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Education on Leaning

Italiancowboy

Active Member
So in my RV6 fixed pitch prop O-320, I only had one EGT and so basically I used my training-days method of leaning: lean until the engine stumbles then give it 1 1/2 turns. That made sure you were on the LOP side then enrich toward Peak a little (keeps you away from too lean and give a little power back).

So now in my RV10 with O-540 CS Prop and EGTs on each cylinder with Dynon monitoring, I can do real leaning . . . if I know what I'm doing.

I've read EI's Pilot Manual for Leaning and Diagnosing Engine Problems and understand the Power, CHT, and Fuel Flow curves.

It's been easy to run "Best Power" ROP with the leanest cylinder 100F ROP. But boy does that burn fuel.

So trying to go to "Best Economy" and run the richest cylinder at 30-80F lean of peak has been a problem. As I lean the EGTs rise but I never seem to get to EGT Peak before the engine starts to stumble; they continue to rise as I lean. I know the CHTs have some lag (lots of metal there to change temp) but EGTs should change pretty quickly. If I enrichen from the stumble, the EGTs go down indicating to me that I'm still on the ROP side.
Fuel flow at 8000ft, 20MP/2100rpm is just less than 10gph at the stumble while leaning. Fuel pressure is good (5 psi).

So educate me. What am I missing ? Am I still on ROP side ? How do I get over the peak ?
 
Can't speak to the process for a big motor like that, but I can tell you I run LOP almost always in my 6A with an IO-360. I start the lean and every time I see EGTs peak, usually around 1500 to 1520 (I know the value is not worth much). I continue to lean and can usually go as far as 100* LOP before the stumbles set in. I'll usually run about 70 LOP for decent speed and fuel consumption.

Not sure if the big motors don't have a good "GAMi" spread or not, but from what I have read that "could" be why you don't see a peak before you feel the stumble (cylinder fuel flow is not balanced).

I'll follow to hear from others and learn the difference of the 4 bangers vs the larger 6 cylinder engines.
 
So educate me. What am I missing ? Am I still on ROP side ? How do I get over the peak ?

You have it right JR. Unfortunately, a carbureted 540 may have rather poor fuel distribution.

Start at a ROP fuel flow where it is smooth. Lean very slowly...like 0.1 gph per increment and let the EGTs settle. Record six settled EGTs at each fuel flow increment. Continue until all have peaked. It may be kinda rough toward the end.

In a perfect world, all six EGTs would peak at the same fuel flow. The test will show you where each is peaking.
 
Ya, I'm thinking the wide range of fuel flow to the carbureted 540 is the problem. Maybe I don't notice that one cylinder gets over the peak and "dies" before the others reach Peak
 
Tools for adjusting lean of peak

As Ironflight pointed out, when leaning all cylinders must peak at very nearly the same fuel flow to be able to run successfully Lean of Peak. The minimum instrumentation required is Fuel Flow and EGT for each cylinder. Most EFIS systems have a recorder that can log that data, or you could create a handwritten log of FF, and EGT for all cylinders in .1 GPM fuel flow increments, as, again noted by Ironflight. Once you have the data, either the richest (last to go LOP) can be leaned a bit, or the leanest (first to go LOP) can be enriched. Don at Airflow Performance manufactures jets in .005" increments. The #3 and #4 cylinders on my new Lycoming IO 360 M1 broke lean first, so I replaced the standard 0.0280" nozzles with 0.0285" nozzles from AFP. all cylinders now peak between 0.0 and 0.1 GPM. I used the data output CSV file from my Dynon HDX per AFP's recommendation. AFP feels that the EFIS "Lean" mode is not quick enough to capture the subtle changes at peak. The engine is very smooth now, even at 80 degrees LOP.
Hopefully this is useful.:eek:
 
You have it right JR. Unfortunately, a carbureted 540 may have rather poor fuel distribution.

Start at a ROP fuel flow where it is smooth. Lean very slowly...like 0.1 gph per increment and let the EGTs settle. Record six settled EGTs at each fuel flow increment. Continue until all have peaked. It may be kinda rough toward the end.

In a perfect world, all six EGTs would peak at the same fuel flow. The test will show you where each is peaking.

Everything that Dan said, plus….if you’re carbureted, bring the throttle back just a touch from wide open before you start leaning - the slightly cocked throttle plate will trip the flow a little, promoting better mixing of the fuel/air and helping give the same mixture to all cylinders. At least that is the theory of WHY it works….I do know that it DOES work (whatever the physics) in a fair number of carbed engines (I’ve proved it many times with our two carbed motors while bored on long cross-countries….)

