Caution - Religious discussion, click here only if you can handle this topic.

[D55Baronpilot1]

That is a great byline, I'm a LOP person in my continental engines. My previous A36 LOP went over 2000 strong hours!

 

[Racerx]

5000ft when it 100f on the ground is a little different than when it is -20f.
So, yeah, I call BS

Tim

I believe Lycoming used density altitude

 

[Racerx]

View attachment 153840

Can we at least update to the current pope?

 

[Sac Arrow]

Idle needs a higher mixture than the normal mixture setting at "full rich" typically will provide. On the carbs, they just have an alternate path for dealing with the low power settings so the mixture becomes largely spurious.

On the injected Continentals, the mixture works all the way down, but there's an additional "mixture rise" adjustment that raised the mixture over the "full rich" at idle settings. There's a whole procedure for calibrating it. Getting this wrong often leads to the engine dying on landing when the throttle is full back once you slow down.

Stated another way, the air flow through a carburetor at idle isn't sufficient to pull fuel in to the jet via the venturi effect, so the idle bypass allows fuel to be drawn directly from the manifold vacuum.

 

[Rick A]

I don't follow Mike Busch so have no opinion regarding his views, but FWIW my positive LOP experiences are similar to what other pilots have also had compared with their own ROP and LOP operations and issues.

Statistically in my realm of contacts, it's a small pool of long term operators who have operated both ways. However I've never heard of any cooked or ruined engine stories that can be definitely attributed to properly equipped aircraft with pilots trained to operate LOP at lower power outputs, reduced airspeeds, and obtaining corresponding lower cylinder and oil temperatures.

Following thousands of ROP flight hours with Lyc IO-360's, I took a gamble and leap of faith and installed GAMI's.

The following is a list of engine operating / maintenance experiences following 40 years of flying 3 different Mooneys, all pampered, and all powered with IO-360's.

During the ROP years (which represent more hours flown per year), in accordance with Lycoming operating parameters and recommendations:
1 Loose exhaust valve (from carbon build up on the valve guide) resulting in a forced landing and reworked cylinder
Multiple fouled massive spark plugs
1 case of glazed cylinders cruising at mostly 75% power
2 clogged fuel injectors (during the same incident occurring during a winter takeoff) resulting in a forced landing
Dirty oil & oil consumptions never better than 1 quart per 8 hours after break-in, then getting worse

Since operating LOP for 2000+ hours (@ less hours per year than flown during earlier ROP ops) at 60% to 70% power output (saving 2-3 gallons of fuel per hour)
No cylinder maintenance required
Cleaner oil and significantly less oil consumption (starting at 15 hours per quart when broken in and slowly dropping after 950+ hours)
5-10 kts slower during cruise (depending upon altitude) than when ROP at 75% power
Lower cylinder and oil temps
No fouled spark plugs

Based upon the above personal experiences I can't find any reasons to go back to operating ROP, except to go a little faster and burn more fuel with higher cylinder temperatures with greater potentials to spend more on maintenance. I view Lycoming recommendations as outdated and developed in an era that lowered the bar for everyone in order to protect an engine when fuel, parts and labor were not priced so crazy. To each their own...

 

[Ed Haywood]

Let's just skip all this nonsense and go straight to high vs low wing.

Or training wheels vs tailwheels.

 

[Tools]

J

All limits are arbitrary to some extent. The speed limit is not 65 because you die at 66. Cylinders don't melt at 501 degrees. Some smart people sit down and come up with a threshold, like "above 5K you lean for T/O, below you don't" and we accept it as earned wisdom. That works out pretty well for much of life, and is more practical than everyone making up their own limit.

Just as many arbitrary compromises are ENGINEERED into our machines… basically invisible to us. Not easily or legally optimized or even changed, so we just ignore them.

Perhaps ignorance is bliss?

 

[BigghHauss78]

This type of conversation always catches my attention to the point of compelling a response. I have owned a few Cessna 182's, both with Continental engines, have had to swap out cylinders on one due to warranty issues, plus I and am highly involved with my maintenance. I don't at all portend to be an 'expert' on any of these subjects here discussed. But I wanted to comment on a few things that I see, that frankly, I don't agree or understand why the authors of these comments feel this way.

