Jan de Jong wrote:
> Yesterday I remembered belatedly that plastic moving on wool (and
> plastic on plastic) can lead to static charge buildup and sparks.
1) Restrict the movement. Ideally, you want to make the tank fit
precisely, so it won't shift during turbulence or scarobatic
manoeuvrings. It will then only move a bit because of thermal changes,
or when the fuel level (and hence weight) changes. This is not enough to
produce a significant amount of static electricity.
2) I wouldn't use a conductive layer on any side of the tank. This will
create a conductive path for anything that has a potential to spark. If
there is no conductor, it is difficult to get a spark. Localizes spots
of static charge won't spark, UNLESS there is a conductor that allows
these charges to collect together, create a massive force, and make them
jump to... something else where they can continue their travel.
Actually, the worst thing you can do is to make both the inside and
outside of the tank conductive, as then you have created a very large
capacitor, very able to build up a large charge, and with the potential
to spark through its dielectricum, that is, the wall of your tank. The
charge will then, due to the conductive layer, search for the weakest
spot, and the entire charge of the tank will spark through this weakest
spot.
3) Don't fix what ain't broken. There are no reports or even suspicions
that any Europa exploded due to static charge buildup of the tank and
ignition of the fuel.
Consider this: if you rub a balloon (these things used for party
decoration) over some plastic, these things will build up huge amounts
of static electricity. They will raise your hair easily from quite a
distance, or stick to a window or ceiling just by their static electricity.
Although they are building up huge amounts of static electricity, never,
never, will this electricity spark to the inside of the balloon (and
thus destroying itself by piercing the latex).
I believe balloons can be forced into building up more static
electricity than you will ever encounter in your Europa tank. And I also
believe that the skin of the tank is much thicker than the skin of the
balloon. ;-)
I wouldn't worry about it, as long as you don't make the tank
conductive. Keep it as is, don't bond it it, but restrict its movement.
Frans
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