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Quite a number of our aircraft engines are designed (that is, via the
carburetor
or injection system) to substantially enrich the mixture in the last several
percent of throttle advancement to provide additional fuel flow for cooling
during full throttle operation. Pull the power back on take-off to below the
point where this enrichment takes effect and you are increasing the thermal
stress on combustion chamber components like piston crowns, exhaust valves
and cylinder heads. In many of the high power engines we use in our
Lancairs, the detonation margins, even with leaded fuel, is probably quite
small and the enrichment feature at take-off power helps keep that under
control.

That all said, everyone should use the power setting methods they are
comfortable with. I for one, however, will try to use aircraft engines I fly
behind in the manner for which they were designed.

Concerning full-power run-ups, anyone who can accomplish that must have an
anchor out! Even with my little O-235, with the brakes locked, my airplane
will start sliding forward at around 2200 - 2300 RPM. Next time at Redmond,
I'd like to see that demonstrated!

Dan Schaefer


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