Differences between automotive & airplane engines

On Wed, 15 Feb 2006 02:14:33 GMT, Ernest Christley
wrote:

Those caveats are the killer, aren't they? You CAN'T 'properly lean'
the average aircraft engine, because they have horribly designed intake
manifolds. The mixture isn't distributed evenly. So to get two of them
properly leaned, you have to send the other two down into detonation
territory. Not knowing who's on first, the best bet is to **** your
money away in wasted fuel out the exhaust pipe.

It gets worse. According to John Deakin who wrote a series of very
very interesting articles on AVWeb (still available by the way) about
how to properly lean an aircraft engine, it's not just useless but may
be harmful to the engine to attempt to lean below peak if you do not
have an EGR guage that reads all cylinders.

He had a chart that showed that "properly" leaned, that is leaned
according to the POH using rpm drop, you could very easily have one of
the cylinders reaching a redline cylinderhead temperature, while
others were safe.

That is, if you are above about 65% power. At or below 65% power, it
doesn't matter where you set the mixture, you won't be able to
overheat the engine.

He also advocated leaning even to the point of roughness, if you could
stand it and were at 65% power, saying that the roughness wouldn't
hurt anything and was just the result of relatively unbalanced
fuel/air charges in the cylinder combustion chamber. This is the kind
of thing you feel because the cylinders of the four cylinder 0-360's
are so big. Any unbalanced fuel charge results in substantially
different pressures inside the combustion chambers from one cylinder
to the other, which can result in a perceptably rough running engine.

Smaller displacement engines with more cylinders would be less
susceptible to this syndrome.

Adjusting the injectors such that they produce aproximately equal
fuel/air distribution within the combustion chambers allows the pilot
to lean to the point where the engine quits, without any roughness to
that point.

Corky Scott

wrote in message
...
On Wed, 15 Feb 2006 02:14:33 GMT, Ernest Christley
wrote:

Those caveats are the killer, aren't they? You CAN'T 'properly lean'
the average aircraft engine, because they have horribly designed intake
manifolds. The mixture isn't distributed evenly. So to get two of them
properly leaned, you have to send the other two down into detonation
territory. Not knowing who's on first, the best bet is to **** your
money away in wasted fuel out the exhaust pipe.

It gets worse. According to John Deakin who wrote a series of very
very interesting articles on AVWeb (still available by the way) about
how to properly lean an aircraft engine, it's not just useless but may
be harmful to the engine to attempt to lean below peak if you do not
have an EGR guage that reads all cylinders.

He had a chart that showed that "properly" leaned, that is leaned
according to the POH using rpm drop, you could very easily have one of
the cylinders reaching a redline cylinderhead temperature, while
others were safe.

That is, if you are above about 65% power. At or below 65% power, it
doesn't matter where you set the mixture, you won't be able to
overheat the engine.

He also advocated leaning even to the point of roughness, if you could
stand it and were at 65% power, saying that the roughness wouldn't
hurt anything and was just the result of relatively unbalanced
fuel/air charges in the cylinder combustion chamber. This is the kind
of thing you feel because the cylinders of the four cylinder 0-360's
are so big. Any unbalanced fuel charge results in substantially
different pressures inside the combustion chambers from one cylinder
to the other, which can result in a perceptably rough running engine.

Smaller displacement engines with more cylinders would be less
susceptible to this syndrome.

Adjusting the injectors such that they produce aproximately equal
fuel/air distribution within the combustion chambers allows the pilot
to lean to the point where the engine quits, without any roughness to
that point.

Corky Scott

I don't always agree with Mr. Deakin; but on the above points, I believe
that you have it nailed!

On the related, though not identical, automotive conversion issue; I am
comming around to a hypothesis that the complete ECM and sensor package of
an unmodified automotive engine may be useable with leaded fuel. I mention
this because the ECM systems in automobiles and trucks to a commendable job
of managing mixture under a wide range of conditions.

My reasoning is that the higher average power levels in aircraft use may
keep the oxigen sensors in the exhaust system hot enough for the inevitable
lead deposits to sublimate off as fast as they would otherwise build. My
best guess is that average power levels in automotive use run around 10% of
maximum, due to a lot of time spent idling. Even allowing for very
substantial derating, aircraft use would involve much higher power. For
example, I just drove a Plymouth Neon on a 450 mile road trip and, judging
by fuel burn, the 130 HP engine produces less than 25% power at 70 MPH (or
about 70-75% rpm).

I regret that I will not be testing my hypothesis, to possibly make it a
theory, in the near future; so I am only offering it for comment at this
time.

Peter

On the related, though not identical, automotive conversion issue; I am

comming around to a hypothesis that the complete ECM and sensor package
of
an unmodified automotive engine may be useable with leaded fuel. I
mention
this because the ECM systems in automobiles and trucks to a commendable
job
of managing mixture under a wide range of conditions.


