Need help leaning by EGT

[David Megginson]

David,
You suggested he lean just rich of peak RPM, based on the chart you posted, why not use peak RPM? Just to be on the 'cool' side of CHT? Isn't the RPM peak represented by the Percent Power curve on the chart?

Thanks for sharing.

I'm suggesting just rich of peak RPM to allow for some mixture spread among the cylinders (especially in a carbureted engine), so that the leanest cylinder has a better chance of landing outside of the red zone.

Before the OP (or anyone else) gets too stressed about this, however, I want to repeat that below 65% power it doesn't matter where you lean with a regularly-aspirated engine. This is only for people who want to get the full performance out of their planes by cruising at (e.g.) 75% power. If I'm willing to give up 15–20 knots in my Piper PA-28-161, I can cruise at 55–60% power all day chasing birds through the sky, and set the mixture wherever the spirit takes me.

 

[farmrjohn]

Wow, a 30% fuel savings from full rich to LOP is huge! I think it's a different story for the O-200-D if my POH is right as it says to expect "fuel savings in excess of 5% when compared to typical flight operations at full rich mixture," which I take to mean maybe 6 or 7% savings, which at 6 GPH if rich would work out to 5.6 GPH if leaned. So the fuel savings seems very small on this particular engine.

Leaning will take the O-200 from 6 gph down to 5 gph.

Just under 20% savings (1/6=.17). That's pretty much what I get with my O200.

 

[Salty]

Is this actually safe to do in flight? I've never tried it -- nervous to do so. But if I pull the mixture and the engine quits, pushing the mixture back in before the prop stops spinning will cause it to fire right back up right?

Not only that, but a small engine like a O-200 is just about impossible to get stopped. I was flying around (at altitude over an airport) with the mixture out and the stall horn blaring and never could get the prop to stop spinning. It was running so slow the display went dark from lack of power from the alternator, but the prop would not stop. Nose down a bit, push in the mixture, and roar!

 

[David Megginson]

Not only that, but a small engine like a O-200 is just about impossible to get stopped. I was flying around (at altitude over an airport) with the mixture out and the stall horn blaring and never could get the prop to stop spinning. It was running so slow the display went dark from lack of power from the alternator, but the prop would not stop. Nose down a bit, push in the mixture, and roar!

There is a chance of a backfire, which isn't great for the engine if it happens too often.

 

[Salty]

There is a chance of a backfire, which isn't great for the engine if it happens too often.

If the engine is spinning with no fuel and then fuel is added with the engine spinning faster than the starter would spin it? How do you figure that?

 

[David Megginson]

If the engine is spinning with no fuel and then fuel is added with the engine spinning faster than the starter would spin it? How do you figure that?

To be fair, I've seen that only after overleaning on the ground, not in the air (though the prop was still spinning faster than starter speed).

 

[William Pete Hodges]

David,
You suggested he lean just rich of peak RPM, based on the chart you posted, why not use peak RPM? Just to be on the 'cool' side of CHT? Isn't the RPM peak represented by the Percent Power curve on the chart?

Thanks for sharing.

Peak RPM can be used to determine best power mixture setting on a fixed pitch prop at any given throttle setting, and it will be slightly richer than peak EGT. Depending on how much power you are producing the engine may or may not be running outside of the Red Box. I ran across the Red Fin concept and liked it because it shows directly how the Red Box changes with load. I used a set of graphs to generate my IO-360-200HP RED FIN Fuel and air flow chart (1st page of the attachment). The EGT-CHT-Power-SFC chart (the 2nd page of the attachment) was used to compute the first chart. Since best fuel economy is 14.9 HP-Hours/Gal I corrected the SFC chart to read 100% at Best SFC. All other mixture settings burn more fuel than that. My Red Fin fuel flow chart looks similar to the SFC chart turned sideways.

 

[GeorgeC]

I used a set of graphs to generate my IO-360-200HP RED FIN Fuel and air flow chart (1st page of the attachment). The EGT-CHT-Power-SFC chart (the 2nd page of the attachment) was used to compute the first chart. Since best fuel economy is 14.9 HP-Hours/Gal I corrected the SFC chart to read 100% at Best SFC. All other mixture settings burn more fuel than that. My Red Fin fuel flow chart looks similar to the SFC chart turned sideways.

