The recent damage to a Europa due to static discharge during fueling inspired
addition of tank grounding to my plane. The information at the sites
suggested by Fred Fillinger was most helpful in deciding how to proceed:
www.chevron.com/prodserv/bulletin/product%5Fsafety.html
www.ccohs.ca/oshanswers/prevention/flammable_static.html
Initial measurements of the resistance of the various fuel lines with an
ohmmeter showed that the large filler hose is conductive but seems to have a
thin interior layer which insulates the conductive outside from the fuel
flowing through it.
The short sections of 1" hose used on the tank outlets are conductive. The
small bore cotton covered line used aft of the firewall is also conductive.
Apparently, Europa recognized the static discharge possibility and took steps
to avoid it by using conductive hose. Unfortunately, US fuel contains
various chemicals which reportedly attack the small bore hose supplied,
causing it to deteriorate more quickly than desired. In an attempt to avoid
this deterioration, I replaced much of the small bore hose with hose from the
auto store but after reading of the static problem noted above found that
this auto hose was non-conductive. Thus, in attempting to avoid one problem
I introduced another.
Interpreting advice from this forum as well as the sites noted above, the
following was done:
The outside of the aluminum fuel filler where it contacts the filler hose was
lightly sanded with fine paper to remove the anodizing which is an insulator.
The inside of this fitting was also sanded on the lower half inch to aid
contact with the fuel filler nozzle. While the insulation breakdown voltage
of the anodized finish is not high, these steps make it easier to evaluate
the results with an ohmmeter.
A short piece of safety wire was twisted onto the gauge vent fitting and run
under the hose clamp used to hold the top of the filler hose. A ground wire
was added under this hose clamp and connected to the aircraft ground at the
connection to the strobe supply which was nearby. The gauge vent provides a
convenient fitting for insertion of a banana plug or a small clip lead for
grounding, plus it is easy to keep a finger on this to maintain a ground
while fueling.
A wire was run under the hose clamps between the 1" tank outlet fittings to
connect these fittings together, then back to join the ground at the strobe.
The ohmmeter shows that all the targeted fittings are connected and in
addition wherever the original cotton covered line has not been replaced
there is a resistive connection.
One additional wire is planned between the engine ground and the
undercarriage to provide grounding via the conductive mainwheel tire - this
will be added when the lower cowl is next removed.
Of course, there is always a question remaining: should a section of safety
wire be added such that it extends from the filler fitting down inside the
filler pipe or is this superfluous due to a low breakdown voltage of the
interior insulating layer in the filler hose?
John, A044
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