Leaning to ROP - But by how much

[BeechSundowner]

Hi all. I wanted to get some opinions and yes I know this has been discussed but I wanted to get some new opinions. I have a Lycoming O-360-A4K with a JPI 830 engine monitor installed in the aircraft. I've done a lot of research on leaning and unfortunately LOP just doesn't work for my plane. I've read Lycomings publications on leaning techniques and found some contradictions. One of their publications from 1994 says to lean 100ºF ROP while another Lycoming publication says to lean 50ºF ROP. I tend to fly around 65-75% HP depending on altitude. I can keep CHTs under 400ºF pretty much all the time but I am seeking clarification or thoughts and opinions on Lycomings claims. I've also read Mike Busch's publications but they tend to focus heavily on LOP operations. Cheers

 

[Steamflyer]

1) Carbureted engines often don't have even enough fuel/air mixtures across the cylinders to run LOP successfully. I'm sure someone will chime in that theirs does it perfectly, but that's what I've observed over forty years.

2) Since you have a multi-cylinder monitor, you are leaning presumably to the hottest cylinder's EGT. Often manuals and such will have two demarcations - between 75 and 100 F ROP of peak EGT for "best power" and peak EGT for "best economy." I don't have my most recent Lyc manual open at the moment, so the best economy thing may be more for Continentals. I doubt the difference between 50 and 75 F is really marked, and many manuals were written when ±50 F was about all you were going to discern on a manual gage, which was often uncalibrated - just relative.

3) CHTs seem to play some role with engine longevity, so If you are happy with those, you are probably ok 50, 75, or 100 F ROP, but that's what the monitor is for - assess and modify as needed during the flight(s).

Like anything on the net, it's just conversation, and the manufacturer's manual or POH govern the operation. I'd certainly take a look at what the POH recommends first and foremost. In the past carbureted engines were leaned to roughness and then enriched 1/2 to 3/4 turn, which is wholly unscientific. But it more or less worked, and in planes that went from little to no engine instrumentation, that the heuristic process was pretty close to something like 75 ROP.

 

[BeechSundowner]

Thanks Steam. POH recommends 75°F ROP for best power and 25°F ROP for best economy but then again it’s a 50 year old POH and things change over time. Both would be in the “red box”. I guess 100ROP would be the safest bet

 

[Steamflyer]

Thanks Steam. POH recommends 75°F ROP for best power and 25°F ROP for best economy but then again it’s a 50 year old POH and things change over time. Both would be in the “red box”. I guess 100ROP would be the safest bet

Red box refers to the maximum combustion pressure or something? I've seen Lycoming four-bangers go way past TBO, abused the whole way by students, and never complain which boxes they were in. Undoubtedly all of them red, yellow, and green.

Also, Lycomings have very efficient exhaust valve cooling via sodium filled valve stems, and run too cool can lead to deposits and stuck valves. YMMV.

 

[Racerx]

The old lean to stumble and enrichen slightly is in play especially closer to 65% power. As long as cht's and oil temp is in the green. You cant really hurt anything.

Lycoming does not advocate any engine to be run LOP. So keep that in mind.

A lot of guys claim theyre 25lop or 100rop... But they didn't actually bring the engine to peak.

Using the leaning to stumble and enrichen until smooth. You're probably on the lean side of peak on on a couple cylinders. 100rop is burning a lot of fuel unnecessarily for very minimal gains.

 

[455 Bravo Uniform]

I run an injected Continental (IO-470) and have always run ROP. I have no opinions either way about LOP or ROP, I just like to go fast.

I ran it from 2017 to 2022 with only the single stock EGT, 125 deg F ROP. I used my spark plug condition and borescope images during my annual to determine if I was running too rich.

I installed the EDM-830 a few years ago. Since “if it ain’t broke, don’t fix it” applied to my system of operation, I kept using the single stock EGT to lean as my primary indicator, but observed what the 830 was telling me that first year as a baseline (rather than bow completely to the new 830 and risk changing something that worked for over 400 hours).