Nice work! FWIW, I came up with a slightly different number for the IO360, but our methods may have varied slightly:

https://www.pilotsofamerica.com/com...hn-deakin-©june-2013.60964/page-3#post-1998074

 

[David Megginson]

This thread has been a lot of fun. Here's some further reading:

Mike Busch's book Engines (part of a four-book series on aircraft ownership; much of it is also available as articles online)

John Deakin's "Pelican's Perch" series from 20 years ago (start with post 15 and move forward).

 

[William Pete Hodges]

Nice work! FWIW, I came up with a slightly different number for the IO360, but our methods may have varied slightly:

https://www.pilotsofamerica.com/community/threads/lop-experts-are-everywhere-–-the-rebuttal-by-john-deakin-©june-2013.60964/page-3#post-1998074

Thank you so much for the compliment!

 

[flyingcheesehead]

In regards to peak egt and running lean of peak, I had the leaning discussion with someone at a fly-in once. His unusual method was somewhat intriguing, but difficult for me to accept. He flew a Comanche 250 with constant speed prop and Lycoming O-540. He only had a single prob egt and cht gage. He said he would try to run rich of peak to his assigned or chosen altitude keeping cht temps below 400. (as he climbed he would have to lean a little obviously) Once at altitude he would level off, set his mp and rpm’s for the percent of power he wanted to run. Then he would pull mixture somewhat quickly to engine roughness and then enrichen just until it smoothed out. He then would then re-adjust his mp and rpm’s slightly if necessary. He claimed that as soon as the engine ran smooth, he would still be lean of peak and could run there economically and safely without having to install a “fancy temperature gauge” on a normally aspirated engine, which he didn’t think was useful unless you had fuel injection anyway. Does anyone have any thoughts on this method?

With a carbureted engine, it is very difficult to run lean of peak. Given that smoothness on most carbureted engines will happen near peak, enriching slightly from there likely puts you in the red box. I would not recommend this technique.

I'm confused. Is that what I should be doing with the O-200-D in my C162? And what does "lean to max RPM" mean? Are you saying to go full throttle in straight and level flight, then lean the mixture slowly until ... when? When it reaches 2750 RPM, the start of the red zone (max RPM?), and then slowly richen the mixture until it drops just slightly below that, and then pull back the throttle to get back to normal cruise? Also, doesn't what altitude you do this at matter, as I've noticed I have a little different RPM speeds at full throttle depending on what altitude I'm at.

Altitude matters when it comes to anything leaning unless you have a turbo, because as you climb there is less oxygen and you need a leaner mixture setting to compensate for that. That's why we lean relative to peak EGT most of the time. More on that below.

I would say yes to what you've said above, EXCEPT that you don't do it at full throttle, you set the throttle where you want it for cruise first. Changing throttle also affects mixture, so you set throttle first, then lean the mixture.

One more question for you guys: What's the downside of just always leaving it full rich on a small carburated engine like the O-200-D? Am I just looking at having to change the spark plugs more often (due to extra carbon deposits), a tiny bit more fuel burn (like the difference between 5.5 GPH and 6 GPH?), and a tiny bit less power (like 5%?) ? Would that be accurate? Are there any other negatives?

On all of the airplanes I've flown that had the instrumentation to measure such things, the difference in fuel burn between takeoff at full rich mixture and cruise at or lean of peak was close to 50%. That is, you're burning TWICE the fuel at takeoff as you are leaned for best economy cruise.

Before I bought my C162, I actually learned on a C162 and on the C162 I learned on it was actually the flight school's policy for some reason to always leave their C162s full rich during ground and flight operations. I'm assuming this is because they deemed the negative effects of not leaning to be less than the chances of having a student screw up and go full power before remembering to go full rich again.

In addition, flight school planes spend most of their time down low. Lots of time in the pattern at no more than 1000 AGL, and lots more time practicing airwork at 1500-2500 AGL. In both cases, it's probably best to leave the mixture full rich. Otherwise, a student may get a nasty surprise when they lean early in a flight and then try to practice stall recoveries and their engine quits when they try to go to full power.

