Should you lean slightly when taxiing?

One thing nobody has mentioned is whether or not the idle mixture has been properly adjusted to begin with. In my limited experience, when the carburetor is adjusted properly you can usually leave the mixture control full rich for ground operations with few problems.

There are a few engines/airplanes that this just doesn't work on though. Even the leanest idle mixture setting can be too rich and you'll foul plugs or have a bad runup check. In those cases, the only real answer is to lean.

Since the majority of my flying lately has been in other people's airplanes and flight school airplanes, the maintenance decisions are left up to other people. Many don't seem to care if the idle mixture is correct or not so I usually just lean everything on the ground since I don't necessarily know which ones require it and which ones don't.
 
mondtster said:
One thing nobody has mentioned is whether or not the idle mixture has been properly adjusted to begin with. In my limited experience, when the carburetor is adjusted properly you can usually leave the mixture control full rich for ground operations with few problems.
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Also doesn't work at altitude. Set it up right here and you'll be having significant problems when you go land downhill somewhere.
 
denverpilot said:
Also doesn't work at altitude. Set it up right here and you'll be having significant problems when you go land downhill somewhere.
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Indeed there will be problems if there are drastic altitude changes. I would not use that as a justification for an improperly adjusted idle mixture though. :)
 
mondtster said:
Indeed there will be problems if there are drastic altitude changes. I would not use that as a justification for an improperly adjusted idle mixture though. :)
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It's not a "justification" of squat. I LIVE at 6000' MSL. If you don't learn to lean on the ground properly here, you won't be flying much. You'll be taxiing back in, no matter how your idle mixture is set, and cleaning plugs, more than you'll be going flying.

If you take a nice leisurely flight up to LXV on a nice day, if you don't learn how to lean properly you may learn what the gap in the trees is for because you aren't going to make it to pattern altitude before you turn down hill to Buena Vista.

You completely missed my point. You don't adjust idle mixture up here for up here. If you do, it'll be way too lean when you fly down to visit the low landers. It's going to run too rich up here if it's set ***right***.

There's a reason the airplane checklist says you ***have*** to lean for takeoff above 3000' MSL.
 
denverpilot said:
It's not a "justification" of squat. I LIVE at 6000' MSL. If you don't learn to lean on the ground properly here, you won't be flying much. You'll be taxiing back in, no matter how your idle mixture is set, and cleaning plugs, more than you'll be going flying.
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You're taking what I said personally, which was not the point. I know what the elevation is where you live.

How do you think a mechanic is going to set the mixture on a carburetor where you're at? Likely so it runs correctly at your home base elevation. It may or may not be possible to get the idle mixture circuit lean enough at 6,000'. I haven't tried to set one up there.

As I said before, when you have a drastic change in altitude you will have to make some adjustments with the mixture knob. For relatively small altitude changes, it really shouldn't be necessary if the mixture is set right in the first place.

My personal feeling from what I have seen and what I read on the web boards is that many owners and mechanics are apathetic when it comes to this subject. They just accept an improper mixture and compensate for it by pulling on the red knob.
 
For those questioning Bent-McKinley, they are probably the foremost authority when it comes to aviation maintenance training publications. The textbook I referenced, acknowledged, 42 organizations for their assistance in providing illustrations and information for the text. It included; Beech, Bendix, Cessna, FAA, Lycoming, Northrop University, Piper, Teletype Continental.
 
They may indeed be the foremost authority but they've never flown my plane and witnessed it eat plugs unless it's aggressively leaned on the ground.

Nor, apparently, have they flown the DA-40 that I've recently been flying and that won't come close to passing a mag check if it isn't leaned during taxi.

Do you even fly? Do you ever actually operate these engines? I seriously doubt it because your stance on this issue is patently absurd. Many of us would never get off of the ground if we didn't aggressively lean while taxiing. Quite literally.
 
mondtster said:
You're taking what I said personally, which was not the point. I know what the elevation is where you live.

