DuoDiscus Wing

"Duane Eisenbeiss" wrote in message
news:3fRab.527488$uu5.88216@sccrnsc04...
Enough time has past such that several DuoDiscus wings must have been
inspected. However, there have been no reports as to what was found
during
the inspection or what, if anything had to be done. All owner should
communicate with each other so that we all can have a better handle on
what
is happening to the fleet.
Duane

The report for the inspection of ship S/N 217 has been received. The left
wing had 1 small void. The right wing had 4 small voids.

Has anyone had an inspection that revealed large voids? say larger than 12
inches or 30 cm.

Duane

One here in NZ had a void of 14-15 inchs long,the engineers here think
the problem has been from making the glue mixture to thin and it has just
flowed out of the rear side as there is a ridged edge on the front side to
make all the mix go towards the rear.
One comment made was they thought that the factory had attempted to
push some mix into that void by hand by reaching through the access point
but had only been partially successful
gary
"Duane Eisenbeiss" wrote in message
news:rQDhb.533114$Oz4.430152@rwcrnsc54...

"Duane Eisenbeiss" wrote in message
news:3fRab.527488$uu5.88216@sccrnsc04...
Enough time has past such that several DuoDiscus wings must have been
inspected. However, there have been no reports as to what was found
during
the inspection or what, if anything had to be done. All owner should
communicate with each other so that we all can have a better handle on
what
is happening to the fleet.
Duane

The report for the inspection of ship S/N 217 has been received. The left
wing had 1 small void. The right wing had 4 small voids.

Has anyone had an inspection that revealed large voids? say larger than
12
inches or 30 cm.

Duane

"goneill" wrote in message ...
One here in NZ had a void of 14-15 inchs long,the engineers here think
the problem has been from making the glue mixture to thin and it has just
flowed out of the rear side as there is a ridged edge on the front side to
make all the mix go towards the rear.
One comment made was they thought that the factory had attempted to
push some mix into that void by hand by reaching through the access point
but had only been partially successful
gary
************************************************** ********************************

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.

"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.

--
bumper - ZZ
"Dare to be different . . . circle in sink."
to reply, the last half is right to left


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"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.

On 14 Oct 2003 22:56:24 -0700, (Slingsby)
wrote:

"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.

Two comments:

- viscous, sticky stuff like epoxy will tend to leave a larger void or
none at all. I think a series of deeper bubbles would be far more
likely than a single sub 0.1mm area.

- it would be extremely difficult to get epoxy into a very narrow void
unless it was rather thin

Does anybody on here know what advantage cotton threads would have
over, say, microballoons or separated glass rovings?
--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

First of all, it is not the epoxy which bears the load but the cotton
threads. Epoxy is just the matrix, and the rated load of cotton/epoxy is
around 7N/mm.

Microballons are much heavier and the composite formed of balloons/epoxy
doesn't hold the same load as cotton threads/balloons (balloons are spheres
so in this case it's the epoxy which finally bears the load). Microballoons
are rather used for surface cosmetics.

Seperated glass rovings would be ideal - but the beasts don't bend easily
into small radii if threaded and a paste made up of them would leave many
mm-sized voids. so it just doesn't work.

I think that people proposing utrasonic quality checks don't have an exact
idea how a wing is constructed. Utrasonic QC basically detects interfaces,
and a composite glider wing is made up from interfaces all over the place.
I'd say that the error rate in an utrasonic QC would be completely through
the roof.

I think it would be more easy (and straightforward) to do just a structural
load test up to 1.5 times max rated load :-)

--
Bert Willing

ASW20 "TW"


"Martin Gregorie" a écrit dans le message de
...

Does anybody on here know what advantage cotton threads would have
over, say, microballoons or separated glass rovings?
--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :