Can running too far LOP be damaging ?

My friend made a comment the other day but forgot to ask his rationale.

He said that you don't want to run the engine more than 70 degrees LOP.

Why? I have a Superior IO-360, CS Hartzell. 180 hp.

My "go to" numbers for cruise are: 22.8 MAP, 2380 RPM, leaned to 7.5 GPH fuel burn, EGT's are usually low 1300's.

The engine runs smooth, no issues. With the Advanced LOP feature I did check it the other day. I am more in the 90-100 degree LOP range.

Since his comments I've been running 8.0 GPH. That's more in the 50-60 LOP range.

Comments, explanations please??

Thanks

Darren

From everything I have read, there is no problem running as lean as you want as long as the engine doesn't start to miss. Many engines won't get that lean and still run smooth. I have never heard any reason not to run further lean if you can except that economy can experience the law of diminishing returns (losing more power and speed without an equivalent drop in fuel flow).

I have heard that above 65% power you need to be more careful with leaning. Your power setting seems to me to be around 70%.

Darren S said:

My friend made a comment the other day but forgot to ask his rationale.

He said that you don't want to run the engine more than 70 degrees LOP.

Why?

Click to expand...

You've asked the most important question! And his answer will probably that somoene else told him that - not that he has any real reference.

From all of the research I have done, I agree with Jesse - if its smooth,i ts fine. Heck, according to Lycoming, if it is below 65%, then even if it is NOT smooth, its OK - just uncomfortable, and maybe not good for somethign else in the airframe - but the engine won't care.

LOP is good until you end up so slow that you wonder if it is worth it.

Paul

Going exrtemely LOP is just like turning the flame down on a gas stove. I've run the RV-8 out to near 150 LOP, and it is smooth as glass. The more I lean, the slower the airplane goes and the cooler the CHT gets, right up to the point where the engine quits.

The ICP and temps are very low, there's not enough fuel/lead to foul plugs... I'd be interested to hear anyone come up with a reason how this can cause harm to the engine.

Not rocket science (Sorry Paul)

Michael, Paul and Jesse are right on. Couldn't have put it better myself.

Steve

Lean of peak will provide more oxygen in the chamber and exhaust post combustion, so that some would say that it would contribute to more rapid oxidation of the exhaust valve. But - the oxidation rate drops by 50% for every 10C in temperature, so going cooler (and leaner) is better.

Large natural gas fueled engines are extremely lean and allow high compression ratios, high levels of turbocharging and thermal efficiency as good as the best diesels.

So, the answer is a qualified NO. The only area of concern is the exhaust valve, and with as many people we have running LOP, there would be evidence of an issue there, indicating, probably not an issue in our specific engines.

What is your compression ratio, that helps keep power up with altitude and LOP operation.

Maybe David Brown will weigh in here with some data, but using the big pull method to keep from creeping past the EGT peak is better as the exhaust valve (as well as other associated hardware) does not reach that peak only to be exposed to higher oxygen exhaust.

BillL said:

Lean of peak will provide more oxygen in the chamber and exhaust post combustion, so that some would say that it would contribute to more rapid oxidation of the exhaust valve.

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I don't buy that. No matter what you do, you can't get the oxygen concentration above 21%. I understand what you're saying, but I don't think it holds stoichiometric water.

Best economy mixture is roughly 20-50 LOP. Leaner than that, you'll burn less fuel per hour but you'll go so much slower that you'll wind up with fewer miles per gallon. There's no harm in running (smoothly) leaner than that, but there's no reason to.

Disclaimer: All of my study and experience with this is in 6-cylinder Continentals, but I don't think the physics is any different.

Recommendation: If you haven't taken the APS class, either in person or online, it makes EVERYTHING related to combustion much more understandable.

There is no problem for the health of your engine operating very LOP. None. Do not let anyone tell you otherwise.

Paul and others are correct, it just results in much slower airspeeds, which is fine if you are trying to extract a long range out of a fuel load, the issue is the engine efficiency is not at its best, but it is more than offset by the greater loss of drag due to less airspeed. The optimum amount LOP is never a fixed number, it simply depends on where you are in terms of power.

John Deakin published this little table years ago on AvWeb, and what it does is gives you the recipes to aim for.

