Lean of Peak

[RV7ator]

All,

This thread is a spin-off from a question asked of me on another thread, response put here because it involves LOP ops with a carburetored Lyc.

Comment was that Lycoming says it can't be done. I'm not surprised. Lyc doesn't think anything can be done until someone else shows them so. That's why ECI and Superior are eating their lunch in the experimental market.

Now to the point. Yes, I do run my carburetored O-360 lean of peak, mostly. That's because only cylinders 2 and 3 are LOP; 1 and 4 are slightly ROP. So I am taking some liberty with the pure definition of LOP wherein all cylinders are LOP. If I were to lean more to make all LOP, I lose way too much power.

What helps me is that the Superior sump I had Aerosport Power install has internal contouring to help even the fuel distribution. Lycoming's design looks more like a septic tank and drain field. Even distribution is the key and it's fuel injection's big (potentially) improvement over carburetors. With a set of GAMI injectors, very smooth LOP operations is the norm. Such a FI system would be many thousands of dollars initially and still more life cycle cost than a carburetor.

Also, I wouldn't even attempt LOP no matter the type of fuel system unless the engine was equipped with all-cylinder CHT/EGT monitoring.

So, I have many more dollars for fuel, and I get a wee bit of a massage to boot. Just how smooth a particular carbed engine runs when you screw down the mixture is an individual experience. I've flown behind carbs and injectors. Some of each type have been smooth as a baby's bottom, while others will remove your fillings. There's a lot of cross-over between the two regarding economy and smoothness. The RV and a 172 I've been operating the same for 2,000 hours work just fine L (mostly) OP.

John Siebold
Boise, ID

[penguin]

John,

My experience is broadly in line with yours. I can't get my current carbed O-320 to run smoothly LOP, probably because of the Lyc sump. Completely agree with the value of all cylinder monitors.

The only other point is that I am skeptical of the benefits of GAMIs on (all)Lycomings. On older Continentals the benefit is clear, but Lycs suffer from a different problem (mostly). They generally don't steal much fuel from other cylinders, but older injectors may not be well balanced, due to wear an manufacturing inaccuracies. So on a new Lyc fitted with either Precision or Airflow injectors I'm not sure that GAMIs will be any better as the they are all made to similar tolerances. On a older Lyc fitted with a Bendix system there may be some value in swapping to GAMIs. In any event a GAMI lean test is very useful in figuring out what is going on.

Pete

[gmcjetpilot]

Originally Posted by RV7ator

All, This thread is a spin-off from a question asked of me on another thread, response put here because it involves LOP ops with a carburetored Lyc.

Comment was that Lycoming says it can't be done. I'm not surprised. Lyc doesn't think anything can be done until someone else shows them so. That's why ECI and Superior are eating their lunch in the experimental market. John Siebold. Boise, ID

John I am the one that asked the question. I have heard of LOP with a FI engine but not a carb. I am not saying you can't do it, but I am not sure how useful it is and if may be you could be doing more harm than good. The FI engines that run "true" LOP have all cylinders within a few degrees EGT and are at least 40F LOP. I am not sure what advantage two cylinders at 20F LOP are doing. Also what are the other cylinders doing? Are they at peak, 10F ROP? Higher EGT, higher temps. I don't like to run hottest cylinder closer than 75F ROP. I have a Carb and can't get LOP operations. If I had FI, I would try for the 40F LOP operations.

Here is someone who ran lean of peak and paid the price:
http://www.eaa49.av.org/techart/hakes08.htm
(There is a correlation to short cylinder life and leaning, which Lycoming has documented. They see more cylinders (die early) as price of fuel goes up.)


Lycoming does say LOP is not practical or possible due to uneven mixture distribution with carbs. If you are running two cylinders lean of peak and two rich you will have different power on the cylinders you would expect rough running. From my experience, when I lean a carb Lycoming, as soon as the first Jug hits lean peak EGT or just past, the engine starts to get rough, since the other cylinders are still rich and making more power. What happens past peak EGT is the power curve drops very quickly. ROP (by 50F) you don't have as much roughness with small difference in mixture / fuel distribution, because the power curve on the rich side is flat compared to the lean side, which drops quickly with mixture. The first cylinder hitting LOP will produce less power and the uneven power pulse, which is unpleasant.

