LOP or ROP, which do you run?

I've always grown up around piston engines with the party thought that ROP is where you run. Period. It's better for cooling, power, longevity, etc.

I've done a ton of reading, especially Mike Busch's articles about the benefits of running LOP. Less internal pressure, less heat produced, less stress on the engine, more longevity.

I was starting to become a believer in this school of thought until I started talking to engine shops/builders. A certain shop has said that not only can they tell immediately if you've been running LOP, they'll void the warranty if you do. Also that people in the LOP crowd are keeping their shop packed with top overhauls.

I'm curious where you guys are at with respect to each crowd. Who here aggressively runs LOP, and how many hours do you have on your engine?

I figure if the engine shops are right, and they're replacing valves and valve trains at 1000 hours... then the $5000 saved over 1000 hours with a 1gph savings doesn't cover the engine work required or the voided warranty.

Discussion, GO!

They are not telling you the whole story

You mean they void the warranty when the engine is not plugged up with lead?

If what they say is true then the real answer is the engines that end up back in the shop are not being run LOP either..More like that are run at peak or just into the ROP side.

Thats where detonation happens.

Truely running an engine LOP cannot "wear out" the top end, tempoeratures are lower...How do you burn a valve seat with lower combustion temperatures..It doesn't make sense.

The big radials that were run by the airlines and WW2 bombers did not suffer from burnt up engines..and some of those would not make across the Atlantic otherwise.

Besides you can do significantly better by running autofuel (with or without ethanol). Add the 1.5 GPH plus the cost difference adds up to the total cost of an overhaul in 2000 hours. At least it did last time I looked.

I have about 500 hours LOP

Frank

I attended a forum at OSH put on by Lycoming. They are not pro LOP due to so many different set ups and applications, and because it requires constant monitoring by the pilot. However, they did say there engines can run LOP safely if done properly. The engine must be set up properly, injectors balanced so that they all peak close to the same fuel flow rate, each cylinder must be monitored accurately, ect. With today's engine monitoring systems experimental use that is no problem.

It makes sense to me to run LOP at altitude due to cooler running temps. After Pierre gave me a refresher course over the phone I am comfortable running LOP.

I started running LOP several years ago while operating an old Bonanza with a Continental IO-470. Reading John Deakins articles in Avweb made me a believer. We had to have that engine overhauled at around 900 hours due to a crack in the case. No relationship to running LOP, just a high time case. The well known overhaul shop that did the work told me that it was a shame that we had to open it up, because it looked great on the inside. He told me that he gets a lot more work from people who run their engines too rich than LOP operators.
I have about 400 hours on my RV-10 and run aggressively LOP most of the time. I had to have a cylinder off a few months ago at the request of the overhaul shop to insure that a part was the correct one. The valves looked great.
Running 35 to 55 degrees LOP at 10000 ft. gives me about 155 Kts TAS at around 10 gph. Running 75 to 100 degrees ROP at that altitude gives me at least 165 Kts TAS, but burns more like 14-15 gph. That is significant at todays prices.
Read John Deakins and Mike Busch and follow their guidance, and your engine and your fuel budget will love you for it.

$.02 worth

LOP on carburetor engines?

I'm still flying with a traditional O320 (150hp) normally aspirated engine. I may be naive so I'll just ask - is it reasonable / possible to run this setup LOP?

I am still trying to wrap my head around the LOP concept. My engine will run comfortably lean of peak however I have 10 to 1 pistons. Its a ECI engine and ECI recommends you don't run LOP. They however recommended that at cruise running at peak was fine which does not make sense to me. Lycon also does not recommend LOP operations with there engines. Most that they build up have higher compressions.
Basically I am still trying to figure out of there are issues with higher compression that make LOP not advisable for long term engine health.

George

The whole subject has devolved into oft-repeated opinion, without much underlying hard data. For example, where is the plot of measured combustion gas temperature vs mixture, or better, a plot of exhaust valve temperature vs mixture?

You can find general trends in something like Taylor's "The Internal Combustion Engine..", but specific to aircraft engine valves even the bibliography there references an SAE paper from 1940 (Cotwell, "Modern Aircraft Valves"). Where is the current research for a flat Lycoming or Continental?

On a different tack, consider the wide variation in installed CHT we see in builder reports and the effect on valve temperature. When Builder A is running 390F at full rich and Builder B is 320F, can we blame subsequent use of the mixture handle when they have different cylinder lives? The difference is baffling and mass flow.

Likewise, consider variation in valve seating quality (the primary heat transfer path). If a particular shop is seeing a lot of their cylinders back with a valve sealing problem, maybe it's not the operator.

Sig600 said:

Discussion, GO!

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Lycoming endorses running at PEAK EGT! I'd like to know how running cooler than that and with less combustion pressure is more damaging?

I run LOP whenever possible. Essentially, if I don't need max power, I'm LOP.

Electronic Ignition?

humptybump said:

I'm still flying with a traditional O320 (150hp) normally aspirated engine. I may be naive so I'll just ask - is it reasonable / possible to run this setup LOP?

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If you have EI with some advance capability - I think it is possible, even with a carb. I run LOP 90+% of the time. Here is a link to some of my early testing.

As Tim Olson once said "I drank the LOP Kool-Aid, and got the T-shirt, too" It works well for me.

I run Rich of Peak EGT on the hottest Cylinder

I run Rich of Peak EGT on the hottest Cylinder all the time but MPG is not my highest priority usually. Operationally it works just fine for me.

Bob Axsom

First off

I only run LOP when I'm trying to stretch a cross country leg. Otherwise I run 100 - 125 ROP for max power (did'nt build a fast airplane to fly slow).

Sig, it is more like 2 gph saving (at least) on fuel flow at 25 -50 LOP. You are going slower, so there is some offset, but the savings are there and they are generally more than 1 gph.

