Markings: Z 89B, Z 89C on the spring loaded charging plate is "Nur für Hand Einstellung" – Not for hand setting.

Arming Times: Immediately on release from aircraft.

DESCRIPTION. The Z 89B is an electrically initiated clockwork fuze to give aerial burst. The mechanism is enclosed in a sheet metal casing similar to the 55 type fuze. The head of the fuze is machined to take a normal charging head but has one single charging plate instead of the two charging plungers. Attached to the charging plate is the contact rod, the lower end of which is machined externally to accept the insulated boss.

The time setting bush is rotatable and has a slot on the upper surface to take the time setting key. Projecting from the lower extremity of the time setting bush is a lug which contacts the nub on the timing disk.

The metallic strip A makes electrical contact with the contact rod when the disc is de-pressed. Strip A is continuous with metal ring B against which spring strip C presses. The latter metal strip is insulated from the body of the fuze and is connected to the firing bridge by means of an insulated wire. The return circuit is completed to the body of the fuze by a second insulated wire. The wires are external to the clock.

The clockwork mechanism is similar to the (17) series clock. It has one spring-loaded de-tent to hold the flywheel of the clock immovable and a second spring-loaded detent for safety device. This second detent holds the striker safety shutter in place.

The electrical igniter is so positioned that when it is fired, the thermal action created re-moves the detents, retaining the plug, allowing the spring loaded detents to remove themselves from the clock. Now the clock can run its set time. (See fig. 179.)

OPERATION. While the bomb is in the aircraft, the charging pins keep the charging plun-ger depressed. On release, a charge is passes through the igniter via the contact ring and second contact strip thereby firing it.

The explosion as mentioned above by either force the thermal action removes the retain-ing plug, the detents fly out and the clockwork begins to function. When the slot in the timing disc rotates to a point opposite the release nib, this spring loaded nib moves into the slot. This action frees the striker which is forced onto the detonator firing the fuze.

Figure 179 – (89)B Clockwork Aerial Burst Fuze