LOP Operations

[AndreiC]

Okay, I have to say that I am thoroughly confused. Here is my experience so far, documenting all the things I have heard from various people I respect, but which contradict each other mightily.

1) On my previous plane, a Cherokee 180 with the O-360, I worked with the 'lean until rough and then increase the mixture 1/2"' approach. That gave me 8-9 gph depending on altitude, running at 2400 rpm. No engine monitor, no CHT/EGT whatsoever. After 1600 hours SMOH the engine compressions were 74 or better, no troubles with the engine. I believe this was LOP, because of the low fuel flow, but I can't confirm that.

2) On my current M20E (IO-360) I have a 4-cylinder digital monitor for both CHT/EGT, and I lean using the "lean-find" option. The temp spread in EGT between the cylinders is about 50 degrees in cruise.

The 60 y/o main pilot at my field (third generation of pilots operating this kind of engine, his grandfather started the airport I am based at; they operate a fleet of about 6 172's with the IO-360) said he does not believe in LOP operations, but his father swears by them, as long as the engine is operated below 60-65% power. They teach student pilot to lean until rough and then move the red know 1/2" forward.

On my Mooney running 25 degrees LOP at 6500 pressure altitude gives me about 8.5-8.8 gph running WOT and 2400-2450 rpm, which I believe is about 70% power. When I actually flew in very hot weather (95 degrees OAT at 6500 feet) LOP was the way to go to keep oil temps lower. I get about 135 knots at this setting.

3) Running at peak EGT gives me about 9.3 gph at the above settings, maybe 1-2 knots faster than LOP. When it's not too hot outside I've been running most of the time at this setting, because I am a stickler for engine manufacturer recommendations, and Lycoming is against running LOP.

4) The mechanic who just did my first annual, Eric Rudningen at Oasis Aviation at Willmar Airport told me that he recommends *not* running at peak EGT because that is where the internal cylinder pressures are the highest. He said to run it at about 25-50 degrees ROP, which should give me 10.5 gph. This was rather strange to me (everyone else seems to suggest that 25 degrees ROP is exactly what should be avoided, be either LOP or 100 degrees ROP). Nevertheless I gave it a try, but fuel flow at 6500 ft, WOT, 25 degrees ROP was about 10.5 gph, while 50 degrees ROP was closer to 11 gph. To get to 100 degrees ROP as listed by Lycoming for best power I needed to be close to 12 gph. At 10.5 gph I saw 148 knots TAS.

I honestly don't know whom to believe now. I would be curious what other people think of my experience, if it is typical, and what settings are fine.

Edited October 11, 2023 by Andrei Caldararu

[EricJ]

11 hours ago, KSMooniac said:

"On a Lycoming IO-360, if you lean until it gets rough and then enrich slightly until it just gets smooth you are LOP."

May or may not be correct. As a blanket statement, it is wrong, though.

On a Lycoming it is generally correct, and it is often less helpful to complicate a response to a simple question by outlining all of the less likely exceptions for corner cases.

11 hours ago, KSMooniac said:

"  Monitor your CHT gauge just to make sure whatever you're doing isn't overheating it."

Partially good advice, but not sufficiently correct either to avoid potential engine damage. You can't lean solely by CHT and be sure you're not at a bad mixture setting that could be really hammering your engine.

The OP does not have an engine monitor, and in the context of the original question with limited instrumentation the actual response of:

"You should have an EGT gauge that just measures one cylinder, and if you have a fuel flow meter you can use those to get a decent idea of where the engine likes to run.   Monitor your CHT gauge just to make sure whatever you're doing isn't overheating it."

is pertinent to maximize the use of the limited instrumentation available without an engine monitor.    Monitoring CHT is prudent because if the CHT on the instrumented cylinder is excessive it is a good indication that a change needs to be made.

Yes, there are exceptions, and, yes, no post on an internet forum is expected or able to cover all of the potential permutations of possible conditions where things might go wrong.   Keeping the tradeoff between simple and useful and overly complicated responses is always a challenge on un-refereed forums.

[KSMooniac]

37 minutes ago, Andrei Caldararu said:

Okay, I have to say that I am thoroughly confused. Here is my experience so far, documenting all the things I have heard from various people I respect, but which contradict each other mightily.

1) On my previous plane, a Cherokee 180 with the O-360, I worked with the 'lean until rough and then increase the mixture 1/2"' approach. That gave me 8-9 gph depending on altitude, running at 2400 rpm. No engine monitor, no CHT/EGT whatsoever. After 1600 hours SMOH the engine compressions were 74 or better, no troubles with the engine. I believe this was LOP, because of the low fuel flow, but I can't confirm that.

That is not LOP on a 180 HP engine, which I presume is the case.

2) On my current M20E (IO-360) I have a 4-cylinder digital monitor for both CHT/EGT, and I lean using the "lean-find" option. The temp spread in EGT between the cylinders is about 50 degrees in cruise.

EGT temp difference doesn't mean much, only what fuel flow is when each individual cylinder reaches peak.  Ideally all reach peak at the exact same fuel flow.

The 60 y/o main pilot at my field (third generation of pilots operating this kind of engine, his grandfather started the airport I am based at; they operate a fleet of about 6 172's with the IO-360) said he does not believe in LOP operations, but his father swears by them, as long as the engine is operated below 60-65% power. They teach student pilot to lean until rough and then move the red know 1/2" forward.

Mixture setting below 60-65% power doesn't "hurt" anything, but there are good and less good settings.    Lean until rough and enrichen is a dumb way to do it, frankly.  Mine does not get rough at all until it quits, so that does not work for me.  "Rough" could be variable depending on what kind of shape the engine is in in terms of ignition health, induction leaks, etc.  

