LOP Questions

[Tom 4536]

My 231 has JPI 900, GAMI, intercooler and Merlyn. I have some questions as to how often we need to check that we are still at a safe LOP mixture:

1. On a multi-hour flight at the same altitude how often should we redo the lean find test and set the mixture.

2. If the MP changes on level flight, and we adjust the MP back to the original MP setting do we need to redo the lean find and adjust mixture, or will we always be safe at the MP we originally set the LOP mixture?

3. When changing altitude, do we need to redo the lean find and adjust mixture if we maintain the same MP at which we originally set the LOP mixture?

Thank you.

[gsxrpilot]

1. Never
2. No
3. No

With your turbo, altitude doesn't play into the equation. Or at least not for this conversation. Use lean find to discover the correct fuel flow for a given MP that puts you where you want to be LOP. Make note of those numbers. For me in my 252 a typical LOP setting was 25"/9.5gph. Once you know the numbers for your engine, you can skip the Lean Find feature and just go to those numbers. And if during a long flight, you notice the MP change or the FF change, just put it back. No need to run lean find.

[Bentonck]

35 minutes ago, gsxrpilot said:

1. Never
2. No
3. No

With your turbo, altitude doesn't play into the equation. Or at least not for this conversation. Use lean find to discover the correct fuel flow for a given MP that puts you where you want to be LOP. Make note of those numbers. For me in my 252 a typical LOP setting was 25"/9.5gph. Once you know the numbers for your engine, you can skip the Lean Find feature and just go to those numbers. And if during a long flight, you notice the MP change or the FF change, just put it back. No need to run lean find.

Exactly.  You need to do it once.  That's it.  If your MP wanders, put it back, if your RPM wanders, put it back, if your FF wanders, put it back.  That's it.

[Tom 4536]

Thank you guys. I have definitely been making it more complicated than it needs to be.

Tom

[KLRDMD]

I see you're in Tucson. I have a fair amount of 231 time and am happy to fly with you sometime.

[gsxrpilot]

25 minutes ago, KLRDMD said:

I have a fair amount of 231 time and am happy to fly with you sometime.

Don't pass up this opportunity!

[Will.iam]

4 hours ago, Tom 4536 said:

My 231 has JPI 900, GAMI, intercooler and Merlyn. I have some questions as to how often we need to check that we are still at a safe LOP mixture:

1. On a multi-hour flight at the same altitude how often should we redo the lean find test and set the mixture.

2. If the MP changes on level flight, and we adjust the MP back to the original MP setting do we need to redo the lean find and adjust mixture, or will we always be safe at the MP we originally set the LOP mixture?

3. When changing altitude, do we need to redo the lean find and adjust mixture if we maintain the same MP at which we originally set the LOP mixture?

Thank you.

I do find on my 252 that with every thing set like 2500rpm 25”mp and 9.5 on the fuel flow it will stay there in cruise but when i start descending even though i haven’t moved any of the engine controls my fuel flow will slightly increase as i get to lower altitudes and i just lean it back to 9.5. I usually have to do it twice, once about 6000ft and another at about 2000 ft don’t know if thats from a tired engine or if that is normal but it is what i see in the descent on mine. 

[Mike A]

On 5/15/2021 at 9:29 PM, Will.iam said:

I do find on my 252 that with every thing set like 2500rpm 25”mp and 9.5 on the fuel flow it will stay there in cruise but when i start descending even though i haven’t moved any of the engine controls my fuel flow will slightly increase as i get to lower altitudes and i just lean it back to 9.5. I usually have to do it twice, once about 6000ft and another at about 2000 ft don’t know if thats from a tired engine or if that is normal but it is what i see in the descent on mine. 

I think that has to do with the altitude compensating fuel pump. 

[Will.iam]

5 hours ago, Mike A said:

I think that has to do with the altitude compensating fuel pump. 

But why would it compensate for altitude when the turbo is keeping the MP i. E. Altitude pressure constant to the engine no matter the altitude. I could see that with a 231 or a NA engine as it’s turbo you have to keep changing the throttle to keep a constant MP pressure in climbs and descents but the 252 does this automatically for you. 

[Mike A]

Have you tried looking at FF during your climb?  I feel like with my 231, full power ( 40”/2700) produces +/- 24 gph on the take off roll (500’ elevation) but by the time I’m at 6k’ to 8k’ the fuel flow has decreased to closer to 22/23 gph with everything else staying the same. 

[jlunseth]

So, Paul is right that the solution is to put the settings back where they were, but it is a little different in the 231 than in the 252. The 252 has a fully automatic controller, so if you set MP at a number, let’s say at Paul’s 25”, then you can enrich or lean the mixture with the fuel knob and the wastegate controller will work hard to maintain 25”. That is not what happens in the 231. There is an interlink between the MP and the fuel flow in the 231, and the wastegate controller does not hold a set MP. What the interlink does, is to try to maintain a given fuel/air ratio once you have made your power setting. So if you set the power at 25” and 9.5 GPH, and then you increase the MP to 32”, the fuel flow will rise with it to try to keep the same fuel air ratio you had at 25/9.5. The relationship is a little weaker fuel flow drifts for some reason, the interlink is still there but it does not appear to me that the MP will change if fuel flow drifts, as much as the fuel flow will change if MP drifts.

So what you need to do is to make sure both the fuel flow and the MP go back where they were. In my plane, if the MP drifts it is usually good enough to just put the MP back where it was and the fuel flow will normally go with it. If the fuel flow drifts and the MP has not moved, or not moved very much, then put the fuel flow back where it was, but always aim to keep both fuel flow and MP at the initial settings that you found.

I haven’t used either the lean of peak or the rich of peak function in the JPI for years. The lean of peak function, in particular, is very inaccurate. What it tries to do, is identify the last cylinder to peak as you pull the mixture from a rich of peak power setting, across peak, to a lean of peak setting. The problem in the 231 is that MP is moving with the fuel flow when you do that, so what you are doing is not leaning the mixture out but rather just reducing the power setting that you started with. The JPI will report a peak, but too much changing is going on, that peak is just not valid. I found a setting that I know is around 20 degrees lean of peak and keeps the TIT at or under 1600. I just use that setting. It works.

[Mufflerbearing]

Great information here for the turbo guys!  Being a n/a guy, it's a little more complicated, but not too much.

 

[Will.iam]

4 hours ago, jlunseth said:

So, Paul is right that the solution is to put the settings back where they were, but it is a little different in the 231 than in the 252. The 252 has a fully automatic controller, so if you set MP at a number, let’s say at Paul’s 25”, then you can enrich or lean the mixture with the fuel knob and the wastegate controller will work hard to maintain 25”. That is not what happens in the 231. There is an interlink between the MP and the fuel flow in the 231, and the wastegate controller does not hold a set MP. What the interlink does, is to try to maintain a given fuel/air ratio once you have made your power setting. So if you set the power at 25” and 9.5 GPH, and then you increase the MP to 32”, the fuel flow will rise with it to try to keep the same fuel air ratio you had at 25/9.5. The relationship is a little weaker fuel flow drifts for some reason, the interlink is still there but it does not appear to me that the MP will change if fuel flow drifts, as much as the fuel flow will change if MP drifts.

So what you need to do is to make sure both the fuel flow and the MP go back where they were. In my plane, if the MP drifts it is usually good enough to just put the MP back where it was and the fuel flow will normally go with it. If the fuel flow drifts and the MP has not moved, or not moved very much, then put the fuel flow back where it was, but always aim to keep both fuel flow and MP at the initial settings that you found.

I haven’t used either the lean of peak or the rich of peak function in the JPI for years. The lean of peak function, in particular, is very inaccurate. What it tries to do, is identify the last cylinder to peak as you pull the mixture from a rich of peak power setting, across peak, to a lean of peak setting. The problem in the 231 is that MP is moving with the fuel flow when you do that, so what you are doing is not leaning the mixture out but rather just reducing the power setting that you started with. The JPI will report a peak, but too much changing is going on, that peak is just not valid. I found a setting that I know is around 20 degrees lean of peak and keeps the TIT at or under 1600. I just use that setting. It works.

