The Airplane - Jay Spenser [33]
Professor Hugo Junkers, a towering figure in the development of flight.
National Air and Space Museum, Smithsonian Institution
From this unusual background sprang the idea of airplanes built entirely of metal. Junkers, a socialist and pacifist, brought this proposal forward with little thought to how it might be employed. To his distress, he found himself forced under the excuse of wartime urgency to pursue a deadly application of this vision.
The first result had been the Junkers J 1 Blechesel (sheet-metal donkey) of 1915, a rugged steel monoplane so heavy that it accelerated slowly and barely climbed at all. Junkers progressed to a lighter design built partly out of duralumin, an early aluminum alloy highly subject to corrosion. Because warplanes weren’t expected to last, this was not seen as a disadvantage.
A passionate advocate for the monoplane, Junkers designed thick wings that did not require external bracing struts or wires. This was too radical for the military authorities, who instead ordered him to prepare a biplane for production. To help with the production side of things, they brought in Anthony Fokker, the young Dutchman whose company was Germany’s premier supplier of fighter aircraft during the war.
The result of this temporary collaboration was the trench-strafing J 4, an angular two-seater also confusingly known as the Junkers J 1 (the former was the company’s name for the airplane, the latter its military designation). The J 4 was actually a sesquiplane, which is a biplane with one wing significantly smaller than the other (sesqui-means “one and a half,” and plane refers to a lifting surface or wing).
Following Fokker’s departure, Junkers went back to a single wing for the all-metal D 1, a low-wing fighter plane with corrugated skin. He also delivered the CL 1, a two-seat version with a second cockpit for a rear-facing gunner. From these two 1918 machines sprang the postwar F 13 of 1920—an astonishing airliner described later in this book—and subsequent Junkers transport planes of the interwar era.
Junkers was a pioneer with good ideas for building airplanes out of metal. For example, he backed smooth sheet metal with corrugated sheets for high strength and resistance to buckling. He also understood that the skins of metal airplanes could shoulder some loads, which is why the Junkers Ju 52 and Ford Tri-Motor have corrugated aluminum cladding. For aerodynamic reasons, these corrugations are aligned parallel to the airflow.
Ultimately, though, Junkers missed the boat when it came to building out of metal. Locked into the reigning paradigm, he failed to question the assumption that metal airplanes must carry their structural loads the way wooden ones had, or for that matter the way vertebrate animals do. As a result, his designs retained an internal skeleton.
Making metal airplanes this way was a bit like dressing a medieval knight in a suit of armor and ordering him to go do a regular day’s work despite the added weight. A compatriot of Junkers’ would be the first to realize this.
Famous for its dirigibles during World War I, the Zeppelin company also built large bombing airplanes at its Staaken plant in the Berlin suburbs. Dr. Adolf Rohrbach, a remarkable young engineer, was the designer of those Staaken Riesenflugzeuge, or giant airplanes.
After the war, Rohrbach set about designing an all-metal airliner with seating for up to eighteen passengers. This machine would advance the state of the art by combining what he and his colleagues had learned about large-airplane design with knowledge gleaned from Zeppelin’s pioneering use of aluminum in dirigibles. The result was the Zeppelin-Staaken E.4250, history’s first all-metal airplane to employ stressed-skin construction. Completed in the fall of 1920, the E.4250 (also known as the E.4/20) was astonishingly modern-looking, with an aerodynamically clean fuselage and four engines inset in a minimally braced high wing.
In addition to semi-monocoque construction, this advanced airliner featured counterrotating propellers to eliminate asymmetries