture setting and then adjust CHT with the cowl flaps?

or...

Should I close the cowl flaps and simply lean up to 380° CHT?



I have myself confused with all the CHT, EGT, cowl flaps, ROP, LOP, etc..
I just want to do what's best for the engine. The POH says to use cowl flaps as needed. I guess I'm not sure how to use them properly.

 

[Henning]

When you lean the engine and then apply some carb heat, you just bypassed the air filter.

Yes, correct.

 

[OkieFlyer]

When you lean the engine and then apply some carb heat, you just bypassed the air filter.

Is that an issue at several thousand feet? We don't run air filters on boats either. Doesn't seem to be a problem there. I wouldn't think there is much to be filtered out of the sky. I could be dead wrong, of course.

 

[Checkout_my_Six]

Is that an issue at several thousand feet? We don't run air filters on boats either. Doesn't seem to be a problem there. I wouldn't think there is much to be filtered out of the sky. I could be dead wrong, of course.

nor is using carb heat an issue while in the pattern with the engine below 1,800 RPMs.....

standard SOP for me....

 

[petrolero]

Kind of like what the Chief Engineer of that Soviet Alfa class sub told Captain Tupolev about pushing the reactor to 115% -- "Possible, but not recommended". As Tom said, with carbureted engines, the f/a ratio varies enough between cylinders that you'll almost certainly have the leanest leaned to the point of uncomfortable roughness before the richest gets lean of peak EGT. This has been borne out by my 20 years of flying with JPI engine analyzers on carbureted engines. So, if you can do it, great, but odds are you won't be able to do it without significant roughness.

This is my experience with my carbed & turbonormalized Lyc. O-540. LOP just ain't happening - it gets really rough. Anyway I don't have a monitor (yet) so it would just be an exercise in scaring the bejebus out of my pax and risking cylinder damage. No thanks.

 

[Neal Howard]

Is that an issue at several thousand feet? We don't run air filters on boats either. Doesn't seem to be a problem there. I wouldn't think there is much to be filtered out of the sky. I could be dead wrong, of course.

It's only an issue if you're flying in a west Texas dust storm

 

[Henning]

This is my experience with my carbed & turbonormalized Lyc. O-540. LOP just ain't happening - it gets really rough. Anyway I don't have a monitor (yet) so it would just be an exercise in scaring the bejebus out of my pax and risking cylinder damage. No thanks.

Really? As soon as I kicked the turbos in on my O-360s it took care of all the issues of running LOP for me.

 

[petrolero]

Really? As soon as I kicked the turbos in on my O-360s it took care of all the issues of running LOP for me.

Yeah I lean it out and get rough running almost as soon as I start down the lean side of peak EGT. But then I am not willing to accept much roughness for pax sake, because I don't have a monitor, and also because I just am not comfortable with it.

 

[Henning]

Yeah I lean it out and get rough running almost as soon as I start down the lean side of peak EGT. But then I am not willing to accept much roughness for pax sake, because I don't have a monitor, and also because I just am not comfortable with it.

It's really hard to play this game without a monitor and fuel flow.

 

[petrolero]

It's really hard to play this game without a monitor and fuel flow.

Yep. For that reason I don't really mess with it much and am in the market for a nice monitor.

I do have fuel flow but it's a 1970s Hoskins that probably hasn't been calibrated in a long time. It's good for me because I know that my FF is consistently higher than actual usage. I know what flow rate it typically reads at my typical cruise (which is much higher than book value). It is also nice to have it as a totalizer. So it's super conservative and that is OK for what I use it for. But I'd like to have a well-calibrated monitor with fuel flow at some point.

 

[Tom-D]

When you lean the engine and then apply some carb heat, you just bypassed the air filter.

Which would you rather do, feed your engine dirty air, or none at all?

 

[jesse]

Bypassing the air filter is a non issue in cruise and is standard op in most Mooneys.

 

[Heftiger]

I just found this very informative video yesterday talking about this very subject:

http://www.eaavideo.org/video.aspx?v=1316946190001


Sent from my iPhone using Tapatalk

 

[poadeleted20]

Do you know why Cessna was successful in doing this ?

"for years the Cessna manuals have advised to lean until you feel the vibrations then enrich until it smooths out."

And now isn't?

I don't believe I said anything to the contrary, only that you're going to feel the roughness before you get all the cylinders on a carbureted engine lean of peak, and that's not in contradiction of what those Cessna manuals recommend..

 

[poadeleted20]

Thanks for all the input guys. Pardon my ignorance on the subject, but the POH simply says to use 125° ROP for best power, 75° ROP for normal lean, and 25° ROP for maximum lean.

Can you share with us the exact aircraft/engine model involved? That might help us make sense of the recommendation you quoted.

 

[Hank S]

Thanks for all the input guys. Pardon my ignorance on the subject, but the POH simply says to use 125° ROP for best power, 75° ROP for normal lean, and 25° ROP for maximum lean. I'm afraid 25° ROP would put my CHT in the advance metal fatigue zone (above 380°) along with high ICP.

so...

Using the POH method, am I just supposed to dial in the mixture setting and then adjust CHT with the cowl flaps?

or...