For the point-to-point flying that most people do outside of the training environment, it's no longer worthwhile to leave the mixture full rich even if you're down low. See the "When to lean" section of this article: https://www.avweb.com/features/the-pilots-lounge-30myths-for-the-last-millennium/

I'm just suggesting that you set your desired RPM (or maybe 50 rpm below) with the throttle, then start leaning. As you lean, at first the RPM will rise, then it will pause, then it will start to fall again. You've found the lean side of peak power. Now enrich slightly again until the RPM rises and starts to fall slightly, and you've found the rich edge of peak power.

Be careful with terminology here. When we say "rich of peak" and "lean of peak" we're talking about peak *EGT*, not peak power. Nothing @David Megginson said above is incorrect (because he did say peak power), but when you are lean of peak *power* you may still be rich of peak *EGT* - And in between those peaks is not a good place to be for engine longevity.

So, when you hit peak *power* you're roughly 100º *rich* of peak EGT, and by enrichening slightly from there, you're ensuring that your leanest cylinder is rich enough to be out of the red box.

This thread has been a lot of fun. Here's some further reading:

Mike Busch's book Engines (part of a four-book series on aircraft ownership; much of it is also available as articles online)

John Deakin's "Pelican's Perch" series from 20 years ago (start with post 15 and move forward).

Heck, start with post 1. It's all good stuff. But yes, #15 "Manifold Pressure Sucks" is by far the one I refer people to the most often. The FAA's explanations of how engines with constant speed props work are terrible, and "Manifold Pressure Sucks" clears it right up and makes it understandable.

 

[David Megginson]

With a carbureted engine, it is very difficult to run lean of peak. Given that smoothness on most carbureted engines will happen near peak, enriching slightly from there likely puts you in the red box. I would not recommend this technique.



Altitude matters when it comes to anything leaning unless you have a turbo, because as you climb there is less oxygen and you need a leaner mixture setting to compensate for that. That's why we lean relative to peak EGT most of the time. More on that below.

I would say yes to what you've said above, EXCEPT that you don't do it at full throttle, you set the throttle where you want it for cruise first. Changing throttle also affects mixture, so you set throttle first, then lean the mixture.



On all of the airplanes I've flown that had the instrumentation to measure such things, the difference in fuel burn between takeoff at full rich mixture and cruise at or lean of peak was close to 50%. That is, you're burning TWICE the fuel at takeoff as you are leaned for best economy cruise.



In addition, flight school planes spend most of their time down low. Lots of time in the pattern at no more than 1000 AGL, and lots more time practicing airwork at 1500-2500 AGL. In both cases, it's probably best to leave the mixture full rich. Otherwise, a student may get a nasty surprise when they lean early in a flight and then try to practice stall recoveries and their engine quits when they try to go to full power.

For the point-to-point flying that most people do outside of the training environment, it's no longer worthwhile to leave the mixture full rich even if you're down low. See the "When to lean" section of this article: https://www.avweb.com/features/the-pilots-lounge-30myths-for-the-last-millennium/



Be careful with terminology here. When we say "rich of peak" and "lean of peak" we're talking about peak *EGT*, not peak power. Nothing @David Megginson said above is incorrect (because he did say peak power), but when you are lean of peak *power* you may still be rich of peak *EGT* - And in between those peaks is not a good place to be for engine longevity.

So, when you hit peak *power* you're roughly 100º *rich* of peak EGT, and by enrichening slightly from there, you're ensuring that your leanest cylinder is rich enough to be out of the red box.



Heck, start with post 1. It's all good stuff. But yes, #15 "Manifold Pressure Sucks" is by far the one I refer people to the most often. The FAA's explanations of how engines with constant speed props work are terrible, and "Manifold Pressure Sucks" clears it right up and makes it understandable.

Lots of good points. Agreed that the PA-24-250 pilot didn't know what he was talking about, because perceived roughness can occur when some cylinders are still rich of peak or all are lean of peak, depending on the mixture spread among the cylinders — "lean to roughness" is useless as a general guideline.

As for carbureted engines, the ability to operate lean of peak varies. Four-cylinder carbureted engines have some success LOP, because it's possible to get fairly even fuel/air distribution to all of the cylinders — the Lycoming O-320 is particularly good for this.

