Leaning during climb

Ed Haywood

Ed Haywood

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Big Ed
My AFM and Lycoming Operators Manual both recommend climbing at full rich to keep the engine cool. I've always followed that advice. But looking at the engine performance graph, it's clear that results in high specific fuel consumption and less than best power.

Now that I have an engine monitor, I'm interested in operating more efficiently. Leaning to best power would be more efficient for cruise climb, both in time and fuel burn.

Cooling is the concern, of course. Each aircraft is going to behave differently, due to design differences and condition. My Decathlon has always had good airflow and cooling, especially now with a fresh engine and new baffling and oil cooler.

MP, mixture and EGT change as you climb, moving you out of the desired range. Periodically repeating the leaning process during a long climb does not seem sensible.

So I'm thinking a more effective method is to lean to best power at the start of the climb, then closely monitor CHT and adjust mixture to keep hottest cylinder at or below a desired value, say 400 F. In practice, that probably involves leaning another twist or two every thousand feet or so.

How do other folks do it?

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I lean to get CHTs of 350-380 during the climb and cruise. I typically climb at 65% power. As long as those two parameters are met, I am not worried about damaging the engine.
 
I read some advice years ago (I'd like to say it was a semi-authoritative source like Deakin) that suggested leaning to 200° rich of peak EGT ie if you typically see 1450, lean to 1250.
(Always consider CHTs when leaning of course; that must be a primary consideration - and I think 400 is too high for Lyc or Cont.)
It has worked well for me.
Yes, in some cases you have to adjust as you climb.
 
Always lean forward.

On my injected Continental, I dial back the fuel flow once I set climb power. I don't bother finely leaning things until I level out.
 
Ed Haywood said:
I trust the engine manufacturer as primary source for data. The Lycoming operators manual for AEIO-360 series says:

View attachment 132421
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Ed, I keep reading that the oem of our engines have that wrong and that the limits they suggest are not ideal for maximum cylinder life.
I can try to find readings on this if interested. (Neither the engine mfg’s nor those proposing lower maximums have good long term data is my undesirable, but once you read what is available it seems that cooler, up to a reasonable limit, is better).
 
Ed Haywood said:
What does that mean?
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From a long, long time ago, on a board far, far away…
I also realized this about the time I saw a barn about 200 feet from the end of the runway.

And that’s when I prayed.

“Oh God, please let my little T-tail climb. Please let it climb. Please let it climb!”

“LEAN FORWARD!!” I screamed to my passenger.

As I yanked the gear up, I think I could hear the wake of air buffeting off the barn as we barely cleared it with my stall warning horn blazing. That was the first time in my life I’ve ever been scared in an airplane. But my passenger, surprisingly, is ice cool – no problems. No sweat, even. Calm as a gentle pond.
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Having an engine monitor is fantastic. I lean to best power (about 1350 for me) and adjust as I’m climbing.
 
Know what your sea level egt is with full mixture (assuming your fuel flow is set correctly) and lean during climb to keep that egt. That should be the right richness for appropriate climb power. For my bonanza climbing out at 800ft the full mixture egt is a bit over 1300, so during climb I keep the egt a bit over 1300.

Also why wouldn’t you climb out at full power unless your poh specifies otherwise? Deakin has pointed out that it makes little sense to climb longer at lower power settings with poor airflow and rich mixtures compared to using full power to get there quicker and dial back to lean cruise setting.
 
With a full engine monitor and the gaping cowl openings, I lean to about 1400 and never see the cylinder temps above 360 unless its a 95 degree day. In that case I shallow the climb.

LycO540
 
Interesting. I was taught (and it was backed up by the poh's of the planes I've flown) to lean above 3000' msl. My strategy is to keep my egt's roughly where they are on the ground. I know that full rich on a normal day is about 1300*, so that's my target. It works out to be a small adjustment every couple thousand feet, so pretty minimal additional workload. This also keeps the engine a bit rich for cooling and extra detonation margin, but not so rich that it loses power.

In planes without egt, I lean until the rpm's pick up a bit, then richen slightly.
 
When I first got my Navion, the carb had issues. I sent it out to Pacific Airmotive to be overhauled. It was arguably better when we put it back on but I spent a lot of time trying to figure out how to lean the thing. It just would start to misfire as soon as we moved the mixture. After much headscratching with the mechanic, we called Pacific up. They politely pointed out that we were idiots. See that dohicky on the side with the safety wire? That's an altitude compensator. You don't touch the mixture control on that engine until above 12,000'.
 