Should I close the cowl flaps and simply lean up to 380° CHT?



I have myself confused with all the CHT, EGT, cowl flaps, ROP, LOP, etc..
I just want to do what's best for the engine. The POH says to use cowl flaps as needed. I guess I'm not sure how to use them properly.

I lean my O-360 using EGT. If they weren't fixed, I could control CHT with cowl flaps. I'd suggest you do that--lean by EGT, use cowl flaps as needed to keep CHT where you want it.

Mooney says that Max Power is 100°F Rich of Peak, and Max Efficiency is at 25°F Rich of Peak. What does your POH / Owners Manual say?

Even with reduced throttle (I always reduce throttle enough to make the MP needle move, to get out of the auto-enrich zone in the carb, and to induce turbulence for better atomization) and varying amounts of partial carb heat, I am unable to run smoothly LOP. But speed at 50°F Rich of Peak (per Bob Kromer's recommendations, former Mooney test pilot, Eng VP and Mooney President), performance and efficiency are quite satisfactory.

 

[Tom-D]

I don't believe I said anything to the contrary, only that you're going to feel the roughness before you get all the cylinders on a carbureted engine lean of peak, and that's not in contradiction of what those Cessna manuals recommend..

I didn't ask that, I asked why Cessna could do it the way they did and get away with it in the early days and not later?

Do you know? I'm not looking for an argument, just an answer.

 

[poadeleted20]

I didn't ask that, I asked why Cessna could do it the way they did and get away with it in the early days and not later?

Perhaps if you post "they way they did" in both "the early days" and "later" side by side, I might be able to come up with a possible explanation.

 

[Tom-D]

Perhaps if you post "they way they did" in both "the early days" and "later" side by side, I might be able to come up with a possible explanation.

IOWs you do not know the method in the book worked in the early days, and lead to cylinder problems later.

Their method written in the manual didn't change basically stayed the same thru out the whole run 1957-1981.

so why the troubles later in the run?

 

[cgrab]

I run my O320 LOP since seeing Mike B at OSH. I have no egt. I checked my POH and if my rpm is below 2350 I'm below 65 percent power and can't damage my engine. At about 4500 ft at full throttle I'm at 2350 rpm. I give it the big pull until it runs rough and then one click in. I don't run for speed but at 6.5 gal per hr on mogas I'm happy.

 

[OkieFlyer]

Can you share with us the exact aircraft/engine model involved? That might help us make sense of the recommendation you quoted.

Sorry 'bout that Ron. It's a C-182 O-470-R . Thought I mentioned it earlier, but alas, I did not.

So after some more study and the great input here, I'm thinking that LOP operation with my O-470 and without and engine monitor is probably not going to work out well, or at the very least, a PITA. It sounds like this engine has notoriously poor air/fuel distribution across the cylinders, and without the engine monitor, I'll have no real idea where the cylinders are on the temp curve. I think I'll stick to ROP.

That being said, where do you stand on the leaning method for ROP?
1. Lean up to roughness, then enrichen until it smoothes out.
2. Lean to peak EGT, then enrichen to a given temp below peak.
3. Lean up to a predetermined CHT (380°)

Mike Busch recommends the 3rd method. According to him, anywhere within about 50° on the rich side of peak EGT will put the CHT in the extreme metal fatigue zone (400°+) and recommends running at least 100° ROP EGT to stay well away from the danger zone. He says the simplest thing to do is just lean it until the maximum safe CHT is achieved, which is about 380° for most legacy aircraft.

What say you?

 

[Tom-D]

Sorry 'bout that Ron. It's a C-182 O-470-R . Thought I mentioned it earlier, but alas, I did not.

So after some more study and the great input here, I'm thinking that LOP operation with my O-470 and without and engine monitor is probably not going to work out well, or at the very least, a PITA. It sounds like this engine has notoriously poor air/fuel distribution across the cylinders, and without the engine monitor, I'll have no real idea where the cylinders are on the temp curve. I think I'll stick to ROP.

That being said, where do you stand on the leaning method for ROP?
1. Lean up to roughness, then enrichen until it smoothes out.
2. Lean to peak EGT, then enrichen to a given temp below peak.
3. Lean up to a predetermined CHT (380°)

Mike Busch recommends the 3rd method. According to him, anywhere within about 50° on the rich side of peak EGT will put the CHT in the extreme metal fatigue zone (400°+) and recommends running at least 100° ROP EGT to stay well away from the danger zone. He says the simplest thing to do is just lean it until the maximum safe CHT is achieved, which is about 380° for most legacy aircraft.

What say you?

You should ask the expert, John Deakins at EAA Pelican's Perch. He wrote the book on LOP.

Your 0-470 has the worst induction system since the IO-360 (its little brother) It feeds the engine from a remote mounted carb (MA4-) to a long tube assembly that distributes fuel to cylinders from rear forward, the two at the end of the pipe gets the least.

When you lean the 0-470 you have a wide spread, going LOP you leave two in the best power range, going ROP you leave the opposite two in the best power range.
The engine is famous for eating cylinders, its a matter of which two, when you run it rich enough you foul plugs.