Now I lean a little more or a little less so as to manage CHTs in the 380 range, which can tend to be more weather dependent than EGT. The stock gauge gives me 75-125 ROP.

Now my plug visual at annuals has a little more lead globules, but my cylinders look a little cleaner (less carbon), which doesn’t quite make sense. I could probably stand to lean a little more aggressively.

This year I started to use the lean function of the 830. Yeah, I’m a late adopter, dinosaur. It actually puts me in almost the exact same place I was with the stock EGT, and the 830 CHT.

Hope this helps you a little.

 

[Racerx]

The red box I think is a bit of fear mongering and something I wish savvy would acknowledge or explain a bit better.

So, you mean to tell me reducing power a couple percent I can run my engine anywhere? But increase ever so slightly and my mixture ratio is in the danger zone?

The red box is cylinder head pressure. We have no way of measuring cylinder head pressure. So we use cht as a proxy.

With carbureted engines being so imbalanced. Only taking a reading from one cylinder is only giving you 25% of what could be a very different story. When you say 100rop... Is that an average between the cylinders? Or is that your hottest?

 

[Racerx]

I run an injected Continental (IO-470) and have always run ROP. I have no opinions either way about LOP or ROP, I just like to go fast.

I ran it from 2017 to 2022 with only the single stock EGT, 125 deg F ROP. I used my spark plug condition and borescope images during my annual to determine if I was running too rich.

I installed the EDM-830 a few years ago. Since “if it ain’t broke, don’t fix it” applied to my system of operation, I kept using the single stock EGT to lean as my primary indicator, but observed what the 830 was telling me that first year as a baseline (rather than bow completely to the new 830 and risk changing something that worked for over 400 hours).

Now I lean a little more or a little less so as to manage CHTs in the 380 range, which can tend to be more weather dependent than EGT. The stock gauge gives me 75-125 ROP.

Now my plug visual at annuals has a little more lead globules, but my cylinders look a little cleaner (less carbon), which doesn’t quite make sense. I could probably stand to lean a little more aggressively.

This year I started to use the lean function of the 830. Yeah, I’m a late adopter, dinosaur. It actually puts me in almost the exact same place I was with the stock EGT, and the 830 CHT.

Hope this helps you a little.

Last xc I wanted to see what would happen going from 50 LOP at 10.9gph and increase to 15 gph. TAS was 3 mph different.

 

[BeechSundowner]

thanks for the reply Racer. I’ve found the literature interesting. In one document, lycoming said do not run LOP, but also said they’ve extensively tested LOP operations and found no issues. My mechanics have mentioned they’ve replaced a lot more cylinders on Lycs that ran LOP than ROP too. I’d have to pull my data from my JPI but they peak around the same time with the hottest cylinder showing anywhere from 1500-1525

And for clarification, I have a JPI 830 installed

 

[Racerx]

thanks for the reply Racer. I’ve found the literature interesting. In one document, lycoming said do not run LOP, but also said they’ve extensively tested LOP operations and found no issues. My mechanics have mentioned they’ve replaced a lot more cylinders on Lycs that ran LOP than ROP too. I’d have to pull my data from my JPI but they peak around the same time with the hottest cylinder showing anywhere from 1500-1525

And for clarification, I have a JPI 830 installed

Was reading another article where they only had one probe installed and got confused. My bad. I would be shocked if you could lean an o360 and get egts to peak roughly the same time. Fwiw, I believe Lycoming recommends to run at peak. People are leary of running at peak because of high egts.... But that's not an issue in a naturally aspirated engine. Your egts cant get hot enough to be damaged.

A fantastic video on leaning.

I also highly recommend pelicans perch "mixture magic"

 

[455 Bravo Uniform]

Last xc I wanted to see what would happen going from 50 LOP at 10.9gph and increase to 15 gph. TAS was 3 mph different.

