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Aviation History
1920
1920 - 0621.PDF
Jvm 10, 1920 H 2 i 5 H-fc J.o I u. method would certainlygsuggest sjm-The metallic"phcity The problem of mooring and towing airships has received-a great amount of attention. Mooring and towing may be considered'one and the same problem ; both evolve stability DIAGRAM. IH \ of the envelope whether stationary or moving. Towing willproduce an air current flowing past the balloon, at a speed of the towing ship or mobile winch, over and above that ofthe wind current. In applying the principles of the captive balloon to that ofmooring an airship, a small ship, similar to the Naval " Blimp " type has been taken, and from this example, some observa-tions for the successful mooring of airships by this method can be obtained. Airships have been moored successfully to a mooring mast,and have in some cases ridden out gales, but the procedure is always attended with the danger of breaking away. Inordinary winds, however, the mooring mast is perfectly safe. The advantages of a system similar to the captive balloonis that the airship could be towed both from the land or sea. In determining the stability of the ship when moored, allthe forces acting must be considered. By the application of dynamics these forces can be resolved to two force com-ponents at right angles acting at any point, and a moment obtained in the manner as given previously for the kiteballoon. In the case of the airship, the centre of buoyancy has been chosen for resolving the forces. The condition forlongitudinal equilibrium being expressed by the equation M + T,c - Tj« = o, where M is a moment about the C.B., due to the wind tending totilt the nose up. Ti is the horizontal force component in the mooring cable.T, is the vertical force component in the mooring cable. ; a is the leverage from C.B. at which T, acts.c is the leverage from C.B. at which T, acts. ' • ' • • Diagram I shows the direction of the various forces aboutthe airship, and where F is the gas force lifting the balloon vertically upwards or the static lift; Z is tbe dynamic liftof the ship ; X indicates the drag force ; W equals the weight of the complete ship acting vertically downwards. The values of M, X and Z are obtained from experimentson the model in a wind channel. Tj or the horizontal force in the cable will equal the drag X.T, or the vertical force in the cable will equal F + Z - W. In diagram I is inserted -also, an approximate position forthe metallic V and point of attachment. The direction of the resultant cable force necessarily cutting the centre ofbuoyancy or approximately the centre of nett lift of the airship. The leverage of the forces T, and T, are factorsdetermining the equilibrium condition. According to whether these are shortened or lengthened, moments in the equationcan be balanced up and a position of the point of attachment arrived at. Diagram II shows the conditions for longitudinal equilibriumin a wind of about 28 m.p.h. with the ship at 40 pitch. The gross lift of the ship or the value of F has been taken at4,190 lbs. The weight of the ship complete has been taken as 2,756 lbs. The values of M, X and Z are obtained from themodel experiments at the pitch angle of 40. The leverages a and c are arranged in order to balanceup, or nearly so, the equation, the point of attachment being
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