Abstract:
A mechanical safe and arm device for rotating munitions reduces arming scatter so that the “no arm” and “all arm” distance are substantially the same. A first spring holds a flywheel, a pinion gear, and a drive gear against rotation until centrifugal forces cause the spring to release them. The drive gear then rotates, causing rotation of the pinion gear and the flywheel. A post depending from the flywheel strikes and unlocks a second spring that unlocks a pivotally-mounted rotor that carries a detonator. The rotor then pivots and brings the detonator into alignment with a firing pin.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates, generally, to munitions. More particularly, it relates to a command to arm fuze that requires no electrical or electronic components. 
         [0003]    2. Description of the Prior Art 
         [0004]    Modern exploding munitions or rounds are required to carry insensitive explosives that have been specially formulated to prevent explosion resulting from exposure of the munitions or rounds to fire or mechanical abuse during transportation, storage, carrying in the field or any other environment they may encounter up until the moment they are fired from a weapon. Since a round must be “sensitive” if it is to explode upon impact with a target, a safe and arm device (SAD) is required to make the round “sensitive” once it has been fired from the weapon. The SAD does this by controlling the alignment of one or two additional explosive components with the main insensitive explosive which forms an explosive “train,” usually located along the centerline of the round. 
         [0005]    The first component of an explosive train is a highly sensitive detonator; the second component is a less sensitive lead explosive, and it is not always required. The third component is an even less sensitive main charge. If all of the explosive components are in axial alignment with one another when the projectile hits a target, a firing pin detonates the detonator and the explosion of the detonator causes explosion of the lead charge and the explosion of the lead charge causes explosion of the main charge. The explosive train is interrupted and the round will not explode if the detonator or lead explosive is not in alignment with the main explosive. 
         [0006]    It is conventional to align the lead explosive and the main charge on the centerline of the projectile and to position the detonator off center until after the round is fired. Movement of the detonator by the SAD from the off-center, or safe, position to the centerline is called “arming.” The round and its fuze are armed when the detonator is in alignment with the other explosive components. 
         [0007]    A SAD and fuze are usually designed to arm at a specific distance (range) from the weapon that fires the round. The arming range must be sufficiently far from the weapon to ensure the safety of the operator should the round hit a target and explode at the exact instant the fuze arms. Due to inherent variations from fuze to fuze, the range at which they arm can vary greatly. After testing multiple rounds, a “no-arm” range and “all-arm” range can be determined for a given type of fuze. Based on the test data, the “no-arm” range is defined statistically as the range from the weapon at which no fuze will ever be armed. The “all-arm” range is defined as that at which all fuzes will be armed. The spread between the no-arm and all-arm ranges can vary greatly. For example, a M549 fuze may vary from sixty feet (60 ft) (no-arm) to two hundred feet (200 ft) (all-arm). 
         [0008]    A fuze that has little or no spread between the no-arm and all-arm ranges is defined in the industry as a “command to arm” fuze. There is a great need for a command to arm fuze due to the close engagement distances of urban warfare. Many times an intended target may be beyond the no-arm range, but well within the all-arm range of a fuze. In this case, the gunner cannot rely on the effectiveness of fired ammunition because some of the rounds will not have armed when they hit the intended target. If the all-arm range can be brought closer to the no-arm range, the weapon will be more reliable and useful over its operating distances. 
         [0009]    Conventional mechanical fuzes such as the M550, M549 and M549A use a “spinning” rotor as the primary component of the SAD. The rotor spins about a pivot shaft that is offset from the centerline of the round. Centrifugal forces move the rotor radially away from the centerline as the round spins during flight. The CG of the rotor is typically offset from the centerline of the round when the fuze is unarmed in a location that will maximize the centrifugal force on the rotor. 
         [0010]    The detonator is mounted within the rotor. The rotor and its pivot location are designed such that the detonator is spaced apart from the centerline when the fuze is unarmed. As the rotor spins about the pivot, the detonator moves to the centerline of the round so that it is aligned with the lead and main explosives. The rotor hits a mechanical stop when it is so aligned. The rotor is locked in the unarmed position by at least two independent safety devices that prevent it from rotating until the round has exited the weapon. A minimum of two safety devices are required by military specifications governing fuzes. 