________________________________________
Red Box = No Fly Zone
• At and below about 60% power, there is no red box. Put the mixture wherever you want it.
• At about 65% power or so, 100ºF ROP to Peak.
• At about 70%, 125ºF ROP to 25ºF LOP.
• At about 75%, 180ºF ROP to 40ºF LOP.
• At about 80%, 200ºF ROP to 60ºF LOP.
________________________________________


________________________________________
Outside the Box
• At 65% power, use richer than 100 ROP, or leaner than peak EGT.
• At 70%, use richer than 125ºF ROP, or leaner than 25ºF LOP.
• At 75%, use richer than 180ºF ROP, or leaner than 40ºF LOP.
• At 80%, use richer than 200ºF ROP, or leaner than 60ºF LOP.
________________________________________


Print that off and keep it in the plane. Remember not all EMS are equal when it comes to % power and if you start at say 75% power ROP by the time you are LOP you will be between 65-70% so you just take a rough stab at something like 10-20dF LOP on the richest cylinder and all is good with the world. Do not split % points. near enough is good enough.

My "go to" numbers for cruise are: 22.8 MAP, 2380 RPM, leaned to 7.5 GPH fuel burn, EGT's are usually low 1300's.

The engine runs smooth, no issues. With the Advanced LOP feature I did check it the other day. I am more in the 90-100 degree LOP range.

Since his comments I've been running 8.0 GPH. That's more in the 50-60 LOP range.

Click to expand...

With all respect to my friends at Dynon and AFS, they lean find features are really a great teaching tool and for establishing the order of peaks, but in flight every day, they are almost useless. Hysteresis in probes, the speed at which you adjust, many things can confuse the algorithms so get comfortable doing it yourself.

I am not a fan of cook book recipes, your "Go To" numbers are fine but you have an RV, you want to go fast or go far. Pick which ever you need for the flight and do it.

Go Fast..... WOT, get every inch you can, use an RPM that is smooth, that could be 2364, 2348, 2507....I dont care, just pick a sweet spot. Then select the appropriate LOP setting, and the best way to do this is do a BMP (big mixture pull) and you will land square in the zone for appropriate LOP. If that is down low at 28.5" you will BMP it and land about 70-90dF LOP, but if you are up high at 22" it will be about 10-20dF LOP. It is almost like magic, but really you are surfing the curves.



Watch the video and play with the tool here > http://www.advancedpilot.com/redbox.html

If you want to actually gain a really good understanding bookings are filling up for the Feb class in Brisbane, or March in Ada OK. It will be the best money spent in aviation.

Ohhh and the excess oxygen eating up your exhaust, you should be worried about that so please fly and store your plane in outer space, perhaps Paul D can suggest how to achieve that one, thats his backyard Seriously, that is an OWT and has zero scientific credibility.

Just be diplomatic in telling your friend the earth is round not flat and he may be enlightened by you.

Hope that helps, but I seriously think investing in a class would be good for everyone. it is the only place you get to see what really happens inside your engine on the GAMI/TAT dyno.

LOP

They are right. I fly a O-470U every day at 23 inches, 2200 rpm and 50 on the lean side for 7 hours a day. It now has 2500 hours on the engine, 70's across the board and has never had a jug off. I also have 1 CHT gauge and 1 egt guage. There is way too much time spent and way too much money spent on probes for every cylinder. The engine will tell you when something is wrong. We used to be pilots that actually listened to our engines. Now we just look at graphs that we download. Just fly the thing.
Don

Ironflight said:

LOP is good until you end up so slow that you wonder if it is worth it.

Paul

Click to expand...

Isn't the intent of LOP to choose a power setting and adjust the mixture LOP while maintaining that setting? Yes, you will have to move at least one more knob, but if your intent is to fly at <say> 65% and 170 knots while minimizing fuel burn, you can do it. You don't have to allow the power to drop below your target setting (density altitude issues excepted)...

hahahaha
"Like"

donoltman said:

They are right. I fly a O-470U every day at 23 inches, 2200 rpm and 50 on the lean side for 7 hours a day. It now has 2500 hours on the engine, 70's across the board and has never had a jug off. I also have 1 CHT gauge and 1 egt guage. There is way too much time spent and way too much money spent on probes for every cylinder. The engine will tell you when something is wrong. We used to be pilots that actually listened to our engines. Now we just look at graphs that we download. Just fly the thing.
Don

Click to expand...