Yes i have noticed the LOP find function is pretty worthless if you rapidly pull to lean as it doesn’t give the egt’s a chance to rise as far as they would if you go slow and thus my LOP number is off. This  is especially true if i run the LOP find at say 35% power and then after I’m well LOP i go back up to my known LOP for 65% power my JPI will report I’m at peak as the egt’s are higher than when i went across peak at 35% power. Disclaimer I don’t have FF going through the JPI so it only has EGT to go off of. For you who have FF on your jpi does it take that into account? I. E. I can tell my LOP find to look for LOP with me starting at LOP and go to full rich and the JPI is saying I’m LOP when I’m actually ROP because who would do it backwards and with the jpi not having FF it doesn’t know i went the wrong way.  

[jlunseth]

The JPI Rich of Peak and Lean of Peak functions are misnamed. They are based on assumptions not measurements. They both assume that you start at a rich of peak setting and then lean out. The ROP function finds the first cylinder to peak (the first peak EGT). It assumes that, starting on the rich side, you lean to peak and then enrich the mixture again to a rich of peak setting of x degrees. The LOP function assumes that you start at a rich setting, that you lean across peak, and it finds the last cylinder to peak. That cylinder is then used to determine degrees lean of peak. The idea is that you want to use the cylinder that is closest to peak EGT in making your ROP or LOP setting. 

The JPI lean functions do not have a clue whether you are rich of peak or lean of peak, the JPI units have no way of measuring the fuel/air ratio and making that determination. The ROP lean function is in reality just a “first cylinder to peak” function, and the LOP lean function is a “last cylinder to peak” function. Using the lean of peak function does not give you valid values in the 231 because too many things are changing too much, and because you are starting with a rich of peak fuel/air ratio, and the interlink is trying to maintain that same fuel/air ratio as you lean the mixture out.  You aren’t just leaning, you are changing the whole power setting, so you don’t get a valid peak. To get a valid peak you would have to keep MP at the same value while you lean the fuel, which would be a good trick.

[carusoam]

It would be so nice to have an air flow sensor... similar to a FF sensor...   

We could be thousandaires!

Just need to start with one millllllion dollars...

Great ideas generated while we speak. 

PP thoughts only, not an aviation businessman...

Best regards,

-a-

[A64Pilot]

what you would want is an O2 sensor, that will tell you mixture ratio accurately based on remaining oxygen, of course it’s how computer controlled automobiles precisely trim fuel. I know someone with a Maule that has one, put it in as a field approval, it is a monitor only of course, it does not control anything

But here’s the thing, leaded fuel is supposed to kill a lambda sensor in a hurry, but last I heard it hasn’t yet. When it does they are relatively cheap and as easy to change as a spark plug

There is a whole lot of misinformation “sold” about LOP, like “excess” air cools your cylinder heads etc. So tell me how does exhaust thats 25 degrees cooler than peak cool anything?

Cylinder head temp is function of power, it’s the lower power that makes the heads cooler.

Flame suit on.

On edit, airflow sensors are easy the more modern ones are just a heated wire, air mass is measured by how which the wire is cooled, the older ones were a door, but it’s air mass you really are measuring, and that’s of course what you want to measure, by measuring mass, it autocorrects for density altitude. 

Edited May 20, 2021 by A64Pilot

[DanM20C]

12 hours ago, jlunseth said:

To get a valid peak you would have to keep MP at the same value while you lean the fuel, which would be a good trick.

It's like trying to draw a perfectly straight diagonal line on an etch a sketch. except harder!

I use the JPI lean lop function for only one reason.  It changes the %power algorithm for lop.  The % power display isn't really any use but my OCD hates seeing it at 86% when I'm running LOP @ 9gph.  After I settle into my LOP cruise I just hit the lean find button, select lop, and hit exit.  

Cheers,

Dan

[N201MKTurbo]

I think you are overly complicating this. When I'm LOP I just increase the FF until either the CHTs or TIT are where I want them. They both increase with FF. 

The RSA5 keeps the mixture dead on, no matter where I set the MP or RPM after I set it. It already has a mass airflow sensor of sorts in it. I have always thought the Continental FI systems were a bit wonky. 

FWIW I can always get more airspeed at the same CHTs LOP than ROP.

[A64Pilot]

15 minutes ago, N201MKTurbo said:

FWIW I can always get more airspeed at the same CHTs LOP than ROP.

That needs qualification, how much ROP?  How much power? Because as you know if high power being rich is the only way to keep temps in check, it’s why we take off so rich.

‘Plus as you know you can get air speeds ROP that you can’t LOP, because the HP limit LOP is much lower than ROP.