         [0011]    If not restrained, the rotor moves from the unarmed to the armed position in a small fraction of a second on the order of one-thousandth of a second (0.001 s). This unrestrained arming time is due to the centrifugal force resulting from the mass of the rotor and detonator. Given the velocity of a 40 mm high velocity grenade when it exits the weapon, the goal of an SAF is to arm the round in one-tenth of a second (0.1 s) to ensure an arming distance of approximately eighty feet (80 ft). Therefore, unless the rotor is somehow slowed down, the SAD will arm much too quickly. 
         [0012]    The speed of the rotor is slowed down by mechanisms that absorb the kinetic energy of the rotor. A classic version of this mechanical absorber is known as a verge and pinion/starwheel. The starwheel is a small rotating disk that is coupled to the rotor via a pinion mounted upon the shaft of the disk. Gear teeth on the rotor spin the starwheel as the rotor moves from the unarmed to the armed position. The spinning starwheel repeatedly strikes a cam, called a verge, causing it to oscillate about a pivot shaft. The starwheel/verge system converts potential energy stored by the rotor to kinetic energy in discrete increments, acting as a brake to slow down the spinning (pivoting) of the rotor. Friction between the various mechanical components of the SAD also absorbs much of the energy of the rotor. Sources of friction include the pivot shafts about which the rotor, starwheel and verge rotate. These shafts are usually positioned radially outwardly from the centerline of the round. 
         [0013]    Due to centrifugal forces on the respective CG&#39;s of the rotor, starwheel and verge, the loads on these shafts can be as much as fifteen hundred (1,500) times the force of gravity. Unfortunately, friction is not easy to characterize due to its variability in different environments; the coefficient of friction between two materials can vary by as much as 100% over a small temperature range. Moreover, the tolerances of the respective components can dictate how tightly they rub together. Accordingly, small variations in tolerances can result in large variations in the amount of friction. This friction problem cannot be easily addressed by adding lubrication to the system. In fact, adding conventional lubrications such as oil can actually cause the SAD to bind and stop functioning. The only practical means of lubricating the SAD is by the use of small, precise amounts of dry Teflon® powder; however, the powder application method must be tightly controlled or the treated SAD&#39;s may bind and not function. 
         [0014]    Electronic SAD&#39;s have been developed, but they are not yet used in mass quantity production. An electronic timer could be used to initiate the arming very precisely and assure a Command to Arm fuze; however, some actuation system is still required to actually move the detonator from the unarmed to the armed position. Battery shelf life has also been a concern that has yet to be adequately addressed. The largest impediment for electronic fuze acceptance remains the cost of production in large quantities. 
         [0015]    However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified needs could be fulfilled. 
       SUMMARY OF THE INVENTION 
       [0016]    The long-standing but heretofore unfulfilled need for a mechanical command to arm fuze is now met by a new, useful, and non-obvious invention. 
         [0017]    The novel command to arm fuze includes a hollow housing, commonly called an ogive, having a rounded leading end, an open trailing end, and a longitudinal axis of symmetry. A cylindrical upper housing having an open top and an open bottom is disposed within the hollow main housing in concentric relation to the longitudinal axis of symmetry. A lower housing is disposed within the hollow main housing in concentric relation to the longitudinal axis of symmetry and has a flat bottom wall and a cylindrical sidewall mounted about the periphery of the flat bottom wall, projecting upwardly therefrom in supporting relation to the cylindrical upper housing. 
         [0018]    A centrally bored flywheel is rotatably mounted in the upper housing about an axis of rotation that is concentric with the longitudinal axis of symmetry. The flywheel has a center of gravity concentric with its axis of rotation. A timing post depends from the flywheel into the lower housing in eccentric relation to the longitudinal axis of symmetry. 
         [0019]    An actuator dome having a central aperture formed therein has a peripheral edge that engages the interior surface of the ogive. 