Six-cylinder carbureted engines are more hit or miss, because the mixture has to travel further from the carburetor to some cylinders than to others, though I do have one friend who manages to do all his flying lean of peak behind a six-cylinder carbureted engine (confirmed by a fancy engine monitor).

And finally, agreed that my talking about "peak RPM" is confusing because people might read too fast and see "peak EGT." I'll talk about "max RPM" from now on.

 

[kicktireslightfires]

All of this is very helpful and lots to take in. Thank you all!

Another question: How do you know what % power you are at? Do your airplanes display the % of power on the avionics? Mine does not. I know the POH tells me % BHP under Cruise Performance. But is % BHP the same as % power? And even if it is, it's still a much slower process to know what % of power I am at by having to look at my OAT, pressure altitude, and RPM to see what % of power I'm running -- definitely not a real-time viewable metric.

 

[William Pete Hodges]

All of this is very helpful and lots to take in. Thank you all!

Another question: How do you know what % power you are at? Do your airplanes display the % of power on the avionics? Mine does not. I know the POH tells me % BHP under Cruise Performance. But is % BHP the same as % power? And even if it is, it's still a much slower process to know what % of power I am at by having to look at my OAT, pressure altitude, and RPM to see what % of power I'm running -- definitely not a real-time viewable metric.

The Actual % of power is a combination of total airflow and fuel flow. Total airflow is basically RPM (volume displaced) combined with manifold pressure and temperature (air density). Most POHs and engine manuals will specify HP produced at these given variables at Best Power Mixture Setting. There is about a 10% loss of power from BPMS to Best Economy Mixture Setting, at about 86% of BPMS fuel burn. On the lean side, the engine will produce about 14.9 HP per Gal per hour. So 8.0 GPH at about 75F LOP is about 120HP, so long as enough airflow is available to get to LOP operation at 8GPH. 120HP / your HP rating is % power LOP. Be aware that the mixture control can reduce power from Best Power available down to zero at any setting of RPM and MP. The best way is to pick a combination of RPM & MP at various altitudes and OATs that give an acceptable max available % of power and lean from there. On my bird at 10k and O°C I'm looking at 2500 RPM and WOT, then do the Big Mixture Pull back to LOP. It ends up being about 8GPH and 60% load.

 

[David Megginson]

All of this is very helpful and lots to take in. Thank you all!

Another question: How do you know what % power you are at? Do your airplanes display the % of power on the avionics? Mine does not. I know the POH tells me % BHP under Cruise Performance. But is % BHP the same as % power? And even if it is, it's still a much slower process to know what % of power I am at by having to look at my OAT, pressure altitude, and RPM to see what % of power I'm running -- definitely not a real-time viewable metric.

Yes, you use the power setting tables. It's not as hard as you think. The OAT and pressure altitude together are just the density altitude, and you'll have a fixed relationship between RPM and % power at any given density altitude. If you know your planned cruise altitude, the altimeter setting, and the temperature aloft, you can pre-calculate on the ground. It's important to figure it out for long trips, b/c if you don't know your power setting, you don't know your fuel burn.

Here's a little cheat — the same % power will give you roughly the same indicated airspeed at all density altitudes ("roughly," because gross weight and vertical air movement both affect it). So if I want to fly at 75% power in my PA-28-161, I ballpark by setting up for 108–112 KIAS first, then fine-tune afterwards. It's important to verify with the tables (or an engine monitor) before you fly too long, in case something else is going on.

 

[David Megginson]

All of this is very helpful and lots to take in. Thank you all!

Another question: How do you know what % power you are at? Do your airplanes display the % of power on the avionics? Mine does not. I know the POH tells me % BHP under Cruise Performance. But is % BHP the same as % power? And even if it is, it's still a much slower process to know what % of power I am at by having to look at my OAT, pressure altitude, and RPM to see what % of power I'm running -- definitely not a real-time viewable metric.

Here's another approach: look at the table like the one below in your POH and check where the 55%, 65%, and 75% power lines cross the 0 altitude line (without temperature compensation). That's where true and calibrated airspeed intersect, so you have your expected calibrated airspeed at any altitude with those power settings and that gross weight. The difference between calibrated and indicated airspeed is usually pretty small in the cruise regime, but you'll still want to adjust just to be sure.