How do you think a mechanic is going to set the mixture on a carburetor where you're at? Likely so it runs correctly at your home base elevation. It may or may not be possible to get the idle mixture circuit lean enough at 6,000'. I haven't tried to set one up there.
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Think about that for just a second. If an engine is set to idle in Denver what would happen when the aircraft was flown to the coast? How would the operator enrichen the mixture for idle?

A properly setup engine is set for sea level operation then the operator (not the mechanic) adjusts the mixture for local conditions.
 
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Henning said:
Imagine that, conflicting advice in manuals for operating a Lycoming.:rofl:
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Lycoming issue a service bulletin, which states to lean during ground ops. Manuals were written by lawyers who were afraid someone would try to takeoff with a overly leaned engine. With new pilots probably not an unreasonable concern.
 
Can't vouch for lycoming (I've been much happier since I got rid of my POS lycoming) but Continental says you ain't going to harm their engines at anything below max recommended cruise by playing with the red knob.

As near as I can tell your "expert" is not telling the truth. I've never seen anything from them on ground leaning period. Rule #1 in their operating tips is:

Never lean the mixture from full rich during take-off, climb or high-performance cruise operation unless the Pilot’s Operating Handbook advises otherwise. However, during takeoff from high-elevation airports or during climb at higher altitudes, roughness or reduction of power may occur at full-rich mixture. In such a case, the mixture may be adjusted only enough to obtain smooth engine operation. Careful observation of temperature instruments should be practiced.​

They later put the point at 75% power and 5000' DA.

The only talk about the mixture control on the ground is to use a lean mixture to clear a suspected fouled plug and in some cases to avoid vapor lock issues (where they specifically say LEAN FOR TAXI).
 
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Clark1961 said:
Think about that for just a second. If an engine is set to idle in Denver what would happen when the aircraft was flown to the coast? How would the operator enrichen the mixture for idle?

A properly setup engine is set for sea level operation then the operator (not the mechanic) adjusts the misture for local conditions.
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I know exactly what I wrote. Those that live in mountainous areas and see large elevation differences at airports they use are in a bit of a unique position.

I just double checked the Lycoming direct drive overhaul manual regarding setting idle mixture. It says nothing about setting it for sea level. Again I'll ask, how do your mechanics set idle mixture up there? Just put the carburetor on and throw their hands up and walk away? I doubt it.
 
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mondtster said:
I know exactly what I wrote. Those that live in mountainous areas and see large elevation differences at airports they use are in a bit of a unique position.

I just double checked the Lycoming direct drive overhaul manual regarding setting idle mixture. It says nothing about setting it for sea level. Again I'll ask, how do your mechanics set idle mixture up there? Just put the carburetor on and throw their hands up and walk away? I doubt it.
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So you don't want to stop and think about it. Fine. At least pay attention when you "double check" the manual:

4) When the idling speed has been stabilized, move the cockpit mixture control lever with a smooth,
steady pull toward the Idle Cut-Offposition and observe the tachometer for any change during
the leaning process. Caution must be exercised to return the mixture control to the Full Rich
position before the RPM can drop to a point where the engine cuts out. An increase of more than
50 RPM while leaning outindicates an excessively rich idle mixture. An immediate decrease in
RPM (if not preceded by a momentary increase) indicates the idle mixture is too lean.
5-4
LYCOMING OPERATOR’S MANUAL SECTION 5
O-360 AND ASSOCIATED MODELS MAINTENANCE PROCEDURES
If step (4) indicates that the idle adjustment is too rich or too lean, turn the idle mixture
adjustment in direction required for correction, and checkthis new position by repeating the above
procedure. Make additional adjustments as necessary until a checkresults in a momentary pick-up
of approximately 50 RPM. Each time the adjustment is changed, the engine should be run up to
2000 RPM to clean the engine before proceeding with the RPM check. Make final adjustment of
the idle speed adjustment to obtain the desired idling RPM with closed throttle. The above method
aims at a setting that will obtain maximum RPM with minimum manifold pressure. In case the
setting does not remain stable, checkthe idle linkage;any looseness in this linkage would cause
erratic idling. In all cases, allowance should be made for the effect of weather conditions and field
altitude upon idling adjustment.
 
teejayevans said:
Lycoming issue a service bulletin, which states to lean during ground ops. Manuals were written by lawyers who were afraid someone would try to takeoff with a overly leaned engine. With new pilots probably not an unreasonable concern.
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Because no instructor can properly setup a new pilot's mind into thinking clearly in the cockpit. It's all about checklists which essentially takes the thought process out of it.