Kyle Boatright said:

Isn't the intent of LOP to choose a power setting and adjust the mixture LOP while maintaining that setting? Yes, you will have to move at least one more knob, but if your intent is to fly at <say> 65% and 170 knots while minimizing fuel burn, you can do it. You don't have to allow the power to drop below your target setting (density altitude issues excepted)...

Click to expand...

I'm not saying that LOP isn't worth it Kyle - I was just pointing out that at some point, you can get so lean that power just goes away - not advocating that anyone would run that way. I always run LOP, from about the time I leave the traffic pattern (and sometimes before.

I live at 4400' msl. We see about 77% at WOT on take-off, and by the time we clear the airport, we're below 75%. I just leave the throttle wide open, bring the prop back to a reasoanble din, and lean until I feel the sag which says Ive gone past peak - that keeps the CHT's from climbing, makes for a nice smooth engine, and gives great economy (while still givign me great cruise).

Ironflight said:

I'm not saying that LOP isn't worth it Kyle - I was just pointing out that at some point, you can get so lean that power just goes away - not advocating that anyone would run that way. I always run LOP, from about the time I leave the traffic pattern (and sometimes before.

I live at 4400' msl. We see about 77% at WOT on take-off, and by the time we clear the airport, we're below 75%. I just leave the throttle wide open, bring the prop back to a reasoanble din, and lean until I feel the sag which says Ive gone past peak - that keeps the CHT's from climbing, makes for a nice smooth engine, and gives great economy (while still givign me great cruise).

Click to expand...

I'm just saying that you don't *have* to slow down. If you maintain 65%, you don't slow down. You also don't get the fuel savings you'd get by starting at 65%, then leaning down to 55%, but you do get better fuel efficiency running 65% LOP than running 65% ROP.

Wow! What great info. and reminders. Thanks all. Love this place. I think my favorite line was, "I don't think it holds stoichiometric water". Whaaaaaat?

GRT accuracy on "lean find"

In another thread parallel to this one, a poster said he found the lean-find feature on his EFIS inaccurate. I have always leaned according to my GRT EFIS/EIS. Has anyone checked the accuracy of the GRT in finding the LOP point? Any reason to doubt it?

Rupester said:

In another thread parallel to this one, a poster said he found the lean-find feature on his EFIS inaccurate. I have always leaned according to my GRT EFIS/EIS. Has anyone checked the accuracy of the GRT in finding the LOP point? Any reason to doubt it?

Click to expand...

I use this often and it works very well. What I find in flying with other pilots is that they move the red knob too fast to get decent egt reading cause they are worried about the big pull. The 'big pull' and EFIS lean features are not to be used together.

The lean find feature works just as well from the other side of the hill right? Just "big pull" to the lean side, then slowly richen the mixture to find peak (allowing the EFIS to do its magic) and then lean back to where you want it.

Stoichiometric info

Darren S said:

Wow! What great info. and reminders. Thanks all. Love this place. I think my favorite line was, "I don't think it holds stoichiometric water". Whaaaaaat? &#55357;&#56899;

Click to expand...

Hi Darren,

Google EAA
When you get there, click on Education & resources blue box
slide down to "View the EAA webinar archives" Click on that (Not the big blue box)
See webinars channel
Click on "Webinars" in lower left hand corner
Underneath the Aircraft Spruce propeller, see "pages". (on right side) Scroll to page 8
On the left side, scroll down to the 4th webinar--"How to destroy your engine in one minute". It's an hour and 1/2, and its by Mike Busch. You'll get all educated on "Stoichiometric"

Well Shoot Darren, It looks like I gave you wrong info. Go to this web address below, and that will give you the correct video. "How to lean your engine"--also by Mike Busch-----Sorry

http://www.eaavideo.org/video.aspx?v=2534345030001

Have fun

Kahuna said:

I use this often and it works very well. What I find in flying with other pilots is that they move the red knob too fast to get decent egt reading cause they are worried about the big pull. The 'big pull' and EFIS lean features are not to be used together.

Click to expand...

That's right. First do a big pull to the lean side, then turn on the "lean" function and slowly push rich to find peak.

Toobuilder said:

The lean find feature works just as well from the other side of the hill right? Just "big pull" to the lean side, then slowly richen the mixture to find peak (allowing the EFIS to do its magic) and then lean back to where you want it.

