In a message dated 1/3/2005 8:21:15 A.M. Central Standard Time,
glcasey@adelphia.net writes:
If
the air flow into the servo changes its "pattern" the reference
pressure
could change, upsetting the calibration. In other words, it
could be that
the air swirls in a particular way under one conditions and
then detaches
from the wall or otherwise changes its flow pattern at
another condition.
This is especially true if the air has to make a sharp
bend at the servo
inlet. So what you are seeing could very well
happen - the effect just
isn't built into the system. As an example,
my Cardinal has a very nicely
designed servo inlet and the air/fuel ratio
is very constant over a wide
range of rpms and throttle openings.
Come help me finish my ES and I'll
report on that...
Gary,
Exactly. This is so much fun. It is another example of why each
homebuilt Lancair can be the same, yet different from each other one and
certainly different from any STC aircraft. I really try to send
enough of the environmental conditions so that the data is usable and maybe even
comparable to other Lancairs similarly equipped. I certainly agree that
the flow pattern can change - In my case primarily from the angle of the entry
air and the pressure that all or some of the "venturis" see in the throat
of the throttle body because there are no bends in the induction system
before the throttle body. It not only is a straight shot, there is no
filter to mottle the air, no expansion chamber, and no flow disruption since the
walls are smooth (polished fiberglass with a plumber's sleeve
interconnect). What I really need is a JPI engine monitor - I can't always
record (write down) all the things (cowl pressure, temp, lower cowl pressure,
injector air pressure, flight parameters, power settings and cylinder data, and
fly the plane thru a transition - not enough sensors, not enough arms and
definitely not enough brains. Hmmmm, maybe I need a video camera with a
wide angle lens pointed at the panel.........
No, I cannot help with your ES as I am using too much gas trying to
understand the effect of all the goofy things I have done. I am certainly
learning a great deal from so many contributors here on LML.
Oh,
and one more thing - the reference pressure applied to the
injectors
does not affect the fuel flow, but it does affect the reading of
a
pressure-type fuel flow indicator. The indicator is a pressure gage
that is
referenced to the pressure inside the cabin. The pressure
drop in the
injector itself is, however, referenced to the vent pressure at
the
injector. It is a small effect, but could change your fuel flow
readings
slightly.
It is not a small effect. I have demonstrated that altering the
airflow that an injector utilizes alters the consequences to fuel
passing thru it. Of course, measured indirectly, like the first cylinder to
lean and the cruise EGT spread. You know, I may draw the wrong conclusions
thru ignorance, but I can't change the data.
Things just happen in flight that don't happen on a dyno stand.
I do not have a pressure-type fuel flow indicator. I have a
sensor that actually measures fuel flow. I have an idiot light (informing
the light-idiot behind the yoke) that warns of low fuel pressure (12 psi) - it
seems to indicate one of the three requirements for combustion might
stop flowing if the pressure (for whatever reason) gets too low.
BTW, you ought to see what .001 injector diameter change can do
to a cylinder's performance - just ask GAMI.
After all, all I am trying to do is get the same max/best power out of each
cylinder so I can get to the head of the line. I enjoy stumbling along
paths not often taken.
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 Aurora, IL (KARR)