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

[xerj]

When a power setting table shows a "best economy" and "best power" setting
for a given power level (say 75%) using a given MP and RPM this is just a
starting point, right?

Once the MP and RPM has been set and the leaning done, the actual power
settings would be more like 78% for best power, and 73% for best economy,
wouldn't they? (%'s are just guesses, no science involved).

Thanks in advance.

[Peter Duniho]

"xerj" > wrote in message
...
> When a power setting table shows a "best economy" and "best power" setting
> for a given power level (say 75%) using a given MP and RPM this is just a
> starting point, right?
>
> Once the MP and RPM has been set and the leaning done, the actual power
> settings would be more like 78% for best power, and 73% for best economy,
> wouldn't they? (%'s are just guesses, no science involved).

Depends on the table. However, generally speaking a power setting table
will indicate how to lean the engine for that power setting, and the actual
power is "exactly" what the table indicates. "Exactly" is in quotes
because, of course, it's unlikely one can get the exact combination of MP,
RPM, leaning, and other factors in operation. But you'll be pretty darn
close.

Assuming the table shows the desired leaning (and most do), you would not
adjust the indicated power setting for any other factor, not even leaning.
If it says you are getting 75% and you've leaned as indicated, then you're
getting 75% (more or less).

If you have a specific table in mind and would like to post the details,
then information based on that table in particular can be provided to you.
Otherwise, the general rule is that the table tells you the correct power
resulting from the power setting. No adjustments required or desired.

Pete

[Ron Rosenfeld]

On Thu, 13 Oct 2005 22:47:25 GMT, "xerj" > wrote:

>When a power setting table shows a "best economy" and "best power" setting
>for a given power level (say 75%) using a given MP and RPM this is just a
>starting point, right?
>
>Once the MP and RPM has been set and the leaning done, the actual power
>settings would be more like 78% for best power, and 73% for best economy,
>wouldn't they? (%'s are just guesses, no science involved).
>
>Thanks in advance.
>

It probably depends on the power table.

For example, the Mooney Ovation2 has separate tables for Best Power and
Best Economy. The former calls to lean 50°F ROP, and the latter 50°F LOP.

Others that I've seen give you a specific leaning parameter in order to
obtain the power in the table.


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

[xerj]

Here's a link to a checklist with a power setting table for a Lyc IO-360.

http://www.dauntless-soft.com/PRODUCTS/Freebies/Handlingnotes/dl/ludwigson_n222bh.pdf

Down the bottom of the MAP/RPM combos it has this:-

************************************************** ************************************

Fuel Consumption Approximations
75% Best Power 11.5 GPH 65% Best Power 10.5 GPH
75% Best Economy 10.0 GPH 65% Best Economy 9.5 GPH
Best power = 50° C rich of peak EGT Best Economy = Peak EGT (or LOP)

************************************************** ************************************
The 75% "Best Power" and 75% "Best Economy" couldn't both be actually 75%,
could they?

[Jose]

> Fuel Consumption Approximations
> 75% Best Power 11.5 GPH 65% Best Power 10.5 GPH
> 75% Best Economy 10.0 GPH 65% Best Economy 9.5 GPH
> Best power = 50° C rich of peak EGT Best Economy = Peak EGT (or LOP)
>
> ************************************************** ************************************
> The 75% "Best Power" and 75% "Best Economy" couldn't both be actually 75%,
> could they?

Yes, they could. You are using more gas at the 75% best power setting
than at the 75% best economy setting.

It depends what you hold constant in the comparision. If we held fuel
flow constant, then for the same amount of gas, best power gives you a
higher percent of power, and best economy gives you less power (so as to
stretch the gas longer).

But if you hold power constant (instead of fuel flow), then best power
=uses= more gas ("wasting" some to give you the same power), and best
economy uses less gas, making the best (most efficient) use of the gas.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

[xerj]

>> The 75% "Best Power" and 75% "Best Economy" couldn't both be actually
>> 75%, could they?
>
> Yes, they could. You are using more gas at the 75% best power setting
> than at the 75% best economy setting.

Sorry, I mean they couldn't both actually be 75% for the same MAP/RPM combo.

The leaner setting would have to be developing less power, wouldn't it?

[Jose]

>>> The 75% "Best Power" and 75% "Best Economy" couldn't both be actually
>>> 75%, could they?
>> Yes, they could. You are using more gas at the 75% best power setting
>> than at the 75% best economy setting.
>
> Sorry, I mean they couldn't both actually be 75% for the same MAP/RPM combo.
>
> The leaner setting would have to be developing less power, wouldn't it?

The thottle and mixture levers may be in a different position in order
to achieve the same MAP/RPM, as a result of using the fuel more or less
efficiently.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

[Thomas Borchert]

Xerj,

> Sorry, I mean they couldn't both actually be 75% for the same MAP/RPM combo.
>

No, but your table doesn't show MAP/RPM settings. So the MAP/RPM settings at
best economy would have to be higher for the same power output. As an aside,
50 degrees ROP is not a good point to run your engine at.