Mike Busch: I don't get the hot/cold with him or why some say his stuff is 'Gospel', where others view it as garbage. I view him as an experienced A&P/IA, who discovered an engine management style while conducting his career business and wants to share what he believes is a positive. It's further obvious that his information is well heeled, which has been confirmed with his work with GAMI and their engine test cell, coupled with the history of this approach, and the subsequent real world applications of that approach. Further, to suggest he has no 'skin' in the concept I think is a bit ludicrous for he clearly fly's his engine LOP, and I'm assuming the airplanes he services and is responsible for, I'm sure he suggests the same meaning their is definitely skin in the game. I find his approach informational, with good data to support, and not wrapped up in 'old wives tales' or purely anecdotal.

LOP vs ROP: There clearly is quite a large data set created that supports both and its steeped with history going back some 80 years. After reading the Lycoming letters, etc., I feel the issue is that pilots don't know how to properly get into LOP, and thus are flying thinking they are LOP, when maybe they are right at peak resulting in burning up engines, instead of getting correctly into the LOP side of the equation. Seems like Lycoming is saying 'stay away from trying to even find LOP, and always run it fat on fuel, otherwise you're on own.' I say do what you feel works for you and your engine, and be happy with your decision, but don't be blasting others who may not agree.

Regarding the comments around Busch's disdain of A&P's: I feel its coming from being an Owners advocate versus the A&P's advocate. And I'll provide you an absolute recent example. My buddy has a 182 that went into Annual. This A&P/IA decided, of his own accord to do a full on cam borescope inspection which is not contained in the Annual Service Checklist nor discussed prior with the owner. Mind you, his compressions were all 75+ on each cylinder, no issues reported (not making metal, no compression or power loss, engine has less than 150 since OH), and not burning oil, running hot, etc. Now, I can't find anywhere that suggests a cam inspection via borescope is at all part of the annual, our would be warranted given the lack of symptoms, but he did it anyway. During this extra inspection, he found spalling on some lifters, as well as possible cam corrosion. This was also in addition to what appears to be some cylinder wall corrosion. He immediately told my buddy he needed a new engine, airplane is not airworthy, and had already put out the calls to find said new engine as well as sent pictures to an engine rebuild company, who said its dead and needs replacing (shocker). My buddy, who is a new aircraft owner with no real mechanical understanding of engines called me with the bad news. I immediately asked him to share pictures, and we met to discuss.

I expressed my frustrations with his decision to go above and beyond the annual requirements but now that he was pregnant with the new information, a path needed to be found recognizing there may be a blessing in disguise here. The pictures showed spalling was apparent on some lifters. The cam corrosion seemed pretty minimal and I felt was only on areas of the cam 'off lobe', meaning, on parts of the lobe where the lifters didn't touch. Further, I felt his cylinders just needed to be ran, and would clean up pretty quick as the crosshatching was in good shape and just had some minor surface corrosion. I pulled up the Continental SID, as well as recommended he contact Savvy and get their take on the situation. After our conversation, he signed up immediately, sent them all the pictures, and they returned to him a very robust guide on how to present the suggestions to the mechanic. The guidance received was to swap lifters, utilized the SID for the cam, and just run the cylinders. My buddy presented this to the mechanic who seemed very reluctant at first and continued to contend the Cam was completely shot and would not be willing to award airworthiness otherwise. However, after discussing the notes provided by Savvy, etc., he decided to contact Continental and would ONLY proceed with their blessing, otherwise, my buddy was SOL. Continental came back and said the Cam would be ok and to inspect after 100hrs. They did suggest some of the lifters would need replacing, and cylinders were of no concern. The mechanic was still somewhat hesitate about the results, but ultimately agreed to replace ALL lifters, as and then would finalize the Annual.

My point - Savvy seemed to be the only one in this entire chain willing to stand up for the owner. So when I hear stories about mechanics taking advantage of owners, I literally just saw it happen. The only way this mechanic was willing to listen was AFTER my friend presented the steps suggested by Savvy. In this case, the $150 spent for the set of eyes from Savvy and suggested plan of attack saved my buddy from a completely unnecessary engine Overhaul, and reduced it to just some lifter work and a run/observe approach. Luckily, this particular mechanic was willing to be open and in the end it all worked out. I think though, what if my buddy hadn't called me, or even knew to contact Savvy or ask the questions I was asking?? He'd be out an engine based purely on this mechanics advice.