On my Mooney running 25 degrees LOP at 6500 pressure altitude gives me about 8.5-8.8 gph running WOT and 2400-2450 rpm, which I believe is about 70% power. When I actually flew in very hot weather (95 degrees OAT at 6500 feet) LOP was the way to go to keep oil temps lower. I get about 135 knots at this setting.

8.8 GPH for your IO-360 is a 65.6% power setting while LOP, which you likely are at that altitude and fuel flow with WOT.  That is an excellent way to keep the engine cool when OAT is that high.

3) Running at peak EGT gives me about 9.3 gph at the above settings, maybe 1-2 knots faster than LOP. When it's not too hot outside I've been running most of the time at this setting, because I am a stickler for engine manufacturer recommendations, and Lycoming is against running LOP.

Peak is fine at 60-65% power, lean a bit more if very hot outside and/or your CHT's go above 380.  

4) The mechanic who just did my first annual, Eric Rudningen at Oasis Aviation at Willmar Airport told me that he recommends *not* running at peak EGT because that is where the internal cylinder pressures are the highest. He said to run it at about 25-50 degrees ROP, which should give me 10.5 gph. This was rather strange to me (everyone else seems to suggest that 25 degrees ROP is exactly what should be avoided, be either LOP or 100 degrees ROP). Nevertheless I gave it a try, but fuel flow at 6500 ft, WOT, 25 degrees ROP was about 10.5 gph, while 50 degrees ROP was closer to 11 gph. To get to 100 degrees ROP as listed by Lycoming for best power I needed to be close to 12 gph. At 10.5 gph I saw 148 knots TAS.

25-50 ROP IS THE WORST PLACE TO RUN YOUR ENGINE ABOVE 60% POWER.  Most mechanics are not pilots or engineers or understand what is really happening inside the engine.  100 ROP for cruise power is fine... a bit faster, a lot more fuel and a lot more load on your engine in terms of heat and pressure.  

I honestly don't know whom to believe now. I would be curious what other people think of my experience, if it is typical, and what settings are fine.

www.advancedpilot.com will help you gain the knowledge you seek to fully understand what is going on under the cowl.  And then you could try to enlighten others on the internet, or argue with folks that don't know or understand.    It is the most efficient and effective way to learn all of this stuff really well.

 

[0TreeLemur]

A good read for you @Andrei Caldararu

https://www.avweb.com/ownership/the-savvy-aviator-59-egt-cht-and-leaning/

[KSMooniac]

3 minutes ago, 0TreeLemur said:

A good read for you @Andrei Caldararu

https://www.avweb.com/ownership/the-savvy-aviator-59-egt-cht-and-leaning/

You'll note early on in his column that he recommends the advancedpilot.com seminar/webinar!  He deviates from their excellent advice on leaning, though, and uses CHT which is not a great idea.  It would be best for every owner to take the seminar themselves and decide on their own, instead of just follwoing random internet advice from strangers.

[ArtVandelay]

… run through the sump which warms the air improving the vaporization of the fuel before it gets to the cylinders.

Is that one of the reasons hot starts are so problematic?

[Echo]

13 hours ago, KSMooniac said:

Every pilot and especially owner should take the www.advancedpilot.com seminar and really learn what is going on with the red knob of death. There are a lot of wrong answers on this thread already, and those that have really learned the topics know.

There is too much to cover in forum format to really teach the fundamentals.

Sent from my LM-V600 using Tapatalk
 

That is a touch dramatic don't you think?

[PT20J]

29 minutes ago, ArtVandelay said:

Is that one of the reasons hot starts are so problematic?

I doubt it. Starting is more a fuel and spark issue. The electronic ignition systems produce a stronger spark and some find that helps starting. The newer light weight starters turn faster and that also seems to help. Massive electrode spark plugs can have the spark buried deeper from the plug tip, so fine wires or BY plugs may improve starting. 

But getting enough fuel without flooding is the most critical factor in a hot start. For me, I always begin with no prime and the mixture in ICO. Then, as I crank, if it doesn’t immediately fire, I slowly advance the mixture control until it starts. 

Here’s the explanation from the RSA manual.

[Echo]

I returned from northern Wisconsin this morning.  I climbed at 2400rpm and 2350MP full rich at 120mph.  280 was warmest cylinder.  NOT 380...280.  Leveled out at 6500 and did big pull to rough and enrichened to smooth.  MP about 23 Full throttle.  No cylinder temp issues.  Ground speed was 170-180mph.  TAS on Aspen said 175.  I could not be happier with the engine.  My guess is 90-9.5GPH.  I was right between this sheet: see attached

[Fly Boomer]

8 hours ago, Andrei Caldararu said:

I honestly don't know whom to believe now. I would be curious what other people think of my experience, if it is typical, and what settings are fine.

Your experience on a public Internet forum is perfectly normal and expected.

[Pinecone]

19 hours ago, Andrei Caldararu said:

because I am a stickler for engine manufacturer recommendations, and Lycoming is against running LOP.

You say that they are against is, but the chart posted earlier in this thread, FROM LYCOMING, says otherwise.  It clearly shows LOP for best economy.

Your POH is 40 - 50 years old.  Fuel was cheap, running ROP at best power was a good thing.  And the manufacturers advice chnages over time also.  The APS guys found that the Continental manuals in the early 60s talked about and recommended LOP operations.  But most POHs did not mention it.  At some point it came out of the Contenintal manuals, but AFAIK it is back in.

Also, do you follow the guidance of the company that made the engine or the airplane?

If you are running at peak, make sure you are under 65% power.  65 - 75% is a grey area and over 75% you are in a range where you can damage your engine.

Here is what your pistons may look like after some detonation.