Power setting table and best economy/best power...

On Sat, 15 Oct 2005 11:01:32 -0700, "Peter Duniho"
wrote:

"Ron Rosenfeld" wrote in message
.. .
Some comments regarding your assertions.

They aren't assertions. I'd prefer to call them suggestions.

OK

I am theorizing, at best, not being an expert in this field, nor having any solid
data one way or the other. But thank you for your contribution.

[...]
So to claim that there is "higher operating temperature" causing "some
additional engine wear" without noting that, other than in the immediate
exhaust area, the engine operating temperature is actually lower, and the
power pulse pressure waveform is less destructive, seems to me to be
overlooking essential data.

I cannot find the post I could swear I posted, in which I suggested that
detonation, rather than excessive temperatures, is the greater and more
genuine hazard. Maybe that post was in a different thread (leaning at
altitude?).

You are certainly in good company to claim that at leaner settings, the fuel
burns more evenly and more gradually, and that overall temperatures are
lower. I don't have an engine monitor, but those who do have told me that
peak EGT and peak CHT don't occur at the same mixture setting.

One would probably still want to be concerned about detonation however.
It's destructive no matter what the temperature.

Of course, some engines are unable to run at peak EGT or LOP EGT due to
imbalances in fuel or air flow. If an operator is not operating any
leaner
than, let us say, 25°F RICH of peak EGT, he may indeed cause increased
wear
and tear on his engine at those settings. I believe the original (1965)
manual for my Mooney recommended that setting for best economy. But I do
not believe that either of the current engine (or airframe) manufacturers
still make that recommendation.

Make which recommendation? To use 25°F rich of peak EGT for best economy?

Correct. The Lycoming engine manual recommends using peak EGT for best
economy for the IO360.

The Mooney Ovation2 manual recommends 50°LOP for best economy for a Cont
IO550G.


Are you saying that they no longer recommend a setting that might be
hazardous to the engine?

I won't go that far. See below.

Or that they no longer think that there might be a
hazard at some other setting?

No they're not writing anything like that.

Any best-economy setting at high enough power
settings seems to me likely to incur some additional wear-and-tear or actual
damage.

Compared to what?

If you are comparing it to a lower power setting, I'd agree there's
probably less wear and tear on an engine at a lower power setting than at a
higher power setting.

If you are comparing it to some other, richer, mixture setting, I'd say the
burden of proof is on you. Of course, we're considering conforming engines
in both instances.

According to George Braly, who routinely runs his turbo-normalized Bonanza
at 85% power and lean of peak EGT, almost all of the detonation that is
experienced by pilots is a result of either fuel quality issues; magneto
and harness cross-firing; or improper magneto timing. A very few are due
to pilots leaning inappropriately -- e.g. leaning in a high-altitude
takeoff in a turbocharged a/c (because that's how they did it with their
normally aspirated bird).

I would agree with you, however, that in an engine with significantly
mismatched fuel-air distribution; operated at high (75%+) power settings;
and no EGT gauge; that leaning to roughness and then enriching a bit may
have some cylinders in a dangerous area. Not so much because of
detonation, but rather because of the fact that some cylinders may be
around 30°-50°F ROP which is where CHT is highest, and stresses are higher.

Given the cost of fuel and the cost of engines (both high), it would seem
to me to be prudent to fix the engine, and install appropriate monitoring
equipment.

You might be interested in Deakin's article on Detonation
http://www.avweb.com/news/columns/182132-1.html

Parenthetically, I find it interesting, in light of all this data, that the
manual for the Mooney Ovation2 does state that Best Power is obtained at
50°F ROP EGT. The only logic I can think of is that this probably does
represent the Best Power setting; and was not published with regard to the
stresses on the engine! Perhaps since the engine is derated to 280hp peak,
the stresses at this setting are acceptable.

Best,
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)