Also 20F LOP, you are running is very close to peak which is not a great place to live. What are your other two cylinders doing? Peak? This might be a bad thing to do to your engine. (?) There are many reasons this is not a good idea. For long life on a Carb engine, Lycoming does not recommend an exact EGT but for Econ operations, lean for smooth operation ROP, which is about 50F ROP. I read somewhere they (Lycoming) recommend not less than 75F ROP for ECON. Running anywhere near peak (lean or rich) I don't think is a great for the engine and will not be as smooth. For best power Lycoming recommends 100-150F ROP.

If you can't run true LOP where every cylinder is 40 LOP, smoothly, I think you should run ROP, where all cylinders are about 50F ROP or more. Fuel is used to cool the engine. LOP uses the fact that you are so lean you are making less heat (and power) and there is no chance of detonation. This also means you will fly slower. Of course always never lean above 75% power. Some feel that fuel lubricates the engine and I can't say yes or no.

Superiors sump: I know they claim their sump has better features. They do look nice: http://www.superiorairparts.com/pieceParts_Sumps.asp

May be your set up is ideal. However Lycoming or Clone, they all have the same carb and will always produce some mis-matched fuel distribution well beyond the +/-0F EGT spread required for true LOP operations. The problem is the induction is not a steady state thing. Induction happens in pulses. Fuel/air backs up in the plenum and induction tubes. There is variation in each cylinder, compression and exhaust. Typical cross over exhaust are really not ideal at all. In fact the tube length between pairs is large. This exhaust difference affects the induction.

As far as Superior and ECI eating Lycoming's lunch, it is from the fact they cost $4,000 to $5,000 less, and less to do with better fuel distribution. It may be more sales hype. Lycomings, ECI and Superior all make about the same power. Carbs have inherent design and limits based on the law of physics, which all the engines share. However tuned intake, tuned cylinders, tuned exhaust and exact fuel distribution (FI) no doubt can improve fuel economy.

Carbs are not bad or terrible, but to run LOP you have to have very precise fuel distribution which no carb on any brand engine can produce. I have an O-360 and it is great. Carbs are simple, reliable, don't require high-pressure pumps and of course are many thousands cheaper. Also those who have FI usually don't have the desire to mess with there fuel system to optimize it for LOP operations. Also LOP operations means slower speed. Fuel savings is from the fact you are making less power. Less power less speed. So even if the Carb engine is using a little more fuel it is making more power ROP. There is no free lunch. If you want to save fuel in a carb engine fly higher for less % power or pull the throttle back**.

**(Pulling the throttle back is one of the worst things to do from a lean stand point, because the butterfly causes a restriction and biases the fuel towards the front or back, so fly high with WOT for best lean condition. That is why 7,000-8,000 feet is the best altitude to fly because it is the lowest altitude that you can fly with WOT and at or less than 75%, which is highest power allowed you can lean at. The higher the better, as power decreases the FF is reduced. Somewhere 12,000'-14,000' (gross weight) is the limit for a good trade off in speed and fuel economy. Above 12,500' will require O2. All this assumes a ZERO wind condition. If you are flying low and want to lean you must throttle back below 75% power, but because of the "pumping loss" and increased fuel distribution difference from the partially closed butterfly it will not be as good as WOT.)

Here is a good explanation of Carb and FI.
http://www.lycoming.textron.com/main...lInjector.html

It is just the way it is, carb?s can?t be run (practically speaking) LOP, except for your engine. How you are getting acceptably smooth operations? I don't know but it is pretty good trick with a Carb. True LOP operations require FI and matched injectors. The savings you are getting from two cylinders running LOP 20F may be very little? Have you measured the fuel burn difference? To get any big gain you need all Jugs at 40F LOP. From what I have hears on a little Lycoming the best you can hope for with FI (running LOP) vs Carb is about 0.6-0.8 gal/hr, which is great, with the fuel prices as such. The pay back time is much less than it use to be. FI not running in LOP operations, typical ROP operations in cruise, will still be better than a Carb, but the difference is very small when compared to LOP operation (like 0.1-0.2 gal/hr). LOP operation is a kind of new thing in GA, especially for small engines. With large high HP engines the savings are greater, and with the multi cylinders, the big engines tend to run smoother even if the mixture is slightly off. Some FI Lycoming (4-cylinders) can not run LOP well, even with injector work.

