BOMBS USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

MAX. BODY DIAMETER

OVERALL LENGTH

COLOR

DELAY TIMES

DESCRIPTION:

The No. 881 Mk I is a combination long delay and anti-disturbance fuze, while the No. 883 Mk I is anti-disturbance only. These fuzes are identical except that a brass plug replaces the delay assembly in the No. 883. Both are similar in external appoarance to the No. 880 Mk II fuze, the only difference being that the arming pins in the former are set off-center, while that of the latter follows the central axis of the fuze.

OPERATION:

When the fuzed bomb is fitted into the cluster, the safety screw is removed and the arming pin is linked to the parachute. When the bomb is released from the cluster, the parachute opens and withdraws the arming pin. This allows the detonator shutter to align the detonator with the striker and the two large locking balls to move into the space vacated by the arming pin. The upper locking ball serves merely to seal the arm-ing pin hole; the release of the lower locking ball pratially disengages the locking sleeve from the bayonet sleeve.

On impact the bayonet sleeve moves downward due to its inertia until stopped either by the main spring or contact with the top of the ball cage. This allows the small locking ball to move into a recess in the bayonet sleeve, fully disengaging the locking sleeve from the bayonet sleeve.

Although the main spring is assembled under considerable torque tension, rotation has been previously prevented by the ball lock between the locking sleeve and the ba-yonet sleeve. The latter is firmly positioned by a pin extending down from the fuze body. The three upward extending fingers of the ball cage engage in similar notches cut in the bottom edge of the locking sleeve. When the locking sleeve and the bayonet sleeve are disengaged, the main spring exerts its torque influence and commences to rotate the ball cage and locking sleeve in a clockwise direction. This rotational move-ment, however, is slowed down by the brake plate and knife assemblies. The brake plate assembly consists of two perforated plastic discs held in a metal housing. Tabs in the outer edge of the brake plate assembly are engaged by the three fingers of the ball cage, causing the assembly to rotate with the cage. The three knife edges of the brake knife extend downward through the perforations in the brake plate assembly and into three holes in the top of the bayonet sleeve. The brake knife, therefore cannot ro-tate, but must cut through the plastic discs of the brake plate assembly when the ball cage rotates. Holding the brake plate and knife assemblies loosely in place is a small screw with a long projecting head. This screw threads into the top of the bayonet sleeve.

Located inside the ball cage are the striker and six retaining balls. The lower end of the release spring is fitted into a screwdriver slot in the top of the striker; the upper end of this spring engages a hole in the base of the bayonet sleeve. The spring itself is loaded under torque tension, attempting to rotate the striker. But the striker is preven-ted from rotating by the guide fork. A notch cut in the upper portion of the striker is engaged in a slot cut in the guide fork, and two upward extending prongs on the guide fork engage in similar grooves in the base of the bayonet sleeve. The six retaining balls are arranged, one on top of the other, in two layers of three balls each. In the unarmed position, these balls are held in place around the striker by the inner walls of the ball cage. The ball cage is prevented from rotating more than 60°, since the fingers of the cage at the end of that distance come up against the ends of the slots in the base of the bayonet sleeve. Rotation of the ball cage through 60°, however, presents cutaway protions of the inner walls to the balls. The balls are then prevented from scattering only by point contact between themselves, the steel ring placed around the striker above them, and the steel plate placed around the striker below the balls.

When the ball cage has completed its 60° rotation, the fuze is fully armed. A delay assembly in the top of the fuze consists of a housing containing a metal plunger and a plastic delay disc. When the bayonet sleeve is disengaged from the locking sleeve, the main spring forces the bayonet sleeve upwards, bringing the extended portion of the screw into contact with the plunger, which gradually forces its way through the delay disc. When the bayonet sleeve has risen sufficiently to disengage the prongs of the guide fork, the striker is allowed to rotate the torque tension of the release srping. The flick motion imparted to the striker scatters the balls and allows the striker to be forced into the detonator by the main spring working through the ball cage. Disturbance of the fuze prior to its long delay functioning will scatter the balls from under the striker, and the ball cage under the compression of the main spring will move downward, bringing the striker into contact with the detonator.