How far do you lean while on the ground before takeoff

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pelmet
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How far do you lean while on the ground before takeoff

Post by pelmet » Tue Jul 03, 2018 12:00 pm

Just reading an article about leaning the engine during ground ops and the pilot suggests leaning as much as is reasonably possible. His reason is that eventually, there will be a time that you will forget to go to the proper mixture setting for takeoff. When this eventually happens, instead of there being a serious takeoff issue, the engine will simply falter almost immediately upon full power application with no harm done at which point full rich(or as required) can be selected and the takeoff continued normally.
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Re: How far do you lean while on the ground before takeoff

Post by photofly » Tue Jul 03, 2018 12:24 pm

There's really no reason NOT to lean as far as is possible, and several plus points for doing so. It keeps your plugs cleaner, burns less fuel, and as you point out, if you forget to move the red knob forward for take off the engine will quit on you. I know this personally. :-)
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Re: How far do you lean while on the ground before takeoff

Post by CpnCrunch » Tue Jul 03, 2018 12:26 pm

photofly wrote:
Tue Jul 03, 2018 12:24 pm
There's really no reason NOT to lean as far as is possible, and several plus points for doing so. It keeps your plugs cleaner, burns less fuel, and as you point out, if you forget to move the red knob forward for take off the engine will quit on you. I know this personally. :-)
Agree with the above. I would just suggest being careful after landing, as you don't really want the engine to cut out while you're taxiing off the runway (done that).
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Re: How far do you lean while on the ground before takeoff

Post by ahramin » Tue Jul 03, 2018 2:10 pm

If someone's reason for leaning on the ground is for when they forget the basics of the before takeoff checklist, that person has bigger problems to worry about than fouled plugs.
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Re: How far do you lean while on the ground before takeoff

Post by trey kule » Tue Jul 03, 2018 2:25 pm

If someone's reason for leaning on the ground is for when they forget the basics of the before takeoff checklist, that person has bigger problems to worry about than fouled plugs.

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Re: How far do you lean while on the ground before takeoff

Post by photofly » Tue Jul 03, 2018 3:00 pm

ahramin wrote:
Tue Jul 03, 2018 2:10 pm
If someone's reason for leaning on the ground is for when they forget the basics of the before takeoff checklist, that person has bigger problems to worry about than fouled plugs.
I don’t pull out a checklist between the time I taxi onto the runway and the time I advance the throttle... do you?
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Re: How far do you lean while on the ground before takeoff

Post by Cat Driver » Tue Jul 03, 2018 4:06 pm

What happens if you do not lean on the ground?

Is there any way to tell if something has changed because you did not lean on the ground?

Is it difficult to rectify the problem should one arise?
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Re: How far do you lean while on the ground before takeoff

Post by ahramin » Tue Jul 03, 2018 4:08 pm

I don't put the checklist away until all the items are done. Even if it's not done when I'm going to position on the runway. Not much point to a checklist otherwise.
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Re: How far do you lean while on the ground before takeoff

Post by aeroncasuperchief » Tue Jul 03, 2018 4:11 pm

What's a checklist?
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Re: How far do you lean while on the ground before takeoff

Post by photofly » Tue Jul 03, 2018 4:26 pm

Ideally you want to enrichen the mixture just before you apply full throttle, not some indeterminate earlier time when you go through a checklist.
ahramin wrote:
Tue Jul 03, 2018 4:08 pm
I don't put the checklist away until all the items are done. Even if it's not done when I'm going to position on the runway. Not much point to a checklist otherwise.
let’s say you’re queuing for departure, with the checklist items done. You’re going to lean the mixture again, while you sit there with the engine idling for twenty minutes, aren’t you? Please tell me you are. Are you going to run a checklist again? What if... (horrors) you forget to run the checklist a second time?? Maybe you need a checklist to remind you to run the checklist again.