Paul
 
Just note that there is really no such thing as "too lean" as far as the engine cares. You can't hurt an engine by being too lean, the cylinder just stops firing. You enrichen the mixture to make it run smoother, but that actually moves you closer to fuel detonation.

So in my RV6 fixed pitch prop O-320, I only had one EGT and so basically I used my training-days method of leaning: lean until the engine stumbles then give it 1 1/2 turns. That made sure you were on the LOP side then enrich toward Peak a little (keeps you away from too lean and give a little power back).

So now in my RV10 with O-540 CS Prop and EGTs on each cylinder with Dynon monitoring, I can do real leaning . . . if I know what I'm doing.

I've read EI's Pilot Manual for Leaning and Diagnosing Engine Problems and understand the Power, CHT, and Fuel Flow curves.

It's been easy to run "Best Power" ROP with the leanest cylinder 100F ROP. But boy does that burn fuel.

So trying to go to "Best Economy" and run the richest cylinder at 30-80F lean of peak has been a problem. As I lean the EGTs rise but I never seem to get to EGT Peak before the engine starts to stumble; they continue to rise as I lean. I know the CHTs have some lag (lots of metal there to change temp) but EGTs should change pretty quickly. If I enrichen from the stumble, the EGTs go down indicating to me that I'm still on the ROP side.
Fuel flow at 8000ft, 20MP/2100rpm is just less than 10gph at the stumble while leaning. Fuel pressure is good (5 psi).

So educate me. What am I missing ? Am I still on ROP side ? How do I get over the peak ?
 
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So educate me. What am I missing ? Am I still on ROP side ? How do I get over the peak ?[/QUOTE said:
The problem is you have a carbureted (O) instead of an injected (IO) engine.
As a result the Air to Fuel Ratio (AFR) on your engine is different for all the cylinders for a given mixture setting.
Have a look on the attached image. You can see the Brake HP versus AFR.
On the rich side it doesn’t matter much. The BHP slope is flat, so whatever AFR, if they are not equal, will result in same output of the cylinders.

On the Lean side however the curve is very steep. So the power output of your leanest cylinder is much lower than your richest cylinder.
That’s the cause of the engine roughness (its not a stumble).

So you can not fly LOP with a carbureted engine because of the unbalance of the AFR in the cylinders. You can try to fly as lean as you can by trying to remove the roughness. As mentioned here by other posters, by not flying WOT but bringing back the throttle just a little to see a small drop in Manifold Pressure. That kills the enrichment of the fuel and keeps AFR better balanced (less unbalanced). If it is cold you can also add a tad of carburator heat.

I fly a TIO-540 with GAMIjectors. Injectors that are precisely tuned for their cylinder position. They are so well balanced that you can lean all the way to engine starvation without engine roughness.
 

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So you can not fly LOP with a carbureted engine because of the unbalance of the AFR in the cylinders.

This is incorrect. It most certainly can be done— just maybe not with every stock carbed engine. It’s that an imbalance is more likely in a carbed engine leading to running LOP being problematic.
 
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Thanks, Joop. I understand the technical aspects of AFR and IO vs O (which I ran very effective on my O-320), guess you missed that declaration in my original post.

My question is “why does it run rough BEFORE any cylinder gets to Peak” ?

The only thing I can figure is that I’m missing seeing the Peak on the first cylinder to Peak.

I’ve read that you want to get to “the other side of Peak” quickly and don’t linger in the “red” or “detonation” zone that is 80F Rich and 30F of Peak. So maybe I’m going too quick to see it ?
 
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Just note that there is really no such thing as "too lean" as far as the engine cares. You can't hurt an engine by being too lean, the cylinder just stops firing. You enrichen the mixture to make it run smoother, but that actually moves you closer to fuel detonation.

Hmm, as my cylinders start to fail to fire and the engine gets rough ….… sure seems like they are telling me I’m too lean (and so do my nerves)
 
Leaning techniques for carbureted engines

It has been mentioned to pull the throttle lever back some to allow the carburetor butterfly to make the air somewhat turbulent on purpose to more evenly distribute the air and fuel to the cylinders.

The second, similar technique, is to pull on partial carburetor heat. Trying different combinations of partial carb heat and slightly reduced throttle to allow better air/fuel distribution to the cylinders may allow running LOP.

Several people successfully running LOP say that as little as 30*F LOP is sufficient to keep cylinder pressures under control. Any time you're under 75% power you can basically set the knobs anywhere you'd like without harming the engine. Check your engine owner's manual to determine some basic parameters to know where 75% power is. Down below 5,000 feet limiting prop RPM might be the best way to corale engine power, then above 8,000 feet the altitude will keep the power in check.

