Why I No Longer Fly Lean of Peak For Now

[RyanB]

Personally, if my O-320 didn't run smoothly LOP-WOT, I'd just operate it at 150°F ROP (peak power/RPM), which is always clear of the red zone at cruise power settings, and then just learn to live with the elevated fuel consumption, reduced range/endurance, and higher risk of CO poisoning when I'm using the heater in winter.

How so? If your exhaust manifold is in good condition, than it shouldn’t make any difference.

 

[wayne]

High time TCM cylinders usually fail rotorcoils.....and most folks don't know what those are....and LOP gets the blame. Rotorcoils are a cheap item, about $25 ea, and they reside on the top of the exhaust valve spring stack. With each spring compression they "rotate" the exhaust valve....allowing the valve to evenly heat and cool. Once the valves stop rotating the classic burnt valve begins.....and LOP gets the blame.

If this is your first time hearing this .....make sure you replace the rotorcoils every 500-600 hrs. Or you will burn a valve and be into repairing cylinders.

What's the labor effort like on that work?

 

[Tom-D]

Sorry to hear you've had that experience. That could certainly happen if #3 cylinder is running richest, the operator routinely operates at 75% power, and they lean only a little bit (not enough) because they're trying to avoid roughness. In the absence of an engine monitor, you have to lean as far as physically possible (LOP-WOT), so that you'll know if one of the cylinders is still rich (if so, the engine will vibrate like crazy, because of the steep power drop-off on the lean side).

Or even better, install an engine monitor, as some O-320 and O-360 owners do, then you'll be able to be certain that you're not operating any of your cylinders in the red zone around 50°F ROP.

I'd also be curious to know how many of those engine owners weren't actually operating LOP, but just "leaning to roughness and then enriching slightly", or "leaning to peak RPM and then a little more", both or which can be recipes for landing right on 50°F ROP and peak CHT.

My opinion... none of the 4 cylinders carb'ed engine will run as well as a injected engine with calibrated nozzles
you will have 1 or more cylinders too rich.
carbs have one place to enter fuel, no 2 cylinders will run the same.
It is just a fact of engineering.

 

[Checkout_my_Six]

What's the labor effort like on that work?

Bout 30-40 minutes per cylinder. Sure is cheaper than replacing a cylinder.

 

[David Megginson]

My opinion... none of the 4 cylinders carb'ed engine will run as well as a injected engine with calibrated nozzles
you will have 1 or more cylinders too rich.
carbs have one place to enter fuel, no 2 cylinders will run the same.
It is just a fact of engineering.

I agree they won't run as closely, but do you not agree that an excessively-wide spread will be very noticeable on the lean side, where the power drops off more steeply? If your leanest cylinder is far LOP while your richest cylinder is still ROP, you're looking at a difference of maybe 10–15% power output among the cylinders, and there's no way that won't be trying the shake the fillings out of your teeth at cruise power.

 

[David Megginson]

FWIW, I've also heard lots of reports of #3 cylinder running hot even far ROP of the red zone (from people with engine monitors), so it might we worth taking a close look at the baffling to see if there's more at work than just the mixture setting. After all, many pilots don't fly above 65% power, and at that point, the cylinders will be cool/lower pressure at any mixture setting.

 

[AA5Bman]

After going from a ROP to LOP devotee, I have finally arrived at peak simplicity in terms of operating my engine: fly high, where the engine can only make about 60% power, and lean to wherever you feel like. Lean further to cool things down, generally, and push it in to go faster. Works for me!

 

[smv]

LOP works on certain 4-cylinder carbureted engines, because it's possible still to get fairly-even fuel/air distribution to all 4 cylinders. Lycoming's O-320 is a very good example (to the point that Piper even recommends LOP operations in my PA-28-161 POH).

I am curious what is the revision date on your POH. Mine was issued December 16, 1976 and the latest revision date is November 20, 1981 and says pretty much exactly the opposite.

