REFLECTOR: Grounding Point

[Alex Balic]

Hey Al,
I don't think that there is too much charge differential building up during
actual fueling operations, I would think that when the fuel is flowing the
charge could pass freely from the tank to the nozzle via the surface of the
fuel and thereby keep the potential at or near zero- I will check up on this
though..............I believe that the problem is that a spark occurs
between the fuel nozzle and the aluminum cap, or between the nozzle and the
skin in the vicinity of the cap when the two are brought into close contact
just prior to fueling- assuming that the aircraft is not "grounded" to the
fueling point.  There can be a lot of charge differential between the
aircraft and the fuel truck due to many different reasons, and I am just
trying to figure out the best way to make the differential zero before the
fuel cap is opened, and/or placing the brass safety screen in the filler
neck to prevent fire from entering the tank.
 Like I said in a prior post I got severely jolted once re-fueling from a
ground based pump station because I had the ground clip in one hand and
touched the spam can I had just finished flying with the other- a mistake I
will not repeat- and if I had fuel on my hand at the time I am pretty sure
it would have ignited...
About the chain- I was referring to the design that has the ball chain
attached to the fuel drain line and it rolls around in the bottom of the
tank- a chain that makes it into the fuel and attaches to the cap would
certainly make more sense- and I think that touching the fuel ring with the
nozzle before opening the cap would help as well.
Alex








 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Al Gietzen
Sent: Monday, October 25, 2004 9:59 AM
To: alex157 at direcway.com; 'Velocity Aircraft Owners and Builders list'
Subject: RE: REFLECTOR: Grounding Point


  Subject: RE: REFLECTOR: Grounding Point



  the fuel itself is non conductive, it is the charge that is stripped from

  the surface of the flowing fuel that builds up on the surface of the skin

  and metal parts that causes the problem, the metal chain in the fuel trick

  is not effective, since there is not any way for the charge to pass to the

  chain.



  Alex;

  Knowing how to deal with this issue would be easier if there was a
consistent understanding of what is happening.  Yes, the fuel in
non-conducting, as is the fiberglass skin. But the static charge does travel
on the surface of both.  If it didn't, there would be no possibility of a
discharge, and no problem.



  My understanding (which I thought was consistent with the conclusions from
the last go around on this) is that a potential (static charge) builds
between the fuel surface and the nozzle because of the electrons being
stripped from the fuel by the surface of the hose and nozzle; creating the
possibility for a discharge from the fuel surface to the nozzle.  Metal
contact at the fuel surface (the chain) provides a conducting path to the
cap ring and, by contact, back to the nozzle/hose; thereby eliminating any
spark.



  Or is my understanding flawed and oversimplified? Maybe there can be a
pre-existing potential difference between fuel truck/fuel pump and the
plane.  Maybe no one really knows what the problem is.  If they do, let me
know.



  Al




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