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Question on LOP operation, POLL as well...

50? LOP on first or last cylinder to peak?

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Brantel

Brantel

Well Known Member
Help me clear up a question I have on LOP operation. I have seen conflicting info here on this very question....

When leaning for LOP operation do you go 50? LOP on the first or last cylinder to peak?

My way of thinking sez that if you go off the first, you may have some cylinders running still in the danger zone. To me this is where most newbies to LOP operation might make a mistake and kill the engine.

If you go last, some cylinders may be way more than 50? LOP and even so far as the engine will run rough. I assume this is the reason why most carburated engines can't do it very well and why well balanced injected engines make it easier to run LOP.
 
IMHO it is dangerous to run LOP in a carburated engine because there is nearly impossible to balance the fuel flow to the cylinders which would lead to a situation that you described where one may be running LOP while another is at peak and a third is ROP. In an injected engine the injectors can be tuned (enter GAMIjectors) so that the cylinders are as close to each other as possible. In this case you would lean based on the last to peak and it may not necessarily be 50 degrees LOP...it depends on the altitude, air density, etc. as to where the engine runs smoothest with best fuel flow. When you find the sweet spot the difference between first and last to peak will be very close to each other. In our 210, we routinely run LOP and there is only 50 - 60 degrees difference between the hottest and coolest.
 
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Now, when I do lean of peak, this is on WOT @ 24, 24 altitude pending. I have about .3gph between cylenders and I'm also fuel injected. I go lean of peak on the last cylender to peak, this is proper for LOP. for ROP you go by the first cylender to peak.

When flying low and pulled back to 20maf I have a different spread on the cylenders and I make it a balance between them all. the leanest might go 65lop and the richest 30lean of peak for my final setting. At anyrate you need to find the sweet spot for going lop, for going LOP on the last cylender could cause a bad running engine and cause trouble, that's what I found anyway. In this case I go 50LOP on the first cylender and all flight ops are great with this setting.
 
allbee said:
I go lean of peak on the last cylender to peak, this is proper for LOP. for ROP you go by the first cylinder to peak.
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This is correct and the way I do it as well. I misstated it above and will make the correction...had to go back and think about it a minute. I do it by routine in the airplane but sitting here at the desk I had to run through it in my mind. :)
 
OK folks, before all the OWT's come out of the closet let me state some FACTS you can take to the bank.


1. You can run a carby engine LOP, just most do not have a good balance of fuel air mix to each cylinder to get them all LOP without the first one starting to stop producing power and hence rough running.

I recently had the pleasure of flying in an RV6 with O-360 and CSU and we could run it at 8000' with WOT and about 2350RPM, and just get the last cylinder around peak or a couple LOP and the first one was about 25-30 LOP, it was barely noticable in roughness, just as it should be.

Some carby engines will run LOP more successfully with carb heat or the throttle cracked enough that you see a small MP drop, the turbulent air from the butterfly stirs things up enough you get a better mix, but its all trial and error.

2.
you would lean based on the last to peak and it may not necessarily be 50 degrees LOP.
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This is true, low altitude you will get a higher number LOP to get away from the potential detonation zone. At 7000' or higher which is generally around 23"MP you can run safely just LOP or say 0-20 LOP, if you start going further the power drops away rapidly.

3. Articles #63 - #66......PRINT THESE OFF and read them through about 7 or 8 times. Yes I am serious, maybe more, you need to understand this stuff, not just have read it once.

4. You guys are lucky over there, its easy for you to do the APS courses. The cost of the course will be paid back in fuel and engine maintenance costs ina very short time. Unless you understand this stuff really well, and you do not attend I think you are foolish. The best money invested in your aviation life. http://www.advancedpilot.com/

5. Study these two tables carefully, found in the JD articles.

-----------------------------------------------------------
Red Box = No Fly Zone
? At and below about 60% power, there is no red box. Put the mixture wherever you want it.
? At about 65% power or so, 100?F ROP to Peak.
? At about 70%, 125?F ROP to 25?F LOP.
? At about 75%, 180?F ROP to 40?F LOP.
? At about 80%, 200?F ROP to 60?F LOP.
------------------------------------------------------------


----------------------------------------------------------
Outside the Box
? At 65% power, use richer than 100 ROP, or leaner than peak EGT.
? At 70%, use richer than 125?F ROP, or leaner than 25?F LOP.
? At 75%, use richer than 180?F ROP, or leaner than 40?F LOP.
? At 80%, use richer than 200?F ROP, or leaner than 60?F LOP.
----------------------------------------------------------

I am not George or John or Walter by any stretch...........but if you have questions post or PM or email me. I am happy to educate anyone willing to learn.

Green of Peak....:D:D:D you guys crack me up :)
 
Matched injectors are almost required to run LOP properly. I said almost - there are a very few carbed engines with good results, but it's very rare. I don't know how the old big radials handled the fuel distribution issue, but apparently they made it work back then. Our small engines don't seem to do as well.

