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Date: Tue, 22 Dec 1998 09:20:32 -0600
From: Snowbird <snbird@ibm.net>
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Subject: Re: Lean mixture during run-up
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Rod Farlee wrote:
 
> just as a footnote (as I'm sure you're aware but others might not be),
> - a small change in mixture results in a large change in EGT and
> spark plug tip temperatures.

Rod: is this true at idle rpms?

If so, I can't see the results on my EGT gauge.  Now granted, it isn't
the world's best gauge.

> - the formation of spark plug lead deposits won't occur if the tip
> temperatures are above about 900 F.

Right, but does not the point at which this temperature is achieved
depend upon a number of things, including what kind of plugs are
being used?

And as a point of curiousity: did you ever compare the effects of
ground leaning vs. leaning during run-up, and doing a pre-shutdown
run-up every time?

> So to students, I suggest that if their FBO or instructor recommends
> leaning during taxi and runup, it is based on experience with that 
> engine and worth listening to if you wish to avoid being stuck 
> somewhere on a long XC because the engine is missing during runup.

This is inarguable.  Anyone renting a plane ought to fly it as the
owners/mechanics maintaining it want it to be flown.

But if the FBO and instructor do NOT recommend ground leaning, I
personally wouldn't say that the student or pilot is following
bad technique or procedure if they don't ground lean.  I would say,
perhaps they have made adjustments so that this isn't necessary.

Snowbird