I also agree GAMI injectors are sales hype and that the Airflow performance has very well matched injectors and will fine tune them. As far as Bendix (now Precision Aeromotive) I don't know.

John, I suggest calling Superior and asking them if it's cool to run 20F LOP for engine health. I would love to know what kind of fuel savings you are getting. G

Here are good articles:
http://www.lycoming.textron.com/supp...ngEngines.html
http://www.lycoming.textron.com/supp...ps/SSP700A.pdf

[wlull]

The best thing about GAMI is all the information and testing they have done. I admit I run a big bore Continental with FI. Still building my Lycoming hauler! So this post is alittle off center. I read the above posts and the articles they sighted and just felt compelled to relate my experience.

When I purchased my plane the IO470 had 1100 hours and had seen about 20 hours use in the last five years. I had read everything I could find on running these engines and opted to try the GAMI way even though I didn't have there injectors. I put 700 hours on that engine over three years before going to overhaul. Because it had set so long it used oil ( about a qt every five hours) but the compression readings never changed. How I ran it is as follows: Always ran 65% or less. Always ran at peak or alittle LOP. The thing is GAMI says you can't hurt the engine at any mixture setting if you run 65% or less and my experience seemed to follow this.

After rebuilding the engine (with GAMIs) and ECI cyls. I follow the same procedure except now I run at least 50 LOP down low and at peak up high. I have over 500 hours to date and contrary to conventional wisdom my compressions have remained 76-78/80 on all six cyls. and I use a qt of oil every 25 - 35 hours ( I do have an air/oil separator).

On the very rare occasion that I run 75% or above I run 125% ROP. I have read several places that running 75% or higher from 25 LOP to 75 ROP is an engine eater. So I just don't do it.

Also another CW no no I do all the time is lean to a EGT temp on all climbs (1100 summer and 1150 winter).

This all works for me, how everone else manages their engine is up to them. I say do your own research and decide what is right for you.

The best to all and I'm sorry for my rambling!
Bill

[RV7ator]

Oy, G, I've an airplane to build, so my response is a bit terse.

Many of your points are good, but old news to me, and some are plain wrong. And to really light your fire, I run my carbed 360 LOP on mogas!

The executive summary of our exchange so far is: It's all relative, EGTs that is (New Agers go away).

The guy who trashed his engine in the EAA link was running 100LL. Poor devil; it killed his engine. He was following Lyc recommendations about which there is a substantial body of evidence against/challenging/refuting many Lyc recommendations. For starters, search around AVweb for articles/columns by Jim Deakin about where to run your engine. Similar, but far less researched and referenced, are occasional fluff pieces in AOPA and other slicks.

Lyc has a lawyer problem. It's why ECI and Superior are encroaching on them, technically for lack of Lyc innovation, and financially because Lyc has a burdensome overhead buying their peace from clueless juries. You can be sure Lyc will never come out with some manner of operation different then they've always prescribed, lest some shark sue them for being wrong in the first place and that's why Uncle Willy CFIT'd.

Where you and I diverge mainly is ROP. +75 or so is the WORST place to be, so I read often outside of Lyc, and completely contrary to your assertion. You can't hurt an engine LOP, but you can ROP. When my #2 and 3 are LOP, the others are near peak. CHTs are wonderful, which speaks more to proper air cooling than whether the EGTs are 25 or 50 degrees one way or the other.

Ambients play a big roll. Most of my flying anywhere requires MEAs above 9k or else I'll hit mountains within 30 minutes. Lean 'till the engine stops; you can't hurt it at 9 or higher. Yes, higher is key to economy. If you have to throttle the engine to get 75% or less you do get higher pumping losses and the airplane's draggier down lower.

Pulling the throttle back a bit can be GOOD. It's common practice on carbed 182s because it does cause extra swirling, therefore better mixing and distribution. I've had a GEM in my 172 for 9 years. The effect is noticeable as stated, the rpm loss undetectable on the mechanical tach. The 172 has a detented mixture control. I would be able to better tune the mixture if it were a vernier, since the detents are either richer or leaner than I would like to set per the GEM. But a vernier control would require an STC (none exist) or 337. So much for the criticallity of mixture as viewed by Cessna and the FAA. The manual says lean till rough, enrich till smooth. Without a GEM and vernier you can't do otherwise.

