Cluster Projectile 500-lb. No. 17 Mk II (Service)

Description: The cluster comprises twenty-six 20-lb. fragmentation bombs arranged in two fagots of thirteen bombs each. The bombs are held in place by a front end plate and a rear end plate, a top beam and a bottom beam, side plates which overlap each other, and tensioning straps and a retaining bar, which hold the components together. The bombs are completely enclosed. Lateral pins on the retaining bar engage tabs form-ing part of shoes attached to the ends of the tensioning straps. A shear wire passes through the retaining bar and a bridge on the top beam. A channel secured to the rear end plate supports a fuze adapter, the outer end of which is closed by a transit plug and leather washer. Inside the adapter is a piston through which is a pin to engage the lower end of a pivoted lever. The fuze adapter and piston are slotted to receive the lower end of the lever. The lever passes into the fuze adapter. Links connect the upper end of the lever to a downwardly projectiong plate, welded to the retaining bar. The rear end plate has two dowels for loacting the tail in position, and a nut welded to the center of the plate to receive one end of a tail tie rod, when the tail unit is fitted to the cluster. The front end plate has two dowels for locating either a blunt nose fairing or a streamlined nose fairing position, and a nut welded to the center of the plate to receive the securing stug of the blunt nose fairing, or the tie rod of the streamlined fairing. The blunt nose fairing is fitted to the cluster if it is to be carried internally in an aircraft. The streamlined nose fairing consists of a hollow metal dome, the base of which is partly covered by an end plate welded to the dome, and is to be fitted to the cluster when carried externally on an aircraft.

Tail Construction: The Tail Unit No. 63 Mk I consists of a taile cone, having an ap-proximately octagonal base and a tail strut secured to the cone by six supports. The tail unit has an arming spindle mounted in bearings, and has a fork at its inner end and a arming vane at its outer end. Two inspection windows in the tail cone are provided to enable the armorer to watch the fork of the arming spindle, when fitting the tail unit to a cluster fuzed with a Tail Fuze No. 855. The Tail No. 63 Mk I is only used when the cluster is carried internally in an aircraft. The Tail No. 63 Mk II is similar to the Mk I except that is generally strengthened and has seven tail drum supports as compared with the six of the Tail No. 63 Mk I, and is to be used when the cluster is carried externally on the air-craft.

Functioning: When the fuzed cluster projectile is released, the fuze functions, and, after a period of delay during which the cluster falls freely, the fuze magazine is fired. The products of combustion of the magazine charge force the piston in the fuze adapter against the lower end of the pivoted lever, which is thus rocked about its pivot and exerts a pull on the retaining bar of the cluster. The pull breaks the shear wire passing hrough the retaining bar and moves the bar so that its pin disengage the tabs on the tensioning straps. The straps then fly outwards and the cluster disintegrates. Its com-ponent parts fall away separately and the individual bombs descend, supported by their parachute, to function in the normal manner.

Suspension: A British type suspension lug is fitted to the top beam, and tapped holes in the top beam are provided for fitting American type lugs.

Figure 115 - Cluster Projectile 500-lb. No. 17 Mk II