Click to expand...

Actually it works MUCH better from the lean side, and you just find the first one to peak and work from there. BMP let cooldown then if you want to split hairs find peak from the lean side and do it with a cooler engine.

DanH said:

That's right. First do a big pull to the lean side, then turn on the "lean" function and slowly push rich to find peak.

Click to expand...

I don't think it matters when you turn on the lean find function if you do the BMP, because you pass through so fast it will re establish a new peak from the lean side.

LOP operation

David,

Thank you for republishing the "Red Box" table. It is a valuable tool to stay out of trouble. LOP operation in my RV8 increases range by about 25% and only costs 5-7 KTAS at 11,000 to 13,000.

Several "Luddites" at our airfield, including a very experienced A&P, have chastised me for flying LOP. They are convinced that I will "burn up" my engine. Charles Lindberg taught bomber crews to extend their range by running LOP during WWII. The doubters are still at it 70 years later!

What will it take to convince them?

Toobuilder said:

I don't think it matters when you turn on the lean find function if you do the BMP, because you pass through so fast it will re establish a new peak from the lean side.

Click to expand...

Exactly. Done it too. I have tested the lean find function from both sides on the GRT and find no difference if done slowly. While I have never flown the other EFISeseses (EFII?) I don't see why they would not be just as accurate.

gear1 said:

David,
What will it take to convince them?

Click to expand...

In the scientific world it is a historical fact that a serious challenge to the status quo does not become dogma until the persons of power unwilling to change or see the evidence pass from the earth.
Don't waste your energy on them. Just fly with a grin on your face and let the A&P work on red box damaged engines.

gear1 said:

Thank you for republishing the "Red Box" table. It is a valuable tool to stay out of trouble.

Click to expand...

Do keep in mind that much of the underlying concept behind those numbers goes right out the window with variable ignition timing.

rzbill said:

In the scientific world it is a historical fact that a serious challenge to the status quo does not become dogma until the persons of power unwilling to change or see the evidence pass from the earth.

Click to expand...

Why just yesterday I had a nice conversation with a Baron owner who told me that electronic ignition and variable timing made no sense at all.

Of course he does own a well-known magneto overhaul facility

SI 1094D vs SI 1497A

This is a very interesting thread and I've captured some of the Lycoming Service Instructions. I notice there's one called "Fuel Mixture Leaning Procedures" and another called "Engine Procedures for Flight Training Operations"

Does one supersede the other?

What would be different with respect to Flight Training as opposed to normal ops?

Thanks!

DanH said:

Do keep in mind that much of the underlying concept behind those numbers goes right out the window with variable ignition timing.

Click to expand...

In what way? Guessing, I'd think maybe the Red Box is much smaller, maybe nonexistent?

Red box

StuBob said:

In what way? Guessing, I'd think maybe the Red Box is much smaller, maybe nonexistent?

Click to expand...

Actually, it'll be bigger. For the red box to be smaller, the EI's out there would have to reduce spark advance over stock magneto values. Im not aware of any that do (except maybe the EFII programmed with a custom ignition curve)

The more conservative EI's such as light speed do not add any spark advance at high manifold pressures, thus in this case the red box would be mostly unchanged. At reduced manifold pressures however, the EI's do increase spark advance over stock values because this is where the biggest efficiency gains result. However, increasing spark advance increases internal cylinder pressures (ICP) and also causes the peak pressure to a occur at fewer degrees of crankshaft rotation (this angle is known as Theta-PP) past piston Top Dead Center (TDC). This results in increased CHT and reduced detonation margin. Therefore, the red box does not shrink as much at reduced manifold pressures with electronic ignition as it would with fixed-timing mags.

Skylor
RV-8

Excellent. Thanks.

Makes me wonder what the implications are as far as required detonation margin, reduced octane fuels, MOGAS, turbos.........Everything affects everything else, doesn't it.

Timing advance

At low manifold pressure and high RPM, (where Lightspeed advances the most), the flame spread is slower than it would be at higher MAP/(lower altitude). The high RPM gives the slower flame spread less time to meet up with the one from the other spark plug and the peak cylinder pressure occurs later than the optimum timing of around 17 degrees after TDC where the connecting rod has the best leverage on the crank. The ignition advance is intended to bring the max pressure back to the place where it can do the most work rather than wasting much of the burning gases on a rapidly retreating piston and a rapidly increasing cylinder volume. True that if the timing advance is too aggressive, it could happen too early causing pressures and temperatures to be higher than what is good for the engine.