You might have something there. But the first time I turned that knob and felt the ‘air brakes’ I said “nah, F this”, lol. Burning cash, for little good reason…

 

[Barrett50]

I don't want to sink this thread, but I'll introduce just a little bit of engineering. First off, the engines in our planes can be thought of as a Carnot heat engine. The best efficiency of the Carnot cycle is to extract the maximum mechanical work(HP) from the amount of heat produced during the full cycle(cold, hot, cold). In a piston engine this is expressed as the hottest point of the engine cycle to the coldest point of the engine cycle. How this plays out in the field is to operate at the maximum heat capable without the mechanical parts coming apart. Example - in the 1950 and 60s, thermostats on engines were around 172-185F, where today they are up around 192 and maybe higher. This has extracted just a bit more Carnot efficiency from the engine due to the cold-hot-cold cycle.

Not much you can do with the above in your plane with a throttle and mixture control except run it hot for efficiency, but run it below the value where things start coming apart.

Next we'll talk about the Carson speed. Completely different than the Carnot engine equation, this is a practical number that any pilot can mess with. Carson speed is a mix of best economy, and quickest trip times. We fly a plane to go fast, but just how fast do we want to go? Well, if we're a doctor and we're flying a Bonanza, it's red lined, all the time with max EGT to produce the greatest HP, and the highest Carnot cycle. If we're in a Rutan Long-Eze, we're tootling around at max L/D which is pretty damn slow, but max aero efficiency. Once again, operate as hot as possible to get the Carnot cycle at it's greatest.

There's something in the middle of those two extremes, and notwithstanding the value of anything from Busch he explains it just fine, and will save me electrons.

Flying Efficiently - SavvyAviation

In a world of $7 avgas, it’s more important than ever to get the best bang for the buck. How can we get the best fuel economy from our airplanes? Given the painful cost of avgas these days, this is a question on lots of airplane owner’s minds. That goes at least double for unfortunate folks like...

www.savvyaviation.com

I usually use Carnot cycle engine operation with an eye to Carson speed. YMMV

Edit to add, of all the planes I've owned, and all the engine work I've done over the years, I would say at least 50% or more had induction leaks at the intake runner hose clamps, or the flange to the manifold pipe to head.

 

[Steamflyer]

All four cycle heat engines are Carnot engines per se. The Carnot cycle describes a theoretical heat engine whose efficiency is a function of the two reservoirs of heat, the hot and cold reservoir. Maximum efficiency is achieved with the greatest differential, but since it is a theoretical cycle, mundane considerations like "crap I melted my engine trying to maximize my Carnot cycle" are not taken into consideration.

The Carson speed is an empirical determination, rooted in the squared vs. cubed scaling laws that permeate aerodynamics, that is provides the "most bang for the buck" or the most airspeed for the least (reasonable) fuel consumption. It is roughly 30% faster than best glide (which is L/D max); the only time one is likely to use it is in a fantastic tailwind to avoid a fuel stop - Carson speed for a Cirrus is around 120 kts, and you don't buy a Cirrus to tool around at 120 kts often!

 

[Racerx]

I don't want to sink this thread, but I'll introduce just a little bit of engineering. First off, the engines in our planes can be thought of as a Carnot heat engine. The best efficiency of the Carnot cycle is to extract the maximum mechanical work(HP) from the amount of heat produced during the full cycle(cold, hot, cold). In a piston engine this is expressed as the hottest point of the engine cycle to the coldest point of the engine cycle. How this plays out in the field is to operate at the maximum heat capable without the mechanical parts coming apart. Example - in the 1950 and 60s, thermostats on engines were around 172-185F, where today they are up around 192 and maybe higher. This has extracted just a bit more Carnot efficiency from the engine due to the cold-hot-cold cycle.

Not much you can do with the above in your plane with a throttle and mixture control except run it hot for efficiency, but run it below the value where things start coming apart.

