leaning while on the ground

[Fysiojohn]

Hi everyone,

I have been getting conflicting messages regarding aggressively leaning the mixture while taxiing, or being on the ground in general. My 1968 M20C Ranger POH clearly states to to keep it at full rich and propellor RPM high during taxiing to prevent overheating. Prevent running the engine at low RPM to prevent fouling of the plugs. My mechanic who has been taking care of my Mooney since 2017, says to not lean on the ground and so far reports that my plugs are very clean and are checked every 50 hours.

Seemingly everywhere on this forum, most indicate that they all aggressively lean on the ground, what seems to be the consensus on either method and why?

 

Thanks,

John

[rbridges]

I lean mine back to the point of it starting to stumble then add a little richness.  You'll foul plugs if you go full rich on the ground much.  I have an engine monitor for all four cylinders, and the temps look great when leaned.

As far as prop RPM, I keep it around 1000-1100.  I read this somewhere for keeping engine internals lubricated.

[Marauder]

Hi everyone,
I have been getting conflicting messages regarding aggressively leaning the mixture while taxiing, or being on the ground in general. My 1968 M20C Ranger POH clearly states to to keep it at full rich and propellor RPM high during taxiing to prevent overheating. Prevent running the engine at low RPM to prevent fouling of the plugs. My mechanic who has been taking care of my Mooney since 2017, says to not lean on the ground and so far reports that my plugs are very clean and are checked every 50 hours.
Seemingly everywhere on this forum, most indicate that they all aggressively lean on the ground, what seems to be the consensus on either method and why?
 
Thanks,
John

John - I’m an aggressive leaner and still end up with lead in my plugs. The theory is that aggressive leaning keeps the excess fuel level low and the cylinder is burning hotter to burn off excess lead.

Think about what you do when you have a fouled plug. You increase the engine speed and aggressively lean it. Also, with lower power settings, like idling, there is little probability of creating an issue.

Here is what an aggressively leaned plug still could look like.




Sent from my iPad using Tapatalk Pro

[RLCarter]

26 minutes ago, Fysiojohn said:

Hi everyone,

I have been getting conflicting messages..... My 1968 M20C Ranger POH clearly states to to keep it at full rich.....what seems to be the consensus on either method and why?

If it ain’t broke don’t fix it.....

[N201MKTurbo]

Taxiing lean is not a problem, just don’t forget to push it in before you take off, that will do some damage.

[Hank]

Wow, @Marauder! I've never seen a plug that bad before!!

@Fysiojohn, my 1970 C Owners Manual says the same thing. Used to find a couple of small lead balls in a plug or two at annual, then I figured out how to properly lean on the ground and viola! No lead balls at all the last ten years or so. I set 1000 RPM and lean way back [about 2/3 of the travel on my quadrant], the engine hums along happily and temps stay in the green.

I've scared myself twice doing this:  (1) parked in the grass, cranked up, leaned, then tried to taxi onto the pavement and the engine tried to die. Gave her some mixture, pulled onto the pavement and leaned again, no problem; (2) left the [flat] ramp to taxi a few thousand feet for downhill takeoff. The first thousand feet or so was flat, then it bent upwards at 3-4º and the engine began choking down. Pushed the red lever forward until engine smoothed out and continued to taxi without issues. [Yes, the first couple of downhill landings there were interesting, since I trained for a 3º descent on final . . . . ].

In the end, it's your airplane and your maintenance bill, so do what you want. You have read all of our advice, but it is still your decision every time you get in the plane. No need to apologize either way.

Have fun, and fly safe!

[tmo]

Isn't that why we lean to the point where "pushing it in" will result in the engine stopping right there and then?  IOW, if you lean, lean it as far as it will go, at 1000rpm you're not making any power to speak of anyway.

I lean on the ground, even without an engine monitor.  I've at times had the engine stop before it made enough power to get me rolling through the grass.

[N201MKTurbo]

31 minutes ago, Marauder said:

 

John - I’m an aggressive leaner and still end up with lead in my plugs. The theory is that aggressive leaning keeps the excess fuel level low and the cylinder is burning hotter to burn off excess lead.

Think about what you do when you have a fouled plug. You increase the engine speed and aggressively lean it. Also, with lower power settings, like idling, there is little probability of creating an issue.

Here is what an aggressively leaned plug still could look like.




Sent from my iPad using Tapatalk Pro

 

Here is my theory about those deposits.

While running ROP lead condenses as small drops just like steam condensing on a pot lid. When you switch to LOP it causes the the outer layer to oxidize into lead oxide which has a much higher melting point and won’t melt at combustion temperatures. They condense in the plug because it is the coolest place in the combustion chamber. 

If you look at those globs while cleaning your plugs you will see this structure. Blue metallic substance covered by a beige shell.

If you run only ROP the oxide shell is not formed and the lead evaporates and goes out the exhaust.

