ROP/LOP Techniques and Lycoming Operators Manual
Let's discuss lean techniques for best engine life. I just read Mike Busch's AOPA article about leaning. I've also watched his webinars. Like he mentioned in his article, most people think 50 degrees ROP is where you want to be. I was one of those. Mike's article says that is NOT where you want to be. You want to to be LOP or more ROP.
I dug out the Lycoming manual and it states for power 75% or higher you want to be NO LESS than 150 degrees ROP (Max Power) and monitor CHT's. For power settings below 75% you want to lean to PEAK EGT or slightly LOP (Max Economy).
According to the Lycoming manual, best fuel flow (max economy cruise) will be achieved at 50 degrees LOP. Of course that will be at the sacrifice of some power and speed. The Piper manual states that Max Economy will be 8 mph slower than Max Power. LOP should also theoretically provide a lower CHT. Peak CHT should occur about 50 degrees ROP which according to Mike's article is an area of engine operation you should avoid.
I have an O-360 A4A. I have always leaned to engine roughness and then in for smooth operation like most manuals dictate. However, I just installed an engine monitor. They few cross country flights I did, I leaned to 50 ROP using the lean find program of the engine monitor. At that combination, I had CHT's in the 320-340 range.....well below Lycoming's recommendations of 400-435. I'm going to have to do some more flying and testing to see if I can operate at Peak EGT or LOP and what the corresponding CHT's and FF will be. If I was time building, I would try to operate at 50 LOP and go slow and save fuel and lower CHT's. I don't need logbook hours so I'm more interested in engine life and getting to my destination quickly and efficiently.
My newly learned observation is...50 ROP is bad because it results in peak CHT's which result in peak cylinder pressures which results in decreased longevity. Is Peak CHT and Peak cylinder pressures bad even if peak is 320 degrees? That I don't know and have emailed Mike for his opinion.
How do operate your engine? How do you lean? Is your leaning based on EGT, CHT, FF or a combination of all?
Comments
You are running a carbureted engine LOP? Do you have probes on all 4 heads and exhausts? Speaking in general, it is very difficult to run a carbureted engine LOP because there is no way to control the fuel on each jug. That is done on injected engines by tuning them with varied injectors, aka GamiJectors.
If you are able to run that engine LOP I’d say you are very fortunate. Having that said, I run my T Lance as deep as I can go LOP where the engine runs smooth. On my Archer with the A4M, I’d run it WOT at 10.5 GPH. On the Arrow there is no engine monitor so I lean on book numbers, which keeps it well ROP. 380 on the CHTs is a good place to be. Staying out of the 400s is very prudent. Ive cooked two jugs to the tune of $6k on my T Lance because there is no way to stay out of the low 400s without the intercooler kit. No matter how you try and baby it, those temps come up quick and only come down when you can lean back aggressively.
On the T Lance, I am only really concerned with TiT and CHT, and more so CHT as long as TiT is under redline. I run LOP just about every time I fly it. Its a thirsty beast and I’m usually in no hurry. But When I really want to get there, well into ROP is the name of the game. I don't have specs on the ROP side. I run it where power is acceptable and I’m not cooking the heads. Thats somewhere around 22-23 gph, more if I’m higher up in the teens and pushing big MP in.
One thing to consider on the manufacture side of things, they will use settings that have liability in mind. So I’d expect to see very conservative numbers from Lyc across the board. One thing you should do is play with your settings and record it all down. Seeing it on paper after the flights helps decide where you should run it. Uploading the data to Savvy will also help in that process and identify trends.
Busch has a bunch of videos on YouTube if you have not seen them. Also, he has done some Podcast style talks that are easy to digest. Hours and hours of talk just on LOP!
I own and fly a 79 PA32RT-300T. Previous aircraft are a 79 Archer and 76 Arrow.
Agree with Unit74 that there is more to it than simply going LOP. Related, am reading that LOP is best for under 75% power (if capable to go LOP).
Overall, leaning is a very fickle thing whether ROP, Peak, or LOP. Done correctly it pays with a longer engine life and optimized fuel burn. Done incorrectly, it tuns into an expensive lesson to stop doing it incorrectly.
When following an engine manufacturer's POH, we need to recognize that it was written based on technology for the time. For a carborated engine, this was a long time ago, yet still 100% valid today. With engines that are still running original equipment, the engine manufacturer's POH will hold true (and am not certain that solely upgrading to multiprobe monitoring counts as upgrading when looking to get into modifying the leaning techniques). While not anywhere near an engine expert, from a lay perspective am seeing that best bets for playing with LOP call for GAMI injectors (which is kind of tough to do on a carborated engine); am sure better experts will correct me on this. By the way, installation of GAMI injectors will provide updated guidance on leaning and proper maintenance of the injectors as part of the POH.
