Downloaded from https://www.everyspec.com AMCP 70.210 far out of range when the time runs oct. On the quires only inexpensive materials. However, such other hand, a fuze equipped to both contact- a fuze is inherently slow in operation when corn- sense the target and to be preset would function pared to actions taking place in the order of en h amicroseconds, and it is not easily adaptable to when hitting a target before the predetermined rime setting. In addition, the versatility of a fuze remote sensing. i si r nFor initiation then, it is necessary to obtain relative motion between firing pin and primer. sensing the target.
A fuze may be built so that For the simplest solution, the forces on muni- the operator may preselect the action(s) desired. tion impact are used to crush its nose, thereby While the impact-time combination mentioned forcing the pin into the primer. In a base fuze, above is the most common, other combinations the pin or primer may float in a guide throuph are also used when needed. which it moves when relative changes in mo. An action often combined with contact sen- mentum occur. Springs are also used to provide sing fuzes is self-deatruction.
In the senre that a relative motion between pin and primer, espe- fuze is informed in advance when to self- cially in time fuzes where inertial forces of im- destroy, this action compares to presetting. It pact are not available. Firing pins for stab initiation are different differs, however, in that no target is expected at from those for percussion initiation as ex. that point. This feature is used most often in plained in the paragraphs which follow. Typical fuzes that are fired at aircraft so that they will firing pins are shown in Fig. 3-1. Ir.itiation by function before hitting friendly territory if they adiabatic compression, on the other hand, does miss their target.
Self-destruction is accomplished not require a firing pin at all. when the fuze senses that a certain amount of time has elapsed or that some change in environ- 3-3.2 INITIATION BY STAB ment has occurred. This may be achieved di- rectly by a timer, or indirectly by spin decay or If the pin punctures the primer case and enters by change in acceleration. a suitable explosive charge, an explosion can be produced. This is referred to as stab initiation. 3-3 MECHANICAL FUZE INITIATION The point of the stab firing pin commonly used in United States fuzes is constructed in the shape 3-3.1 THE INITIATION MECHANISM of the frustum of a right circular conec.
A firing pin with a point in the shape of a pyramid seems should start target action, a number of complex manufacture. The criteria below have been de- veloped for the design of stab firing pins. They mechanis s may start to operate. The necessary are Pustrated in Fig. 3-2. power to operate the fuse must be made imme- (1) Flat Diameter. Variations in this diam. diately available. This power must then activate eter have shown little effect on energy input re- any time delays or other necessary devices prior quired for initiation below a diameter of 0.015 to initiation of the first element of the explosive in. for stab initiated items of currently prevalent train, design.
For larger diameters, the energy input re- In a mechanical fuze, contact sensing (impact) quirements increase at a much higher rate. or presetting (time) is converted directly into (2) Included Angle. As this angle is de- mechanical movement of a firing pin which in creased, the apparent primer sensitivity is in- turn is driven either into or against the first ele- creased. However, some compromise must be ment of the explosive train. This is a simple and reached; for, the smaller is the angle, the weaker straightforward process. Functioning delays are is the firing pin.
The angle should be hcld under usually obtained by pyrotechnic delays which 260 where practical because above this value the are an intimate part of the explosive train (see required energy input increases rapidly. par. 4-4.1). (3) Corner Radius. A sharp corner is desir. A mechanical fuze is simple to produce, rea- able but a small radius is permissible. A radius Once the fuze receives information that it to improve sensitivity, but is more difficult to 3-3