On Sun, 27 Feb 2005 17:13:07 GMT, "Cy Galley"
wrote:

I'm sorry but your airplane is not just like a large lawnmower. You dump
small quantities of gas into your lawnmower. The longer you pour the larger
the static charge. Pouring small qualities is safer than dumping an entire
can. Grounding the can, funnel and tank together DOES help. It prevents
that charge from building to the point of discharge and explosion.

You can also point to fueling a car as a NON-grounded application but you
couldn't be farther from the truth. Look at the UL or DOT label on the
hose. It MUST be a conductive hose meeting certain specs.

Remember the longer you fuel, the larger the charge. The more important
grounding becomes as well.

One thing this doesn't take into consideration.

"Grounding an airplane" to ground works when the fuel source is
grounded but does absolutely nothing for static discharge when fueling
from a can because it does nothing to equalize the charge differential
between the can and the airplane.

We need to realize that static electricity is like any other DC
voltage. It is "The potential difference" (the definition of voltage)
between two points and in the case of filling from a can one of those
points is not ground. One is the can and one is the airplane.

The static charge comes from the fuel flowing out of the can and the
process works like a Vandegraf generator. It does not come from
moving the can or swirling the gas in the can.

Once a solid fuel stream is flowing from the can to the tank and the
operator is against the metal airplane you have effectively reduced
the systems ability to build a charge.

Even with the underground fueling system, *IF* the proper procedure is
followed there will be no potential difference developed. HOWEVER in
the case of the underground fuel system the operator/owner has no way
of knowing if the user is going to touch the nozzle to the bare metal,
open the tank, insert the nozzle and maintain contact against the edge
of the metal take while fueling. The underground system also operates
and a higher pressure and substantially higher flow rate than pouring
out of a can, hence it would have a much higher potential for
developing a high potential difference were the hose not conductive
and the plane not grounded.

IF the source and destination are held at the same potential the
static can not develop.

If you are holding the can and touching the metal of the airplane the
electrons flowing out of the can with the gas, flow through the
airplane, through you and back to the surface of the can even though
it is plastic. Certainly it would be better if the can were
conductive but that doesn't usually seem to be a problem.
it takes very little conductivity to keep the charge neutralized, but
it does take some.

When filling from a can, I'd guess the worst possible conditions would
be holding the can up and pouring into an open funnel where the
operator holding the can is insulated from the plane

Normally you are in more danger when filling the plastic can at the
pumps than when pouring it into the airplane, unless of course you
hold the tank way up and pour through the center of the opening while
avoiding contact with both the airplane and can.

BTW, the ground to the plane from an underground system removes the
likely hood of a spark when initiating the fueling if procedures are
not followed.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com