Frans,
Speaking from the US, the additives to the fuel here makes it a low
conductivity fluid. I don't recommend it, but aviation fuel
conductivity it is so low that you can hook a bulb with an attached bare
wire submerged in the fuel and then approach the bulb with the ground
wire and there will be no jump of electrical arc until virtual contact.
At 12 volts, it isn't a problem, but in 250 volt power fuel storage it
can arc.
Your point on the elbow is in error if the elbow is in contact with the
aluminum fuel cap ring as I understood the hookup was. The cap/aluminum
cobra neck will ground to earth through the wire to the aircraft ground
system. However you are exactly right if the plastic cobra is installed
and only the aluminum elbow connects the plastic cobra to the plastic
tank. Why do that at all? Now the nozzle has a path to arc if it
hasn't already as you indicated. Your are correct, it helps nothing
and can be a potential hazard...
Flowing and sloshing fuel would cause an electrical charge buildup while
fuel flows in during fuelling or sloshing, so when fuelling keep
yourself in contact with the aircraft skin and nozzle. As for sparking
with the nozzle in, if you have fuel flowing or not, if you leave the
handle and vehicle without re-grounding, you will potentially be
creating a discharge hazard.
My experience comes from an accident investigation of a fuelling
accident. The fuels engineers talked over my head (not hard to do) and
in a nutshell, JP-4 is a wide cut gasoline and had virtually nil
conductivity just like gasoline. However, moving to JP-8 the
conductivity jumped considerably screwing up all our fuel senders, and
in a shorted imbedded fuel pump, it was found that it would conduct over
a small distance (1/4 inch) and jump a spark at 250 volts. Normally
there was no damage even if it arced because of the imbedding of the
pump into the fuel and a virtual nil oxygen environment even at low fuel
levels... However with fuel sloshing (low fuel in the bulk tank), it
was enough to jump a spark. The spark arced a pin hole leak into a
corroding tank bottom near the pump (added iron sulfides was what they
found aided the arc). The pin hole leak provided a path for a discharge
---From the short through the fuel stream to the ground, so that was their
cause... I still think it was the young airman and his cold weather
nylon coat that was the ignition source.
Later when the FAA was approving the STC of gasoline in aviation
engines, again we were fine until in California they had interesting
required additives for emissions. One was an iron carbide molecule that
with tolulene and other ionized cleaning additives screwed up the
capacitance probes, resistive senders and in tank fuel pumps shourted
out internally left and right. Then they required added ethanol (the
plague) and again, we had another measured jump in conductivity by a
factor of two, and the FAA stopped all auto fuel use in aircraft until
investigated. These government mandated changes in fuel caused small
increases in conductivity, but enough to cause the industry to change
its fuel refining requirements for California. We all know that the
difference in conductivity is enough to prevent capacitance systems from
maintaining their accuracy when changing from one fuel to another, or
simply one brand to another, but they no longer kill capacitance probes
any longer as in the 80's. The good news is SO CAL Transportation Dept
forced its own state government to cease further development of new
additives unless stringent tests were conducted and quality of the fuel
produced be monitored and tested carefully. As all our systems require
a very low conductivity to allow safe operation of submerged pumps, fuel
level senders etc. those of us pushing for auto fuel in our old low
octane aircraft engines, were pleased. Too bad ethanol is still with us
here in the States and ethanol free fuel is somewhat scarce.
So, do you have to run a wire anywhere inside the tank to ground our
fuel system...Like we both said...NO. I only stated that if the metal
ring on the outside of the aircraft fuel tank inlet, had a wire running
to ground, and the tailpipe is grounded to earth, the outside of the
aircraft should have the charge on the outside of the aircraft
dissipated to earth. Is it just as effective as putting ones ungloved
hand on the earth contacted fuel can and the aircraft using our somewhat
low conductivity body as a ground wire.
You know that the static electricity stays on the outside of a vessel,
and if a spark is going to jump it will most probably be caused by
static discharge to a ground such as a fuel nozzle from the outer skin
of the aircraft. The vapor around an open fuel tank then becomes a
hazard.
I agree that fuelling on a trailer is not a major concern except for the
guy in rubber soles being handed a fuel nozzle via gloved hand while
standing on the trailer in winter rubber boots in a cold weather
environment. Sparks will occur. Don't jump through hoops changing
the airplane, just be aware and dissipate your static charge before
opening the cap and putting the fuel nozzle to the filler neck...
