Lean of Peak or Rich of Peak
I've been flying my 1977 Piper turbo Arrow for a few months. The discussion of LOP or ROP came up and I thought of posting it to get some opinions from the experts. I'm not sure if it makes a difference on the make and model of the engine or the aircraft itself. I'm flying a 1977 Turbo Arrow III with an TSIO-360-FB.
Thanks,
Todd
Comments
For some, this is an emotional question.
From a data perspective, it depends.
With a turbo, am seeing where pilots are more likely to go with ROP mostly due to cruising at 75% power, or higher.
But with the correct equipment (key two words) and pulling back on the throttle, LOP is a good option. Will admit that my perspective is biased from the naturally aspirated world.
If seriously considering LOP, my personal minimum equpment list is a set of balanced injectors and multiprobe engine analyzer.
Thanks Jacobsja,
I don't have the Gami injectors yet but hopefully will soon.
Will argue that GAMI injectors are a worthwhile investment. Got lucky as a previous owner installed them and the broker did not mention the injectors, so was surprised to see them in the POH during pre-settlement inspection.
Toward the math of balanced injectors, if willing to trade off some speed and fly in power settings which allow LOP, the potential reduction in fuel consumption is significant. Am deliberately not calling-out actual fuel flows as I do not want anybody frying their engine based on my observations. While running the numbers, do some napkin math for time differences from shaving off 10 - 20 kts to cruise at 65% power (or less) and most will agree that increase in flight time is nominal compared to speeds at 75% power, even for long cross country. And, all of this is per POH (caveat: as ammended per the GAMI injectors).
For pratice when in cruise, I re-lean whenever there is a hint of change in density altitude. Specifically, when ATC gives a barometer setting that is different from the last, and I watch OAT for a change in temperature (my tolerance is +/- 1*C from when I last did a lean). If baro or OAT changes, enrichen the mixture, adjust altitude if necessary, and re-lean. To date, this practice is getting me good comments from borescope inspections and data analysis. If anything, CHTs run on the low side of normal.
GAMI injectors do need regular cleaning, so factor that into maintenance plans.
The only other power element which has potential to quickly pay for itself is electronic ignition. But have received enough inputs to sence where the best time to make the switch away from magneto-only is during major engine work (overhaul or replacement) or if a magneto either dies or is at its end of life.
Thanks for the input jacobsja. Taking care of the engine out weighs getting there 5 minutes earlier every time.
I also have a 1977 Turbo Arrow with a TSIO-360-FB engine.
The Continental Motors manual for the TSIO-360-FB recommends 25 deg F ROP for leaning during cruise. I know there are lots of arguments on both sides, but right or wrong, I am leaning (no pun intended) toward following the manual.
Ben
Completely agree with following the POH.
If GAMI supports the engine, installation of the balanced injectors includes an update to the POH which details new procedures for leaning. With the new POH, LOP turns into a supported option.
Good info jacobsja. That's what I love about this group, the brain trust.
Ben
I've had a turbo Arrow for seven years and I run rich of peak. Also, I've had three Seneca's over the previous 30 years (same engine, TSIO-360) and have run all of them rich of peak. All made TBO!
Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.
Need help? Let me know!
I am a big proponent of LOP but I don't have an engine monitor so always fly ROP in the Seneca.
The Cirrus crowd is the biggest proponent of LOP and they have all the monitoring for it. For it to make a big difference you need to be flying 75%+ LOP so these are aggressive lean settings at high power to avoid detonation risk/high cylinder pressures, etc.
This is an excellent article on LOP operation:
From the graph above the higher the power the richer you should run (ROP). While LOP at an aggressive 85% power you would want to be ~ -75 LOP. Most plane engine set ups will not run this lean. I think the LOP crowd is mostly running -20 at ~ 65% power settings. The other way to look at this graph is below 60% power you can do anything you want. I would usually fly my Cirrus at 70% power LOP (-25).
Here is another description from Gordon Feingold that is specific to the IO-550 and includes target fuel flows. These numbers will vary by engine. One of the interesting aspects of LOP operation is the % power is easy to determine as it is just dependent on fuel flow as air is in abundance and therefore temp/pressure don't matter like they do ROP.