Dan, I think that there is scientific data out there. Check Deakins and you will find lots of references to documented info on combustion temps and pressures etc. All derived from their thoroughly instrumented test stand. Maybe the most extensivly instrumented test stand data available in the public domain.

I am sure that you can get engine damage from poorly managed engines - whether they be ROP or LOP. My understanding is that per cent power is key - 75 - 65% be careful, below 65% you can ham fist it. Everyone including Lycon seems to agree with this. For instance, you certainly can not run LOP without risk of damage during low altitude WOT take off's.

Not sure what engines Sig's experts are seeing, but I really doubt that they are properly managed, ROP or LOP.

The debate goes on!!

gereed75 said:

Not sure what engines Sig's experts are seeing, but I really doubt that they are properly managed, ROP or LOP.

The debate goes on!!

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They've been mentioned in this thread.

gereed75 said:

Dan, I think that there is scientific data out there. Check Deakins and you will find lots of references to documented info on combustion temps and pressures etc. All derived from their thoroughly instrumented test stand. Maybe the most extensivly instrumented test stand data available in the public domain.

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They run the GAMI dyno for profit. Perfectly reasonable, but the knowledge goes into products or sales support, not published papers. Prove me wrong.....show me the late model Lycoming data.

The debate goes on!!

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Sad ain't it?

They've been mentioned in this thread.

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Lycon? Their guy is quoted in this recent AOPA article as fine with LOP....well, under "carefully controlled conditions": http://www.gami.com/articles/frugalflyer.php

So the real question to all this then is, what role does fuel play with the valves as far as cooling. Seems to be the guides/seats that are taking the punishment LOP depending on who you talk to.

I'd just really like to find ONE engine shop/builder to corroborate the LOP philosophy. The arguments make sense, but I've yet to find any real data to back it up.

yep Dan your right

Looked back at all the articles and did not see any published data, only reference that the data exists.

When I said Lycon I meant Lycoming.

Dan's link to an article on the GAMI site quotes builders who attest to good internals on engines run LOP. Monty Barrett is one who says that regularly LOP engines are more healthy inside on tear down. Dan knows Monty well. Dan, can you coroborate that for Sig??

allbee said:

I also found that to reduce cht temps the only way to do it is LOP operations, ROP does nothing.

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I assume you are saying that when your ROP, richening the mixture further does not reduce your CHT's. If that is the case you have a problem somewhere.

another data point

Just to add my experiences to the discussion and perhaps provide someone another data point, I submit the following information.

I have been running aggressively LOP every since my engine was broken in. This started after about 25 hours on a new ECI IO-340. I now have just over 100 hours.

I run ~30-50 deg LOP whenever possible. I have also run around ~50-100 deg ROP at cruise to compare temperatures. What I have seen is that when looking at CHT & EGT temps I get the following trends:

During LOP operations I tend to see CHT temps ranging from 310-320 degrees. EGT temps ranging from 1375-1400.

During ROP operations I tend to see CHT temps ranging from 350-375 degrees. EGT temps ranging from 1250-1325 degrees.

An interesting thread so far

A certain shop has said that not only can they tell immediately if you've been running LOP, they'll void the warranty if you do. Also that people in the LOP crowd are keeping their shop packed with top overhauls.

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Sig, my first comment is thats just rhetoric, anecdotal rubbish, unless its back by hard factual data. I bet they did not have any. Did they show you a properly set up engine Dyno with the ability to monitor ALL the parameters necessary to prove their claim. Of course not, if they did they would suddenly change their tune.

Frankh .....so true.

humptybump

I'm still flying with a traditional O320 (150hp) normally aspirated engine. I may be naive so I'll just ask - is it reasonable / possible to run this setup LOP?

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Yes it is, you need all 4 EGT probes accurately positioned at the same distance (typically 2-3") from the head, and 4 CHT probes and an engine monitor with fuel flow. They you can experiment safely. If you know what you are doing you can do it but numbers.....but thats a mental exercise too big for this post.

Sailvi767........you need more detonation margin than us, so more ROP or more LOP....... Attend an APS seminar....NOW!!!

Now here is a can of worms

For instance, you certainly can not run LOP without risk of damage during low altitude WOT take off's.

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Lets think about this for a minute, WOT say 29.5"MP, say 2500RPM, and lean of peak at a suitable temp LOP.

Now apart from the fact the time it would take to get to something like 100LOP or whatever the number would need to be is going to take longer than the runway allows, so its impractical, compare that to a turbo IO550 or IO540 in the cruise or gentle LOP climb?

What you cant do is do it at 10-20F LOP.........

So the real question to all this then is, what role does fuel play with the valves as far as cooling. Seems to be the guides/seats that are taking the punishment LOP depending on who you talk to.

I'd just really like to find ONE engine shop/builder to corroborate the LOP philosophy. The arguments make sense, but I've yet to find any real data to back it up.

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OK so lets have a look at your real question. What role does fuel play with the valves as far as cooling is concerned. Answer is simple. NONE, it actually provides heat, otherwise your engine would not run. now before you get all cranky at my seemingly wise guy answer, think about this for a minute. Fuel makes heat in the combustion process, not cooling. No arguments, end of story. Evaporative cooling if you pour it on your skin is not inside your running engine.

So lets look at the combustion process. Adding more fuel into the mix seems to drive CHT's down, but why? Well the best way to drive CHT's up is through detonation, getting a perfectly correct mixture and firing it at the worst possible time so the peak pressure pulse happens nead TDC. In your motor car you have knock sensors and all sorts of things to control fuel delivery (mixture) and spark delivery (timing). So in your IO-XXX you have fixed 25deg BTDC timing so to slow down the combustion event and get the peak average pressure on the downward stroke and avoid detonation you can retard the event by what means? Timing=No, so the only other option is fuel volume. Two way's, more fuel will make it hard to go bang so richer retards the event, or leaner, which is harder to get the bang going and then does so with less heat (because less calories inserted).

