DuoDiscus Wing

Simple fix was to make sure the mix of chopped cotton and resin was thick
enough!
Maybe the problem is when they mixed the resin and cotton together, the
temperature of the resin was relativity low which made it more viscous and
while the whole thing was heat cured, the viscosity of the resin decreased
and ran before gelling. The rotating jig is a good idea but the size of the
reinforcing to keep the wing true would be problem. ( and expensive :-)
Paul
"goneill" wrote in message
...
One simple fix would be to have the entire assembly on a rotating jig and
have the leading edge
45degrees nose down while curing
"John Galloway" wrote in
message ...
My understanding is that any part of the rear flange
that is not actually bonded will show as a 'white'
area even if there is no visible or probe-able gap.
The thin flange is being bonded to a black spar cap
and resin bonded to both surfaces gives the see through
effect.

As the resin gets squeezed out from the front to the
back apparently if no voids reach near the shear web
there aren't going to be any farther forward.

The factory have looked at ultrasonic inspection and
have been that it won't work for the spar problem because
of all the diferent layers it would have to look through
- apparently.

If there are continuous stalactites or curtains of
resin hanging from the rear spar flange and no visible
voids or white areas the spar is safe.

All this is stuff from various reliable sources at
various times but there is a need for a full statement
IMHO - I hope it will happen once all the inspection
data have been analysed

John Galloway


At 06:00 15 October 2003, Slingsby wrote:
'John Morgan' wrote in message news:...
'Slingsby' wrote in message

It would be interesting to know if there is a commonality
between all
of these discrepancies. Was the bonding paste always
too thin or did
they mix it according to the clearances of each wing?
If the mixture
really was too thin causing a void of 14-15 inches
long then there are
probably many other voids which can't be seen on
video. There needs
to be an ultrasonic inspection procedure developed
which can map the
bonding interface.


I have no first hand knowledge. Talked to the owner
of a well known,
respected composite repair shop who said that cotton
threads are added to
the epoxy to thicken it and keep it from running.
And that apparently they
had failed to add enough cotton fiber and this resulted
in epoxy running
out, creating the voids.

According to the DG website the bonding paste should
be about as thick
as cake icing. I suppose too much cotton would also
weaken the bond
as cotton fibres aren't as strong as epoxy. I still
believe that if
there are voids which can be seen and can have wires
poked into them
then there must also be voids which can't be seen and
are far to thin
to allow wire into them. A .0005 to .008mm thick gap
between the spar
cap and shear web could not be seen on a video but
it would still be
an area where there is no bond. Ultrasound would still
reflect off of
the interface and show a gap. The ultrasonic technique
would need to
be proven and calibrated on actual wings where voids
have been found.
Filling the voids immediately makes the chances of
developing another
inspection method unlikely.