Message-ID: <3C2D86C1.FD8D1BD1@earthlink.net>
Date: Sat, 29 Dec 2001 04:02:57 -0500
From: Marcelo Pacheco <macpacheco@earthlink.net>
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To: lancair.list@olsusa.com
Subject: Re: lancair.list V1 #273
References: <20011229052556.AAA25865@pop3.olsusa.com>
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Reply-To: lancair.list@olsusa.com

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>     Gotta admit, though, there were times I wasn't quite sure what to do
> with that mix knob.  Say, you're at FL140, start down, hit bumps around 6K,
> and slow to something around spam can speed.  Flip over to rich now?  Or do
> you just chase the peak down, easing the mix in to keep the same LOP margin?
> It's one of the times that FADEC would be nice to handle such chores, but of
> course, TCM's FADEC will never, ever, set things up for lean of . . . .
> sigh.

I think the question is what power setting would you like ? If you want 65%
power, find out what fuel flow gives you 65% power at LOP. Use slightly less
than full power to improve turbulence on the air entering the carburator for
better fuel-air mixture, and set the mixture to obtain the fuel flow that gives
you the desired power setting. You should just confirm then that you are lean of
peak, by observing the behavior of the EGT when you enrich or lean. The fuel
flow should be low enough that you'll either be really lean of peak, or if
you're high enough where that fuel flow puts you rich of peak you're generating
too little power to cause any damage to the engine, but at that point I would
continue leaning for peak or slightly lean of peak, to get close to maximum
available power.

When lean of peak, the HP produced is directly proportional to the fuel flow,
and the multiplier is directly based on the compression ratio of the engine,
just look up avweb for John Deakin's articles on mixture control, he has the
constants there, so HP=GPH * constant, I just don't have the constant handy.

Marcelo Pacheco
PP-ASEL IFR

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