Mixture--science vs witchcraft?

Douglas Paterson wrote:
: "BillJ" wrote in message
: ...

: 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?!? Every instructor I've approached on the subject has one
: of two answers: "if the POH says full rich, put it there," or "lean it, oh,
: about *that* much...." ARGHH!!

: Speaking as a big-iron guy w/ military procedures drilled deeply into his
: skull from day one, I find the lack of information on this disturbing....

As a avid "Deakin-reader" and a cheap-******* pilot/owner, I can try to paraphrase as follows:

- It's impossible to hurt the engine at or below approx 70% power no matter what you do with the mixture, PROVIDED you keep
the CHT below 350-380 as measured at the bayonette lugs.
- For normally-aspirated engines, it's impossible to exceed 75% power below about 6000-8000' DA.
- EGT will remain roughly the same for a given fuel/air ratio.... SO
.... find out what your full-rich EGT is at a sea-level takeoff and lean to that as DA increases.... whether it's at a high DA
takeoff or as you do a long climbout. It's generally about 200-250 rich of peak.

e.g.... On my plane, I see about 1400 EGT on a sea-level, standard-day full-rich takeoff. During a long climb I'll lean to
the same EGT as I climb. On a hot summer day (2100' MSL field, 4500' DA takeoff) I'll see 1300 full rich and doesn't make
full power. Leaning to the 1400 before takeoff I get full power, and still have good cooling.

In cruise below 70%, I'll lean until it wheezes so long as CHT stays below 375.

-Cory


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* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
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