To put a button on this post is this: I personally find the information valuable. I think there has been exhibited enough well reviewed data that suggests a properly ran LOP operation can be beneficial from both a mechanical standpoint, as well as an efficiency standpoint. The issue is getting to that can be difficult, and is probably responsible for smoking some engines along the way. It seems to work well with tuned injectors on a fully digitized engine, and thus, makes sense. For those carbureted guys, or those lacking the multi-point data, then should probably pass and keep it fat. I just don't understand the heated passion around this subject. But what do I know is that I'm just an owner pilot trying to keep the prop turning, and wings in the air.

 

[Roger Wilco]

Of course I didn’t. But like my A&P and unlike people like Busch, I was definitely, personally on the hook for the decisions I made with the data for the patient/airplane in front of me. That’s why I had liability insurance. I doubt Busch needs that.

LOL. Yeah. He’d have hurt feelings. Not much more.

Add: there are those who follow Don Gryder religiously as well and he’s not always wrong.

One “beef” I have with Busch is his seemingly relentless public attacks on other A&Ps in the name of promoting his services. I get frequent emails from Savvy bragging about the tens of thousands of dollars they’ve saved some pilot from the opinion of some dastardly A&P. The stories may be true - they also seem disingenuous.

Very well then: You dislike Mike Busch for...reasons. Fair enough.

My objection to your posts originates with #24 in which you wrote, "I’m a physician and . . ." When you whip out the credentials, I expect to be dazzled with brilliance, not baffled with bullxxxx. If, trading on those estimable credentials, you do not follow-up with a rational argument based on fact and data but instead merely indulge your personal opinion, then you just inject more noise into an ever-weakening signal.

Further, you compare Busch to Dan Gryder. That, sir, is a low blow. But can you see how, from my perspective, post #24 puts you in that same select coterie for the reasons stated above (and in my previous posts)?

As for the ROP/LOP argument, as a MM in music composition, I really don't care. And, as a retired airline pilot, don't get me started on Foucault.

 

[Llewtrah381]

So...

First, as stated earlier, I've never dissed LOP operations and, although I only have a lowly normally-aspirated O-360, I've seen where I could lean even that engine to below peak EGT and see the CHTs start to drop. If I had a fuel injected engine with GAMIs I'd operate LOP consistently.

Aside from my dislike for how Savvy chooses to advertise by bashing other A&Ps, justified though the criticisms may often be, my biggest "disagreement" is over the "red box"/"red fin" stuff. I've seen too many people (my retired AF A-10/F-16 pilot brother who flies a Lycoming-powered Lance included) seem downright fearful of having their Lycoming go above 400 and aren't comfortable until CHTs are below 380 or so, all based primarily on Savvy teachings.

My highly scientific ChatGPT search of "what is the data behind the "red box" Mike Busch speaks of?" gave this answer: https://chatgpt.com/c/6a6b9633-fc48-83ea-a9c5-abfb9fc90e30

The box is "conceptual" as even Savvy says and the highest CHTs shown in at least the graphs I've seen peak out in the low 400's. I haven't seen whether that's for Lycoming or Continental but even Continental gives 400 as a "preferred" max with a redline of 460 yet their purple "ultra abusive" box starts at 400. I'm not following how that's "ultra abusive", even for a Conti.

The ChatGPT search included the following:
"Why is that region considered dangerous?

At high power:

• combustion pressure is highest,
• combustion temperatures are high,
• detonation margin is smallest,
• CHT tends to climb,
• piston crown temperatures increase.

These conditions make detonation and preignition much more likely."

I haven't found any explanation for the harm or "ultra abuse" of operating in the "purple box" for these parameters. To me, the most imminently threatening thing listed is detonation margin. OK - it's "smallest"; is it a risk, though? For my O-360, whenever I talk about leaning, etc. with pretty much any A&P and express pretty much any concern about detonation risk, they typically blow off the risk in that engine. I may be wrong but I sense Braly was trying to validate that operating LOP wouldn't unduly raise the detonation margin when using his injectors, which drove his testing of the issue.

Savvy says CHT is actually a proxy for internal cylinder pressure. But CHT is affected by more than just ICP. Bad baffling, high OAT, and a handful of other things will raise CHT without ICP being raised. Basically, there are times when CHT can be above desired temps yet ICPs will not be unduly high. CHT is not a perfect proxy for ICP and ICP is the "real" threat (debatably, other than metallurgy and temps).

I've heard mention of people being concerned about the cylinder metallurgy and temperature - that it loses X% of its strength at y degrees. I haven't been able to find good data for that and am not sure if that's linear (I doubt it) or exponential. I'm sure the data is out there - I just haven't seen it. So, I'm not sure if any temp below the manufacturers' limits (460 for Conti, 500 for Lycoming) reduce strength to a significant, worrisome degree relative to the ICPs involved.