Checklists aren’t the answer to everything. Aggressively leaning the mixture does no harm, and some good.
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Re: How far do you lean while on the ground before takeoff

Post by pelmet » Tue Jul 03, 2018 7:09 pm

Yes, I use a checklist but I also operate in the real world. That is why I feel that the leaning advice is valid. Why? Because things happen in the real world, like an interrupted checklist that doesn't get completed or something else happens that I guarantee you has happened to those on this thread changing the subject to talk about pilots having bigger problems to worry about......a checklist item gets skipped. It has happened and will keep on happening and I have done it more than once.
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Re: How far do you lean while on the ground before takeoff

Post by ahramin » Tue Jul 03, 2018 8:00 pm

photofly wrote:
Tue Jul 03, 2018 4:26 pm
Aggressively leaning the mixture does no harm, and some good.
I completely agree.
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Re: How far do you lean while on the ground before takeoff

Post by C.W.E. » Wed Jul 04, 2018 6:41 am

Conversely what " harm " does not leaning on the ground do?
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Re: How far do you lean while on the ground before takeoff

Post by photofly » Wed Jul 04, 2018 6:51 am

I assume photofly means that he leaves the mixture lean until right before takeoff power is applied and doesn't mean that he puts the mixture full rich for the before takeoff checklist, then leans the mixture again after the checklist is complete. In either case, I don't see how this checklist is useful. If it's a read and do, there seems to be a big disconnect between when the item is read and when it is to be done. If it's a vital action, then the checklist shouldn't even be started until all the items on it are already thought to be done. What am I missing here?
I lean the mixture after engine start. I enrichen the mixture immediately before applying full power before takeoff. Other than that I adjust the mixture to suit what I’m trying to accomplish at the time with the engine, just as I do the throttle.

You’re the one who raised the topic of checklists in this thread, so I don’t know what you’re missing. The mixture control isn’t mentioned in either my or Cessna’s pre-takeoff checklist. Neither is using the foot pedals to steer the airplane, nor using the throttle and/or using the brakes to control the taxi speed, for that matter.
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Re: How far do you lean while on the ground before takeoff

Post by C.W.E. » Wed Jul 04, 2018 7:17 am

I lean the mixture after engine start.
Why?
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Re: How far do you lean while on the ground before takeoff

Post by photofly » Wed Jul 04, 2018 7:43 am

I believe it keeps the plugs cleaner. That’s mostly why.
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Re: How far do you lean while on the ground before takeoff

Post by Posthumane » Wed Jul 04, 2018 7:49 am

Some engines will foul the plugs very quickly when idling with a rich mixture on the ground. There is not enough heat developed to burn off the carbon deposits at idle. This seems to vary quite a bit from plane to plane though - some have no problems being left rich, and others have to be leaned every time.

In regards to how far to lean:
The Marvel-Schebler carburetors that are commonly used on small lycomings and continentals have a main jet and one or more idle jets. The mixture control is quite effective at controlling flow to the main jet, but the idle jet flows so much less fuel that it's much more restrictive than the mixture control until the mixture is leaned almost all the way to cut-off. In other words, most of the travel of the mixture knob has no effect on the mixture at idle. If you're going to lean at idle you need to lean "aggressively" (almost to cut-off) for it to have any effect on the idle jet. Of course, leaning aggressively at idle basically restricts the fuel flow to whatever is required to idle at that particular RPM, so any addition in power will require enriching the mixture to prevent rough running due to an overly lean condition.
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Re: How far do you lean while on the ground before takeoff

Post by ahramin » Wed Jul 04, 2018 8:04 am

photofly wrote:
Wed Jul 04, 2018 6:51 am
I assume photofly means that he leaves the mixture lean until right before takeoff power is applied and doesn't mean that he puts the mixture full rich for the before takeoff checklist, then leans the mixture again after the checklist is complete. In either case, I don't see how this checklist is useful. If it's a read and do, there seems to be a big disconnect between when the item is read and when it is to be done. If it's a vital action, then the checklist shouldn't even be started until all the items on it are already thought to be done. What am I missing here?
I lean the mixture after engine start. I enrichen the mixture immediately before applying full power before takeoff. Other than that I adjust the mixture to suit what I’m trying to accomplish at the time with the engine, just as I do the throttle.

