ROCKET USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

VANE SPAN

MAX. BODY DIAMETER

OVERALL LENGTH

3-1/2" (without booster)

GENERAL:

The body of this fuze is converted nose plug from a 5" projectile. The working parts of the fuze are very similar to those of the Mk 148 A.I.R. fuze, which it is replacing. The essential changes are the addition of a second setback block, shutter locking pin, a nose cap and clamp, and smaller but less sharply pitched vanes. The fuze body itself is more streamlined. The addition of the spring loaded weather cap over the vanes pro-tects the vanes from icing up during flight of the aircraft at high altitudes. This cap does not spring off until the arming wire is pulled from the clamp when the rocket is fired.

OPERATION:

When the rocket is fired, the arming wire is pulled free from the clamp pin and the compressed weather cap spring forces the weather cap up, spreeding the clamp until the weather cap is free. The force of inertia causes the top setback blocks to fall bach against the pressure of the setback spring. This accomploshes two things: First, the vane locking pin is freed from the vane boss and the vanes are free to rotate and screw the striker upward. Second, the lower setback block forces the shutter locking pin down into the shutter cavity, preventing the shutter from moving over and lining up under the striker as long as the rocket is accelerating (i.e. as long as the rocket motor is burning). After 8 vanes revolutions, the point of the striker will have risen clear of the shutter; and upon reaching the end of the threads, the spindle will rotate freely as the striker collar rides in the groove in the fuze body. After the rocket propellant has ceased burning, decelartion occurs and both setback blocks are fored up by the set-back spring. The shutter locking pin is thus lifted from the shutter cavity and the shut-ter moves across the fuze under influence of its spring until stopped by the stop pin. A spring-loaded detent in the detonator shutter springs up into a recess in the striker guide, locking the shutter in the armed position. On impact, the striker shears the body threads and is driven into the detonator, setting off the booster lead-in and booster in succession.

Mk 155:

The Mk 155 is used in the Mks 6 and 9 smoke filled 3.5" rocket heads. The fuze is similar to the Mk 149 with a burster tube instead of a booster charge.