Per the manufacturer, my O-360 "For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operation and below 400°F (205°C) for economy cruise powers." I'd like to know the actual data behind people's fear of operating between 400 and 435. What specific issues have arisen as a direct result of operating in that range?

Also from the ChatGPT result:

"Is there published raw data?

This is where the discussion becomes controversial.

The underlying pressure measurements were obtained during years of proprietary GAMI engine-cell testing. While many pressure traces and graphs have been presented in:

• APS (Advanced Pilot Seminars)
• GAMI presentations
• EAA articles by Mike Busch
• articles by George Braly

the complete experimental dataset has never been publicly released in a peer-reviewed form.

Has anyone challenged the Red Box?​

Yes. Critics have argued that:

• the exact boundaries vary by engine model,
• ignition timing changes the location,
• compression ratio matters,
• fuel octane matters,
• induction balance matters,
• cooling system design matters.

Even Busch acknowledges these limitations. In later articles he describes the red box as a conceptual guide rather than a sharp boundary and notes that CHT, OAT, cooling efficiency, and other factors affect how it should be interpreted." (italics and underlining are mine; the bold is the bot's)

THAT's my verbosely-stated frustration with Savvy and the CHT topic. A "concept" has morphed into a sense of hard rules. And it seems likely the whole box was developed to validate LOP with GAMIjectors was safe when CHT was managed; applying the box to other situations may or may not be as relevant - not sure.

And again, the thread title is a good one.

 

[Sac Arrow]

haha he said red box

 

[wayneda40]

Just so credit is given where due...

John Deakin's the one who popularized the Red Box/Fin concept — his Pelican's Perch columns on AvWeb are where most pilots first ran into the term, and it's often attributed to him alone in forums and casual references as a result. But credit-wise it's really an APS/GAMI group product along with George Braly and Walter Atkinson.

AvWeb: Feb. 2, 2003 — Pelican's Perch #65: "Where Should I Run My Engine? (Part 3 — Cruise)," published Feb. 2, 2003, is the article that introduces the "red box" (also referenced in reader summaries as "The Dangerous Red Box"). That's the first Deakin column that names and lays out the concept — parts 1 and 2 in the same series (Dec. 2002, Jan. 2003) set up the discussion but the red box itself shows up starting in #65.

 

[Martin Pauly]

Oh man, what kind of hornet nest did I step into here?

I just taught a class on mixture management at AirVenture again (been doing that for a while). What I tell the audience there is that ROP and LOP are both fine when done properly.

Here is how I pick: When I am flying to go visit the in-laws, and arriving a bit later is a good thing, I fly LOP and save some gas. If I have the in-laws on board and I want to drop them off asap, I fly ROP and save some time. Different tools for different problems.

You pick what you want to optimize on a given day. Just make sure you are rich enough when ROP, or lean enough when LOP, to avoid the high CHTs and high ICPs (internal cylinder pressures) that are in the space in between those. Don't make the engine hot (hot metal = weak metal) and then overstress it with excess pressure, and you'll be in good shape.

Furthermore, when an A&P tells me that I shouldn't cruise LOP, I ask "which is damaging my engine, the lower pressures or the lower CHTs?" and without fail I'll get the deer-in-the-headlights look. None of them has been able to tell me what the exact failure mode is that is triggered by LOP.

And finally, to those who say "I don't fly LOP, I just lean until rough and then enrichen a bit": Many engines, when leaned that way, will be on the lean side of peak. You just won't know it for sure without an engine monitor.

Aviation is full of old-wives tales, where "facts" are handed down from generation to generation without explanation and without much questioning, though I think engine management is a contender for first place here in the old-wives tales contest. Don't accept a statement without rationale; dig deeper and ask questions, and if you don't get real answers to those questions, be careful about what you believe.

Regards,
Martin

 

[Roger Wilco]

So...

First, as stated earlier, I've never dissed LOP operations and, although I only have a lowly normally-aspirated O-360, I've seen where I could lean even that engine to below peak EGT and see the CHTs start to drop. If I had a fuel injected engine with GAMIs I'd operate LOP consistently.

<snippity snip>

And again, the thread title is a good one.