In my case, the lines cross zero altitude at 95 KCAS for 55% power, 105 KCAS at 65% power, and 112 KCAS at 75% power. Applying the adjustments from the airspeed calibration table, that means that, in a mint-condition plane — at 2,300 lb (140 lb under max) and with my wheel fairings installed — I should expect to see 96 KIAS (55%), 103 KIAS (65%), or 110 KIAS (75%) no matter what altitude I'm flying at. If I remove my wheel fairings, I need to subtract 7 knots. If I'm at a different weight, I can ballpark it (for a single-engine piston) by adding or subtracting 1 knot for every 100 lb, so at 2,100 lb, I'l add 2 knots to all of those speeds.

Of course, my plane might not be perfectly rigged, my paint isn't in great shape, I have a couple of extra antennas, etc. etc., so I needed to figure out what the actual values are for my plane (about 2–3 knots less, as it turns out), but Piper's POH numbers got me very, very close.

All that one-time prep work makes flying by power setting very simple. I still verify with RPM, of course (and I have a portable optical tachometer to cross-check my dubious mechanical one), but in general, if I set power so that I'm flying at 110 KIAS when it's just me on board in air without strong updrafts or downdrafts, then I'm flying at 75% power, and my fuel burn (which I've logged for every long flight over the past 19 years) has confirmed that, repeatedly. So this is my normal approach (flying LOP-WOT, which your POH doesn't recommend):

1. Leave the throttle wide open and pull back the mixture until I'm flying at about 110 KIAS (if I want 75% power and it's just me on board).
2. Check that the RPM is about where I'd expect it to be at my current altitude/temperature.
3. Land 4 hours later, fill up, and find that my fuel burn was accurate within a gallon or so of what I'd planned.

 

[Jeff767]

Running the engine as you describe will keep it in a safe zone. It will also be very inefficient and leads to excessive lead buildups in the engine. There is nothing wrong with operating most lower powered engines at peak EGT. Even though 50 ROP to peak ROP is the highest ICP and CHT it’s simply not a issue if the engine is properly baffled and installed. These engines are just not that stressed. It’s a different story with big bore high compression engines.
What is not mentioned in the replies is the effects of carb verses injection and how every engine is somewhat different. In general carbed engines don’t like to run LOP because their fuel distribution is not good enough to provide smooth operations. There are exceptions and tricks to get better distribution but I suspect the recommendation to not run LOP is based on the manufacturer knowing the engine won’t operate smoothly in that area. Even injected engines often need to make changes in injector sizing to get all cylinders hitting peak EGT at about the same point. A perfectly balanced engine will not run rough regardless of leaning. It will simply quit when leaned to much. They are rare.

 

[David Megginson]

Running the engine as you describe will keep it in a safe zone. It will also be very inefficient and leads to excessive lead buildups in the engine. There is nothing wrong with operating most lower powered engines at peak EGT.

My preference is to operate my O-320-D3G LOP-WOT, where it runs well. Peak EGT is OK if you have EGT probes in all cylinders, and can make sure that the richest one is at peak, but with a single-cylinder EGT probe, it's not unlikely that one of the other cylinders is still around 50°F–75°F ROP, in the red zone. That's why, with a fixed-pitch prop and no advanced digital engine monitor, if you can't operate smoothly LOP-WOT, I suggested slightly rich of max RPM, which ensures you're well outside the red zone. True that you'll burn 15% more fuel than LOP, and will have to deal with lead fouling on your plugs (and a significantly-elevated risk of CO poisoning if there's a breach in the exhaust system), but them's the breaks.

There is nothing wrong with operating most lower powered engines at peak EGT. Even though 50 ROP to peak ROP is the highest ICP and CHT it’s simply not a issue if the engine is properly baffled and installed. These engines are just not that stressed.

