Posted for N301ES <lancair@ustek.com>:

 Tim,
 
 We guessed at a few possibilities for the reduction but once the it was
demonstrated we moved on to other things.  Metallized carbon composites did
not exhibit this same loss in effectiveness so we went with the winning
technique instead of trying to improve the loser.
 
 The aging involved temperature cycling (equipment gets hot when on and
 field sites get cold when off).  We thought that this permitted microfissures
within the coating layer.  These slots re-radiate at frequencies depending on
their length and that would diminish the effectiveness of the ground place.
 Paints use roughly spherical grains of metals whose oxides are electrically
conductive - nickel and silver.  So long as the particles are close to each
other the film is quite conductive even though the metal has reacted with
oxygen, water, or whatever else migrates into or through the film.  Fissures
are a different matter.
 
 Metallized fibers (glass or graphite) have a much higher aspect ratio and the
overlapping and interweaving makes it less likely for a fissure to open.  We
showed higher effectiveness with graphite than glass but that was in melt
processed compounds.  In a layup I would not expect much if any difference.  I
was able to get samples of a non-woven metallized graphic scrim so that is
what I tested for the ground plane.  Had I equal access to metallized glass I
would have tested that as well.
 
 Our aircraft are subjected to similar temperature excursions to the testing
done, and in addition also deal with vibration, flexing, and in the case of
the ES-P and the IV-P stretching due to pressurization.  The best plane for
the plane might be plain Al sheet.  Not as cool though.
 
 Robert M. Simon,  ES-P N301ES