US2850978A - Safety device for ordnance fuzes - Google Patents

Description

Sept. 9, 1958 P. J. FRANKLIN 2,850,978

SAFETY DEVICE FOR ORDNANCE FUZES FiledMarch 2, 1955 LOW- MELTI NG ALLOY FUZE CIRCUITRY SETBACK DEVICE INVENTOR Ph/Y/p J. Frank/in I ATTORNEYS SAFETY DEVICE FOR ORDNANCE FUZES Philip J. Franklin, Washington, D. C.

Application March 2, 1955, Serial No. 491,809

8 Claims. (Cl. 102-701) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

" This invention relates to fuzes for ordnance missiles and to safety-and-arming mechanisms therefor.

Typical ordnance fuzes are designed to change from an insensitive condition, known as the safe or unarmed condition, to a sensitive or armed condition in response to setback-4. e., in response to forces due to the acceleration applied to the missile at the beginning of its flight. The fuze is adapted, when in the armed condition, to cause explosion of the missiles warhead when the missile encounters certain influences such as contact with or proximity to a target. When the fuze is in the unarmed condition, however, it is insensitive to these same influences.

It is essential to the safety of using personnel that an ordnance fuze remain in the unarmed condition until the missile in which it is mounted has been propelled toward its target and is a safe distance away from using personnel. In particular, the fuze must not accidentally arm as a result of rough handling or accidental dropping. Setback-responsive safety-and-arming mechanisms for fuzes are very carefully designed to minimize the possibility of such premature arming. Nevertheless, the possibility does exist of accidental arming, as a result of mechanical failure or extraordinary combinations of forces or both. The newer tactics of airborne warfare present a particular problem, calling as they do for ammunition that can be dropped from the air to using troops; such ammunition may be subjected to very severe forces on landing, particularly in the event of failure of parachutes or other acceleration-reducing devices. The accidental arming of even a very few setback-arming fuzes may be quite intolerable.

The ordnance fuzing art has increasingly felt the need for safety and-arming devices insensitive to setback devices that would remain safe regardless of forces due to acceleration but that would arm, in flight, at a safe dstance from using personnel, in response to some effect not related to setback. Such setback-insensitive safetyand-arming devices could be used alone but would preferably be used in combination with setback-responsive or other arming devices; with such a combination arrangement the fuze would not become fully armed until both the setback-responsive device and the setback-insensitive device had independently changed from the unarmed to the armed condition. Such a setback-insensitive arming device, if reliable and practical, could make practical the fuzing ofordnance missiles with a degree of safety hitherto unknown. The principal object of my invention is to provide such setback-insensitive safety-and-arming devices and methods for ordnance fuzes.

Briefly, my invention provides safety-and-arming devices in which heat developed by air friction against the body of the missile is utilized to cause a change from the safe to the armed condition. For use in combination with well-known safety-and-arming devices having detonator-carrying rotors adapted to rotate from an unarmed to an armed position, I prefer to provide a mechanical element constrained to a first position by a lowmelting solid mounted inside the missile close to the periphery of the missiles nose. When in this position the element is adapted to prevent rotation of the rotor to the armed position. When the nose of the missile reaches a temperature to be expected in normal flight, the solid melts and the element moves automatically to a second position in which it no longer prevents rotation of the rotor to the armed position. If the fuze is of an electrical type, a desirable form of my invention is one in which the same low-melting solid is electrically conductive and short-circuits an electric detonator, or other critical circuit component; the detonator cannot function until the alloy has melted and removed the short circuit.

Other aspects, objects, uses, and advantages of my invention will become apparent from the following description and from the accompanying drawing, in which:

The drawing is a longitudinal section, not to scale, showing principal features of an ordnance missile incorporating my invention.

