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Lycoming's views on best economy settings



 
 
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  #1  
Old June 29th 04, 05:55 PM
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Default Lycoming's views on best economy settings

I was searching via Google for informational schematics, or even just
a written description, on Lycoming's fuel injection system because
it's different from Continental's.

I came across Lycoming's website in which a number of technical and
informational articles reside.

One of them
http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/leaningEngines.html

discusses various mixture settings for their fuel injected engines.

Here is item no. 5 from that article, it's a description of how to
achieve "best power" and "best economy" when an EGT guage is
available:

5. The exhaust gas temperature (EGT) offers little improvement in
leaning the float-type carburetor over the procedures outlined above
because of imperfect mixture distribution. However, if the EGT probe
is installed, lean the mixture to 100oF on the rich side of peak EGT
for best power operation. For best economy cruise, operate at peak
EGT. If roughness is encountered, enrich the mixture slightly for
smooth engine operation. ***editorial note*** If you do this (richen
slightly from peak), the only place for the cylinderhead temperatures
to go is up. Slightly to the rich side of peak on the graph described
below is where the cylinderhead temps peak. So it would pay to be
careful how much you richen from the peak setting, if the engine is
running rough at that point. The Cessna 172 I rent has the EGT guage,
but no CHT guage. So you can richen from peak and drone happily along
not knowing that you are cooking the cylinderheads.

This particular section of the website includes a nice graph, which,
if you are familiar with John Deakin's "Mixture Magic" article, will
look very familiar. It should because all fixed spark engines will
show the exact same performance curves for things like EGT, CHT,
percent power and BSFC.

What was interesting to me is if you look at where peak EGT is
occuring and then go down to the BSFC curve is, you will see that you
have not yet reached the lowest BSFC. That doesn't occur until you've
leaned a bit further. But then you would be **LOP**. Notice it does
not take much additional leaning to get the lowest BSFC the engine is
capable of producing.

Here's the interesting part: At peak EGT, the cylinderhead temps are
already starting down from their peak, and the downward curve is
pretty steep once you get to peak EGT.

Just a tiny bit more leaning and the cylinderhead temps dive down
another full ten degrees, while the EGT has hardly gone down at all.

While this is going on, the percentage of power is dropping off too,
which is why economy cruise is slower than best power, of course.

Lycoming finishes the graph with the following statement: "Textron
Lycoming does not recommend operating on the lean side of peak EGT."

Yet as their own graph shows, best economy is ONLY achieved lean of
peak. What extremely interesting to me is that the difference between
peak and lean of peak where best economy occurs is only a matter of a
very few degrees EGT.

Remember, when you are cruising at 60% power, you cannot hurt the
engine no matter where you set the mixture control. You can't burn
valves or cook the cylinderheads or cause detonation, it just isn't
producing enough power to do that. Lycoming themselves recommends
that for maximum engine life, cruise power should be limited to 65%
and CHT's kept below 400 F. But since the instrument panel doesn't
include a CHT guage, the only way to avoid high temps is to be way
rich, or at peak EGT or below.

Why Lycoming recommends against LOP operation is a mystery. MUCH
cooler CHT's and less fuel being burned... what am I missing here?
Does the engine run roughly at this setting? Only those who try LOP
will know.

Corky Scott
  #2  
Old June 29th 04, 08:15 PM
Julian Scarfe
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Default

wrote in message
...
Why Lycoming recommends against LOP operation is a mystery. MUCH
cooler CHT's and less fuel being burned... what am I missing here?
Does the engine run roughly at this setting? Only those who try LOP
will know.


http://www.lycoming.textron.com/supp...ps/SSP700A.pdf

sets out their case, at least for larger turbos. (I'm not suggesting I
endorse it.)

Another thing to bear in mind is that mixture distribution is imperfect in
most factory engines. If you operate at a steep part of the power vs
mixture curve, small differences in mixture mean large imbalances of power
between the cylinders. That can't be good for the engine. The point of
Braly's Gamijectors is to even out the mixture distribution so that the
imbalance disappears.

Julian Scarfe



  #3  
Old June 29th 04, 10:21 PM
Stan Prevost
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"Julian Scarfe" wrote in message
...
The point of
Braly's Gamijectors is to even out the mixture distribution so that the
imbalance disappears.


They don't even out a power imbalance, they just make all the cylinders
reach peak EGT at the same mixture setting.



  #4  
Old June 29th 04, 10:28 PM
Tom Sixkiller
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"Stan Prevost" wrote in message
...

"Julian Scarfe" wrote in message
...
The point of
Braly's Gamijectors is to even out the mixture distribution so that the
imbalance disappears.


They don't even out a power imbalance, they just make all the cylinders
reach peak EGT at the same mixture setting.


Which likely produces a balancing of power, no?

Also, IIRC, it leads to the piston achieving ignition at the optimal point
in the stroke (at LOP??).


  #5  
Old June 29th 04, 10:33 PM
Tom Sixkiller
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wrote in message
...
Lycoming finishes the graph with the following statement: "Textron
Lycoming does not recommend operating on the lean side of peak EGT."

Yet as their own graph shows, best economy is ONLY achieved lean of
peak. What extremely interesting to me is that the difference between
peak and lean of peak where best economy occurs is only a matter of a
very few degrees EGT.


Corky,

Isn't it also true that LOP optimizes the point in the stroke that the
cylinder achieves the peak ignition point?

