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  • 8/16/2019 Inflation of the Metalclad Airship, ZMC-2

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    227arch, 1930 I N D U S T R I A 4 LAND ENGI,VEERISG CHEM ISTRY

    Inflation of the Metalclad Airship, ZMC-2 Chemical Control during Inflation

    A. R . Carr2 and A. C . Good

    COLI.EGE O F THE CITY P D E T R O I T KD -4IRCRAFT DEVE1,OPMENT CORPORATION, DE TR OI T, I I C i i

    HE first succesful all- m e t a l a i r s h i p , th eT M C - 2 , was designed

    and built at the Grosse Ile airport by the Aircraft De- v e l o pin e n t Corporation, a dirision of the De troit Air- c r a f t C o r p o r a t i o n , for th e United States Xavy. It was Completed after five years of en g in ee r in g re search and stud y. The ship is a single

    structural unit in which themetal plating is not only the gas container but also carries a consideraljle portion of the direct stresses. It s size of 200,000 cubic feet, w hile large

    The inflation of th e metalclad airship, the Z M C - 2 , was carried out in two stages. In the first stage the air in the hull was displaced by carbon dioxide. In the second the carbon dioxide was displaced by helium. Carbon dioxide was separated from the helium by scrubbing the gas in a caustic tower and the purified helium returned to the ship. In this manner a purity of over 92 per cent helium was obtained in the gas- filled hul l.

    Although the helium has diffused outward at about 1 cubic feet per 24-hour day, no appreciable quantity of air has come through the metal wall of th e hul l,

    which would cause a decrease in t he lift of the ship.Although th e capacity of t he sh ip, 200,000 cubic fee t, makes it too small for commercial purposes, its per- formance and characteristics prove the feasibility of similar construction for larger, commercial units. This is a distinct contribution to lighter-than-air con-

    enough to meet all expeFi- mental requirements, is too small to meet the demands of a commercial airship. However, its performance and characteristics compare very favorably with the non-rigid fab ric blimps used as trainin g ships by the Go vern me nt. Moreover, it proves th at airships can be built, possessing the adv antag es of all-metal construction wit hout adding materially to the weight as compared with fabric ships and that these metal ships can be built large enough

    for commercial purposes. Description of Sh ip

    The X C - 2ma de its first flight on August 19, 1929 (Fig- ure I ) , and passed its filial tests a t Lakehurst about a m onth later. Its general characteristics and performance d at a are given in Tables I and I1 1).

    struction.

    Ta b l e I -- G e ne r aI C h a r a c t e r i s t i c s of t h e Z M C - I Length of hull. 149 f t . 5 in. Diame ter of hull (max .). . . . . . . . . . . . . . . . . . . . . . . . . Fineness rat io . . . . . . . . . . . . . . . . 2 . 8 3 Displacement of hull 202,200 cu. f t .

    , , , 50,600 cu. f t . Front bal lonet displacement, , . . . . . . . . . . . . . . . . . . . . . . . . . 22,600 cu. f t Rear bal lonet displacement, , . . . . . . . . . . . . . . . . . . . . . . . . . . 23,000 cu. ft Ratio of bal lonet volume to hull vo lume. . . . . . . . . . . . . . . . . . 25 per cent Thickness of ski n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 .0095 in. Length of ca r. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 f t . Width of car. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 f t . 6 in.

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Number of gas valve s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Number of f i n s . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Tota l fin area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 sq. f t . Total elevator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 sq. f t Total rudder area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 sq. f t . To ta l au tomat i c rudder a rea . . . . . . . . . . . . . . . . . . . . 95 sq. f t . Su mb er of engines (Wright Whirlwind J-5) , , , , , , , 2 Power at 1800 I. p. m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 hp .

    9 ft. 2 in.

    Th e hull is 149 feet 5 inches long an d 52 feet8 nches in maxi- mu m diame ter. Th e me tal covering consists of Alclad alloy sheets 0.0095 inch in thickness. These sheets are sewed together by means of a special riveting machine invented by the Aircraft Developme nt Corporation. Since this covering contains the lifting gas, helium, the seams and riveting m ust be gasproof. This is accomplished by trea ting the lap seam with a special bit uminous ma terial after riveting. Th e skin

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    Propeller diameter (all-metal). . . . . . . . . . . . . . . . . . . . . . . . . .