Thanks for taking time to put a little effort into the issue. There is quite a lot of information available online, free of charge, for your thoughtful consideration. Flyingcheesehead and Wayneda40 mentioned John Deakin (speaking of verbose...), who, along with Braly and others, invested a great deal of time, money, and effort into understanding the issue and creating an easy way to present it to pilots. If you doubt the credibility of those sources, perhaps your perspective would benefit from a deep dive into the hidden mysteries of the combustion process in a piston engine, a complex study in physics, chemistry, etc. but a journey that your background has prepared you to undertake.

But you won't do so, will you. Because certain statements in your posts stand out, and a pattern emerges: "[Busch] makes a profit from aggregating (cherry picked) data they didn’t personally do the research..." (#17); "Just packaged what he could scavenge from others, pontificated, and sold it." (#24); "Mike is the salesman with no real risk exposure" (#37); "...I sense Braly was trying to validate that operating LOP wouldn't unduly raise the detonation margin when using his injectors..." (#90)

Based on those sentiments, your real objection to Busch et al. seems deeply rooted in your conviction that they are merely trying to sell you something and therefore shouldn't be trusted. So be it.

As for your trusty A&P, please consider the fact that most A&P's have very little in-depth training in this area. In #24 you dismissively asked "has [Busch] done any tests on engines in a test cell...?" Maybe a better question would be, has your A&P, whose advice you do seem to respect, done so?

I found it amusing that, in #63, you wrote, "...some rando podcaster can voice medical opinions based on what they’ve gathered from ChatGPT and sound as “authoritative” to (some) people..." yet in #90 (when you finally began to engage with the topic in a meaningful way), you turned to . . . ChatGPT.

Lastly, I recognize that my self-indulgent little crusade has rendered this thread unbearably tiresome and annoying for many, and for that I apologize.

Wilco, over and out.

 

[Llewtrah381]

“Caution - Religious discussion, click here only if you can handle this topic.”​

Right in the thread title. No need for ad hominem stuff…

 

[flyingcheesehead]

Of course I didn’t. But like my A&P and unlike people like Busch, I was definitely, personally on the hook for the decisions I made with the data for the patient/airplane in front of me. That’s why I had liability insurance. I doubt Busch needs that.

Well, there's no malpractice insurance in aviation, no. I'd be he has liability insurance, though.

LOL. Yeah. He’d have hurt feelings. Not much more.

If it was definitively shown the LOP is bad for your engine, he'd lose his entire business and livelihood. That's skin in the game.

Add: there are those who follow Don Gryder religiously as well and he’s not always wrong.

Broken clock is right twice a day, blind squirrel sometimes finds a nut, etc...

In defense of @Llewtrah381, it is possible to simultaneously think that LOP operations are fine and the Mike Busch is a blowhard.

Yeah, but if that were the premise of the thread, you wouldn't find enough disagreement for it to last very long.

Savvy says CHT is actually a proxy for internal cylinder pressure. But CHT is affected by more than just ICP. Bad baffling, high OAT, and a handful of other things will raise CHT without ICP being raised. Basically, there are times when CHT can be above desired temps yet ICPs will not be unduly high. CHT is not a perfect proxy for ICP and ICP is the "real" threat (debatably, other than metallurgy and temps).

I've heard mention of people being concerned about the cylinder metallurgy and temperature - that it loses X% of its strength at y degrees. I haven't been able to find good data for that and am not sure if that's linear (I doubt it) or exponential. I'm sure the data is out there - I just haven't seen it.

You really need to go looking for the data before you argue against it.

It is roughly linear up until about 400º, and then it really goes south quickly. That's where the 400º thing comes from.

Furthermore, when an A&P tells me that I shouldn't cruise LOP, I ask "which is damaging my engine, the lower pressures or the lower CHTs?" and without fail I'll get the deer-in-the-headlights look. None of them has been able to tell me what the exact failure mode is that is triggered by LOP.

Hah! I'm gonna have to remember that one.

 

[MackMooney]

Or training wheels vs tailwheels.

aww heck naw, he went there

 

[Llewtrah381]

You really need to go looking for the data before you argue against it.

I did, as noted above. Can you help me find it? ChatGPT (yeah, I know...) seems to say it wasn't publicly released, as I noted.

It is roughly linear up until about 400º, and then it really goes south quickly. That's where the 400º thing comes from.

I'm not sure what you're referring to here. Do you mean the CHT is linear up to a certain EGT (fuel flow) and then the CHT drops? Or do you mean cylinder life is linear but then drops off when going above 400? I can't tell but I think you mean the first (and I'd honestly like to see a graph or data for the latter).

