US3528249A

US3528249A - Stored energy thrust termination device

Info

Publication number: US3528249A
Application number: US732954A
Authority: US
Inventors: Robert B Weaver; Stuart E Weaver
Original assignee: WEAVER ASSOCIATES Inc
Current assignee: WEAVER ASSOCIATES Inc
Priority date: 1968-05-29
Filing date: 1968-05-29
Publication date: 1970-09-15
Anticipated expiration: 1987-09-15

Description

Sept. 15,1970 WE VER ETAL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 5 Sheets-Sheet 1 1 INVENTOR. Robert B. Weaver BY Stuart E. Weaver Attorneys Sept. 15, 1970 R. B. WEAVER ET AL 3,523,249"

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 '5 Sheets-Sheet :2

INVENTOR. Robert B. Weaver Stuart E. We ver BY Attorneys Sept. 15, 1970 R. B. WEAVER ET AL 3,528,249

STORED ENERGY THRUSI TERMINATION DEVICE Filed May 29, .1968

5 Sheets-Sheet 5 s R! V! mwmwwm w r l 0 VWM m J/ E m Mm 5 Y; B

Sept. 15 1970 WEAVER ET AL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 5 Sheets-Sheet 4 INVENTOR- Robert B. Weaver BY Stuart Weaver I f Attorneys Sept. 15, 1970 R. B. WEAVER ETAL 3,528,249

STORED ENERGY THRUST TERMINATION DEVICE Filed May 29, 1968 I 5 Sheets-Sheet 5 COMBINED LOAD FROM TENSION BAND 5 SPRINGS sooow POINT c g POINT B ,5 POINT A ts LOAD FROM SPRINGS ONLY :5 LOAD REou/R 8 2000 TO MOVE CUT ER v \\--?L0AD FROM TENSION BAND ONLY D 3 2 looo- Q C I I I I l l I .05" lo" '5" 20" 25" 30" Cutter Travel Radially Inward -|ooo- Fig. 13

attorneys United States Patent 011?? 3,528,249 Patented Sept. 15,, I970 3,528,249 STORED ENERGY THRUST TERMINATION DEVICE Robert B. Weaver, Palo Alto, and Stuart E. Weaver, Los Angeles, Calif., assignors to Weaver Associates, Inc-, Palo Alto, Calif., a corporation of California Filed May 29, 1968, Ser. No. 732,954 Int. Cl. F021; 9/04 US. Cl. 60254 11 Claims ABSTRACT OF THE DISCLOSURE A device for terminating the thrust on an accidentally ignited solid propellant rocket including metal bands which encompass the rocket casing to retard expansion of it during pressure built-up within the casing caused by burning of its solid propellant. Coupled to the encompassing bands are rupturing means which are actuated by the build-up of tension in the band to cause a longitudinal cutter to penetrate the casing thus rupturing it. The cutter is driven by the combination of stored energy from two pairs of Belleville springs and the tension in the bands. The springs are coupled to the cutter by oilcenter toggle struts; these are located at an angle to the casing to provide a bias or lockout force Which prevents accidental triggering. Thus, before the spring force can move the cutter into the casing the lookout force also provided by the springs must be overcome by the band tension.

BACKGROUND OF THE INVENTION This invention relates to a stored energy thrust termination device and more particularly to a device for use with solid propellant rocket motors.

In the utilization of solid propellant rocket motors, there is a possibility of accidental ignition during transportation, handling and storage, or while in launch position during the preparation of a missile for flight. This is especially critical with smaller rocket motors which are used and carried by ground forces, for example, by truck. Possible causes of accidental ignition are fire, sparks, hot fragments, lightning, and inadvertent actuation of the igniter as, for example, by a collision of the rocket motor with another object or the ground.

Once ignited the propellant Will burn to exhaustion because there is no known way of extinguishing the flame. Unless the thrust forces are counteracted in some manner or the motor destroyed, an accidentally ignited rocket can cause damage and injury at a great distance from the point of the accident. If free flight should be obtained, populated areas could easily be jeopardized.