Considering the wear on the engines moving parts that provides, maybe George
Patterson is right, that they'd like us to buy new engines? :~) I also
wonder how they are trying to cover their legal asses if they were spreading
wrong (negligent) information for all these years, or merely just PP QC on
their engines??

Tom
--
"Flying an airplane is just like riding
a bike -- it's just a lot harder to put
baseball cards in the spokes" -- Capt. Rex Cramer


  #6  
Old June 30th 04, 02:45 AM
Mike Rhodes
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On Tue, 29 Jun 2004 12:55:39 -0400,
wrote:

[trim]

Lycoming finishes the graph with the following statement: "Textron
Lycoming does not recommend operating on the lean side of peak EGT."

Yet as their own graph shows, best economy is ONLY achieved lean of
peak. What extremely interesting to me is that the difference between
peak and lean of peak where best economy occurs is only a matter of a
very few degrees EGT.

Remember, when you are cruising at 60% power, you cannot hurt the
engine no matter where you set the mixture control. You can't burn


That since an aircraft engine will not usually detonate at the lower
power. But turbo engines, I've read, may have difficulty...

valves or cook the cylinderheads or cause detonation, it just isn't
producing enough power to do that. Lycoming themselves recommends
that for maximum engine life, cruise power should be limited to 65%
and CHT's kept below 400 F. But since the instrument panel doesn't
include a CHT guage, the only way to avoid high temps is to be way
rich, or at peak EGT or below.

Why Lycoming recommends against LOP operation is a mystery. MUCH
cooler CHT's and less fuel being burned... what am I missing here?
Does the engine run roughly at this setting? Only those who try LOP
will know.

Corky Scott


As for Lycoming recommending against LOP, there was an article in
Flying magazine (p. 74-75, 7/02, inset article, J.Mac) , where there
was some sort of lead crystalline deposit (lead oxybromide) forming in
_turbo_ engines only in LOP operations. That deposit would cause a
"light" detonation, and eventually destroy the engine. The deposit
apparently does not form in normally aspirated engines, regardless of
mixture. Lead oxybromide was also found to harm the rod and
crankshaft bearings.
If true, I would think this would be common knowledge, and pilots
would not have to run to Lycoming for it. And other authorities would
not suggest lean in turbo engines. (Do they?)
Running lean, by a moment of carelessness (pilots have lots of
things to tend to) invites catastrophic trouble in any engine. And
for the pilot to get in that habit in normally-aspirated engines can,
after the pilot upgrades, apparently inflict harm on turbo engines.
Anyone else familiar with this?

--Mike
  #7  
Old June 30th 04, 06:13 AM
John Clear
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In article ,
Mike Rhodes wrote:

As for Lycoming recommending against LOP, there was an article in
Flying magazine (p. 74-75, 7/02, inset article, J.Mac) , where there
was some sort of lead crystalline deposit (lead oxybromide) forming in
_turbo_ engines only in LOP operations.


I've snipped the rest since it is full of old wives tales. The
theory of lead oxybromide came from a poorly investigated accident
in Austrailia.

John Deakin analyzes the accident, and Flying's coverage of it.

Accident: http://www.avweb.com/news/columns/182152-1.html

Flying's coverage: http://www.avweb.com/news/columns/182153-1.html

Deakin also covers LOP in alot of his articles, specifically the
ones titled 'Where should I run my engine?' He goes into the
science of how an engine actually works, and examines how the
'your engine will burn up if you do that' OWTs relate to reality.

All of Deakin's articles: http://www.avweb.com/news/columns/182146-1.html

John
--
John Clear - http://www.panix.com/~jac

  #8  
Old June 30th 04, 06:29 AM
Peter Duniho
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"Stan Prevost" wrote in message
...
The point of
Braly's Gamijectors is to even out the mixture distribution so that the
imbalance disappears.


They don't even out a power imbalance, they just make all the cylinders
reach peak EGT at the same mixture setting.


Which they do by ensuring the same actual fuel/air mixture at a given
mixture setting. Further, since the difference in fuel/air mixture at a
given mixture setting plays a big part in the power differences between each
cylinder, why wouldn't the Gamijectors help improve the power imbalance?

Pete


  #9  
Old June 30th 04, 08:12 AM
Julian Scarfe
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"John Clear" wrote in message
...

I've snipped the rest since it is full of old wives tales. The
theory of lead oxybromide came from a poorly investigated accident
in Austrailia.

John Deakin analyzes the accident, and Flying's coverage of it.

Accident: http://www.avweb.com/news/columns/182152-1.html

Flying's coverage: http://www.avweb.com/news/columns/182153-1.html


You missed the best bit, where the coroner slates the ATSB investigation.
:-)

http://www.airsafety.com.au/whyalla/default.htm

has the chronology.

Julian Scarfe


  #10  
Old June 30th 04, 08:18 AM
Dylan Smith
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In article , Mike Rhodes wrote:
things to tend to) invites catastrophic trouble in any engine. And
for the pilot to get in that habit in normally-aspirated engines can,
after the pilot upgrades, apparently inflict harm on turbo engines.

snip

I've never bought the argument of "don't get in the habit of this,
because if you move to X type of different aircraft, it's bad".
Operating one engine sub-optimally because it's not done in another type
seems a bit silly to me - surely pilots should fly each different type
appropriately, instead of by habit?

If someone tells me "don't operate your C140/Auster/Champ [...] like
this because if you move to a turbo Bonanza, doing that will be
harmful", I tend to ignore them and continue to operate each aircraft
appropriately.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"
 




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