  

[cferr59]

The instructions in the POH are straight out of the Lycoming Operators manual.   And the 100/130 fuel that the O-360 used to run on has an even higher lead content that 100LL.   

I lean on the ground, but that isn't what Lycoming says to do.   You won't hurt the engine by leaning on the ground because the power setting is so low.  I also question how much it really would prevent overheating, but maybe on a hot day...

[steingar]

Always lean on taxi both before and after. Pushing it back in is in my pre-takeoff checklist.  Nothing worse than trying to get going and having a fouled plug.

[mooneyflyer]

1 hour ago, N201MKTurbo said:

Taxiing lean is not a problem, just don’t forget to push it in before you take off, that will do some damage.

If you lean on taxi til it runs rough, then richen a tad, then if you forget to richen the mixture, your engine will stall when you add takeoff power.  It's impossible to do any damage that way.

[DXB]

1 hour ago, Fysiojohn said:

Hi everyone,

I have been getting conflicting messages regarding aggressively leaning the mixture while taxiing, or being on the ground in general. My 1968 M20C Ranger POH clearly states to to keep it at full rich and propellor RPM high during taxiing to prevent overheating. Prevent running the engine at low RPM to prevent fouling of the plugs. My mechanic who has been taking care of my Mooney since 2017, says to not lean on the ground and so far reports that my plugs are very clean and are checked every 50 hours.

Seemingly everywhere on this forum, most indicate that they all aggressively lean on the ground, what seems to be the consensus on either method and why?

 

Thanks,

John

Fellow '68 C owner here.  Both the POH and your mechanic are wrong. Your idle mixture setting , which adjusts flow through a separate jet past the throttle plate in your carb, may be adjusted too lean if you are getting away with it. That overly lean idle mixture could make it quit on you one day at an inopportune moment when you pull the throttle all the way closed.  Lean aggressively on the ground to prevent deposits on your plugs and your valve seats. The latter may cost you a lot in cylinder work from burning exhaust valves, though cylinder longevity like this may not be a major concern of Lycoming.  The POH recommends a fairly high idle rpm (1200) to prevent fouling, but that approach is still problematic in my experience when full rich, and will also make your CHTs on the ground hard to manage in the summer if you require ground runs of significant length.  Instead set the idle mixture correctly, lean aggressively on the ground after startup, and idle at a slower speed to help manage temps on the ground.  

Come to think of it, there are three different carbs found on these planes - a lean one, a richer one, and the lean one that's been modified to the rich version.  Having the lean one might explain your running full rich at idle with relative impunity but make CHT control at WOT on takeoff more difficult.  

[ArtVandelay]

The instructions in the POH are straight out of the Lycoming Operators manual.   And the 100/130 fuel that the O-360 used to run on has an even higher lead content that 100LL.   
I lean on the ground, but that isn't what Lycoming says to do.   You won't hurt the engine by leaning on the ground because the power setting is so low.  I also question how much it really would prevent overheating, but maybe on a hot day...

Lycoming changed their outdated Op manual, IIRC they issued a SB that stated to lean on the ground after complaints from Emery Riddle that the new engines in the new 172s were fouling.


Tom

[cferr59]

I don't think they changed the manuals.  I found the same ground operation instructions on page 3-3 of this document.

https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO %26 TIO-360 Oper Manual 60297-12.pdf

I also found the SI that I believe you are referring to which describes a more sensible technique.

https://www.lycoming.com/sites/default/files/Engine Procedures for Flight Training Operations.pdf

Regardless, I agree that it is silly to taxi full rich and I lean aggressively on the ground.   I agree with some of the posts above that it is good practice to lean to the point where you cannot advance the throttle without the engine stumbling.  That way you cannot accidentally take off with the mixture too lean.

[HIghpockets]

Agree with aggressive leaning on the ground and idle 1100-1200RPM.

[Two7Victor]

From Bob Kromer-

"After engine start, I leaned the mixture out aggressively for smooth and clean engine operation on the ground. You should do this with any Mooney. Most engines are set up too rich at or near idle. Aggressive leaning will make the engine run smoother and will keep the spark plugs much cleaner. Most spark plug fouling occurs during ground operations with a too rich mixture. You can remedy this by simply leaning the mixture after engine start for all ground operations. We always wanted to put this procedure in the POH while I was flying engineering flight test at the factory, but we were concerned that too many pilots would forget to enrichen the mixture before rolling onto the runway for takeoff. But do it anyway - your engine will run much smoother and cleaner on the ground. Just don’t forget to enrichen prior to takeoff."