What does "ZERO wind conditions" have to do with running an engine? I think I get your drift in that you might want higher power when bucking a headwind. But I could really run with this one and start a thread about the dreaded downwind turn.

In sum, it is relative. Your engine may vary, and I think we've learned more in recent years than Lyc will admit. Get a GEM, fly high, use mogas!, and run LOP. Or ROP if that feels good; Mother Lycoming says it's all right.

John Siebold

[dlloyd3]

Most of the good stuff has already been said. Anyone curious about running their engine LOP really should read all those articles by John Deakin on AvWeb. After reading his stuff, I am scared to run ROP.
Balanced fuel flows on an injected engine is generally better than fuel air distribution in a carburated engine. But this is only one factor in making an engine run smoothly. Both intake and exhaust manifolds of varying lengths and restrictions complicate matters. Fluid dynamics are never stable due to opening and closing valves. Change some variables like RPM or air density, gosh, it's a wonder these things don't shake right off their mounts.
In the last issue of Flying, Richard Collins again poo poos LOP operation during a demonstration of a Lancair Columbia 400 saying it wasn't smooth as operating ROP. Fuel flow was down three or four gallons but not worth the slightly rough running engine. Couldn't get his GAMI injected P210 to run smooth either.
I have been running the IO550 in my spam can many years LOP. Two engines went well past TBO with not one cylinder problem. Another reman engine ate it's way through 8 exhaust valves in 1550 hours (see what John Deakin says about this). Some engines have been smooth LOP, others not so. I run WOT all the time above 5000 feet. Usually cruise at 7-9000. The only time the present engine (675 smoh by Superior, with GAMIs) runs rough is when I attempt to burn less than 12.5gph. This is so at higher density altitudes and 2500 rpm or at lower altitudes and rpm. Typical fuel flow is 13.5. Same conditions but ROP would be 16.5, and cylinder head temps would be 40 to 50 degrees hotter.
Everyone should investigate on their own how their engine performs at various fuel flows. Set up cruise flight, record temperatures at incrementally lower fuel flows. Doing this will demonstrate the absolute hottest CHT's that can be produced occur at 40 degrees ROP. Richer or leaner mixtures will produce lower CHT's. You pays your money and makes your choice.

[gmcjetpilot]

RV7ator, John Siebold wrote: The guy who trashed his engine in the EAA link was running 100LL. Poor devil; it killed his engine. He was following Lyc recommendations about which there is a substantial body of evidence against/challenging/refuting many Lyc recommendations. For starters, search around AVweb for articles/columns by Jim Deakin about where to run your engine. Similar, but far less researched and referenced, are occasional fluff pieces in AOPA and other slicks.
I have read his articles. He he got a free set of injectors and wrote an article. I am sure they are great for large Continental. Most LOP operations that work are on 6 cylinder engines. Small Lycomings are going to get less advantage from LOP operations. INJECTORS: You know an injector is, a very simple piece of brass with a hole in it, that squirts fuel into the intake port near the valve. There are no secrets. Squirt Squirt. It is like the TV info-commercial and the "Fuel Tornado 2000" or "Fuel Magic-Magnets" you put on your car or truck's fuel system to improve HP and fuel economy. Once you pay all that money you have to prove it works to justify it (I never bought one BTW). You drive your car with more care to show it works.

FI systems for the Lycoming, like Airflow performance, come with well tuned injectors out the box. They will custom tune/ flight test your injectors on your plane for $300. There is more to it than just the injector. You not only have to match your injectors, but your whole engine. If your exhaust is imbalanced, have a weak jug or two, injectors are not going to do it all. You can always try for LOP operations, but your mileage may vary (pun intended). 4 bangers, FI or not, are not as good as 6-cyl in LOP operations.

