Claims
- 1. A safety and arming delay fuze for spinning munitions comprising a housing, a cavity in said housing, a ball rotor in said cavity having a polar moment of inertia larger than either transverse moment of inertia, a detonator within said ball rotor, a firing pin means in said housing, means to hold said ball rotor in a first safe position with said detonator out of alignment with said firing pin means and to release said ball rotor when said munition is launched, means for increasing arming distance by reducing substantially all friction forces between the walls of said cavity and the ball rotor, the latter means involves the use of a low viscosity liquid to exert a buoyant force on the ball rotor such that as the munition rotates after launch, the detonator revolves many times about the axis of the projectile and eventually spirals into alignment with the firing pin means thereby providing longer arming delays for the fuze with the revolving motion of the detonator being controlled primarily by the friction forces between the cavity and the ball rotor.
- 2. The invention in accordance with claim 1, wherein said liquid has a density greater than 1.4.
- 3. The invention in accordance with claim 1, wherein the nominal radial clearance between the ball and its housing is greater than 0.004 inches.
- 4. The invention in accordance with claim 1, wherein a boundary lubricant is mixed with said liquid to lower the coefficient of friction between the ball rotor and its housing.
- 5. The invention in accordance with claim 3, wherein said boundary lubricant is oleic acid.
- 6. The invention in accordance with claim 1, wherein the average density of the ball rotor is reduced through the inclusion of a low density material.
- 7. The invention in accordance with claim 6, wherein said material is a plastic.
- 8. A safety and arming delay fuze for spinning munitions comprising a housing, a cavity in said housing, a ball rotor in said cavity having a polar moment of inertia larger than either transverse moment of inertia, a detonator within said ball rotor, a firing pin in said housing, means to hold said ball rotor in a first safe position with said detonator out of alignment with said firing pin and to release said ball rotor when said munition is launched, means for increasing arming distance by supporting the ball within said cavity at set back on a small portion of the ball located near its initial spin axis and to delay the spin-up of the ball rotor such that the angular velocity of the ball rotor is substantially less than the angular velocity of the munition when the munition leaves its launch site such that as the munition rotates after launch, the detonator revolves many times about the axis of the projectile and eventually spirals into alignment with the firing pin thereby providing longer arming delays for the fuze.
- 9. A safety and arming delay fuze for spinning munitions comprising a housing, a cavity in said housing, a ball rotor in said cavity having a polar moment of inertia larger than either transverse moment of inertia, an explosive material within said ball rotor, firing means in said housing to ignite the explosive material, means to hold said ball rotor in a first safe position with said explosive material out of alignment with said firing means and to release said ball rotor when the munition is launched, means for increasing arming distance by reducing substantially all friction forces between the walls of said cavity and the ball rotor such that as the munition rotates after launch, the explosive material revolves many times about the axis of the munition and eventually spirals into alignment with the firing means thereby providing longer arming delays for the fuze with the revolving motion of the explosive material being controlled primarily by the friction forces at the point of contact of the cavity by the ball rotor, said arming distance increasing means involving the use of a liquid to exert a buoyant force on the ball rotor, said liquid having a density greater than 1.4.
REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No. 470,152 filed May 15, 1974 which in turn was a continuation-in-part of application Ser. No. 288,026 filed Sept. 11, 1972 both of which are now abandoned.
Safety and arming delay devices which comprise a ball rotor having a polar moment of inertia larger than either transverse moment of inertia have been in use since their invention in the late 1800's. In such a device the ball rotor contains an explosive element which is part of the firing train. Such a firing train usually begins with the detonator or primer and ends with the main charge of the projectile. In most cases the detonator itself is contained in the ball rotor. Prior to firing the munition the rotor is held with its polar axis at some angle, such as 60.degree. to 80.degree., with the spin axis of the projectile. The explosive element contained in the ball rotor lies on the polar axis of the ball rotor thus in this condition an accidental explosion of the detonator or primer will not result in explosion of the munition. When the munition is launched, forces arising out of the difference in moments of inertia of the ball, projectile spin, and friction act in such a way as to cause the ball rotor to align its polar axis with the spin axis of the projectile. At this time the projectile is armed and an explosion of the detonator will result in an explosion of the projectile if the firing train is not broken at some other point.