I think you're referring to this (from the Pelican's Perch #65)?



Both CHT and ICP seem to relatively flat-line at a surprisingly low/rich EGT and then both drop off substantially and together, which sounds like what you're referring to?

This one is from a Mike Busch article and has the "red box" as well as the "purple box":


In either, how would one move deeper into the purple zone? Not by leaning: as shown, that caps the CHT at around 400. Hot OAT? That increases the CHT but does it increase ICP? The hotter air is thinner and therefore seems less capable of generating max power, so it would seem ICP would actually be less than peak for hot OAT.

And is this for Conti or Lycoming? Makes a difference.

Oh - and what's too high of an ICP? ADD: Don’t forget: ICP is what gives airspeed.

Basically, I'm honestly trying to understand why the Lycoming guidance to stay below 435 (not 400) is bad and I'm not seeing a good explanation either in this thread or on Savvy stuff. It feels like it's "because I said so".

 

[Skymac]

I’m generally more of a ROP person but given the right scenario I have no issue running my IO580 LOP in cruise. On my airframe it’s exactly 10kts TAS at 6-7k and 13.5gph vs 18.5gph.

I’ve never ever seen temps above 375 in any situation. It’s well cooled but ROP cruise is 350 at 68/70% on the hottest for me and LOP that same cylinder is around 338.

All that said… I think the hate from LOP is because people go to primacy of what we all grew up working on…. 2 Strokes… Where LOP is death… That’s my theory.

 

[Tarheelpilot]

In defense of @Llewtrah381, it is possible to simultaneously think that LOP operations are fine and the Mike Busch is a blowhard.

Truth

 

[flyingcheesehead]

I did, as noted above. Can you help me find it? ChatGPT (yeah, I know...) seems to say it wasn't publicly released, as I noted.

Yeah, ChatGPT is full of crap as usual. I mean, it's a really helpful tool when used correctly, but that caveat only applies to maybe 5% of queries at best!

I'm not sure what you're referring to here. Do you mean the CHT is linear up to a certain EGT (fuel flow) and then the CHT drops? Or do you mean cylinder life is linear but then drops off when going above 400? I can't tell but I think you mean the first (and I'd honestly like to see a graph or data for the latter).

Nope, I was referring to metallurgy. Cylinder strength vs temp is relatively linear up to 400 and then accelerates significantly.

And is this for Conti or Lycoming? Makes a difference.

Kinda. And depending on the engine, the actual limits may be different (your 435º is one of the lowest I've heard). That said, our local engine guru @Ted said it best: "Limits are not goals." Unless you're talking takeoff fuel flow, but I digress. Getting your cylinders to the limit temp is pretty much guaranteed to result in premature replacement. 400 should keep them happy for a much longer time.

Oh - and what's too high of an ICP?

Who knows, because we can't really measure it directly. CHT is one indication of ICP, but as you noted, other factors affect CHT as well: Airspeed, OAT, cowl flap position, baffling, etc...

Basically, I'm honestly trying to understand why the Lycoming guidance to stay below 435 (not 400) is bad and I'm not seeing a good explanation either in this thread or on Savvy stuff.

Limits are absolute, hard-stop numbers above which you must not operate. 380/400 is a guideline to promote maximum engine longevity.

 

[tspear]

Lycoming/CMI give the design limit based on what in theory the metal can take. From a practical viewpoint, we can never measure everywhere, and our measurements are not perfect, our cooling is always uneven....
The list goes on. Therefore, it you run at the temperature limits specified by Lycoming and CMI, you will find there is very little to no margin. Anecdotally at least (never seen any documented "proof") this is often then known to cause premature cylinder and/or engine replacement. Since this is past the warranty period, neither company has an incentive to fix it.

The advice provide to stay below 350/380/400 is based on trying to build that margin; knowing higher the higher temperature is associated with metal fatigue.

Tim

 

[Llewtrah381]

Yeah, ChatGPT is full of crap as usual. I mean, it's a really helpful tool when used correctly, but that caveat only applies to maybe 5% of queries at best!

How was it wrong in this case? And let’s say it was: can you point to the data? I couldn’t find it via other means

Nope, I was referring to metallurgy. Cylinder strength vs temp is relatively linear up to 400 and then accelerates significantly.