Yesterday I was at 7500 in my 172 (with IO360 and Gamijectors) running WOTLOP and demonstrated to my carb-owner pilot passenger that I could reduce power all the way down to 1800 rpm by mixture alone before the first hint of roughness appeared. I think he's planning a conversion this morning...:)
 
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Carb LOP - more questions

For you that understand LOP operations, I have some questions. My airplane (O-320-D1A fixed pitch prop and with ported cylinders from Lycon) runs within 15 degrees of EGT spread....IF I am at WOT. If I use less than WOT, the cylinders are as much as 190 degrees apart, but ROP.

It is further complicated by the fact that at WOT and the altitudes I travel in (10-12K) the RPM is 2720 or 2730:eek:

So...I can get balanced and LOP, but only at very high RPM, which I worry isn't great for the TBO and oil burn. Not sure, I only do it for 20 minutes or so then get uncomfortable and go to unbalanced ROP and 2550 or 2600, higher fuel burn and slower speed:(

All I have for fuel flow is the GRT EIS 4000, no wiz bang AFS stuff.

Any carb LOP gurus out there with some input would be appreciated.
 
Peak EGT is merely a reference point, a marker. You don't actually care about peak EGT; you care about peak temperatures and pressures. The highest in-cylinder temperatures and pressures are in a zone well over on the rich side of the marker, thus the real goal is to simply get as lean as possible while still maintaining mechanical smoothness and desired power. That may put all cylinders at peak, 25, 50, or 75 LOP, or spread across the entire range. The exact numbers don't matter.

Back to ROP; the "red box danger" is a guideline. It's not the same for everyone. If you're running a parallel valve motor, a turbo, 10:1 compression, advanced timing, or high CHTs, you have reason to be cautious, and combining them should make you a lot more cautious. On the flip side, with low CHT and 20 BTDC you should be able to run an 8.7:1 angle valve motor at best power ROP without much concern. It may not the best plan for maximum life, but it shouldn't knock a hole in a piston.
 
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Brantel, it is the "richest" cylinder LOP that is the concern. In our carbed engines or injected engines without balanced injectors, you can cook one cylinder while all the others are lean and happy.

I have an o-320 with dual P-mags and have trouble running LOP. It seems like if I get the right combination of DA, carb heat, OAT, moon phase, it'll run fine 50 LOP (richest cylinder). However, most flights, I get too much roughness before everything is LOP properly. Of course, this is to be expected with a carb.

I pretty much always use the old school method of leaning. Lean to rough and then rich a 1/4 turn or so. The difference in fuel flow is about .5-1.0 gph from LOP. However, I lose about 10KTAS LOP. Using the old school leaning, I lose about 5KTAS.

Someone asked the forum a while ago and never got an answer. I'll throw it back out there. When leaning to roughness, WHAT IS THE ROUGHNESS? It's not preignition, not detonation. Lycoming describes it as "mis-fiiring". Never have I read or heard anyone describe it as harmful (other than to your nerves). Am I right on that?
 
apkp777 said:
Someone asked the forum a while ago and never got an answer. I'll throw it back out there. When leaning to roughness, WHAT IS THE ROUGHNESS? It's not preignition, not detonation. Lycoming describes it as "mis-fiiring". Never have I read or heard anyone describe it as harmful (other than to your nerves). Am I right on that?
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The roughness you experience with a carbed or non-matched injected engine when leaning comes from the fact that the mixture distribution is uneven, and some cylinders are producing more power than others. As you continue to get leaner the cylinder will produce less power - but with a poor mixture distribution you might have one or two cylinders that are very lean and barely firing (almost a miss, very little power) while one or two others are at near full-power. This mis-balance of power is what produces the roughness.

patterson said:
For you that understand LOP operations, I have some questions. My airplane (O-320-D1A fixed pitch prop and with ported cylinders from Lycon) runs within 15 degrees of EGT spread....IF I am at WOT. If I use less than WOT, the cylinders are as much as 190 degrees apart, but ROP.

It is further complicated by the fact that at WOT and the altitudes I travel in (10-12K) the RPM is 2720 or 2730:eek:

So...I can get balanced and LOP, but only at very high RPM, which I worry isn't great for the TBO and oil burn. Not sure, I only do it for 20 minutes or so then get uncomfortable and go to unbalanced ROP and 2550 or 2600, higher fuel burn and slower speed:(

All I have for fuel flow is the GRT EIS 4000, no wiz bang AFS stuff.

Any carb LOP gurus out there with some input would be appreciated.
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Patterson - the often quoted "50 degrees LOP" is only a guideline, you don't want to operate richer than that for fear of overheating a cylinder, but leaner is safe. If you are operating WOTLOP at cruise altitude and your RPM is too high, simply go leaner. The leaner mixture will further reduce power production from the engine, and with a fixed-pitch prop that will reduce the RPM. This is how I cruise my 172, I run ROP during climb to keep the engine temps happy, as soon as I level off at cruise (usually 7500 or 8500) and the airspeed comes up I leave the throttle wide open and pull the mixture to LOP, and tweak it to maintain 2500 rpm (for me that's about 100 degrees LOP). On descent I go even further LOP for power reduction until about 4000', then I go back to ROP and use throttle for power control. My throttle stays wide open from the start of the takeoff roll until about 4000' on the descent and I control power by mixture.