So fuel does not cool. But by varying the mixture we control the combustion event.

Now back to valves......which of the three has a higher heat content? The lean of peak, low calorie, slow moving combustion event, The really good volatile bang event or the even higher calorie but slower rich event? The answer now is obvious, the big bang or near detonation has the highest, the ROP is next and the LOP is the least amount.

So which is better for your heads valves etc? LOP of course, but LOP enough to be out of the detonation zone.

I do not have an engine shop like GAMI, but I have proven this myself with engine data from the Dynon D180. Its simple once you know what is truth and what are Old Wives Tailes peddled by these head in the sand engine shops, flying instructors, chief pilots and engine manufacturers.

Now you would think I am on commission, and I am not, but I will keep saying this for as long as people keep asking, whether you believe or not, the best $900 or so Yankee greebacks you have ever spent on your education, engine preserving, fuel saving and life saving is by attending an APS seminar.

Go in with a non believer attitude if you wish, they will not berrate you with anecdotal rhetoric, they may make a few jokes, but seriously they will give you HARD FACTUAL DATA, and whats more if you do not understand what you see they will explain it all. Then you make up your own mind.

If I have made mistakes above....I apologise, its 1am, I have been up since 4am, and its zzzzzzzzz time now.

Hope this helps.

PS if you want to read about leaned not enough or not rich enough causing engine failures and deaths of paying passengers, read here;

http://www.airsafety.com.au/pelp0057.html

http://www.avweb.com/news/pelican/182153-1.html

You will want an engine monitor, and the knowledge on how to use and understand what its telling you.......yes...APS seminar!

Nitey nite!

Sig600 said:

So the real question to all this then is, what role does fuel play with the valves as far as cooling. Seems to be the guides/seats that are taking the punishment LOP depending on who you talk to.

I'd just really like to find ONE engine shop/builder to corroborate the LOP philosophy. The arguments make sense, but I've yet to find any real data to back it up.

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Mike Busch is 200% beyond TBO with his airplane. LOP is part of the equation to this success.

Some of what he has written -

"Unfortunately......50?F ROP is almost precisely the worst possible mixture setting from the standpoint of engine longevity. The maximum cylinder head temperature (CHT) and peak internal cylinder pressure (ICP) occurs almost precisely at 50?F ROP. So using the "recommended lean mixture" assures that your engine operates at the hottest, most stressful corner of its operating envelope."

"Given the choice between operating ROP or LOP, LOP operation has some compelling advantages: It's cleaner, cooler, less stressful on the engine, and uses a lot less fuel. Or, as the latest APS mantra goes: "Leaner is greener."

Mr. Busch's forum talks at OSH were very informative, don't miss them next year. He knows as much about the internal workings of a Lycoming engine as anyone. One has to believe something in this business, his philosophy is credible, backed up with lots of experience and worth following.

I lean as much as possible, it makes good sense. Even Lycoming now recommends leaning after start before take off. LOP in cruise is a no brainer, do it. The fuel savings is about 8% and you loose 3% speed, what a good deal!

Instrumentation to run LOP....

....is very reasonable if you are currently with a basic steam gage panel.

EIS-4000P $995

Package for Lycoming/Continental 4-cylinder engines includes EIS Model 4000 Instrument, 4 EGT probes, 4 CHT bayonet-type CHT probes with adapters, Oil Temperature Sensor, Oil Pressure Sensor, and pre-wired cables. Save $145.

I'd do it even with a carb set up. You can't balance the induction fuel flow to each cylinder but you sure can monitor what's going on and get into LOP if the flow is reasonably close. If they all show a negative EGT number soon after the first peak, you are in. That will depend on altitude, temperature and a host of other things that can affect fuel flow with a carb.

I have EIS 4000 and it provides as much useful data as any system on the market.

What about Peak?

Maybe I am crazy but I always cruise at peak EGT. I have a Superior XP IO360 and JPI EDM800 engine analyzer in my RV8. The Superior manual states running at peak is fine below 75% power. According to the engine OM graphs the lowest specific fuel consumption (lbs/hp-hr) is at peak. This means to me that I am getting the most useable energy out of the fuel I burn. LOP would give best endurance if you want to fly around in circles but peak gives best range. So far 450 hours and no issues. I have also participated in nine Sport Air Race League races and run those at WOT, 2700 erpm and 100 ROP for best power.

jrovey said:

........run those at WOT, 2700 erpm and 100 ROP for best power.

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and it seems "best power" was a bunch more than I had.

Largely about CHT management

jrovey said:

Maybe I am crazy but I always cruise at peak EGT. I have a Superior XP IO360 and JPI EDM800 engine analyzer in my RV8. The Superior manual states running at peak is fine below 75% power. According to the engine OM graphs the lowest specific fuel consumption (lbs/hp-hr) is at peak. This means to me that I am getting the most useable energy out of the fuel I burn. LOP would give best endurance if you want to fly around in circles but peak gives best range. So far 450 hours and no issues. I have also participated in nine Sport Air Race League races and run those at WOT, 2700 erpm and 100 ROP for best power.

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Welcome to the VAF forums!

It is all about cylinder temperatures - see the Lycoming chart below:



Per the chart, best economy and range is in the left most grey column. The specific fuel consumption shows essentially flat from peak egt towards the left down to about 80 or 90 degrees F LOP. Yes, one will fly slower at the LOP speeds, but one will not give up specific fuel consumption (range), until about 100 LOP. However, what is dramatic in the LOP side is the reduction in cht. It is very easy to drop the cht's by 50 degrees F simply by dialing back the fuel burn slightly. Most seem to agree that cylinder life is improved by lower temperatures. I have documented this same area of the chart using my plane elsewhere in these forums, and it correlates very well with this ancient Lycoming chart.

