REFLECTOR: Grounding Point

[Alex Balic]

John, I would bet that the brass screen is available through McMaster Carr-
that is where I will go to get mine- they might even have brass screens
already formed to the correct size for our use- the ones that come with the
OSHA cans are too small in diameter.
  -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of John Dibble
  Sent: Friday, December 03, 2004 11:27 AM
  To: alex157 at direcway.com; Velocity Aircraft Owners and Builders list
  Subject: Re: REFLECTOR: Grounding Point


  After the previous round of discussion, I've been trying to understand
this ground issue.  I've noticed as the weather gets colder and drier that I
infrequently get a shock.  It seems that for the shock to happen I need to
first rub something and then touch something that is GROUNDED, like a water
faucet.  So it seems to me that an electrically insulated fiberglass tank is
actually a good deal and why do we want to provide a ground where a static
charge can discharge??
  Also I think it is unlikely that flowing fuel can develop a charge.  >From
what I remember about boundary layer theory, the fuel molecules adjacent the
hose/nozzle "stick" to the hose/nozzle surface and do not move.  There is a
gradual transition of fluid velocity between the hose/nozzle surface and the
bulk of the fluid flow.  So there is little opportunity for the fuel to
"rub" against the hose/nozzle surface and develop a charge.
  I think the safety screen is the best idea.  Where can I get or make one?
  John

  Alex Balic wrote:

    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
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