There are a number of cross-checks that someone can perform shortly after takeoff that should catch an improperly set mixture control.

I can't stand "INOP" engine instrumentation.
 
If I have some guy that smells bad in the other seat, I lean to the left. If I have a babe in the other seat I lean to the right.
 
GlennAB1 said:
For those questioning Bent-McKinley, they are probably the foremost authority when it comes to aviation maintenance training publications. The textbook I referenced, acknowledged, 42 organizations for their assistance in providing illustrations and information for the text. It included; Beech, Bendix, Cessna, FAA, Lycoming, Northrop University, Piper, Teletype Continental.
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No mention of the folks at Advanced Pilot Seminars, I see.

When evaluating conflicting statements from presumed aurhorities, I usually go with the ones that agree with repeatable, observable events.
 
Palmpilot said:
No mention of the folks at Advanced Pilot Seminars, I see.

When evaluating conflicting statements from presumed aurhorities, I usually go with the ones that agree with repeatable, observable events.
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why...? A lawyer, a dentist, and a 777 captain ....:goofy:
 
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Clark1961 said:
So you don't want to stop and think about it. Fine. At least pay attention when you "double check" the manual:

4) When the idling speed has been stabilized, move the cockpit mixture control lever with a smooth,
steady pull toward the Idle Cut-Offposition and observe the tachometer for any change during
the leaning process. Caution must be exercised to return the mixture control to the Full Rich
position before the RPM can drop to a point where the engine cuts out. An increase of more than
50 RPM while leaning outindicates an excessively rich idle mixture. An immediate decrease in
RPM (if not preceded by a momentary increase) indicates the idle mixture is too lean.
5-4
LYCOMING OPERATOR’S MANUAL SECTION 5
O-360 AND ASSOCIATED MODELS MAINTENANCE PROCEDURES
If step (4) indicates that the idle adjustment is too rich or too lean, turn the idle mixture
adjustment in direction required for correction, and checkthis new position by repeating the above
procedure. Make additional adjustments as necessary until a checkresults in a momentary pick-up
of approximately 50 RPM. Each time the adjustment is changed, the engine should be run up to
2000 RPM to clean the engine before proceeding with the RPM check. Make final adjustment of
the idle speed adjustment to obtain the desired idling RPM with closed throttle. The above method
aims at a setting that will obtain maximum RPM with minimum manifold pressure. In case the
setting does not remain stable, checkthe idle linkage;any looseness in this linkage would cause
erratic idling. In all cases, allowance should be made for the effect of weather conditions and field
altitude upon idling adjustment.
Click to expand...

This article by John Deakin also mentions the need to take field elevation into account when idle mixture is set:

http://www.advancedpilot.com/articles.php?action=article&articleid=1844
 
Quote:
Originally Posted by Clark1961
So you don't want to stop and think about it. Fine. At least pay attention when you "double check" the manual:

4) When the idling speed has been stabilized, move the cockpit mixture control lever with a smooth,
steady pull toward the Idle Cut-Offposition and observe the tachometer for any change during
the leaning process. Caution must be exercised to return the mixture control to the Full Rich
position before the RPM can drop to a point where the engine cuts out. An increase of more than
50 RPM while leaning outindicates an excessively rich idle mixture. An immediate decrease in
RPM (if not preceded by a momentary increase) indicates the idle mixture is too lean.
5-4
LYCOMING OPERATOR’S MANUAL SECTION 5
O-360 AND ASSOCIATED MODELS MAINTENANCE PROCEDURES
If step (4) indicates that the idle adjustment is too rich or too lean, turn the idle mixture
adjustment in direction required for correction, and checkthis new position by repeating the above
procedure. Make additional adjustments as necessary until a checkresults in a momentary pick-up
of approximately 50 RPM. Each time the adjustment is changed, the engine should be run up to
2000 RPM to clean the engine before proceeding with the RPM check. Make final adjustment of
the idle speed adjustment to obtain the desired idling RPM with closed throttle. The above method
aims at a setting that will obtain maximum RPM with minimum manifold pressure. In case the
setting does not remain stable, checkthe idle linkage;any looseness in this linkage would cause
erratic idling. In all cases, allowance should be made for the effect of weather conditions and field
altitude upon idling adjustment.