Let us know how it goes for you, we are all interested in the results of your testing.
 
Everything that Dan said, plus….if you’re carbureted, bring the throttle back just a touch from wide open before you start leaning - the slightly cocked throttle plate will trip the flow a little, promoting better mixing of the fuel/air and helping give the same mixture to all cylinders. At least that is the theory of WHY it works….I do know that it DOES work (whatever the physics) in a fair number of carbed engines (I’ve proved it many times with our two carbed motors while bored on long cross-countries….)

Paul

Just to add my two cents to the whole “pull the throttle back” method. I feel there is some value from the induced turbulence of the throttle blade helping to stir the mixture, but I really feel on carburetors, that pulling back a little closed the “enrichment valve” and you can actually see the EGTs climb when you start to come off the full throttle stop. You can go full throttle again and see them all cool off. It’s my understanding that at full throttle, excess fuel is dumped into the engine for cooling purposes and for best economy, you close the throttle just a little, then lean. Also the reason why partial throttle takeoffs may be more stressful to an engine than full throttle takeoffs..
 
Just to add my two cents to the whole “pull the throttle back” method. I feel there is some value from the induced turbulence of the throttle blade helping to stir the mixture, but I really feel on carburetors, that pulling back a little closed the “enrichment valve” and you can actually see the EGTs climb when you start to come off the full throttle stop. You can go full throttle again and see them all cool off. It’s my understanding that at full throttle, excess fuel is dumped into the engine for cooling purposes and for best economy, you close the throttle just a little, then lean. Also the reason why partial throttle takeoffs may be more stressful to an engine than full throttle takeoffs..

Just to add clarification - We’re talking about doing this in cruise, when you are at 75% or below, not at full seal level take-off power. And whether it is the tile throttle plate causing turbulence, or the enrichment valve change… the results work (on most carbed engines I have flown behind).
 
Injector Tuning

You might not get your engine to run decent LOP without tuning the injectors. I did on my RV10 with a Barret 540-X with 9-1 pistons. The problem is the cylinders usually don't get the same amount of air. So even if the injectors put out the exact same amount of fuel the mixtures won't be equal. Go to Airflow Performance and order six .0260 injectors. Install them and download their injector tuning chart. Instructions come with it, but you are basically setting up normal cruise power and starting well rich of peak. Then reduce fuel flow .2 gal at a time and record EGT's each .2 gal until all have peaked and started back down. You will probably see that some cylinders peaked much earlier than others. These are getting more air. Send the results in and Don Rivera will tell you which size injectors to put in each cylinder. After installing them run the test again.



I went from 19" MP 2300RPM at 12.5 gal/hr to 21"MP 2300RPM at 10.5 gal/hr. I reduced fuel flow 2 gal/hr while increasing cruise speed about 5 knots. It was very well worth it. I also increased range a little. Now I get 16 nm/gal. 50 gal will get me 800 nm with 10 gal reserve.
 
I've been able to get my 160hp O-320 RV-4 to run LOP at full throttle and higher altitudes (8k and up). It required the SDS Aero O-ring Sealed Induction Tube Flanges (http://www.sdsefi.com/sdsaero.htm), pmags, reworking the intake tube to sump fitting (leaks), and an air deflector in front of the stock air filter. I'm not saying all these things are required - just the things that I tried and believe helped. Even then, it is isn't 'perfect' like some of the injected engines I've flown (meaning all temps nearly the same and ultra smooth).

It's been said but I'll say it again, the ability of a carb'd engine to run LOP varies widely (at cruise and 8k' and up). I was flying last week with a friend in his Grumman Tiger (O-360). It simply would not run LOP (all four cylinders) no matter what I tried. One or two cylinders were always ROP while the LOP cylinders were 50 degrees LOP. That said, I imagine this could be 'resolved' with some effort (though I don't know if that effort is allowed on a certificated airplane, probably not).
 
The OP is running a carb so... no injectors...

As FlyinTiger mentioned, a bit of carb heat (experiment as to how much) can make a big difference. Best MPG is generally achieved at around 30 LOP. With the carb you'll have some richer than that and some leaner most likely.

Some carbed Lycomings are really bad, some not so bad.

Pete Howell runs LOP on his 4 banger with good success- over 2600 hours on it now, maybe he'll pipe in here.

Let us know how this turns out for you here.
 
I’ve flown for about 80 hrs now trying different settings.
Still can’t get it over to LOP w/o running too rough.
Vic says “run it 100F ROP and enjoy the speed, that’s what you bought it for”
 
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