Hello,

we have a sailplane that had some water inside one of the wings.
The sailplane is made in GFRP.
The sailplane was disassembled and stored but a nearby water pipe has
broken and sprayed some water inside the wing about 5-6cm (2-3in.)
deep along the leading edge.
The problem is that it happened during the winter and most probably
the water has FROZEN!!!

Visual inspection of the outside has given NO signs of damage!

We were planing to send the glider to the nearest authorized workshop
BUT someone with knowledge in GFRP says that inspecting GFRP for
damage from frozen water is quite complex and that only a few BIG
companies have such facilities/technology/know-how to do it!

Does anyone know anything about this subject or has more experience in
dealing with GFRP?

We are especially interested in the technology of such inspection,
which instruments are used, what are the most important tests and so
on!
You do not have to go into details, just enough info so we can ask the
workshops if they have that technology and/or know-how!

Blue Skies
Vladimir

On Apr 7, 6:24*pm, Vladimir > wrote:
> Hello,
>
> we have a sailplane that had some water inside one of the wings.
> The sailplane is made in GFRP.
> The sailplane was disassembled and stored but a nearby water pipe has
> broken and sprayed some water inside the wing about 5-6cm (2-3in.)
> deep along the leading edge.
> The problem is that it happened during the winter and most probably
> the water has FROZEN!!!
>
> Visual inspection of the outside has given NO signs of damage!
>
> We were planing to send the glider to the nearest authorized workshop
> BUT someone with knowledge in GFRP says that inspecting GFRP for
> damage from frozen water is quite complex and that only a few BIG
> companies have such facilities/technology/know-how to do it!
>
> Does anyone know anything about this subject or has more experience in
> dealing with GFRP?
>
> We are especially interested in the technology of such inspection,
> which instruments are used, what are the most important tests and so
> on!
> You do not have to go into details, just enough info so we can ask the
> workshops if they have that technology and/or know-how!
>
> Blue Skies
> Vladimir


Was the water that may have frozen, in a confined space in the wing
that was completely filled up with water, or was there just some water
that had gotten into an open space the wing? Expanding water (ice) if
not in a filled, enclosed compartment should not cause a problem. No
cracks at the leading edge? Delaminations can usually be found by
tapping lightly with a metalic object. Borescopes would allow you to
see inside the wing.

Good luck.

Mike

Questions like this come up a lot here. My thoughts as always, are
ask a certified mechanic with repair experience/authority on your
particular make and model. If you can't find such a person, contact
the Mfg. They are the Overarching Authority in a case like this,
unless of course they are out of business, where you have other
options. Before you do, read the repair manual so you can accurately
describe the water location.

FWIW, The HK-36 has an excellent treatise in the way of a S/B on this
problem, albiet in the spoiler box, not the wing LE. Google up the
Diamond_at (Austria) website at look at the service bulletins.
Sorry, I am not going to take the time to reward your post on RAS
with an easy link!.

For visual inspection, you don't need a boroscope anymore than you
would use a film camera. I am sure you know someone with a newer
digital camera you can borrow or rent- Most have HD video
capability. Again, a competent repairman can best interpret/document/
sign off the results, and with the right materials can cut a hole and
repair it if you don't have an access hole where you need it.

Most people that work at the big companies are not exposed to the
specific aspects of glider construction at the workplace. If they
did, they would probably say to contact the Mfg or repair station with
a appropriate licence - that is what their customers do. BTW, NDI
methods such as ultrasound (A, B, and C scan), lazer UT, shearography
and X-ray require a standard, your source seems not to have mentioned
that to you.

Don't suprised if a repair station wants to see the ship and charge
for an inspection. That means they are likely trying to be competent
and responsible, or at least limit liability. Spend the money and
time to get an legal/expert opinion. This board IMO is not exactly
the glider equivalent of WebMD...

BTW, are you sure your ear is good enough to tell if there is a delam
in the inner most plies of the solid laminate of the LE overlap
splice? If I was water, that's where I would go, right through the
exposed edges of the trimmed sandwich shell laminate at the splice.

