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Aviation History
1917
1917 - 0340.PDF
APRIL 12, 1917. speed meter, fire extinguisher (chemical sprinkler type),searchlight. The contractor must show that the fabric factor of safetyunder normal running conditions for any part of the dirigible exceeds 8. The strength to be taken as a basis, to be foundby the methods given below. . All fabric used in the envelope or ballonets to contain twoor more plies of cloth, one of which is to be laid on a bias of 45°. Sufficient rubber of proper quality shall be placed inthe fabric to meet the requirements as to diffusion and weather- resisting properties, which are given below. The protectivecoating on the outside of the envelope shall be at least 0-4 oz. per square yard, and on the inside 02 oz. per square yard.No fabric in the balloon is to weigh over 12 oz. per square yard, and no fabric is to test less than 40 lbs. per inch in thedirection of any of the threads, either bias or straight, test to be made as described below : Fabric in the top of theballoon shall show an average strength over 60 lbs. per inch for the four different directions of threads ; or a strengthover 100 lbs. per inch in either warp of filler if the two piles are doubled straight together for a sample test. Each contractor for one or more dirigibles shall constructa model of linear dimensions one-thirtieth the size of the JM. JSotfo/n Details of the lower safety and gas control valve onthe U.S. Navy dirigible. balloon, made of identical fabric, provided with suitablesuspension disposed in similar fashion to that on the full- size balloon. This model to be inflated (upside down) withwater to correspond with the full-size balloon when inflated to five times its normal running pressure. This will mean onthe model a head of water at the top equal to 12J ft. Leave pressure on for 10 minutes. Each envelope when completed shall be blown partiallyfull of air and all fabric inspected from the inside against a light to detect small leaks. After inflation with hydrogenat normal operating pressure, the envelope must show a leakage of gas less than 1 per cent, per day, with all valves andaccessories in place. Envelope, with ballonets in place,'after inflation with hydrogen shall be inflated to a pressure of 3 ins.of water at lowest point and held there for one minute. This is three times the normal pressure for flight, but no defectsshall be developed by this proof test. The nose shall be reinforced by a doubling patch of fabricsimilar to that in the envelope and wood battens about f in. by 3 ins. in section equally spaced, converging at the nose,every alternate batten to extend beyond the doubling 3 ft. An eye shall be provided in the nose for a mooring line. Thiseye will consist of a if in. metal thimble secured in an eye splice of a four-strand manila rope. The rope will be unlaidand the eight strands let in beneath the doubling patch, equally disposed radially, the ends of the strands frayed andthe whole setin cement. The breaking strength of the mooring attachment shall be about 5,000 lbs. Rip panels, four in number, shall be located as shown witha rtp cord, dyed red, run from each through light agate guides to the pilot. By pulling the rip cord weak stops securingthe end of the panel are to break and tear open the panels for rapid deflation in an emergency. Grab ropes, eight in number, shall be secured to patches onenvelopes. These to be ij-in. circumference manila rope secured to crows'-feet of f-in. flax signal halyard stuff (braided°i 3-Ply thread in eight strands ol flax twine; breaking strength, 800 lbs.). Ballonets are located as shown. Their combined volumeis 25 per cent, of the total volume of the envelope. The relative sizes of ballonets are to be adjusted so that theirdisplacements give equal moments about the centre of buoyancy of the envelope when completely inflated. Theballonets are to be fitted with a suspension band of fabric running around the plane of symmetry to which a light flaxsuspension is to be attached. Sight holes of transparent material are to be placed in the envelope for inspection of thissuspension. The lower part of the ballonet to be secured to a patch of doubled envelope fabric sewed and cemented to the envelope, itiis patch when removed carries with it the ballonet and wind-pipe connection. A sight hole shall be located in the ballonet patch for inspection of inside of ballonet. The safety valve will be located on top of the envelope. Con- struction of the valve is shown on detail sheet. This valve is to automatically open outwards when pressure in envelope at lowest point exceeds 1 in. of water. The manoeuvre valve will be located under the envelope, and will operate as a safety valve also, but may be opened by means of a line to pilot s seat. The belly band or suspension band is to be a heavy fold of canvas, running around the lower part of the envelope, bearing at intervals hardwood toggles for the crows -feet of the car suspension. This band shall be securely sewed and cemented to the envelope in a manner which on ri18 Sh°wn t0 develoP the full strength of the latter Stability of route is assisted by two horizontal fins andthree vertical fins, as shown. These fins are to be 170 square it. in area each, except the vertical fin shown on top of theenvelope, which will be 80 square ft. area, and are to be made up of a light structure of steel tubing and wood withinternal wire bracing and covered with airplane linen treated with five coats of dope and varnished to give a smooth, tautsurface. The fins to be braced by wires with turnbuckles, and crows'-feet to doublings on the envelope. Weight offans to be kept down to one-half 1b. per square ft. Doubling patches shall be fitted on envelope to secure butt edges oifins by lacing. Two horizontal rudders, each 70 square ft. area, and twovertical rudders, each 35 square ft. area, are to be provided. Both the horizontal and vertical rudders are to be balancedand to work in ball bearings. Rudders to be securely trussed and operated by non-conducting leads (flexible cable of flaxline) passing through agate guide rings, or ball-bearing bronze sheaves as indicated on the plans. -Rudder operating lead;*to give the least number of turns to reduce friction to a minimum. Fins and rudders to be readily detachable. All steering controls shall be in duplicate and inter-connected. Tanks shall be provided sufficient for a ten-hour supplyof fuel and oil at full power for the engine. The main fuel tanks shall be interconnected and so arranged that fuel maybe ta'ken from any tank or combination of tanks. Valves shall be operated from the rear seat, and shall be quick-acting. Fuel tanks shall be of non-corrosive material. . If copper tanks are used, they shall be tinned On the inside.Tanks shall, before installation, be tested to an internal pressure of 5 lbs. per square in. and must show no permanentdeformation. The water-ballast tank shall be located in the body andbe of 300 lbs. capacity, and provided with means for rapid discharge from the pilot's seat. The tank is to be made ofwaterproof fabric and shall be tight when full. In addition to trimming the dirigible by manipulation ofhorizontal rudders or shifting air between ballonets, small water containers are to be placed near the bow and stern of.the envelope, fitted with spring loaded valves, and means whereby such valves may be pulled open by the pilot. Theforward tank shall contain 40 lbs. of water and the after tank 50 lbs. of water, and these tanks shall be located at thepoints shown in the genera:! arrangement plan. The forward tank should be a fabric tube laced along a meridian with avalve in its lower after end. The after tank shall be as flat as possible and secured in a fabric pocket under the envelopeand between the lower vertical fins. A 2 h.p., 900 r.p.m. engine of motor-cycle type is to bearranged to drive through a 2 to 1 gearing a multivane blower of a cjapacity of 600 cubic ft. per minute against a head of2 ins. of water. A crank is to be provided for starting the motor, which is to be accessible from the rear seat. Precau-tions similar to those stipulated for the main^engine shall 34O
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