Patent GB-800078-A (GB)
Title: Improvements in or relating to rocket motors
Inventor: PLATT JAMES
IPC: F02K9/80
Filed: 1956-01-13
Abstract: 800,078. Safety devices for rocket motors. BRISTOL AIRCRAFT, Ltd. April 12, 1957 [Jan. 13, 1956], No. 1314/56. Classes 9(1) and 9(2) A rocket motor casing 1 has, at the end remote from the nozzle, an opening 2 reinforced by a ring 3 and closed by a plug 4 which can be blown out to vent the motor if accidentally ignited during storage. The plug is held in position by three equi-spaced latches 6 and a dishshaped retaining member 7 of sheet metal, each latch being housed in an axially directed slot of the skirt 8 of the plug 4, and having a surface bearing against the plug and a second surface bearing against the ring 3. The rounded tail 14 of each latch bears against a flange 15 projecting into the skirt'8 from a casting 16 and the other end of each latch bears against the member 7. With rise of pressure in the motor the plug 4 exerts a thrust on the latch surface 10, which causes a thrust on the member 7. At a given pressure the member 7 collapses allowing each latch to pivot inwardly about the tail 14 and so release the plug. To lock the plug in position for normal operation of the motor, a metal disc 18 seated during storage in the flange 15 is moved to engage surfaces 17 of the latches 6. To hold the latches in position during assembly and before the casting 16 is placed in position a spring ring 19 is pressed into grooves 20 in the latches, while a sealing ring 5 prevents the entry of moisture around the plug 4. A shaft 21 carrying the disc 18 extends through a bore 22 in the casting 16 into a chamber 24 closed by a plate 25. Through a bulge 26 in the chamber wall extends a shaft 27 carrying a lever 28 by means of which the rocket is armed. This lever may be locked in the unarmed position by a strut (not shown) engaged in a hole 29 in the lever and in a recess 30 in the casting 16. Projecting into the chamber from the shaft 27 is an arm 31 having pin-and-slot connection with a transmission lever 34 mounted on the shaft 35 of a rotary switch 36, the lever 34 having pin-and-slot engagement with a bolt 33 extending from the shaft 21. The bolt 33 comprises two plates, one on each side of the lever 34. Thus when arming lever 28 is rotated clockwise the transmission lever 34 moves the bolt towards the rocket motor after overcoming the resistance of a spring-pressed detent 45 and thus the disc 18 is moved to the latch-retaining position. Simultaneously, switch 36 closes contacts in the circuit from electric leads 41 to an igniter terminal 42 mounted in the motor casing. To lock the disc 18 in the armed position, the lever 34 is further rotated until the pin 38 engaging the bolt 33 leaves its slot and a pin 44 on the bolt enters a slot 43 in the lever 34. The casting 16 is attached to the plug 4 by setscrews 58. To orientate the casting on the motor, a plate 61 may be secured to the casting, the plate 61 having a projection 63 to fit a recess 64 in the wall of the combustion chamber. In a modification, Fig. 2, the latches are replaced by balls 6 housed in the skirt 8 and bearing against a deformable member 7 attached to the disc 18. In this case, the rocket is armed by moving the plate 18 into contact with the balls 6. In a further modification, each ball is associated with a separate resilient retaining member attached to the plug. The balls may be arranged to move outwardly under the blow-out pressure, a rotatable sleeve being used to prevent escape of the balls. This sleeve is weakened at intervals, the weakened parts being brought into, or out of, alignment with the balls according to whether the rocket is unarmed or armed. In this case the arming lever has pin-and-slot connection with a cam carried by the sleeve. Alternatively, the sleeve may be plain or castellated and moved axially to the armed position.