Rib stitching vs glueing

wrote:

...

I also recall reading somewhere that the glue area doesn't really
affect the strength of the bond between the fabric and wood rib ( which
I can't believe )
...


IIRC the explanation runs something like this:

When the fabric is glued to the rib some of the glue extends
slightly down the side of the rib/ribcap forming a sort of
bead or fillet, the rest forms a ribbon of glue between the
fabric and the ribcap.

As the fabric lifts from the rib the bead/fillet is stressed
in shear, while the ribbon is stressed in tension. The glue
is much stronger in shear than it is in tension, so if the
bead/fillet fails, the fabric will then peel away from the
broad flat surface of the rib cap. No matter how wide the
rib cap is, as the fabric peels the stress is concentrated
on a thin line adjacent to where the fabric has already
pulled away.

The bead/fillet is independent of the width of the rib/ribcap
hence the conclusion that the width does not matter.

Another conclusion is that, no matter how wide the rib caps
are, one should make sure the glue extends all the way to the
edge.

This suggests that the bond might be improved by running grooves
circumferentially around the rib caps. Sort of like what is
called 'tooth' in veneer work.


--

FF

On 12 Oct 2005 14:33:47 -0700, wrote:



Thoughts? Thanks

Neal

On my 20 year old Jungster II I attached the fabric to 1" wide
capstrips. They were not varnished, they were generously coated with
Goodyear Pliobond. The wing was then covered and the ribs were brushed
over with acetone or MEK, I forget which to pull the adhesive up
through the fabric. So far so good and up to 170 mph in a dive.

The technique Tony Bingelis was refering to in his book was covering a
plywood covered aircraft in model airplane weight fiberglas. I used
the same material for the last layer on my wing and empennage tips as
well as the leading edge. Makes a real smooth finish without excess
filling.

Ed Sullivan

Ed Sullivan (a really big show tonight) wrote:

...

The technique Tony Bingelis was refering to in his book was covering a
plywood covered aircraft in model airplane weight fiberglas. I used
the same material for the last layer on my wing and empennage tips as
well as the leading edge. Makes a real smooth finish without excess
filling.


Adding a layer of fiberglass must greatly inprove the stength,
durability, impact reisstance and water resistance, that is why
it's freqently done on plywood canoes, kayaks and small boats,
as well a producing a smooth finish.

If a smooth finish over wood is the only goal, then surely covering
with fiberglass is a lot of unecessary work. Fine Furniture makers
have been starting with rough wood and producing a very smooth
surface for a couple of hundred years. Grain filler and a cabinet
scraper (NOT a paint scraper) should do the trick for the airplane
builder.

--

FF