Source? And if true, why is Lycoming’s limit 100 degrees higher than this?

(your 435º is one of the lowest I've heard)

You do realize the 435 was not a limit (which is 500) and that it’s a recommendation, right? Please re-read my quote from the Lycoming manual

A "self-sealing" conspiracy theory is a belief system structured so that any evidence against it is reinterpreted as proof of its truth, making it completely immune to disconfirmation. The term describes the closed-loop, circular logic that seals the theory off from external reasoning or factual correction

 

[Llewtrah381]

Who knows, because we can't really measure it directly.

Add: that has to be the most befuddling statement in this whole thread: if the reason for monitoring CHT is to use it as a proxy for ICP (per Busch) yet we don’t know what is a good or bad ICP, then why do we care about CHT? And again, more ICP translates to more airspeed, so knowing how high we can get it safely is of significance.

This is really starting to feel like unsubstantiated dogma.

 

[pfarber]

Lycoming is full of it. if thier certified motors require full rich to 10k they would not get certified. SBs are not operating limitations in the POH.

They want to reduce liability. plain and simple.

 

[Ed Haywood]

Therefore, it you run at the temperature limits specified by Lycoming and CMI, you will find there is very little to no margin.

Why do you think Lycoming and CMI engineers do not build margins into their operating limits?

 

[MauleSkinner]

Lycoming is full of it. if thier certified motors require full rich to 10k they would not get certified.

Lycoming doesn’t say that.

Apparently the Lycoming rep decided to go off reservation, along with a couple of people here.

 

[tspear]

Why do you think Lycoming and CMI engineers do not build margins into their operating limits?

I said little to no margin, and this is based on the anecdotal comments, here and everywhere.
You run the CHTs to 435, expect to do a top end overhaul at least once before TBO. That is the common expectation.
You keep the CHTs under 400, even as low as 350, you likely make TBO.

Tim

 

[Half Fast]

And finally, to those who say "I don't fly LOP, I just lean until rough and then enrichen a bit": Many engines, when leaned that way, will be on the lean side of peak. You just won't know it for sure without an engine monitor.

Considering the fuel distribution of my carb'd Lycoming O-360, I suspect that leaning to roughness then richening puts me lean of peak on one or two cylinders and rich of peak on one or two others, possibly at peak on some cylinder. I don't really know where I'm operating. OTOH, if I only lean until I first see an RPM rise with the engine still smooth, I'm pretty sure I'm ROP and my baby Beech will go a teeny bit faster.

Am I missing something?

 

[Martin Pauly]

I don't really know where I'm operating. OTOH, if I only lean until I first see an RPM rise with the engine still smooth, I'm pretty sure I'm ROP and my baby Beech will go a teeny bit faster.

Am I missing something?

What you say is correct - without an engine monitor, you won't really ever know for sure, but a mix of ROP and LOP between the cylinders is a likely possibility when you've done the "lean until rough, then enrichen" thing.

But from a practical perspective, for the ROP leaning technique you describe, your power output and thus RPM will increase immediately when you start leaning (whether you can see it on your gauges right away or not). There is not a truly flat spot on the HP curve. And even if that did work, how would you rule out the possibility of ONE of your cylinders being a bit lean and thus operating in the famous red box?

That's why a digital engine monitor is one of the best investments you can make for engine longevity and safety (along with some education on how to interpret the data).

- Martin

 

[M20K]

And most people's ground leaning does absolutely diddly. We were given an instruction to do so in the 152s that I learned to fly in at BJC. I've subsequently learned that just backing the mixture back a bit at idle doesn't do anything as the idle loop isn't affected by the mixture control until you get right to the idle cut off point.

Sounds like you're not doing it correctly. And yes, correct ground leaning can help keep sparkplugs from fouling and cleaner in general as multiple engine gurus an I believe Continental and Lycoming now (older POHs don't show it) recommend ground leaning.

And you ground lean basically the same as you do in flight. Keep leaning until the engine stutters or significanly loosed power. Then enrichen just a bit. Two things to keep in mind as you're doing this.... At Taxi Power, you cannot hurt your engine by leaning too much. Also if you ground lean correctly, you should not be able to create Takeoff Power, so there is no you will take off and climb with your mixture not set to Rich.

 

[Half Fast]

That's why a digital engine monitor is one of the best investments you can make for engine longevity and safety

Granted, but without an engine monitor, what leaning technique do you recommend?