High compression pistons have the effect of increasing burn rate and that's why we retard the timing on those engines. It's all about getting max pressure at the point where the rod can transfer the most power to the crank without hammering.

If you base your red box on CHT rather than degrees EGT rich or lean of peak, it will still be easy to lean even when the ignition timing is advanced. The actual size of the red box doesn't matter much. If your CHTs are high, pull throttle and/or mixture. Unless, of course, you are ROP. In that case push mixture and/or pull throttle and/or lower the nose until you've got a handle on it.

Ed Holyoke

skylor said:

Actually, it'll be bigger. For the red box to be smaller, the EI's out there would have to reduce spark advance over stock magneto values. Im not aware of any that do (except maybe the EFII programmed with a custom ignition curve)

The more conservative EI's such as light speed do not add any spark advance at high manifold pressures, thus in this case the red box would be mostly unchanged. At reduced manifold pressures however, the EI's do increase spark advance over stock values because this is where the biggest efficiency gains result. However, increasing spark advance increases internal cylinder pressures (ICP) and also causes the peak pressure to a occur at fewer degrees of crankshaft rotation (this angle is known as Theta-PP) past piston Top Dead Center (TDC). This results in increased CHT and reduced detonation margin. Therefore, the red box does not shrink as much at reduced manifold pressures with electronic ignition as it would with fixed-timing mags.

Skylor
RV-8

Click to expand...

Ok, so the idea is to advance timing in order to optimize theta-PP? If that's the case, what effect is there on detonation margin?

Detonation margin

Detonation margin can decrease with advance, but only if it causes the peak pressure to occur well before about 17 degrees ATDC. Since the ignition system is only advancing the timing when MAP is low, it shouldn't be possible to detonate under most conditions.

The conditions that reduce detonation margin are high induction heat, high CHTs, and high manifold pressure as well as advanced timing. At altitude, MAP is limited and induction heat is usually reduced. If your CHTs are not above, say, 380 and rising, you are in no danger of detonating and advanced timing is merely decreasing efficiency loss by making up for slower flame spread. If you allow CHTs to rise out of control, it will possibly detonate. In fact, a sudden spike in CHT is a classic symptom of detonation.

Even down low on a hot day, it's hard to make a normally aspirated engine detonate if you keep the CHTs under control. You do that by staying rich, by reducing MAP, and/or by going lean enough to stay out of the infamous red box as defined by higher than 380 to 400 degrees CHT. Remember that, if you reduce MAP and or go well LOP, you are reducing % power which reduces the size of the red box and increases detonation margin.

Auto fuel was mentioned. 100LL burns slower under pressure than auto gas. Octane doesn't increase gas' power output. It just keeps it from exploding all at once when the heat and pressure in the cylinder is approaching its maximum. High octane gas allows us to have fairly high compression ratios, operate at high power settings, and still not detonate. Lower octane would mean that we would have more propensity to detonate under adverse conditions, the most critical of which would be CHT.

Ed Holyoke

StuBob said:

Ok, so the idea is to advance timing in order to optimize theta-PP? If that's the case, what effect is there on detonation margin?

Click to expand...

Bicyclops said:

. . . 100LL burns slower under pressure than auto gas. Octane doesn't increase gas' power output. It just keeps it from exploding all at once when the heat and pressure in the cylinder is approaching its maximum. High octane gas allows us to have fairly high compression ratios, operate at high power settings, and still not detonate. Lower octane would mean that we would have more propensity to detonate under adverse conditions, the most critical of which would be CHT.

Ed Holyoke

Click to expand...

Heat release (burn rate) of 100LL should be the same than gasoline, but your octane comments are spot on. Temperature/pressure under which a detonation burn front as opposed to deflagration burn front is most assuredly increased (octane).

