Leaning AT peak ... not ROP or LOP

Ed Haywood

Ed Haywood

Final Approach
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Lately I've been putting more attention into following actual Lycoming guidance for the operation of my IO-360 instead of:

A. What my CFI taught me 30 years ago
B. What the SGOTI consensus says
C. What some YouTube guru says

Listening to the Lycoming presentation at Oshkosh reminded me that I have not tried their recommended Best Economy method of leaning to peak EGT. I always do 100 degree ROP so I don't get in the dreaded fin zone and melt my engine.

I thought I would have trouble with high CHT, but it worked great. Got up high at 9.5K, dialed in 65% power, and leaned it to peak EGT with no drop. I got it down to 7.2gph at one point. Hottest CHT stayed just below 400, right where Lycoming says to keep it for max longevity. Added nearly an hour to my endurance.
 
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My new plane has an injected Lycoming and a dynon SkyView efis that shows when it's lean of peak. It loves LOP and the hottest CHT typically settles out around 325 f. If I filled the tanks and ran LOP she would have a 1500 nm range with 69 gal fuel capacity.
 
FORANE said:
My new plane has an injected Lycoming and a dynon SkyView efis that shows when it's lean of peak. It loves LOP and the hottest CHT typically settles out around 325 f. If I filled the tanks and ran LOP she would have a 1500 nm range with 69 gal fuel capacity.
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Please note I am talking about at peak, not lean of it.

The Lycoming field service rep at Oshkosh was asked about LOP, and gave a very good engineering answer why they do not recommend it.
 
asicer said:
If you are "Leaning at peak", doesn't that mean you are at peak and then leaning to lean of peak? ;)

(I get it. You really mean "lean until peak". Just teasing.)
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But it's really leaning past peak, then backing up. So technically I am "enriching to peak".
 
Ed Haywood said:
Please note I am talking about at peak, not lean of it.

The Lycoming field service rep at Oshkosh was asked about LOP, and gave a very good engineering answer why they do not recommend it.
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My mechanic doesn’t recommend it either. Saving a few bucks on fuel isn’t worth replacing a cylinder or two down the road.
 
Ed Haywood said:
Please note I am talking about at peak, not lean of it.

The Lycoming field service rep at Oshkosh was asked about LOP, and gave a very good engineering answer why they do not recommend it.
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Oh no. You can’t say anything about LOP being bad.
 
Ed Haywood said:
Please note I am talking about at peak, not lean of it.

The Lycoming field service rep at Oshkosh was asked about LOP, and gave a very good engineering answer why they do not recommend it.
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So what was the engineering answer given for not running LOP? Of course Mike Busch is all about LOP. My IO-360-M1A will run reasonably smooth at 10-20 degrees LOP but I usually run it at peak for a bit more speed.
 
My read is that running at peak is perfectly fine at 65% power or less. Keeps the spark plugs very clean; no signs of detonation in my engine. Running 75% you need to pick ROP or LOP. In my plane, ROP gives me maybe 5 knots for plus 3-4 GPH. LOP loses about 15 knots, which I'm not willing to give up. 65% peak is the most efficient way to run my engine.

Fwiw, the old "lean it until it stumbles, then richen till smooth" will put you right there at peak. Lots of flight school engines have gone past tbo operated that way.
 
David Loftus said:
So what was the engineering answer given for not running LOP? Of course Mike Busch is all about LOP. My IO-360-M1A will run reasonably smooth at 10-20 degrees LOP but I usually run it at peak for a bit more speed.
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Has to do with localized heat in the cylinders being higher with LOP. Cylinders are good heat sinks, so the CHT measures the average temperature. But the temperature along the flame front can actually be much higher, which causes localized damage. He analogized it to when you turn down a torch and get a very hot thin blue flame along the edge. Or something like that. He also said they see a lot of warranty issues for LOP damage.

Obviously I don't have the qualifications to evaluate whether it was a good engineering answer or not. But IMO neither does virtually anyone else with an opinion on the matter, including the saavy guru. Appeal to authority is not a logical fallacy when one lacks another valid way to evaluate an argument. I consider Lycoming the authority until proven otherwise.
 
Ed Haywood said:
Has to do with localized heat in the cylinders being higher with LOP. Cylinders are good heat sinks, so the CHT measures the average temperature. But the temperature along the flame front can actually be much higher, which causes localized damage. He analogized it to when you turn down a torch and get a very hot thin blue flame along the edge. Or something like that. He also said they see a lot of warranty issues for LOP damage.