Below 65% power, We're in full agreement. Up at 75% power, you're right that the simpler engines are more robust, but the main reason we have a CHT limit isn't because of heat damage to the engine (as much as that matters for cylinder life), but because peak CHT—which we can measure easily—is more-or-less proportional to the maximum internal cylinder pressure. If the internal pressure gets too high, your cylinder might get confused and think it's in a diesel engine, and then detonate the fuel/air mixture (through pressure alone) at the wrong part of the stroke, before the spark fires. But fully agree that it's a lower risk — but still a real risk — with low-compression cylinders.

Also note that the old-timers claimed that it was normal to need a top overhaul halfway to TBO, even on lowered-powered planes. Those are the same old timers who thought it was fine to operate their engines in the red zone, and even wrote that into the POHs. Draw your own conclusions.

What is not mentioned in the replies is the effects of carb verses injection and how every engine has somewhat different In general carbed engines don’t like to run LOP because their fuel distribution is not good enough to provide smooth operations.

We discussed that, but easy to miss in such a long discussion. With a carbureted engine, you don't need a POH or digital engine monitor to know if it runs smoothly LOP — you'll feel it easily enough. My O-320 gets slightly throatier in the LOP range, but it will usually lean right to idle cutoff without any noticeable roughness (e.g. a pencil on top of the dash won't start vibrating). As I mentioned in an earlier post, 4-cylinder carbureted engines have a much better shot at running smoothly LOP than 6-cylinder, because with 6 cylinders the fuel/air mixture has to travel further to some cylinders than others, though I do have one friend — with fancy engine monitor — who manages to operate his 6-cylinder engine in a PA-28-236 LOP. Agreed that with a 6-cylinder carbureted engine (and some 4-cylinder ones), it's hit or miss.

 

[flyingcheesehead]

Six-cylinder carbureted engines are more hit or miss, because the mixture has to travel further from the carburetor to some cylinders than to others, though I do have one friend who manages to do all his flying lean of peak behind a six-cylinder carbureted engine (confirmed by a fancy engine monitor).

Mike Busch or John Deakin - Y'know, one of those engine guys - once said something about pulling the throttle back just a hair - maybe 1" MP - seemed to help some carbureted engines be able to run lean of peak, something about the turbulent airflow behind the throttle helping out in some fashion. But IME, on an O-470 or O-520 with a full engine monitor, I wasn't able to get either to run smoothly LOP. The O-320 thing is interesting, I'll have to borrow a friend's 172 with engine monitor and mess with that. He's been wanting me to teach him about the engine monitor too, so win win.

All of this is very helpful and lots to take in. Thank you all!

Another question: How do you know what % power you are at? Do your airplanes display the % of power on the avionics? Mine does not. I know the POH tells me % BHP under Cruise Performance. But is % BHP the same as % power? And even if it is, it's still a much slower process to know what % of power I am at by having to look at my OAT, pressure altitude, and RPM to see what % of power I'm running -- definitely not a real-time viewable metric.

It's fairly rare for avionics to say what % power you're at in a piston. There's a lot of variables, and even the avionics that do guess % power probably aren't accounting for all of them. Especially in between when the first cylinder peaks and the last cylinder peaks, it's not necessarily an easy calculation - Really, your engine is kind of four or six separate "engines" that happen to share a crankshaft.

When you're rich of peak, you're limited by air flow. When you're lean of peak, you're limited by fuel flow. Your air flow will be roughly (RPM/Max RPM)*(MP/29) but since you have a fixed pitch prop and likely no idea what your manifold pressure is, that doesn't really help. Lean of peak, in theory your hp is 14.9*gph = hp, divide that by your rated hp and you've got percent power. So, for example, if I'm at 12 gph in my Mooney (280hp max), 12 * 14.9 = 178.8 / 280 = 63.8%.

But, with all of the variables involved, including spark timing and such, and the fact that you likely don't have enough information to calculate percent power on the fly in the 162, your best bet is the performance charts in the POH. Not nearly as cool as having an actively displayed % power, but until we have FADEC and even better instrumentation, you probably won't see that... And I doubt we'll ever see that sort of thing become common, unfortunately.

 

[William Pete Hodges]

Am I understood correctly, that by leaning until roughness and then giving back 2-3 twists to enrich you should be in the ballpark of -50* F LOP EGT?