Lop

I know this may sound like an old dinosaur talking but before all this fancy gear and in aeroplanes ✈ that didn't have even an egt gauge we just pulled the red knob till it ran rough and then wound it in a couple of turns till it ran smooth. Never had any problems and never had to put all this thought into it. In saying this I will probably fit the latest gizmos and spend half the flight fiddling.

salto said:

I know this may sound like an old dinosaur talking but before all this fancy gear and in aeroplanes ✈ that didn't have even an egt gauge we just pulled the red knob till it ran rough and then wound it in a couple of turns till it ran smooth. Never had any problems and never had to put all this thought into it. In saying this I will probably fit the latest gizmos and spend half the flight fiddling.

Click to expand...

Yep. Thats what I was taught too. That initial pull to rough has been renamed the "BMP", and the roughness and back to smooth is now called LOP.

...we've been doing it for years, but now there is mass confusion.

I was taught that way too. The only problem is that if you have fuel injection and went to the trouble of balancing the injectors there is no "rough". You wind up pulling until you feel a very noticable sag in power. You are now very lean of peak. If you didn't use the lean funtion on your engine monitor or pay attention to peak egt you have to start enriching to find peak from the lean side. Nothing wrong with that though, but with balanced injectors you do need the egt to know where you are. The only feel you get is when the mixture drastically affects power and by then you are definitely lean.

On the lean side, the difference between 40 degrees lean and 100 degrees lean is something on the order of 10 kts for me. On the rich side that 60 degree difference is more like 3 or 4 kts. I'm not entirely sure why.

With the carbed training aircraft, I think the onset of rough was still a hair on the rich side or right at peak, so when you went rough and enriched to smooth you were likely around 50-75 degrees rich of peak. At least that was my understanding.

jjconstant said:

On the lean side, the difference between 40 degrees lean and 100 degrees lean is something on the order of 10 kts for me. On the rich side that 60 degree difference is more like 3 or 4 kts. I'm not entirely sure why.

Click to expand...

This is APS 101: The power curve on the rich side of peak is relatively flat. i.e. relatively large mixture changes do not result in much change in power. However, on the lean side of peak EGT, power drops off fairely rapidly as fuel flow is decreased. This is why cylinder to cylinder fuel flow imbalance is very noticeable in the form of engine roughness when trying to run lean of peak (LOP), but not noticeable when running rich of peak (ROP) mixtures.

Skylor

I'm just getting to know my IO360 with two bendix mags. I can lean past -50 peak EGT but if I go to far I will get a "backfire"! Is this normal?

Mike,

I don't think you're getting a backfire, but an "afterfire".

The combustion event from what I understand is slower the leaner you go. Sometimes so slow, it's still going on when the exhaust valve opens.

The noise you're hearing is that process occurring out in the exhaust tubing. Not harmful is my understanding.

At least that's what I remember from Mike Busch's leaning webinars on the subject.

Good gouge and worth a listen, well worth the investment of your time.

Rob S.

Webinars found on EAA's video player website....

It will sure get your attention! Dont take long for me to get a turn back in!

Bicyclops said:

At low manifold pressure and high RPM, (where Lightspeed advances the most), the flame spread is slower than it would be at higher MAP/(lower altitude).
Ed Holyoke

Click to expand...

I don't believe this is true. Obviously higher RPM's require more advance, as the piston is moving faster relative to the constant flame propagation/flame travel speed. Variable timing started with RPM compensation.

The only major factor that changes flame propogation is the air fuel ratio (aerodynamics associated with head/chamber design also have an impact but are constant for any given design) . Overly rich and lean mixtures burn slower than max power mixtures (12.3-13:1). RPM-based advance is set based upon max power mixtures. This advance setting does not result in optimum ICP, as it has a detonation margin built into it. Vacuum/MAP-based advance is used to advance the timing under lesser "load." This slowly takes out the margin and also accounts for the slower flame propogation (assumes lesser "load" conditions have leaner mixtures). It's all about hitting getting ICP at the proper ATDC point, but also building in detonation margins under high load conditions.

Larry

Chamber turbulence also changes flame propagation rates and this varies with rpm. RPM advance for MBT does not change in a linear fashion with rpm, in other words, you don't double the advance if you double rpm. Detonation margins usually increase above torque peak rpm as well because peak cylinder pressures are lower.

I have fuel flow on my RV. To run LOP I just pull the mixture (big pull) to 7.4 GPH
after establishing 2380RPM @ 25.8 MP (or WOT if I'm too high to get 25.8). I do not peak from the lean side at all, because I have already established that this flow is well LOP and well outside the "Red Box".