--
Thomas Borchert (EDDH)

[xerj]

> No, but your table doesn't show MAP/RPM settings.

It does in the upper section above the bit I cut and pasted. It has % power
settings columns, and then the various MAP/RPM settings.

> So the MAP/RPM settings at best economy would have to be higher for the
> same power output.

That's what I was pretty sure of.

[cwby-flyer]

Thomas Borchert wrote:
>
> No, but your table doesn't show MAP/RPM settings. So the MAP/RPM settings at
> best economy would have to be higher for the same power output. As an aside,
> 50 degrees ROP is not a good point to run your engine at.

I definitely agree that 50 ROP is not a good place to run your engine,
much better to keep it around 100 - 125 ROP.

As for your assertation that MAP/RPM setting, I must repectfully
disagree (and if I'm mistaken, please let me know - I'm always looking
to learn more). Your power combinations are determined by your MAP &
RPM at a given density altitude and expressed as a percentage of HP.
When you lean the mixture, the RPM/MAP combination will move (assuming
you're not at sea level on a standard day) and then to place the engine
back on your desired % power, you re-adjust the throttle and Prop
levers so that the MAP/RPM match what is in the POH for your density
altitude.

Mike

[Mike Rapoport]

"xerj" > wrote in message
...
> When a power setting table shows a "best economy" and "best power" setting
> for a given power level (say 75%) using a given MP and RPM this is just a
> starting point, right?
>
> Once the MP and RPM has been set and the leaning done, the actual power
> settings would be more like 78% for best power, and 73% for best economy,
> wouldn't they? (%'s are just guesses, no science involved).
>
> Thanks in advance.
>

Yes, the chart (which you may or may not have for your airplane) which gives
best economy is "maximium range chart" which shows the best power setting
for each altitude.

Mike
MU-2

[Ross Richardson]

I have a O-360 and if you look at the Lycoming manual you can have
different settings for the same power and save fuel one compaired to the
other. Usually it is the MP over the RPM that gives you the better fuel
burn.


-------------
Regards, Ross
C-172F 180HP
KSWI


Jose wrote:
>>>> The 75% "Best Power" and 75% "Best Economy" couldn't both be
>>>> actually 75%, could they?
>>>
>>> Yes, they could. You are using more gas at the 75% best power
>>> setting than at the 75% best economy setting.
>>
>>
>> Sorry, I mean they couldn't both actually be 75% for the same MAP/RPM
>> combo.
>>
>> The leaner setting would have to be developing less power, wouldn't it?
>
>
> The thottle and mixture levers may be in a different position in order
> to achieve the same MAP/RPM, as a result of using the fuel more or less
> efficiently.
>
> Jose

[Ron Rosenfeld]

On 14 Oct 2005 08:00:10 -0700, "cwby-flyer" > wrote:

>Thomas Borchert wrote:
>>
>> No, but your table doesn't show MAP/RPM settings. So the MAP/RPM settings at
>> best economy would have to be higher for the same power output. As an aside,
>> 50 degrees ROP is not a good point to run your engine at.
>
>I definitely agree that 50 ROP is not a good place to run your engine,
>much better to keep it around 100 - 125 ROP.
>
>As for your assertation that MAP/RPM setting, I must repectfully
>disagree (and if I'm mistaken, please let me know - I'm always looking
>to learn more). Your power combinations are determined by your MAP &
>RPM at a given density altitude and expressed as a percentage of HP.
>When you lean the mixture, the RPM/MAP combination will move (assuming
>you're not at sea level on a standard day) and then to place the engine
>back on your desired % power, you re-adjust the throttle and Prop
>levers so that the MAP/RPM match what is in the POH for your density
>altitude.
>
>Mike

Mike,

If I understand you correctly, I don't think I agree with you <g>.
Air-fuel ratio as set by the mixture control also significantly effects
fuel consumption.

POH tables take into account not only altitude (and the ones I'm familiar
with is PRESSURE altitude, not density altitude) but also whether one is
leaned to best economy or best power mixture.

For example, for the same MP/RPM settings on my Lycoming IO-360, bhp will
be less at best economy vs best power.

On the other hand, IF I keep bhp unchanged by adjusting the MP, then fuel
consumption will decrease at best economy vs best power.

Example: IO360A; 65% power (130 bhp); 2400 rpm
@ best power (125°F ROP): 64 lbs/hr
@ best econ (at Peak EGT): 54.5 lbs/hr

Here's another example for a Continental IO550-G
10,000' pressure altitude; 2400 RPM 65% power
@ best economy (50°F LOP) 21.0" MP 12.3 gal/hr
@ best power (50°F ROP) 19.8" MP 14.0 gal/hr

The airspeeds at the same power settings will be the same.

The settings in the manuals for best power and best economy are defined in
terms of degrees rich or lean of peak EGT.

One difference in addition to fuel burn is that, since you require a lower
MP at best power setting, you can achieve that power at a higher altitude
than with a best economy setting.