         [0020]    A firing pin is slideably received in the central aperture of the actuator dome and in the central bore of the flywheel in coincidence with the longitudinal axis of symmetry. 
         [0021]    A zip rotor positioned atop the bottom wall of the lower housing is rotatably mounted about an axis of rotation defined by a rotor shaft and has a center of gravity eccentric to its axis of rotation. A detonator is mounted in the zip rotor. The zip rotor has a first, unrotated, safe position of repose where the detonator is misaligned with the firing pin. 
         [0022]    A first spring prevents the flywheel from rotating when centrifugal forces acting on the first spring are below a preselected threshold and a second spring holds the zip rotor in its safe position of repose even when the centrifugal forces are great enough to cause the first spring to disengage. The first spring has a first end permanently secured to a cylindrical sidewall of the upper housing and the first spring has a second end releasably secured to the flywheel. The first spring could also engage the timing post. The first spring is biased radially inwardly and the bias is overcome when centrifugal forces acting on the first spring exceed the predetermined threshold so that the flywheel is free to rotate about the firing pin. 
         [0023]    The flywheel has a central hub and a pinion gear is mounted on the central hub for conjoint rotation therewith. A rotatably mounted drive gear has teeth that meshingly engage the pinion gear so that when the flywheel is held against rotation by the first spring, the drive gear is also held against rotation. 
         [0024]    The drive gear is rotatably mounted about a pivot shaft and has a center of gravity eccentric to the pivot shaft. The drive gear rotates in a first rotational direction about the pivot shaft when the first spring releases the flywheel and hence the pinion gear. The pinion gear and flywheel are driven by the drive gear teeth to rotate in a second rotational direction opposite to the first rotational direction when the drive gear rotates in the first rotational direction. 
         [0025]    A second spring holds the zip rotor against rotation. The second spring has a first radially outward end permanently secured to a cylindrical sidewall of the lower housing and a second radially inward end releasably engaged to the zip rotor. 
         [0026]    A timing post depends from a peripheral edge of the flywheel. The timing post abuts the second end of the second spring and knocks the second end out if its releasable engagement with the zip rotor when the flywheel is rotated in the second rotational direction. 
         [0027]    The zip rotor center of gravity causes it to pivot from its safe position of repose to an armed position when released from the safe position of repose by the timing post striking the second end of the second spring. The detonator enters into axial alignment with the firing pin when the zip rotor is in the pivoted, armed position. 
         [0028]    An actuator is formed integrally with the hollow housing on an interior side of the rounded leading end. The actuator is centered on the longitudinal axis of symmetry and is closely spaced apart from a head of the firing pin. When the hollow housing impacts against a hard target, the leading end of the hollow housing is deformed and the trailing end of the actuator is driven into the head of the firing pin. 
         [0029]    A mounting pin depends from a bottom edge of the upper housing and is received within a bore formed in an upper edge of the lower housing. 
         [0030]    A support arm has a first, radially outermost end secured to the mounting pin and a second, radially innermost end disposed radially inwardly from the mounting pin. A firing pin aperture is formed in the second, radially innermost end of the support arm and the firing pin extends through the firing pin aperture. 
         [0031]    A rotor shaft is mounted in upstanding relation to the flat bottom wall of the lower housing. More particularly, a first end of the rotor shaft is mounted in a blind bore formed in the flat bottom wall and a first rotor shaft aperture is formed in the zip rotor. A second rotor shaft aperture is formed in the support arm and the rotor shaft extends through the first and second rotor shaft apertures. 
         [0032]    An anti-creep spring has a first, radially outermost end secured to the mounting pin and a second, radially innermost end disposed in abutting relation to the zip rotor. A rotor shaft aperture is formed in the second end of the anti-creep spring so that the rotor shaft extends through the rotor shaft aperture. When the hollow housing impacts against a soft target and the hollow housing is not deformed by the impact, the actuator is not driven into the firing pin. The zip rotor in its armed position slides along the rotor shaft in the direction of hollow housing travel due to the sudden deceleration of the hollow housing caused by the soft target impact. The zip rotor overcomes the bias of the anti-creep spring and the detonator carried by the zip rotor impacts against the firing pin. 
