On Thu, 13 Oct 2005 09:13:37 -0700, Smitty Two
wrote:

In article ,
Stealth Pilot wrote:


btw dont be beguiled by the semantics.
the glue strength doesnt change with the glue area since it is a force
per unit area measurement.
the glue area directly changes the amount of total force that the rib
fabric join can stand.
a pound per square inch strength applied to a square inch can hold a
pound
a pound per square inch strength applied over a square foot can hold
one hundred and fourty four pounds.

Stealth Pilot
Australia

I'll bite into this topic from an intellectual curiosity perspective.
What are the forces acting on a rag plane that would tug against the rib
bond? Source? Direction? Magnitude? How common are such bond failures?
What is the cause? Poor surface prep or other application shortcomings?
Deterioration of the glue or fabric over time? Other?

I'll reply for the other guys benefit. I dont know what you'll read
into this :-)

glue bonds fail over time from the stress rise at the edge of the
joint.

air pressure will create a force perpendicular to the surface.
have a look in a text at one of the manometer photos of a wing section
under test to get an idea of the pressure distribution.

the predominant cause of failure in fabric bonds is the reversing
loads created by turbulence from the slipstream off the prop. outside
of the slipstream competently bonded fabric seldom fails.
the fabric bond fails from the edge and slowly the failure creeps
inward across the joint. ribstitching in the area of the slipstream
works to correct the problem because it doesnt have stress risers
occurring at the edges of the thread.

my method of checking the stits fabric on my tailwind is to look
inside the tailcone out in the bright sunlight and pick the areas
where the uv opaquing was poorly done. I then make the "bird" with one
hand and walk along those areas banging the finger into the fabric as
hard as my hand will allow. If I ever get a puncture I'll initially
repair it. If I get areas of punctures then it is in for a refabric.
I've wanted to refabric the aircraft for a few years now but the stits
seems to have an infinite life. I cant detect any deterioration other
than in the visual appearance of the paint.

not a complete disertation but then the other guy wasnt asking much.
Stealth Pilot