On Sat, 15 Oct 2005 00:23:34 -0700, "Peter Duniho"
wrote:

"Peter Duniho" wrote in message
...
[...]
Once the mixture is "in the ballpark" on my airplane, whatever change
occurs in MP isn't enough to prompt me to readjust the throttle, I can
tell you that much.

Upon re-reading my own post, I'm not convinced the MP would change at all in
this situation. MP is simply a measurement of the air pressure in the
intake manifold. It *ought* to be, as far as I know, strictly a function of
engine RPM and throttle position. I wouldn't expect fuel flow to affect it
at all.

So I think that part was in error. It's not that the change is too small to
notice. It's that it just doesn't exist (not counting some completely
inconsequential effects that alter the pressure due to temperature and
density changes as a result of the fuel).

However, I still don't see anything inconsistent with the table you posted.
It may very well be that the only difference between the "best power" and
"best economy" power settings is fuel flow and engine temperature. I
certainly don't see anything in the table to suggest otherwise.

Pete


Peter,

Some comments regarding your assertions.

It may very well be that the only difference between the "best power" and
"best economy" power settings is fuel flow and engine temperature.

In the Lycoming O-360 engine operators manual, there is a chart that
indicates an 8% drop in BHP going from best power to best economy settings.

There seems to be approximately a 5% drop looking at power tables for a
Continental IO550 in Mooney Ovation2 which has separate tables for best
economy vs best power.

---------------------------
(from a different post)

... but that the "best economy" setting incurs some additional engine wear
and tear, due to higher operating temperaturs (note that the "best economy" setting is "Peak EGT").

I think that it is extremely arguable on several grounds.

Lycoming data shows that as a percentage, CHT's drop considerably more than
EGT's rise. Also, even at peak EGT, in a normally aspirated engine, one is
well below the "red line" for exhaust components whereas even under normal
operating conditions, say 425°F CHT, one is still stressing the cylinders.

Furthermore, data from both Continental and GAMI show that at best economy
and especially LOP settings, the cylinder head pressure pulse waveform is
more gradual and, although more sustained, has a lower peak pressure
(GAMI). Continental charts indicate just that the interior cylinder
pressures are lower.

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.

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.




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