One method of terminating thrust is disclosed and claimed in Pat. 3,167,910 in the name of Robert B. Weaver, entitled Thrust Termination Device and Method and assigned to the present assignee. This utilizes a band encompasing the casing which is responsive to expansion of the casing during pressure build-up, caused by an accidental ignition, to trigger a cutter which ruptures the casing rendering it harmless. In a specific embodiment of this patent the force for the cutter is directly obtained from the tension in the encompassing band. This method is very eifective for types of rocket motors such as those for ballistic missiles where there is appreciable circumferential growth of the rocket casing. However, in the smaller tactical missiles which are, for example, for ground use and are built for more rugged handling, the casing is thicker in proportion to its diameter and therefore stressed lower. Thus, the amount of circumferential growth in relation to the size of the casing is less to somewhat reduce the efliciency of the type of thrust of termination device as shown in the above patent.

There is therefore a need for a thrust termination device which is especially applicable and useful on the smaller tactical missiles.

OBJECTS AND SUMMARY OF INVENTION In general it is an object of the present invention to provide an improved thrust termination device in which propulsive hazards associated with the accidental ignition of solid propellant motors are eliminated.

Another object of the invention is to providea device as above which is especially suitable for rocket motors having a relatively small circumferential growth.

It is another object of the invention to provide a device as above in which stored energy is utilized but in which the forces created by ignition of the solid propellant rocket motor are utilized for triggering this stored energy; and

Another object of the invention is to provide a device as above in which the force characteristic applied to the cutter which ruptures the rocket casing is idealized.

In accordance with the above objects there is provided a device for terminating the thrust on an accidentally ignited solid-propellant rocket motor of the type having a casing, means encompassing the casing to retard expan sion of the casing during pressure build-up within the casing caused by burning of the solid-propellant Within the casing, and means actuated by the encompassing means as it is expanded to rupture the casing to thereby destroy the rocket motor. The improvement of the present invention comprises energy storage means and means responsive to the encompassing means for releasing the stored energy of the energy storage means and coupling at least a portion of this energy to the rupturing means to thereby aid in rupturing the casing.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view of the thrust termination device embodying thepresent invention including the bands which encompass the rocket casing;

FIG. 2 is a plan view of an interlocking portion of the bands of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 2;

FIG. 4 is a plan view of FIG. 2 but in an unlocked or exploded condition;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4;

FIG. 6 is a plan view, partially broken away, of the actual mechanism of the thrust termination device of the present invention with the top cover removed;

:FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 6;

FIG. 8 is a cross-sectional view similar to FIG. 7 but showing the cutting device in an extended position;

FIG. 9 is an elevational view taken along the line 9-9 of FIG. 6;

FIG. 10 is a cross-sectional view taken along the line 10-*10 of FIG. 6;

FIG. 11 is a cross-sectional view taken along the line 1111 of FIG. 6;

FIG. 12 is a cross-sectional view taken along the line 1212 of FIG. 6; and

FIG. 13 is a set of composite curves useful in understanding the operation and theory of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown the complete thrust termination device which includes encompassing band means 10 which are divided into the two halves 10a and 10b which would normally encompass or be locked to a rocket casing (not shown). The axis of the rocket 3 would of course be vertical with relation to the drawing. The rupturing device itself is shown at 11 with bands 10a and 10b having one of their free ends coupled to each side of it. The other end of the bands are tied together by coupling means 12 which is shown in greater detail in FIGS. 2 through 5.

Referring now more specifically to these figures, in FIGS. 2 and 3 the coupling means are shown in a locked position and in FIGS. 4 and 5 an open position ready to 'be placed around the circumference of a rocket motor casing. Band halves a and 10b include at their end terminations locking sections 13 and 14, which are oppositely oriented with respect to each other and mesh as shown in FIG. 3. The section 14 carries thereon a threaded stud 16 with a knurled fastening knob 17. This slides into a cutout 18 in section 13 to provide a permanent fastening after interlocking of the sections 13 and 14. A bar 19 is mounted on section 13 (the bar also being shown in FIG. 1) and has a cutout portion 21 to allow passage of knob 17. The bar serves to re-enforce the coupling 12 and also to provide protection for knob 17 and stud 16 to prevent against accidental opening of the coupling.

