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Leaning at idle, how much ?

lockeed

lockeed

Well Known Member
I have a O-360 180hp in my RV-6A. They always say you should lean when you're taxing or at idle on the ground.

Is there a rule of thumb or we just have to lean it by sound...? Should we lean untill the engine drops rpm then bring it back a bit?

Please share you thoughts!
 
lockeed said:
I have a O-360 180hp in my RV-6A. They always say you should lean when you're taxing or at idle on the ground.

Is there a rule of thumb or we just have to lean it by sound...? Should we lean untill the engine drops rpm then bring it back a bit?

Please share you thoughts!
Click to expand...

Pull it as lean as it will go without dying. If the engine coughs when you advance the throttle a little it is just right. If you have a carb, and it is set correctly you will hear the rpm speed up a little just before it goes lean enough to die.
 
If you lean at 1000 rpm, the rpm will increase to about 1200. When that happens cut back the rpm to your taxi speed. If you forget to enrich the mixture, you won't get past the mag check.....
 
Is this what the engine manufacturer recommends? It is always better to cite a source or reference point.

There are two mixtures adjustments. A ground idle and an in-flight idle. The ground idle specifically runs richer on the ground to provide additional cooling.

I would recommend NOT leaning useless there is a problem fouling plugs. Follow the recommended guidance.
 
Chris Thomas said:
Is this what the engine manufacturer recommends? It is always better to cite a source or reference point.

There are two mixtures adjustments. A ground idle and an in-flight idle. The ground idle specifically runs richer on the ground to provide additional cooling.

I would recommend NOT leaning useless there is a problem fouling plugs. Follow the recommended guidance.
Click to expand...

Of course, it also depends on the airport's altitude. Around here, at 4600' msl, it's an automatic pull of about 5/8" just after the engine starts . If you don't and start taxiing, you'll really notice the difference.
 
There are two mixtures adjustments. A ground idle and an in-flight idle. The ground idle specifically runs richer on the ground to provide additional cooling.
Click to expand...
Okay, lets hear the story behind this. I don't think the throttle plate knows when its flying. The idle mixture knob is a simple air bleed needle valve. Couple of holes in the venturi (idle circuit). There is a power enrichment valve, but it's not active anywhere near idle.
 
Leaning at idle

See Lycoming Service Instruction 1497A. You can locate it by Google search. Synopis: after startup set RPM to 1200. Lean until rpm decreases then richen until smooth. Leave this mixture setting for all ground operations including mag check (hard to believe, I know). Return to full rich for take-off.

Also see EAA Webinar with Mike Burch on Leaning Basics

John Ciolino
RV-8 N894Y
 
John Ciolino said:
See Lycoming Service Instruction 1497A. You can locate it by Google search. Synopis: after startup set RPM to 1200. Lean until rpm decreases then richen until smooth. Leave this mixture setting for all ground operations including mag check (hard to believe, I know). Return to full rich for take-off. Also see EAA Webinar with Mike Burch on Leaning Basics

John Ciolino
RV-8 N894Y
Click to expand...

And somewhere, it hopefully mentions leaning around 5000' desnsity altitude takeoffs, if not before. Don't go full rich for landing at high altitude airports either.
 
John Ciolino said:
See Lycoming Service Instruction 1497A. You can locate it by Google search. Synopis: after startup set RPM to 1200. Lean until rpm decreases then richen until smooth. Leave this mixture setting for all ground operations including mag check (hard to believe, I know). Return to full rich for take-off.

Also see EAA Webinar with Mike Burch on Leaning Basics

John Ciolino
RV-8 N894Y
Click to expand...

That SI is rather specific to one model of engine in one particular airframe

MODELS AFFECTED: Lycoming IO-360-L2A engines installed in Cessna C172R and 172S aircraft used in training operations.

...and it's a FI engine...

http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1497A.pdf

It also says this...

6. Do a ground check in accordance with the POH or AFM

I bet the Cessna POH does not say mag checks at 1200 rpm...:rolleyes:
 
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think of that red knob as being green. the more you pull the more you save $$. it is amazing how many people dont understand leaning procedures.

VAF_008%20Nov.%2015,%202012%2016.53.10.jpg


this is my favorite pic yet. :)
 
I think fuel flow gauges should be calibrated in "Dollars Per Hour", you would see some serious leaning then :D
 
Leaning basics video

This video is very informative and well done.
When you have some time to kill check it out.

The best anology: "we don't have a choke on our airplanes"
Effectively, full rich acts as a choke at start up.

The EGT curve and running the engine between lean
Economy and richer max HP while not exceeding 400 deg.
On the CHT, spells it all out.