I find it interesting that the line for specific fuel consumption is flat through the best economy range, the top of which is at peak. That suggests to me that jrovey's point is pretty correct in saying that his specific fuel consumption is best at peak. I'm assuming your speed at that point is slightly better than where you would be at lean of peak as well. So to me, that says that running at peak is the fastest economy speed you can go.

Geico266 said:

I attended a forum at OSH put on by Lycoming. They are not pro LOP due to so many different set ups and applications, and because it requires constant monitoring by the pilot. However, they did say there engines can run LOP safely if done properly. The engine must be set up properly, injectors balanced so that they all peak close to the same fuel flow rate, each cylinder must be monitored accurately, ect. With today's engine monitoring systems experimental use that is no problem.

It makes sense to me to run LOP at altitude due to cooler running temps. After Pierre gave me a refresher course over the phone I am comfortable running LOP.

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I attended this forum as well and to echo what Larry posted above, here's my notes:

- Randy Jenson, Lycoming Director of their Advance Solution Center was the presenter

- BLUF: Lycoming?s stance is LOP is an acceptable operating mode, but you need to know when and how to do it safely

- Started off with some theory ? Why go LOP? Answer to get best economical fuel flow (ie BSFC), or IOW the most HP for the least fuel flow (FF)

- Trade-offs: power (very sensitive to small changes in FF LOP), decreased detonation margin, need for complete instrumentation to ?navigate? the ?danger zone? (used the analogy of ROP=VFR and LOP=IFR)

- Lycoming?s perspective ROP gives more detonation margin and reduces their concern over EGT spread and the fact that as cylinders lean out one or more could end up in the danger zone

- Stopped short of actually recommending LOP ops: Here?s why (Personal note: I think this has to do more with their legal dept than anything):

-- Over 600 engine configs in production

-- Large number of variables involved in safely running LOP, some of which are airframe dependant and out of Lycoming?s control (ie instrumentation)

-- Lycoming SI 1094D Fuel Mixture Leaning Procedures is written to accommodate the widest range of installations possible so is necessarily generic in nature

-- Not matter what, they recommend the following: 1. Calibrate engine instrumentation annually, 2. Adjust mixture slowly, 3. Observe max temp limits, 4. Return mixture slowly (Note: this is their ROP advice)

- ROP vs. LOP is a personal choice

- Lycoming is in the process or reviewing and updating SI 1094 and is also working with some airframe manufacturers (he didn?t say which) for LOP procedures in POHs

- Admitted POH?s and other documents needed refinement

Randy did not really talk about LOP procedures. In fact he spent most of the presentation basically tap dancing around LOP ops. While they recognise that the move to glass cockpits and complete instrumentation makes LOP a viable option, they are clearly providing recommendations based upon the most denominator, the guy with one EGT probe that may or may not be calibrated.

LOP climb out, LOP at Low Altitude, LOP with Pmags

LOP is how I usually run. Does not work well on a cold engine by the way! I even run LOP on climb out, if I already have a warm engine. After initial pullup, I prefer a cruise climb for visibility anyway, so reduced power is okay.

I run dual Pmags and have full Grand Rapids instrumentation, which really makes it easy. I suspect that the dual ignition also reduces the cooling effect of extra fuel because it burns it so well. My CHTs do not drop nearly as dramatically ROP as the chart indicates.

I have flown in conditions where I had to run LOP just to maintain CHTs below 400 at full throttle, I mean high DA, high temp conditions. A more typical cruise for me is 7.2 GPH, 325 F CHTs, 165-172 knots true, running 75 LOP.

Since my homebase is 4500 feet, I don't get to fly low very often, and had been reluctant to run LOP at low altitudes, but a couple of recent runs through the Columbia Gorge got me tuned into LOP down low. What I do to avoid detonation potential "the Red Zone" while transitioning ROP-LOP down low is to pull power, then pull the red knob, then push the power back in.

I got my full burn down to 8.6 at 700 MSL which I think is fantastic, before it was more like 12! Sure you lose twelve knots, but the fuel burn is so much better, plus who needs to fly faster than 175 knots through the Gorge!?!

If I forget to lean, I am reminded by my CHT's, they start pushing 400 in warm weather, then I lean and they drop by 75 degrees or so. And my fuel burn goes down by about 3 gallons an hour or so.

When I used to run rich down low, I had a few minor lead fouling problems on the spark plugs, but no more.

I run NGK auto plugs by the way, and have through experimentation determined that the EIX (Iridium) versions really do improve LOP operation. My experiment was simple, regular NGK on one pmag, EIX on the other, then switch off the pmags in LOP mode, both on the ground and in the air for comparison. EIX's clearly run smoother further LOP. I can get as far as 130 LOP without stumbling.

CHTs are a big determining factor for me. Sometimes in the winter at altitude my CHTs get too low, (I consider anything under 325 F to be a little low) so then I run the engine at peak EGTs to warm it up.

Hans

Phlyan Pan said:

I find it interesting that the line for specific fuel consumption is flat through the best economy range, the top of which is at peak. That suggests to me that jrovey's point is pretty correct in saying that his specific fuel consumption is best at peak. I'm assuming your speed at that point is slightly better than where you would be at lean of peak as well. So to me, that says that running at peak is the fastest economy speed you can go.

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The chart shows specific fuel consumption the same at peak as in the LOP area (until going beyond the grey LOP area). I don't believe it.

Fuel flow drops when going into LOP, typically like 8%, but speed drops about 3%. That has been documented. BSFC has to improve in the LOP operation over peak CHT operation.

Beyond that, operating at peak CHT will shorten engine life. High EGT, cold starts, dry starts, cycles, internal rust and dirt all contribute to engine life.

If you must fly fast, it does not come free. Even Lycoming acknowledges this fact in the Flyer "Longer engine life may be expected from most engines when the operator is willing to sacrifice maximum performance for conservative cruise operation in the 60% to 65% power range."

Flying fast may be fun and necessary at times, but you can't have your cake and eat it too. It ain't free.

