Paul,

    I have been secretly working on my fuel gauge/probe problem.  I
couldn't
    get your suggested circuits to work (probably my limited electronics
    ability), so I broke down and purchased two capacitance-to-voltage
    converters, the same ones used by the Dynon folks and sold by ACS.
I've
    installed one and hooked it to a voltage channel on my efis box, and it
    works as I would have expected.  The sad part is that the new circuit
    has the same problem as the old circuit in that it drifts in flight.
    But it returns to normal when back on the ground.  That's telling me
    that something is going wrong with the signal.  My guess is static
    buildup across the wings is affecting the capacitance readings of the
    probes.   How can I check this theory?  Any suggestions on how to
    fix it?

    Additional info:
    1)  CTV is mounted inside the cabin (old circuit was in wing root)
    2)  Pigtail from probe to CTV is shielded (old was unshielded)
    3)  CTV uses voltage a channel (EI circuit used frequency channel)

    My thought at this time is to disconnect the CTV output from the EFIS
    and connect it to a volt-ohm meter and go fly to see if the voltage
    reading increases or decreases unexpectedly (drawing off the other
    tank).  This should tell me if the problem is with the EFIS or the
probe
    circuit.  I doubt it is the EFIS as other instrumentation feeding into
    the EFIS is rock solid.

    Mark S.
    (rain today)

    Interesting theory. Plastic wings as opposed to metal wings.
    Do you have any static discharge wicks on your wings?

    One way to check for temperature affects is keep the same fuel
    (about half full) in the wing and check it in the morning when it
    is cold soaked overnight and again in late afternoon after the sun has
    its way with the fuel tank.

    Paul Lamar ...No rotor no motor.


Mark:

FWIW: To help narrow down your options:  I believe my Lancair ES has the
same EI fuel probes as yours, but mine are connected to a standard EI fuel
gage.  I have no problems with wandering indications in flight.

Composite wings do generate static charges in flight--especially in light
rain.  I flew through a very light rain shower enroute to Oshkosh in 2003.
The electric trim position indicators went absolutely wild, flashing all
kinds of lights, and then went blank.  The trim motors still worked, and the
EI fuel gage indications remained steady.

Tom Parkes


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.