On Thu, 15 Apr 2004 16:39:33 -0400,
wrote:



Ernest, it isn't the dope that provides the strength, not with
Razorback fabric or with any fabric. The fabric itself is what gives
the wing it's strength and/or stiffness against the wind. The initial
application of the correct dope, in the case of the Razorback fabric,
or a calibrated heating iron, in the case of the Polyfiber fabric, is
what shrinks it.


Corky Scott you surprise me cobber. mistakes like the one contained in
the paragraph above are what led to Steve Wittman's death.

in the case of cotton, irish linen, razorback and any of the non
shrink fabrics it IS the dope which causes the fabric to tighten as
the solvents evaporate from the dope.

polyfiber is unique in that the fabric is applied in the grieged state
and ironing it at the appropriate temperature shrinks it to create
it's taughtness. the vinyl finishes applied have solvents in them to
displace the manufacturing lubricants in the fabric. the vinyls simply
fill the weave.

dopes should not be applied to polyester fabrics that still have the
manufacturing lubricants in them. they will simply not adhere. even
on clean fabric the dope does not penetrate the fibers.

my Auster had a section of the turtledeck applied this way and once
cracked the finish peeled off with about the tenacity of a 3m post it
note also there is a ceconite covered piper cub on the local
commercial field that has areas of the underside wing finish held in
place with tape because it has peeled away.

dopes work well with absorbent natural fibers.
polyfiber is different in the way it works.
make the mistake of mixing the two and the headlines will be
"Corky Scott's fatal accident identical to Wittman's, when will they
ever learn?"

end of safety lesson

Ernest if you are an EAA member hunt out the construction articles in
Sport Aviation for an aircraft called "ol' Ironsides".
it is a wood frame single seat wittman tailwind I think. the
construction techniques were quite well described and are epoxy/glass
panels as you have been asking about. the guy used the polished faces
of masonite sheets with release agent to do his layups. the resultant
sheets were then bonded to the framework. afaik it is still flying.
the articles were quite charming - well written. lots of photos. a
good aircraft I think.

(you're forgiven corky. it is THE fatal error with fabric finishes and
it must be understood or people will die. simple as that.)
Stealth Pilot
Australia.