On Aug 19, 10:58 am, "Douglas Paterson"
wrote:
Maybe flying with an instructor who knows about this critical question
would help?

Indeed!! Even--or perhaps "especially"--some ground school on the subject,
and I have been actively pursuing (not finding) just that. Know where I can
find such a CFI?!?

Yes. Walk around the hangars, and find someone who owns an airplane,
flies it a lot, works on it himself (preferably a lot), has a day job
(preferably outside aviation), and teaches on the side. There are
some out there. For that matter, a CFI ticket isn't really
important. They're not very hard to get and don't assure much in the
way of knowledge or instructional ability. Just find an owner who
flies a plane in the same performance class as yours (a lot) and works
on it himself. Buy him lunch (or better yet, help with the
maintenance) and you will get all the ground school you need.

As for your specific situation, since your engine is instrumented with
CHT/EGT/fuel flow, I can give you a prescriptive system for
determining and applying the proper procedure, as well as the reasons
that underlie it. Here goes.

Aviation engines at takeoff are normally operated 200+ deg F ROP (rich
of peak). Contrary to popular belief, this is neither maximum power
(which occurs about 25-50 ROP) nor primarily for cooling (although
cooling can be a factor). The primary reason we do not lean for peak
power for takeoff is engine timing. The spark advance on aviation
engines these days is fixed some number of degrees (of crankshaft
rotation, not temperature) before (typically 15-25 degrees before) the
piston hits top dead center (TDC). Since it takes some time for the
flame front to propagate from the ignition point (spark plug) to the
piston surface, by the time the flame front hits the piston surface
and transfers the energy to the piston (yes, I am simplifying
tremendously here, but go with it) the piston is already well on the
way down, meaning past TDC. This is critically important -
transferring energy to the piston before that is terrible - it can put
excessive stresses on the crankshaft, rods, etc. It can damage the
engine, much like pre-ignition and detonation.

The time the flame front will take to travel through the combustible
gas is primarily a function of two things that are somewhat under your
control - charge density (meaning basically how much air is there) and
mixture. The denser the charge (meaning the denser the outside air
and the more open the throttle) the faster the flame front moves. The
closer the mixture is to stoichiometry (meaning just enough air to
burn all the fuel and no more) the faster the flame front moves. At
sea level on a standard day at full throttle, you can actually damage
the engine by leaning - because the flame front will arrive too
early. At a density altitude of 10,000 ft this is impossible unless
something is really wrong (for example, the bolts securing your
magnetos are loose and the magnetos have moved increasing the spark
advance - it is actually true that you set the spark advance on these
engines by loosening those bolts, moving the magneto by hand until the
points open the number of degrees before TDC you want, then securing
the bolts again).

Now I have neglected the cooling aspects somewhat here, but they are
important. You really don't want to weaken your cylinders by letting
them get above 400F. 380F is better. 350F is VERY conservative.
This is because the aluminum your jugs are made of does start to lose
tensile strength appreciably above these temperatures.

So having laid out the background, here's what you do. Pull into
position, hold the brakes, full power, lean until EGT's peak, then
enrich (for how much - see below), and take off. No need to do this
every time - pretty soon, you will know where peak EGT is for your
engine at a given density altitude, so you will just pull the mixture
back to that number. You will also soon learn the position of the
mixture control that is appropriate, so you will be able to do it
quickly. Do your initial practice at strips with plenty of room for
error. Once you get to where you can set what you need quickly, you
are ready for the challenging ones.

So how far rick of peak should you be?
Al less than 5000 DA, leave it alone. At 8000 ft DA, probably about
100-200F. That's because you can still hurt your engine by
overleaning. By the time you hit 10,000 DA maybe 50-100. Above that
25-50. Even peak EGT can't hurt above 10,000 DA or so, so as long as
you haven't leaned enough to lose power, anything you do at 10,000+ is
OK. Interpolate between the given points however you want to - the
error in the method of interpolation will be less than the error of
setting the mixture, which is why there is some room for error in the
numbers I give you.

Now this isn't going to be enough for long term cooling - but you're
not going to overheat your cylinders in two minutes by doing this -
and after that point, you should be solidly climbing, absolute best
performance won't be critical anymore, and you can monitor CHT's and
increase fuel flow and/or airspeed as needed.

Is that sufficiently scientific for your tastes?

Michael
CFI, ATP, A&P, PhD, and other good alphabet soup