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Scientific Data on Engine Operations



 
 
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  #1  
Old July 15th 05, 08:03 AM
O. Sami Saydjari
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Default Scientific Data on Engine Operations

This is actually a split off from the "Rotating Injectors Among
Cylinders" thread. I prefer not to distract that thread any.

I must say that I find the evidence presented in support on LOP to be
uncompelling. Although it is certainly appealing at the gut level, it
is a far cry from scientific evidence that LOP operations is better for
the engine and will lead to longer TBOs.

I am not saying that the assertion is false; I am saying that I have yet
to see properly controlled long-term experiments that prove the
hypothesis that is so emphatically stated as truth.

I hasten to add that it does not appear that the engine manufacturers
have done any scientific experiments to suggest that ROP operations lead
to longer TBOs or better operation. This is what I find so frustrating.
So much depends on quality information about proper engine
operations, yet there appears to be little science behind the assertions.

OK, I said my piece. I am done venting now.

-Sami
N2057M, Piper Turbo Arrow III
  #2  
Old July 15th 05, 01:22 PM
Denny
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Sami:
GAMI is producing certified STC / PMA injectors for a number of
years... They have a large amount of engineering data from test
engines, and a huge base of customer recorded engine operating data out
in the field... This constitutes a database of real world engine data,
more than the manufacturers ever dreamed of recording and magnitudes
more than the manufacturers use to have an entire engine certified...
To certify an engine the manufacturer runs it on a test stand for ~200
hours, tears it down for wear measurements, and that is it; It's
certified...
A case in point is the ongoing Lycoming crankshaft saga... The customer
is LYCOMING's engine test stand... GAMI has recorded more test stand
and flight hours just developing their injectors than Lycoming has for
rest of the entire engine itself...

If GAMI injectors and LOP operation was lunching engines we would know
it by now ... If you don't like LOP operations then don't do them
and save your angst for something that is a real problem... Simple, eh
wot...

cheers ... denny

  #3  
Old July 15th 05, 02:11 PM
Doug
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I have often thought that what is needed is a scientific study of what
works best in aircraft engines. Get a statistically signifigant number
of engines. Rebuild them. Put monitoring equipment in the aircraft.
Instruct each owner of the aircraft to run the engine in specific ways.
Numerous groups of engines being run different ways. Oil selection, oil
change frequency, leaness, shock cooling etc could all be studied.
After 2000 hours of running one would have a pretty good idea of cause
and effect.

  #4  
Old July 15th 05, 02:16 PM
Paul kgyy
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I agree with Denny - George Braly has been using sensors that actually
record internal cylinder pressures in real time. I believe they do
know what they are talking about. I just went to Lycoming's web site
to do some reading on this yesterday, and their publications appear to
have no basis other than company CYA.

  #5  
Old July 15th 05, 03:27 PM
Michael
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So much depends on quality information about proper engine
operations, yet there appears to be little science behind the assertions.


You are quite correct - there is very little science here. There is
certainly a lack of solid statistical evidence. In this situation, you
pretty much have to work from engineering first principles.

Let's start from what is scientifically defensible:

Operating 50 degrees LOP vs 50 degrees ROP (which is what many
manufacturers recommend) means that:
The engine runs slightly rougher. Extra vibration.
The peak pressures in the cylinder (and thus transmitted to the
crankshaft) are lower. Less stress on crankshaft, bearings, etc.

That's about it. Everything else is rumor, conjecture, and guesswork.

The slightly rougher running may in the end reduce the life of the
engine more - or less - than the higher peak pressures in the
cylinders.

Oops, I guess we're done until an actual controlled study shows us
which factor is more important.

Michael

  #6  
Old July 15th 05, 04:03 PM
Paul kgyy
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The extra vibration occurs only if you don't have proper fuel
distribution LOP. Admittedly, this is normal for carburetion and
common for fuel injection, but that's the point of using GAMI injectors.

