DuoDiscus Wing

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.
I wondered, as the fibreglass on my glider is a translucent green but
I am not sure I am looking at bonding paste which has cotton fibres in
it.

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.

I would guess that if the spar caps didn't get bonded correctly on
several wings, then the ribs in the D-tube, the tops of other ribs,
the air brake box and other areas of the wing didn't get bonded
correctly on some wings also. Shemp-Hirth should be looking into this
and possibly cutting some wings open. Especially wings with known
voids in them.

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.

It could also be that the only entities with ultrasonic equipment
capable of doing the inspections are major airlines and the military.

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.

Its at least as safe as the G103 fuselage which is now speed and acro
limited because the "margin of safety" is not as great as they shought
it was. Until a couple of weeks ago I would have said that the G103
was one of the strongest, most durable, over engineered, tolerant of
abuse soaring trucks ever produced.

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.