Page:EB1922 - Volume 30.djvu/119

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85
AIR BOMBS


Light case bombs have practically no fragmentation and depem for effect on their charge alone. Heavy case bombs are made o single castings of steel or iron such as the heavy case H2-lb. born shown in fig. 2. Its cast-iron body varies from -5 in. to I in in thick ness and it carries about 28 Ib. of 80/20 amatol. The fragmentation of these bombs is of the highest importance. Bombs are usually provided with a central tube running the! whole length, fitting into screwed sockets for which the bomb i tapped at nose and tail, except when the bomb, like the light cast 23p-lb. bomb, is provided with_a sharp nose, when a tail socket alone exists. This central tube is divided into two parts by a steel ring called the diaphragm for convenience in loading and keeping com ponents in their place. In the heavy case 2o-lb. and 5o-lb. bombs, the tail is prolonged outside the bomb proper by a light construction called a fairing, to provide a suitable shape for aerial flight. The 2O-lb. bomb is peculiar in having only a nose socket and in the shape of its central tube. Lifting, lugs are attached to many bombs They are made of wrought iron and are riveted to the case so as tc be in the same vertical plane as the centre of gravity of the fillec bomb, when the latter is suspended in a horizontal position. Al first bombs were released when horizontal; but now they are fre- quently suspended vertically from an eyebolt attached to the nose fuze or screwed into the nose socket. When a bomb is thus releasec it turns over in flight and falls nose- first. Lifting bands of steel are sometimes used in place of lifting lugs. Four vanes or fins, placed in quadrature, are riveted to the case of all bombs about the tail end, to ensure steadiness in flight. The interiors of bombs are varnished or lacquered; they are then filled with high explosive. High Explosives used in H.E. Bombs_. Trinitrotoluene, known as trotyl and T.N.T., is used as the main charge of a bomb or as a topping to a charge of amatol, which on account of its hygroscopic nature has to be protected from damp. T.N.T., when compressed into pellets, is also used in exploders and relays. Amatol is used as a main charge for bombs. It is a mixture of ammonium nitrate and T.N.T. ; at first it consisted of 40 parts ammonium nitrate and 60 parts T.N.T. (40/60 amatol) ; later on, 80 parts ammonium nitrate and 20 parts T.N.T. (80/20 amatol) was the mixture adopted. Tetronitromethylaniline, known as tetryl, Composition Exploding or C.E., when compressed into pellets is used in exploders and relays. Fulminate of mercury is used for detonators. Bomb Components. Bomb components consist of fuzes, exploders, relays, detonators and igniters. Those selected for a given purpose are called an assemblage. The assemblage varies with the bomb and the purpose for which it is to be employed ; but in every case an H.E. bomb is detonated on impact by the action of the striker of a fuze, which explodes a cap or patch of cap composition, detonating a relay or exploder, which detonates the main charge of the bomb. Exploders are hollow cylinders of sheet brass or paper filled with compressed pellets of JT.N.T. or C.E. They are provided at one or both ends with metal envelopes or sleeves for the reception of the particular detonator with which they are to be used. Exploders vary in length and other details. Relays are exploders of a special kind, usually filled with pierced C.E. pellets; thev are always next the fuze, to which they are sometimes attached* by screwed thimbles called adapters. Detonators are copper tubes of various sizes and are charged with from 45 gr. to 60 gr. of fulminate of mercury according to the use for which they are intended. When they are to be fired by a striker they are closed by a cap. Igniters are a special form of detonator, which carry between their charge and the cap a piece of match designed to cause a certain delay (up to 15 sees.) between the moment of impact of the bomb and its explosion. The match com- position consists of nitrates and chlorates of potash, etc., mixed with shellac and methylated spirit. Fuzes. Both nose and tail fuzes are provided for H.E. bombs. The former are all on the percussion principle and are usually called direct-acting fuzes (D.A. fuzes). The first to be used by the British was a modification of the No. 1 8 gun percussion fuze made for a tapered fuze hole. The motion of the striker, however, was controlled by a collar carrying two small vanes, called arming vanes. The vanes rotated as the bomb descended, eventually screwing the collar off the striker and leaving it free to act in the same way as it would in No. 18 after undergoing the shock of discharge when fired in a gun. A tapered fuze hole being found an unnecessary refinement in the nose bushes of bombs, the latter were tapped cylindrically and fuzes with corresponding threads were adopted. The latest development is the D.A. pistol (see fig. 2) which is an ordinary percussion fuze fitted at the top with a cover to which the vanes are attached, as is also a hanging eyebolt for the suspension of the bomb. At the bottom end the fuse is attached by an adapter to a detonator and relay and the assemblage thus complete can be screwed into the bomb. In certain special nose fuzes the action of the vanes is utilized to screw the striker into position. Safety devices exist in all fuzes. Tail fuzes are all of that type to which the term pistol was originally given. (See figs. I and 2.) The striker at its upper end terminates in a screw upon which works a collar with vanes attached. As the bomb falls the collar screws off and releases the striker, which is then only held in position by a spiral spring; on impact this spring is compressed and the striker is forced down upon a cap which ex- plodes the bomb. If desired, however, a match burning a certain number of seconds may be interpolated between the cap and the charge, thus forming an igniter which secures the desired delay action. When a nose fuze is employed the striker is on impact driven on to a detonator which causes a practically instantaneous explosion ; but all tail fuzes must of necessity have a slight delay, for they only act after the speed of the bomb has been reduced considerably by meeting with some serious resistance, and this results practically in a delay of at least a quarter of a second, which delay can, as already explained, be extended up to 15 sees, by the use of igniters. It is evident, therefore, that a bomb set in action by a nose fuze has no chance of penetrating a target before explosion takes place; there is but a small crater formed and fragments of the bomb are scattered over a wide area. A nose fuze, therefore, is used with heavy case bombs in the attack of personnel and light structures, such as aeroplanes in transit, where crater effect is not required. With tail fuzes, on the contrary, bombs falling in suitable ground Will bury themselves before exploding, producing considerable craters but scattering no fragments. Tail fuzes in connexion with light case bombs are therefore employed in the attack of railways, dumps, buildings, and for general local destruction. In the attack of certain buildings a combination of a nose and tail fuze is adopted. The shearing pin of the former is such as not to be broken as the bomb passes through the roof, while the tail fuze has a delay which will cause an explosion inside the building. If in such a case a tail fuze only were used, should the bomb break up on impact, the delay action might entail incomplete detonation or there might be no detonation at all. When bombs are made of cast iron both nose and tail fuzes are always employed. Carriage of Bombs. Filled bombs are stored with all sockets, etc., plugged; components are packed in their own receptacles. Before the various detonators, relays, fuzes, etc., which constitute the assemblage, are inserted in the central tube of a bomb, the latter is tested in the dropping gear; when all is proved to be satisfactory the bomb is made " live "; but all safety devices are kept in opera- tion till the moment of ascent. If a machine lands with bombs unexpended, all safety pins and other devices are made operative before the bombs are removed from the carrier. Sighting of Bombs. If a machine be flown directly on a target at a known constant height and with a known constant speed, a sighting apparatus can be employed from which, however, accurate results cannot be expected. Its use depends upon the following theoretical considerations: a bomb, when released, will continue to travel with the velocity of the machine and will pass over a horizontal distance before striking earth, which will depend on this velocity and the time taken to fall from the height at which the machine is flying. If then a right-angled triangle be formed with an altitude equal to the given height and a base equal to the horizontal distance passed over by the bomb, the slope of the hypothenuse will give the direction of Che line of sight which must be employed. The sighting apparatus is fitted with a horizontal wire which acts as a foresight and with three other similar wires which act as back- sights, each for a given speed and height. Thus an observer using the backsight will have his line of sight so directed that when it passes through the target he knows he must release the bomb. The heights and speeds provided for are : a height of 6,000 ft. and a speed of 90 m. an hour; a height of 10,000 ft. and a speed of 80 m. an hour; a height of 15,000 ft. and a speed of 70 m. an hour. The foresight is capable of fore-and-aft movement by which cor- rections for wind and density of the air can be given. Two fore-and- aft wires in the. apparatus, placed vertically one over the other, serve in preserving the proper direction of flight. Typical Bombs. The following are typical bombs for the purposes lamed: The 2O-lb. is a small heavy case bomb, capable of carriage >y light machines ; it is used in the attack of personnel, aerodromes and road transport. It is made of steel, its actual weight being 24 b. ; it will take a charge of 4 Ib. 9 oz. of 40/60 amatol or 4 Ib. of io/2o amatol. The so-lb. bomb is a medium heavy case bomb for