I kicked my usual 8 gph cruise up to 9 gph returning from OSH because I wanted to get home sooner than later. Speed increased about 12 knots but I was still running at 58%.

With my engine, I figure 10 gph is 65% but the fuel mileage goes down. All LOP 30-40F.

I normally run 100 ROP, 75% power, and burn in the neighborhood of 10.8-11 GPH.

On the way back home from Oshkosh this year, at 10500MSL, I followed the LOP operations advice I'd learned and tried it, and got 57% power, 20.7" manifold pressure WOT @ 2400RPM, 160kts GS and 7.4-7.5 GPH, which gave me 20.5 nm per gallon according to the Dynon with whatever headwind component I had on the nose.

CHTs came down into the low 300's, EGT in the mid 1300's and incidentally, my usual hottest cylinder #2 became the lowest CHT at 300.

The engine was still running smooth as silk and only got a bit rough immediately before flameout when pulling the mixture back further. Airspeed suffered much at lower power settings, so I just used the 7.4-7.5 GPH which seemed to maximize the "miles per gallon" the Dynon was telling me.

I want to throw a wrench into the equation here. Lets look at an automobile. In the old days we use to set the engine up with carbs for best idle. That's turning in the mixture(carb) until it stumbled, than back out until the highest rpm. That's what we did. Than came the emissions standards, they set the carb at the factory and put those covers over that gave a little adjustment but not much, than they eventually sealed the mixtures, which I would just drill out and do over anyway. But the factory setting was always in about 1/4 turn from the highest rpm. Which in my book is a lean of peak senerio. Than altimately came fuel injection, which is set by the computer for 12:1 burn. We only have computers to maintain 12:1 fuel burn, there is no other reason for the technology. So If an automobile 4stroke engine can run LOP or 12:1 air fuel ratio, than why can't our 4stroke aircraft engines do it.

Oh and if you do LOP your doing the green thing, better on emissions. Your not stinking up the air and creating harmfull gasses. So not only are you saving money in your pocket, your helping out the air we breath.

allbee said:

So If an automobile 4stroke engine can run LOP or 12:1 air fuel ratio, than why can't our 4stroke aircraft engines do it.

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Water-cooled vs air-cooled cylinders & heads, and the different kinds of power settings that an aircraft runs versus how hard the engine is run in a passenger car.

Engine-destroying detonation occurs much more easily with CHTs climbing above 300 degrees F, than they do in an auto engine with its CHTs in the low 200's. If you ran a passenger car engine like you run an aircraft engine, then you'd be lugging the car engine in high gear, at low rpm and wide open throttle, and uphill all the time.

allbee said:

I want to throw a wrench into the equation here. Lets look at an automobile. In the old days we use to set the engine up with carbs for best idle. That's turning in the mixture(carb) until it stumbled, than back out until the highest rpm. That's what we did. Than came the emissions standards, they set the carb at the factory and put those covers over that gave a little adjustment but not much, than they eventually sealed the mixtures, which I would just drill out and do over anyway. But the factory setting was always in about 1/4 turn from the highest rpm. Which in my book is a lean of peak senerio. Than altimately came fuel injection, which is set by the computer for 12:1 burn. We only have computers to maintain 12:1 fuel burn, there is no other reason for the technology. So If an automobile 4stroke engine can run LOP or 12:1 air fuel ratio, than why can't our 4stroke aircraft engines do it.

Oh and if you do LOP your doing the green thing, better on emissions. Your not stinking up the air and creating harmfull gasses. So not only are you saving money in your pocket, your helping out the air we breath.

Click to expand...

Actually modern car ECUs are set to run AFRs at 14.7 (stoich and peak EGT) or even leaner (up to 17 to 1) with targeted AFRs using wideband sensor feedback during light load cruising. The new cats are capable of cleaning things up even well LOP. Engines will run in the high 11s or low 12s at full load and high rpm for max power and to preserve piston integrity but this is usually only for short durations in automotive use where 95% of the time the engine is at light load and running very lean for mileage and emissions.

Until the sample size of engines run exclusively LOP to TBO (whatever that number ends up being) becomes sufficiently large it is all just smoke and mirrors....

RV8R999 said:

Until the sample size of engines run exclusively LOP to TBO (whatever that number ends up being) becomes sufficiently large it is all just smoke and mirrors....

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...The physics of LOP are not new - running big MP/low RPM and LOP was promoted heavily by Lindbergh back in the P-38 days as a way to stretch range. The thing that?s new is the ability to really get in and monitor the engine effectively. Back when it was rare to have an engine with even a single EGT probe, it?s no surprise that navigating the danger zone of detonation was risky ? you?re blind. Relate this to the navigation aids we have today ? after flying with GPS and on board XM weather, would anyone ever really try fly an approach to minimums with only an ADF?

The fact that Lycoming itself recommends peak EGT - the most potentially damaging condition short of detonation ? for economy cruise provides all the endorsement I need to run LOP. LOP simply ?takes it down a notch? (temp and pressure).

I think comprehensive engine monitors are a game changer, just like GPS and XM weather... It will just take a while to embrace the tools we have available.

Phlyan Pan said:

I find it interesting that the line for specific fuel consumption is flat through the best economy range, the top of which is at peak. That suggests to me that jrovey's point is pretty correct in saying that his specific fuel consumption is best at peak. I'm assuming your speed at that point is slightly better than where you would be at lean of peak as well. So to me, that says that running at peak is the fastest economy speed you can go.

Click to expand...

My Superior BSFC chart is not flat and it is lowest at peak EGT. I would post the graph but don't have permission yet. I agree the specific fuel consumption does not increase much and fuel savings is small when running a little on the LOP side but I like peak. Fastest way to get there for the least amount of fuel at a given power setting. I also agree with the cooling concern comments but my baffling works well and CHT's are in the 320 to 350 range.

