Jetrader - January/February 2009 - 21

A wrecked German Junkers Ju 52 in Tunisia. The Junkers Ju 52. Photo by rivo/ﬂickr.com. he repeated the hardness test on the following Monday, it showed a considerable increase and continued to harden during the following days. As many of you know, variants of this alloy, plus the bonding of a thin layer of pure aluminum to prevent corrosion due to the copper (Alclad) has been the principle material in most airframes since the early 1930s. In 1919, Junkers produced the ﬁrst all metal transport airplane—the J-13—some versions of which could carry six passengers. It had a ﬁxed landing gear, and the airframe structure was duralumin with a tin plate skin. It was sold to 18 countries, including the U.S., where instead of the usual inline liquid cooled engine, a P&W radial engine was ﬁtted; some British and French versions also had radial engines. In 1931, Junkers introduced the bestknown of all its ﬁxed gear commercial designs—the Ju-52, with its corrugated skin and three radial engines, which were originally P&W Hornets. A reﬁned version of this engine was manufactured in Germany as the BMW 132. Some export models were ﬁtted with P&W Wasp and Bristol Pegasus engines. A total of 4,845 J-52s were built, the majority being for the military, and it ﬁrst saw service with the Luftwaffe during the Spanish Civil War as a troop carrier The New Frontier and bomber (Guernica). It had a retractable garbage can under the belly, where a gunner was condemned to sit with a 7 mm machinegun to later fend off the British eight-gun ﬁghters over the Mediterranean during WWII when the Wehrmacht was forced to supply Rommel’s army in North Africa by air. Major commercial users were Lufthansa, Swissair and Air France. It sat 17 passengers and could ﬂy from Berlin to Rome in eight hours. When ﬂights from Berlin’s Tempelhof International Airport ceased on October 30, 2008, a J-52 and a DC3 took off, symbolizing the historic signiﬁcance of one of the most architecturally beautiful air terminals ever built with its sweeping canopy roof so aircraft could taxi in to shelter passengers from the elements. Flying into there between those apartment buildings in poor visibility was always a bit of a nail biter. With London’s Croydon long gone, (where I soloed), only Le Bourget remains active. In 1927 Tempelhof was the ﬁrst airport with an underground railway station. (U.S.) coach Knute Rockne in a Fokker trimotor, manufactured in New Jersey at Hasbrouck Heights, adjacent to Teterboro Airport. This was due to wing separation resulting from moisture causing deterioration of the glue in the laminated wing spar. Ironically, both the British Government and the U.S. National Advisory Committee for Aeronautics, (NACA), forbade the use of duralumin in aircraft for some years after Junker’s paper was published. The corrugated skin of the Junker airplanes provided the necessary stiffness to carry ﬂight loads without adding weight, but at the expense of increased drag. It was another German engineer, Adolf Rohrback, who around 1922 developed the smooth-stressed skin structure we are all familiar with today. He used in the wing an aluminum box beam with the nose and trailing sections attached to create the desired airfoil curvature with the skins riveted to the frames. In 1925, one of Rohrback’s engineers, Herbert Wagner, discovered it was not required to make the beam and frame massive enough to prevent the panels from buckling. On the contrary, provided the panel loads did not exceed the safety margin from failure, buckling was acceptable, so the internal structure could be made much lighter. From the 1930s on, with the government research institutions, industry and universities of the Western industrialized nations developing a body of theoretical and practical aeronautical knowledge, the metal airplane design advance was breathtaking, leading hardly without pause to the next step—the all-composite airframe. Resounding Research REFERENCES: • John D. Anderson Jr., The Airplane, A History of its Technology, American Institute of Aeronautics and Astronautics, 2002. www.wikipedia.com: Junkers aircraft; Al materials; TWA ﬂight 599 (Knute Rockne) Others as cross checks: too numerous to list here In 1923, Junkers presented a paper at London’s Royal Aeronautical Society, which listed the advantages of metal over wood, which tends to rot in airplane structures. This was tragically conﬁrmed in 1931 with the death of famed Notre Dame football • • Jetrader 21

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Jetrader - January/February 2009

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