         [0033]    The drive gear is disposed in overlying, substantially parallel relation to the support arm. The pivot shaft is mounted to the support arm in upstanding relation thereto and a pivot shaft aperture is formed in the support arm and the pivot shaft extends through the pivot shaft aperture. The drive gear is pivotable about the pivot shaft. 
         [0034]    A setback e-ring is disposed in encircling relation to the hollow housing and the lower housing. A first groove is formed in a peripheral vertical wall of the hollow housing and accommodates a radially outward edge of the setback e-ring. A second groove is formed in a peripheral vertical wall of the lower housing for accommodating a radially inward edge of the setback e-ring. The setback e-ring prevents relative movement between the hollow housing and the lower housing. 
         [0035]    A base plate is disposed in underlying, supporting relation to the flat bottom wall of the lower housing. The lower housing has a radially inwardly disposed flange that circumscribes a trailing end of the lower housing and abuttingly engages a trailing wall of the base plate to maintain the base plate in abutting relation to the flat bottom wall of the lower housing. 
         [0036]    A bore is formed in a trailing side of said zip rotor and a recess is formed in the base plate. A setback pin having a head and a reduced diameter post is disposed in the recess and the reduced diameter post is disposed in the bore. A bias means holds the reduced diameter post of the setback pin in the recess. The setback pin maintains the zip rotor in the safe position of repose until acceleration forces acting on the round/projectile as it is launched from a weapon overcome the bias of the bias means and causes the reduced diameter post to withdraw from the recess and thereby unlock the zip rotor so that the zip rotor is free to rotate about the zip rotor shaft when said zip rotor is also released by the second spring. 
         [0037]    A central aperture is formed in the base plate and a central aperture is formed in the flat bottom wall of the lower housing. A lead explosive is positioned in the central aperture formed in the base plate and in the central aperture formed in the flat bottom wall of the lower housing. A leading end of the lead explosive is disposed in open communication with the detonator and a trailing end of the lead explosive is disposed in open communication with a main charge. Striking the detonator with the firing pin triggers detonation of the detonator, thereby triggering explosion of the lead explosive which then causes explosion of the main charge. 
         [0038]    The primary object of this invention is to provide an all-mechanical command to arm device having no electrical or electronic parts. 
         [0039]    A closely related object is to provide an all-mechanical command to arm device that changes from a “no arm” configuration to an “all arm” configuration in as little time as an electronic fuze. 
         [0040]    Another important object is to meet the foregoing object in an inexpensive way. 
         [0041]    These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
         [0042]    The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
           [0044]      FIG. 1  is a diagrammatic view of a round in flight that is equipped with the novel fuze; 
           [0045]      FIG. 2  is a longitudinal sectional view of the novel fuze; 
           [0046]      FIG. 3  is a transverse sectional view depicting the fuze in a safe configuration; 
           [0047]      FIG. 4  is a view like that of  FIG. 3  but where centrifugal force has caused a flywheel centrifugal lock spring to disengage from the flywheel; and 
           [0048]      FIG. 5  is a transverse sectional view depicting the novel fuze in its fully armed configuration. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0049]    Referring now to  FIG. 1 , it will there be seen that a diagrammatic representation of a projectile or round equipped with the novel structure is denoted as a whole by the reference numeral  10 . 
         [0050]    Round  10  in this example is a typical 40 mm round. The novel command to arm fuze is denoted  12 . Round  10 , having been fired from a weapon, is depicted in flight, travelling in the direction of directional arrow  14 . It is also spinning about longitudinal axis of symmetry  16  of round  10  and fuze  12 . The trailing end of round  10  is filled with main explosive charge  18 . As used herein, the leading end of any part is the end nearest the top of the drawing and the trailing end of any part is the end nearest the bottom of the drawing. 
         [0051]    As best understood in connection with  FIG. 2 , fuze  12  includes hollow housing  20  having a generally inverted “U” shape, sometimes referred to in technical writings as a nosecone or an ogive. Hollow housing  20  houses all of the components of novel fuze  12 . 
