Nose Fuze No. 899 Mk I (Service)

Rockets used in

Action

Armed condition

Arming time

Body diameter

Over-all length

Color

Description: This fuze consists of the Rocket Fuze No. 712 Mk III modified for safe carriage on aircraft. These modification consist of the removal of the safety cap and safety clip from the standard Fuze No. 721 Mk III and the addition of two semi-discs fit-ted with vanes, a circlip, a setback collar, an inner sleeve, a spring, and a spring-retain-ing washer.

In the unarmed position, the two semi-discs are inserted between the pressure plate of the striker and the head of the fuze body, preventing the striker from moving down-wards. The semi-discs are retained by a circlip which fits into an annular groove machi-ned around the top of the two discs. Rotation of the vanes and the semi-discs is pre-vented by two grooves on the top edge of the setback collar in which the vanes engage. A pin, located inside the setback collar ridges in a slot cut in the inner sleeve, preventing the collar from rotating. The inner sleeve, in turn, is prevented from rotaing by its en-gagement with the protruding ends of the shear wire of the fuze. The setback collar is held in the raised position by the inertia spring, which is retained by the spring-retaining washer.

Operation: When the rocket is projected from the aircraft, the setback collar rides down against the action of the inertia spring. The semi-discs are thus disengaged from the set-back collar, and are free to be rotated by the attached vanes. When the rota-tional speed of the semi-discs reaches about 3000 r.p.m., the centrifugal force thus created overcomes the restraint of the circlip, and the two semi-discs fy free of the fuze.

Impact with the target causes the pressure plate to force the striker through the alu-minum shear wire into the detonator, firing the magazine and exploding the shell.