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Aviation History
1931
1931 - 0492.PDF
FLIGHT, MAY 22, 1931 Unusual Interior View of Metalclad Airship ZMC—2. The metal is strong enough to sustain the full weight of men shown in the picture. problems was taken up in turn and solved, and thoroughlytested in the laboratory, before any actual construction was considered.A study of weights of metalclad construction showed that for large sizes of moderate speeds the weights of a fabric-covered ship would be equalled, and that for large sizes of high speeds (100 m.p.h. and over) the metalclad heldpromise of being superior to the fabric-covered ship, par- ticularly from a weight consideration. It was decided that the hull could best be erected ver-tically in sections. Using this method, it was logical to assemble the hull plating from a series of transverse rings,which, in the vertical position, were then parallel to the floor. The hull sections, then being suspended from thehangar roof, could be raised and the successive transverse rings assembled from the floor, raising the section withthe addition of each ring. After assembling a section of hull plating, the internal framing could be expandedtightly into place and riveted to the plating. When each section was completed, it could be turned into the hori-zontal position and the various sections joined together to form the complete hull. This method was executed in theconstruction of the first experimental metalclad substan- tially as dictated by early engineering study, and proveda practical method of construction. Automatic Riveting Machine The joining of the thin sheets of hull plating, it wasdecided, could best be done by riveting. An automatic riveting machine was developed employing a new principlein riveting, a remarkable achievement and an economic necessity in the construction of large size metalclad airships.In its operation, three strands of wire are fed like thread into the machine and three rows of rivets are " sewed " simultaneously. The machine shears off the wire, rivetlength. The tiny wire sections are punched through the two sheets of metal and the revolving cams head up therivets. The spacing of rivets is also automatic. With this riveting machine two men are able to accomplish as muchwork in a given time as 128 men working by hand. It inserts and completes rivets at the rate of about 5,000rivets per hour. This machine successfully drove about 3,500,000 rivets of 0.035 in. diameter in the hull of tb<-first experimental airship with only one-third of 1 per cent, defective rivets. After the perfection of the riveted seam it was necessanto find a satisfactory sealing compound to seal the seam gastight. Such a compound with a bitumastic base wa.1-finally developed, and laboratory tests indicated a per* meability less than other buoyant gas containers.During this initial period of investigation and develop- ment, the best material available was thought to be plau-duralumin. Exposure tests were started to determine n> resistance to corrosion and various protective coating? w^'investigated. At the time of starting actual construction of the first experimental metalclad, plain duralumin t*eate(Jby the anodic process was considered the best material aui the best protective coating available.The thin duralumin sheets and riveted seams were to determine the effect of vibration and snap diaaction. By a specially designed machine the sp«-= ^. ^ were subjected to millions of continuous vibrations at f?*^speed, and the conclusion arrived at was that any - 8 of the metal and seams, due to snap diaphragm ^uwas a very remote possibility. r toThis exhaustive research occupied seven years P*T°' , the actual construction of the ZMC-2, and has continue- without interruption ever since. 462
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