My question and yet to get my head around the issue.
Why other than start up, would you want to run full rich beyond
Max HP (100 deg rich of peak EGT)?? Especially on take off when you want
Max HP. The only thing I can think of is that full rich keeps the cylinders cooler on
climb out. Can anyone elaborate on this?

http://www.eaavideo.org/video.aspx?v=1678859198001
 
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Full rich when at high power settings reduces CHT but most importantly protects agains severe knock (detonation) which will destroy your engine in short order.
 
Chris Thomas said:
Is this what the engine manufacturer recommends? It is always better to cite a source or reference point.

There are two mixtures adjustments. A ground idle and an in-flight idle. The ground idle specifically runs richer on the ground to provide additional cooling.

I would recommend NOT leaning useless there is a problem fouling plugs. Follow the recommended guidance.
Click to expand...

If you have any data to back up that statement, I would sure love to see it. Facts and data, not some myth about "fuel cooling".

Just on the topic of fuel cooling, lets examine this, fuel when it evaporates on your hand makes your hand feel a bit cooler, barely worth measuring and the latent heat transfer is very small. Now imagine how much effect that has with a very tiny volume of fuel inside a combustion chamber at 3-4000 degrees F. I think you would agree it is not even worth thinking about let alone measuring.

Fuel ONLY EVER adds heat to an engine. It never cools the engine.

Why you see the CHT change with fuel/air ratio changes is to do with the peak pressure generated and the the angle of that peak pressure from TDC. The gas expansion pressure at a greater Theta PP for a given fuel air ratio will generate a lower PP than one closer to TDC, and the higher the PP the higher the CHT, given the same rate of cooling air of course.

Now what does all this mean, well inside the cylinder, around the surfaces of the head, walls and piston crown there is a small boundary layer, just like the boundary layer on a wing. This layer is like a thermal blanket. The greater the layer the better, and when the PP reaches higher levels this layer is reduced. More heat transfer to the head, and your CHT is higher.

If fuel cools, and thus less of it means hotter, why does CHT start dropping again once past30-40dF ROP? The CHT is cooler at peak EGT than it is at 30-40f ROP.

So back to ground operations, the vast majority of the previous posts are correct and are optimal operations.

The engine manufacturers do not always issue optimum information, they are often trying to appeal to the lowest common denominator, and often shoot themselves in the foot doing so.

Blind faith is a dangerous thing.

Probably the best source of education is found here
http://www.vansairforce.com/community/showthread.php?t=93201

and here, and a thorough understanding of the graph in the original posters opening post is paramount.

http://www.vansairforce.com/community/showthread.php?t=75132

Cheers! :)
 
L.Adamson said:
Of course, it also depends on the airport's altitude. Around here, at 4600' msl, it's an automatic pull of about 5/8" just after the engine starts . If you don't and start taxiing, you'll really notice the difference.
Click to expand...

I start the engine with it leaned to approximately the correct mixture (~6800 foot field elevation). Then lean more to taxi.
 
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I love all the information there is on the subject. I'm embarrassed to say how long I have done this wrong at near-sea-level airports.

Of course, at the same time I started leaning on the ground my #2 EGT probe went berserk, not exactly inspiring confidence, but I'm sure it's just confidence.

Thanks for the video link - I'll watch it next time I'm on the treadmill.
 
Leaning

agirard7a said:
This video is very informative and well done.
When you have some time to kill check it out.

The best anology: "we don't have a choke on our airplanes"
Effectively, full rich acts as a choke at start up.

The EGT curve and running the engine between lean
Economy and richer max HP while not exceeding 400 deg.
On the CHT, spells it all out.

My question and yet to get my head around the issue.
Why other than start up, would you want to run full rich beyond
Max HP (100 deg rich of peak EGT)?? Especially on take off when you want
Max HP. The only thing I can think of is that full rich keeps the cylinders cooler on
climb out. Can anyone elaborate on this?

http://www.eaavideo.org/video.aspx?v=1678859198001
Click to expand...

Interesting webinar. Good basic to advanced info.

I have understood for decades that, a full rich mixture, full power climb-out (below 5000') will help keep CHT below 400.
Doug's VAF site has helped collect needed links of information to enlighten many to the facts of how and why.

The information links provided by members on just this subject is worth more than the minimum $25 donation to VAF.
Donate to VAF for this and other valuable information we all get in one place here. Great site Doug! Thank you.
 
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I am past explaining this multiple times and to be fair it can't be done justice in one, two or three posts.

Please, if you want to learn.........

http://www.vansairforce.com/community/showthread.php?t=93201

Fuel does not cool.....EVER....it adds heat, it burns, and thus cant cool. Do not bother thinking otherwise. Cooler CHT as a function of fuel is all about PP and theta PP.

Please kill off the Old Wives Tales.
 
I have a vague recollection of Don at AFP saying that there would be no need to lean on the ground if you are using their fuel injection system and it is properly set up. Can anyone confirm this, and if true, explain why this is so?

Erich
 
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