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

[xerj]

> For example, for the same MP/RPM settings on my Lycoming IO-360, bhp will
> be less at best economy vs best power.

That's what my original understanding was, and why I was confused by the
presentation of the power setting table I linked to.

You can prove it simply by leaving the prop and throttle where they are, and
moving the mixture in between best econ and best power. At best econ, you
will be slower than best power. Slower = less power being produced.

If you actually could just get the same power at a lesser fuel flow without
adjusting MP and RPM, putting aside CHT considerations for the moment,
there'd never be a reason to run at best power. It'd just be burning more
fuel for the same result.

[Ron Rosenfeld]

On Fri, 14 Oct 2005 21:45:42 GMT, "xerj" > wrote:

>> For example, for the same MP/RPM settings on my Lycoming IO-360, bhp will
>> be less at best economy vs best power.
>
>That's what my original understanding was, and why I was confused by the
>presentation of the power setting table I linked to.
>
>You can prove it simply by leaving the prop and throttle where they are, and
>moving the mixture in between best econ and best power. At best econ, you
>will be slower than best power. Slower = less power being produced.
>
>If you actually could just get the same power at a lesser fuel flow without
>adjusting MP and RPM, putting aside CHT considerations for the moment,
>there'd never be a reason to run at best power. It'd just be burning more
>fuel for the same result.
>
>

Your understanding is correct. The older a/c power charts only showed best
power MP/RPM settings.

One method:

1. Decide on your power setting -- e.g. 65%
2. Set MP/RPM appropriately per POH with adjustments for altitude,
temperature.
3. Set mixture to best power.
4. Note IAS.
5. Set mixture to best economy.
6. Increase MP to regain lost airspeed.

You will now be at 65% power, but with best economy setting, and burning
less fuel for the same airspeed.

It's hard to apply this method unless air is calm.

You might want to obtain the Operator's Manual for the -360- series of
engines from Lycoming. It has a wealth of charts that are much more
detailed than that in the older Mooney's, and might be interesting reading
for you.



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

[Peter Duniho]

"xerj" > wrote in message
...
>> For example, for the same MP/RPM settings on my Lycoming IO-360, bhp will
>> be less at best economy vs best power.
>
> That's what my original understanding was, and why I was confused by the
> presentation of the power setting table I linked to.
>
> You can prove it simply by leaving the prop and throttle where they are,
> and moving the mixture in between best econ and best power. At best econ,
> you will be slower than best power. Slower = less power being produced.

However, as Jose pointed out, RPM and/or MP will not remain constant as you
adjust the mixture. Just because the controls have not moved, that does not
mean that the power setting hasn't changed.

> If you actually could just get the same power at a lesser fuel flow
> without adjusting MP and RPM, putting aside CHT considerations for the
> moment, there'd never be a reason to run at best power. It'd just be
> burning more fuel for the same result.

Well, that's a matter of current debate, as it happens. The primary
argument in favor of a product like the GAMI fuel injectors is that you CAN
get the same power at a significantly lower fuel flow. In that argument,
you ARE just "burning more fuel for the same result" by using the "best
power, rich of peak" mixture settings suggested by engine operating manuals.

I find the argument compelling. The proponents explain that the
rich-of-peak, "best power" mixture settings exist to provide enough excess
fuel to ensure that no cylinder is actually running at peak EGT (since in
most engines, the actual mixture from one cylinder to another varies by a
significant amount), and to provide cooling for all cylinders to compensate
for the high power setting used.

They go on to explain that if the fuel mixture is actually well-matched from
one cylinder to another, one can accomplish the same effect by running the
engine lean-of-peak, ensuring that all of the fuel in the air/fuel mixture
is burned (rather than some of it being used to cool the engine), but still
keeping the EGT low enough in each cylinder to avoid heat-related problems.

Whether all of that is correct, I do not know. I'm not the expert. But it
does makes sense to me, and yet is still consistent with operating the
engine rich-of-peak for engines that aren't designed to ensure evenly
matched fuel/air mixtures for each cylinder.

Pete

[xerj]

> However, as Jose pointed out, RPM and/or MP will not remain constant as
> you adjust the mixture. Just because the controls have not moved, that
> does not mean that the power setting hasn't changed.

It's one of those "I just can't remember, exactly" things and I'm very much
grounded by my wallet at the moment, dammit. Although this could be a really
good excuse to get in and fool around "in the name of science". Better
justification than a $200 Coca Cola.

RPM with a constant speed should stay the same (or at least quickly revert
back to the same) shouldn't it? 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?

[Peter Duniho]

"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]

"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

[Ron Rosenfeld]

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)

[Peter Duniho]

"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

[Ron Rosenfeld]

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)

[xerj]

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.

[Friedrich Ostertag]

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

[Peter Duniho]

"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

[Ron Rosenfeld]

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)

[Friedrich Ostertag]

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

[Peter Duniho]

"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. :)

[Morgans]

"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

[Ron Rosenfeld]

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)