Note - if you do run far LOP on descent, when you get to that point where you want to go back to ROP, reduce the throttle FIRST until you get an rpm sag, then enrichen the mixture and adjust the throttle. At lower altitudes and higher airspeeds during descent, you can easily overspeed the prop if you go full rich at wide open throttle - or at least I can on my bird.
 
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Greg (or anyone else),

Do you suppose that a little "lean" roughness, can actually damage the cylinders? With a carbed engine (mine at least) I would have a slight roughness to run LOP.
 
RV10inOz said:

2. This is true, low altitude you will get a higher number LOP to get away from the potential detonation zone. At 7000' or higher which is generally around 23"MP you can run safely just LOP or say 0-20 LOP, if you start going further the power drops away rapidly.
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I don't have any indebt knowledge of engine work but my experience confirms this. My LOP numbers are not that spread, usually within 10-20F while LOP, but if I want to go 50F LOP the engine will not run that great and I sacrifice much speed.


RV10inOz said:

3. Articles #63 - #66......PRINT THESE OFF and read them through about 7 or 8 times. Yes I am serious, maybe more, you need to understand this stuff, not just have read it once. .
Click to expand...


Do you have a link for the above article or where it can be found?
 
The Deacon articles are excellent and I have read them many times. However, it is important to note that their work is primarily on big bore injected engines. I firmly believe that it is nearly impossible to have detonation on the average 4 cylinder lycoming.
I sat with the major sponsor of this program at Osh a few years ago and he told me straight out that he did not think it could happen even if they tried.
Correct me if I am mistaken in my understanding but it would take excess MP and Redline CHT's to produce even mild detonation. Your engine would make a lot of really bad noises but no real damage would occur unless left that way.
You would have to mis manage your power in a big way to have a destructive event if you could even get it to happen.
This is not to say that understanding this is not important. The idea here is to operate our engines optimally, not just casually.
I have yet to hear of a single detonation event in our fleet outside of an examply a few years ago with a electronic ignition advance runaway and I can not even remember or find reference that it actually detonated.
Find one for me and make me a believer in detonation....
 
Bavafa

The spread in your EGT numbers is not what matters, its the spread in the fuel flow as each one peaks. So if the first one peaks when the fuel flow is 8.0GPH and the last one at 7.8GPH, you have a 0.2GPH spread. What the actual EGT is does not matter.

The end result may be the EGT's are all around 10-20F of each other but it really does not matter.

The links you need are here
http://www.avweb.com/news/pelican/182544-1.html

#63 onwards are what you want, the others make good reading also. And so does this one http://www.airsafety.com.au/pelp0057.html and here is another http://homepage.mac.com/ghim/Bearhawk/page13/files/Mixture Magic.pdf


JonJay

I do agree that it would take a pretty naive pilot to kill a Lyc IO360, but the IO540 is just a 360 x 1.5, and I can assure you I have had a cylinder or two go into mild detonation. The beauty of all cylinder monitors showed the rapidly rising CHT, it was traced back eventually to mixture control cables from Van's not being long enough, the engine rubbers sagging and the mixture cable bracket flexing enough that the mixture was being leaned on takeoff just enough. This dispite the lever was full forward on the stop.

Sure the couple of events we saw while trouble shooting (3 or 4) did not do any damage, we have scoped and watched these cylinders closely since, but had this engine been equipped with 1xEGT and 1xCHT gauge we would have blissfully flown on forever. Another 1000 hours and we may have had two cylinders junked half way to TBO. Who knows??? :confused: Either way it can not be good.

By the way our CHT's in the cruise are all around 300-310F and when its warmer 320-330F. So a CHT rising through 380-400 all by itself in a matter of seconds really gets your attention.
 
RV10inOz said:
Bavafa



I do agree that it would take a pretty naive pilot to kill a Lyc IO360, but the IO540 is just a 360 x 1.5, and I can assure you I have had a cylinder or two go into mild detonation. The beauty of all cylinder monitors showed the rapidly rising CHT, it was traced back eventually to mixture control cables from Van's not being long enough, the engine rubbers sagging and the mixture cable bracket flexing enough that the mixture was being leaned on takeoff just enough. This dispite the lever was full forward on the stop.

Sure the couple of events we saw while trouble shooting (3 or 4) did not do any damage, we have scoped and watched these cylinders closely since, but had this engine been equipped with 1xEGT and 1xCHT gauge we would have blissfully flown on forever. Another 1000 hours and we may have had two cylinders junked half way to TBO. Who knows??? :confused: Either way it can not be good.

By the way our CHT's in the cruise are all around 300-310F and when its warmer 320-330F. So a CHT rising through 380-400 all by itself in a matter of seconds really gets your attention.
Click to expand...

I believe you. Personally I would not try to run LOP without individual cylinder monitoring. You can not balance your injectors without that data either.
 
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