aadamson

aadamson

Well Known Member
Walter,

Thanks for dropping by. I always enjoy reading about this topic.

I've seen, but can't lay my hands on, a pretty simply method for getting to LOP. Sorta a "close your eyes" method.... I think it's called the "big pull". Last time I read about it, it seemed most who tried it, could repeat their results quite nicely vs. the labor intensive way of watching the engine monitor like a hawk.

I'm sure you've described it a million times, so you must have some "boiler plate" somewhere that you can cut and paste and save your fingers.

For those of us, just getting used to the concepts. Maybe a quick primer is in order? If you feel so inclinded, perhaps, this is justification for a "new thread"?

Anyway, if my memory serves me, you set up from climb to cruise, let your airspeed build, then you "pull the red knob, until you feel a slowdown (using your most sensative instrument in the airplane, your butt ), and basically you are LOP"? Can't be that easy can it? I'll assume it means you have worked to get to a balanced F:A ratio prior?

Thanks in advance,
Click to expand...

Walter, thanks again for the comments, at your request, I've started this as a new thread.

Now refresh my memory, what they heck is "BMP"? Big Mixture Pull maybe?
 
"Pull Big"

It's on AvWeb.

http://avweb.com/news/reviews/182501-1.html

It's the method GAMI suggests for setting LOP. It's not good idea to slowly screw-out the mixture vernier through peak all the way down to LOP. This potentially leads to a significant amount of time spent "in the detonation red zone" (-20dF lean through -100dF rich of peak).

Given an fuel/air ballanced engine (which runs smoothly LOP) GAMI suggest "pushing vernier button" and in one smooth motion going right till the RPMs just start to drop. Then adjusting RPM with mixture (for the desired power) as you see fit. Using mixture to set power in this configuration is perfectly acceptable. They suggest writing down or memorizing your engine's typical peak EGT so you have them as references after the pull.

I've actually always done "the big pull method" for my 60% econo-cruiser regardless of fuel system. Detonation is not a concern bellow 70% power on any normally aspirated engine. For an unballanced engine, I pull till it gets rough, then back in till it's just smooth. Based on my carburated -3, running a fuel/air-imballanced engine; "in the rough zone" didn't add any efficiency, it used as much less fuel as it went slower. YMMV. On mine, it just added the shakes, and there's no reason to run an engine rough. But if I'm going 70+% to buck a headwind or just get there on someone elses gas, I use the standard published ROP method always.

-Bruce
 
The Big Mixture Pull (BMP)

First one must address any problems which could result in a rough running engine while LOP:

a) GAMI lean Test -- need balanced F:A ratios adequate to be smooth LOP.
b) No induction leaks -- many engines have induction leaks that are undected.
c) Ignition -- many ignition systems will operate fine ROP but the plugs are too weak to fire properly LOP. LOP mixtures require a higher voltage on the plug to jump the gap.

Once those issues have been addressed, then:

1) Level off
2) Do nothing for three or four minutes.
3) ACCLERATE
4) Pull the mixture to deceleration

You're done!

After a few minutes, you can find peak from the lean side and reset the mixture more precisely if you are as anal as I am! <g>

Walter
 
The leaning instructions for my Lycoming O-360 with carburetor, from the Lycoming manual, are very simple. This is for 75% power or less.

"(1) Slowly move mixture control from 'Full Rich' position toward lean position.

(2) Continue leaning until engine roughness is noted.

(3) Enrich until engine runs smoothly and power is regained."

Really simple, and since I have 4 cyclinder egt monitoring I know that this is lean of peak for some cylinders, rich of peak for others and likely at peak for one or more.

To be honest I go more by leaning just past roughness, than regaining all the power, but I find this method gives good economy and I have had no engine problems at close to 1,000 hours. I rarely fly below 6,000 feet and might lean a bit differently down low.

Sometimes I think we make things more complicated than they need to be. Maybe this thought comes from flying quite a bit in the days of no EGT at all, no CHT at all and no oil filters, etc.
 
I've got my engine tuned to the point that after I level off, I can pull the mixture back to a specific fuel flow and know that I'm at 50 dF LOP. Takes all the guess work out. Of course, this assumes my cruise settings for RPM and MAP.
 
Larry:

Yes, those instructions are the way they are because they expect the F:A ratio balance to be poor. If it is poor, that's the only choice you have. Sounds like that's your situation. That standard leaning recommendation covers up the fact that the engine is non-conforming.

If, OTOH, the F:A ratios are well balanced and the engine is a conforming engine, that recommendation is sub-optimal.

Note my three requirements in the original post. Those ensure that the engine is a conforming engine.

(a conforming engine is one that conforms to the engineering drawings and operational design criteria. Included in those criteria are balanced F:A ratios.)