Lyc has a lawyer problem. It's why ECI and Superior are encroaching on them, technically for lack of Lyc innovation, and financially because Lyc has a burdensome overhead buying their peace from clueless juries. You can be sure Lyc will never come out with some manner of operation different then they've always prescribed, lest some shark sue them for being wrong in the first place and that's why Uncle Willy CFIT'd.
I don't have any Textron Lycoming stocks, but I believe them more than I believe AvWeb who is writing about how great a product is. The company the invented the modern horizontal piston aircraft engines, making them for +60 years and has ten's of thousands of hours of test stand and flight test hours can't be too dumb. Law, Lawyers and legal issues a side, LOP is not a given, slam dunk, sure thing, works for all engines, installations and method of fuel metering (Carb, FI). Engines have been run well lean of peak for almost 70 years. They (engineers) know all about it. NACA (now NASA) did research in the 1940's on LOP operations with all kind of engines. Lycoming has done the same studies, this is old news. Lycoming does not say it can't be done, just it is not practical for small carbureted engines. You are not correct saying Lycoming will never change procedures. Lycoming calls for LOP operations on the Piper Malibu, with a large 350HP FI and turbo engine: http://www.avweb.com/news/usedacft/182792-1.html , Why? It is worth it. What fuel savings do you think you are getting, really, on a MPG basis with a little 160-180 hp engine. I never read how much fuel LOP is saving over ROP and what the TAS is. I personally doubt you can get worth while LOP ops with a Carb, but I am ready to be amazed. I have heard of moving the butter-fly (slightly) to get better fuel distribution bias (front to back), but never tried it. Still it is apple sauce.

Where you and I diverge mainly is ROP. +75 or so is the WORST place to be, so I read often outside of Lyc, and completely contrary to your assertion. You can't hurt an engine LOP, but you can ROP. When my #2 and 3 are LOP, the others are near peak. CHTs are wonderful, which speaks more to proper air cooling than whether the EGTs are 25 or 50 degrees one way or the other.
Again LOP, if you can achieve smooth operations, than go for it. However most find it is not practical. As far as running on the ROP side and damage, that is not true. As long as you are below 75% power and the CHT and Oil Temp are acceptable you are safe. Lycoming recommends ROP and smooth operations for ECON. They don't specify an exact EGT but it is around 50F to 75F ROP. They recommend 100F-150F for best power. This is cool with Lycoming. No one is saying run at peak EGT. I understand how LOP works and why it should not damage your engine, you are making less power and therefore making less heat. No extra fuel is available to cool the engine, but it is not needed. All this LOP stuff is good if you can get smooth operations, and all cylinders are LOP by 40F-50F. Even than, fuel saving on a small 4-cyl Lycoming is smaller than on a large Continental or 350HP Lycoming. LOP airspeed is slower than ROP operations. You are burning less fuel but you are making less HP and therefore going slower. To save fuel fly higher (as long as there is favorable winds or winds are not too adverse). Otherwise PULL the throttle back (way back) and you will save way more fuel than all the monkey motions to get true LOP operations.

I don't think Lycoming is lying about finding more cylinder damage with lean operations. I agree if done carefully, with full engine instruments, LOP Ops can be safe. However the 2 jugs at 20F LOP with the other two near peak on the rich side does not sound good. That is why carbs should not operate LOP, the 50F EGT spread is too much. LOP needs all EGTs to be close.

Ambient play a big roll. Most of my flying anywhere requires MEAs above 9k or else I'll hit mountains within 30 minutes. Lean 'till the engine stops; you can't hurt it at 9 or higher. Yes, higher is key to economy. If you have to throttle the engine to get 75% or less you do get higher pumping losses and the airplane's draggier down lower.
I agree hitting a mountain is bad. Leaning till it stops is bad technique, but to each his own.

Pulling the throttle back a bit can be GOOD. It's common practice on carbed 182s because it does cause extra swirling, therefore better mixing and distribution. I've had a GEM in my 172 for 9 years. The effect is noticeable as stated, the rpm loss undetectable on the mechanical tach. The 172 has a detented mixture control. I would be able to better tune the mixture if it were a vernier, since the detents are either richer or leaner than I would like to set per the GEM. But a vernier control would require an STC (none exist) or 337. So much for the criticallity of mixture as viewed by Cessna and the FAA. The manual says lean till rough, enrich till smooth. Without a GEM and vernier you can't do otherwise.
Yes full instruments like GEM are great. However most C-172 are LUCKY to have one EGT, if that. I have about 150 hours in C-182's, most giving dual instruction. I did not know about this trick 15 years ago, so I never tried it. I was happy if the pilot checking out got the cowl flaps. I do know how to clear carb ice with a back fire in a C-182.

