Aircraft technical Basics: TM 1-409, Aircraft Armament and Pyrotechnics, 1941: XII. - Fragmentation Bombs And Fuzes

Section XII - FRAGMENTATION BOMBS AND FUZES

79. General.-a. Fragmentation bombs are designed to produce destructive effect against personnel, animals, and light material targets such as motor transports, airplanes on the ground or in flight, etc., primarily by the fragments of the bomb body projected at high velocity. The blast at the point of impact will cause additional damage to nearby objects. Some fragmentation bombs are designed with stabilizing fins, others with parachutes for retarded flight. The design of the bomb body is such as to produce the greatest number of effective fragments. A 0.2-ounce fragment, having 60-foot pound energy, will disable personnel, while against material targets, a 0.3-ounce fragment is more effective. Fragmentation bombs are fitted with a nose fuze only. The weight of the high explosive in these bombs is about 15 percent of the total weight of the bomb. Since the fragments are projected normal to the axis of the bomb, the most uniform distribution and greatest destructive effects occur when, at the instant of functioning, the bomb is vertical. Because of their small size and weight, many fragmentation bombs can be carried on an airplane. Hence, by properly distributing the points of impact, a large target may be effectively swept by fragments. Fragmentation bombs are painted yellow, with marking in black.

b. Since the fragmentation bomb is relatively light, only one suspension lug is required. However, in order that. the bomb may be suspended either horizontally or vertically, two suspension lugs are provided, one on the side, for use when installed in horizontal bomb racks, the other at the tail end for use when installed in vertical bomb racks. On some airplanes, designed for vertical suspension of bombs, the lower end of the parachute is covered by a door closed by the action of a spring. In such installations the impact of the released bomb forces the door open to let the bomb fall through. In order to avoid damage to the fuzes and to secure satisfactory and uniform release, fragmentation bombs will not. be released from airplanes which have such doors or covers at the bottom of the bomb parachutes; that is, those intended to be opened by the impact of the released bomb.

c. Functioning of bombs is primarily dependent upon the action of the fuze, which, for fragmentation bombs, is usually instantaneous in action. The action and functioning of each fuze is described in the paragraph devoted to that fuze. Fragmentation bombs for low altitude bombing are provided with parachutes to retard the flight of the bomb so that the airplane from which the bomb is dropped will be out of the danger space when the bomb fragments. Fragmentation bombs, stabilized with parachutes, are fitted with impact type instantaneous action fuzes. Finstabilized fragmentation bombs are fitted with either impact type instantaneous action fuzes or time fuzes, dependent upon the mission. Dependent upon the type of fuze, the bomb fragments instantaneously on impact or at the time for which the fuze is set, project a large number of fragments at high velocity.

80. Bomb, fragmentation, 20-pound, M41.-a. General.-This bomb is intended for destructive effect. against such targets as personnel, motor convoys, airplanes on the ground, etc. For the complete round assembly, the following components are required :

Bomb, fragmentation, 20-pound, M41, unfuzed.

Fuze, bomb, M109 (nose).

Wire, arming, assembly.

These components are shown "as received" but. with packing material removed (fig. 15). The clip, paper, wire, Type A, No. 1, serrated, on the arming wire assembly is used to hold the swivel loop temporarily to the fin during installation of the bomb in a vertical bomb rack.

b. Description-The body of this bomb is a closely wound helix. It weighs approximately 20.4 pounds, contains approximately 2.7 pounds of high explosive, and is adapted for a nose fuze only. For shipment, a closing plug is fitted to the adapter opening.

c. Assembly and disassembly (fuzing and unfuzing).-The prior examination of components prescribed in paragraph 69 is for the purpose of insuring that all components at the bomb fuzing point are serviceable. The complete round is assembled as follows: After removing the closing plug, assemble the fuze as prescribed in paragraph 69. The bomb is now an assembled complete round, ready for installation in the bomb rack.

Note.-If the bomb is assembled for installation in a horizontal rack, the arming wire must be shortened. For assembly for horizontal suspension, cut the wire to such length so that when the swivel loop is pIaced approximately 2 1/2 inches to the rear of the suspension lug on the side of the bomb, the free end of the wire will protrude from 2 to 3 inches beyond the arming pin. After the bomb is installed in the bomb rack, the cotter pin is withdrawn from the fuze in accordance with instructions on the tag attached thereto. When removing the cotter pin, care will be exercised not to disturb the adjustment of the arming wire. Should it be necessary to disassemble the complete round into its components, the above steps will be carried out in the reverse order and the components restored to their original condition and packings.