PIC: ibb.co/4MFFFMd

View attachment 100964

Not necessarily. One of the results of running LOP is a noted loss of power. One of the tricks that you can use is to set up a cruise at 75% power ROP. (You can use less than 75% if you want, but not more) Give the airplane a couple of minutes to stabilize airspeed and trim. Note the airspeed, then do a smooth semi-robust Big Mixture Pull until you feel the airplane decelerate from a loss of power. Once you feel the power loss, stop leaning immediately. You are now running lean of peak at less than 75% power. If the engine is running rough increase fuel to smooth it. Let the airspeed stabilize and adjust trim. A 10% loss of power should produce a 3-5% loss of airspeed (check your POH), and be about 68% of power. (.75 x .9 = .675). If you increase fuel too much and regain your lost airspeed you are no longer LOP. Be sure to monitor the hottest cylinder head temp to stay out of the Red Box. Hope this helps.

 

[Trogdor]

Choices:

A. Do what your aircraft and engine manufacturers recommend in the official FAA-approved handbook for your aircraft.

B. Do what some guys on the internet say, because they are really emphatic that the manufacturers are wrong, and they have impressive graphs to back it up.

Tough call.

Choices:

A. Do what your aircraft and engine manufactures recommend in the official FAA-approved handbook for your aircraft written 40 years ago by techs who had no clue what was going on in their engines nor understood the long term effects of what they were recommending.

B. Do a little research, ask other owners, read, read some more, and then either keep with A or listen to the guy on the Internet who may have also done the same and came to a different conclusion based on real numbers, tons of data, and more modern techniques of measuring engine degradation over long periods of time.

Even tougher call.

 

[Robert Gee]

As for carbureted engines, the ability to operate lean of peak varies. Four-cylinder carbureted engines have some success LOP, because it's possible to get fairly even fuel/air distribution to all of the cylinders — the Lycoming O-320 is particularly good for this.

Six-cylinder carbureted engines are more hit or miss, because the mixture has to travel further from the carburetor to some cylinders than to others, though I do have one friend who manages to do all his flying lean of peak behind a six-cylinder carbureted engine (confirmed by a fancy engine monitor).

Ive been reading about electronic ignition STCs, im pre-sold on the idea and think they could use running LOP as another selling point if they bothered to do some testing on it. Anyone here have one?
Consider the smog and gas crunch of the 70's. Auto carbs were leaned to the brink of self destruction for lower emissions, maybe a timely coincidence but auto makers came up with higher voltage electronic ignitions which better ignite the leaner mixtures.
Things that make you go, hmmmmmmm.

 

[William Pete Hodges]

I know this is an older thread now but replying to it made me realize there is an interest for more understanding in this area. I think I have a good enough understanding of this subject to teach a class on it, which I intend to do for the local EAA chapter in January. In preparation for the class I wrote 45 paragraphs with illustrations, including a new RFFA chart of my own design. The big improvement is this new RFFA chart can be easily adapted to any piston engine at any power level.

Understanding Engine Stress, Power, and Fuel Mixture Management (UESP&FMM Rev6) is presented here for your enjoyment. It is copyrighted, and paragraph 45 includes a terms of use license granting any private pilot the ability to post and copy as required for personal use. I ask that POA allow this material to be shared on this website.

 

[Archimago]

Sorry to add to this old threat. I've searched through the Lycoming Operators Manual and I can't find the Red Fin or Red Box charts. My recent experience with poor engine management is going to be very costly and I am highly motivated to not repeat the past.

 

[Jeff767]

In regards to peak egt and running lean of peak, I had the leaning discussion with someone at a fly-in once. His unusual method was somewhat intriguing, but difficult for me to accept. He flew a Comanche 250 with constant speed prop and Lycoming O-540. He only had a single prob egt and cht gage. He said he would try to run rich of peak to his assigned or chosen altitude keeping cht temps below 400. (as he climbed he would have to lean a little obviously) Once at altitude he would level off, set his mp and rpm’s for the percent of power he wanted to run. Then he would pull mixture somewhat quickly to engine roughness and then enrichen just until it smoothed out. He then would then re-adjust his mp and rpm’s slightly if necessary. He claimed that as soon as the engine ran smooth, he would still be lean of peak and could run there economically and safely without having to install a “fancy temperature gauge” on a normally aspirated engine, which he didn’t think was useful unless you had fuel injection anyway. Does anyone have any thoughts on this method?