‘Also be careful of enriching until you get the temps you want, if your LOP percent power is an important variable in that equation, although if you set the limits low enough that ought to keep you safe.

The fuel control must have some sort of compensation for air density, if I open the ram air it increases fuel flow significantly, enough so that if I want to stay well LOP I need to lean.

‘I really don’t use the ram air, or only rarely do.

Edited May 20, 2021 by A64Pilot

[N201MKTurbo]

5 minutes ago, A64Pilot said:

That needs qualification, how much ROP?  How much power? Because as you know if high power being rich is the only way to keep temps in check, it’s why we take off so rich.

‘Plus as you know you can get air speeds ROP that you can’t LOP, because the HP limit LOP is much lower than ROP.

‘Also be careful of enriching until you get the temps you want, if your LOP percent power is an important variable in that equation, although if you set the limits low enough that ought to keep you safe.

The fuel control must have some sort of compensation for air density, if I open the ram air it increases fuel flow significantly, enough so that if I want to stay well LOP I need to lean.

‘I really don’t use the ram air, or only rarely do.

How much ROP, which cylinder are we talking about? Usually 50 ROP. if I go 100 ROP the FF is like 2 GPH more. Who wants that? How much power? who knows. I can use the magic LOP formula for FF vs power, but I don't trust my FF gauge. ROP power is any body's guess. The STC for the turbo system says to just use the sea level power charts. I don't believe it for a second.

The only hazard to increasing power is temperature and detonation. I have found out how to make this thing detonate. It is not subtle, and nowhere near where I operate. Mechanically the engine is rated for continuous full power. You cannot get anywhere near that limit without shoving all the levers forward.  

[N201MKTurbo]

FWIW,

According to my FF meter, I'm burning 9.3 GPH typically so 9.3 * 14.9/200 = 69.2% power. That was getting me 160 KTS TAS at 8500 last week.

[EricJ]

3 hours ago, A64Pilot said:

what you would want is an O2 sensor, that will tell you mixture ratio accurately based on remaining oxygen, of course it’s how computer controlled automobiles precisely trim fuel. I know someone with a Maule that has one, put it in as a field approval, it is a monitor only of course, it does not control anything

But here’s the thing, leaded fuel is supposed to kill a lambda sensor in a hurry, but last I heard it hasn’t yet. When it does they are relatively cheap and as easy to change as a spark plug

We see this a lot in race cars, where people get 100LL or some other leaded race fuel in an attempt to make more power, and very often the O2 sensors don't last very long.  So lead has definitely killed many an O2 sensor.   

Most of the race crowd uses ethanol instead, for a more significant power increase while maintaining the ability to use the O2 sensor to manage the ECU tune.

 

[exM20K]

On 5/15/2021 at 5:43 PM, gsxrpilot said:

1. Never
2. No
3. No

With your turbo, altitude doesn't play into the equation. Or at least not for this conversation. Use lean find to discover the correct fuel flow for a given MP that puts you where you want to be LOP. Make note of those numbers. For me in my 252 a typical LOP setting was 25"/9.5gph. Once you know the numbers for your engine, you can skip the Lean Find feature and just go to those numbers. And if during a long flight, you notice the MP change or the FF change, just put it back. No need to run lean find.

I start with the end (fuel flow) in mind:  set an approximate power setting (29 x 2400, for example).  Lean till the last-to-lean is 50* LOP.  Add back MP to increase FF to my desired level (17).  Re-check that richest cylinder is 50* LOP.  Operated my 231 the same way.

-dan

 

[A64Pilot]

I did a little search as of course you can too, I was seeing that wide band sensors last over 100 hours and narrow band 300 or more.

‘For accuracy you want wide band

But even 100 hours is in excess of needs, if you were really into this kind of thing, 10 hours is more than enough to develop a graph that will tell you stoichiometric A/F ratio at different density altitudes and varying combinations of manifold pressure and RPM, so you would know peak without having to go through the trouble of finding it.

‘I usually do it the way it’s been done forever, the way I was taught to lean as a student pilot. lean it until it gets rough, then enrichen just until it smooths out again, that puts me well lean of peak

[jaylw314]

17 hours ago, carusoam said:

It would be so nice to have an air flow sensor... similar to a FF sensor...   

We could be thousandaires!

ROTFL.   You cracked me up -a-