eneral use especially against material, and can be carried by the

mailer bombing machines on long-distance raids. Its actual weight s 49s Ib. ; it carries a charge of 10 Ib. 80/20 amatol ; it is made of ast iron, J in. thick in the body and f in. thick at the nose; the iverall dimensions are 281 in. long by 7 in. maximum diameter, t is sometimes carried vertically slung from the eyebolt of the nose uze, sometimes horizontally when it is attached to the dropping 'ear by means of a steel band. The 112 Ib. bomb is a larger heavy ase bomb (see fig. 2) used for similar purposes in larger machines, he 230-lb. bomb is a large light case bomb, used for crater production n the attack of railways and buildings (see fig. i). In addition to these types of bomb, special bombs have been designed for special purposes. Thus the 336-lb. bomb was designed o effect demolitions by the distribution of heavy fragments. It arned a bursting charge of 70 Ib. of compressed T.N.T. and the ody was built up of bulged segments of steel I in. at their thickest >arts. The l8o-lb. bomb was designed as an armour-piercing bomb, t consists of a pear-shaped steel case varying in thickness from -9 n - to 3-3 in. from tail to nose, being provided with a cap of mild teel on the same principle as a capped armour-piercing projectile or a gun, and carrying a bursting charge of 20 Ib. of 40/60 amatol r T.N.T.