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At 8500 and 9500 feet, you haven't gone wrong at all with anything.
However, if you were flying at 4500 and 5500 (maybe for some weather,
bad winds, etc), then you would have went way wrong with your mixture
setting IMHO, and your power would be important to be able to set that
properly.
At any altitude below about 7500 in a NA engine above 60% power, there
is a "danger zone" or "red zone" you want to keep your engine out of.
(On a turbo engine, this zone is a box, and stays the same width from
sea level all the way up, as you are normalized). This zone is a
triangle that gets smaller as you go up in altitude, and ranges from
250ROP-40LOP at sea level to 100ROP-10LOP at 5000, and it peaks to a
single point at about 7500. Stay out of that triangle and you are okay.
Get in it and you are probably still ok until your CHT's get real high
and you develop a hot spot and extreme detonation and pre-ignition
begin. If your below 60% power, I wouldn't worry about it...however, if
you are high power like most of us would like to run, it does matter.
I have a graph I can share that shows this in graphical form if anyone
is interested. You can easily generate it yourself; draw a graph with
Altitude on the x axis, from sea level to 15k. Draw Mixture (100LOP to
300ROP, with zero being the reference) on the y axis centered at 0, -100
as the minimum, 300 as the max. Put a point at sea level and -40
(40LOP) and another at sea level and +250 (250ROP). Draw a third point
at 7500 feet and +15 (15ROP). Now, connect the dots. Stay out of the
inside of that triangle, either on the ROP side or LOP side.
I stay on the ROP side of this for takeoff and climbout, reducing the
mixture every 2-3000 feet to the EGT (~1300) I was at shortly after I
took off (this keeps me out of the danger zone, but close to max power
throughout the climb). After leveling off (if I'm below 7500), I do a
big mixture pull to the LOP side, one quick motion, from about 22gph
(started at 27 on the ground, leaned a couple times on the way up) to
about 15.5gph (300hp IO-540). This sets me up at 15.5gph*15hp/gph=
about 232hp, or 77%, using the LOP calculation. This works out to be
about 25-40 LOP, and I lose about 2-3knots. At these settings, CHT's
hover around 330 all the time.
On decent, since I'm not hot at all (below 380), I can pull the prop
back to 2100rpm and the throttle back to 15-17" to come down like a
crowbar. Shock cooling is not an issue, as I'm not hot. I can also
lean the mixture a little more if I want to reduce power even more, or
can even enrichen it a bit if shock cooling is a concern. You can
enrichen it to about 50ROP and generate the highest CHT's possible for
the decent to keep things slowly cooling if you prefer. I personally
never enrichen the mixture, just leave it alone....all the way until on
the ground, and then still leave it alone for ground leaning until ready
to pull to cut-off, as 330 isn't hot.
I'm sure this will open a can of worms of disagreement, but I'm
convinced this is the way to run the engine, and will defend it :)
---
Shannon Knoepflein <---> kycshann@kyol.net
You wrote>>>>
This is after one martini and into my second glass of wine, but why do I
need to calculate my power? I'm going somewhere, I climb to 8500 ft.
westbound and 9500 ft. eastbound and I'm at full throttle, 2350 RPM,
leaned
to about 50 deg. rich of peak in my IO-320,
<snip>
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