Walter
 
The Big Pull Clear Now

I think Walter mentioned that method of leaning on his spot on "Wings To Adventure" and how easy it was and how it was nothing to worry about. I couldn't believe it and had to record the same show at a later date so I could replay it over. He didn't say anything about LOP and I thought it was just a general rule for good leaning and Engine/fuel management. Seems like I've been trying to follow these threads for weeks to try and learn something and the depth of the subject is about ready to make my head explode. I purposely bought a carbed 0-360 and a FP prop to keep it simple so I guess the discussion is finally getting to my level. With all the controversy on how to lean it gets kind of scary hoping that your doing the right thing.
God I love this Forum
NYTOM
6A TMX FP
N822PM (res)
 
A Little Knowledge Is A.... Complicated Thing.

n5lp said:
Sometimes I think we make things more complicated than they need to be. Maybe this thought comes from flying quite a bit in the days of no EGT at all, no CHT at all and no oil filters, etc.
Click to expand...

Went flying in my Vari-Eze (0-200A, carb) yesterday. This was my chain of thought: Cruising level, lean like I always have ? mixture out to roughness then in a bit to smooth it out. BUT this could put me in that scary area around peak EGT I have been reading about in the forum. I?ll just push the mixture in a bit. What if I was running LOP before, putting the mixture in a bit may have put me in the scary zone, so I?ll just pull the throttle back a bit to increase the detonation margin. Hang on! This is crazy. I am now flying slower and using more fuel than I have in the past. I?ll lean it again like I always have in the past and be done with it. Might watch the CHT gauge this time (usually don?t look at it much except to check that temps are within limits). Interesting, CHTs went up about 50 degrees, wonder if that?s normal. The CHTs went up all the way through leaning, no drop at the end so I am most likely near peak EGT ? BAD?? Could be the gauge (cheap Westac 4 probe, switchable). Maybe the gauge is inaccurate and my cylinders are hotter than the 360 degrees indicated. This plane really needs an engine monitor ? where would I put it on the panel. Hang on! This is crazy, they cost thousands of dollars and I have a 9A to get in the air. Woops, climbed 200 feet ? get back to flying the aircraft. (5 minutes later) - I wonder what those EGTs are doing??..

Fin,
9A (coincidentally installing the VM1000C engine monitor)
Australia
:confused:
 
The simple life....

Ya' Know....I don't even think my old trusty J-3 even HAD a mixture control in the cockpit....ahhh, for the simple days... :rolleyes:

(I'm sad becasue the airplane is in the paint shop, or I could go out and try some of these ideas!)

Paul
 
Hey, Fin. Thanks for the chuckle. To be sure you are okay, just pull that red knob all the way out!

Yeah, it can sound like witchcraft, but in practice, it's pretty easy. However, this is with some ifs and buts.

If the engine will run smoothly LOP. As many have said, not all will. Many which will not in factory form will if equipped with tuned injectors. Carbs? It's possible, but it takes some tweaking, and there are no guarantees you'll achieve it. Do all the testing at a power setting below 60 percent, and you can't hurt the engine with the mixture knob. Just saw that sucker back and forth and . . . well, maybe not.

Take it a piece at a time.

NYTOM: That piece on Wings To Adventure could/should have been clearer. I'll take the hit on that one. We were rushed to get those shows on the air, and I didn't have time to clear that one up.

We just finished shooting more instructional tips with Walter last weekend. They will be much easier to follow next season.
 
Wings To Adventure

[/Quote]
NYTOM: That piece on Wings To Adventure could/should have been clearer. I'll take the hit on that one. We were rushed to get those shows on the air, and I didn't have time to clear that one up.

We just finished shooting more instructional tips with Walter last weekend. They will be much easier to follow next season.[/QUOTE]

Thanks Tom
There's only one thing that I can find wrong with your show which I now Tivo so I don't miss anything and that is that it's only a half hour long. You've put together a nice balance of technical, historical and travel features that seems to make that half hour go by muck quicker. Looking forward to next season.
Tom
 
Please don't ask for a full hour. This half-hour show is darn near killing us!

When I have the video of the Harmon Rockets (Jim Thompson and Warren Rice) we shot in Sedona, I'll throw a clip on the web site. That should be in a week or so.

This morning I tossed a short clip of a Beech Staggerwing onto the web. It's like a stunning swimsuit model. You can't take your eyes off it.

http://www.wingstoadventure.com

Tom
 
"That Great Gig"

Just checked out your site. You are a very lucky man Mr. Tom Gresham.
I'm sure your work is appreciated and enjoyed by anyone who watches it.
I just wish it was available here in HD.
Tom
 
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