         [0052]    The open trailing end of hollow housing  20  is closed by base plate  22 . Radially inwardly-extending crimp  20   a  is formed integrally with hollow housing  20  at its trailing end and circumscribes base plate  22  to hold said base plate to said hollow housing. 
         [0053]    Actuator  20   b  is formed integrally with hollow housing  20  at the leading end thereof. Said actuator  20   b  is centered on head  24   a  of firing pin  24 . Detonator  26  is centered on point  24   b  of firing pin  24 . Actuator  20   b,  firing pin  24 , and detonator  26  are all centered on longitudinal axis  16 . It should therefore be understood that this  FIG. 2  position is the armed position of the fuze. If it were unarmed, the detonator would not be aligned with the firing pin and the actuator. 
         [0054]    Impact of 40 mm round  10  with a target begins the detonation process if command to arm fuze  12  has successfully armed. Ogive  20  is crushed if round  10  impacts a hard target. The deformation of ogive  20  drives actuator  20   b  into firing pin  24  which then strikes detonator  26  and initiates a detonation train disclosed hereinafter. 
         [0055]    Setback e-ring  21  locks command to arm fuze  12  into ogive-shaped hollow housing  20 . As depicted, said setback e-ring is positioned in a groove formed collectively by a groove that circumscribes an inner sidewall of ogive-shaped hollow housing  20  and a coplanar groove that circumscribes an outer sidewall of lower housing  30 . Setback e-ring  21  therefore prevents relative movement between lower housing  30  and hollow housing  20 . Radially inwardly turned crimp  20   a  at the trailing end of hollow housing  20  performs the same function but setback ring  21  provides a more robust interlocking of parts. 
         [0056]    Base plate  22  is centrally apertured to accommodate trailing end  28   b  of lead explosive  28  and said trailing end of lead explosive  28  is attached to said base plate  22 . Firing pin  24  is driven into detonator  26  to cause explosion of round  10  as aforesaid. The explosion of detonator  26  causes lead explosive  28  to explode. 
         [0057]    Lower housing  30  is positioned atop base plate  22  and cavity or central aperture  31  is formed therein to accommodate leading end  28   a  of lead explosive  28 . Aperture  31  is open at its trailing end so that when lead explosive  28  explodes in response to explosion of detonator  26 , the blast causes explosion of main explosive charge  18  as best understood from  FIG. 1 . 
         [0058]    Since the force of the explosion of lead explosive  28  is directed in a trailing direction, i.e., in a direction opposite to direction  14 , lead explosive  28  is referred to in the industry as a spitback and base plate  22  is referred to as the spitback and base plate assembly. 
         [0059]    Lower housing  30  supports upper housing  32 . Upper housing  32  houses flywheel  34  and drive gear  36  which together provide the novel timing means. Flywheel  34  is centrally apertured and firing pin  24  extends through said central aperture and therefore provides a pivot shaft for flywheel  34  so that flywheel  34  is free to rotate about centerline  16 . The center of gravity of flywheel  34  is coincident with axis of symmetry  16 . 
         [0060]    Actuator dome  38  is tightly fit about its periphery to an inner surface of hollow housing  20  as depicted. Actuator dome  38  is centrally apertured and receives the leading end of firing pin  24 . Locking e-ring  40  holds firing pin  24  in place. 
         [0061]    Pin  33  depends from upper housing  32  and provides a mounting means for support arm  42  and anti-creep spring  43 . 
         [0062]    Support arm  42  is apertured at its radially outermost end and pin  33  is received within said aperture. Support arm  42  extends radially inwardly from said pin. 
         [0063]    Flywheel  34  is therefore trapped between locking e-ring  40  and support arm  42 . 
         [0064]    Flywheel  34  and support arm  42  are held onto firing pin  24  by locking e-ring  44 . 