  #7  
Old July 15th 05, 04:52 PM
O. Sami Saydjari
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Yes, exactly. -Sami

Doug wrote:

I have often thought that what is needed is a scientific study of what
works best in aircraft engines. Get a statistically signifigant number
of engines. Rebuild them. Put monitoring equipment in the aircraft.
Instruct each owner of the aircraft to run the engine in specific ways.
Numerous groups of engines being run different ways. Oil selection, oil
change frequency, leaness, shock cooling etc could all be studied.
After 2000 hours of running one would have a pretty good idea of cause
and effect.

  #8  
Old July 15th 05, 04:55 PM
O. Sami Saydjari
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Default

Denny,

Just to be clear here, I have no angst at all, only uncertainty. The
GAMI data is admirable and is a good start...but it is only suggestive.
As others have pointed out, the connection between some of what GAMi
measures and the impact on TBOs for example, is really speculation at
this point. It does not need to be. Some scientific controlled
experiments could do wonders here. That is my only point. Hats off to
the GAMI folks for starting us down the right road. -Sami

Denny wrote:

Sami:
GAMI is producing certified STC / PMA injectors for a number of
years... They have a large amount of engineering data from test
engines, and a huge base of customer recorded engine operating data out
in the field... This constitutes a database of real world engine data,
more than the manufacturers ever dreamed of recording and magnitudes
more than the manufacturers use to have an entire engine certified...
To certify an engine the manufacturer runs it on a test stand for ~200
hours, tears it down for wear measurements, and that is it; It's
certified...
A case in point is the ongoing Lycoming crankshaft saga... The customer
is LYCOMING's engine test stand... GAMI has recorded more test stand
and flight hours just developing their injectors than Lycoming has for
rest of the entire engine itself...

If GAMI injectors and LOP operation was lunching engines we would know
it by now ... If you don't like LOP operations then don't do them
and save your angst for something that is a real problem... Simple, eh
wot...

cheers ... denny

  #9  
Old July 15th 05, 06:11 PM
Frank Stutzman
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Default

O. Sami Saydjari wrote:
Denny,


As others have pointed out, the connection between some of what GAMi
measures and the impact on TBOs for example, is really speculation at
this point. It does not need to be. Some scientific controlled
experiments could do wonders here. That is my only point. Hats off to
the GAMI folks for starting us down the right road. -Sami


Several of the GAMI principals hang out on the Bonanza owners list. While
I guess there hasn't been a double blind (if you could do such a thing)
scientific test, the evidence is pretty much out there.

You've got to remember that LOP operations are nothing new. When the
radial engine was king, airlines ran their DC-4, DC-6 and Constellations
LOP as a regular practice. Engines almost always made TBO.

Now I guess you could say that the engines in our little planes aren't the
same as the large radials. Could be, I'm no engine expert. The GAMI
folks, though, will tell you that it doesn't matter wether your running a
lawn mower or a double-wasp radial, the combustion event is the same.

--
Frank Stutzman
Bonanza N494B "Hula Girl"
Hood River, OR

  #10  
Old July 15th 05, 07:27 PM
Michael
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The extra vibration occurs only if you don't have proper fuel
distribution LOP


I have never seen an engine, GAMI equipped or otherwise, that was as
smooth LOP as it was ROP - and I've seen a lot of them. That's not to
say that I haven't seen a lot that were acceptably smooth - I have.
That's also not to say that I haven't seen engines that ran smoother
LOP with GAMI's than ROP without - I have. But those engines with
GAMI's ran even smoother ROP. When operating LOP, the fuel-air
distribution needs to be much closer to perfect than ROP for the same
level of vibration, simply because the power vs fuel curve is MUCH
steeper. By the same token, unless the distribution is absolutely
perfect (which it never is except maybe at one altitude and power
setting) ROP will always be smoother. I'm sure that at some point the
difference isn't important anymore (the vibration due to power
imbalance is swamped by other factors) but nobody can say with any
authority what that point is.

Of course all the piston airliners routinely ran LOP - but it's
important to remember that over the course of its life, the cost of
fuel the engine burns is significantly higher than the cost of the
overhaul - and thus LOP operation, which can easily save 10-15% for the
same power and speed, can be economically advantageous even if it does
measurably shorten engine life.

Michael

 




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