Figure 2-7.—Nozzle and fin assembly (2.75-inch).NOZZLE AND FIN ASSEMBLIES.— The nozzleand fin assembly (fig. 2-7) used with the Mk 4 andMk 40 motors consists of a nozzle plate, four nozzleinserts, a fin-actuating mechanism, four fins, and a finretainer contact disc. The nozzle assembly for theMk 66 consists of the nozzle body, carbon insert, fins,contact band assembly, and weather seal.The fins are attached by pivot pins to lugs machinedon the aft part of the nozzle plate. When folded, the finslie within the 2.75-inch diameter of the rocket. The finsare notched at the tips to allow attachment of a fin retainer.The fin-actuating mechanism is a steel cylinder anda piston with a crosshead attached to its aft end. Whenthe rocket is fired, gas pressure from the motor operatesthe piston, cylinder, and crosshead. The crosshead ispushed against the heels of the fins, causing the fins torotate on the fin pivot pins to the open position after therocket leaves the launcher. After the fins have openedto the final flight position, the crosshead prevents thefins from closing.There are four nozzle inserts and the detent groovein the aft end of the nozzle plate. They hold the rocketin position after it is loaded in the launcher (fig. 2-8).The major difference between the nozzle and finassemblies used on the Mk 4 and Mk 40 motors is thetype of nozzle inserts used.Figure 2-8.—Nozzle and fin assemblies. (A) Mk 4 Mods motor (B) Mk 40 Mods motor.2-6
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