In a message dated 12/28/2004 9:08:44 P.M. Central Standard Time,
Walter@advancedpilot.com writes:
One of
the problems with some fuel pressure systems is that they
maintain a fixed
pressure with little change while the FF actually
changes
significantly. If the system is a fuel pressure system of
gauge
display, you will not see the FF change that is actually
happening.
If you have a FF transducer in one of those systems, you
can see this by
the differences between the two instruments.
Walter, where is this going? I said I have a fuel flow sensor
(located between throttle body and spider) and it did change when the MAP was
reduced 1".
This
is one thing I do not like about the TCM FADEC. It displays a
fuel
pressure which does not change significantly with rather large
changes in
FF.
In many carbureted installations, the fuel flow instrument is
actually
fuel pressure and does not show the FF changes accurately.
I am not
sure how the Mooney system is set up. I do have a great
deal of
confidence in telling you that as you reduce throttle from WOT,
the
first 3/4 to 1 inch of throttle travel does not reduce MP -- it
reduces
FF only. This is the very important fuel enrichment feature
that is
built into almost all carburetors. A very, very few do not
have this,
and they are almost always found on turbo-supercharged engines
like the
big radials.
I was talking about injected systems. I have no idea how a Mooney is
set up. I do not have a carburetor.
Anyway, we are so far from my observations that I have no idea what your
point is.
In a fuel injected system, the reduction of WOT by 1" MAP is a power
reduction of similar magnitude as the dropping of the WOT 2500
RPM by 100 - The drop in airspeed should be similar and so should the drop in
fuel flow - similar, not identical. In our slick Lancairs with little
parasitic drag, the drop is merely a few knots. If the "indicated" 1" MAP
drop resulted in a large drop in airspeed and fuel flow, there is something
wrong with the MAP sensor circuit, such as a problem with the snubber
valve (if VM engine instrumentation is used). The
procedure is an in-flight diagnostic tool. Do I need more
qualifications or specificity?
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 Aurora, IL
(KARR)