Sounds reasonable to me. So, if I where comparing wing loads of
plywood
and fabric, how would you suggest I measure this against composite or
other materials? I'm open to suggestions.
Lou.



Maule fabric punch?

I don't think so.

The punch test tells you if your fabric is rotten, or not. The load it puts
on the fabric is a result of testing to know how much force the punch should
be able to apply, and not have the system of fabric and attachment fail, or
not.

If your punch test fails, you could develop a long rip , or a rip at a
stitch and/or glue by the rib, or in the middle of the fabric, and it could
let you fall out of the sky.

A point load like a punch is not the kind of load the (lets say) top fabric
will see. It will be an evenly distributed load, pulling up, with the glue
or stitching (on the ribs) resisting the upward lifting forces. The load at
the ribs would be a long attachment, or lots of small point loads from the
stitches, but still, the dope should be gluing the fabric to the ribs, also.

So, if there is two feet between the ribs, and the bay is 3 feet long, you
have 6 square feet of area. If you have a 20 pound per square foot wing
loading, you could have 120 pounds of force pulling at the attachments of
the ribs and spar caps. (front and rear spars) You want to know if the
fabric will fail or hold at those pressures.

You could make an airtight box with an open top, of 2' X 3', which would be
864 square inches area of the top. Glue and stitch the fabric on the top
flange (same sizes as the ribs or cap, and spar caps) of the box and put
120 pounds of force on the fabric, which would be 864 sq inches/120 lbs per
sq ft = 7.2 psi air pressure inside of the box. If it holds, you might not
fall out of the sky. g

You could then substitute the material you want to test for this application
(plywood, fiberglass, fiberglass/foam sandwich, aluminum foil g, or
whatever you want to test, and whatever holding method you want to use, and
test it.

That's my thinking in/out of the box, so to speak. Right, or wrong. I
don't know. It is how I would likely go about it. I'm not an aeronautical
engineer. I did stay at a Holiday Inn last night! ;-)
--
Jim in NC