Discus Cs grounded in France-long

Thanks Robert for the nice summary. Also one should mention the shrinkage
that will normally follow with the broad areas of bonding paste, which
(depending
on post-cure handling) may lead to expensive refinish for a relatively new
glider...
Best Regards, Dave

"Robertmudd1u" wrote in message
...
There are two commonly used ways to get a spar into a composite glider
wing.
There are several variations to either method.

Method 1.
Build up the spar, shear web and cap, separately of the wing. This is done
by
laying up the web and cap all at once, there are several variations to
this
step also. Lay up the wing skin and cure it.
Bond the spar onto one of the skins. This bond line is easy to control as
you
can see it going together. The next step is to pick up one of the wing
molds
and place it on top of the other. The bonding paste between the cap and
the
skin is squeezed out and controlled by the dams as the wing is closed.
When the
spar and it adhesive mixture comes in contact with the second skin the
bonding
is done. This side is much more difficult to inspect. Very careful
preparation
is needed and foam or composite dams are helpful to control the squeeze
out of
the bonding paste. Typically there is a good fit of the spar cap to the
skin on
the first skin. The second spar/skin bond line is much thicker, mostly to
insure that everything fits and there is enough room for lost of bonding
paste.


Method 2.
Lay up the wing skins and lay in the rovings for the spar cap at the same
time,
(several variations of this exist). The shear web is made separately and
its
top and bottom edges have a broad V flange that will act as a dam to
control
bonding paste flow. Once the wing and its cap are cured the shear web can
be
bonded to one skin. This bond is again fairly easy to control. Next, just
as in
method 1. One of the wing molds is lifted up and placed on top of the
other and
the bonding paste between the top of the shear web and the cap is squeezed
out
and controlled by the dams as the wing is closed.

Either way involves the bonding of long, relatively wide areas, thus
opening
both methods to the same potential for bonding problems. From a
manufacturing
point of view I do not see an advantage of one method over the other.
There may
be other considerations but both methods can work equally well and both
are
equally open to problems stemming from lack of correct procedures and
quality
control. Obviously wings using either method are able to pass the strength
requirements of the JARs.

There are pros and cons to each method. The method used mostly depends on
the
chief designer's experience and beliefs, i.e. what University Flying Group
did
he/she belong to, or what is the current method used in the factory. The
problem, I suspect, is not in the method but in the process and quality
control
existent in the Czech factory. I have seen indications of other quality
problems from this factory. I am sure SH will correct the problems and
keep a
closer watch on them. The Czechs have a proud history of manufacturing and
technical development, however a lot of that was beaten out of them by the
oppressive Soviet system.

You can easily tell which skin, wing or fuselage, had the spar, rib or
bulkhead
bonded to it first. The bond line will be much thinner and neater looking
that
the one on the opposite side. The bond line that is formed when mold
halves are
put together is thicker and may have drips associated with it.

Robert Mudd

From: ojunk (Robertmudd1u)
Date: 9/20/2003 7:30 AM Pacific Daylight Time
Message-id:

.... The Czechs have a proud history of manufacturing and
technical development, however a lot of that was beaten out of them by the
oppressive Soviet system.


Thanks for the post. I was wondering if you could cite your sources on how 13
years after the collapse of the Soviet Union the Czechs' are so repressed as to
not properly glue a wing together. I have not done a study on sociological
effects of the Soviet influence on the Czech people but apparently you have.
Are you published? I have lived in the Czech Republic and I have traveled in
Russia and Ukraine. The Czech infrastructure is much more advanced than what I
have seen in Russia or the Ukraine.

I would not want to fly, drive or own a British designed and built vehicle and
they have not suffered under the "oppressive Soviet system." The Soviet system
was proven not to work, however I do not think there is a causal connection
between the Discus problems and a failed system whose lights burnt out 12-13
years ago.

This was a German problem. The German manufacturer has licensed the
manufacture of their product, they have a duty to successfully transfer the
process with written SOP's and to establish a quality control program. Schempp
Hirth is selling these products through their dealers and buyers on buying
based on the Schempp Hirth name. The former West Germany was not under the
Soviet system either. This is a classic case of poor management, not a
social/political problem.

Looking at the inspection issue we are dealing with from a Nuclear Power point
of view provides some interesting points. (Not that you would want full NRC
approved type Quality Assurance, gliders would start at about $500,000 and come
with a second trailer full of paper!)

The owner is directly responsible for the quality of the work of any supplier,
sub suplier, etc. This can be done by
-Tthe supplier/contractor having a full NRC approved QA program. Still you are
responsible for the product and are required to routinely audit the suppliers
execution of their program.
-Preparing your own QA inspection plan, specifically written for the work being
done and placing you own qualified inspectors in the suppliers house.
-For some smaller parts or pieces that cannot be reasonably purchased in either
of the above, buying them comercially. You then have an Engineer develop what
are the critical characterics of the item and an inspection plan to verify they
are met when the piece arrives.

Also from our NDT (Non-Destructive Testing) experience, I have seen some
amazing visual inspection techniques. One is a movie taken of a spent fuel
assembly (rad levels over 5,000 R/hr) going down a .177 dia hole over 40 feet
underwater,where a fuel pin was removed. Used a video recorder on the surface
and a very expensive fiber optics "lens" that went down the hole and could be
swiviled like an eyeball. Picture was as clear as a bell.

Something like this sure could be used to inspect a wing spar glue line when it
was still fresh. Some design work would have to be done to provide a
inspection path. Inspection techniques available today leave no excuse for
something a simple as the glue up of a spar to go unispected, in real time.

Bruce Patton
596S