Nose Ejection Clusters

1394-203

Nose ejection clusters were put into production near the end of World War II. The information presented here is a generalized summary of nose ejection clusters, due to the fact that many of the individual clusters of this type are still in the developmental stage.

General Requirements

The fundamental requirement of any cluster is to provide a means of placing cluster contents effectively on the target, the effectiveness being regarded broadly as a function of the angle and velocity of strike, functioning of fuzes or strikers, density of pattern, and accuracy of aim. Complementary requirements of equal importance are that the cluster shall provide an economical aircraft bomb load, that its preparation for use shall be simple and speedy, that it will withstand road, rail, and ship transport without endangering its safety or usefulness, and that it will meet the strength requirements specified for carriage of bombs in British and American aircraft.

The type of nose ejection cluster now being developed and in production goes far towards meeting these requirements in a simple and direct manner. It is not possible to generalize on the stability of nose ejection clusters as a group, since this depends on weight and dimensional characteristics, which are mainly due to the type of cluster contents carried. Ballistic stability resulting in an aiming error of between 2 and 6 mils is being obtained, and will be improved upon as the development of folding and telescopic tails progresses.

The effectiveness of cluster contents from nose ejection clusters is largely fortuitous. It appears to depend mainly on the inherent stability of the cluster contents and the parent cluster, although the velocity and height of disintegration of the cluster has some bearing. Control of cluster velocity at disintegration is a problem now being explored. Earlier investigation showed that decreased velocity at disintegration is invariably accompanied by a closing in of the scatter pattern, and much work on the control of the scatter pattern remains to be done.

Increasing the size of scatter patterns by means of attachments to the cluster contents and asymmetric parasheets is being investigated, but the results so far obtained, though promising, do not justify immediate embodiment.

Body Construction

The cluster body consists of a cylindrical steel shell made from 10- or 12- gauge steel plate, and is closed at the rear end by a steel plate of similar gauge, which is welded in position. Two fuze pockets, which are deep enough to accommodate the burster ejectors, are attached to the end plate, which also embodies a centrally tapped hole for attaching the cluster tail. A test plug, by which air pressure is applied at the filling factory to check that the rubber sealing joints in the nose are properly tight, is also provided in this plate. The end plate is shaped to form a shallow truncated cone, the sloping surface of which locates the tail centrally on the cluster body. The nose end of the cluster is closed by an iron casting secured in place by a number of screws. On the inside of the casting is an internal steel squash plate secured by a central screw. Its purpose is to compress the rubber sealing ring against the internal surface of the cluster body to exclude air. A knife is attached at the front end of the cluster for the purpose of cutting the steel straps as the fagot of cluster contents is ejected. A pressure plate is assembled in the cluster behind the fagot of cluster contents. Suspension lugs for British and American type bomb stowage are permanently attached to the cluster body.

The cluster is designed, manufactured, and tested to withstand the climatic conditions experienced in the Far East. After assembly at the filling factory, the rubber sealing joints in the nose and under the knife fixing screws are tested for tightness by an air-pressure test.

Tail Construction

Two types of cluster tail are in use, the conventional type with a tail cone and cylindrical strut, and one having collapsible fins, which is used where the space available is loo small to permit the use of a normal-type tail. Twin arming mechanisms are locked by means of fuzing wires engaging holes in the arming vanes. Windows are provided through which the fuze can be observed as the tail is assembled to the cluster. The tail is located on the tapered end plate of the cluster body, and is secured by a single central bolt. It is designed, manufactured, and boxed for use in tropical climates.

Transit Bases

To prevent the cluster from sustaining damage affecting the safety of its contends, or destroying the hermetic seal in the nose, each cluster is fitted with transit bases which are intended to remain in position until the cluster is prepared for use.

The transit bases consist of two light-gauge steel rings filled with a material designed to withstand shock loads resulting from rough large area of the cluster and so prevent damage to the nose seal, which would inevitably result from a blow concentrated at any one point on the nose cover. The material used in the Mk I design is a resin-bonded sawdust, which is light in weight and resistant to tropical climatic conditions, fungi and insect growth, etc. The bases are fitted one at each end of the cluster, and secured by tie rods, which embody a quick release device designed to enable the bases to be removed in a minimum of time.

Fuzing

One fuze and burster only are necessary to disintegrate the cluster, but two of each are used as an insurance against complete failure. Clusters containing 4-lb. I.B.’s are fuzed with two Tail Fuzes No. 42 Mk IV, while all others use two Barometric Tail Fuzes No. 886.

Burster Ejectors

Ejection of the cluster contents in effected by a burster ejector, which is ignited by the cluster fuze. The bursters are placed in the cluster at the time of fuzing. There are two types of burster, the No. 6 Mk I containing 70 grms. of G. 20 powder for large clusters, and the No. 7 Mk I containing 50 grms. of G. 20 powder for the smaller clusters. The powder is contained in a plastic cylinder manufactured from a polyvinal chloride. This material is fully resistant to tropical conditions and does not affect the gunpowder. The cylinders are provided with two small extrusions by which they can be removed from the cluster if required.

For transport and storage the bursters are packed two or four (according to size) in a sealed metal cylinder, 18 of which are packed in one wooden box. The metal cylinders are opened by means of a tear-off metal strip.

Contents

The cluster contents are assembled in two or more banks of bombs, with light-gauge steel end plates and longitudinal steel struts, to form a fagot, which is firmly secured by a number of circumferential steel straps. When properly assembled to a fagot, the cluster contents are safe and the fuzes cannot arm accidentally. Damage to components of the cluster contents by the force of the ejector charge is prevented by the steel struts, which transmit the force of the explosion from the pressure plate directly to the nose cover, and not through the bombs themselves.

Developmental Priority

The following is a list of nose ejection clusters in order of their development priority. The first six items were cleared for production on 7 July, 1945.

Cluster N. E. ANM 69 I.B., 600-lb. Mks I & II

Cluster N. E., 18-lb. Mg. I.B., 800-lb. Mk I

Cluster N. E., J. 20-lb. I.B., 800-lb. Mk I

Cluster N. E., ANM 40 H.E., 600-lb. Mk I

Cluster N. E., ANM 40 H.E., 350-lb. Mk I

Cluster N. E., F. 8-lb. H.E., 550-lb. Mk I

Cluster N. E., F. 8-lb. H.E., 350-lb. Mk I

Cluster N. E., F. 8-lb. H.E., 1,000-lb. Mk I

Cluster N. E., ANM 69 I.B., 550-lb. Mk III

Cluster N. E.,. 4-lb. I.B., 800-lb. Mk I

Cluster N. E., J. 30-lb. I.B., 500-lb. Mk I

Cluster N. E., 4-lb. I.B., 500-lb. Mk I

Cluster N. E., 4-lb. I.B., 950-lb. Mk I

Cluster N. E., ANM 69 I.B., 1,000-lb. Mk I

Cluster N. E„ 3-lb. I.B. 1,000-lb. Mk I

Source(s)

OP 1665, British Explosive Ordnance (1946)