In the drawing, numeral 12 designates the ogive or outer shell of the nose of an ordnance missile. The missile is provided with a fuze having a safety-and-arming mechanism that includes an arming rotor 14, which may be of a well-known type. Rotor 14, shown in the unarmed position, rotates on shaft 16 and is adapted to arm the fuze upon rotation to an armed position. Rotor 14 is loaded by a spring (not shown) that urges it into the armed position. Until actuated by acceleration forces corresponding to those produced on normal setback, however, a setback-responsive device 18 holds rotor 14 in the unarmed position as shown. When rotor 14 is in the armed position, an electric detonator 40 is adapted to detonate upon receiving an electrical voltage from appropriate fuze circuitry 42. Fuze circuitry 42 is adapted to provide a detonating voltage upon receiving an appropriate indication of the presence of a target, in accordance with well-known practice. The elements thus far described are well known and their operation will be well understood, without more detailed description, by persons skilled in ordnance fuzing.

In the embodiment of my invention shown in the drawing, I have provided a hole 20 through rotor 14, the axis of hole 20 being generally perpendicular to the axis of rotor 14. A wire 22 passes through a protective tube 23 and through the hole 20. End 26 of wire 22 is held by a low-melting alloy 24 that constitutes the'forward tip of the missile. The other end 27 of wire 22 is held under spring tension by a spring-loading device 25. Besides holding wire 22, alloy 24 electrically grounds an electrode 31 to tube 23 and/or to ogive 12. Electrode 31 is electrically connected to one terminal of an electrical detonator 40, the other terminal of which is grounded to tube 23. Detonator 49 is thus short-circuited by alloy 24.

Even though mechanical setback device 18 may have been actuated and may no longer impede the rotation of rotor 14 to the armed position, rotor 14 is prevented from so rotating as long as wire 22 passes through hole 20 and is held under tension. Furthermore, as long as alloy 24 short-circuits electrode 31 to tube 23, detonator 40 will not detonate, even though a detonating voltage be prematurely generated by fuze circuitry 42.

When low-melting alloy 24 is raised to a temperature corresponding to that resulting from friction of air thereag'ainst in normal flight, however, alloy 24 melts, unshorting detonator 40 and freeing end 26 of wire 22.

Patented Sept. 9, 1958 Spring-loading device 25 now withdraws wire 22 from hole 20, so that wire 22 no longer prevents rotor 14 from rotating to the armed position. Provided setbackresponsive device 18 has been actuated, the missile will now be fully armed.

It will be understood that'spring-loading device 25 maytake any of a number of 'well-known forms adapted to maintain tension-on wire 22 prior to release of end 26 and to thereafter withdraw wire 22 fromhole 29. A coiled spring of the type used in ordinary clocks and watches is one such form.

I prefer to select for wire 22 a material having a slight stiffness, the stiffness being suflicient to resist rotation of spring-loaded rotor 14 to the armed position until wire 22 is fully withdrawn from hole 20, even though end 26 may have been'released by the melting of alloy'24. Alternatively, however, a material may be selected'for wire 22 having a stiffness so low that, as soon as the tension of wire 22 is released upon the melting of alloy 24, rotation of spring-loaded rotor 14 to the armed position is not resisted.

It will be apparent that various alternative ways of releasing a lock on rotor 14 upon the melting of alloy24 can be provided, One advantage of the wire arrangement I have described, however, is that it is readily adapted to missiles of existing designs in which the fuze rotor is located a considerable distance rearward of the forward extremity of the missile. It is in general readily feasible to modify the design of such a missile to provide for wire 22 to run from the forward extremity to rotor 14.

In the embodiment shown in the drawing, part of alloy 24, upon melting, may be forced into protective tube 23 by air pressure. Tube 23 may be adapted to protect critical parts of the fuze from unwanted effects that the alloy particles might otherwise cause.

It will be understood that the drawing is not to scale and that alloy 24 preferably comprises a relatively small part of the nose of the missile in relation to the overall size of the missile. Modification of the aerodynamic characteristics of the missile caused by the melting of alloy 24 will thus be minimized and can be made negligible.

It will also be understood that the outer surface of alloy 24 need not be directly exposed to the atmosphere; I

allow 24 can, if desired, be separated from the atmosphere by a layer of high-melting material. Such a layer should preferably be thin, have high thermal conductivity, and make good thermal contact with alloy 24. Furthermore, to facilitate flow of alloy 24 upon melting, such a layer should preferably be vented.

Although I have shown an embodiment of my invention in which alloy 24 fusibly short-circuits an electric detonator 40, it will be understood that, alternatively, other critical circuit points may be fusibly short-circuited when my invention is used in association with fuzes of electrical types.

