Ref. J.E. Gordon's book, "New Science of Strong Materials"

I should have given this link in my earlier posting.  Gordon's books --
he has another one called 'Structures,' which is equally great -- are
available at Amazon.com.  They've been re-issued over the years.
  http://www.amazon.com/Science-Materials-through-Princeton-Library/dp/0691125481/ref=pd_bbs_sr_1/002-1730731-3328012?ie=UTF8&s=books&qid=1175270159&sr=1-1

I imagine that the European Amazons can get the book as well.

Gordon referred to the problem with the plywood as 'case-hardening,'
a term that's principally used in metallurgy, but applicable here.
His illustration shows the cellular tubes extending slantwise, their
open ends burnished over by the rollers, the glue unable to penetrate.
What they finally had to do was 'shot-blast' all of the plywood that
came through the works.

It should be noted that the 'case-hardening' problem was not a common
one and appeared on only occasional pieces of plywood.  However, you
don't want the wings to fall off _any_ of your airplanes.

Gordon is a marvelous writer.  There were lots of wooden aircraft
in World War II, and they were a constant source of difficulty.
Mice would get inside them (there was an official issue of cats by the
RAF) and if you didn't drill the drain holes in the wings properly,
the inevitable water buildup wouldn't drain out and there would be rot.
On occasion, grass seed would blow in, and then you'd have a flying,
internal garden.

Life was tough even when the experimental glues did their jobs.  On the
other hand, he says, wooden aircraft can last virtually forever when
things go right.

Mark Kinsler
Lancaster, Ohio, USA
http://www.mkinsler.com/
http://howthingsoughtawork.blogspot.com/