         [0065]    First, radially outermost end  43   a  of anti-creep spring  43  is secured to mounting pin  33  and therefore abuts the underside of support arm  42 . Second, radially innermost end  43   b  abuts the top of zip rotor  56 . The bias of anti-creep spring  43  urges zip rotor  56  into abutting engagement with floor  30   a  of lower housing  30 . Said bias prevents displacement of zip rotor  56  and hence detonator  26  along rotor shaft  58  into engagement with firing pin  24  while the round is in transit, and said bias is overcome when round  10  strikes a soft target. 
         [0066]    Aperture  45  is formed in support arm  42  about mid-length thereof, and aperture  45  is in alignment with an aperture formed in drive gear  36 . Pivot shaft  46  extends through aperture  45  and said aperture formed in drive gear  36  so that drive gear  36  is mounted for rotation about said pivot shaft  46 . Stop means  46   a  prevents drive gear  36  from traveling in the direction of directional arrow  14 . Stop means  46   a  can be an integrally formed enlargement of pivot shaft  46  or it may be a separate mechanical fastener. 
         [0067]    Pinion gear  48  is rotatably mounted to a depending central hub that is formed integrally with flywheel  34 . It is secured to said central hub and rotates conjointly therewith. 
         [0068]    Timing post  50  is also formed integrally with flywheel  34  and depends from an outer peripheral edge thereof. Said timing post extends into the cavity defined by lower housing  30 , said cavity housing the arming system of this invention. 
         [0069]      FIG. 2  also depicts above-mentioned zip rotor  56  and rotor shaft  58  which extends through an aperture formed in said zip rotor, providing an eccentric pivotal mounting for said zip rotor. Zip rotor  56  rests atop a bottom wall or floor  30   a  of lower housing  30 . Leading end  58   a  of rotor shaft  58  is received in a bore formed in support arm  42  and trailing end  58   b  of rotor shaft  58  is received within a blind bore formed in said lower housing bottom wall. Detonator  26  sits within a bore formed in zip rotor  56  and is eccentrically disposed with respect to centerline  16  and firing pin  24  when the fuze is in its safe configuration. 
         [0070]    Setback pin  57 , also depicted in  FIG. 2 , is inserted into countersunk cavity  57   a  formed in lower housing  30 . A reduced diameter part of the setback pin extends through a bore formed in lower housing  30  and into an aligned bore formed in zip rotor  56 . The bore in zip rotor  56  is located such that setback pin  57  can engage said bore only when zip rotor  56  is in its unarmed configuration. A setback spring, not depicted, holds setback pin  57  in place until round  10  is fired from a weapon. When the round is fired, inertial forces acting on setback pin  57  overcome the bias of the undepicted setback spring and force setback pin  57  to displace in the direction opposite to direction of travel  14  of round or projectile  10 , i.e., into cavity  57   a.  When setback pin  57  is thus disengaged from zip rotor  56 , said zip rotor is free to rotate to the armed position when timing post  50  releases zip rotor release lock spring  60  as disclosed hereinafter. 
         [0071]      FIG. 3  provides a plan view of the configuration of the timing system before round  10  is fired from a weapon. Flywheel  34  and drive gear  36  are depicted in their respective initial safe positions and timing post  50  is depicted abutting support arm  42 . Pivot shaft  46  protrudes upward as drawn from support arm  42  and through the central aperture formed in drive gear  36 , allowing drive gear  36  to rotate in the plane of the paper. Gear teeth  36   a  are integrally formed in a radially inward edge of drive gear  36  and meshingly engage pinion gear  48 . Clockwise rotation of drive gear  36  about pivot shaft  46  therefore causes counterclockwise rotation of flywheel  34  about firing pin  24  as gear teeth  36   a  engage pinion gear  48 . The center of gravity of drive gear  36  is denoted  36   b.    
         [0072]    Flywheel centrifugal lock spring  52  has a first end  52   a  attached to upper housing  32  and a second end  52   b  that engages slot  54  formed in timing post  50 , preventing flywheel  34  and timing post  50  from rotating about firing pin  24 . When round  10  is fired from a weapon, centrifugal forces act upon flywheel centrifugal lock spring  52  and second end  52   a  thereof moves radially outwardly from slot  54  of timing post  50 , thereby freeing flywheel  34  to rotate about firing pin  34 . 