I think it is easier/cheaper to clean plugs.

 

[OkieFlyer]

You should ask the expert, John Deakins at EAA Pelican's Perch. He wrote the book on LOP.

Your 0-470 has the worst induction system since the IO-360 (its little brother) It feeds the engine from a remote mounted carb (MA4-) to a long tube assembly that distributes fuel to cylinders from rear forward, the two at the end of the pipe gets the least.

When you lean the 0-470 you have a wide spread, going LOP you leave two in the best power range, going ROP you leave the opposite two in the best power range.
The engine is famous for eating cylinders, its a matter of which two, when you run it rich enough you foul plugs.

I think it is easier/cheaper to clean plugs.

Is the plug fouling issue because of the lead, or rather the lack of lead scavenging at the richer settings? If so, would running mogas eliminate the issue?

 

[Tom-D]

Is the plug fouling issue because of the lead, or rather the lack of lead scavenging at the richer settings? If so, would running mogas eliminate the issue?

It's just a matter of not scavenging. there are a few pilots/ owners that have found the proper GPM at their cruise setting to get the sweet spot, but it is more experimenting than any other thing.

 

[OkieFlyer]

Thanks Tom. I reckon I need to just go up and do some fiddlin' with it. Needed to get few things straight before I go experimenting though.

'Preciate all the help guys.

 

[Tom-D]

Thanks Tom. I reckon I need to just go up and do some fiddlin' with it. Needed to get few things straight before I go experimenting though.

'Preciate all the help guys.

Clean your plugs, then run at 1 richness, and check your plugs see which is running lean and which are running rich.

each 20 hours try a different setting. see which works best in your engine.

Your plugs will tell you where you should be.

 

[Checkout_my_Six]

If you are not able to lean past peak EGT, 20 or 30 deg.....What Mike says is good info.

But, when you are at altitude at or above 7,000 feet your engine is makine 65% HP or less.....in which case, leaning to peak EGT and then enrichening a bit for best power is also acceptable and fine on your cylinders.

Sorry 'bout that Ron. It's a C-182 O-470-R . Thought I mentioned it earlier, but alas, I did not.

So after some more study and the great input here, I'm thinking that LOP operation with my O-470 and without and engine monitor is probably not going to work out well, or at the very least, a PITA. It sounds like this engine has notoriously poor air/fuel distribution across the cylinders, and without the engine monitor, I'll have no real idea where the cylinders are on the temp curve. I think I'll stick to ROP.

That being said, where do you stand on the leaning method for ROP?
1. Lean up to roughness, then enrichen until it smoothes out.
2. Lean to peak EGT, then enrichen to a given temp below peak.
3. Lean up to a predetermined CHT (380°)

Mike Busch recommends the 3rd method. According to him, anywhere within about 50° on the rich side of peak EGT will put the CHT in the extreme metal fatigue zone (400°+) and recommends running at least 100° ROP EGT to stay well away from the danger zone. He says the simplest thing to do is just lean it until the maximum safe CHT is achieved, which is about 380° for most legacy aircraft.

What say you?

 

[poadeleted20]

IOWs you do not know the method in the book worked in the early days, and lead to cylinder problems later.

Which book? What aircraft? What is "early days"?

 

[poadeleted20]

Sorry 'bout that Ron. It's a C-182 O-470-R . Thought I mentioned it earlier, but alas, I did not.

Thanks -- makes it a lot easier to help. :wink2:

So after some more study and the great input here, I'm thinking that LOP operation with my O-470 and without and engine monitor is probably not going to work out well, or at the very least, a PITA. It sounds like this engine has notoriously poor air/fuel distribution across the cylinders, and without the engine monitor, I'll have no real idea where the cylinders are on the temp curve. I think I'll stick to ROP.

Since you don't have an engine monitor (or at least all-cylinder EGT), you have no idea whether you're ROP or LOP anyway, so the discussion is moot.

That being said, where do you stand on the leaning method for ROP?
1. Lean up to roughness, then enrichen until it smoothes out.
2. Lean to peak EGT, then enrichen to a given temp below peak.
3. Lean up to a predetermined CHT (380°)

My answer depends on what engine instrumentation you have, i.e., whether you have EGT and/or CHT, and whether it's on all cylinders or just one.

Mike Busch recommends the 3rd method. According to him, anywhere within about 50° on the rich side of peak EGT will put the CHT in the extreme metal fatigue zone (400°+) and recommends running at least 100° ROP EGT to stay well away from the danger zone. He says the simplest thing to do is just lean it until the maximum safe CHT is achieved, which is about 380° for most legacy aircraft.

That's good as general statement, but isn't much use as a practical matter unless you have all-cylinder EGT/CHT instrumentation. Otherwise, you really don't know what's going on. Note that generally using method 1 for cruise leaning will result in being around peak EGT, and maybe 20F on the lean side of peak CHT, which is usually a pretty good place to be (see the figure below, which is a Lycoming chart but the thermodynamics in a Continental engine are pretty much the same) as it produces about the same CHT as running 100F rich of peak EGT while saving a lot of gas and reducing fouling. However, again, without all-cylinder instrumentation, you're shooting in the dark.