The most important part of engine operation is to be confident in what you are doing, ROP or LOP, and enjoy the flight. Bringing up a topic like this in the winter time it could go on forever - or at least till good spring weather! There are people with adamant positions on boths sides of this with plenty of good reasons. I take a middle ground approach and see the merits of both. Almost all will agree that LOP requires the ignition system and fuel balance to be ideal and that per cylinder engine monitoring is essential for aggressive power settings.
I would say in general people trying pull the mixture back too fast and too far, the speed drops off, the engine starts running rough and they conclude it is not for them. If you want to play around with LOP I would suggest bringing a safety pilot the first time as there is a fixation risk staring at EGT's bouncing around. If LOP is part of your regular practice you will climb to cruise, pull back to a target fuel flow, check EGT's, tweak FF and done - very low workload.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Eric brings up a good point in terms of LOP procedure as it truly does require a sssssllllllloooooowwwww pull-back of the mixture. Pulling the knob back too quickly will make the engine run rough even though the monitor does not show LOP yet. Another factor to LOP is watching the monitor for a few minutes after reaching LOP just to make sure that none of the cylinders stray back to Peak.
Similar for when it is time to re-lean due to a change in density altitude. The readjustment needs time at each phase. Must enrichen by several GPH (no need to go slow with this step), then let the engine adjust for a minute or so with the more rich mixture. Have found that if I do not let the engine stabilize at the more rich setting, going back to LOP will result in a rough engine and I have to start the process over again.
Mike Busch of Savvy Aviation is a leading proponent and expert in LOP operations. He has authored several articles on the theory and how to do it properly. I have a read many of these articles and viewed several of his YouTube posts on the subject. If you Google Mike Busch and LOP, you will find some videos and articles on the subject. Here is a very good one for starters:
https://www.avweb.com/ownership/the-savvy-aviator-59-egt-cht-and-leaning/
The above link includes some FAQs about LOP operations.
The slow pullback in mixture mentioned by jacobsja is not recommended. This slows the transition a could keep the fuel-air mixture into the dangerous detonation zone depending on your power setting. In the Red Fin chart provided by empannin, the "Big Mixture Pull (from ROP to LOP) should be done quickly, (2 to 3 seconds.)"
Jack
I think the key is pulling back to a target value and letting it stabilize. This is easier vs watching the gauges move. The "red zone" below 85% power is not detonation - just elevated cylinder pressures which is cumulative impact and probably a challenge cooling. From 85% to 100% power is not a good place to pull mixture. I think detonation risk is real in this zone (not charted in the above graphs)
If you want to play around with LOP then the easiest is 60% power or less. You can do anything you want at this power setting. Once you get the hang of it you can try at progressively higher power settings (fuel flows) until you reach a point where you can't get lean enough on all cylinders or the engine is running rough.
50deg ROP is peak cylinder pressure (ICP). 100+ ROP is better for climbs as same power but lower ICP, CHT, EGT.
Here is a good article on detonation from Deakin too. Save it before it is gone entirely as it is already in the wayback machine and AvWeb no longer has the images direct.
http://web.archive.org/web/20020614174032/http://www.avweb.com/articles/pelperch/pelp0043.html
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Awesome info everyone!
Found another reading source:
https://www.jpinstruments.com/FAQ/lean-of-peak-procedure/
Looks like we might have conflicting theories among industry experts regarding the actual technique. IIRC, Busch is a Cessna driver with push-pull vernier control which might explain the difference in perspective of more rapid adjustments versus slow. IIRC, few Pipers use a vernier control.
In any event, here is a take-away from the JPI Procedure:
After letting the engine run for a minute at ~50*F ROP, "With a non-vernier or quadrant mixture control, lean slowly and smoothly about 1/16 inch every five seconds (note: leaning accurately with a quadrant system is difficult due to its mechanical linkage)."
From experience, the quote needs a bit of adjustment to address that attempts to lean while in moderate turbulence is even more difficult than usual.
Have found that if not leaning per JPI's recommendation, the system will not really balance out and the monitor will take the mixture all the way down to running rough even though it shows that LOP was not achieved yet. If this happens, go back to ~50*F rich, wait a minute, reset the monitor, and lean again.
You can also find LOP from the lean side. Lean until well LOP then enrich until the first cylinder peaks - that’s your richest. Then lean back out until 20deg LOP or what ever your looking for. Busch has made claims that spending too much time looking for peak may contribute to problems staying in the red zone too long.
