Mk 16 motor, nozzle, and fin assembly

Figure 2-9.—Mk 16 motor, nozzle, and fin assembly. The nozzle inserts of the Mk 4 motors are standard or straight cut (fig. 2-8, view A), while the Mk 40 motor nozzle inserts are scarfed or cut at an angle (fig. 2-8, view B). The scarfed nozzles used on the Mk 40 motor impart a stabilizing spin to the rocket when launched at low initial-launch speeds, such as from helicopters and low-speed aircraft. A rocket using the Mk 40 motor is designated a LSFFAR (low-speed, folding-fin, aircraft rocket) and is used only on helicopters or low-speed aircraft. All Mk 16 motors have a single nozzle with four straight folding fins (fig. 2-9) that attach to the aft end of the motor tube by threads. To protect the propellant grain from moisture and to promote propellant grain ignition, the nozzle opening is closed by a thin metal seal and a foam plug. A light plastic fin retainer holds the fins folded within the diameter of the rocket until propellant ignition. On ignition, the fin retainer is blown off. Gas pressure exerted on the heels of the fins pushes the fins open as they emerge from the launcher tube. The fins are then locked in the flight position by the spring-loaded pawls. The Mk 16 Mod motor has a modified igniter and a modified nozzle and fin assembly. The nozzle and fin assembly (fig. 2-10) contains four, spring-loaded, wraparound fins inside the motor diameter. The steel nozzle expansion cone has flutes that cause the rocket to spin during free flight. This permits the rocket to be launched from high-speed aircraft, helicopters, and low-speed aircraft. Figure 2-10.—Mk 71 Mod 0 motor, nozzle, and fin assembly. 2-7