What??? The A/F ratios shouldnt change as a function of altitude. If the
"magic numbers" are 12.6, 14.7, and 15.7 those numbers should hold
regardless of altitude. What changes as a function of altitude is the

air

density. Go to Big Bear where the air density is lower than sea level

and

you need less fuel to obtain  the 12.6 A/F ratio for best power.

Mike Wills

You are right Mike. Of course. Brain fade. What I was thinking of
was the mixture *** KNOB *** needs to be changed. Yes of course the

mixture

will not change. That comes from flying an antique carb  C182 too much

where

the knob position and mixture are synonymous in our minds. No such thing

as

an O2 sensor in a C182 although it would be good idea. Stupid of me not
to remember that. Must be getting old.

Thanks for catching that.

But hold on!  It gets even trickier.  The O2 sensor curves are for sea
level.  These sensors work by comparing oxygen concentration (ie,  moles per
liter of gas) between ambient air and the exhaust gases.  The the same
mixture will read lower (leaner) at altitude than at sea level.  This is why
some cars have a baro sensor in addition to the O2 sensor.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

 
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