Lycoming vs Continental operation lean of peak (LOP)

[jaylw314]

Most of the valve's cooling comes through the valve seat.  Even though 50 ROP and 50 LOP have the same exhaust gas temp, if the LOP cylinder is cooler, the valve is cooler.

Also, IIRC, while LOP produces less carbon monoxide, it does produce more nitric oxide and nitrogen dioxide, neither of which are particularly healthy alternatives, even if they won't immediately kill you

[ilovecornfields]

Didn’t mean to start the theoretical LOP vs ROP discussion (or talk about T&G or anything like that) I was just wondering if there were actual facts to supplement the theoretical discussion. Sometimes we focus on one variable and another confounding variable ends up actually being the cause.

 

I took the APS class and drank the Kool-Aid. My engine just seems to run better ROP despite GAMI injectors, good plugs and a good spread. I’m usually not in a hurry to get anywhere so my temps are very reasonable. I guess I’d love to see data that shows that ROP engines run at the same temps have different outcomes than LOP engines. Maybe Savvy knows…

[A64Pilot]

1 hour ago, Andy95W said:

100° Lean of Peak EGT = cooler exhaust gases than 50° Rich of Peak EGT.

With fewer exhaust byproducts being the bonus. 

Who runs 100 LOP? and why not 150 ROP? You can run cooler ROP than LOP, and if you really are 100 LOP, then you are WAY down on power.

‘My little IO 360 Lyc will run 100 LOP, but it’s the first motor I have had that will. the 540, maybe 50 LOP but it would stumble at that point,25 was about as low as it woud go and stay smooth, the 520 may have but with the throttle wide open at 7500 MSL and 2500 RPM I would be 20 kts slower than ROP if I did.

‘I’m not saying LOP isn’t often the best setting, I use it often, and cruise at about 135 kts where I could cruise 155-160  ROP, my J won’t cruise 155-160 LOP. LOP is my default cruise now.

‘Now that I’m Retired I’m not in as big a hurry, the 210 was a business airplane and it’s purpose was to get me somewhere as fast as it could, often not the smoothest of strips, and often carrying parts, tools etc. So I flew it ROP as fast as it would go, and it tolerated that “abuse” just fine.

‘I think most Conti’s do fine if run hard, just don’t try to save fuel if your doing so, if you want to save fuel go deep LOP and accept the speed loss.

‘I think some people lose jugs in a Conti by wanting to run it hard, and lean it out too. The Bonanza guys I fly with are the worst for that, they want to go fast, but don’t want to spend the fuel doing so.

The Crop Duster guys run those motors HARD, they have to, airplane won’t fly at lower power until the hopper load comes way off, and most don’t touch the mixture, and yet seem to get decent cylinder life.

‘Most of those aircraft are down in Honduras, Costa Rica, Ecuador, Columbia etc and they have to follow TBO.

 

All I am saying so that a Continental cylinder will last if run hard, but if you do run it hard, run it very rich is all. Of course they will run LOP very well, I am not saying they won’t.

My Lycoming 540 was happy at 50 ROP run hard, but it was only a 235 HP engine too with Sodium filled exhaust valves, run a 300 HP Conti at 300 HP or even close to 50 ROP and your going to burn it’s solid exhaust valves.

Why doesn’t Continental run sodium filled valves? I don’t know, but I’d love to hear the reason.

[A64Pilot]

1 hour ago, ilovecornfields said:

Didn’t mean to start the theoretical LOP vs ROP discussion (or talk about T&G or anything like that) I was just wondering if there were actual facts to supplement the theoretical discussion. Sometimes we focus on one variable and another confounding variable ends up actually being the cause.

 

I took the APS class and drank the Kool-Aid. My engine just seems to run better ROP despite GAMI injectors, good plugs and a good spread. I’m usually not in a hurry to get anywhere so my temps are very reasonable. I guess I’d love to see data that shows that ROP engines run at the same temps have different outcomes than LOP engines. Maybe Savvy knows…

Engines have been run forever ROP and have done just fine doing so. They have also been run forever LOP by a few and done just fine, my Father used to cruise his 210 at higher altitudes leaned as far as it would and still stay smooth, and that’s LOP for most injected engines and even some carbureted.