 

[Pugs]

We've had this discussion a bunch in my club in particular about the carbureted O-540 in the 182RG. It has a JPI so you can lean it pretty carefully for LOP and that's the current recommendation.

The driving factor in the club's mind is the cost of fuel (since we charge wet) vs the potential of having to replace a cylinder is worth the lower fuel flow.

That plane gets flown a lot, I don't have a report on it but easily 250+ hours a year @ $190 (tach)/hour with local fuel currently $5.45 a gallon so I won't argue with them. If it was my own plane I reserve the right to another answer.

 

[k9medic]

In Cheroke 6/260, I lean it to a fuel flow rate when the power is set at 22/2300. Whatever that gets me is what it is. The book calls the power setting 65%. I'm not sure if that's LOP or ROP and really don't care.

The CHT's are always under 400. The EGT's are always under 1400 and my fuel flow hovers around 13gph.

 

[David Megginson]

I am curious what is the revision date on your POH. Mine was issued December 16, 1976 and the latest revision date is November 20, 1981 and says pretty much exactly the opposite.

View attachment 91341

Warrior II Information Manual, P/N 761 780, 1982 (with later revisions). It's the same revision that increased the max gross weight for the PA-28-161 from 2,335 lb to 2,400 lb. I don't see 4-27 in the later revisions list, so they must have added that passage about LOP-WOT ops right in 1982. That's pretty impressively early for recognising LOP operations (the trend didn't really get going for general aviation until the late 1990s, aside from a few pioneers — before that, manufacturers assumed light-piston pilots were just to stupid to operate their engines in any way that wasn't brain-dead simple, as illustrated by the passage you quote from the earlier manual).

 

[George Mohr]

LOP vs ROP vs Peak only matters if flying at higher power settings. We operate our O470U at peak EGT at 65% power for most cruise operations. Getting fussier is just not worth it due to the fuel distribution. I also like some other folks suggestions that ROP in a carbureted engine at higher power settings had better do more then 50 deg F. The distribution differences will cause some of those cylinders to operate in "the red box".

 

[smv]

Warrior II Information Manual, P/N 761 780, 1982 (with later revisions). It's the same revision that increased the max gross weight for the PA-28-161 from 2,335 lb to 2,400 lb. I don't see 4-27 in the later revisions list, so they must have added that passage about LOP-WOT ops right in 1982. That's pretty impressively early for recognising LOP operations (the trend didn't really get going for general aviation until the late 1990s, aside from a few pioneers — before that, manufacturers assumed light-piston pilots were just to stupid to operate their engines in any way that wasn't brain-dead simple, as illustrated by the passage you quote from the earlier manual).

Ahhh... I see the difference now. You manual is for model years 1983-1994 whereas my manual (Part number 761-649) is for model years 1977-1982. Seeing as how we are flying a 1977 vintage, I think we will stick with the POH from that era.

Closer review of the revisons in my manual shows that the latest revision is Rev. 13 -761 649 (PR900913) signed October 1990.

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[David Megginson]

Ahhh... I see the difference now. You manual is for model years 1983-1994 whereas my manual (Part number 761-649) is for model years 1977-1982. Seeing as how we are flying a 1977 vintage, I think we will stick with the POH from that era.

Closer review of the revisons in my manual shows that the latest revision is Rev. 13 -761 649 (PR900913) signed October 1990.

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Same plane, but obviously, your call. I wouldn't advise anyone to operate their engine outside their comfort level.

Have you applied the STC to increase the gross weight to 2,400 lb? If so, the STC does require you to carry the newer PIM in the plane for performance numbers (but not, of course, to reference the note on LOP-WOT).

That's the difference between the two POHs — the 1983 PA-28-161 authorised a max gross weight increase to 2,400 lb to (very belatedly) acknowledge the increase to 160 hp. Earlier PA-28-161s were still stuck with the max gross weight of 2,335 lb from the older 150 hp PA-28-151. To fly at 2,400 lb with a 160 hp PA-28-161 from 1982 or earlier, you need to get a paper-only STC (no physical alterations required).

