I would say that the polyethylene fuel tank of the composite Europa is
in a particularly favourable position with regard to static discharge.
The hazard in refuelling a metal aircraft is that static generated by
fuel rushing through pipe and being collected in a metal tank could
build up a charge at a high voltage which is free to travel through the
metal to discharge to a grounded object such as the fuel filling nozzle.
In the case of a polyethylene tank the charge cannot conduct through the
tank to discharge anywhere. The only hazard would be if there were
sufficient metal parts in the tank which could collect the charge and
then conduct back to the fuel cap. To ignite fuel vapour a certain
discharge energy needs to be exceeded and I doubt whether the fuel
filler cap has sufficient capacitance to store sufficient energy. If the
metal parts of the fuel system are all connected back to the metal fuel
cap then there would start to be a problem which would have to be solved
by earthing the fuel nozzle (or metal fuel can) to the filler cap.
Ken Whiteley
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