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Aviation History
1931
1931 - 0493.PDF
FLIGHT, MAY 22, 1931 First Successful Metalclad, ZMC-2 Hit- first rivet was driven in the bow section on March 7of 1928, and on August 10 of the following year the ship was completed, inflated with helium, and ready for trialflights. The substitution of alclad sheet for duralumin in the hull covering is explained later. The internal structure of the ZMC-2 hull is composed ofH equally spaced longitudinals and 12 circular frames which are riveted to the outer cover of alclad sheet 0.0095 inchthick. Five of the transverse frames are of built-up type heavy girders, braced with wiring in their own planes.These frames carry all concentrated loads due to handling lines, weight of car, engines, lin loads, landing loads, etc.The rest cf the structure is built of very light sections primarily designed to maintain the shape of the hull andsupport the outer cover when the ship is deflated. Three sir valves a.nd two gas valves are used, as well as severalmanholes to provide accessibility to the gas chamber. Handling lines are attached to the fittings on the mainwire-braced frames. The car, or control cabin, is suspended from two mainframes near the maximum diameter of the hull. It is 24 feet long and 6.5 feet wide at the maximum section.The structure consists of eight transverse frames and several longitudinals braced by diagonals and covered with0.014 inch corrugated alclad sheet. Two 220-h.p. Wright Whirlwind engines are suspended from the car by tubularoutriggers. The bow of the car is occupied by the pilots, navigation and radio equipment, while in the stern aredisposed the gasoline and ballast tanks. The total fuel capacity is 250 gallons. The mechanic's controls, instru-ments and seat are placed in the middle, and the landing gear is attached to the bottom of the car. A handling railis provided on each side for ground handling by the landing crew. The ballonets, made of two-ply rubberised fabric, arelocated -aside the hull, forward and aft of the car. The IMIIOHKK are interconnected by a duct system, into whichair is supplied by scoops. One dynamic scoop is located at the forward end of the car and two propeller scoops on theoutriggers. An auxiliary hand-operated blower is also provided in the car to maintain pressure during groundhandling. Fins Instead of the conventional four-fin . arrangement, theship is equipped with eight fins equally placed around the circumference, four of Ihem acting as vertical surfaces andthe other four as horizontal surfaces. This arrangement of tins allows a higher aspect ratio than is customary, thusgiving unprecedented efficiency to the fin group as a whole. The fins are mounted to two hull frames and are bracedby streamline wires. To the trailing edge of the fins are attached movable control surfaces, which are operated bycables running to the car. The structure of the fins is covered with corrugated alclad sheet of an average thick-ness of 0.008 inch. The general characteristics and performance data of theZMC-2 airship are given in the following tables. GENERAL CHARACTERISTICS OF THELength of hull Diameter of hull (max.)Fineness ratio Displacement of hullTotal hallonet displacement Front ballonrt displacementHear ballonet displacement Ratio of ballonet volume to hull volumeThickness of skin Length of carWidth of car Number of air valvesNumber of gas valves Number of finsTotal lin area Total elevator area . .Total rudder area Total automatic rudder areaEngines (Wright Whirlwind J-5) Power at 1,80(1 r.p.m.Propeller diameter (all metal) Lineal feet of seam . .Surface area ZMC-2 METALCLAU. . . 149 ft. 5 in.52 ft. 8 in. 2 83202,200 cu. ft. 50,600 cu. ft. 22,fi00 cu. ft.28,000 cu. ft. 25 per cent.0 0095 in. 24 ft.H ft. 6 in. 3 440 sq. ft.190 sq. ft. 95 sq. ft.95 sq. ft. 2 440 h.p.9 ft. 2 in. 17,800 ft.19.436 sq. ft. PERFORMANCE DATA OF THE ZMC-2 METAI.CI.AC Gross lift (100 per cent, inflation with 92 per cent, pure helium at 60; F. and29-92 in. Hg). 12,242 1b. Weight empty .. . . . . .. 9,115 1b.Useful load ' 3.127 lb. Crew (three) . . . . . . . . 600 lb.Fuel (200 gal.) 1,200 lb. Oil (25 gal.) 200 lb.Ballast (50 gal.) 420 lb. Passengers and cargo . . . . 707 lb.Kange with 250 gall, (cruising speed) 760m. .Maximum possible range (still air) .. .. 1,120 m.Maximum speed at 440 h.p. . . . . . . 70 m.p.h. Cruising speed at 220 h.p. . . .. . . 56 m.p.h.Static ceiling .. .. 9,000 ft. Alclad Substitute for Duralumin The original specifications of the ZMC-2 provided for a hull covering of plain duralumin 0.008 inch thick. It was the first time that sheet of this thickness had been rolled in commercial sizes, consequently its resistance to corrosion was not definitely known. Through the co-operation of the British Air Ministry the anodic process developed in England was made available, and the sheet metal was given this treatment. When the hull of the ship was one- fourth completed, exposure tests conducted by the Bureau of Standards had progressed to the point where an appraisal could be made of corrosion and embrittlement of the material. Six months' exposure revealed that a serious deterioration resulting from inter-crystalline attack had occurred, the tensile strength, 60,000 1b. I'm.', dropping to 50.000 lb./in.! and the elongation, originally 15 per cent., diminishing to 4 per cent. It was evident that this was not a safe Forward View of Car showing two Wright J—5 Whirlwind Engines of 220 h.p. each. 463
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