With only one EGT on a carbureted 0-540 he had no real idea if none, 1 or more cylinders were LOP. In general the majority of carbed engines won’t run smoothly LOP because the mixture distribution is so poor. Some find that cracking the throttle just a bit closed can induce some turbulence and improve fuel mixing and distribution in carbed engines allowing for LOP. Roughness starts in a engine while leaning when one cylinder no longer fires. Two things allow for efficient LOP operations. Balanced fuel flow and a strong ignition system that can ignite a lean charge. In the injected world if you want to run LOP it’s common to run a test to determine where each cylinder peaks and swap injector nozzles to attempt to get them all peaking at the same fuel flow. Having all cylinders peak within .2 GPH fuel flow is considered excellent. I have seen carbed motors that were more than 1 GPH apart. In a really well balanced engine it never runs rough. It simply quits if you lean to much as all cylinders quit firing at the same time. Modern engine analyzers with A LOP mode will show you exactly how many degrees ROP or LOP each cylinder is. They will also provide the fuel flow spread between all cylinders. It’s not at all uncommon on a carbed engine to have one or two cylinders running 50 degrees ROP another at peak and the last 50 LOP. The cylinders running 50 ROP are experiencing the highest temps and internal cylinder pressures and likely will need replacement first.
If you can get all cylinders 50 LOP with the engine running smoothly you will be getting great economy and are being very kind to your engine. Usually that’s going to be a injected motor and probably have a electronic ignition however properly maintained mags with a good harness will do the trick. For reasons I don’t know Continental injected motors run better LOP out of the box than lycomings which usually need tweaking.

 

[mandm]

Peak EGT refers to the highest you can get the EGT when leaning. It may never get to the actual top.

As you pull the mixture back, the EGT will rise. If you keep leaning it, at some point it will start to drop. That is Lean of Peak. Enrich until it gets as high as it will go and that is Peak.

Thank you, learned something new!

 

[mandm]

Or in some cases, once the noise stops. (the screaming if you are riding with an inexperienced passenger.....)

Have you ever done that?? I would be the screaming pilot lol.

 

[mandm]

Is this actually safe to do in flight? I've never tried it -- nervous to do so. But if I pull the mixture and the engine quits, pushing the mixture back in before the prop stops spinning will cause it to fire right back up right?

In theory, the wind in flight would hand prop the engine to start provided the mags are on. I think.

 

[OneCharlieTango]

Sorry to add to this old threat. I've searched through the Lycoming Operators Manual and I can't find the Red Fin or Red Box charts. My recent experience with poor engine management is going to be very costly and I am highly motivated to not repeat the past.

First, it’s highly unlikely that poor engine management has caused any significant damage to your engine. Maybe by “costly” you just mean you’ve bought more gas than you had to. Or maybe you’ve had some cylinder cracks from running the CHTs too high.

Second, the Red Box is an invention of Advanced Pilot Seminars. You can Google them and sign up for their online course. It’s truly brilliant.

Or, you can watch Martin’s video for free and get a good feel for it.

 

[LesGawlik]

Some say adding a little carb heat can help a non-injected engine run LOP. I found that also in a manual for a Beech 18 with big round engines.

 

[William Pete Hodges]

Sorry to add to this old threat. I've searched through the Lycoming Operators Manual and I can't find the Red Fin or Red Box charts. My recent experience with poor engine management is going to be very costly and I am highly motivated to not repeat the past.

Search the internet for "Red Box, Red Fin". You should find a very good article written by Mike Bush. This will explain the basics of what you are trying to do. The "lean find" feature of most engine monitors describes the leaning by ET method as the manufacturers have it programmed in their devices. Reading their manuals will help you get your brain around it.

 

[Jeff767]

Can you detail a bit about what happened that has you questioning your engine management. Learning from others mistakes is a key way to learn rather than have to make them all yourself!

 

[Clip4]

Best power is the highest ground speed for a given power setting.

 

[NotarPilot]

Mike Busch does a very in-depth video about how to lean. I learned from him about 9 years ago by reading and listening to his method. I highly recommend watching this webinar.