Obviously I don't have the qualifications to evaluate whether it was a good engineering answer or not. But IMO neither does virtually anyone else with an opinion on the matter, including the saavy guru. Appeal to authority is not a logical fallacy when one lacks another valid way to evaluate an argument. I consider Lycoming the authority until proven otherwise.
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@Ted , can you comment?
 
The chemistry and operating practice of huge steam boilers for 500 million watt generators have some food for thought on lean of peak.

They have near perfect control of air and fuel flow, typically 32 or more co-axial fuel and air injectors. They have about 8 color TV screens showing the color of the fireball at all crucial areas. The final guide is the redundant stack gas oxygen meters. They read to hundredths of a percent free oxygen. They regulate to as near zero as possible. At the temperatures in the boiler, free, or excess oxygen is at high temperature, and looking for anything to combine with. The boiler tubes and walls are attacked.

Oxygen present shortens time to overhaul "TBO" . Their overhauls cost many millions of dollars, so they give up a tiny bit of unburned fuel to extend TBO.

This means that they are running right at peak, with any error on the rich side.

For your aircraft engine, is there anything inside the cylinders including valves and exhaust ports, that could be attacked by super hot free oxygen?

How much are you willing to give up on time to TBO for a little more miles to the gallon?

Edited to add: Consider the thin film of oil that is left n the cylinder bore as the piston goes down on the power stroke, how much will be oxidized by that super hot free oxygen?
 
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RyanB said:
Serious question - why is Mike Busch so romanticized? Is his opinion more credible than the other thousands of well seasoned IA’s?
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Lycoming has been building engines for 115 years although aircraft specific engines came a bit later. That means they only have ninety six years of experience as a leading manufacturer of aircraft engines. I don't doubt the high intelligence of others but I believe that Lycoming should be the first choice of who to hearken to when it comes to the care, maintenance, and operation of their engines. :smilewinkgrin:
 
Tarheelpilot said:
Mike is a salesman first.
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Well Mike's engines have gone well past 3000 hours, so I would not completely discount his approach. It’s not a binary situation where LOP is bad or good and ROP is vice versa. Some people may think they are running LOP correctly, but are not. I have known many people who run LOP with engines that go well past tbo.
 
kujo806 said:
Well Mike's engines have gone well past 3000 hours, so I would not completely discount his approach. It’s not a binary situation where LOP is bad or good and ROP is vice versa. Some people may think they are running LOP correctly, but are not. I have known many people who run LOP with engines that go well past tbo.
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I’m possibly throwing out a small baby with the bathwater but having been on the business end of that guys B.S. I’m ok with it.

He’s a self proclaimed expert and there are plenty of engines well past TBO operated by people that have never heard of the guy. His engines TBO performance mean nothing to me. As grandpa used to say “Even blind squirrels find nuts occasionally.”
 
geezer said:
The chemistry and operating practice of huge steam boilers for 500 million watt generators have some food for thought on lean of peak.

They have near perfect control of air and fuel flow, typically 32 or more co-axial fuel and air injectors. They have about 8 color TV screens showing the color of the fireball at all crucial areas. The final guide is the redundant stack gas oxygen meters. They read to hundredths of a percent free oxygen. They regulate to as near zero as possible. At the temperatures in the boiler, free, or excess oxygen is at high temperature, and looking for anything to combine with. The boiler tubes and walls are attacked.

Oxygen present shortens time to overhaul "TBO" . Their overhauls cost many millions of dollars, so they give up a tiny bit of unburned fuel to extend TBO.

This means that they are running right at peak, with any error on the rich side.

For your aircraft engine, is there anything inside the cylinders including valves and exhaust ports, that could be attacked by super hot free oxygen?

How much are you willing to give up on time to TBO for a little more miles to the gallon?

Edited to add: Consider the thin film of oil that is left n the cylinder bore as the piston goes down on the power stroke, how much will be oxidized by that super hot free oxygen?
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That’s the first plausible argument I’ve heard on why LOP may be harmful.
 
Hate to break up the LOP / Busch bashing party. Amazing how long Old Wive's Tails (OWT) remain alive in the aviation world.

