Lesson Learned: Magneto Check & Leaning

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
I've recently joined a flying club that has a nice C182P. This is my first airplane with the big motor and CS Prop. So I've engaged a CFI to teach me what I need to know to be safe and gain proficiency.

Yesterday was my first flight in the airplane as PIC (I had rides in it before). Plan was to have two sessions with a break for lunch. First session went great, no problems, and some good air work to gain familiarity with the plane and it's systems.

We landed at KGLE, took the cop car to lunch, returned, preflighted, started up, and began our taxi to the runway.

Per the instructor's guidance from the first start up, I leaned the mixture about 40% out and left it there as we taxied from the ramp to the runup area.

Got to the runup area, added power to 1700 RPM, and ran the checklist from memory. All good until I turn the key to Right Mag. The RPM dropped 600, but slowly.


Rut-roh.


Switched back to both, needle goes back to 1700, but same rate. Hmmm... Switched to Right again and the same result.. a slow drop to 1100RPM. Instructor says, "Try the left one". Also a slow drop to 1100RPM.


Just as I'm thinking, "Aww nutz... my first flight in this wonderful machine and something seriously broke", the instructor goes, "Oh, I see what's happening." and pushes the mixture to full rich. "Now try it," he says.

Click to Right mag, 150 RPM drop. Back to both, normal. Click to Left Mag, same 150 RPM drop.

Problem solved, and we're off continuing the lesson.


This was my first encounter of mag checking a leaned out engine and what the Tachometer indication would be.

This is shared since we have pilots hear of all sorts of experience levels, and many might not have yet encountered this. It will be something I definitely will remember from now on, especially emphasis on checklist usage!
 
next time lean it more. so much that you can't get up to run-up RPM without the engine coughing. that will remind you to richen it :) it will also prevent you from taking off with the mixture leaned out.
 
I once tried to taxi while leaned at 1000 rpm and the engine wheezed when I increased throttle....I learned the same lesson that day.
 
(thread drift)
I have a dual mag IO540 in an RV10. Instead of doing the usual powering up to say 50% power and switching mags, I take it to 1200 rpms and primarily watch the EGTs rise as I switch mags.

The idea is outlined here:
http://blog.savvymx.com/2010/03/mag-check.html

Of course I'm flying experimental so I write the POH. But it's an interesting approach that takes advantage of modern engine monitoring technology.

Back to the thread; seems that years ago when I wasn't always leaning out the engine for taxi, the mag check would cause a stumble because it seemed that the engine loaded up. I'd lean it, run at 1700+ rpms for a minute or less, then the mag check would complete successfully. Can't say I really ever understood what was happening then.
 
Leaning 40% does nothing at idle throttle settings. As pointed out, you need to be almost at the cut-off to get any real change in mixture at idle.
 
Lean it more. It should be lean enough that it coughs above 1000rpm.
 
My 182rg (lycoming 540) has always been very sensitive to being run rich on the ground. I lean it on the ground to the point it's pretty rough then smooth it. Even then when I do a mag check sometimes I need to clean the plugs off. It has been like that since I've owned it. In the air it also needs to be leaned quite a bit or it runs rough. Cleaning off the plugs is no big deal. I set power to the top of the green and lean until peak rpm drops then back to peak. Cleans them and doesn't damage anything. Not a big deal at all.
 
flyingron said:
Leaning 40% does nothing at idle throttle settings. As pointed out, you need to be almost at the cut-off to get any real change in mixture at idle.
Click to expand...

I have the same IO-540/RV-10 with dual mags like Bill Watson.

My fuel flow does decrease when leaning after start up.

I use aggressive leaning until runup then only richen slightly(663 msl), so that rpm drop is around 125-150. If I go full rich I will get about 200-225 rpm drop on each side. After runup I go full rich. I am flowing 25.7 gph on typical takeoff.

I have not tried your method Bill, but remember talking about it. I will read up on that. Thanks.
 
I need to remember to lean more aggressively on the ground - especially in my latest new-to-me rental. Thanks all, for the reminders.
 
Is there some science about NOT leaning non big-motored and CS-propped planes for ground ops?
 
Jaybird180 said:
I once tried to taxi while leaned at 1000 rpm and the engine wheezed when I increased throttle....I learned the same lesson that day.
Click to expand...

That's a good thing. On taxi, it should be leaned so it will run smoothly at taxi power but cough at higher power settings :)
 
dell30rb said:
That's a good thing. On taxi, it should be leaned so it will run smoothly at taxi power but cough at higher power settings :)
Click to expand...

Exactly the way I keep mine during taxi. About an inch or so pulled out which is equivalent to 35F LOP position at 12,500' for my IO-540.
 
dell30rb said:
That's a good thing. On taxi, it should be leaned so it will run smoothly at taxi power but cough at higher power settings :)
Click to expand...
That's how I was taught to do it since training in a 172. I have the T182T and if you lean it that way not only will it not make it to 1800 rpm on mag check it will never take off. Though and I hate to admit it, because I am sure I will be laughed at, I have forgotten once or twice when I started flying my T182T to push the mixture in full when in the pattern(despite the sticker of GUMPS stuck on top of the mixture, throttle, and prop knobs, and doing a GUMPS check(must have had a brain fart or something, though if I remember correctly the tower called me while I was doing my GUMPS check, and I stupidly did not start over)), and did a go around and the plane had absolutely no problem climbing, and did not realize it until I went to pull it out for my climb.

Doug
 
JoeSelch said:
Is there some science about NOT leaning non big-motored and CS-propped planes for ground ops?
Click to expand...

My AI/MEI says not to lean the 421 on the ground, I do it anyway or it's too rich on the mag check.:dunno:
 
The way I understand it, leaning at low power settings can't hurt anything on anything. Low power and lean mixture mean that you can't detonate, overheat or anything else that is potentially damaging.

You don't want to takeoff that way however. That's the case for aggressively leaning while on the ground.
 
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