For example who leans trainer airplanes? Almost no one and yet what engines seem to make TBO more regularly than most? Trainer engines, which of course are operated in a manner we have all been taught is abusive, many wide open then idle cycles, inadequate warm up, lots and lots of full throttle climbing, on and on.

‘I think our motors are tougher then we want to think they are, we want to believe they need to be or at least will respond to excessive cuddling, but that doesn’t seem to be the case, run them often in the manner recommended by the manufacturer and they seem to do fine, yes there will always be the exception and those should be rare.

There is a lot of evidence that engines that normally cruise at lower rather then higher power will last longer, Lycoming makes that statement several times in their publications. 

Anything above 7500 with RPM in the middle of the green for a NA motor is low power

[A64Pilot]

4 minutes ago, A64Pilot said:

Engines have been run forever ROP and have done just fine doing so. They have also been run forever LOP by a few and done just fine, my Father used to cruise his 210 at higher altitudes leaned as far as it would and still stay smooth, and that’s LOP for most injected engines and even some carbureted.

For example who leans trainer airplanes? Almost no one and yet what engines seem to make TBO more regularly than most? Trainer engines, which of course are operated in a manner we have all been taught is abusive, many wide open then idle cycles, inadequate warm up, lots and lots of full throttle climbing, on and on.

‘I think our motors are tougher then we want to think they are, we want to believe they need to be or at least will respond to excessive cuddling, but that doesn’t seem to be the case, run them often in the manner recommended by the manufacturer and they seem to do fine, yes there will always be the exception and those should be rare.

There is a lot of evidence that engines that normally cruise at lower rather then higher power will last longer, Lycoming makes that statement several times in their publications. 

Anything above 7500 with RPM in the middle of the green for a NA motor is low power

Only actual facts I think you could gather is to talk to a DOM of large operations and ask how often they make it to TBO or beyond. Most of not all of those are operated ROP and run hard as the operator isn’t buying fuel, they want to complete the flights and go home 

‘I doubt anyone has gathered enough actual data to render anything but an opinion, most manufacturers I have talked to aren’t interested in beyond TBO. Pratt & Whitney Canada and GE anyway.

Edited August 28, 2021 by A64Pilot

[Guest]

50 minutes ago, A64Pilot said:

Engines have been run forever ROP and have done just fine doing so. They have also been run forever LOP by a few and done just fine, my Father used to cruise his 210 at higher altitudes leaned as far as it would and still stay smooth, and that’s LOP for most injected engines and even some carbureted.

For example who leans trainer airplanes? Almost no one and yet what engines seem to make TBO more regularly than most? Trainer engines, which of course are operated in a manner we have all been taught is abusive, many wide open then idle cycles, inadequate warm up, lots and lots of full throttle climbing, on and on.

‘I think our motors are tougher then we want to think they are, we want to believe they need to be or at least will respond to excessive cuddling, but that doesn’t seem to be the case, run them often in the manner recommended by the manufacturer and they seem to do fine, yes there will always be the exception and those should be rare.

There is a lot of evidence that engines that normally cruise at lower rather then higher power will last longer, Lycoming makes that statement several times in their publications. 

Anything above 7500 with RPM in the middle of the green for a NA motor is low power

Our local flight school, with a varied fleet of four cylinder Lycoming powered airframes routinely exceed 3500 hours and in many cases 4000 hours.  They run on straight weight oils, 80 in winter, 100 in summer.  The key to success seems to be loads of flying, 500-1000 per year.

Clarence

[Schllc]

50 minutes ago, A64Pilot said:

Only actual facts I think you could gather is to talk to a DOM of large operations and ask how often they make it to TBO or beyond. Most of not all of those are operated ROP and run hard as the operator isn’t buying fuel, they want to complete the flights and go home 

‘I doubt anyone has gathered enough actual data to render anything but an opinion, most manufacturers I have talked to aren’t interested in beyond TBO. Pratt & Whitney Canada and GE anyway.

That may be big the biggest challenge to settling the debate. No two engines are run the same way, same environment, altitudes, temps etc.

