Mixture--science vs witchcraft?

250 HP needs about 20-22 gph for takeoff. After takeoff and throughout
the climb set mixture to achieve 1250-1300 EGT, any altitude. For
landing leave the mixture where it was for cruise. If you need to do a
go around then make sure to advance the mixture a little as you ease the
power in.



Douglas Paterson wrote:
Still getting to know my new baby (1990 TB-20, normally aspirated 250hp
Lycoming IO-540). I imagine my question here must apply to most non-turbo,
non-FADEC pistons (though I gather there's some sort of altitude compensator
on some airplanes' engines?). I live in Colorado, which means routine
high-elevation airport ops.

I'm looking for guidance on proper mixture setting for takeoff & landing at
high-elevation (with correspondingly high DA) fields. What's the best way
to achieve maximum power in these conditions?

The "book" answer, per the POH, of full rich for takeoff and landing is
clearly wrong--indeed, I stalled the engine on my first landing roll-out
back here (I was lean of full rich, but, obviously, not enough!). I'm
looking for some "science" to put behind this, instead of "mmm, about
*there*".... I've been tweaking the mixture for highest rpm during the
run-up (2,000 rpm), then looking for a couple of gph above the book's climb
fuel flow for the existing DA on takeoff roll. That seems to work OK for
takeoff, but, of course, I'm somewhat back to guessing for landing
(especially at a different field or if the DA has significantly changed).
Any suggestions or comments?

FYI, the field I'm basing from is 7,030' elevation, with 9 - 10K' DAs
typical; and we've been to Leadville (LXV)--elevation 9,927', North
America's highest municipal airport & highest paved runway, DA of 11,700'
when we visited. This is far more than just an academic discussion for me!!