M149 (Nose Impact or Blast Pressure)

Bombs

Armed condition

Fuzes used with

Arming time

Vane span, inches

Body diameter, inches

Over-all length, inches

Material

Cadmium- or zinc-plated steel

General: The Nose Fuze M149 is a detonator-safe nose fuze. The fuze is designed both for instantaneous action on impact and for air-burst a short distance above the target as a result of the blast wave from the first bomb of a stick of bombs. The first bomb will detonate on impact, while its blast, if of sufficient intensity, will detonate the second bomb, etc., in the air over the target. For example, if 500-pound bombs are dropped in train at 0.05 second intervalls at air speed of 200 m.p.h. (14.7-foot spacing) from 10,000 feet, the burst of the second bomb in air will be at a point approximately se-ven feet ahead of (horizontal separation) the first bomb and 23 feet avove (vertical  se-paration) the first bomb. Other bombs in the stick will function the same distances from the bomb which precedes them.

Operation: As the arming wire is withdrawn the vane cup rotates. After approxima-tely eight or nine turns of the vane cup, the release pin is ejected by its spring. The arming stem rises under pressure of its spring, permitting the detonator slider to align it-self below the flash tube. After 12 to 13 turns of the vanes, the vane cup falls off, and the fuze is now fully armed. Bombs fuzed with the Nose Fuze M149 should be released in close train, to take advantage of the air burst feature of the fuze. The first bomb of a stick will detonate on impact with the ground; impact simply snaps the diaphragm to its reversed position, causing the firing pin to strike the pimer.

The second bomb of the stick will be detonatd by the pressure blast of the first bomb. The blast of the first bomb will cause the diaphragm in the fuze of the seond bomb to snap over while the bomb is still in the air a relatively short distance above the target, and thus cause detonation.

Should the diaphragm fail to function for air burst, the fuze can still fire from impact action.

Remarks: When installing the M149, check the vane cup to see that it is free to turn. However, do not unscrew the vane cup, as only a few turns are required to arm the fuze. In the armed condition, the fuze must of necessity be very sensitive.

The fuze is equipped with three expansion chambers, so that, as the diaphragm snaps in, it will not be resisted by an air cushion, which might prevent complete inward move-ment of the diaphragm.

This fuze is detonator safe. In the unarmed position, the detonator is lined up with the safety expansion chamber. If the detonator should function prematurley, the force of detonation is dissipated in this cavity, and will not set off the lead-in and booster char-ges.

Production of the Nose Fuze M149 has been discontinued, since V.T. fuzes offer more assurance of air burst.

Figure 353. Impact or Blast Pressure Fuze M149