81. Fuze, bomb, M109 (nose).-a. General.-This fuze (fig. 16) is an arming pin type fuze with time delay arming, similar in general design to the fuze, bomb, M104 (nose) (fig. 18). It is designed for instantaneous action and is used in the bomb, fragmentation, 20-pound, M41.

b. Description.-The description of the fuze, bomb, M104 (nose) (par. 83) applies to this fuze with one exception; namely, the addition of a resistance spring and spring cover under the striker. The fuze, M109, may be distinguished from the fuze, M104, by the smaller diameter of its striker plate. The spring cover can be seen in figure 16.

c. Assembly and disassembly (fuzing and unfuzing).-No attempt will be made to disassemble this fuze. The only authorized assembling operations are those required to assemble the fuze to the bomb as described below.

(1) Remove fuze from sealed container.

(2) Screw fuze into the nose of the bomb until it, seats-handtight, using no tools.

(3) Thread end of arming wire through the inner of the two eyelets in the arming pin in accordance with instructions on tag. The inner eyelet is ordinarily not visible-hand pressure on the head of the arming pin will expose the inner eyelet.

(4) Adjust arming wire to protrude from 2 to 3 inches.

NOTE.-No safety clip is to be used on the arming wire. After the fuze is assembled to the bomb and the arming wire inserted, it is necessary only to remove the cotter pin, in accordance with instructions on tag.

d. Functioning.-(1) Released armed.-When released armed, the arming wire is withdrawn from the fuze, thereby releasing the arming pin which is then ejected, leaving only the delayed arming plunger as a restraint, against the movement of the slider into its armed position. Ejection of the arming pin initiates firing of the time delay train which burns for approximately 2 1/2 seconds, at which time the delay arming plunger is ejected, thereby permitting the slider to move to its armed position. On impact the firing pin is driven into the primer, thus initiating the explosive train. The action is instantaneous. Should the bomb impact before the time delay train has burned through (2½ seconds), the detonator is out of line and the bomb does not detonate. However, after the time delay train has burned through, the slider may be expected to move to its firing position. A dud in this condition is dangerous and will not be handled. Such duds will be disposed of in accordance with TM 9-1900 (now published as TR 1370-A).

(2) Released .safe.-If the bomb is dropped safe, the arming wire is released from the arming mechanism of the bomb rack and drops with the bomb, thereby preventing the fuze from arming. Being unarmed, the fuze does not function on impact.

82. Bomb, fragmentation (parachute), 23-pound, M40.-a. General-The general design of this bomb is similar to that of the bomb, practice, 17-pound, M37, and is shown in figure 17 as a complete round assembled. It is intended for use against ground targets by airplanes flying at low altitudes. For the complete round assembly, the following components are required :

Bomb, fragmentation (parachute), 23-pound, M40, unfuzed. Fuze, bomb, M104 (nose). (Arming wire assembly attached to bomb, as shipped.)

b. Description.-The body of this bomb is the same as that used in the bomb, fragmentation, 20-pound, M41 (fig. 15), but is fitted with a parachute rather than fins. It contains approximately 2.7 pounds of high explosive and is adapted for a nose fuze only. For shipment, a closing plug is fitted to the adapter opening.

c. Assembly and disassembly (fuzing and unfuzing).-The prior examination of components prescribed in paragraph 69 is for the purpose of insuring that all components at the bomb fuzing point are serviceable. The complete round is assembled as follows:

After removing the nose fuze closing plug, assemble the fuze. Remove parachute case cover by means of tear strip ring, exposing the pull wire. The bomb is now an assembled complete round, ready for installation in the bomb rack.

NOTE.-After the bomb is installed in the bomb rack, the cotter pin is with-drawn from the fuze in accordance with instructions on the tag attached thereto. When removing the cotter pin, care will be exercised not to disturb the adjustment of the arming wire. Should it be necessary to disassemble the complete round into its components, the above steps will be carried out in the reverse order and the components restored to their original condition and packings.