My reasoning is that the higher average power levels in aircraft use
may
keep the oxigen sensors in the exhaust system hot enough for the
inevitable
lead deposits to sublimate off as fast as they would otherwise build.
My
best guess is that average power levels in automotive use run around
10% of
maximum, due to a lot of time spent idling


////////////////////////////////////////////////////////////////////////
Alot of ECM controlled motors have optional ECMs for "offshore" markets
and those don't use a O2 sensor. The LS1 Gm motor can be bought with
the US puter or the "offshore" one. The offshore one doesn't need
Oxygen info to run properly. I agree the high output of a aircraft
engine will burn off alot of the lead plating that happens on a O2
sensor but it still will lose value and give the ECM a bad reading
after a 100 hours or so. Ya just make it a givin that during every
annual ,oops, conditional inspection you just replace the O2 sensor
with a new one and toss out the old one. They are less then 45 bucks.
That equates to about 1.78 Faa approved certified spakplugs...

("Chris Wells" wrote)
Ok, I've been scolded for using the word "automotive" and then I was
scolded for using "automobile". It would seem to me that in this context,
"automobile" would be correct, but can someone give me a final ruling?


Have you floated the term horseless carriage yet? :-)


Montblack

Ernest Christley wrote:
....................................... You CAN'T 'properly lean'
the average aircraft engine, because they have horribly designed intake
manifolds. The mixture isn't distributed evenly. .............

Don't know about lycoming, etc. but my Franklin 200+ hp has two long
curved intake tubes from the carb before going to the manifolds. Near
160kts cruise I easily get 8gph overal average - with near 2000 lbs. If
I slow down to about 120kts that jumps to about 5gph.
I think the long tubes allow the fuel to mix better and the mixture
floats around until sucked in by cylinders. In fact the engine was
uprated by 5hp from one model to another just by lenghtening the tubes
a little.
-----------------------------------------------------------------
SQ2000 canard: http://www.abri.com/sq2000

Not realy.I don't know what your asken me?

Ernest Christley wrote:
LJ wrote:

Also level the plane as it would fly though the air.Only my $0.02.
LJ


And use the measurement to the engines CG. You do know where the CG is
on each of the engines, don't you?

"abripl" wrote

In fact the engine was
uprated by 5hp from one model to another just by lenghtening the tubes
a little.

You are probably dealing with tuned intakes, or in other words, the pulses
of the valve opening and closing causes a high pressure wave to reach the
intake valve, just as it closes. That gives a small supercharging effect,
thus more power.
--
Jim in NC

....................................... You CAN'T 'properly lean'
the average aircraft engine, because they have horribly designed intake
manifolds. The mixture isn't distributed evenly. .............


Don't know about lycoming, etc. but my Franklin 200+ hp has two long
curved intake tubes from the carb before going to the manifolds.

The length of tube doesn't affect the mixture distribution.
The length of manifold immediately after the carbe and before the
divisions to the various cylinders does affect it, and in most of these
engines the intake divides within a couple of inches of the carb. Fuel
spraying from the main nozzle hits the throttle plate at anything less
than full throttle and is deflected to one side or another, striking
the manifold wall and clinging to it, so that cylinders that feed from
that side get more fuel than others.

Dan

The length of tube doesn't affect the mixture distribution.
The length of manifold immediately after the carbe and before the
divisions to the various cylinders does affect it,....

These tubes are about as wide as manifolds - so should have the same
as your effect "length of manifold after carb(e) and before divisions".
Have you actually seen a working Franklin 6A-350?

and in most of these
engines the intake divides within a couple of inches of the carb. Fuel
spraying from the main nozzle hits the throttle plate at anything less
than full throttle and is deflected to one side or another, striking
the manifold wall and clinging to it, so that cylinders that feed from
that side get more fuel than others.

The throttle plate rotates perpendicular to the engine line, so fuel
should
get deflected symmetrically to both sides and not to one side.
Its really a fairly symmetrical arrangement. Probably not as
good a fuel injection but pretty good as far as carbs go.

"stol" wrote in message
ups.com...
On the related, though not identical, automotive conversion issue; I am

comming around to a hypothesis that the complete ECM and sensor package
of
an unmodified automotive engine may be useable with leaded fuel. I
mention
this because the ECM systems in automobiles and trucks to a commendable
job
of managing mixture under a wide range of conditions.


My reasoning is that the higher average power levels in aircraft use
may
keep the oxigen sensors in the exhaust system hot enough for the
inevitable
lead deposits to sublimate off as fast as they would otherwise build.
My
best guess is that average power levels in automotive use run around
10% of
maximum, due to a lot of time spent idling


////////////////////////////////////////////////////////////////////////
Alot of ECM controlled motors have optional ECMs for "offshore" markets
and those don't use a O2 sensor. The LS1 Gm motor can be bought with
the US puter or the "offshore" one. The offshore one doesn't need
Oxygen info to run properly. I agree the high output of a aircraft
engine will burn off alot of the lead plating that happens on a O2
sensor but it still will lose value and give the ECM a bad reading
after a 100 hours or so. Ya just make it a givin that during every
annual ,oops, conditional inspection you just replace the O2 sensor
with a new one and toss out the old one. They are less then 45 bucks.
That equates to about 1.78 Faa approved certified spakplugs...

Your points are well taken. The cost of just replacing the O2 sensor is not
exorbitant.

Is there any really easy way to tell what engines are available with non O2
sensing ECMs?