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

"xerj" wrote in message
...
RPM with a constant speed should stay the same (or at least quickly revert
back to the same) shouldn't it?

Yes, the governor will ensure that the RPM remains constant (hence "constant
speed" ).

If so, then it's the MP that would vary as you pull the mixture back. Off
hand, do you remember by how much it varies in a typical type you fly when
you go from best power to best econ?

No, not specifically. To be sure, it doesn't vary by much. But a few
percent change in power (what I might expect with changes in mixture changes
alone, at the most) wouldn't require much of a change in MP. It might not
even be detectable with the typical 2 or 3 inch MP gauge found in most small
airplanes.

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.

Keep in mind the rest of my post as well. The reference you posted doesn't
provide the details, but it's entirely possible that the "best power"
setting and "best economy" settings DO provide essentially the same power
(within a percent or so), 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").

Pete

"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

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)

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

They aren't assertions. I'd prefer to call them suggestions. 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?
Are you saying that they no longer recommend a setting that might be
hazardous to the engine? Or that they no longer think that there might be a
hazard at some other setting?

It seems to me that absent fuel-flow matching, any setting in the
neighborhood of peak EGT (rich, lean, or exactly on) runs roughly the same
risk of engine damage (assuming there's a risk of engine damage at all).
Without having an all-cylinder monitor, one doesn't know what the other
cylinders are set to. Any best-economy setting at high enough power
settings seems to me likely to incur some additional wear-and-tear or actual
damage.

Pete

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)

Peter Duniho wrote:

"Peter Duniho" wrote in message
...

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.

On a turbocharged engine egt affects the enthalpy delivered to the
turbocharger turbine and in turn the power deliverd to the compressor.
This will result in a slight change in boost pressure and therefore MP
for a given throttle setting.

Whether this will be a big enough change to be noticed under typical
operating conditions of an airplane engine I don't know.

regards,
Friedrich

--
for personal email please remove 'entfernen' from my adress

"Friedrich Ostertag" wrote in message
...
On a turbocharged engine egt affects the enthalpy delivered to the
turbocharger turbine and in turn the power deliverd to the compressor.
This will result in a slight change in boost pressure and therefore MP for
a given throttle setting.

Whether this will be a big enough change to be noticed under typical
operating conditions of an airplane engine I don't know.

Thank you for trying to save me. However, I have to admit a couple of
things: I wasn't meaning to restrict my (erroneous) comments to turbocharged
engines; and your point, while an interesting take on the question, is
probably only valid for turbocharged engines with manual wastegates.

Of course, that second point requires qualification too: I have noticed in
my own airplane (turbocharged engine, with an automatic wastegate) that at
high altitudes, above the critical altitude for the turbo, RPM becomes the
primary power control. It's as if at lower RPM, there just isn't enough
energy in the exhaust to keep the turbo working effectively. Throttle at
full, then adjust RPM. Small adjustments to RPM can make significant (1" or
more) changes in MP.

The RPM thing isn't really what you were talking about, but it seems related
in context.

Anyway, thanks for posting more to think about.

Pete

On Wed, 19 Oct 2005 00:31:26 -0700, "Peter Duniho"
wrote:

"Friedrich Ostertag" wrote in message
...
On a turbocharged engine egt affects the enthalpy delivered to the
turbocharger turbine and in turn the power deliverd to the compressor.
This will result in a slight change in boost pressure and therefore MP for
a given throttle setting.

Whether this will be a big enough change to be noticed under typical
operating conditions of an airplane engine I don't know.

Thank you for trying to save me. However, I have to admit a couple of
things: I wasn't meaning to restrict my (erroneous) comments to turbocharged
engines; and your point, while an interesting take on the question, is
probably only valid for turbocharged engines with manual wastegates.

Of course, that second point requires qualification too: I have noticed in
my own airplane (turbocharged engine, with an automatic wastegate) that at
high altitudes, above the critical altitude for the turbo, RPM becomes the
primary power control. It's as if at lower RPM, there just isn't enough
energy in the exhaust to keep the turbo working effectively. Throttle at
full, then adjust RPM. Small adjustments to RPM can make significant (1" or
more) changes in MP.

The RPM thing isn't really what you were talking about, but it seems related
in context.

Anyway, thanks for posting more to think about.

Pete


I notice that on my turbo-normalized, manually waste-gated engine, too. As
a matter of fact, if I'm climbing into the low teens, and maintaining say
25/2500 during the climb, at my target altitude, decreasing RPM to 2400 RPM
will usually drop my MP by 2-3" or so.


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

"Ron Rosenfeld" wrote

I notice that on my turbo-normalized, manually waste-gated engine, too.
As
a matter of fact, if I'm climbing into the low teens, and maintaining say
25/2500 during the climb, at my target altitude, decreasing RPM to 2400
RPM
will usually drop my MP by 2-3" or so.

That would logically follow, since when you reduce RPM, you are putting less
volume through the turbocharger turbine, and that will slow it down, and
give less pressure to the intake manifold.
--
Jim in NC

On Wed, 19 Oct 2005 21:42:44 -0400, "Morgans"
wrote:


"Ron Rosenfeld" wrote

I notice that on my turbo-normalized, manually waste-gated engine, too.
As
a matter of fact, if I'm climbing into the low teens, and maintaining say
25/2500 during the climb, at my target altitude, decreasing RPM to 2400
RPM
will usually drop my MP by 2-3" or so.

That would logically follow, since when you reduce RPM, you are putting less
volume through the turbocharger turbine, and that will slow it down, and
give less pressure to the intake manifold.

Yes it does; and it confirms what Peter wrote about his observations at
critical altitude with his a/c.


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