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

"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)

Found something in a Navajo Chieftan Information Manual which does actually
give a percentage to do with leaning. On a table entitled "Altitude Cruise
Speed, Fuel Consumption and Range" it says in a note down the bottom:-

* Power levels shown are for best power mixture; a 4.5% power loss results
when leaned to best economy mixture.

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)

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.

You're welcome :-)

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.

It depends on how the automatic wastegate is controlled and what are the
operating conditions. If you have an automotive-type control with an
spring controlled actuator operated by boost pressure, that should keep
the boost pressure (upstream throttle) fairly constant, as long as there
is enough turbine enthalpy. Once the boost pressure cannot be maintained
with fully closed wastegate, turbine enthalpy controls the boost. This
is exactly what's behind your observation mentioned below.

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.

Exactly the same behavior is demonstrated by turboed automotive engines
- a lack of torque below a certain engine speed. The "critical" speed,
above which the rated torque can be produced, rises significantly with
altitude, as more turbine energy is required to boost the lower ambient
pressure to the desired MP.

The physics behind this are quite interesting, it basically comes down
to a contradiction between the piston engine being a so called positive
displacement machine and the t/c being a continuous flow machine. The
positive displacement machine likes a constant pressure ratio over a
wide range of massflow, while the turbine pressure ratio (without
wastegate) must rise with massflow.

To the exhaust gas, the turbine is just a hole, through which it needs
to pass. High massflow creates a high pressure drop (and therefore high
power output!), low massflow creates low pressure ratio and low turbine
power. But it is even worse: As the higher or lower turbine power
increases or decreases boost, it increases or decreases the massflow and
therefore in turn the turbine power even more.

Anyway, thanks for posting more to think about.

regards,

Friedrich

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

"Ron Rosenfeld" wrote in message
...
I notice that on my turbo-normalized, manually waste-gated engine, too.

Stands to reason. After all, past the critical altitude, at full throttle,
my automatic wastegate turbocharger is basically a fixed (or manual)
wastegate turbo.

"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)