"John Morgan" wrote in message ...
"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.