83. Fuze, bomb, M104 (nose).-a. General.-The M104 nose fuze (fig. 18) is an arming pin type of fuze in which the primer detonator and booster are made integral parts thereof. The fuze is arranged for instantaneous action only. Additional features incorporated in the fuze include time delay arming and detonator safety. This fuze is used in the bomb, fragmentation (parachute), 23-pound, M40.

b. Description (fig. 18).-A mushroom shaped striker assembly extends approximately 1/2 inch beyond the nose of the fuze. body. The firing pin, supported by a spring which keeps it in contact with the striker assembly, is housed within the body of the fuze. The booster, encased in an aluminum cup, protrudes from the base of the fuze. A time relay train located near the midpoint of the fuze provides for time delay arming. The primer and detonator are mounted in a slider located below the firing pin and are normally held out of firing position by the arming pin which extends through the body of the fuze. In addition, a delayed arming plunger prevents the slider from moving to its firing position until the time delay train has burned through. When the time delay train has burned through, the delayed arming plunger is ejected and the slider moves to its firing position. The time delay train is initiated by an auxiliary firing pin which is driven forward by a compressed spring after the arming pin is ejected.

e. Assembly and di assembly (fuzing and unfuzing).-No attempt will be made to disassemble the fuze. The only authorized assembling operations are those required to assemble the fuze to the bomb as described below.

(1) Remove fuze from sealed container.

(2) Screw nose fuze into the nose of the bomb until it seats-handtight, using no tools.

(3) Unwrap arming wire from bomb.

(4) Thread end of the arming wire through the inner of the two eyelets in the arming pin in accordance with instructions on tag. The inner eyelet is ordinarily not visible. Hand pressure on the head of the arming pin will expose the inner eyelet.

(5) Adjust arming wire to protrude from 2 to 3 inches.

NOTE.-No safety clip is to be used on the arming wire. After the fuze is assembled to the bomb and the arming wire inserted, it is only necessary to remove the cotter pin, in accordance with instructions on tag.

d. Functioning.-Functioning is identical with that of the fuze, bomb, M109 (nose), described in paragraph 81d(1).

FIGURE 19.-Bomb, fragmentation, 30-pound, M5, complete round.

84. Bomb, fragmentation, 30-pound, M5.-a. General-This bomb, with principal data and marking, is shown as a complete round assembly in figure 19. It is intended for destructive effect against such targets as personnel, motor convoys, airplanes on the ground, etc. For the complete round assembly, the following components are required:

Bomb, fragmentation, 30-pound, M5, unfuzed.

Fuze, bomb, Mk.XIV (nose).

Primer detonator, Mk.IIB or Mk.IIC, instantaneous.

Wire, arming, assembly.

The clip, paper, wire, type A, No. 1, serrated, on the arming wire assembly is used to hold the swivel loop temporarily to the fin during installation of the bomb in a vertical bomb rack.

b. Description.-The cylindrical body portion of this bomb is built up of steel rings mounted on an inner steel sleeve. As an alternative to the steel rings, a closely wound helix of bar steel is sometimes used. This type of construction (rings or helix) is used to produce optimum size fragments. The complete round bomb weighs 30 pounds, contains approximately 4.5 pounds of high explosive, and is adapted for a nose fuze only. To keep the fuze cavity clean of foreign matter, a closing plug is fitted to the adapter opening.

c. Assembly and disassembly (fazing and unfuzing).-The prior examination of components prescribed in paragraph 69 is for the purpose of insuring that all components at, the bomb fuzing point are serviceable. The complete round is assembled as follows :

(1) The tail suspension lug, if not assembled to the bomb, is shipped in the accessory tube in the bomb crate and must be assembled in place of the fin lock nut when the bomb is assembled for vertical suspension. This is not necessary when the bomb is assembled for horizontal suspension.

(2) After removing the closing plug, assemble the primer detonator and fuze. The bomb is now an assembled complete round, ready for installation in the bomb rack.

Note.-If the bomb is assembled for installation in a horizontal rack, the arming wire must be shortened. For assembly for horizontal suspension, cut the wire to such length that when the swivel loop is placed approximately 2 1/2 inches to the rear of the suspension lug on the side of the bomb, the free end of the wire will protrude from 2 to 3 inches beyond the arming pin. After the bomb is installed in the bomb rack, the cotter pin is withdrawn from the fuze in accordance with instructions on the tag attached thereto. When removing the cotter pin, care will be exercised not to disturb the adjustment of the arming wire. Should it be necessary to disassemble the complete round into its components, the above steps will be carried out in the reverse order and the components restored to their original condition and packings.