Not trying to scare you, I think you can get this resolved quickly,
leagally, and possibly have insurance cover the cost!

aerodyne

!
>>
>> Blue Skies
Expanding water (ice) if
>not in a filled, enclosed compartment should not cause a problem..


Try putting a half filled jar of water in a freezer compartment overnight.
I think you'll notice a problem.

On Apr 8, 12:48*am, Mike Oliver >
wrote:
> !
>
> >> Blue Skies
>
> *Expanding water (ice) if
>
> >not in a filled, enclosed compartment should not cause a problem..
>
> Try putting a half filled jar of water in a freezer compartment overnight..
> I think you'll notice a problem.

Wings are not made of brittle glass for a reason.


But your point does point to the probablility that the wing would fail
at a weak point, in this case probably the leading edge seam, that is
basically a reinforced epoxy/filler glued toggle that results in a
large squeeze out on the inside of the wing. The squeeze out would
make it very difficult for water to get into that seam. Now if water
got into the seam somehow or even between some of the squeeze and a
skin, and froze, IF anything would happen it would most likely be a
split in the leading edge. The borescope would show any delaminations
in the inner ply of glass fiber, where the water was trapped, by
appearing milky in color - borescopes give amazing clarity and detail
inside a wing. When viewing the inside of a wing, borescopes are
prefered because they have a remote screen where detailed inspections
can take place in real time. A simple video camera or film camera does
not allow this to be done, especially in tight areas. Carbon would be
more difficult to check for delaminations.

Actually I would be just worried about 3" of water in the leading edge
for several months, having seen the results and worked a bit on a
leaking Ventus water ballast tank.

But this is just speculation on my part. Off course the sailplane
should be taken to a composite repair shop, or manufacturing facility,
like the ones I have worked in, to have it checked out by a qualified
aircraft mechanic and inspector.

Mike

On Apr 8, 2:12*am, mike > wrote:
> On Apr 8, 12:48*am, Mike Oliver >
> wrote:
>
> > !
>
> > >> Blue Skies
>
> > *Expanding water (ice) if
>
> > >not in a filled, enclosed compartment should not cause a problem..
>
> > Try putting a half filled jar of water in a freezer compartment overnight.
> > I think you'll notice a problem.
>
> Wings are not made of brittle glass for a reason.
>
> But your point does point to the probablility that the wing would fail
> at a weak point, in this case probably the leading edge seam, that is
> basically a reinforced *epoxy/filler *glued toggle that results in a
> large squeeze out on the inside of the wing. *The squeeze out would
> make it very difficult for water to get into that seam. *Now if water
> got into the seam somehow or even between some of the squeeze and a
> skin, and froze, IF anything would happen it would most likely be a
> split in the leading edge. *The borescope would show any delaminations
> in the inner ply of glass fiber, where the water was trapped, by
> appearing milky in color - borescopes give amazing clarity and detail
> inside a wing. When viewing the inside of a wing, borescopes are
> prefered because they have a remote screen where detailed inspections
> can take place in real time. A simple video camera or film camera does
> not allow this to be done, especially in tight areas. *Carbon would be
> more difficult to check for delaminations.
>
> Actually I would be just worried about 3" of water in the leading edge
> for several months, having seen the results and worked a bit on a
> leaking Ventus water ballast tank.
>
> But this is just *speculation on my part. *Off course the sailplane
> should be taken to a composite repair shop, or manufacturing facility,
> like the ones I have worked in, to have it checked out by a qualified
> aircraft mechanic and inspector.
>
> Mike

I would think that if the ice had done any damage to the laminate, it
would have left visible damage to the gell coat. That said, ultrasonic
is the definitive testing method for composite structures. A
transducer sends an ultrasonic pulse that reflects off the inside
surface and is picked up by the same transducer. Delamination will
cause reflections at points were there shouldn't be any. An
alternative to ultrasonic is to tap lightly with a plastic mallet;
delamination will change the pitch of the sound. A digital
oscilloscope and microphone would be another approach.

Tom