I do think the history of ROP is a function of the limited instrumentation of the day. 
This engendered generations of conventions, habits and empirical experience. 
Technology, understanding of metals, ignition and instrumentation has changed. 
The constant, which is temperature management, hasn’t changed, but the ability to monitor, and the average understanding of how to manage, has radically changed. 
Every plane I have owned has been a continental 550, turbo or NA. 
They have all run cooler LOP than ROP.  One had gami”s when I bought it, and it runs beautifully either way, but I prefer LOP because the speed gain at ROP isn’t worth an extra 3.5gph. 
One acclaim wouldn’t run LOP until I put in gami’s. Once they were installed, it did the exact same speed ROP but at almost 3gph less. 
How many engines out there over time had a spread this bad and owners never knew because of poor instrumentation and always running ROP?

Readers digest versions...

Keep your temps in check and your engine will last longer than if you don’t..

[A64Pilot]

You can safely run LOP without big money monitors, just run at a power setting where you can’t hurt anything, which is simple to do, but you need or should have a fuel flow meter, not required but it will tell you power output when LOP. Simply put if I’m at 8.5 GPH or less, then I’m under 65% power and can’t hurt the motor no matter what I do with the red knob. 10 GPH is 75% if your want to push it, I don’t, not worth it to me.

This is where mine sits

I agree, because I’m buying the gas and aren’t in a hurry, the additional fuel isn’t worthy the extra speed, for people who are doing it for work, it may be.

Largely motors run cooler when LOP because power output is down. But too cool isn’t good either, you should have at least 300f cyl head temps to be hot enough to prevent deposits. and probably below 400 for maximum life or at least to extend life. Middle of the green and life’s good.

You can safely run LOP or ROP without any kind of monitor if your choose to, it’s been done for a long time.

Edited August 29, 2021 by A64Pilot

[aviatoreb]

11 hours ago, M20Doc said:

Our local flight school, with a varied fleet of four cylinder Lycoming powered airframes routinely exceed 3500 hours and in many cases 4000 hours.  They run on straight weight oils, 80 in winter, 100 in summer.  The key to success seems to be loads of flying, 500-1000 per year.

Clarence

That's a lot of hours!  With original cylinders?

I know that one of our regional carriers, Cape Air, that runs Cessna 402's that have the TSIO520VB, they regularly get 2600 hrs, which once past standard tbo there is a special paper work they need to file on a regular and on condition basis with the FAA since they are a scheduled carrier.  Then at 2600 that avenue runs out and they are forced to overhaul.  They too gets lots of hours per year.  And lots and lots of fleet experience with this.

[Guest]

4 minutes ago, aviatoreb said:

That's a lot of hours!  With original cylinders?

I know that one of our regional carriers, Cape Air, that runs Cessna 402's that have the TSIO520VB, they regularly get 2600 hrs, which once past standard tbo there is a special paper work they need to file on a regular and on condition basis with the FAA since they are a scheduled carrier.  Then at 2600 that avenue runs out and they are forced to overhaul.  They too gets lots of hours per year.  And lots and lots of fleet experience with this.

On some of the C-152’s they have to hone and re ring a few cylinders, but generally cylinders make the distance.

Clarence

[aviatoreb]

2 hours ago, M20Doc said:

On some of the C-152’s they have to hone and re ring a few cylinders, but generally cylinders make the distance.

Clarence

That's cool.  4000hrs is crazy!

What I find interesting about the cape air example is those are big bore turbo charged continentals.  They are operated rop I've notices as a passenger, but pretty low power settings.

[Shadrach]

5 hours ago, M20Doc said:

On some of the C-152’s they have to hone and re ring a few cylinders, but generally cylinders make the distance.

Clarence

I don’t have a lot of experience with C152s. Do you find it O-200s to be as reliable as the O-235s? The C150 that I trained in provided an early foray into maintenance.  I had to replace two cylinders over the course of 18 months both of which because of cracks spanning the exhaust valve to spark plug.

[ArtVandelay]

Our local flight school, with a varied fleet of four cylinder Lycoming powered airframes routinely exceed 3500 hours and in many cases 4000 hours.  They run on straight weight oils, 80 in winter, 100 in summer.  The key to success seems to be loads of flying, 500-1000 per year.
Clarence

So IIRC, in Canada, prop manufacturer recommended overhaul cannot be exceeded, but I guess engine can?

[A64Pilot]

0-200’s are tough little engines, they have a long family history evolving from the A and C motors.

I have a friend on Fraed Naught’s team, an f-1 racer, they all have to run basically stock 0-200’s but turn them upwards of 5,000 RPM or so I’m told

250 MPH on a C-150 engine, listen to them and look at how long the wings are, which is interesting for a 500 lb airplane.

This is the race Fraed Naught won Gold.

[A64Pilot]

18 minutes ago, ArtVandelay said:

So IIRC, in Canada, prop manufacturer recommended overhaul cannot be exceeded, but I guess engine can?

Just about everywhere TBO extensions are available, some manufacturers will based on previous overhauls, Pratt & Whitney for example does fleet extensions all of the time

https://www.pwc.ca/en/airtime-blog/articles/technical-tips/fashionably-late-does-not-apply-to-your-engine-tbo---here-is-why

Then there is an STC that I think is kind flaky where you do a vibe analysis and oil sample, called the more program I believe and for quite a few $$$$ you buy an STC that extends your TBO, I’m sure there are others.

https://www.aviationpros.com/home/article/10387088/adding-time-to-your-tbo-a-discussion-on-pt6-engine-stcs

Of course my opinion of it is irrelevant, it’s legal.

These are PT6 but that’s my fleet background

It is or should be real important to note that TBO’s are not determined based on when an engine will become un-airworthy, they are based on maintaining the lowest cost of engine operation over time, of course one may run way past TBO, but the cost of overhaul is an ever steepening curve the further past TBO you go.

Edited August 29, 2021 by A64Pilot

[Guest]

1 hour ago, ArtVandelay said:

So IIRC, in Canada, prop manufacturer recommended overhaul cannot be exceeded, but I guess engine can?

Per CAR 625C fixed pitch propellers require a 5 year corrosion inspection and constant speed propellers require overhaul every 10 years or the manufacturers hourly TBO which ever comes first.

Engines are treated as On condition for private aircraft and commercial operators can extend their TBO.

Clarence

[PT20J]

On 8/28/2021 at 2:23 PM, jaylw314 said:

Most of the valve's cooling comes through the valve seat.  Even though 50 ROP and 50 LOP have the same exhaust gas temp, if the LOP cylinder is cooler, the valve is cooler.

Also, IIRC, while LOP produces less carbon monoxide, it does produce more nitric oxide and nitrogen dioxide, neither of which are particularly healthy alternatives, even if they won't immediately kill you

That's true for Continentals, but not Lycomings. The Lycoming sodium filled valves heat rejection is about 50% through the valve stems to the guides and the oil.

https://aslcamguard.com/sticking-exhaust-valves/

Skip

[PT20J]

On 8/28/2021 at 5:26 PM, M20Doc said:

Our local flight school, with a varied fleet of four cylinder Lycoming powered airframes routinely exceed 3500 hours and in many cases 4000 hours.  They run on straight weight oils, 80 in winter, 100 in summer.  The key to success seems to be loads of flying, 500-1000 per year.

Clarence

Everyone kind of forgets the Lycoming TBO is 12 years. I think they are saying that if you want to get to 2000 hours, you need to do it in 12 years. Flying a lot is a well proven way to get lots of hours from an engine. Most of us can't fly enough to get the same benefits that fleets get.

Skip

[A64Pilot]

From a manufacturers perspective TBO is looked at as sort of a guarantee. 

If you operate the engine or device in the recommended manner, it’s expected to last at least as long as TBO.

Think of TBO as the use by date on packaged food, very often that date has nothing at all to do with how long the food will last, especially if stored correctly, it’s a date that  the manufacturer feels safe as saying it will last at least that long. Most feel that 12 years is plenty, heck back in the day these things were designed the life expectancy of the average aircraft may have been thought to be 10 years or so.

If you told Mooney or Cessna back in the 60’s the aircraft they were building would still be viable and flying deep into the 21st Century, they would have thought you crazy.
 

Use and care means everything, a friend restored the one flyable XP-82 twin Mustang, they found an apparently pretty rare backwards turning complete Merlin engine in Mexico still in its shipping can, when they opened it, it was in perfect new mint condition, because it had been stored in that air tight can.

So in other words sometimes your lucky to get 12 years depending and other times 12 years is nothing.

I need to overhaul my C-85 in my 140, it runs strong, but leaks badly, it was last overhauled mid 1970’s.

Ref flying a lot and getting long life out of cylinders, very often if not most often when we let out engines sit, the cylinder walls and maybe even other parts flash rust, ever seen water dripping from an exhaust? Moisture is formed from burning fuel of course.