85. Fuze, bomb, Mk.XIV (nose).-a. General.-The Mk.XIV nose fuze (fig. 20) is a mechanical firing mechanism of the arming vane type containing no explosive. The explosive elements for the fuze are contained in the primer detonator, Mk.IIB, instantaneous, which is inserted in the booster of the bomb just prior to assembling the fuze to the bomb. With this primer detonator, the fuze is used in the following bombs :

Fragmentation, 30-pound, M5.

Gas, persistent, HS, 30-pound, Ml.

Smoke, phosphorus, WP, 30-pound, Ml.

b. Description. (fig. 20)-The fuze consists of two main sub-assemblies, the vane cup assembly and the firing pin sleeve assembly, the latter serving as the body of the fuze. A short pin, through the firing pin, extends on either side into slots in the firing pin sleeve. This presents rotation of the firing pin when its arming vane is unscrewing. A shear wire holds the firing pin in place after the arming vane has unscrewed. The vane cup which screws freely on to the firing pin (left-hand thread), retains eight steel balls in place between a flange on the firing pin and the firing pin sleeve, thereby preventing movement of the firing pin while the vane cup and steel balls are in place. A cotter pin, inserted through the vane cup and firing pin, prevents rotation of the vane cup during handling. One of the two screw eyes on the firing pin sleeve serves as one eyelet, while one of the two holes, one in each vane, serves as the other eyelet for the arming wire.

e. Assembly and disassembly (fuzing and un-fuzing).-No attempt will be made to disassemble the fuze. The only authorized assembly operations are those required to insert the primer detonator into the booster of the bomb and assembling the fuze to the bomb as described below.

(1) In the case of the chemical bomb, insert the appropriate booster and see that it is properly seated. In the fragmentation bomb, the booster is assembled to the bomb as shipped.

(2) Test the threads of the nose adapter by screwing the fuze into

FIGURE 20.-Fuze, bomb, Mk.XIV (nose).

the adapter until the fuze seats, then out again. The fuze should screw in and out freely without the use of force or tool.

NOTE.-This test is made prior to inserting the primer detonator into the booster, but, in the case of the chemical bomb, after the booster has been inserted. (See (1) above.)

(3) Gage the primer detonator socket in the booster to insure that the primer detonator will freely enter and properly seat in the socket. For this purpose, a gage of the same size and shape as the service primer detonator, Mk.IIB, made locally, may be used.

(4) With the cotter pin in place, test the vane cup for freedom of movement by rotating it back and forth.

(5) Insert the primer detonator into the booster.

(6) Screw the fuze carefully into the nose adapter of the bomb by hand until it seats. Do not use undue force or any tool.

(7) Thread the free end of the arming wire through the nearer screw eye and eyelet in the vane of the fuze. Should the nearer screw eye and eyelet be occupied by the cotter pin, place a second cotter pin in the screw eye and eyelet diametrically opposite before removing the original cotter pin. For vertical suspension the arming wire will not be threaded through either the horizontal suspension lug or the vertical lug of the bomb. Adjust the arming wire to protrude from 2 to 3 inches.

(8) Slip one safety clip over the end of the arming wire until it just. touches the face of the vane. To facilitate installation in vertical bomb racks, a serrated wire paper clip is assembled to the eye of the swivel loop and then temporarily attached to the upper edge of the. fin directly above the point where the arming wire is assembled to the fuze. This prevents dangling of the arming wire. The fuze is now completely assembled to the bomb, except that the cotter pin must be removed after the bomb is installed in the bomb rack of the airplane. If limitation of space in vertical racks prevents the removal of the cotter pin after the bomb is installed, the cotter pin may be removed just prior to installation. Should it. be necessary to disassemble the fuze from the bomb, the above steps will be carried out in the reverse order and the components restored to their original packings.

d. Functioning.-(1) Released armed-When the bomb is released armed, the arming wire is withdrawn from the fuze, thereby permitting the arming vane to be rotated by the air stream. The arming vane is thus unscrewed from the fuze and is carried off by the air stream. With the unscrewing of the arming vane, the eight steel balls are released and fall away, leaving the shear pin as the only mechanical restraint which prevents movement of the firing pin. Upon impact, the firing pin is driven into the primer, thus initiating the explosive train. The action is instantaneous.

(2) Released safe-If a bomb is released safe, the arming wire is released from the arming mechanism of the bomb rack and dropped with the bomb, thereby preventing the fuze from arming. Being unarmed, the fuze does not function on impact.