My typical long distance flight starts with takeoff and climbout at 100 ROP and constantly pull on the mixture to keep it at 100 ROP. Once I get below about 70% I pull mixture back to peak. The entire flight except for decent is with the throttle all the way in. Assuming wind is not against me I climb to the percent power I want to cruise at which is usually about 65% and somewhere around 11-12,000 feet.

I just don't believe it is as simple as lower pressure and temp when LOP.

Based upon the chart for the 0-360, running LOP results in lower power. If you run LOP and accept lower power (slower A/S) to save fuel that is great but why not run ROP and throttle back to the same power you had at LOP which also lowers pressure, temps.

The throttle is the most efficient fuel control we have.

The real test is to fly two runs at the same DA both at WOT (altitude sufficient to fly LOP at WOT of course)

Run 1: lean to whatever LOP setting you think is good noting FF, A/S, CHT, EGT, etc.. while maintaining alt

Run 2: lean to 100 deg ROP, then throttle back to the FF noted during the LOP test and note the A/S, CHTs, EGT and see how they compare.

Honestly I have not done this test and I'm very curious so I'll fly it tomorrow and tell you what happens.

I get just a little worried when I read of folks being happy LOP because of the "precision" of our available instrumentation these days. Oh, I'm not really worried (I don't think anyone is going to get in trouble....maybe "amused" is a better word. I say this because I can lean using time/temp EGT graphs, fuel flow, bar graphs, "Lean Prompt" functions....or leaning until things get rough, then smoothing it out - and I always end up in the same place.

it's just not as much as a rocket science as some might lead you to believe. The four-cylinder Lycs are just not the same as the turbo-charged big engines in the Bonanzas and 210's (the real target audience for Deakin and GAMA). I DO agree with Deakin on most all points, but I am just not that worried about the O-360's we fly normally aspirated. Peak, LOP, ROP - if it is smooth, it runs pretty well.

I personally run as lean as I can, and that is a good 1.0 gph below the "best power" line on Lycoming's "%HP vs. Fuel Flow" graph most of the time. That is generally LOP, and CHT's are always nice and coo. the absolute value of EGT doesn't mean a thing (depends on where you put your probes), so i don't worry about them. 1350 hours on the Valkyrie's engine running this way so far, with no issues.

Now one thing that I do pay attention to is that if you are deep LOP, you are going t go slower - by a measurable amount. But having the current mpg displayed on the EFIS has shown me that once you get close to peak on the Rich side, the mpg really doesn't change much you just get there slower if you go leaner.

Fly the way that you are comfortable, for sure! I like having an 800 mile range, so I lean it until it squawks, then smooth it out a little. The graphs are happy, as the engine appears to be. I haven't seen much evidence that running this way hurts the powerplant - so long as I don't lean above 75% HP (as recomended by Lyc), and am reasonable between 65-75%. Below that, you can't hurt a thing!

RV8R999 said:

Until the sample size of engines run exclusively LOP to TBO (whatever that number ends up being) becomes sufficiently large it is all just smoke and mirrors....

Click to expand...

Shack.......

LOP -50-60*

IO-360, HI COMP. AFP BALANCED INJECTION, JAMES COWL-PLENUM, IN A -6 IT's FAST AND COOL. 298-306 CHTS AT 8000' CRUISE, OVER 700hrs. A LOT OF THIS AT 75%. YES I GET MORE POWER ROP, JUST CAN NOT PAY THE FUEL BILL.

allbee

I also don't believe in peak operation for that is the hottest temps on the EGT which can kill your exhaust valves. Now if you let things go without monitoring than yes you can have an egt go high on lop and that would be desasterous.

Click to expand...

While reading about your method of operation I was pleased you are doing many things right for the right reasons, but this statement above has me worried. It is plain wrong to say the higher EGT will kill your exhaust valves. That is simply not true, do the research and you will see why.

If you are motoring along all nice fat and happy, LOP and you see on your dynon EMS with its EGT display start flashing a rising and falling EGT, what would that mean to you? A disaster? Lets ask the question with more details to help, the EGT starts rising and stays up, maybe the odd retraction but its fluctuating above 1500F, and likely the CHT is dropping a bit. What does that tell you?

Also, fly along at 20-40 LOP and turn one mag/ignition off for 10-20 seconds, what happens? EGT's all go over 1500 +, speed drops off a bit and CHT's do what?

You are operating your engine nicely but it seems not fully understanding why you are doing a good job. And maybe not appreciating the fault finding value of all the science and information you have at your finger tips.

RV8R99

I just don't believe it is as simple as lower pressure and temp when LOP.

Based upon the chart for the 0-360, running LOP results in lower power. If you run LOP and accept lower power (slower A/S) to save fuel that is great but why not run ROP and throttle back to the same power you had at LOP which also lowers pressure, temps.

The throttle is the most efficient fuel control we have.

The real test is to fly two runs at the same DA both at WOT (altitude sufficient to fly LOP at WOT of course)

Run 1: lean to whatever LOP setting you think is good noting FF, A/S, CHT, EGT, etc.. while maintaining alt

Run 2: lean to 100 deg ROP, then throttle back to the FF noted during the LOP test and note the A/S, CHTs, EGT and see how they compare.

Honestly I have not done this test and I'm very curious so I'll fly it tomorrow and tell you what happens.

Click to expand...

You should do the test, and then you will see exactly what we are all on about. At the same %HP and in the safe detonation margin area, you will get the same speed however your Fuel Flow will be greatly more ROP. I do not recall the numbers now, but for me it was around 35-40% more fuel. Look at the charts you can work it out for yourself.


As for the LOP guys getting better life out of there engines, mate the data is in, it was in back in the 50's and 60's. ANd its back again now. The data and knowledge is here now, just some folk take a long time believing something different to what they were taught and practised for so long.