Will add to the chorus of woes from leaning gone wrong. First example is an off-script practice which was maybe ROP, maybe Peak, maybe LOP, but never based on the atmosphere or POH tables. I was in a club where its Chief CFI conditioned everybody on leaning the carborated 4 cylinder engine / fixed pitch prop to 1,250*F when in cruise based on the OE single probe EGT meter. Not cooler, not hotter. Always 1,250*F. Any altitude over 3,000': 1,250*F. Hot day: 1,250*F. Cold day: 1,250*F. 29.90"/hg: 1,250*F. 30.40"/hg: 1,250*F. 75% power: 1,250*F. 50% power: 1,250*F. If there was any question, do not challenge the Chief CFI and set it to 1,250*F. Engine #1 under that guidance lasted about 1,200 hours (out of 2,000 TBO) until it developed an irregular power delivery, made metal, and need an overhaul. Engine #2 under that guidance lasted about 500 hours until it showed visible scoring on all cylinder walls and needed an overhaul. That CFI continued to defend the practice as clearly it was the pilots (plural) fault and not the guidance.
Another tale comes from a different CFI whom discovered the LOP concept (based on an engine fully capable to go into this territory), leaned the engine once cruise altitude was reached, and then left the mixture alone until time to descend. In short order, the engine needed expensive repairs due to the leaning technique. That CFI learned from the experience, takes full ownership of the judgement, and now coaches pilots on regular evaluations of whether the last lean setting remains appropriate given changes in the atmosphere.
So, what's my point: Leaning is a fickle beast. Doing it correctly requires following the POH AND re-leaning every time there is a change in altitude, temperature, or pressure (or density altitude per computation). Am open to correction here, but have not seen a POH which calls for a set EGT temperature in all conditions, nor doing a set-and-forget.
Back to the carburetor 4 cylinder / fixed pitch prop. In engines without EGT, I set to peak RPM: pull out throttle until about where I want the speed, slowly pull back mixture until the RPM's start falling off, then slowly add fuel until the RPM's peak. Engine is smooth and happy at this configuration and also gives a nice burn rate.
Toward inputs on leaning technique, I get flight following on cross country legs. And regularly monitor outside air temperature. Whenever I change altitudes (above 3,000'), the controller states a pressure different than the previous (even by .01 up or down), or notice a change in temperature (as measured in Celsius), I re-lean the engine. Based on inputs from Savvy, this practice is showing good results in the data.
The airplane is fairly new to me. The engine monitor is new. I've have not even attempted LOP yet. Busch says Lycoming is easier than Continental. On a carb engine it depends on intake distribution. Some planes have a very even intake system that makes it more likely. I have to look at the Archer engine to see. I can't recall how it looks.
With 4 EGT's and 4 CHT's at least I can experiment a little and see how it works. The ROP lean find mode works great. I've not tried the LOP lean find mode yet.
The Lycoming manual says PEAK is better than 50 ROP when below 75% power. At high power, I won't be going less than 150 ROP according to the manual.
It will be interesting to see and compare PEAK, LOP, and 50 LOP to the old lean til rough method and enrichen. I"ll post more when I can compare the methods.
Ignore MB, RAM has excellent info on leaning, so does Lyc as you have seen. You cant run LOP anyway on your engine or should not be. . carl
48 yrs A/P IA DAL aircraft inspector. 172N
From what I have gathered, LOP really needs all cylinders to have almost equal / uniform fuel delivery so that all of them go on the lean side and do not stray back to Peak or ROP. Cannot see where a carburetor has the ability to assure all cylinders get the same amount of fuel. With that, I'd stick with the POH.
Having the multi-probe setup is still a good thing as it provides valuable feedback. As an example, one of the planes I flew had a multi-probe engine analyzer upgrade (it previously had just a single probe EGT). On hot days, I noticed that a couple of the cylinder heads would alarm during the take-off climb. Cure was to lower the nose and increase speed which kept the CHT's within POH guidelines (and not alarm any more).
Jacob, your observation are correct. Also if there were ever any EGT numbers that manufacturers wanted you to avoid, it would have been in the poh and engine data decades back. If you have a monitoring system you can use all the data you see for best ops for a given condition, for the rest of the probably 150k planes that may not have a egt probe, they will still make TBO. Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Why does it matter if one or two cylinders stray back to Peak? The Lycoming manual says that you can to lean to Peak EGT when operating below 75% power and seeking Max Economy. So if one or two are LOP and one or two are at max peak, it still seems you are running the most efficiently and running according to the manual. Of course CHT has to be watched to confirm you are ok.
On a carb engine, you will be limited to the leanest cylinder. Kind of a misconception, so everyone starts leaning untill the last of the rich cylinders is now at peak, NORMALLY, the engine roughness should clue you that the other 3 or 5 cylinders are WAY past peak on the lean side . Also remember that very few aircraft had egt gauges, if it had one probe that was normal, and that normally went into the leanest cylinder per the manufacturer ( #3 on most lyc) that data normally in the TCDS. At 75% lyc isn';t worried about detonation margins or over temping. If you were installing a scanner system, there should be very different range limits for red line or warning indications. Like on cht for carbs may be 250 deg diff and if setting on a injected engine, down to like a 125 deg difference. Injection is that much tighter. Had a owner with a 172 and he was trying to lean as i mentioned above, could not understand why the eng ran like crap when leaned. some carb engines just do not have a wide margin to play with. Hope this helps. carl
48 yrs A/P IA DAL aircraft inspector. 172N