The rupturing means which are actuated by the tension in bands 10a and 10b for rupturing a rocket casing to terminate thrust is best shown generally in FIG. 6 where the individual bands 10 are mounted on

upstanding wall portions

23 and 24 which are mounted and welded to a base 26. The base which is best shown in FIG. 9 has a curved concave bottom surface to fit a particular rocket casing. A cover 27 protects the entire mechanism of the rupturing device. This cover is, however, removed in FIG. 6. Four compression springs 28a, b and 29a, b are mounted on

walls

24 and 23, respectively to provide the stored energy for powering the cutter of the thrust termination device. These are compression springs of the Belleville type. Each individual spring is made of four single Belleville discs stacked in series and eight parallel pairs of two stacked in series. The maximum output of each individual spring is 3,000 pounds. This is applied through

respective coupling plates

31 and 32 to the cutter means in a direction parallel to the axis of the actual rocket motor. FIGS. 7 and 8 show the coupling plates each of which include horizontally extending

ram portions

33 and 34 respectively which are suspended between

abutments

36 and 37 in the case of ram 33 and

abutments

38 and 39 in the case of ram 34. Needle bearings 41 allow for free longitudinal or horizontal movement of the rams. Belleville springs 28a, b and 29a, b all include spring guide means 42 which are in the form of rods fitted through the individual

respective walls

23 and 24 to protect against accidental sliding of one of the spring discs out of the spring. Although Belleville type springs have been shown in the preferred embodiment other springs may be used.

FIG. 7 illustrates the bladed cutter 43 of the present invention in a first or retracted position with springs 28 and 29 in a stored energy position. FIG. 8 shows cutter 43 in a fully extended position as it would be when the rocket casing was fully ruptured with the stored energy of springs 28 and 29 expended and the spring expanded.

Cutter 43 as shown in its first position in FIG. 7 includes a shank portion 44 having upwardly extending fingers 46 through which a pin 47 extends. Pin 47 is maintained in place by abutments 48 and 49 which extend from

blocks

36 and 38 respectively. As will be explained below, downward force is applied to cutter 43 by means of pin 47. Shank 44 includes shear pins 50 and 51 extending through the shank and, as best shown in FIG. 12, each shear pin includes an end designated with the suffix a, for example 49a, which extends into mounting block 52 which is mounted to base 26. Block 52 includes a key-way 53 in which the cutter 43 is guided downwardly.

The energy storage means which are, of course, the Belleville springs 28a, b and 29a, b are coupled to the rupturing means which include cutter 43 by means of two toggle struts 56 and 57. In their first position, as shown in FIG. 7, they are in a compressed condition due to the force of ram 33 which produces forces on the strut in the direction of

arrows

58 and 59. Struts 56 and 57 include rounded ends which are adapted to mesh with the

open V construction

33a and 44a of the ram 33 and shank 44. The struts 5'6 and 57 in their first position, as shown in FIG. 7 are set at an approximate angle of 3 /2 with respect to the horizontal. Thus, the resulting forces on the cutter 43 are in the directions as shown by

arrows

58 and 59; force 59, the major force, is horizontal and force 58 is vertical. These two force vectors are essentially the components of the force delivered by

rams

33 and 34 as indicated by the arrows. Because of the upward 3 /2 cant of struts 56 and 57, force 58 is in a direction away from the rocket casing to thus prevent accidental triggering of the cutter 43. Upward force 58 is a function of the tangent of the angle the struts make with the horizontal. Thus, for example, with a 3 /2 angle and a 3,000 pound force in each separate spring each

ram

33 and 34 will produce a 6,000 pound force. Multiplied by the tangent of 3 /2" this yields an individual upward force of 366 pounds or a combined force of 732 pounds. Therefore, the cutter 43 cannot be moved until at least a 732 pound force overcomes the spring force. Thus, for example, if the cutter itself has a weight of only 3 ounces the shock required to move the cutter would have to be in exces of 3,700g. The shear pins 49 and 51 provide an additional safety factor, which along with associated friction raises the force to move cutter 43 from its first or stored energy position to approximately 1,000 pounds.

The 3 /2 cant or angle of the struts away from the rocket casing is believed to be the ideal angle. If the angle is less than 2 then the device is susceptible to accidental triggering; on the other hand, an angle of greater than 6 would require a release force to be supplied by the bands which would be excessive.