Here is a little story......., What colour is a Swan? Ask your child to draw a picture of a swan. I bet it is White in colour. Go back a couple of hundred years.....ask the question and all the scientists of the time would swear on a stack of bibles ALL Swans are white. end of argument. Well the British or the Dutch (cant recall who it was) sailed into Western Australia and they saw all these Swans, and they were jet Black. So if you ask me what colour is a Swan, I say it depends. But ask most people 200 years ago they would continue to swear balck and blue they are all white. And take some convincing too!

Have I ever mentioned attending an APS seminar......

And Paul Dye's comments for lower HP Lycomings operated as he suggests. Simple as that but it pays to understand exactly why. It also pays to know what your monitor is telling you. It will save you money longer term and may save your life.

DB

DENMACRES said:

IO-360, HI COMP. AFP BALANCED INJECTION, JAMES COWL-PLENUM, IN A -6 IT's FAST AND COOL. 298-306 CHTS AT 8000' CRUISE, OVER 700hrs. A LOT OF THIS AT 75%. YES I GET MORE POWER ROP, JUST CAN NOT PAY THE FUEL BILL.

Click to expand...

What compression are your pistons?

George

Ironflight said:

I get just a little worried when I read of folks being happy LOP because of the "precision" of our available instrumentation these days. Oh, I'm not really worried (I don't think anyone is going to get in trouble....maybe "amused" is a better word. I say this because I can lean using time/temp EGT graphs, fuel flow, bar graphs, "Lean Prompt" functions....or leaning until things get rough, then smoothing it out - and I always end up in the same place.

it's just not as much as a rocket science as some might lead you to believe. The four-cylinder Lycs are just not the same as the turbo-charged big engines in the Bonanzas and 210's (the real target audience for Deakin and GAMA). I DO agree with Deakin on most all points, but I am just not that worried about the O-360's we fly normally aspirated. Peak, LOP, ROP - if it is smooth, it runs pretty well.

I personally run as lean as I can, and that is a good 1.0 gph below the "best power" line on Lycoming's "%HP vs. Fuel Flow" graph most of the time. That is generally LOP, and CHT's are always nice and coo. the absolute value of EGT doesn't mean a thing (depends on where you put your probes), so i don't worry about them. 1350 hours on the Valkyrie's engine running this way so far, with no issues.

Now one thing that I do pay attention to is that if you are deep LOP, you are going t go slower - by a measurable amount. But having the current mpg displayed on the EFIS has shown me that once you get close to peak on the Rich side, the mpg really doesn't change much you just get there slower if you go leaner.

Fly the way that you are comfortable, for sure! I like having an 800 mile range, so I lean it until it squawks, then smooth it out a little. The graphs are happy, as the engine appears to be. I haven't seen much evidence that running this way hurts the powerplant - so long as I don't lean above 75% HP (as recomended by Lyc), and am reasonable between 65-75%. Below that, you can't hurt a thing!

Click to expand...

I'm with Paul on this - I've been leaning my plane for cruise pretty much by hauling back on the mixture til it starts to croak, then dialing it forward a little. Then I look at fuel flow - and usually (for 22", 2300) I'll see something like 7.2 to 7.5 gph. If I were (and I have many times) to look at where the egt's end up, this will be something like 20 to 50F LOP. Then, I'll watch cht's, which are my "final" arbiter of where to run the mixture. Need cooler cylinders? Lean more. This is where EI helps - one can generally run leaner with EI than without. Of course there are lots of variables, hence the word generally. Balanced FI helps as well, but carb heat and partial throttle seems to work for many carb'd RV's.

Of course, this is likely to ruin the crankshaft gear... (see separate thread started by me...)

Ironflight said:

...
Fly the way that you are comfortable, for sure! I like having an 800 mile range, so I lean it until it squawks, then smooth it out a little. The graphs are happy, as the engine appears to be. I haven't seen much evidence that running this way hurts the powerplant - so long as I don't lean above 75% HP (as recomended by Lyc), and am reasonable between 65-75%. Below that, you can't hurt a thing!

Click to expand...

I think this really is the salient point for this discussion... Below 75% there is nothing you can do with the mixture to harm the engine.

The well taught method of leaning until stumble takes you right through the "red box", or "danger zone" anyway, so once you get to the "other side", why not stay there? The real difference we see today thanks to electronic ignitions is the fact that if "leaning to stumble", you will often go FAR more lean than you would with a set of mags. For example, the -8 used to stumble at 30 LOP, but now with dual Pmags, it will run smooth at 150- 200 LOP... Slow, but smooth.

RV8R999 said:

...Based upon the chart for the 0-360, running LOP results in lower power. If you run LOP and accept lower power (slower A/S) to save fuel that is great but why not run ROP and throttle back to the same power you had at LOP which also lowers pressure, temps...

Click to expand...

It may be a minor point, but WOT is generally the most efficient way to run an air pump, so I suspect that WOT and leaned to a particular speed would net you better efficiency than throttled (and rich) to the same speed.

In any case, there's no harm in getting up high (below 75% power) and playing with it to see how things work out. The change in fuel flow/speed is an interesting dynamic

allbee said:

Just an example, vehicles do not run ROP in any way shape or form. except when the computer system goes funky. Even when first started they are sort of rich just for a few seconds. I don't feel in any way shape or form that we are hurting our aircraft engines running LOP.

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I'm not sure where you are getting this information from? Every time you nail the throttle on a car, the ECU will take AFRs well ROP into open loop mode. Completely normal on every EFI equipped vehicle. Running LOP at high throttle/ high rpm would destroy the pistons in most automotive engines in less than 5 minutes. Peak EGT occurs at stoich which is about 14.7 AFR. Before the advent of wideband O2 sensors, ECUs would target 14.7 AFR in closed loop mode during light throttle/ low rpm to obtain good mileage and provide the best environment for catalysts to work. Most car engines are running around 12.0 AFR (well ROP) at sustained full throttle and anything over about 3000 rpm. When hp and the rate of heat transfer is low, the ECUs run in closed loop mode at peak EGT or LOP for emissions and mileage.

