Leaning and power settings

[gevertex]

So far I have just followed my POH and run 100ROP using lean finder over ~60 seconds. As altitude changes (in descent or cruise climbs with the same power setting), I change the mixture to maintain that 100ROP setting as altitude changes.

But... I have been reading more about LOP operations and I have some questions.

Does changing the throttle setting really not change the mixture at all with constant speed props? The throttle controls a baffle in the intake letting more or less air in, right? Does the fuel servo have some coupling to the throttle? If not there would have to be a mixture change with more or less air for the same fuel.  I have seen some advocate finding the right mixture at a safe lower power setting then power up once the mixture is set, so this is why I am asking.

I have also seen some advocate for not finding peak EGT, rather doing a big mixture pull quickly to LOP and using "suitable" fuel flow values. How can you know what numbers are suitable? Is this a matter of identifying a combination of RPM, manifold pressure, fuel flow, and keeping them all the same over altitude changes? Does that hold over all other conditions (temperature, altitude, etc)? So far, I have used lean finder mode to find the peak EGT then richen to 100ROP.

I know all of this has been discussed to death, but wanting to learn about some of the finer points.

[Fly Boomer]

27 minutes ago, gevertex said:

So far, I have used lean finder mode to find the peak EGT then richen to 100ROP.

Mike Busch does not like using EGT as a leaning reference.  A corollary to that rule is don't use "lean find".  Here is a video explaining why.  The most salient point is made starting at 18:20.

https://youtu.be/X-tKyiUZ3ts

[Will.iam]

4 hours ago, gevertex said:

So far I have just followed my POH and run 100ROP using lean finder over ~60 seconds. As altitude changes (in descent or cruise climbs with the same power setting), I change the mixture to maintain that 100ROP setting as altitude changes.

But... I have been reading more about LOP operations and I have some questions.

Does changing the throttle setting really not change the mixture at all with constant speed props? The throttle controls a baffle in the intake letting more or less air in, right? Does the fuel servo have some coupling to the throttle? If not there would have to be a mixture change with more or less air for the same fuel.  I have seen some advocate finding the right mixture at a safe lower power setting then power up once the mixture is set, so this is why I am asking.

I have also seen some advocate for not finding peak EGT, rather doing a big mixture pull quickly to LOP and using "suitable" fuel flow values. How can you know what numbers are suitable? Is this a matter of identifying a combination of RPM, manifold pressure, fuel flow, and keeping them all the same over altitude changes? Does that hold over all other conditions (temperature, altitude, etc)? So far, I have used lean finder mode to find the peak EGT then richen to 100ROP.

I know all of this has been discussed to death, but wanting to learn about some of the finer points.

Ok first off you finding peak egt and then enriching to 100ROP means you are going throught the most harsh area (50 degrees ROP) twice!!! Once going to peak and again going back to 100ROP. Only by staying 65% or less contintal or 70% lycoming is it ok because your power setting is low enough to not damage the engine even if you left it at 50ROP. So don’t be afraid to go into LOP as you already past the worse area getting there. The least damaging would be to set your power below 65% then pull mixture until engine runs rough then enrichen just until the roughness smoothes out. That is the deepest LOP you can run until you balance out your injectors better. That might be peak, just a little lean of peak or if you are lucky with your injectors being closely matched deep lean of peak.   Yes any time you move the throttle it changes the mixture as well. Just readjust the mixture after your new throttle setting back to the fuel flow you had. If you increase throttle with same ff as before you will be more deep lop and vice versa if you pull back on the throttle and readjust the ff back to what it was before the throttle (MP) change. 

[Ragsf15e]

4 hours ago, gevertex said:

So far I have just followed my POH and run 100ROP using lean finder over ~60 seconds. As altitude changes (in descent or cruise climbs with the same power setting), I change the mixture to maintain that 100ROP setting as altitude changes.

But... I have been reading more about LOP operations and I have some questions.

Does changing the throttle setting really not change the mixture at all with constant speed props? The throttle controls a baffle in the intake letting more or less air in, right? Does the fuel servo have some coupling to the throttle? If not there would have to be a mixture change with more or less air for the same fuel.  I have seen some advocate finding the right mixture at a safe lower power setting then power up once the mixture is set, so this is why I am asking.

I have also seen some advocate for not finding peak EGT, rather doing a big mixture pull quickly to LOP and using "suitable" fuel flow values. How can you know what numbers are suitable? Is this a matter of identifying a combination of RPM, manifold pressure, fuel flow, and keeping them all the same over altitude changes? Does that hold over all other conditions (temperature, altitude, etc)? So far, I have used lean finder mode to find the peak EGT then richen to 100ROP.

I know all of this has been discussed to death, but wanting to learn about some of the finer points.

