On Fri, 25 Jun 2004 11:44:30 -0500, Greg Copeland
wrote:

Well, keep in mind that it was the first article of his that I read. It
presumed that I had already been introduced to the LOP concept. I had
not. In fact, for some engines that I used (r/c nitro and car engines),
too lean is a great way to completely destroy an engine.

But Greg, you just described a situation worlds apart from what Deakin
advocates. Running a race engine, any race engine, at full power and
too lean is not anywhere near the LOP description for aviation
engines. Yup, running an engine like that probably would blow it up.

Deakin is talking about cruising, with the engine producing no more
than 60% power. At 60% power virtually all experts agree that there
is no way to hurt the engine no matter where you decide to set the
mixture. Full rich, lean to the point where it's stumbling, it won't
matter, the engine can't hurt itself while making only 60% power.

For takeoff, his recommendation is to use FULL RICH. Not only full
rich, he recommends those who are flying behind the large 6 bangers
check out the mixture setup to make sure that it is reaching the
proper full fuel pressure. If it's set a little too low, something
below the specified maximum pressure, *THAT* situation is worrisome
and could cause engine problems. That's because the engine needs to
have the full rich mixture at takeoff power to stay cool. Having the
mixture on the rich side of ideal slows the burning down enough to
keep the Peak Pressure Point at around 16 degrees past top dead
center.

If the mixture isn't rich enough to achieve this, in other words if
it's a bit leaner, it may burn fast enough to cause the PPP to occur
with the piston closer to top dead center. The closer to top dead
center the PPP occurs, the higher the pressures and the more heat
produced, and THAT is why running rich keeps the engine cool.

This only happens, of course, because aircraft engines are stuck using
fixed timing. If they had automatically adjusted variable timing, the
mixture could be set for best power and left there (saving gas) with
no need to worry about whether the engine will overheat or not because
the timing would adjust to the proper 16 degrees ATDC regardless the
conditions or power setting.

And you thought "cooling the engine with fuel" literally meant that
the rich mixture hosed down the cylinder? Big smile

Corky Scott