Next we'll talk about the Carson speed. Completely different than the Carnot engine equation, this is a practical number that any pilot can mess with. Carson speed is a mix of best economy, and quickest trip times. We fly a plane to go fast, but just how fast do we want to go? Well, if we're a doctor and we're flying a Bonanza, it's red lined, all the time with max EGT to produce the greatest HP, and the highest Carnot cycle. If we're in a Rutan Long-Eze, we're tootling around at max L/D which is pretty damn slow, but max aero efficiency. Once again, operate as hot as possible to get the Carnot cycle at it's greatest.

There's something in the middle of those two extremes, and notwithstanding the value of anything from Busch he explains it just fine, and will save me electrons.

Flying Efficiently - SavvyAviation

In a world of $7 avgas, it’s more important than ever to get the best bang for the buck. How can we get the best fuel economy from our airplanes? Given the painful cost of avgas these days, this is a question on lots of airplane owner’s minds. That goes at least double for unfortunate folks like...

www.savvyaviation.com

I usually use Carnot cycle engine operation with an eye to Carson speed. YMMV

Edit to add, of all the planes I've owned, and all the engine work I've done over the years, I would say at least 50% or more had induction leaks at the intake runner hose clamps, or the flange to the manifold pipe to head.

Very interesting technical analysis. So would you be on board with what Lycoming recommends about running at peak...provided you can keep cht's in the green?

Also, good point on the induction leak and something for OP to look at. There's a lot of GA planes that have an induction system that is an afterthought at best and usually flat out ignored. With an induction leak you're allowing unmetered air which creates a lean condition and high cht's on that cylinder

 

[Ed Haywood]

Every Lycoming operators manual I have seen recommends 2 options: best power at 100 ROP, and best economy at peak EGT. Both are under 75% HP, with CHT under 400 F for max life.

In my tests, the difference between the two is 2-3 gph and 5-10 mph. I keep power at 65% when running peak EGT.

Lycoming does not recommend LOP. Every year at Oshkosh someone asks the Lyc engineers at their presentation and they explain why. The gist of it is they do a whole lot of warranty service for Mike Busch fans.

 

[SkyGazer]

I used my spark plug condition and borescope images during my annual to determine if I was running too rich.

Last xc I wanted to see what would happen going from 50 LOP at 10.9gph and increase to 15 gph. TAS was 3 mph different.

I'll add to the data noise from the injected perspective. I start my lean procedure by trimming for cruise speed while at least 50* ROP. Then I go LOP per the multi-probe JPI. I lose 5 knots (~4% speed reduction), lower gph by ~5 gph (~35% fuel burn reduction), and CHT's are in a zone with nothing to worry about. Each annual I ask the IA to borescope and keep getting comments to continue doing what I'm doing. Reminder: this is for an injected system running GAMI injectors which allow for LOP per STC.

Carson speed is a mix of best economy, and quickest trip times.

Will argue that Carson speed is something slightly different: marine hull speed adopted to GA. Boaters knew about the relationship of hull length to economical cruise speed long before Dr. Carson found the equivalent for planes. Definitely not knocking Dr. Carson as he was the one who did the math and took the time to publish results for all of us to benefit. Just seems a little coincidental that a professor at the USNA, in Annapolis (a notable pleasure boating location), did not know about the established marine math and not want to do the same for flying. Especially since the Navy had deep exposure to both worlds when Dr. Carson derived the formula.

Regarding Bush's analysis on airspeed, am not sure I'd fly at the max range speed of Vg / 1.316. This is barely above the 0* AoA stall speed for my current plane where an updraft at this speed can induce a stall. IIRC, even CAP does not fly this slow when performing SAR grids.


OP, Here is a thought. If the hop is on the short to medium duration in terms of distance, what is the time difference between setting speed around the Carson point, or something like 5, 10, or 15 knots faster? While there is no wrong answer, the math will provide time differentials and fuel cost differentials. So, is it worth a higher fuel burn to save that time? Related, the use of extra power to gain that extra speed will probably effect the TBO. Again, no wrong answer just as long as the engine likes the leaning technique.


