Re: Ground leaning

Re: Re: Ground leaning

gentlemen,
I can safely say that since i started using this forum Ive NEVER seen close to 50 posts on a single subject.They eyes are blurred(and I dont drink) and some of these long posts seem to run together.
Ive trusted Mr.Horns judgement in the past,and even though we do disagree about a couple of things in principal,I value his opinion even though weve never met personally,I kinda wonder however why one would post so many replies finishing with his Business title................. New subject time.........my.03

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Re: Re: Ground leaning

Gregg,
I will have to stop in to see you on one of my visits to Tucson.
My sister lives just a few miles away in north Tucson. Nearly everytime I come out, I go to Ryan field to rent an aircraft for sightseeing. Since no one is going to let you loose with an airplane, I rent something besides a 182 so I can also get abit of experience in something different.
This has been a learning thread. I think we all gleaned some good advice from this one.
Have a good day.
Glenn

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Re: Re: Ground leaning

I have enjoyed this thread on many levels....

In fact, I started reading some technical material on IC engines.  I've never bothered to learn about engine design as I make my living in a different industry. (I'm a mechanical engineer with a master’s degree from Cal Tech.)  Nevertheless, I am still having trouble deciding who was right and could not decide. 

From what I learned to date, I think the best way to determine the answers to these questions, is to do testing, guided by fundamental principles, but realizing how inadequate the analytical tools are for the analyses of these processes.  It is very important to listen to personal and anecdotal experience from experienced pilots and mechanics.  I agree, however, that the empirical approach is essential.  (Data gathering by many corroborating investigators will come to the truth.) 

Further, I do not believe there is one correct answer to all the topics discussed here for all engines.  From what I learned of the combustion process from intake through exhaust, it consists of numerous phenomena that do not lend themselves very well to the analytical process.  Certainly a lot of "hand waving" and qualitative arguments are not going to be better.  There is just too much going on.  Too many variables, where F:A ratio is just one.  Engine load, engine cylinder geometry, RPM, timing, two versus one spark plug operation, intake design, carburetor/injector design, fuel design, fuel additives, octane rating, etc. I'm getting a headache...

As to the subject of the thread "Ground leaning" during idle and before run-up, I really don't see what's all the fuss.  I spend very little time, typically 5 - 10 minutes before doing a run-up prior to each flight.  If the plugs foul, which has occurred very infrequently, I find out during run-up and lean the mixture for maximum take-off performance and to correct the problem.  So subsequent to the run-up I have leaned the engine (I purposely used valid pilot jargon and not the equally valid technical jargon - less rich).  (But Walter, if I’m at idle do I ever do a peak RPM and then LOP setting? just kidding no answer needed.)  With the engine properly pilot “leaned” (or less rich) then this should prevent any further fouling and I'm ready to go.  There were however, many other very important topics discussed, in particular, regarding how and when to do mag checks and whether my engine cylinder temperature should be low or high before take-off. 

As to the last topic, at a gut level, I would want my cylinder temperatures as close to final operating temperature prior to take-off (full power operation).  In particular, I do not want them at a low temperature (meaning much less than final operating temperature.  A rapid thermal transient is the last thing I want during takeoff!  Again just on gut level reaction and no technical data to support this. 

Certainly, a very informative, passionate, and interesting thread.....well done and entertaining to boot

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Re: Re: Ground leaning

George, 

Since you refuse to blow your own "horn" I have decided to tell everyone about your wonderful web site.
 
http://www.globalair.com

Very good articles and discussions.

I enjoy and have learned a great deal from you and Walter.

Please continue to educate the aviation community.


Clay

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Re: Re: Ground leaning

Ha!  Well, it's not really my website, I merely write an informal article on a monthly basis there.  But I'm sure globalair.com appreciates your "plug"!

As for this message thread, having re-read the whole thing, I never would have imagined so many words would have been spent agreeing with each other.  For some reason it seems Walter ignores the fact that I do not disagree (in fact promote) the idea of leaning on the ground, and I do not disagree with LOP operations, providing proper instrumentation is available.  This long silly dialogue mostly stemmed from my attempt to bring to everyone's attention the fact that very low rpm operations (only on the idle metering circuit) will not gain any benefit from ground leaning and will likely harm the engine due to lack of splash lubrication.  Ground leaning, to be effective, must be done at rpms above the very minimums, where sufficient scavenging of the cylinders are more likely to take place anyway.

