Figure 2-5.—Mk 71 Mods motor, nozzle, and fin assembly

the 2.75-inch diameter of the rocket. The fins are notched at the tips to allow attachment of a fin retainer. The fin-actuating mechanism is a steel cylinder and a piston with a crosshead attached to its aft end. When the rocket is fired, gas pressure from the motor operates the piston, cylinder, and crosshead. The crosshead is pushed against the heels of the fins, causing the fins to rotate on the fin pivot pins to the open position after the rocket leaves the launcher. After the fins have opened to the final flight position, the crosshead prevents the fins from closing. There are four nozzle inserts and the detent groove in the aft end of the nozzle plate. They hold the rocket in position after it is loaded in the launcher. The Mk 71 Mods motor has a modified igniter and a modified nozzle and fin assembly. The nozzle and fin assembly (fig. 2-4) 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. The Mk 71 Mods spring-loaded fins (fig. 2-5) deploy after emerging from the rocket launcher tube. They lock in place (open) by sliding into a locking slot in the flange at the aft end of the fin nozzle assembly. When not actually installed in the launcher, the fins are held in the closed position by a fin retainer band, which must be removed when the rocket is installed into the launcher tube. The fin retainer band is not interchangeable with the shielding band. REVIEW NUMBER 1 Q1. List the two rockets currently used by the Navy. Q2. If a rocket does not fire when the firing circuit is energized, it is known as a _____________. Q3. What is meant by the rockets thrust? Q4. In rocket propulsion, the Venturi nozzle decreases turbulence of escaping gases and increases thrust. Gas pressure inside the container provides about _______, and the escaping gases provide about __________ to move the container forward. Q5. List the three components of a rocket. Q6. List the components of rocket motors. Q7. What is the purpose of the inhibitor? Q8. What rocket component is salt coated to prevent unstable burning of the rocket propellant? Q9. When should you remove the fin retainer band on a Mk 71 rocket motor? Warheads Different tactical requirements demand different types of rocket warheads be used with airborne rockets. 2-5 Figure 2-5.—Mk 71 Mods motor, nozzle, and fin assembly.