Rich of Peak (ROP) vs Lean of Peak (LOP)/Engine operation

[Nick Bailey]

(Note from webmaster: This thread has been split. Please answer the rich of peak/lean of peak questions here, and engine analyzer questions in this thread:

http://www.337skymaster.com/messages...&threadid=1209

Thank you.)


I am the new owner of a NA 75 337 with GAMI jectors and JPI 760 analyzer which I am trying to sort out. Anyone with this setup or similar who might be able to give me feedback on their experiences, settings etc., would be appreciated. I have been reading a little about the raging debate on LOP and ROP and will be attending an Advanced Pilot Seminar at GAMI facility. Anyone have any comment on this topic? With fuel at $3.60/gal, in the US Virgin Islands where I live, I sure am inclined to go LOP. Any 337 owner visiting St. Thomas in the USVI is welcome to give me a call for a sightseeing tour in return for pearls of wisdom. More questions to come.
Regards,
Nick Bailey
nickbailey23@hotmail.com

[docbob]

I have been running my NA engines LOP for years.
Bob

[Ernie Martin]

Nick:

Arguably, this website was created partly as a result of a vociferous argument on ROP vs LOP on another website. I'm a mechanical/aerospace engineer (MS Caltech) who attempted -- unsuccesfully -- to mediate the discord. You can read the for-LOP arguments in GAMI's website (I attended a mini-version of their seminar and had an opportunity to discuss it with their people).

Here's my take, for what it's worth, and I should alert readers that my views have changed a bit since my GAMI visit and given the escalating price of fuel (I fly the Bahamas a lot, where fuel is the same as in the Virgin Islands).

For the average pilot (read: not technically savvy) with standard instruments and unwilling to give added attention to engine management in flight, stick with the POH directions to operate at ROP (typically 50-100 degrees ROP).

Those who are technically astute (you don't have to be an engineer or a mechanic, just someone who is technically inclined and understands the subject), who have installed GAMI injectors for smooth operation across all cylinders at LOP, who have cylinder-by-cylinder engine management/monitoring equipment, who are willing to to give a bit more attention to engine management in flight, and whose engine is no longer under warranty (notice this new point) can run LOP at cruise, and I think they will benefit from it.

BTW, 6 years ago I cruised the Virgin Islands for a week on a rented boat (something between a yacht and a trawler) with 3 other couples and loved it. My favorite: the Baths at Virgin Gorda. Would love some day to see the islands from the air, so I might take you up on your offer.

Ernie

[Ernie Martin]

The website page below has a Lycoming technical paper on operating lean of peak (LOP). It's "must read" for anyone planning such operation. The website was listed in the other Skymaster message board.

http://www.lycoming.textron.com/supp...ps/SSP700A.pdf

Ernie

[Kevin McDonnell]

For completeness, it's worth reading Deakin's rebuttal to the Lycoming paper.

http://www.avweb.com/news/columns/182131-1.html

By the way, Peter Garrison mentions this subject in his November 2004 Flying column.

[Ernie Martin]

Nick Bailey has started a more recent thread entitled "Advanced Pilot Seminar" which deals in part with LOP operation. If they haven't done so already, readers of that thread are encouraged to also read this thread, especially the two references cited immediately above this message.

Ernie

[Richard]

I've been running my engines LOP for a year now. Panel includes the JPI as well. Run the front 50 LOP and rear 75-100 ROP. Fuel flows

8.5 front
10.3 rear

Pretty amazing. Head temps on my bird has never been above 410 yet. JPI with the EGView program is just like having a black box. I have every second of data from every flight from the last 250 hours. Neat program.

[Mark Hislop]

Richard:

Just curious. Why do you run one engine LOP and the other ROP?

Mark

[Guy Paris]

Richard,
Do you have have GAMMI injectors? If you do, how close in degrees are the EGT's during lean find mode? I have a JPI and run at peak when at 65% or less which is usually #5 or #6 cylinder on either engine. Not sure exactly but I think there is about 100 degrees difference in EGT's between hotest and coolest cylinder. guy....

[Richard]

I do have Gami injectors. Looking at my last flight.

Front engine:
Lowest EGT = #1 @ 1398
Highest EGT = #4 @ 1424

Rear Engine
Lowest EGT = #1 @ 1373
Next to Hightest = #4 @ 1433
Highest EGT = #5 @ 1475

I'm having some tuning issues with the rear engine #5. Too lean.

[Kevin McDonnell]

Guy,

The absolute temps for EGT's are actually not very important. Among other things, a difference in probe placement introduces some variations.

What matters is where they are relative to peak. In an ideal world (or with the aid of GAMIs), all EGTs would peak at nearly the same fuel flow. If the spread is too wide, it means some cylinders are much richer than others. Let's say you want to run 125 dROP, then your leanest cylinder (the one that peaks first) should be set to that temp. This means that your richest cylinder might be 225 dROP - which is clearly just wasting gas - perhaps to the tune of 1 to 3 gallons per hour.