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Re: Re: Ground leaning

Barry:

Some good points in your note.

1)  Maybe I misunderstood you, but it is not a good idea to lean ANY on takeoff to clean fouled plugs. Do that BEFORE you apply full power, than go full rich before applying max power.  Some very bad things happen to a less than full rich mixture at full power.

2) If you aggressively ground lean, you will never experience this issue.

3) The way to test these hypothese is to use EGT.  It is independent of all other issues and is the only thing that matters.

4) According to the OEMs, any CHT above about 200dF is adequate to apply takeoff power.  (P&W and Wright all the way up to TCM and Lycoming.  Some engines (TCM) were actually designed to run at 240dF in cruise--using the same cylinders as on 470s, 520s and 550s. So, we can say with some assurance that you need not get them up to your normal operating temp before applying power.  Besides, the cooler (within reason) they are, the lower the takeoff and climb CHTs will be.  This is good.  Cooler CHTs are stronger (aluminum loses 50% of its strength at 400dF) and a cooler cylinder puts out more HP just when you need HP!

Things to think about...

Walter Atkinson

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Re: Re: Ground leaning

*Walter ignores the fact that I do not disagree (in fact promote) the idea of leaning on the ground,*

Somehow I did not garner that from the post.  Sorry if I misread your statement.

Here's the good news.  It was educational.  <gg>

This whole thing got out of hand and I appologize for my part in that, whatever that was.  RATZ.  It is frustrating.  It's one of the reasons I consider the keyboard to be a poor way of communicating.

Walter Atkinson

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Re: Re: Ground leaning

Walter,

I apologize if I was unclear.  I don't lean on takeoff to clean fouled plugs.  I enrichen the mixture ROP at ~ 2000 rpm on the ground to clear the plug so I can pass my run-up rpm mag drops. 

Maybe I misunderstood your post.  When I lean for max performance during takeoff, I go ROP on the runway before releasing the brakes.  This is a full throttle mixture adjustment. 

I understand that at full throttle in the carburated engines that some fuel may "cling" to the intake and not fully vaporize before reaching the cylinders. So the FA in some cylinders may be too lean if the mixture adjustment is made before full power and then full power is applied. So going from cruise to climb, enrichen the mixture slighty before applying full power to climb.

Regardless of the mechanism, if I adjust mixture for a full power setting ROP prior to takeoff, this I should have compensated for this anomoly. Is this wrong?

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Re: Re: Ground leaning

Hi all -

I'm leaning now after starting my O-470-S for warmup and taxi - and sometimes I forget to enrichen before the run-up.  No problem figuring it out - when I pull the Carb Heat (with the lean mixture) nothing much happens!  Without a rich mixture, the Carb Heat doesn't cause such an overrich mixture that the RPMs drop (per the checklist!)  Good warning to get that mixture in for takeoff!

I'd like to get LOP, but my engine pretty much quits as soon as I go over peak per the EGT.  I understand I ought to 1) pull the throttle a little, and 2) pull out the carb heat a little to get to LOP, right?

MiltonBill
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Re: Re: Ground leaning

If that's true, then how do you kill the engine with the mixture on the ground?

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Re: Re: Ground leaning

George Horn Wrote:
-------------------------------------------------------
> Allow me to quote from the Marvel-Schebler
> Carburetor Maintenance Manual for MA-3SPA
> carburetors (and this note applies to every other
> carb. they made):

<snip for length>

  All fuel delivery on idle, and also at
> steady propeller speeds up to approximately 1000
> R.P.M. is from the idle system. ....."
>
> In other words, the mixture control has no effect
> at such low R.P.M.s.

Sorry, I'm having a little trouble working this forum software.  I meant to respond to the post above. 

If the mixture has no effect at idle RPM, then why does the engine die when you pull the mixture all the way out?

Jim

BTW, I've started this aggressive leaning and it has really helped eliminate the fouling problems.  I'm definitely sold.

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