[PT20J]

https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html

https://www.avweb.com/ownership/leaning-on-the-ground/

[DXB]

47 minutes ago, PT20J said:

https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html

Wow this guidance is contrary to much advice I’ve received: to run at very low rpm for several seconds on initial startup, particularly at cold temps, to limit damage while oil distributes.    The downside per this article would be poor ring sealing, so more toxic corrosive blowby in the oil, and poor lead scavenging causing more deposits due to the slow warmup.  I will say that I have to taxi at the absolute minimum rpm possible at busy fields in the summer to limit CHTs on takeoff, and I am very hesitant to stop doing that. Otherwise  I’m really not sure now what the best approach is 

[Fysiojohn]

Cheers all, always good to have more food for thought!

[carusoam]

Congrats on your first post, John!

This summary is for you... Cheers!!!

Cool things to know/remember....

1) The POH is a great resource... the more recent, the better...

2) The arrow documents still require the POH to match the plane... so get a copy of the most recent one to have the best numbers... and most information...

3) The shell document and the AvWeb article Skip shared... is a gem for the temps that lead oxide, with the lead scavenger, becomes lead  bromide at... this is the CHT range to avoid... quite possible when it is winter on the East coast...   unfortunately, it says 200-250°C... which is 392°F+.... which is higher then the target best temp for CHTs to be kept below about 380°F... (a strength of materials that is best for the health of the cylinders... (this might explain why @Marauderlower plugs look like a sand box... he has tremendous data and control skills... getting the sandbox above 392°F may be good for a while...)

4) +1 on anything Bob Kromer says or writes... he was a test pilot at Mooney, an engineer too... speaks incredibly well, and writes too... find his writing in the MAPA archives on how to fly an M20C... the paper is 20 years old... I bought my M0C after reading that article...

5) Kromer can often be found at Mooney Summit... he gave a presentation on T/O and climb out... last I remember... VX, vs. Vy... when to use what, for how long...

6) The original POHs are imperfect like a path... you need to know when to stay on the path.... and when it is OK to leave the path...

7) Get to know your mechanic... some will give you some advice on engine operation that is good... but you are probably looking for better...

8) If you have an engine monitor... you can know more about your engine operation in real time,  than your mechanic can know when he sees the plane at annual...  optimum would be bringing your mechanic along with you... or flying with him... plane ownership is a  team sport... pilot, mechanic, CFI...

9) Leaning on the ground is good... lean excessively...

10) why excessively... so you notice that you didn’t follow the procedure when the engine stumbles before getting to full power...

11) Being too gentle has a cost... “i don’t want to lean excessively... it might be dangerous...” so you lean partially... and, due to distraction... you depart unknowingly, with the mixture halfway out... the EGTs skyrocket, the CHTs skyrocket, and you are now at risk of pre-ignition... 

12) so... understand why you are doing what you are doing... know where the limits are before proceeding...

13) leaning on the ground is important to avoid fouled plugs... plug fouling is caused by all kinds of things from half burnt carbon bits to lead ball deposits...

14) 1000 rpm is a typical slinging speed for oil and engine parts... many bits inside the engine get oiled by the oil splashing around inside the engine... too slow... no splash...too fast oil may not be flowing enough until it warms up... 1krpm is a compromise of the two...

15) Build and share your check lists...Use multiple resources... the old POH, a new POH, MS has a few...  purchased check lists are. Missing some details as time moves on...

16) this is about you and your machine, not about your mechanic and old books... 

17) Too soon to discuss engine pre-heaters?

 

PP summarizing what I read in this thread, not a mechanic...

Best regards,

-a-

[jakearey]

13 hours ago, carusoam said:

 

4) +1 on anything Bob Kromer says or writes... he was a test pilot at Mooney, an engineer too... speaks incredibly well, and writes too... find his writing in the MAPA archives on how to fly an M20C... the paper is 20 years old... I bought my M0C after reading that article...

5) Kromer can often be found at Mooney Summit... he gave a presentation on T/O and climb out... last I remember... VX, vs. Vy... when to use what, for how long...

 

great post, A!  Any idea where to find the article about flying the C that you referenced? I googled but only found the article about engine power in the climb.  Is that the article you are referring to? 
 

- JA 

[skydvrboy]

2 minutes ago, jakearey said:

Any idea where to find the article about flying the C that you referenced?

I think this is the post he is referring to http://www.mooneypilots.com/mapalog/M20C Evaluation/M20C_Evaluation_Report.html

Anthony, please correct me if I'm wrong.

[Browncbr1]

Lean to max rpm, then set throttle for 1000-1200 rpm.  You might hear some missing if on the ground longer than about 10 minutes.   A starvation miss sounds different from a fouled plug miss.   Starvation miss is ok, just add a little more fuel to the mixture.   If you’re still fouling plugs, you need to lean the idle mixture screw.    You’re leaning correctly if you try to add throttle and the engine starts to stumble or isn’t making more power.   Some people on here actually control their taxi power with mixture alone.   

[Fysiojohn]

A,

thanks so much for the summary and will take your advice to heart. 

John

[carusoam]

John,

Ask a lot of questions...

There are many MSers with real answers around here...

Best regards,

-a-