Regards,
Bud
----- Original Message -----
From: Frans Veldman<mailto:frans@privatepilots.nl>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Sunday, January 13, 2013 5:15 AM
Subject: Re: Europa-List: Grounding & Fuelling
<frans@privatepilots.nl<mailto:frans@privatepilots.nl>>
On 01/13/2013 02:02 AM, Bud Yerly wrote:
> Since auto's with plastic tanks have the fuel grounded to the
vehicle
> ground via the fuel pumps, and the capacitance probe, injectors,
fuel
> regulators, etc. Your point of ground of the whole fuel system is
> already accomplished by the engine fuel systems in our aircraft,
just as
> in the autos.
You seem to assume (know?) that fuel is conductive. I'm pretty sure
however that fuel is quite a good isolator, just like the rest of the
carbohydrate family members. So, various components in contact with
the
fuel may carry a different electrical charge and will not relieve
themselves via the fuel. It is entirely possible that the skin around
the fuel filler opening has a neutral electrical charge, while the
aluminium elbow carries a static charge. Now you think since you have
grounded the skin, engine, fuel nozzle/can and your body that nothing
can happen, but at the moment you insert a long fuel nozzle deeply and
it gets far enough to get close to the elbow the static charge of the
elbow might relieve itself to the fuel nozzle with a spark.
Ok, so grounding the aluminium elbow sounds like a good idea?
Unfortunately this creates a new problem:
Fuel itself may become electrically charged due to sloshing and
friction
within the plastic tank. Imagine what will happen when you pour fresh
fuel in and the fuel level of the electrically charged fuel starts
rising, slowly approaching the grounded elbow...
I think you can't really solve this problem in a plastic aircraft with
a
plastic fuel tank carrying non-conductive fluids. It looks to me that
you either should try to ground every individual component in contact
with the fuel and run a metal wire through the tank so all the fuel
molecules frequently run into the wire and discharge themselves before
they reach the sparking level potential, or, to accept that the whole
system may carry a charge but as long as it has nowhere to go there is
no sparking risk, i.e. do not ground anything in contact with the
fuel.
Except for the fuel filler opening, but since it is plastic just a
wipe
with a wet rag accomplishes this task. Never insert a hose or
something
deeply inside the fuel filler opening. Although it sounds scary: The
fuel itself is not conductive so you can pour neutral fuel from a
grounded nozzle into a static charged tank without a problem, as long
as
there are no grounded objects (like the elbow) to cause sparks when
the
fuel level starts rising.
> Problem is with the trailered aircraft.
We carry our Europa home after every local flight and we always refuel
at the local gas station while trailering to the airfield. We think it
is nearly impossible to refuel without making contact with the
trailer,
various aircraft parts, the fuel opening and the fuel nozzle. It is
usually my wife who climbs onto the trailer (her belly is flatter than
mine so she just squeezes herself between the wing and the fuselage)
to
reach the fuel opening and by the time she is in position I step on
the
fender of the trailer and hand over the fuel nozzle over the wing
flap,
my next task is holding on to the fuel hose to keep it from pulling on
the nozzle while reading out the liters on the display so my wife
knows
when to stop. It would be very hard to accomplish the refueling
procedure without making solid contact with all the aircraft, trailer,
fuel nozzle, etc parts. Also keep in mind that we live in a very "wet"
country with high humidity levels being the norm, and static charge is
quite unlikely to build up on vehicles (except for rubbing certain
clothes against the upholstery while sitting in the car, but this
usually relieves itself while getting out of the car -ouch- before you
can even approach the fuel related objects)
When we fly to drier climates we usually leave the trailer behind as
it
is too heavy to keep it strapped to the aircraft. ;-) so we never find
ourselves in a situation where we have to refuel a trailered Europa in
a
very dry environment.
> Gas Stations use valves with cutoffs to allow the grounded fuel line
to
> be placed into a vehicles open hole by a woman wearing a static
> generating outfit in reasonable safety providing she stays in
contact
> with the nozzle at all times... The person can not lose contact
with
> the nozzle and vehicle skin during the fuelling.
In the Netherlands (but probably entire Europe) you can't lock the
fuel
nozzle in the open position. You have to keep squeezing until the tank
if full. This ensures the person stays in contact with the fuel nozzle
all the time. Of course you can walk away but this would be pointless
because the fuel flow stops the very moment you loose contact with the
thing.
> Your wet rag idea is great, if you have really dry hands or are
messy
> like me.
I have to add that the "wet rag" is usually not purposedly wetted, but
we always carry a rag in the airplane which we use to dry the airplane
from condensation in the morning, and to clean the windshield from
bugs.
The rag usually stays wet during the entire multiple day travel,
especially because we keep the rag in a plastic bag to keep the
interior
as dry as possible. Usually it is much more difficult to find a dry
rag
than to find a wet rag. ;-) We use the very same rag to wipe off the
skin around the fuel opening before opening it.
Frans
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