    Received December 3 0 , 1929. Chemical engineer in ch arge of control tests during t he inflation.

    ib then firmly riyeted to supporting structu re consist- ing of equally spaced longi- tudinal frames running from bow to stern and a number of transv erse frames. Inside the bottom part of the hull a r e t w o ba l lo ne t s , one of 22 ,6 00 cu b ic feet and the other of 28 ,000 cubic fee t capaci ty, the former being placed toward the bow and

    the latter toward the sternofthe ship. These ballonets are m a d e of rubberized fabric laced to t he hull an d are filled with air. The ir purpose iq t o co mD en sat e for change in pressire inside the 1 1 ~ 1 1 ~

    The car is suspended from the hull by suitable attachm ents. The power plant con+ts of two Wr igh t Whirlwind J-5-A engines carried on tubular outriggers, one on each side of the car. Eigh t fins, a unique featu re, are equally spaced around the hull. Th e carcon- tains fuel tan ks, control instrum ents, radio, blower, and char t table, and has places for two pilots, one mechanic, and about four student pilots.

    The hull was constructed in two sections erected vertically.When completed, the two sections were placed in a horizontal position and riveted together. (Figure 2)

    Tab le 11 -Pe rfo rmance Da ta of t h e Z M C - I Gross lift (100 per cent inflation with 92 per cent pure

    helium at 60 F. and 29.92 in. H g ) . . . . . . . . . . . . . . . . . . . Weight empty Useful load. .

    12,242 Ibs. 9,113 lbs. 3 127 Ills

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    Crew (three) . . . . . . . . . . . . . . . . . . . . . . . . 600 Ih? Fuel 200 ga l . ) . . . . . . . . . . . . . . . . . . . . . Oil 2.5 ga l . ) . . . . . . . . . . . . . . . . . . . . . . . . Ballast (50 ga l . ) . . . . . . . . . . . . . . . . . . . . Passengers and cargo. . . . . . . . . . . . . . . .

    1 i O O l b i . 200 Ibs. 420 Ibs. 7 0 7 Ibs.

    Range with 230 gal. fuel Maxim um possible range Maximum speed at 440 h Cruising speed at 220 hp.

    680 miles

    Stat ic cei l ing. , . . . . . . . . . .

    Apparatus Used for Inflation Because it is very difficult o separate helium from air, the

    infla tion of t heZ M C - 2 was carried out in two stages. I n the first stage carbon dioxide displaced the air in the ship. The carbon dioxide was introduced at the bottom and the air forced out a t t he topof the hull. I n the second stage the proc- ess was reversed. Helium was led in a t the top while carbon dioxide was forced out the bottomof the hull.

    When ready for inflation, the hull was suspended in the hangar with the car, fins, valves, and connections in place. The carbon dioxide cylinders were stored between the hull and the wall of the hangar. These cylinders were atta che d by means of two octopus manifolds to a 6-inch pipe line. These manifolds were mad e of pressure tub ing , allowing six- teen cylinders of carbon dioxide to be discharged into the pipe line a t the same time. Th e 6-inch pipe line ran the lengt,h of the ship. This line was tapped a t three points by lines

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    March, 1930 I S D U ST RI AL AAYD ESGIlYEERIA-G CHE MIST RY 229

    ballonet n-as deflated first, helium being used to replace its and the exhaust line. Eac h sta tion except the exhaust line volume. Th en the front ballonet was deflated while air was controlled three sampling tubes from the top, e quato r, and being admitted to the rear ballonet. d heck analysis indi- bottom of the hull, respectively. Th e arrangement of the cat ed tha t a small amo unt of carbon dioxide was trapp ed in sampling tubes is shown in Figure3. Samples were analyzed the ballonet folds. Th e inflation was completedon the morn- a t th e four stations simultaneously. These samples were ing of iiu gus t 3. drawn through small rubber tubes inserted into the hull, the

    tubes remaining open to insure a fair sample from the ship at all times. Th e gas was sampled a t 10-minute intervalsso th at the time between two successive analyses a t any level was one-half hour . Th e results of these analyses are shown in Figure 4. During the carbon dioxide inflation the per- centag e of carbo n dioxide indicate d directly the progress of

    the inflation. During the helium inflation the per- centage of carbon dioxide subtra cted from 100 in- dicated approxim ately the per cent of helium in the ship. White s m odification of t he Hem pel bu ret and a pipet filled with caustic solution were used for absorbing the carbon dioxide.

    Final tests made a t the end of th