Since this safety and arming device consists primarily of one moving part, its simplicity has never been equalled by other safety and arming devices. For this reason a great deal of effort has been applied over the years to adapt the ball rotor to fuzing of all types of spinning projectiles. In spite of this effort, however, gear train escapements and other safety and arming delay devices have generally been used in every application except 20-30mm. projectiles even though the cost of these safety and arming delay devices is generally two to five times higher. Ball rotor fuzing is currently being used in the 20-30mm. projectiles because of the extreme size limitations imposed on the fuze by this projectile. Nevertheless, even in the 20-30mm. projectiles a considerable effort has been undertaken to find a substitute for the ball rotor.
The reason ball rotor safety and arming delay devices have not found greater use in spite of the substantial research and development efforts that have been expended, lay in the wide dispersion of arming distances which have resulted and in the failure of most ball rotor systems to achieve a minimum safe arming distance. Even in the now standard M505A3 20mm. fuze, some of the projectiles begin arming at 20 feet and all are not armed until somewhere over 100 feet. When these projectiles are fired from wing located guns in high performance aircraft, some of the projectiles could be armed while very close to the nose of the plane. An accidental explosion of one of these armed projectiles could seriously damage the plane and injure the pilot.
A careful mathematical analysis supported by test firings has shown that the cause of the short arming distances is due to partially high friction forces. Similarly, the cause of the wide dispersion in arming distances is due to a wide dispersion of the magnitude and location of the friction forces acting on the ball rotor. The key to successful ball rotor fuzing, therefore, lay in reducing and controlling these friction forces. This has been accomplished by this invention.
The approach taken in the Ziemba et al U.S. Pat. No. 3,397,640 granted Aug. 20, 1968 is illustrative of an attempt to solve the problems of ball rotor safety and arming devices.
This invention is primarily concerned with modifying the Coulomb friction forces which determine the time of alignment of the polar axis of a ball rotor with the spin axis of the projectile to reduce the dispersion of the arming distances and in some cases to control the location of the mean arming distance. The Coulomb friction forces are modified through one or more techniques including the use of buoyant forces exerted on the ball by a low viscosity liquid which substantially fills the ball cavity, a boundary lubricant, a solid film lubricant, a substantially enlarged clearance between the ball and its cavity, and the inclusion of known eccentricities in the ball or ball cavity.
One of the primary objects of this invention is to provide for a ball rotor safety and arming delay device having a substantially reduced arming distance dispersion.
Another object of this invention is to provide a ball rotor safety and arming delay device having a longer mean arming distance than heretofore possible.
A further object of this invention is to provide an acceptable safety and arming delay device for all spinning munitions.
Another object of this invention is to provide an inexpensive safety and arming delay device capable of meeting current requirements for fuzing 20-30mm. projectiles.
Still another object of this invention is to provide an exceedingly inexpensive safety and arming delay device capable of meeting the requirements for artillery projectiles.
A further object of this invention is to provide for a low cost safety and arming delay device capable of meeting the requirements for other spinning munitions including bomblets and 40 mm grenades.
Both teachings of the Ziemba patent and the present invention result in a longer arming delay, however, for entirely different reasons. In the Ziemba patent, the ball rotor is immersed in a very viscous grease or liquid. This causes the ball rotor to always spin at an rpm which is almost identical to that of the projectile. If an observor were rotating with the projectile and looking down on the top of the ball rotor, one would see a smooth motion of the detonator from its out of the line position to a position where it is aligned with the spin axis of the projectile. The detonator in other words would not appear to be rotating around the observor. This is a very heavily damped system. In the present case, on the other hand, the same observor would watch the detonator spinning around underneath him and instead of a single smooth curve involving a total relative motion of the detonator of perhaps less than 180.degree. relative to the projectile, he would see the detonator making many revolutions as it gradually spirals into alignment. This system does not experience significant damping from the liquid and its motion is primarily controlled by the Couloumb friction forces between the ball and its housing. In the Ziemba case, the arming distance is primarily determined by the viscosity of the fluid. In the present case, the viscosity is insignificant. In the Ziemba case, fluids are used having a viscosity in the neighborhood of 100,000 centistokes. In the present case, a typical fluid has a viscosity of approximately 1 centistoke. For some applications, fluids having somewhat higher viscosity could be used in the present case, however, but most likely not as high as 1,000 centistokes which would operate according to the teachings of the present application.
Other objects and advantages of this invention will become apparent as the description progresses.
US Referenced Citations (6)
Non-Patent Literature Citations (1)
| Entry |
| The Condensed Chemical Dictionary; 1971, Van Nostrand Reinhold Co., pp. 426, 592 and 643. |
Continuation in Parts (2)
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Number |
Date |
Country |
| Parent |
470152 |
May 1974 |
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| Parent |
288026 |
Sep 1972 |
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Patent Grant
4098192