Structurally, these are much the same reasons why Lycoming does not recommend LOP above 75% power although aircraft engines are generally more tolerant due to their low rpms and low specific outputs

Ken

I have also been very curious about the equivalency of reduced power created by simply throttling back vs reduced power by leaning. The amount of HP it takes to fly at say 130 KIAS at 5000' is constant (assuming constant atmospheric parameters). For discussion, let's say that is 130 HP.

The question is - Does it take less fuel to create the 130 HP doing it ROP part throttle, or LOP WOT??

This will really be a question of most efficient engine operation. I am convinced that there are long term advantages to LOP ops - lower combustion pressures and cooler temps as Ross explains above, but is there a practical fuel savings realized in flight ?? I suspect that the amount of fuel required to create 130 HP and the same airspeed in flight will be very close to the same whether it's done at 100 ROP part throttle or 35 LOP WOT. My gut says the LOP fuel flow will be just slightly, very slightly, less than the ROP flow.

Your experiment should tell. Look forward to seeing the numbers.

(I'm sure some engine design guru's already know the answer (like Ross) as there is lots of work being done in the auto world regarding efficiencies at various A/F ratios. Maybe the Lyc charts tell us and I'm just to dumb to see it. I just wonder what it will translate to in flight.)

gereed75 said:

I have also been very curious about the equivalency of reduced power created by simply throttling back vs reduced power by leaning. The amount of HP it takes to fly at say 130 KIAS at 5000' is constant (assuming constant atmospheric parameters). For discussion, let's say that is 130 HP.

The question is - Does it take less fuel to create the 130 HP doing it ROP part throttle, or LOP WOT??

This will really be a question of most efficient engine operation. I am convinced that there are long term advantages to LOP ops - lower combustion pressures and cooler temps as Ross explains above, but is there a practical fuel savings realized in flight ?? I suspect that the amount of fuel required to create 130 HP and the same airspeed in flight will be very close to the same whether it's done at 100 ROP part throttle or 35 LOP WOT. My gut says the LOP fuel flow will be just slightly, very slightly, less than the ROP flow.

Your experiment should tell. Look forward to seeing the numbers.

(I'm sure some engine design guru's already know the answer (like Ross) as there is lots of work being done in the auto world regarding efficiencies at various A/F ratios. Maybe the Lyc charts tell us and I'm just to dumb to see it. I just wonder what it will translate to in flight.)

Click to expand...

I think a good number of us have run this experiment already, but let me give you some numbers from yesterday in my C-172 with IO360 and Gamijectors. In stable cruise at 8500 maintaining 121 knots true, I set the mixture for best power (well ROP) and throttled back to maintain 2500 rpm on my fixed pitch prop. The airplane stabilized at 121 knots true at 2500rpm - with a fixed pitch prop that is a given horsepower under those conditions, and my fuel flow was 9.0 gph. Then I opened the throttle and dialed the mixture back to LOP, about 75 degrees LOP, and controlled RPM by the mixture until I stabilized again at 2500rpm, with the airplane again trueing out at 121 knots. This time my fuel flow was only 7.8gph. Both times I was making the same horsepower, as evidenced by the same RPM on a constant speed prop and the same true airspeed. My fuel flow ROP was 9.0, and LOP was 7.8. I've been running this way for years, I don't need anymore convincing.

I'm surprised at the number of respondents who use LOP operations to control CHT.

Here's a take-it-to-the-bank fact about a fixed exit cooling system: If the components are sized, fabricated and installed to provide proper cooling under climb conditions, the system will have considerable excess cooling capacity in cruise.

So....take this the right way, please, because I'm not saying it to insult anyone: If you must use LOP to maintain an acceptable cruise CHT, you have problems elsewhere. There are thousands of well constructed dead stock RV's whose builders enjoy nice cool cylinders while cruising at best power or peak EGT.

especially after fixing the leaks!

If you are LOP and need to advance the throttle in a hurry to max blast what happens?

RV8R999 said:

If you are LOP and need to advance the throttle in a hurry to max blast what happens?

Click to expand...

Depends on the scenario. Most of the time I'm LOP is at or above 7500 feet, so I'm already at WOT. If I need to climb suddenly, then it's just a matter of setting mixture and prop to the desired settings for max output.

If I'm down around 3500 feet, then I'm still usually WOT, but the prop is pulled way back. In that case, I just jump quickly over to ROP, and then set the prop.

In any case, I don't often put myself in a position to need "max blast" if LOP... The LOP condition (for me) is reserved for relatively stable, long durration flight. Trying to run LOP for pattern or formation work is just too much fiddling, IMHO.

Thanks Greg

That is exactly the info I was looking for. So essentially the engine is running more efficiently LOP (making the same horspower on less gas).

And Dan, it's not to control temps, it is to enjoy lower temps than you would get at ROP. My "normal" (100 ROP) temps are in the mid 300's. LOP is low 300's.

And Toolbuilder, those are my same operating modes - generally already WOT in cruise and often LOP. At variable throttle ops (formation, accro or just screwing around) - comfortably ROP (not always full rich), and throttle jockey yourself silly.

I am also seeing a consenus building for the IO-360 at typical criuse altitudes 8500-9500'. Seems to be 10.5 to 11 gph at WOT ROP, about 7.5 at 25-50 LOP and about 8 knots slower.

One reason for the question is to affirm the best operating mode if you were in extremis - trying to stretch range to the max. Sounds like certainly LOP will get you the best range (as opposed to just throttling back).

Now I have to sit down and figure out exactly what it means for "got plenty of gas, just want to get there fastest" modes of operation. I guess it is a question of "do I want to compromise a bit, burn less fuel, be gentler on my motor, and get there only slightly slower" instead of my usual WOT, 100 ROP.

Gettin' smarter!