A slow leaning definitely leaves you in the red for too long. GAMI recommends what they call the big pull. If you have properly calibrated gami injectors you can pull back until the engine shuts down and it will run smoothly. Of course in real life you wouldn’t do that but you definitely want to set the mixture from the lop side. Just get very lean then slowly enrich the mixture until a CHT or TIT gets close to your own comfort level. I have found in my Seneca that I can enrich to almost 75% and still be within limits. This is not only not bad for the engine but actually allows for very little speed loss while running much cooler than ROP. If running rich of peak you must run at least 100 degrees rich of peak.
Splechajr has some good feedback on operations. In practice you will have your rpm, altitude, and MP settings you typically use for cruise and will just pull back to the last LOP fuel flow use used and make some tweaks from there.
It is very similar to operating a TSIO-360. "Everyone" warns you about the dangers of overboost and how it is complex with risks not seen in any other engine every made. How they knew someone that knew someone that read about a pilot that came across another pilot that overboosted the engine to 60 MP and it exploded.
If you set up for 65% power ROP you can do anything you want with the mixture knob with no risk at all. Slow, fast, till they all cut out, doesn't matter. This is the best way to learn. Once you get the hang of it then try at 75% settings.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Amazing amount of experience here. Thank you everyone for your input.
What speeds do you see LOP? I've tried in my Seneca but was too slow to justify.
Tokirbymd,
One path is to go to LOP at 65% power and then increased MP for 75% while nudging even farther LOP.
Think of this as adding MP for power but from the LOP side vs ROP. So, instead of richer or full rich you go leaner as you add power.
This will recover performance but will also likely require some effort on tuning injector flows, ignition timing, spark plugs and harness, maybe mags.
The perfect setup would also include engine monitors that scale engine hours based on tach time so you could dial the RPM back, bump up the MP and perfect your LOP flow. ;)
On the flip side, LOP often favors a higher RPM as this translates into a faster piston speed that works better with the slower LOP flame fronts.
I think electronic advancing ignitions make a big difference for LOP operations but personally I think the SureFly advances too far.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
I haven't tried bumping up the MAP to regain the lost power yet. In theory, that would work since fuel flow is limiting when LOP. But my concern is how the fuel throttle body works- as the throttle butterfly is opened for more MAP, it alters the fuel delivery as well and therefore you may have some cylinders go peak or slightly ROP without knowing it? Wouldn't you have to go find the peak again at a different throttle body position? In a normally aspirated plane it doesn't matter as you really can't hurt it at normal cruise altitudes. But the turbo is a different beast (although have seen recommendations from GAMI to consider 33" as "full throttle" in their APS seminars). So the question that I haven't been able to find a reliable answer for- if I start at 65% LOP and increase MAP to 75% MAP settings, will I still be LOP? If my CHT and TIT all remain similar or can be adjusted back to that value is my engine safe?
`Hi,
The fuel/air mixture should be stable over this range of power setting. When I was a partner in an RV-10 we installed a wide band Air/fuel O2 sensor in the exhaust and I was wondering similar but it turns out the fuel system did an excellent job of maintaining a consistent air fuel ratio over a very wide band of power settings.
Generally there is an idle setting and at high power most will run a little richer but in between the mixture does not change if the mixture lever is not moved.
going from 65% to 75% by bumping MP would likely require a slight tweak at most in mixture.
The big challenge is you want to pull to 65% power, adjust LOP mixture for 75% LOP settings and then increase MP to match 75% fuel flows.
The challenge is 75% power is -50 deg LOP and most planes are not dialed in enough to operate here. Usually there is an issue with the mags, plugs, wires, air/fuel/balance and one or more cylinders start to misfire at x% frequency and you get a rumble that is uncomfortable.
The Cirrus crowd loves fiddling with stuff like this and some run even higher than 75% power LOP in cruise. If the system is set up perfect you will have smooth operation all the way to -75deg LOP and then just a little leaner and the engine shuts off on all cylinders at the same time.
I think to consistently operate here you need engine monitor, electronic ignition with advance/long duration spark, fine wire plugs, new harness, dialed in injectors, etc.
The experimental crowd has a much easier time of it as they have access to advanced ignition systems like this one. The next best would be ElectroAir systems (that are certified)
https://lightspeed-aero.com/Products/IgnitionBasics.htm
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)