 

[ateamer]

My RV-8 had a carbed O-360 and an engine monitor. Doing the lean-until-rough-then-enrich procedure put it LOP, CHT stayed within 30 degrees of each other (generally 355-365 at 65%), with EGTs staying close as well. The highest CHT I ever saw was 410 while climbing at max power Vy on a 93 degree day.

 

[Bill]

Here is how I pick: When I am flying to go visit the in-laws, and arriving a bit later is a good thing, I fly LOP and save some gas. If I have the in-laws on board and I want to drop them off asap, I fly ROP and save some time. Different tools for different problems.

I look at winds, >10kt headwind? 2500 and 100ROP, power up against that headwind.

Tailwind >10kts? Pull the prop back to 2400, set 50LOP, and enjoy the savings.

Between the two a mid power setting 2500 50LOP.

 

[Ed Haywood]

Granted, but without an engine monitor, what leaning technique do you recommend?

Put an EGT gauge on the hottest cylinder, lean to peak on that, then either leave there for best economy or enrich 100-125 for best power. As done in days of yore.

 

[flyingcheesehead]

How was it wrong in this case?

It simply didn't find the data. And then it made up several plausible but incorrect answers instead.

And let’s say it was: can you point to the data? I couldn’t find it via other means

You need to find all of John Deakin's columns, and READ THEM.

Sadly, this has gotten more difficult as the index on AvWeb is full of broken links since their last CMS update. However, if you search the title of the article you can find it.

Source? And if true, why is Lycoming’s limit 100 degrees higher than this?

If you exceed the limit, damage and failure are imminent and your engine might quit before the flight is over.

If you want to make TBO, you keep far away from the limits.

You do realize the 435 was not a limit (which is 500) and that it’s a recommendation, right?

No, I just saw you say it enough times without further context that I thought it was the limit for your engine.

Add: that has to be the most befuddling statement in this whole thread:

We can't directly measure ICP. However, ICP has an effect on CHT, along with the other items I noted earlier. If you see a higher CHT even though you're at a lower OAT, that should tell you something. Gotta use your brain.

if the reason for monitoring CHT is to use it as a proxy for ICP (per Busch) yet we don’t know what is a good or bad ICP, then why do we care about CHT?

Again, most things won't kill your engine instantaneously. There's no binary, black and white value of ICP that is good or bad. It's about finding the right spot along the scale that leads to the best combination of performance and engine longevity to minimize cost.

This is really starting to feel like unsubstantiated dogma.

Then do whatever you wish. I don't have to pay for your engine, so I really don't care what you do.

I do, however, have to pay for *my* engine, so I very much care what I do, and I try to learn as much as I can to that end.

 

[flyingcheesehead]

Granted, but without an engine monitor, what leaning technique do you recommend?

Lean until you save enough on gas to afford an engine monitor.

 

[flyingcheesehead]

Put an EGT gauge on the hottest cylinder, lean to peak on that, then either leave there for best economy or enrich 100-125 for best power. As done in days of yore.

It's not the hottest cylinder. It's the leanest cylinder, the one that will peak first.

This does not work for LOP, of course, because you don't know where any of the other cylinders are. You just have to find the peak on the measured cylinder and make it sufficiently rich from there that you're not gonna cook your engine. 100-125 ROP is best power, but it's also a good margin away from the red box. Remaining at peak on a single EGT isn't a great idea because your other cylinders are ROP, and probably some of them are in the red box.

 

[Martin Pauly]

Granted, but without an engine monitor, what leaning technique do you recommend?

I heard praying works pretty well!

But seriously, the best you do without engine instrumentation is to fly at 65% power or less. Then lean any way you want, and you'll be OK.

At full power (e.g. sea-level take-off, initial climb), if you had a lean cylinder in the red box, there'd be no way of knowing that without an engine monitor.

In other words, if you don't have an engine monitor, it's not about what leaning technique to use, but about avoiding (or minimizing) time at conditions where a poor mixture setting could be harmful.

I wish I could give you a magic recipe for how to avoid trouble, but I keep coming back to this: get an engine monitor.

Regards,
Martin

 

[flyingcheesehead]

I was able to find a couple of different indexes at AvWeb that appear to have the right links to the articles:

Pelican's Perch - AVweb

John Deakin

avweb.com

"Pelican's Perch" Index

Pelican's Perch #80: Gear-Up Landing In A 747? - (Articles - Nov. 21, 2004)

avweb.com

At least, I didn't get any broken links this time.