Page:EB1922 - Volume 30.djvu/168

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parted, whereupon the spring drove the needle on to the detonator and exploded the fuze. (D. D. T. O'C.)

French Fuzes, in marked contrast to German, are deliberately simple in type and the number of types also is limited. The four patterns described below may be taken therefore as fully represen- tative of French practice.

The typical pre-war percussion fuze is the direct-action fuze shown in fig. i"8. The action will be readily understood from the figure. Before firing, a heavy ferrule is supported between a compressed spiral spring and a stirrup spring which surrounds the detonator pellet. On shock of discharge (aided by the decompression of the spiral spring) the ferrule sets back, straightening the stirrup spring, and fits over both stirrup spring and detonator pellet, being held there by the spiral spring acting as a creep-spring. On impact the pellet and ferrule fly forward together on to the needle, and the de- tonator is fired. The spiral spring can be adjusted for tension by screwing the closing plug in or out.

A more highly developed design of the same class is Fuze 24/31 P.R. model 1916, distinguished by an ingenious combination of safety pellet and detonator holder which has been copied in the British Fuze No. 134 (fig. 2).

As in other French fuzes, and in British, impact or delay effect is arranged by the design of explosive filling below the main detonator and not by that of elements in the fuze itself.

French instantaneous fuzes are characterized by simplicity and great projection from the nose of the shell, the latter being intended to ensure that the fuze shall act before the shoulders of the shell strike the ground and begin to bury themselves.

Crayo

Strike

Striker hud

Safety collar

FIG. 19.

A simple representative is shown in fig. 19, which is a cheap and effective trench-mortar fuze. (French trench-mortar projectiles are vaned and so fall nose first.) The striker consists of a head, which in transport is kept off the head of the fuze by a safety ring, and a long striker which is kept centred by a wooden " crayon " in much the same way as the lead is held in an ordinary lead-pencil. Through the head of the striker passes a shearing wire of copper alloy (Cu 67%, Zn 33 %). Before firing, the safety ring is removed and only the shearing wire keeps the striker point off the detonator. This resists the shock of discharge (which is relatively slight in a trench mortar) but is sheared on impact. It will be observed that the fuze is not sensitive during flight, as the German fuzes and the British No. 106 are, but relies for its instantaneous effect chiefly on the fact that the striker head takes the ground a moment before the shoulders of the shell do so. A fuze of this class when used with a rifled gun would have a centrifugal unwrapping tape similar to that of the British 106 Fuze in lieu of the safety ring. The actual detonator arrangements, not shown, may be varied in the usual way by introducing or omit- ting a delay pellet. The lower end of the fuze is screwed to receive a steel gaine.

I

FIG. 20.

The French T. and P. Fuze (Fusee double effel 23/31, fig. 20), designed in 1897, remained in service throughout the war of 1914-8

as the standard time-shrapnel fuze for the 75-mm. field gun. Unlike the British, German, and other T. and P. Fuzes, it is set, not by means of a movable powder ring, but by punching a hole at the appropriate point in a composition-filled lead tube by means of a fuze-setting machine called a dcbouchoir.

The time composition is contained in a sealed lead tube fitting into a spiral groove on the upper and slightly tapered portion of the body. Over the body is a cover on which a long spiral scale is engraved, with graduations corresponding to the appropriate points in the composition worm which lies exactly under it. Certain points on the scale are marked with a hole instead of a figure ; these subsequently act as a relief for the gases and slag. To set the fuze a hole is punched by the debouchoir through the cover, lead tube, and body, thus making free communication with the interior. The time ignition pellet (which carries the needle in this case) is kept away from the fixed detonator by a coiled spring which it overcomes on shock of discharge. The resulting flash from the detonator ignites a powder pellet, which gives a powerful flame filling the interior of this part of the fuze, and lighting the composition in the lead tube as it passes through the hole punched by the fuze-setter. The composition then burns along the tube until the flame reaches the end of the lead tube, whence it passes by a cross channel to the magazine. (A peculiarity of the French fuze is that the flash from the magazine, instead of passing by a channel of its own to the interior of the shell, ignites the detonator pellet of the percussion system, which thus acts as a relay.)

The percussion system consists essentially of : (a) a ferrule provided externally with a collar and internally with a spring catch device ; (6) a detonator holder, hollow to take the detonator and a magazine of fine-grain powder underneath it, and provided externally with a broad flange at the bottom and peripheral ratchet-like notches at the top; and (c) a strong retaining spring and weaker creep-spring. Until the gun is fired the retaining spring, bearing on the collar of the ferrule, keeps this pressed up against the top of the cavity; above the collar the creep-spring is'under a slight compression, but this does not affect the security of the fuze. On discharge, the ferrule, overcoming its retaining spring, sets back over the detonator holder, where its internal spring catches engage under one or other of the peripheral ratchet-notches on the holder. The ferrule, compressed spring and detonator holder are now locked together. Held steady during flight by inertia and the creep-spring, on impact they fly forward on to the needle.

FIG. 21.

In the illustrations, which are diagrammatic, the parts are not to scale, and details (e. g. the centring sleeve for' the ignition needle pellet) are omitted so as to show the operation of the fuze more clearly.