Components

Head: This is the part which is functionally similar to a projectile and which contains the payload and the initiating device. This payload may be solid shot, high explosive, chemical, incendiary, window, flare, or a special load.

Motor tube: This contains the propelling charge and the igniter. It is a combustion chamber in which the propellant is burned to provide the motive power for the rocket. It generally threads to the rocket head and is usually shipped separate from the head and fuze. The diameter of the motor is generally less than the diameter of the body with which it is used.

Grid or trap assembly: The Navy refers to the assembly which supports the powder grain as the grid. This grid supports the grain in such a position that sufficient clearance is allowed between the grain and the motor tube to allow the gas to flow from the pro-pellant to the nozzle. The Army uses a trap assembly, which is somewhat more compli-cated thant the Navy grid. The trap assembly consists of spacing discs and wires running between them, on which the sticks of ballistite are supported. Such an assembly is ne-cessary where numerous small grains are used.

Nozzle: The number of nozzles varies with the type of motor and method of stabiliza-tion. The nozzle has several functions. It directs the gas jet in the desired direction and provides for expansion of the hot gas in the exit cone, thus giving additional thrust (about 33%) over that obtainable from a simple orifice. In spin-stabilized rockets, it im-parts a clockwise rotation to the rocket when launched.

Fins: During burning, the action of the air against the fins gives a restoring moment against side forces at the nozzle, thus improving the accuracy of fire. When there is a tail shroud, it supports the rear end of the rocket in the launcher and may also provide electrical contacts for firing.

Propellant and igniter: The igniter contains loosely packed black powder and an electric squib with a high-resistance bridge running through a match composition. The propellant is a double-base smokeless powder called ballistite, which burns slowly and uniformly. Production of ballistite differs somewhat for the Army and the Navy, the Army preferring the solvent extrusion process and the Navy specifying the solventless extrus-ion process. The solvent extrusion process is impracticable for grains having a web of more than 1-1/4-inches.

Grain shapes also vary. Army rockets generally have several small cylindrical grains of ballistite, with an axial hole to increase the burning surface and uniformity of burning. The Navy rockets use either a single solid cruciform grain without perforations or a sing-le cylindrical grain with an axial hole and radial perforations. The latter, used in Navy ground- or shipboard-mounted rockets, is characterized by three ridges 120° removed and running longitudinally along the grain. Inhibitors are not used on this type. The cru-cifrom grain, in Navy aircraft rockets, is a symmetrical cross with rounded ends. If all the exterior surface of this grain were permitted to burn, there would be a gradual decrease of area, and a regressive rate in burning. Hence, a number of slower burning cellulose acetate strips are bonded to parts of the area exposed on the outer curved ends of the arms, to give desired burning characteristics.

Figure 113. Type Rocket Components