Ed Haywood said:
My AFM and Lycoming Operators Manual both recommend climbing at full rich to keep the engine cool. I've always followed that advice. But looking at the engine performance graph, it's clear that results in high specific fuel consumption and less than full power.

Now that I have an engine monitor, I'm interested in operating more efficiently. Leaning to best power would be more efficient for cruise climb, both in time and fuel burn.

Cooling is the concern, of course. Each aircraft is going to behave differently, due to design differences and condition. My Decathlon has always had good airflow and cooling, especially now with a fresh engine and new baffling and oil cooler.

MP, mixture and EGT change as you climb, moving you out of the desired range. Periodically repeating the leaning process during a long climb does not seem sensible.

So I'm thinking a more effective method is to lean to best power at the start of the climb, then closely monitor CHT and adjust mixture to keep hottest cylinder at or below a desired value, say 400 F. In practice, that probably involves leaning another twist or two every thousand feet or so.

How do other folks do it?

View attachment 132412
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Yes, you lean in a climb. In many models there will be a minimum fuel flow placard advising how lean the engine may be at various altitudes in a climb.

The 182S has a climb fuel flow of 15GPH or fuel rich (whichever is less)
 
Clip4 said:
Yes, you lean in a climb. In many models there will be a minimum fuel flow placard advising how lean the engine may be at various altitudes in a climb.

The 182S has a climb fuel flow of 15GPH or fuel rich (whichever is less)
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yes, full rich during climb…..except….when you start the climb at 5000 msl. I’ll be full throttle but not full rich.
 
Ever since I got the engine monitor always full rich when I can.
 
kujo806 said:
Know what your sea level egt is with full mixture (assuming your fuel flow is set correctly) and lean during climb to keep that egt. That should be the right richness for appropriate climb power. For my bonanza climbing out at 800ft the full mixture egt is a bit over 1300, so during climb I keep the egt a bit over 1300.

Also why wouldn’t you climb out at full power unless your poh specifies otherwise? Deakin has pointed out that it makes little sense to climb longer at lower power settings with poor airflow and rich mixtures compared to using full power to get there quicker and dial back to lean cruise setting.
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One suggestion that I use is to note EGT after takeoff and when configured for the climb. For me that is about 500 feet. Depending on outside air temp EGT is about 1300-1325 degrees. I make my first lean when EGT drops to about 1250 and lean back to 1300, then repeat as necessary. Easy.
 
MauleSkinner said:
Functional or dysfunctional?
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I put the fun in dysfunctional. (I got swag with that saying on it for when my wife was a special ed teacher, but she declined to take them to school).
 
William Pete Hodges said:
One suggestion that I use is to note EGT after takeoff and when configured for the climb. For me that is about 500 feet. Depending on outside air temp EGT is about 1300-1325 degrees. I make my first lean when EGT drops to about 1250 and lean back to 1300, then repeat as necessary. Easy.
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The engine monitor in my Cirrus made that easy. There was a “Normalize” function that set the EGT bars to “zero”. Then it was easy to lean as necessary to keep them there. As I recall, if the bars moved down, you needed to lean enough to bring them back up. Easy peasy. I suspect some other engine monitors may have that same or a similar feature.
 
FastEddieB said:
The engine monitor in my Cirrus made that easy. There was a “Normalize” function that set the EGT bars to “zero”. Then it was easy to lean as necessary to keep them there. As I recall, if the bars moved down, you needed to lean enough to bring them back up. Easy peasy. I suspect some other engine monitors may have that same or a similar feature.
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My JPI 830 has normalize but I haven't learned to use it yet.
 
Given that my POH also says to lean on the ground to max RPM then enriched a bit when taking off at high DA, I tend to use that to rationalize leaning while climbing when above 5000 feet. I also have an 830 and tend to adjust the mixture - in both directions - to keep it as lean as I can while keeping the CHTs acceptable (for my engine, I use 400). I also keep climb speed at around 90 to help with cooling.
 
murphey said:
yes, full rich during climb…..except….when you start the climb at 5000 msl. I’ll be full throttle but not full rich.
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The altitude you want to use is density altitude, not MSL.

One can in the winter can take off with a density altitude of negative 2500 feet in winter and + 5000 in summer.
 
In my Lycoming IO-390-powered RV-14, I have taken to full-rich climbs. I messed with leaning in the initial climb at first. The method I used is basically what @William Pete Hodges and @FastEddieB posted above: Note a target EGT early in the climb and lean to maintain that as you go up. But I gave up on that because the CHTs tended to get a bit warm and the difference between full-rich (~15 gph) and leaned (~12 gph) for the 5-10 minutes I spend getting to altitude is on the order of a third of a gallon.

