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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