Another leaning technique for fixed prop planes, which I rarely see commentary on its use, is leaning to peak RPM. Used to do this on a carburated 4 cylinder with good results.


Last thought on leaning is that it is NOT a set-and-forget event once at cruise altitude. The mixture setting needs to change as conditions around the plane change. I know of a flying club that trained it's members to lean the engine to a set EGT temperature. No more. No less. Period. And those folks wondered why their seemingly bullet proof engines always imploded well short of TBO. Point is, with significant enough changes in humidity and / or temperature at the same cruise altitude, the fuel mixture must change as well. Easiest way to determine when it is time to adjust mixture is by calculating Density Altitude where this is usually a feature within current GPS units. When the DA changes enough, re-lean the engine.

 

[Racerx]

Every Lycoming operators manual I have seen recommends 2 options: best power at 100 ROP, and best economy at peak EGT. Both are under 75% HP, with CHT under 400 F for max life.

In my tests, the difference between the two is 2-3 gph and 5-10 mph. I keep power at 65% when running peak EGT.

Lycoming does not recommend LOP. Every year at Oshkosh someone asks the Lyc engineers at their presentation and they explain why. The gist of it is they do a whole lot of warranty service for Mike Busch fans.

The difference between peak egt and LOP ops is even narrower. I've gone from LOP to operating at peak, largely because I read the manual. Thanks to you pointing it out in another thread and realizing the difference was negligible.

 

[SkyGazer]

Just curious, with OE injectors or balanced injectors?

 

[Ed Haywood]

The difference between peak egt and LOP ops is even narrower. I've gone from LOP to operating at peak, largely because I read the manual. Thanks to you pointing it out in another thread and realizing the difference was negligible.

I've always been an RTFM kind of guy.

 

[Racerx]

Just curious, with OE injectors or balanced injectors?

Assuming this was for me..Ironically just ordered Gami's yesterday. But I've got a Lycoming which I've heard are more balanced than Conti's.

 

[Racerx]

I've always been an RTFM kind of guy.

The piper manual from 1967 was a bit spartan aside from a power setting chart. Also got an overly rich idle mixture taken care of when reading the Lycoming manual.

 

[Ed Haywood]

The piper manual from 1967 was a bit spartan aside from a power setting chart. Also got an overly rich idle mixture taken care of when reading the Lycoming manual.

IMO the PoH is second hand material, while the Lycosaur manual is authoritative. Rev date is 2005 so it incorporates modern experience.

 

[Barrett50]

Woohoo for ChatGPT AI! All the Carnot engine and Carson speed experts get to show their (harumph, harumph) stuff. Aint it grand?

 

[Steamflyer]

Woohoo for ChatGPT AI! All the Carnot engine and Carson speed experts get to show their (harumph, harumph) stuff. Aint it grand?

Huh? Some of us just happen to be mech/aero engineers. And mostly just yawn at all the rubbish that is put forth on the interwebs about LOP, ROP, "I build race car engines so know more than all of you," MCP, and other similar stuff. Run an octane engine and learn to make the curves yourself if you really want to understand an internal combustion engine running at extremes. Otherwise RTFM and go FLY.

@SkyGazer - it's 1.3 or so time best glide speed, not divided by. So the speed, while generally slower than is fun, is not near stall speed.

 

[midwestpa24]

Every Lycoming operators manual I have seen recommends 2 options: best power at 100 ROP, and best economy at peak EGT. Both are under 75% HP, with CHT under 400 F for max life.

In my tests, the difference between the two is 2-3 gph and 5-10 mph. I keep power at 65% when running peak EGT.

Lycoming does not recommend LOP. Every year at Oshkosh someone asks the Lyc engineers at their presentation and they explain why. The gist of it is they do a whole lot of warranty service for Mike Busch fans.

I know a handful of guys that insist on LOP like a cult. I also know a handful of guys that seemingly replace cylinders on a regular basis. Coincidence?