As best shown in FIGS. 11 and 12, the bands 10a and 10b, when placed in sufficient tension, to provide a triggering force to overcome the above 1,000 pound force to move struts 56 and 57 over-center (that is through a horizontal position) to allow the spring force to move cutter 43 downwardly into the rocket casing to thereby rupture it. This tension is applied substantially through band half 10a which is coupled to pin 47 of cutter 43 through a series of levers. These levers are best shown in FIG. 12 where the band 10a is coupled to a band attach link 61 by a pin 62. Link 61 is pivoted on an abutment 63 on base 26 to force a cutter drive rocker arm 64 to rotate in a clockwise direction to move cutter 43 downwardly. Specifically, link 64 includes a left end 64a which is in contact with link 61 and a right end 64b which meshes with fingers 46 of cutter 43 into contact with pin 47. Link 64 is pivoted on a pin 66 which in turn is mounted on a link 67 which is pivoted to base 26 by a pin 68. The purpose of link 67 is to allow movement of link 64 toward the cutter 43 as it moves the cutter downwardly. Link 61 is pivotally attached to base 26 through links (see FIG. 6) which couple to blocks 52' mounted on the base.

Band half 10b is coupled to the other side of cutter mechanism 11 by a link 69 which includes a tongue 70 which slides within a U-shaped groove 71 cut into block 52. The extend of the protrusion of tongue 70 into groove 71 is adjusted by means of a screw 72 best shown in FIG. 6 which, carries V-shaped

wedges

73 and 74 which space the link 69 from the base 26 (see also FIG. 12).

Wedges

73 and 74 are extensions of

collars

76 and 77 which are carried by screw 72. The collars are oppositely threaded to allow opposite movement toward each other or away from each other when screw 72 is rotated to thus adjust the tension in the band 10. The screw 72 is rotated through a ratchet block assembly 78 which in turn is turned by a wrench 79 having a shear pin 81.

The ratchet block is manufactured so as to have a maximum torque of 60 inch pounds. The shear pin 81 of wrench 79 has a shear torque of 70 inch pounds to serve as a backup in case of failure of the ratchet block release. Thus, accidental triggering by over-tightening of the band is prevented.

The specific construction of 'band 10, as best shown in FIGS. 11 and 12, includes a multiple-layer construction for flexibility and to allow for sliding friction. Specifically, as is shown in FIG. 11 the multiple-layer band includes as its load carrying portion two

stainless steel bands

81 and 82 which are welded to opposite sides of a shank 83 mounted by pin 62 to base 26. A band 84 is adjacent to band 83 and is nonloaded. On its outer surface which is in contact with band 82 it is coated with Teflon in order to provide sliding friction between itself and band 82. On its inner surface it has bonded to it neoprene with Teflon impregnated glass cloth. The Teflon provides for sliding friction between the load band layers and the rocket casing. Surrounding the entire band is a rubber outer coating 86. Thus, with the above band construction the

load bands

81 and 82 may move freely over the outer Teflon coating of band 84 to minimize friction between the load bands and the rocket casing.

The cutter assembly 11 is basically constructed of stainless steel which has been hardened by precipitation methods to have a pH of 17-4. It is corrosion resistant and in the hardening process it has its distortion reduced to zero.

OPERATION The curves of FIG. 13 will be used in explaining the operation of the present invention. Initially, the band halves a, 10b are fastened around the rocket casing by means of the coupling 12, as shown in FIGS. 2 and 4. The band is then preloaded by, as shown in FIG. 6, the rotation of wrench 79 until the ratchet 78 begins to slip at a predetermined torque.

The thrust determination device is now ready to come into action if the rocket should accidentally ignite. Upon accidental ignition the rocket casing expands placing a load on the band which is applied to the mechanism at band half 10a. The curve labeled load from tension band only shows the downward load on cutter 13 which is applied as best shown in FIG. 12 on pin 47 through the

intermediate links

64 and 61. This curve is shown as dashed line since it is a theoretical curve only. If this were the only force on the cutter 43 it would naturally reduce as the cutter traveled radially inward as. shown by the horizontal axis since the tension on the band Would be relieved.

Initially, the curve labeled load from springs only is at a negative value due to the shear pins and the upward force produced by struts 56 and 57. After the cutter travels through its center position this load becomes positive, meaning radially inwards toward the rocket casing. The curve labeled combined load from tension band and springs is the actual load on the cutter 43 which is a combination of the load from tension band only curve and the load from springs only curve. Note that at zero cutter travel the combined load curve is, of course, less than the downward force contributed by the tension hand because of the negative spring load which provides the stored energy lock-out feature of the present invention.