 

[smv]

Same plane, but obviously, your call. I wouldn't advise anyone to operate their engine outside their comfort level.

Have you applied the STC to increase the gross weight to 2,400 lb? If so, the STC does require you to carry the newer PIM in the plane for performance numbers (but not, of course, to reference the note on LOP-WOT).

That's the difference between the two POHs — the 1983 PA-28-161 authorised a max gross weight increase to 2,400 lb to (very belatedly) acknowledge the increase to 160 hp. Earlier PA-28-161s were still stuck with the max gross weight of 2,335 lb from the older 150 hp PA-28-151. To fly at 2,400 lb with a 160 hp PA-28-161 from 1982 or earlier, you need to get a paper-only STC (no physical alterations required).

I see what it happening here... The PDF POH I downloaded for ease of quick reference is the older version. The actual physical copy in the airplane is the correct, updated, version. I never did look at the PDF version for specific values and see now that it still shows the lower max gross. I need to update my PDF version and all will be right again.

 

[capg2000]

Wow! A whole lot of S*** here. As everyone sees it, carbed is ROP...
I have almost 1100 hrs on O470R. Factory remained, all new cylinders... I'm in Fla. CHT s run high at 375. I run ROP, +/_ 30. Cylinders all show mid-low 70s. For a Conti, that's not bad. Never pulled a Cyl.
Bore scoped 2 yrs ago. All clean. Oil analysis every change....

 

[David Megginson]

Wow! A whole lot of S*** here. As everyone sees it, carbed is ROP...

A good number of the pilots on this forum will be surprised to hear that it's impossible to fly LOP with a carbureted engine, because they've been doing it for years. Nothing wrong with ROP if that's what you prefer, of course, or if your engine (carbureted or injected) won't run smoothly LOP.

 

[smv]

Have you applied the STC to increase the gross weight to 2,400 lb? If so, the STC does require you to carry the newer PIM in the plane for performance numbers (but not, of course, to reference the note on LOP-WOT).

After confirming the STC was actually applied to this aircraft, the next time I flew I tried the leaning procedure given in the "new" POH but it simply did not work as advertised. There never was an increase in RPM. It simply goes from smooth to rough without an increase. Weird thing is, I know leaning works because while leaning on the ground we get a slight increase in RPM before it starts running rough.

 

[David Megginson]

After confirming the STC was actually applied to this aircraft, the next time I flew I tried the leaning procedure given in the "new" POH but it simply did not work as advertised. There never was an increase in RPM. It simply goes from smooth to rough without an increase. Weird thing is, I know leaning works because while leaning on the ground we get a slight increase in RPM before it starts running rough.

That's very interesting -- usually RPM will go up a bit before it goes down. You didn't even see a bump of, say, 25 RPM before it started running rough? Peak power occurs around 150°F rich of peak, so this has nothing to do with LOP ops.

 

[smv]

That's very interesting -- usually RPM will go up a bit before it goes down. You didn't even see a bump of, say, 25 RPM before it started running rough? Peak power occurs around 150°F rich of peak, so this has nothing to do with LOP ops.

Notta... Tried it multiple times. Even starting at 2300 RPM in level cruise and pulling back real slow it simply goes from smooth to rough with no increase.

 

[David Megginson]

Notta... Tried it multiple times. Even starting at 2300 RPM in level cruise and pulling back real slow it simply goes from smooth to rough with no increase.

Maybe some of the engine specialists on the list can comment -- what could cause an engine with a fixed-pitch prop not to show an increase in RPM when you lean it from full rich towards 150°F rich of peak EGT? Or conversely, what could cause roughness on the rich side of 150°F ROP?

 

[smv]

Maybe some of the engine specialists on the list can comment -- what could cause an engine with a fixed-pitch prop not to show an increase in RPM when you lean it from full rich towards 150°F rich of peak EGT? Or conversely, what could cause roughness on the rich side of 150°F ROP?

To be clear, there is no EGT so where it sits on the ROP/LOP scale is anyone's guess.