M111, M111A1, M111A2, M127, and M138 (Nose Clockwork Aerial Burst)

Bombs

M111A2

M127

M138

Functioning

Armed condition

Fuzes used with

Arming time

Vane span, inches

Body diameter, inches

Over-all lenght, inches

Material

Aluminum alloy body with zinc- or cadmium-plated steel body

General: The Nose Clockwork Aerial Burst Fuze M127 is formed by assembling the booster and detonator assembly from a Nose Mechanical Impact Fuze AN-M110A1 to a M111A2 fuze body. The result is a mechanical time fuze with an 18-gram tetryl booster instead of a black powder booster such as in the M111A2. The Nose Clockwork Aerial Burst Fuze M138 is the same as the M127, except that the M138 has only 7 grams of te-tryl, the balance of the space being taken up by an inert clay pellet. (M127 booster was too powerful for Cluster Adapter E6R2 and damaged the bombs in the cluster; hence, re-duction of tetryl.)

Operation: The desired time interval is set on the graduated scale, and the locking screw tightened. Upon release of the cluster or flare from the plane, the arming wire is withdrawn from the fuze. The vanes are then free to rotate, and the arming pin jumps out. The arming vane, nut, outer ball race, arming hub, and stationary gear rotate as a unit. As the vanes and stationary gear rotate on the ball race, the idler gear is rotated, thus rotating the movable gear and the arming sleeve to which it is attached. The arming sleeve is threaded into the arming hub and extends inside the safety block. Since the movable gear has one more tooth than the stationary gear, it lags one tooth on every roatation and gradually uscrews downward. After approimately 260 vane revolutions, the arming sleeve has unthreaded far enough to be withdrawn from the safety block, which is then thrown clear by centrifugal force. The timing disc, meanwhile, has been rotated by the spring-driven clockwork. After the predetermined time has elapsed, the slot in the timing disc will be positioned opposite the timing disc lever. Through a series of levers, pressure forces this timing-disc lever into the slot, thus freeing the firing lever. Since the half-round pin is no longer retained by the firing lever, it is free to rotate under the pres-sure of the spring-loaded firing pin, a collar on the firing pin bearing on one side of the notch in the half-round pin. As the half-round pin rotates, the firing pin is released and impinges on the primer, firing the booster. If the timing mechanism should fail, the fuze would still detonate on impact, because the striker would be forced down and would shear any obstruction between it and the primer.

Early designs: The original Nose Clockwork Aerial Burst Fuze M111 had a setting range of from 15 to 93 seconds, and, because of the greater number of teeth on its gears, required 570 vane revolutions to arm.

M111A1 reduced minimum setting time on the scale from 15 to 5 seconds. The fuze, however, could not be set for less than 8 seconds, since, if set for less, the clockwork functioned before the fuze was armed, and the firing pin spring pulled the striker down tightly against the safety blocks, stopping the rotation of the vanes, thus preventing aerial burst. Both of these early designs had three 120° section safety blocks with a groove which received the arming sleeve of the movable gear. They also had weaker gears with more teeth; and larger weaker vanes.

Remarks: The M111A2 booster contains 70 grains of black powder.

Neither the M127 nor the M138 should be assembled to their respective clusters, until the cluster has been locked in place in the bomb rack.

The Nose Clockwork Aerial Burst Fuze M127 is being replaced by the M128; the M138 is being replaced by the M145; the M112A2 is being replaced by the M146.

These fuzes are equipped with a spinner device to force the safety block to rotate with the arming vane and insure positive ejection of the safety block after the arming sleeve has withdrawn. Only later lots of M111A2 are equipped with the spinner device.

Figure 336. Aerial Burst Fuze M111A2