Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 22 Jul 2003 14:51:28 -0400
Message-ID: <redirect-2501010@logan.com>
From: "Robert Overmars" <robert.overmars@tiscali.it>
Subject: Hysol, conducting
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Salutti tutti,

My question about 'conducting' Hysol comes about because here in far away
Italy I have a workshop space in a corner of the Arrow Company which makes
the little Sky Arrow aeroplane. Arrow is restarting the design/building of
their next project, a four seat Frati design all carbon fibre aeroplane.
From time to time Arrow engineering people come down to the LIV reparto to
see how our LIV is progressing and we talk about all things aeroplane and
one of the considerations of building in carbon fibre which is lightning
protection. This is an important matter for them as they intend to build a
certified aeroplane and lightning protection I understand is a requirement
of this.

Arrow have elected to build their fuselage halves with left and right parts
with the joggle in the vertical plane. This leads to the question of how to
protect this bond in the event of a lightning strike especially so that with
the joggle in the vertical plane it sits in a zone more likely to be struck
by lightning  than for instance the Lancair IV's horizontal fuselage joggle.
One way  used I understand, to protect the fuselage bond (and other parts of
the aeroplane most likely to be struck by lightning) is to lay an expanded
copper foil over the joggle extending down the fuselage sides,  the copper
then being a better conductor carries and disperses the lightning current.
If for instance there is no copper foil over the joggle then lightning
current must pass across the joggle, from the carbon fibres of one half of
the fuselage shell to the carbon fibres of the other half of the fuselage
releasing lots of energy passing through a non conductor, that is the
adhesive bonding the parts together possibly resulting in debonding...which
could really ruin one's day.

Relating this back to the LIV wing the top and bottom skins are bonded
together in a joggle just under the leading edge.....in what I recall is a
Zone 1 lightning strike area. For sure lightning current will arc straight
through the joggle adhesive releasing lots of heat but by electrically
connecting the carbon fibres of the top and bottom skins I hope to preclude
the likelihood of damage to the leading edge joggle bond...especially
considering that it forms the leading edge of the fuel tank. What I'm hoping
to do is this: in the event of a lightning strike to have a structure, that
is the carbon fibre shell  which provides few, if any, points of high
electrical resistance for the lightning current to develope lots of
localised heat, except that is at the entry and exit points where obviously
the lightning current is concetrated. This also means connecting major
carbon fibre parts such as wing skins to the fuselage skins with conductors
capable of carrying lightning currents and also looking at other ways that
lightning currents can travel around the airframe such as through pushrods
and providing suitable protection, and also connecting the metal engine
mount to the solid carbon fibre longerons that extend down the left and
right sides of the aircraft with suitable lightning capable conductors.

I've sourced a supply of silver powder/flakes which is specifically
manufactured for inclusion in epoxies to provide electrical conductivity.
It's far cheaper by the way to buy the silver powder/flakes and mix one's
own rather than buying very expensive conducting silver epoxies.

Ciao,

Roberto d'Italia.