What does "ZERO wind conditions" have to do with running an engine? I think I get your drift in that you might want higher power when bucking a headwind. But I could really run with this one and start a thread about the dreaded downwind turn.
It has nothing to do with leaning; it has everything to do with flight planning. Winds aloft affect range and ground speed. (Yes I hope) From a pure performance stand point "zero winds" are used to compare performance (apples). No matter how efficient your airframe and engine is at high altitudes, when faced with 50 kt head winds at 8,500' and little winds down low, say at 2,000', you would be better flying at high power (not leaned) and lower altitude, terrain permitting. Right? (Tail wind fly slower, head wind fly faster) Using LOP operations means going slower and more exposure (time in) the head wind. You may have lower fuel flow with LOP but more fuel burn, miles per gal, for the trip and take longer. I never tried much LOP operations because none of the planes I have fly or have flown can do it. I would love to hear real actual numbers on fuel burn and speed at LOP and than ROP.


In sum, it is relative. Your engine may vary, and I think we've learned more in recent years than Lyc will admit. Get a GEM, fly high, use mogas!, and run LOP. Or ROP if that feels good; Mother Lycoming says it's all right.
I have a GRT EIS4000 engine monitor. I would never use MOGAS, it is only $1.00 less if you even can get it. To me that it is not worth it. Although that is a total different debate. However there have been so many accidents from autogas users I would not risk it.

I am not saying LOP is not good or can't work; I don't think Lycoming says that either, but everything has to be right (near perfect) to get the advantage, large engines (6 cylinders) have more to gain and carbs are just not able to produce fuel distribution that will allow consistent LOP operations. As far as damage from LOP, if done well, not a problem. If not done well it can cause grief. I am sure that is where Lycomings experience comes in. They know that in the field pilots may screw it up.

I have a O-360A1A and I am happy to throttle back to 2250 rpm (Hartzell limit)/ 20" map and back through town at 175 mph and 7.5 gal/hr. If I want to really fly slow and save gas, 20-squared, 168 mph @ 6.5 gal/hr. G

Here is a Avweb article I agree with on the subject:
http://www.avweb.com/news/reviews/182501-1.html

[rv7 2003]

I have used gamis on a 540 lycoming and they work very well indeed. IMHO it was money well spent, even thogh I feel they were pushing thr price.
AVWEB has many good articles on LOP. I think the authors name was Deakin .

[RV7ator]

Well, G, what have we?

You're O.K. with LOP, but not with a carb.

Just because an engine is carbed, however, doesn't exclude an airplane from the club. Mine are carbed, they're smooth enough with even enough burns to allow LOP, maybe not on every cylinder, but I've realized benefits from doing so (lower temps, lower fuel bills). The engines remain in a steady state of health. I've fiddled with the 172 extensively over 2000 hours. One year I leaned by the book, lean til rough, enrich till smooth: 7.5 gph. The next year, I ran LOP as best I could: 7.2 gph. Since LOP is, indeed, slower, the mpg is only slightly in favor of LOP. I've only 130 hours on the RV, but regularly achieve 7.2 gph LOP (By the Hobbs, it's 7.0; I've adjusted for rolling around on the ground). It burns a lot more down low, just like a 360 should, and it's always ROP.

I use LOP. And I've got carburetors! Just like so many other aspects of airplane operation, you need to know what you're doing.

I'm done. See you at the gas pump.

John

"Sinatra"? I did it my way.

[akarmy]

Originally Posted by gmcjetpilot

I have heard of moving the butter-fly (slightly) to get better fuel distribution bias (front to back), but never tried it.

Not going to touch the rest of this interesting discussion... but on the subject of moving the butter-fly.

My Aerosport 0-320 D2A will run nice and smooth between 2300-2400 and 2500 and above. At those RPM's the leaned EGT spread is 25deg. But put the throttle at 2450 and the EGT spread goes to 250deg and it starts running rough! From that condition if you pull the throttle slightly back you can feel a bit more power from the engine as the EGT's level. In talking to Bart about it he indicated that this was normal for Carbed engines to have certian conditions that would create these uneven burns.