Anyway of course this slight rust is cleaned off almost immediately, but it is wear, not an insignificant amount of material is cleaned off each time. so infrequently flown aircraft cylinders don’t last as many hours as ones that fly several times a week.

Edited August 30, 2021 by A64Pilot

[cwaters]

On 8/27/2021 at 11:31 PM, carusoam said:

Find new aviation enthusiasts….  

 

Running LOP is all about….

1) gasoline distribution being as close to equal for all cylinders….

2) air distribution being as close to equal for all cylinders…

 

Fuel distribution is….

3) Much easier with four cylinders…

4) More challenging with six cylinders…

 

When you have a six cylinder engine…

5) It is better to have the curvy intake pipes for air flow balancing… see pics of Continental IO550s…

6) The log style intake pipes are good… at a more narrow range of operations…  see pics of the Bravo’s engine…

 

How you know LOP is acceptable…

7) Some POHs clearly state power charts for both LOP and ROP…

8) Some POHS ignored what the customer wanted, as if LOP didn’t exist…

 

How to get up to speed yourself….

There are resources that cover the technical things to look for… 

9) Power settings where LOP can’t possibly harm the engine…

10) Something called the red box or red fin…

 

It helps to have…

11) a good engine monitor…

12) interest in what this is all about…

13) a drive for speed and efficiency…

 

Or get an NA Mooney and fly it above 8k’ and experiment until you like what you get…  

Go Mooney!

Best regards,

-a-

I'm still pretty new to the ownership side of the house. Can you explain a little more on your last comment of flying over 8k? why does that matter, is it just power available ?

[ArtVandelay]

I'm still pretty new to the ownership side of the house. Can you explain a little more on your last comment of flying over 8k? why does that matter, is it just power available ?

Yes, you’re max power is limited due to lack of air.

[Shadrach]

1 hour ago, cwaters said:

I'm still pretty new to the ownership side of the house. Can you explain a little more on your last comment of flying over 8k? why does that matter, is it just power available ?

It is air available which indirectly translate to power available.  I try to run the most fuel through the engine I can at the most favorable part of the Brake Specific Fuel Consumption (BSFC) curve with acceptable CHTs.  That means I am typically anywhere from 30ish LOP to peak on the richest cylinder.  I run best power above 10K unless I have a good tail wind.

 

My little lyc loves LOP.  I broke in the cylinder in 2010 running WOTLOP at 3000msl (it was Feb so DA was about -500msl).  Oil control was established in one flight of less than 3hrs and highest CHT was in the high 360ish range IIRC.  It's been running like a top ever since.

[PT20J]

Sometimes it helps to think of the engine as an air pump. Every time a piston travels down the cylinder on an intake stroke it admits a cylinder full of air. The throttle actually controls the amount of air admitted by restricting the airflow. In a normally aspirated engine, as you climb, the same admitted volume contains less air, just as if you were at sea level and reduced the throttle.

To run, the engine requires combustion of course. The purpose of the fuel metering system (carburetor of fuel injection) is to add a precise amount of fuel to the air based on the airflow through the metering device. Combustion can occur over a fairly wide range of mixtures. Peak EGT occurs at about 15 pounds air for one pound of fuel. Combustion is complex chemical process. During combustion fuel and oxygen combine in a chain of chemical reactions that require finite time and are temperature dependent. Mixture strength has a significant effect on the reactions. For instance, maximum power is achieved at a rich mixture of perhaps 100F ROP and max CHT is somewhere between max power and peak EGT. The power is greater at rich mixtures primarily because of the increased amount of substance in the cylinder due to excess fuel and the peak CHT occurs due to chemical dissociation effects. Lean of peak, the engine is more fuel efficient (the excess air tends to ensure that little or no fuel goes uncombusted) but the power is lower.

Even with perfect mixture distribution, there are cycle-to-cycle combustion (and hence power) variations in each cylinder. These variations are greater when LOP and this is why engines tend to run slightly rougher LOP. How well an engine runs LOP is primarily determined by how even the flow of air is to the cylinders and how evenly the mixture is distributed within that flow. Anything that reduces cycle-to-cycle variation (such as stronger ignition and fine wire spark plugs) will help.

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