Here is a chart from the Cessna 310R POH, so it applies to a Continental IO-520. The original fuel flow gauge has blue tick marks more or less as aiming points for altitudes from maybe 4000 or 6000 up. I throw this out the window if the CHTs are trending toward the upper edge of my comfort zone. These flow rates are per side. And they add up to about 4 gallons of savings during a normal climb. Not only is that money in my pocket, but it's also 30 more miles of range.
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Normally aspirated Lycoming O-320-D3G in my Warrior with a CHT-only monitor. I may lean during run up depending on the airport altitude. During climb, I'll randomly lean to best power-ish keeping the hottest CHT below 380-390F. I'm not anal about it. More often, if I have to lower CHT, I'll do a step climb, but this is rare. My baffling is in great shape. I always lean when establishing cruise altitude and power.
 
Clip4 said:
The altitude you want to use is density altitude, not MSL.

One can in the winter can take off with a density altitude of negative 2500 feet in winter and + 5000 in summer.
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Clip….my ground is 5500 msl. You can use any definition of altitude but I lean on the ground.
 
With my EDM 830, i lean to best power and closely monitor CHTs to stay below 400

My AFM says similar things, but it came with only a single probe and full rich keeps it cool. And since you don't actually know the all the CHTs with a single analog probe, it's a safe conservative way. But since you do know, you can be more efficient.
 
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I am reading that many aluminum alloys have a permanent reduction in strength - up to 50% - reaching 200°C (400°F)

T or F?
Applicable here, or not?
 
Let'sgoflying! said:
I am reading that many aluminum alloys have a permanent reduction in strength - up to 50% - reaching 200°C (400°F)

T or F?
Applicable here, or not?
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The reduction of strength is true, but at 400F it is not permanent. At least that is my understanding.
 
A few things.

Turbo and non-Turbo are different. Turbo is everything forward for the climb. For non-Turbo, I use the lead to maintain take off roll EGT.

Reducing power to climb is old school. Unless you have a continuous power limit (like full power limited to 5 minutes) most efficient is to climb at full power if you can keep the CHTs cool. How cool? Under 380 for Continental, below 400 for Lycoming
 
William Pete Hodges said:
The reduction of strength is true, but at 400F it is not permanent. At least that is my understanding.
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I’m sure it depends on the alloy, heat treaments etc… plus the conditions of exposure to high temps - but I occasionally read things such as this:

“At temperatures above 150 °C, the alloy suffers a loss in strength with deterioration increasing over time. Above 200 °C, the weakening is substantial, and is accompanied by some gain in ductility.“
150C=300F
200C=400F

It has to do with changes in grain size (which is not reversed with cooling).
Even if they are not specifically talking about aircraft cylinder alloy, I have wonder if a similar effect applies.
 
I look at it as the hotter the metal is, the softer and more susceptible it is to being damaged. It doesn’t necessarily mean it is toast if it hits 400, but it is probably a good idea to keep it at reasonable temperature to avoid damage. My #4 runs hot and on summer days can hit 408 or so in the climb even with 120knot IAS. It is not there long and outside of climb it is always below 380. So far so good with great bore scopes and clean bills of health.
 
The “Target EGT” method makes the most sense to me for a climb with a normally aspirated engine. Pick any one cylinder, then lean in the climb to maintain the EGT you saw at (or near) sea level. That keeps you lean enough for good power while not getting so lean to end up in the famous “red box”. Don’t sweat it over a few degrees - just keep the EGT roughly at the target.

Note that some engines have altitude-compensating fuel pumps. They do a reasonable job of leaning in the climb without a need to touch the mixture knob. How do you know whether you have an altitude-compensating fuel pump? Well - if the EGTs don’t drop significantly in the climb, then you probably have one. (Or you are turbo-charged.)

I am very much opposed to leaning in reference to CHT. CHT takes a long time (a minute or so) to stabilize after a change in power setting, so there’s no immediate feedback. You can also mask a dangerous situation on a cool day or with good baffles. CHTs are important and need to be monitored, of course - but they should not be your primary guidance for leaning, regardless of what Mike Busch says. Only EGT will tell you accurately where you are on the power/leaning chart.

Regards,
Martin
 
Martin Pauly said:
You can also mask a dangerous situation on a cool day or with good baffles.
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This a concern I have with my plane. The straight tailed Lance is overcooled. Not unusual to see my CHTs stay under 300 in a max power climb on a cool day, but you know the cylinder pressure is very high. If I ran my engine based on CHT, I'd fly everywhere at max power and leaned to peak EGT. I suspect my valves wouldn't be too happy though.
 
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