Mike Busch is right. Just follow his advice if you have a fuel injected Lyc IO-360 with GAMI's and an electronic engine monitor, with a good chance of running a super clean engine well past TBO without any expensive cylinder work.

Nearly 5000 engine hours ago my A&P (at the time) said don't do it, you'll be back in here for a top overhaul before you know it, but that's OK with him because he enjoys my business.

Mooney maven Paul Lowen of Lake Aero Styling said don't believe the OWT's, and explained why it's better to cool the engine with air rather than fuel. He was right. Thank you Mike and Paul, from the inside of my heart and wallet. Approaching 1000 hours (had been flying ROP, and at lean above 8000') made the change and purchased the GAMI tuned injectors (already had the engine monitor), then began aggressively operating LOP in accordance with Busch's, Lowen's and GAMI's recommendations.

Around 2400 hours TTSN (and done the dual mag conversion) it was running strong. Oil analysis was superb, oil burn rate was still better than 8 hrs/qt, and compressions were all in the high 70's. But I started getting scared so had it overhauled for no reason except the fear factor. During that time period I was flying a fair amount of night X/C's and hard IFR for business (mostly alone), and I didn't want to push my luck with an engine issue when almost everybody in my pilot's circle of friends said follow Lycoming's recommendations or you're just a crazy and cheap bastard looking for trouble to save a few gallons of fuel per hour (they were right regarding the fuel - that's one reason I fly a 201).

Overhauled that engine and started from scratch operating LOP (not just the last 1400 hours on a new engine). Flew it up until 2685 hours when one cam follower started making metal. Sent the engine out to Zephyr Engines in Florida for an overhaul. Other than the CAM and follower, the engine was fine and super clean. Replaced more parts than I had to, but IMO that's the sign of a quality overhaul. Didn't buy new cylinders, went with Zephyr rebuilds. Then after break in, started using CamGuard.

Right now I'm at 950+ hours on this engine. Zero trouble (knock on wood). Still burning only one quart of oil every 14 to 15 hours (which I understand is amazing for an IO-360 high compression engine). Engine oil still has some yellow visible after 40 hours of flight time. The inside top of the dipstick cover is beautifully clean, so I'm fairly confident the inside of the engine is the same. Last annual had compressions all in the high 70's.

Bottom line on LOP ops.
Negative: A loss of 5 to 10 knots of TAS, depending upon altitude, as compared to typical M20J ROP cruise speeds of 155 to 160 knots.
Positive: Fuel burn of 7.2 to 8.2 gal/hr depending upon altitude.
Positive: Lower Cylinder head and oil temps. Winter time 260 to 285 F during cruise. Summer time hot / heavy cruise above 5000' 315 to 330 F.
Positive: No production of Carbon Monoxide while LOP. And clean, no ROP engine deposits.
Positive: Because of the lower cylinder temps I don't worry about "shock cooling", and run it like similar to a turbine, reducing the power in large increments.
Disclaimer: The aircraft has a LoPresti Wow Cowling mod which helps with cooling, so a typical M20J cowl will probably not see temps as low. Climbing out ROP (a must) I never have seen any cylinder above 365 F, even hot and heavy, with oil never above 200 F.

Operating LOP is not for everyone. Some of my pilot friends say they'd rather keep flying ROP, go a little faster, burn more fuel, experience higher oil and cylinder head temps, and live with the occasional cylinder / valve issues. That's their choice. IMO, flying ROP is operating in accordance with fear generated by a decades old OWT.

FYI... I've always used Phillips X/C 20-50 oil. And started adding CamGuard in recent times. All good.

Flame away....
 
RyanB said:
Serious question - why is Mike Busch so romanticized? Is his opinion more credible than the other thousands of well seasoned IA’s?
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Mike has a practical, logic based approach to many problems. That helps his credibility. Also, he only tells (and publishes) stories that show how his approach is/was superior to that of the shops his clients select. But wrench turning and logic (decision tree?) based maintenance is a vastly different subject than LOP operations which are a matter of hard science. I'll trust the factory guys with temperature and wear sensors on issues like that.
 
