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

2. Engineering enthusiasm: World War I and the origins of the metal airplane,   pp. [22]-43


Page 25

ENGINEERING ENTHUSIASM
Figure 2.2. The unsuccessful J1, 1916. Hugo Junkers' first all-metal airplane was
made from sheet iron. National Air and Space Museum, Smithsonian Institution (SI
neg. no. 96-15636).
Jl's structure prototype embodied a number of novel features. Junkers de-
signed the wings of the J I using a principle he called the "supporting cover,"
in which "all tensile, compressive and shearing forces are taken up by the
wing cover." This principle anticipated the stressed-skin designs that have
dominated metal airplane construction since the 1930s. Junkers built his
wings of soft sheet iron (Eisenblech), between 0.5 and 1 mm thick. Junkers
stiffened the thin iron sheets by welding a second, corrugated sheet to the
inside surface, using the new process of electric resistance welding. The
wing was assembled from these stiffened panels.7
Flight testing of the J1 began in December. The airplane was not well
received by the military authorities, despite its impressive top speed of
106 mph with a 120-horsepower motor. Junkers attributed this poor re-
ception in part to "the prejudice against metal construction" and also to the
mistrust of unbraced wings by pilots. In fact, as Junkers himself later admit-
ted, the J1 was heavier than a comparable wooden airplane and had a very
poor rate of climb. A good rate of climb was essential for combat, so the
army made additional orders conditional on its improvement.8
The failure of the J1 led Junkers to make fundamental changes in his
approach to metal construction. His most important step was the substitu-
tion of duralumin for sheet iron. Duralumin was a high-strength aluminum


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