Patent GB-552587-A (GB)
Title: Improvements in or relating to anti-aircraft shells of the type containing a parachute mine
IPC: F42C7/02
Filed: 1941-10-15
Abstract: 552,587. Parachute mines ; ammunition projectiles ; fuzes. WHITSETT, C. A. Oct. 15, 1941, No. 13294. Convention date, Oct. 18, 1940. [Classes 9 (i) and 9 (ii)] An anti-aircraft shell of the type containing a parachute mine constructed to form the forward one of two separable sections of the shell which are adapted during the flight of the shell, and at a predetermined altitude, to be automatically separated, and wherein the explosion of the charge embodied in the mine is controlled before and after said separation, is characterized in that the charge is detonated by a firing device including a slidable primer actuated by a percussion plunger or the like, the primer being held in a rear operative position during the flight of the shell and being again rendered operative only after the shell sections have separated and the mine is suspended from the parachute. If the parachute floats to earth with its mine unexploded, the mine is rendered harmless by the weight thereof being taken off the parachute. The shell explodes before separation if impact with an aeroplane occurs. The fuze may be such that the shell may be converted into a timed high-explosive shell. The shell comprises two separable parts 31a; 31b, the front part 31a constituting the mine and containing high explosives 43, while the rear part contains the parachute 41. when the shell is fired from the gun, a consussion plunger 96 breaks away (by inertia) from its retaining ring 97 and strikes a firing pin 98 which ignites a primer in the plunger. The flash from the primer ignites a powder train contained in adjustable rings 92, 93, 103, which train burns around to a detonator 67 which, via a conduit 66, fires a parachute-releasing charge 47 of black powder, the explosion of which separates the two parts 31a, 31b which have hitherto been joined by a shear wire 35. The charge 47 blows rearwardly a two-part piston 49a, 49b, which is secured to a sleeve 159 sliding freely on a tube 132; the sleeve has fixed thereon a head 167 which, via a sliding ring 163, compresses a heavy spring 161 which limits the rearward movement of the piston. When the part 49a stops, the part 49b travels on, the consequent relative movement (which is limited, e.g. by pin and slot 207, 208) resulting in the cocking of a series of angularly-spaced devices 51, each comprising links 187, 188 pivoted to each other and to the parts 49a, 49b. A spring 199, disposed betweel links 187, 188 tends to separate the parts 49a, 49b, The construction is such that the links 188 form struts which just resist the forward pull of the heavy spring 161. A slight tripping force applied forwardly on the part 49b or laterally inward on the links 187 trips the devices 51, whereupon the spring 161 thrusts forward the sleeve 159, and spring strips 171, secured to the sleeve, strike an extension 145 of a Semple centrifugal firing plunger 76 which fires a primer 75 which, via a booster charge 72, fires the high explosive 43. Trigger notches may be formed in the links 187 to engage with the edge 213. A spring 215 may supplement or replace the springs 199; if the springs 199 are omitted, the links may be flung outwards by centrifugal force, or the pivots 202 may be located inwardly of a line joining the pivots 189 and 197. The spring strips 171 are initially disposed within the extension 145, but, on opening: of the shell, spring outwardly into slots 172 in the extension and bear against right-angled shoulders 172b so that on impact of an aeroplane with the wire 42 the plunger 76 is retained in the rearward position; in a modification, the shoulders may be bevelled, as at 172c or omitted, so that on said impact inertia throws the plunger forward. The sensitivity may be graduated, an impact near the bomb firing it and an impact remote from it not firing it. In this sensitized modification, the wall 54 of the explosion chamber may be made weak so that it, with shrapnel balls placed inside it, may be blown out. The primer 75 is contained in a thimble 115 secured to rods 128 fixed on the head 131 of the tube 132 which houses a spring 133 surrounding a plunger 134 having a head 137 to which is secured one end of the parachute wire 42. A spring 126, bearing against a flange 117 on the thimble, tends to urge the thimble forwardly into a position in which its explosion ports 121 will register not with ports 109 (in the ring 103) leading o the booster charge 72 but with a chamber 84a leading to vents 89, 91 which may vent outward or inward. During the flight of the shell, the tube 132 (and hence the thimble 115) is retaine din the rearward (firing) position by a split wire ring 138 engaging in a groove 139 in the tube, so that if the shell strikes an aircraft the plunger 76, moving forward by inertia against the action of the spring 126, fires the primer. During the opening of the shell, when the ring 138 has been displaced, the spring 126 forces the thimble to the forward (non-firing) position. When the shell has opened, and the bomb 31a hangs from the parachute, the weight of the bomb compresses the spring 133 and the thimble is returned to the firing position. When the shell reaches the ground, the weight of the bomb is taken off. the spring 133, and the spring 126 moves the thimble to the non-firing position. The third powder train ring 103 has two angularly spaced grooves 265, 266, which may be flash passages or may be packed with black powder. The ring may be rotated relatively to the ring 93 so that (a) (Fig. 24) the groove 265 registers with a flash passage 196 leading from the ring 93; in this position the flash will pass through the passage 108 and the fuze is set for opening the shell to release the parachute, (b) (Fig. 25) the groove 266 registers with the flash passage 106; in this position the flash will pass through ports 109 and passage 74 to the booster charge 72 the fuze being thus set to fire the high explosive 43, or (c) the ports 109 are out of registry with passages 122 in the rings 118 in which the thimble 115 slides; in this position neither of the grooves 265, 266 registers with the port 106, and more over, the primer is cut off from the booster charge, so that accidental firing of the primer will not be transmitted to the latter. The parachute wire 42 is in two or more reel sections 42a, 42b, the wire being unwound from each section simultaneously. The wire is embedded in resin, pitch or rubber, which offers resistance to the unwinding and enables the sections to be packed as units, e.g. in cardboard containers 221. The rear section 42b may function as a plug having a flange engaging behind a ring 181, so that the parachute is retained in place until most of the wire has been unwound.