Half Fast said:
Perfect combustion of a hydrocarbon fuel produces only H2O and CO2, not CO. Whether LOP achieves that, I don't know.
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Racerx said:
Wuttt??
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If you have excess oxygen, as in LoP operations, the reaction tends to more carbon dioxide rather than carbon monoxide. RoP means there is not enough oxygen to convert all of the hydrocarbon fuel to water and carbon dioxide. Some of the fuel will be converted only to carbon monoxide. This is basic chemistry.
 
geezer said:
The chemistry and operating practice of huge steam boilers for 500 million watt generators have some food for thought on lean of peak.

They have near perfect control of air and fuel flow, typically 32 or more co-axial fuel and air injectors. They have about 8 color TV screens showing the color of the fireball at all crucial areas. The final guide is the redundant stack gas oxygen meters. They read to hundredths of a percent free oxygen. They regulate to as near zero as possible. At the temperatures in the boiler, free, or excess oxygen is at high temperature, and looking for anything to combine with. The boiler tubes and walls are attacked.

Oxygen present shortens time to overhaul "TBO" . Their overhauls cost many millions of dollars, so they give up a tiny bit of unburned fuel to extend TBO.

This means that they are running right at peak, with any error on the rich side.

For your aircraft engine, is there anything inside the cylinders including valves and exhaust ports, that could be attacked by super hot free oxygen?

How much are you willing to give up on time to TBO for a little more miles to the gallon?

Edited to add: Consider the thin film of oil that is left n the cylinder bore as the piston goes down on the power stroke, how much will be oxidized by that super hot free oxygen?
Click to expand...
If you operate lean of peak, what happens to the temperature? It isn't so hot anymore. Are the materials in those boilers the same as in aircraft engines?
 
Rick A said:
made the change and purchased the GAMI tuned injectors (already had the engine monitor), then began aggressively operating LOP
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So you don’t have an engine that the Lycoming rep was talking about, you have a modified engine that you’re running LOP. I think that’s an important distinction.
 
Your car runs at peak nearly all the time. Even wide open throttle (for a while at least).
Unless, of course, you have a diesel. Then you run LOP 100% of the time. (exception: You have modified the injection system for "Coaling" when you pass a Prius.) Heavy duty diesels last a long time.
Power-plant steam boilers run continuous combustion and are limited by the boiler materials - the closer you are to failure, the more efficient the boiler is. Yes, the operators watch carefully. Turbines have the same problem.
The metal in the 4-stroke engine you are flying behind is only intermittently exposed to combustion temperatures and the walls remain much cooler than the peak temperatures inside the cylinders. Usually, when things go wrong, it is the piston that melts first. A piston with a hole in it is no good as an ash tray, but it doesn't matter because you can't smoke at work anymore anyhow. If a valve doesn't close all the way it can burn because it will be leaking during peak temperatures / pressures. But, under normal operation, the burnt charge mass cools significantly during the expansion stroke (which is how the energy gets transferred to the crankshaft) before it goes past the valve.
2-strokes are more prone to meltdowns for a number of reasons.

CO in the exhaust goes down by about a factor of 10 or more when you go from ROP to LOP. If you go far enough LOP it can go back up a bit, but you start running rough at that point.
 
I'm with @Rick A , both in approach and positive experience. Running religiously LOP in cruise since day 1, my DA40 (Lyc IO360) passed 3000 tach hours a few months ago... on 3 original cylinders (out of 4). Just completed the top overhaul with hopes of getting another thousand tach hours or more on this engine.
 
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I believe that while Mike Busch may have popularized LOP operations via AvWeb and then his webinars, it was George Braly/GAMI, John Deakin, and Walter Atkinson that really started the movement via their Advanced Pilot Seminars on the subject. Deakin also spread the gospel via his Pelican’s Perch articles on AvWeb.
 
I am not meaning to be an *hole here. But, why . . . exactly . . . is it surprising that an engineer from the manufacturer knows more than SGOTI? And why is that "news"?
 
If I could confidently fly my Cessna 177RG LOP at >=75% power I would. It is equipped with a Lyc IO360 and about 12 years ago I sprang for GAMIjectors. Went through several rounds of revisions, trying to get the 4 cylinders to all peak within 0.6 gph of each other, but was never able to and eventually gave up. I'm also not willing to take the 15-kt hit in speed to fly at the recommended LOP settings at <65%. So I'm in the "peak below 65%" club. (I say "below" rather than "at" just for a little added safety.)

Yes, you might ask which cylinder I run at peak. "Peak" for me has the 4 cylinders straddling peak, some a little ROP, others a little LOP.
 
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