You’re the one who raised the topic of checklists in this thread, so I don’t know what you’re missing. The mixture control isn’t mentioned in either my or Cessna’s pre-takeoff checklist. Neither is using the foot pedals to steer the airplane, nor using the throttle and/or using the brakes to control the taxi speed, for that matter.
Just reread the thread and you're quite right, I assumed you were talking about forgetting something on a checklist, not forgetting something like foot pedals. Apologies for the thread drift.

As for leaning, Lycoming does have some guidance in support of leaning on the ground, but only for IO-360s in training operations:

https://www.lycoming.com/content/servic ... n-no-1497a

Despite the very limited scope of the SI, I find it good advice for all the aircraft I fly.
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Re: How far do you lean while on the ground before takeoff

Post by geneticistx » Fri Jul 06, 2018 7:13 am

interesting podcast i posted before https://www.npr.org/2017/10/30/55999627 ... checklist
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Re: How far do you lean while on the ground before takeoff

Post by FL007 » Fri Jul 06, 2018 7:25 am

I always preferred to have a cooler cylinder head temp on takeoff. The last thing I'd want to worry about on takeoff is an engine that is at its thermal limit (considering age of engine, students beating it up, etc.), and that thermal stress is even more pronounced at colder temperatures where shock cooling is a factor. To each their own though!
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Re: How far do you lean while on the ground before takeoff

Post by tbayav8er » Sun Jul 22, 2018 7:51 am

Good topic - I'm on the side where I think it's quite important to lean the whole time during taxi. As photofly posted, what if you're waiting in line for 20 mins for takeoff? After you get the takeoff clearance is not a fun time to realize the plugs are all fouled!

One cool thing I've seen on a plane I was flying for some time that had a 540 lycoming was that in the runup checklist, you had to go to full throttle and lean to a specific fuel flow depending on the pressure altitude on the ground.
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Re: How far do you lean while on the ground before takeoff

Post by Kaykay » Mon Jul 23, 2018 3:05 pm

I do the same as a lot of others said; lean during taxi and enrich prior to takeoff. As for forgetting, I think it's no different than the way I would do it in a light twin vs a 172. I was always taught with power application for takeoff, go right to left. So for takeoff in a light twin, I verify mixtures full fwd, props full fwd, and then apply throttle. I do the same if it's a 182 or 172 with only mixture and throttle. Then I never forget.
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Re: How far do you lean while on the ground before takeoff

Post by Cat Driver » Mon Jul 23, 2018 3:13 pm

After you get the takeoff clearance is not a fun time to realize the plugs are all fouled!
Well if the plugs fouled bad enough to cause a power loss you could always reject the take off.

I have been trying to remember if I ever had a situation where the plugs became fouled during ground operations and so far I can not remember it ever happening......not that it can not of course, it just never happened to me as far as I can recall.
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Re: How far do you lean while on the ground before takeoff

Post by photofly » Mon Jul 23, 2018 4:44 pm

That’ll be because you always leaned the mixture on the ground :)
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Re: How far do you lean while on the ground before takeoff

Post by Cat Driver » Mon Jul 23, 2018 5:25 pm

That’ll be because you always leaned the mixture on the ground :)
Like everything in aviation leaning the fuel mixture varies from airplane to airplane, some of the little four bangers tend to be more prone to plug fowling than others and of course the altitude at which you are operating is also a factor.

Operating out of a sea level airport is less problem mixture wise than say Leadville Colorado at ten thousand feet ASL.

When operating any aircraft the engine manufacturer will determine how and when to lean.

I have over ten thousand hours operating big radial piston engines and "" always "" started, taxied, took off and climbed with them in Auto Rich and plug fowling was never a problem.
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