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