If you go up to ~9000’, you can just leave the throttle full and play around with it to get a good feel for how it plays out.  At that altitude, you can’t get more than about 65% anyway and you won’t hurt anything by going slow with the mixture as you lean and watch your egts.
If you know the ff specifically for the power setting you want, pulling straight to that is great, but I like to see where peak is and watch each one peak, so that’s what I do.  So just start leaning with or without lean find.  Watch each cylinder peak, stop just after the last one peaks.  Should be around 8.5-9gph for 65% power.  Look at your chts, they’re cooler than 100rop.  If you stop right at peak on the last one, that might be cool enough as well (and you’re running “peak egt”), but say you’re chts are around 380 and you want cooler, go slightly leaner.  you’ll want to stay pretty close to peak because power drops off quicker on the lean side of peak.

I disagree with not using lean find and just doing a big pull until you’ve played around with it a lot, got a great feeling for your engine, and know your exact lop power settings.  Just play around up high enough that you’re below 65% power.  Leave throttle full, lean to get lop and then to control desired cht.

If you’re down lower, just pull the mixture back to 9gph or less as that’s 65% power.  If i was learning, I’d go up higher so I could play around without worrying about hurting anything.

[NickG]

20 hours ago, gevertex said:

So far I have just followed my POH and run 100ROP using lean finder over ~60 seconds. As altitude changes (in descent or cruise climbs with the same power setting), I change the mixture to maintain that 100ROP setting as altitude changes.

But... I have been reading more about LOP operations and I have some questions.

Does changing the throttle setting really not change the mixture at all with constant speed props? The throttle controls a baffle in the intake letting more or less air in, right? Does the fuel servo have some coupling to the throttle? If not there would have to be a mixture change with more or less air for the same fuel.  I have seen some advocate finding the right mixture at a safe lower power setting then power up once the mixture is set, so this is why I am asking.

I have also seen some advocate for not finding peak EGT, rather doing a big mixture pull quickly to LOP and using "suitable" fuel flow values. How can you know what numbers are suitable? Is this a matter of identifying a combination of RPM, manifold pressure, fuel flow, and keeping them all the same over altitude changes? Does that hold over all other conditions (temperature, altitude, etc)? So far, I have used lean finder mode to find the peak EGT then richen to 100ROP.

I know all of this has been discussed to death, but wanting to learn about some of the finer points.

Here is a link to articles by John Deakin https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-index/. Numbers 8, 15, 16, 18, 19, 43, 63-66, 77 & 78 deal with engine management and running LOP.

[PT20J]

People can make this infinitely complex, but it's really pretty simple:

First, yes the throttle position (over the normal cruise power range) at constant altitude will not affect mixture. The primary function of the servo is to meter fuel according to airflow in order to maintain a constant fuel/air ratio. The mixture does change as altitude changes because the servo measures airflow volume not mass and so as you climb the number of oxygen molecules in a given volume of air (i.e., the air density) decreases and the mixture will richen.

Extra fuel beyond what is required for combustion can provide cooling and is required at high power to prevent overly high CHTs. Lean mixtures and high CHTs can cause detonation. But Lycoming approves leaning at powers below 75%, so at powers below that you can do anything you want with the red knob and not hurt anything. Makes it fun to experiment. 

The engine power and efficiency depend on how much air it can ingest, so throttling is counter productive. Thus, the "best" throttle position is wide open (WOT). So, if you climb a normally aspirated engine to some altitude where WOT yields 75% or less power then you are free to set the mixture to achieve whatever result you desire. Somewhere around 100-120 deg ROP gives best power, fastest speed and highest fuel consumption. Somewhere around 50 deg LOP gives the best efficiency (most mpg) but lower power and lower speed. Often at higher altitudes, peak is a good compromise.

At lower altitudes you can reduce the manifold pressure to something below 75% and then it is safe to lean. This is good enough to start with. Some like to run WOT at all altitudes for the increased efficiency and there are techniques for doing this safely, but I think it is easier to just reduce power first until you really have the hang of it because it is always safe. Others will, I'm sure, disagree with me.

 

 

[PeteMc]

1 hour ago, PT20J said:

Thus, the "best" throttle position is wide open (WOT).

It's been quite a while since I've flow a plane with a carbureted engine.  Was it an ol' wives tail or reality that you shouldn't really use "wide open" but crack the throttle back just a bit so the butterfly valve added a little turbulence to the airflow for better mixture? 

I remember the discussion way back when, but then stopped flying anything with a carburetor.  

 

Edited Wednesday at 07:40 PM by PeteMc

[kortopates]

It's been quite a while since I've flow a plane with a carbureted engine.  Was it an ol' wives tail or reality that you shouldn't really use "wide open" but crack the throttle back just a bit so the butterfly valve added a little turbulence to the airflow for better mixture? 
I remember the discussion way back when, but then stopped flying anything with a carburetor.  
 