Palmpilot said:
This article by John Deakin also mentions the need to take field elevation into account when idle mixture is set:

http://www.advancedpilot.com/articles.php?action=article&articleid=1844
Click to expand...

If the plane is based at a high altitude airport and not flown to sea level then I would agree to set the idle mixture for local conditions....

The problem is if it is ever taken down lower ( sea level) there is no way to enrichen it without a A&P doing the rework of the carb settings....
 
N801BH said:
If the plane is based at a high altitude airport and not flown to sea level then I would agree to set the idle mixture for local conditions....

The problem is if it is ever taken down lower ( sea level) there is no way to enrichen it without a A&P doing the rework of the carb settings....
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Which is what Lycoming is saying. The sentence that I emphasised by making bold wouldn't be needed if they intended for the engine to be set up for local conditions.
 
Clark1961 said:
Think about that for just a second. If an engine is set to idle in Denver what would happen when the aircraft was flown to the coast? How would the operator enrichen the mixture for idle?

A properly setup engine is set for sea level operation then the operator (not the mechanic) adjusts the mixture for local conditions.
Click to expand...

This means that every couple of years, you should fly to a sea level airport and recalibrate, especially FI systems, though carbs creep as well and should be readjusted somewhat regularly. I wouldn't let it go more than 2 years, especially wth FI.
 
Any one here wonder why we are allowed 10 to 50 RPM rise on the idle circuit mixture check?
 
Tom-D said:
Any one here wonder why we are allowed 10 to 50 RPM rise on the idle circuit mixture check?
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Required actually. To make sure you have more than enough available under any circumstance. Typically circumstance doesn't dictate you need all of it.
 
Henning said:
This means that every couple of years, you should fly to a sea level airport and recalibrate, especially FI systems, though carbs creep as well and should be readjusted somewhat regularly. I wouldn't let it go more than 2 years, especially wth FI.
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Tell us what is allowed to be calibrated in a MA-3SPA carb.
 
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Henning said:
Required actually. To make sure you have more than enough available under any circumstance. Typically circumstance doesn't dictate you need all of it.
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Is the Carb or engine manual required ?
 
Tom-D said:
Is the Carb or engine manual required ?
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The manuals I was sent to were for the aircraft/engine which state the rise to lean to. We had the carb manuals, but you don't really need it to adjust the idle metering screw. It's not a particularly complex process.
 
Tom-D said:
I understand you do not know the difference between an adjustment and a calibration.
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Calibration I used more in line with the FI systems where you set the pump pressure with a calibrated instrument rather than relying on the dash instrument. The carb you just adjust the metering screw, simple 20 minutes once you get to sea level.
 
RickG said:
Do you lean as aggressively after landing and while taxiing back to the tie-down?
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When my engine is running and the tires are in contact with Mother Earth, either all knobs are fully forward for takeoff or the red knob is aggressively leaned. Start engine. Scan gages. Lean way back. Begin taxi. Stop at hold short, begin checklist. At "Mixture--Full Rich" it goes forward and stays for takeoff and initial climb.

After landing, Flaps Up, slow down plane; exit runway or turn around for back taxi, aggressively lean mixture, taxi to wherever I'm going. Set 1000 RPM, Mixture to Idle Cutoff, watch for 50 RPM rise, Throttle to Idle, wait for engine to quit.

Got so used to pulling my mixture about 3/4 to Cutoff that when I flew a friend's Skyhawk, I leaned like my plane and the engine stopped just before the runway exit. :blush: Rolled clear, Mixture Rich, restarted engine and leaned somewhat less . . .
 
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