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Schatzberg, Eric, 1956- / Wings of wood, wings of metal : culture and technical choice in American airplane materials, 1914-1945
(c1999)

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


Page 115

PLYWOOD STRESSED-SKIN CONSTRUCTION
Early Stressed-skin Plywood Structures
Plywood was the key to using wood in stressed-skin structures. Plywood
consists of several layers of wood veneer, arranged with the grain of adjacent
layers at right angles and held together with glue. Although woodworkers
have used veneer for centuries, plywood is an industrial product, dependent
on the machinery used to cut large thin layers of wood from logs. Plywood
offers several advantages over standard forms of lumber. By crossing the
grains of the veneers, plywood compensates for the highly directional prop-
erties of wood, giving the sheet strength in two directions instead of just
one. This property permits the use of plywood in thicknesses that would be
impossibly fragile with single veneers. Plywood also reduces the variability
of wood by allowing adjacent layers to compensate for small defects and
variations. The thin veneers are also easier to inspect for defects than solid
lumber. In addition, plywood can be more easily formed into curved shapes
than solid wood.'
One of the earliest uses of plywood in airplane structures was for mono-
coque fuselages. The monocoque fuselage initially attracted the interest of
airplane designers who sought a well-streamlined body with unobstructed
interior spaces. The first technically successful application of plywood
monocoque construction was in the Deperdussin racing plane of 1912.
Fuselages of the Deperdussin type were built in three layers, with each layer
consisting of strips of tulip-wood veneer wound spirally around a tempo-
rary frame. The workers first tacked a layer of veneer in place, and then
glued a layer of linen over the veneer. The linen was followed by a second
layer of veneer wound in the opposite direction, so that the grain of the two
layers of veneer crossed at right angles. Another layer of fabric was added,
followed by the third layer of veneer wound opposite to the second layer.
When the glue had dried sufficiently, the framework was collapsed and re-
moved from the shell.2
The monocoque Deperdussin won the prestigious Gordon Bennett race
in 1912, and a number of designers in France and elsewhere imitated its
construction. Manufacture of the Deperdussin-type fuselage was difficult,
however, and involved much skilled hand labor. Furthermore, drying time
for the glue lengthened the production process. Each fuselage shell required
about seven days before it could be removed from the temporary frame.3
These disadvantages in production outweighed the advantages in stream-
lining. Until the adoption of the steel-tube fuselage in the early 1920s, most
manufacturers continued to build wooden framework fuselages covered
with fabric or plywood.
When the United States entered World War I, army engineers at Mc-
Cook Field decided to take another look at the monocoque fuselage. These


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