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<< Lancair Builders' Mail List >>
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I agree with Chris who says, "In Australia it seems to be accepted as good
practise to electrically bond all the metal bits especially in the fuel
tank area" The spam cans all do it here in the USA too.
I think the main reason for electrically bonding all metals and other
conductive surfaces is to prevent in flight arcing which causes a lot of
obnoxious RF interference. I'm building the carbon fiber 360, each panel is
a conductive surface insulated from the other nearby conductive surfaces
with a thin layer of Hysol. In flight, all these conductive surfaces are
going to be at different charge potentials. Static charge is proportional
to the surface area times the wind velocity squared, (same as drag). The
way I see it is that the propeller is going to have the highest charge.
Since this is connected to the engine which in turn is connected to all the
wiring, all the avionics are going to be at a slightly higher potential
than the rest of the plane. Next I think the wings, then next the body. It
doesn't really matter which is higher or lower all that matters are that
they are going to be different. All these different potentials are going to
create a lot of arcing in flight, especially at high altitudes. This arcing
will generate RF interference in the radio and Navaids. So, I am planning
to put a tinned copper braided ground strap going to every panel and
surface that is out in the slip stream and epoxy this with some conductive
epoxy. This will also go to the filler cap mounts and finally bond to the
engine block. I thought about adding carbon powder to the Hysol, but I
don't want to get that experimental. To emphasize how important this is,
even the aluminum spam cans have ground wires going to all the different
panels. For example, If you look at an aileron in a spam can, they have a
ground strap on it even though it is connected with a metal hinge, just to
make sure there is no temporary break in ground. Since these spam cans
ground everything and they don't even go as fast as our 360's, I figure it
must cause enough trouble that I should probably ground everything too.
Ed Armstrong
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Please send your photos and drawings to marvkaye@olsusa.com.
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