Manifestly, the principal utility of my invention is in its application to missiles having normal velocites sufficent to cause substantial temperature rises as a result of air friction. Many if not most of the missiles now known and used by the military do fortunately have such velocities, and a continuing trend to higher velocities and higher resulting missile temperatures may be expected. Some missiles that have been used by the military for years quickly develop skin temperatures of the order of 400 or 500 degrees centigrade in flight. Such temperatures are obviously well above those to which missiles are subjected in normal shipping, storage, and handling prior to use. Furthermore, for purposes of my invention, slight modifications of the surface of a missile in the region of its forward extremity may be found to increase the temperature rise in such region. Alloys and other materials having suitable melting points and other properties for use in my invention are well known and readily available. It will thus be clear that my invention, besides being readily practicable at low cost in the light of the foregoing disclosure, has great utility and wide applicability.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim:

1. In an ordnance missile, in combination with an arming mechanism having safe and armed positions, means for preventing the arming of said fuze until a portion of the body of said missile reaches a predetermined temperature, said means comprising: a solid material mounted in the nose portion of said missile, said solid material being'adapted to melt when the nose of the missile attains a temperature to be expected as a result of air friction in normal flight; and a mechanical element held in a first position by said solid material and adapted to move automatically to a second position upon the melting of said solid material, said element constraining said mechanism to said safe position when in said first position and permitting said mechanism to move to said armed position when in said second position.

2. In an ordnance missile, in combination with. an ordnance fuze having a mechanical rotor, said fuze being adapted to become armed upon the rotation of said rotor from an unarmed to an armed position, safety means for preventing the arming of said fuze until a portion of the body of said missile reaches a predetermined temperature, said means comprising: a solid material mounted in the nose portion of said missile, said solid material being adapted to melt when the nose of the missile attains a temperature to be expected as a result of air friction in normal flight; and a spring-loaded mechanical element held in a first position by said solid material and adapted to move to a second position upon the melting of said solid material, said element when in said first position being adapted to mechanically prevent rotation of said rotor from said unarmed position to said armed position and said element when in said second position being adapted to permit rotation of said rotor fromsaid unarmed position to said armed position.

3.; In an ordnance missile, in combination with an ordnance fuze having a mechanical rotor, said fuze being adapted to become armed upon the rotation of said rotor from an unarmed to an armed position, safety means for preventing the arming of said fuze until a portion of the body of said missile reaches a predetermined temperature, said means comprising: an alloy mounted in the nose portion of said missile, said alloy being adapted to melt when the nose of the missile attains a temperature to be expected as a result of air friction in normal flight; said rotor having an aperture therethrough, the axis of said aperture being generally perpendicular to the axis of said rotor; a wire fusibly held at its first end by said alloy, said wire passing through said aperture when said rotor is in the unarmed position; and spring means for holding the second end of said wire under tension, so that the wire prevents said rotor from rotating from the unarmed to the armed position until said alloy melts and releases the first end of the wire.

4. The invention according to claim 3, said spring means being of the coiled spring variety and bein adapted to withdraw said wire completely from said aperture.

5. The invention according to claim 3 comprising additionally: firstand second circuit points, said fuze being adapted to detonate only if a voltage is applied to said circuit points; and first and second electrodes electrically connected to said first and second circuit points respectively, said first and second electrodes being fusibly short- .circuited by said alloy, said electrodes being adapted to become open-eircuited upon said alloy reaching a temperature to be expected as a result of air friction in normal flight.

6. The invention according to claim 5 comprising additionally an electric detonator connected across said first and second circuit points.

7. The invention according to claim 5 comprising additionally a voltage source across said circuit points.

8. In an ordnance missile, in combination with an electrical ordnance fuze having first and second circuit points, the fuze being adapted to detonate only if a voltage is applied to said circuit points, safety means comprising: a fusible low-resistance electrical path effectively short circuiting said circuit points, said path including at least a fusible portion located in proximity to the surface of the nose portion of said missile, said fusible portion being adapted to melt when the nose portion of the missile reaches a temperature produced by air friction during normal flight and thereby to unshort said circuit points.

References Cited in the file of this patent UNITED STATES PATENTS

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