 

[Steamflyer]

I know a handful of guys that insist on LOP like a cult. I also know a handful of guys that seemingly replace cylinders on a regular basis. Coincidence?

Who knows, insufficient data. Are those guys starting with brand new cylinders or do their engines have a hodgepodge of cylinders of different ages, some once new, some already at least once overhauled? How often do they fly? Warrantees are based on 30 or 40 hours a month for reference. Disuse/corrosion is the killer, not usually method of operation. Very few GA airplanes are flown enough to rule any other cause than lack of use as the culprit.

Basically in a large bore engine with six cylinders and fuel injection, it may makes sense to fly ROP into the headwind and LOP with a decent tailwind. That's about it. Don't make a cult out of it!

 

[SkyGazer]

@SkyGazer - it's 1.3 or so time best glide speed, not divided by. So the speed, while generally slower than is fun, is not near stall speed.

From the referenced material by Mike Busch (in post #12): "Two other contenders for the title of most efficient speed can be derived from this max L/D speed (aka best range speed). One is slower, the other is faster.
If we divide [emphases added] max L/D speed by 1.316, we get best endurance speed or minimum power required speed."

Busch then moves to describe Carson which is L/D (or Vg) times 1.316.

So, will stand-by the comment about the slower speed as a concern as my performance tables put "best endurance speed or minimum power required speed" as calculated by Vg / 1.316 extremely close to stall at 0* AoA.

Does that help, or am I still missing something?

Woohoo for ChatGPT AI! All the Carnot engine and Carson speed experts get to show their (harumph, harumph) stuff. Aint it grand?

Sure hope this was not intended for myself. If you do actually feel the input was driven by AI and regurgitated by me, might reconsider the thought process next time around. Or, just confidently sit ChatGPT in the left seat and go fly

I know a handful of guys that insist on LOP like a cult. I also know a handful of guys that seemingly replace cylinders on a regular basis. Coincidence?

Just curious, are these same folks following their POH, or just trying it to see what happens? It is easy to blame something when the supporting equipment is not in place. If LOP is allowable, then the POH will state how to use proper technique. If the POH does not cover LOP, then I definitely agree that is opening an scenario of seeing what happens when coloring outside the lines.

FWIW, I happen to know some Vans drivers who need to replace their cylinders a little more frequently than what seems usual. Does this make them less than ideal pilots? Truly is tough to tell, but I'm suspecting it is not the pilots.

Assuming this was for me..Ironically just ordered Gami's yesterday.

Am suspecting that you will like them. The POH gets an update as well. This is one of the few mods that can return more money than its cost.

Do agree that the difference from Peak to LOP is smaller than ROP to LOP. But at least with the correct injectors, the engine now has supporting equipment when wanting to go LOP.

 

[Barrett50]

^ Well, you did want to argue Carson speed, and then went off on a boating rant(that has nothing to do with aviation V or Carson speeds). Plus regurgitate a section of Busch's discussion of loiter speed, which is sort of the inverse of Carson speed and you clearly don't like. I guess you made your point(s), but I have no idea if it was an argument from my general statement of Carson speed. Frankly, if you wanted to argue, I'd be more impressed if you quote me and then start with... "Jane, you ignorant slut" and then tell me how wrong I presented my analysis.

Ya know, it's funny, I say I don't want to bury the discussion, and within a few hours, we've got people going off on an engineers POV and delivering their own interpretation of both of the engineering principles I offered. What - a coinkeedink!

BTW, when Rutan flew the around-the-world flight, they spent a lot of time at best endurance. I happen to fly a Bonanza, and I can easily loiter along at 81Kts, I can do it all day and not have one worry about a stall upset. I'm also not going to do the doctor mode at full throttle, max rich EGT to go fast. Use Carson, don't use Carson, but going boating while telling me you disagree with a 'mix of economy and best trip times'. Because, that is exactly what Carson himself describes it as.

 

[SkyGazer]

... but I have no idea ...

 

[Barrett50]