If you wanted to run LOP, a wide EGT peak spread would imply that's not possible. A cylinder's not going to run much leaner than 100 dLOP. So if your target was 50 dLOP (for the richest cylinder), that means the leanest would be at 150 dLOP - and would not be producing power. LOP operation requires all cylinders to peak at nearly the same fuel flow. So if you set you’re your power such that the richest cylinder was 50 dLOP, then the leanest might be 80 dLOP. All othes would be between those numbers.

[Nick Bailey]

Kevin is right on about EGTs. important thing is CHTs in terms of engine life. EGTs are for reference only, absolute temps do not matter much except as giving info about the timing of the combustion event. Cool CHTs are supposed to translate to longer engne life, and more importantly if they are cool LOP. ROP operation is typically not as clean a combustion event, not to mention the much higher fuel flows. Empirical Data supporting this was shown at at the AP Seminar. But as Kevin mentioned in the APS thread, the worst place to operate an engine is typically in between ROP and LOP. Most of the engine manuals actually call for operation in this "red box" which actually makes for higher CHTs, and much higher internal combustion pressure (IPC), which shortens engine life. This is because as Kevin mentioned, factory injectors are so poor that the cylinders vary wildly in fuel flow. Hence a typical factory engine, without signifigant tinkering, swithcing of injectors etc, cannot be run LOP. Do the GAMIS make a difference? The AC I bought had them installed already so I can't say. One thing you notice with Gamis is as you lean, engine does not ever start missing cylinders. It just loses power and then all cylinders stop working at the same time. Best test i've had so far regarding fuel flow, is a 450 mile round trip at 7000-8000 ft. and engines averaged about 8.3 gals each at cruise, 2300 RPM, wide open throttle (21 In rear, 22 In front), 149-152 TAS. CHTs were 310-340, oil about 180 front, 195 rear. I was hoping to hear from other owners about their numbers. If you fly 200 hours a year and the GAMIs can save you 4 gals an hour, plus clean plugs, clean engine, potentially longer engine life due to cooler cleaner running, they may start to look more attractive. another thing i have never had a problem with is hot starts, and i wonder if the GAMIs have something to do with that too... Would like to hear more from other owners with monitors and Gamis...

[KyleTownsend]

Kevin M. mentioned John Deakin's rebuttal of the Lycoming paper earlier in this thread.

I recently went over to the avweb.com site and read most of Deakin's articles on engine management (he writes "Pelican's Perch" under the columns section - look for the Pelican's Perch index).

All of this was incredibly interesting. Deakin is unabashedly a LOP advocate. He backs up his arguments with a lot of very good data (much of which comes from GAMI). If you want to get a "full dose" of the rationale behind LOP operation without having to go to a seminar, these articles are the best source that I have found. I highly recommend them.

[KyleTownsend]

On the subject of LOP operation, I am going to summarize my current understanding of the subject, as it would apply to operating a P337 in the real-world. I would like to hear from any of you that are knowlegable on the subject if you detect in errors in my thinking.

1. The main argument for running LOP is that you can save around 10% on fuel at the same effective power setting (same BMEP). Secondary arguments are that LOP operations are cleaner, and therefore better for the engine and the environment, and that peak cylinder pressures and temperatures are also lower.

In a P-skymaster flown 100 hours per year, this would translate into approximately 250 gallons saved per year, or around $750 on fuel costs (about $7.50 per hour). There is the potential for further savings resulting from cleaner running and having good engine monitoring (eg: spotting problems early). These savings could be substantial, but are difficult to quantify.

2. The main impediments to running LOP are that (1) the air/fuel distribution to individual cylinders varies too much and, therefore, they peak at different times. So, if you lean enough to get the richest cylinder running LOP, the leanest cylinder will probably be too lean to run properly, resulting in rough operation. This is the problem that GAMI injectors are designed to solve.

3. The secondary impediment to running LOP is that you need good instrumentation to make sure that each individual cylinder is running within appropriate temperature limits even if you have GAMI injectors, because there is still some variability between cylinders. This problem is solved by getting an engine monitor (eg: JPI).

4. While some people do climb LOP, most people restrict LOP operations to the cruise mode of flight. To implement LOP in cruise, the power is set at some known level (eg: 65%) according to the POH settings. The engine is then leaned so that the richest cylinder is operating at around 50 degrees LOP. This leaning should be done fairly quickly (especially at higher power settings) because you don't want to spend much time at settings in the neighborhood of 50 degrees rich of peak (this is where temperatures and pressures are greatest). The manifold pressure is then advanced to restore the lost airspeed (used as a proxy for power). If done correctly, this should result in the engine operating at the same power, but with CHT's approximately 30 degrees cooler than the same power given by the POH at "best power" settings. It will also result in the roughly 10% fuel savings.

5. In any event, one is not likely to cause detonation, or otherwize damage the engine, if indivual CHT's are kept below 400 degrees or so, no matter what you do with the mixture control (or the manifold pressure for that matter).

Comments?

[Ernie Martin]

You're essentially right. The only other points to add, and some may consider them minor, are these: a) I would expect the pilot to be somewhat knowledgeable in what he's doing (like you are); b) he/she must be willing to devote somewhat more time to engine management during flight than ROP, taking away from sightseeing and other chores; c) engine is not under warranty (LOP voids it); and d) make sure payback period works for you.

Ernie