The mirror., 1919-09-25
A WOOD STRONGER THAN STEEL
How Waterproof Pywood Discovered by Yankee Experts
Revolutionized Anplane Construction.
By E. T. Bronsdon in Popular Mechanics.

n Popular Mechanics.
capable of sustaining 254 lb. with
a total weight of $50 o., the ply
wood rib has improved still fur
ther. The rib last used on the De
Haviland weighed 5.12 o., and
could carry 274 h.; this was a
clear ledge" for plywood of 1915
per cent in strength per ounce of
weight. Only an airman, trusting
his life continually to the wings of
his cloud steed, can appreciate
fully what one-third more strength
for the same weight means to him.
1t would be of interest only to
an aviation fan to detail all the
places in an airplane where ply
wood now is used. Suffice it to
say, that in the best machines,
now practically every part of the
fuselage subject to strain, and sew
eral other parts, are made from
plywood. So admirably has this
construction material proved, that
forest : products experts have
started extensive experiments on
the wings themselves, of which it
just now is permissible to speak.
Heretofore vanished linen has
been practically the only material
with which wings have been COW
cred. At the laboratory, however.
a process was invented late in 1918
of making plywood SO thin as to be
suited for the same purpose.
In doing this. the panels are cut
.01 in. in thickness, in squares of
3-ft. length. Under any process
of gluing used up to 1918, it was
impossible to make sheets of this
thickness stick together without
disintegrating. The glue soaked
through, causing warping and
other troubles. The new gluing
means consists in coating thin
sheets of tissue paper with blood
glue, letting it dry, and then ap-
plying the plywood panels to each
side in steam-heated press. The
resultant material, lao in. thick,
is surprisingly strong.
This extremely thin plywood
actually was tested on airplane
wings built especially for the pur-
pose. Though with it's first de-
velopment it did not seem suf-
fciently superior to linen to cause
an immediate displacement of the
latter, it nevertheless gives be-
tween six and eight per cent added
lifting power for the reason that
the flap" of the cloth is eliminated
entirely. Weight for weight, its
strength is approximately the
same; in the future it is quite like
ly that all wings may be covered
with this material
When plywood was first thought
of in connection with airplanes, an
apparently insurmountable diff
Guilty presented itself. A machine
that had to be out in all weathers
and spend much of it's time in
dense fog and in thick clouds
often approaching 100-per-cent
humidity for long periods-must
not be held together in any way
by glue that water could dissolve.
Though several so-called water
proof" CLUES were on the market,
not one of them showed satisfac-
tory strength when subjected to
wetting. Also. these Clues were
secret preparations. for which the
government would have to pay q
high premium.
The laboratory experts, how
ever, busted themselves with the
problem and evolved two new
CLUES, one made from the blood of
animals and one derived from
casein = obtained from milk.
Panels were glued together with
these and tested.
The plywood test pieces were
boiled in water for eight hours.
At the expiration of this time none
of the pieces showed any separa-
(Continued on nag 5. column 81