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Schatzberg, Eric, 1956- / Wings of wood, wings of metal : culture and technical choice in American airplane materials, 1914-1945

6. Neglected alternative i: plywood stressed-skin construction,   pp. [114]-134

Page 116

116                                                     CHAPTER SIX
engineers recognized that the difficult manufacturing process of the Deper-
dussin fuselage was not an inherent characteristic of wood monocoque
structures, and they launched a study to simplify the production of wood
monocoques. This study focused on semimonocoque structures, which in
general weighed less than "true" monocoques. Semimonocoques used bulk-
heads and longerons (or stringers) to reinforce the inside of the wood shell,
while the true monocoque derived all of its strength from the shell itself.
The army brought in two plywood manufacturers and a furniture maker to
design and build experimental semimonocoque fuselages. These firms in-
vestigated a number of methods to speed the production process. All of the
methods involved molding flat sheets of plywood to the required shape, in
contrast to the Deperdussin process, which relied on the pliability of indi-
vidual veneer strips.4
Two of the firms developed similar methods for molding large sheets of
plywood. One firm was the Haskelite Manufacturing Company, a plywood
manufacturer located in Grand Rapids, Michigan. In the Haskelite process,
a plywood sheet was first boiled for several hours to make it pliable. Metal
clamps then gripped the edges of the sheet, holding it above a cast-iron die.
A hydraulic press forced the die into the plywood sheet, producing the de-
sired shape. Steam pipes heated the mold to speed drying. When dry, the
curved plywood was glued and nailed to the longerons and bulkheads.
Using the Haskelite process, the entire covering of the twenty-five-foot fuse-
lage comprised only five pieces.5
Neither of the large-panel methods proved successful before the Armi-
stice. The McCook Field engineers found that the best results were obtained
when the face grain (the grain of the outer layers of veneer) ran parallel to
the longitudinal axis of the fuselage. However, the Haskelite molding pro-
cess only worked on plywood with the face grain running circumferentially
A third process, involving smaller panels formed directly onto the frame-
work, permitted the use of plywood with longitudinal face grain. This
method demonstrated its practicality, but the Armistice ended the project
before production could begin.6
At the end of the study, the McCook Field engineers were quite optimis-
tic about the potential of the wood monocoque. They concluded that wood
monocoques could be built lighter than framework types, and that they
were "an excellent production proposition." Designers could easily obtain a
well-streamlined shape with a monocoque fuselage. In addition, plywood
veneers could be cut from timber rejected as unfit for standard aircraft con-
struction, thus easing concerns over wood shortages. Monocoque structures
also needed less maintenance, since they did not require the frequent ad-
justments necessary to maintain the alignment of wire-braced wood frame-
works. These opinions led Lt. Col. Jesse G. Vincent, wartime head of Mc-
Cook Field, to endorse further development of the plywood monocoque
over the metal fuselage.'

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