Still very true but done in the context to balance EGTs using an engine monitor.


Sent from my iPhone using Tapatalk

[EricJ]

13 minutes ago, PeteMc said:

It's been quite a while since I've flow a plane with a carbureted engine.  Was it an ol' wives tail or reality that you shouldn't really use "wide open" but crack the throttle back just a bit so the butterfly valve added a little turbulence to the airflow for better mixture? 

I remember the discussion way back when, but then stopped flying anything with a carburetor.  

 

That's sometimes helpful for carburetors to more evenly distribute the mixture, but not so much for fuel injection.    The other issue with many carburetors is the "economizer" circuit that richens the mixture more at WOT than if pulled back a bit.  

[PT20J]

A lot depends on the design of the induction system. The Piper Warrior II had a carbureted 0-320 and the POH has a procedure for setting power using the mixture control which actually results in running LOP.

WOT LOP_20190615_0001.pdf

[0TreeLemur]

Where I usually fly, above 8,000',  I've realized something lately.  The technique of using the "Big Mixture Pull" then the Lean Find function on the JPI EDM900 to establish something like 25 or 50 F LOP, is not dissimilar from the way I was originally taught to lean an engine while a student pilot.   Lean it out until it starts to run roughly, then enrichen until it smooths out.  Admittedly, the trainer was carbureted vs. the fuel injection on my J, but the procedure and end result is surprisingly similar. 

My J will run deep LOP.  The engine just gets quieter and quieter as it produces less and less power.  When it starts running rough, it's waaay LOP.  On long flights up high, especially in the winter, I find that the critical limit is running rich enough to keep CHT above 300 in all cylinders.

[gevertex]

On 11/13/2024 at 1:37 PM, PT20J said:

People can make this infinitely complex, but it's really pretty simple:

First, yes the throttle position (over the normal cruise power range) at constant altitude will not affect mixture. The primary function of the servo is to meter fuel according to airflow in order to maintain a constant fuel/air ratio. The mixture does change as altitude changes because the servo measures airflow volume not mass and so as you climb the number of oxygen molecules in a given volume of air (i.e., the air density) decreases and the mixture will richen.

Extra fuel beyond what is required for combustion can provide cooling and is required at high power to prevent overly high CHTs. Lean mixtures and high CHTs can cause detonation. But Lycoming approves leaning at powers below 75%, so at powers below that you can do anything you want with the red knob and not hurt anything. Makes it fun to experiment. 

The engine power and efficiency depend on how much air it can ingest, so throttling is counter productive. Thus, the "best" throttle position is wide open (WOT). So, if you climb a normally aspirated engine to some altitude where WOT yields 75% or less power then you are free to set the mixture to achieve whatever result you desire. Somewhere around 100-120 deg ROP gives best power, fastest speed and highest fuel consumption. Somewhere around 50 deg LOP gives the best efficiency (most mpg) but lower power and lower speed. Often at higher altitudes, peak is a good compromise.

At lower altitudes you can reduce the manifold pressure to something below 75% and then it is safe to lean. This is good enough to start with. Some like to run WOT at all altitudes for the increased efficiency and there are techniques for doing this safely, but I think it is easier to just reduce power first until you really have the hang of it because it is always safe. Others will, I'm sure, disagree with me.

 

 

This is what I was taught, but I never understood why. Thanks for the explanation!

[gevertex]

On 11/14/2024 at 12:24 PM, 0TreeLemur said:

Where I usually fly, above 8,000',  I've realized something lately.  The technique of using the "Big Mixture Pull" then the Lean Find function on the JPI EDM900 to establish something like 25 or 50 F LOP, is not dissimilar from the way I was originally taught to lean an engine while a student pilot.   Lean it out until it starts to run roughly, then enrichen until it smooths out.  Admittedly, the trainer was carbureted vs. the fuel injection on my J, but the procedure and end result is surprisingly similar. 

My J will run deep LOP.  The engine just gets quieter and quieter as it produces less and less power.  When it starts running rough, it's waaay LOP.  On long flights up high, especially in the winter, I find that the critical limit is running rich enough to keep CHT above 300 in all cylinders.

Last I did the GAMI spread mine was split on cylinder 3, but I expect that will be better once I get it back.

 

How do you use lean find, after the big pull? I imagine something like BMP, let the EGTs settle, enable lean find, richen to peak then lean back to 25/50LOP?

