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Date: Thu, 17 Dec 1998 23:35:51 -0600
From: Snowbird <snbird@ibm.net>
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Subject: Re: Lean mixture during run-up
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Hilton Goldstein wrote:

> Jim Sokoloff wrote:

> >"Hilton Goldstein" writes:
> >> In addition, this leaning keeps the plugs 'unfouled'.  

For what it's worth, I note that ground leaning is NOT recommended
in the POH, is NOT recommended by the Lycoming Service Instruction
on leaning (to be found at http://www.prime-mover.org), and it is
suggested by John Schwaner of the Sacramento Skyranch
(http://www.sierra.net/~skyranch) that the idle mixture
adjustment on the carb be appropriately set to avoid plug fouling
without ground leaning.  Because there is a separate idle fuel
flow channel, the idle mixture screw on the carb has much more
effect upon fuel flow at low power (500-800 rpm) than does the
mixture.  

Hilton and I have had this discussion before, so I mention this 
solely for the benefit of anyone who missed that earlier discussion, 
and who would like to look into the subject themselves rather than
blindly concurring that failure to ground lean is an indication of 
poor pilot technique, tendency toward sarcoptic mange, and bound to foul
the plugs (at the same DA, the latter depends upon what engine it is,
what spark plugs are being used, what fuel is being used, how the idle
mixture is adjusted, and the rpms at which ground ops are conducted)

[zap your "don't set up for the go-around" suggestions]
> For what it's worth, I disagree with you 100%, and I bet you'll find >that  almost all POHs and training does too. 

If we're voting, I'll point out that a pilot should be ready to
do a full power climb *at any time* and therefore should work to
develop the automatic reflex of saying "mixture rich" while
pushing on the mixture knob, before pushing on the throttle,
*whether or not the mixture has already been enrichened for a
 possible go around* on final.  It's a double check in that case,
and I think a worthwhile one.

> A go-around should require no hesitation, none, zip, zilch.  
> Stay ahead of the aircraft, not behind it.  

Um, I don't think touching the mixture (to confirm that it's in)
or pushing it in requires any hesitation.  I know I have four
fingers and a thumb on my right hand, and am quite capable of
pushing in carb heat, throttle, and mixture near simultaneously.

So personally I set the mixture full rich on final, but I don't
think there's all that big a difference between someone who always
checks that it's full rich before pushing in the throttle, and
someone who always sets it full rich before pushing in the throttle.

> And I don't think neighbors could tell the difference between 
> high RPM and fractionally short of that when you're making an 
> approach at very low power.

I think this depends upon the specific engine and prop in question.

Snowbird