The last curve shown is labeled load required to move cutter which is experimentally determined by loading the cutter with a hydraulic ram and measuring the cutter movement as the ram pressure increases. The initial part of the curve where cutter movement is small represents the force required for deflection of the rocket casing before puncture and the more linear portion of the curve is the force required as the cutter is penetrating the rocket casing. This curve neglects the shear pin force which, of course, is an added safety feature. Thus, in operation, to have movement of the cutter the combined load curve must always exceed the load required curve. For example, note that cutter movement would stop at point A absent the spring force. Similarly, springs alone would not force the cutter to rupture the casing since at any cutter movement to the left of point B the springs do not produce a suflicient force. Point C indicates the actual case rupture point where the cutter has produced a crack long enough to allow a longitudinal rupture of the rocket casing.

Note that the load from springs only curve increases with increasing cutter travel even though the Spring force is decreasing as the springs expand. This is because the downward force is a function of the tangent of the angle that the toggle strut makes with the casing and this tangent function is, of course extremely non-linear. Thus, the decrease in spring force is more than compensated for.

In summary, therefore the present invention provides an improved thrust termination device which is especially useful on smaller tactical missiles since it utilizes combined characteristics of the tension in the bands surrounding the rockets and the stored energy of springs to provide for the proper force characteristic for rupturing the rocket casing. By use of the canted toggle strut construc tion accidental triggering of the stored energy is prevented even under extreme conditions. This is especially valuable when the tactical rocket is being transported over rough terrain or is subject to being dropped from its carrying vehicle.

We claim:

1. A device for terminating the thrust on an accidentally ignited solid-propellant rocket motor of the type having a casing, means encompassing the casing to retard expansion of the casing during pressure build-up within the casing caused by burning of the solid propellant within the casing, and means actuated by the encompassing means as it is expanded to rupture the casing to thereby destroy the rocket motor, wherein the improvement comprises, energy storage means, and means responsive to said encompassing means for releasing the stored energy of said energy storage means and coupling at least a portion of said stored energy to said rupturing means to thereby aid in rupturing said casing.

2. A device for terminating the thrust on an accidentally ignited solid-propellant rocket motor of the type having a casing, means encompassing the casing to retard expansion of the casing during pressure build-up within the casing caused by burning of the solid propellant within the casing, and means actuated by the encompassing means as it is expanded to rupture the casing to thereby destroy the rocket motor, wherein the improvement comprises, energy storage means for providing a predetermined force, and means coupling said storage means to said rupturing means, said coupling means having a first position for coupling a component of said predetermined force to said rupturing means which is in a direction away from said casing and a second position for coupling a component of said predetermined force to said rupturing means in a direction toward said casing to thereby aid in rupturing said casing.

3. A device as in claim 2 in which said energy storage means are Belleville type springs.

4. A device as in claim 2 in which said predetermined force is exerted in a direction parallel to said casing.

5. A device as in claim 2 in which said coupling means includes a toggle strut disposed at a predetermined angle away from said casing in said first position.

6. A device as in claim 5 in which the amount of force transmitted by said strut to said rupturing means varies non-linearly with respect to the angle formed between said strut and easing.

7. A device as in claim 6 in which said non-linear relation is a tangent function of said angle.

8. A device as in claim 7 in which said angle in said first position is between 2-6 degrees.

9. A device as in claim 2 in which said energy storage means include a ram which has an end face with an open V configuration which couples to said coupling means and said rupturing means also includes an open V portion which also couples to said coupling means.

10. A device as in claim 2 in Which said encompassing means include a multilayer band at least one of the layers being substantially a load carrying band and where another one of the layers carries substantially no load but is interfaced with a load carrying band by a substantially frictionless surface.

11. A device as in claim 2 in which the force necessary to cause said rupturing means to rupture said casing is a combination of a portion of the tension force in said encompassing means and a portion of said predetermined force contributed by said energy storage means.

References Cited UNITED STATES PATENTS 2,470,371 5/1949 Roessner 222-87 XR 3,038,303 6/1962 Gose 60-254 3,167,910 2/1965 Weaver 60-254 XR 3,295,324 1/ 1967 Conard et al. 60254 CARLTON R. CROYLE, Primary Examiner US. Cl. X.R.