[jlunseth]

If you want the icicle display to work, or to get degrees lean of peak, you have to start the lean find process when you are on the rich side of peak and then lean over to the lean side. You don’t do the big pull first, you put the engine monitor in lean find first. I don’t bother with the LOP lean find function anymore, in my aircraft, the 231, the manifold pressure changes when you bring the fuel flow back so you are changing the whole power setting and the “peak” you find is not valid. But in an NA the MP should stay constant at ambient pressure provided you are not changing altitude, so you are only changing fuel flow. The engine monitors don’t somehow “know” you are rich or lean of peak. They do not have a way to measure the air/fuel ratio as it changes. Rather, they assume that you start on the rich side and that you are changing fuel flow while manifold pressure remains constant. That applies whether you are using LOP mode or ROP mode. 

There is a trick you can use to do the big pull and still get an accurate reading. You could put the unit in LOP mode and then use the big pull and use the degrees LOP that is then displayed, but the monitor manufacturers want you to make small moves, not big ones, so their units can give you an accurate reading. What the monitor is trying to do, whether in rich or lean mode, is to find the cylinder that is nearest to peak and then use that cylinder to determine how many degrees rich or lean that cylinder is operating. It assumes, as I said, that you start the process on the rich side. In ROP mode it will find the first cylinder to reach peak and use that cylinder to determine how many degrees rich of peak. In LOP mode, it assumes you started on the rich side and leaned over, so it uses the last cylinder to peak to determine how many degrees rich of peak. As I said, it does not actually know whether you are rich or lean of peak, it makes assumptions. ROP mode simply means it finds the first cylinder to peak. LOP mode simply means it finds the last cylinder to peak. Sooooo…if you use the big pull first, before you put the monitor in any leaning mode, and then you put the monitor in Rich of Peak mode (you read that right), and then enrich back towards peak, the monitor will find the first cylinder that hits peak and when you then lean back again the result will be a fairly accurate reading of the degrees lean of peak the cylinder closest to peak is operating. It will display that as degrees rich of peak, but it is not, it will be degrees lean of peak. And you will have made the reading by making small moves once the monitor was put into ROP mode so the reading will be accurate.

[Will.iam]

55 minutes ago, jlunseth said:

If you want the icicle display to work, or to get degrees lean of peak, you have to start the lean find process when you are on the rich side of peak and then lean over to the lean side. You don’t do the big pull first, you put the engine monitor in lean find first. I don’t bother with the LOP lean find function anymore, in my aircraft, the 231, the manifold pressure changes when you bring the fuel flow back so you are changing the whole power setting and the “peak” you find is not valid. But in an NA the MP should stay constant at ambient pressure provided you are not changing altitude, so you are only changing fuel flow. The engine monitors don’t somehow “know” you are rich or lean of peak. They do not have a way to measure the air/fuel ratio as it changes. Rather, they assume that you start on the rich side and that you are changing fuel flow while manifold pressure remains constant. That applies whether you are using LOP mode or ROP mode. 

There is a trick you can use to do the big pull and still get an accurate reading. You could put the unit in LOP mode and then use the big pull and use the degrees LOP that is then displayed, but the monitor manufacturers want you to make small moves, not big ones, so their units can give you an accurate reading. What the monitor is trying to do, whether in rich or lean mode, is to find the cylinder that is nearest to peak and then use that cylinder to determine how many degrees rich or lean that cylinder is operating. It assumes, as I said, that you start the process on the rich side. In ROP mode it will find the first cylinder to reach peak and use that cylinder to determine how many degrees rich of peak. In LOP mode, it assumes you started on the rich side and leaned over, so it uses the last cylinder to peak to determine how many degrees rich of peak. As I said, it does not actually know whether you are rich or lean of peak, it makes assumptions. ROP mode simply means it finds the first cylinder to peak. LOP mode simply means it finds the last cylinder to peak. Sooooo…if you use the big pull first, before you put the monitor in any leaning mode, and then you put the monitor in Rich of Peak mode (you read that right), and then enrich back towards peak, the monitor will find the first cylinder that hits peak and when you then lean back again the result will be a fairly accurate reading of the degrees lean of peak the cylinder closest to peak is operating. It will display that as degrees rich of peak, but it is not, it will be degrees lean of peak. And you will have made the reading by making small moves once the monitor was put into ROP mode so the reading will be accurate.

Thanks. I had not really thought about ROP find it the first cylinder compared to LOP find is the last. I had been coming from LOP in LOP find so was going to last cylinder to peak. I see now that ironically ROP find is the better correct way to do the lean find from the LOP side so that you are not dragging through the red box slowly. 

[MikeOH]

For my NA airplane I really don't worry about the 'red box' as I don't go LOP until I'm at cruise (>5,000 ft).  So, if I want to 'slowly' go LOP by passing through peak I take my time  Typically, though, I just perform the 'big pull' and set fuel flow; usually around 9 gph (<70%).  Then check the CHTs are okay. Easy peasy.

At low altitudes I'm usually just sight seeing and have the power nowhere near WOT (I'm below 75% to begin with), so I don't worry too much about the 'red box' in that situation either.