         [0073]      FIG. 3  also depicts rotor release lock spring  60  having first end  60   a  secured to lower housing  30  and second end  60   b  disposed within slot  62  formed in peripheral edge of zip rotor  56 . Rotor release lock spring  60  prevents the rotation of zip rotor  56  until the required arming time has elapsed after the round is fired from a weapon. Rotor release lock spring  60 , when said second end is engaged in said slot, prevents zip rotor  56  from rotating about rotor shaft  58 . 
         [0074]    The center of gravity of zip rotor  56  is denoted  56   a  in  FIG. 3 . 
         [0075]      FIG. 3  depicts timing post  50  in its unarmed starting position where it abuts support arm  42  as aforesaid. Upon disengagement of flywheel centrifugal lock spring  52  from slot  54  formed in timing post  50 , said timing post travels in a counterclockwise circular path of travel around zip rotor  56 . When timing post  50  contacts rotor release lock spring  60 , it knocks second end  60   b  from slot  62  formed in zip rotor  56 , thereby freeing zip rotor  56  to rotate about rotor shaft  58 . Lock spring  52  could also engage flywheel  56  instead of slot  54  formed in timing post  50 . 
         [0076]      FIG. 4  is a plan view depicting the configuration of the novel timing system shortly after round  10  has exited a weapon. Second end  52   b  of centrifugal force lock spring  52  has disengaged from slot  54  of timing post  50 , thereby enabling but not causing rotation of flywheel  34 . Centrifugal forces acting on drive gear  36  along a vector extending from centerline  16  through CG  36   b  of drive gear  36  cause clockwise rotation of drive gear  36  about pivot shaft  46 . Meshing engagement between gear teeth  36   a  and pinion gear  48  causes flywheel  34  and timing post  50  to rotate counter clockwise about firing pin  24 . Rotation of said flywheel and timing post ends when said timing post abuttingly engages the opposite side of support arm  42 . 
         [0077]      FIG. 5  depicts the arming system after zip rotor  56  has traveled to the armed position. The spin of round  10  and SAD produces centrifugal force vector  66  which is applied through CG  56   a  of zip rotor  56  in a radially outward direction relative to centerline  16 . Force  66  causes zip rotor  56  to rotate about rotor shaft  58  in a counter clockwise direction, thereby positioning detonator  26  into alignment with centerline  16 , firing pin  24 , spitback  28 , and main explosive charge  18 . Before such rotation of zip rotor  56 , detonator  26  was secured in an eccentric location away from said centerline  16 , firing pin  24 , spitback  28 , and main explosive charge  18 . Zip rotor  56  has sufficient mass to rotate from the unarmed to the armed position within a small fraction of a second, which is much less than the time required for timing post  50  to complete its orbit. As zip rotor  56  moves into the armed position, rotor arm lock  68  moves inward and engages slot  70  formed in the periphery of zip rotor  56 , locking said zip rotor in position and preventing it from rotating in the clockwise direction. 
         [0078]    Standard fuze safety regulations require that all SADs have at least minimum two safety locks that prevent the fuze from arming until it has been intentionally fired from a weapon. These safety locks must not be removed until the round has been subjected to “environments” that can only occur after a round has been fired from a weapon. The same regulations require that the two safety locks respond to independent and distinct environments. In this application of the command to arm fuze, one of the environments is the centrifugal forces generated by the rapid rotation of round  10  about centerline  16  which are typically in the range of twelve thousand revolutions per minute (12,000 rpm) for 40 mm ammunition. The radially inward bias of flywheel centrifugal lock spring  52 , the first safety lock, prevents flywheel  34  from rotating. Centrifugal forces acting upon flywheel centrifugal lock spring  52  when round  10  is fired are sufficient to overcome the inward bias and displace second end  52   b  radially outward until it disengages flywheel  34 . 
         [0079]    Setback pin  57 , disclosed in connection with  FIG. 2 , provides the second safety feature of command to arm fuze  12 . 
         [0080]    The first safety lock, flywheel centrifugal lock spring  52 , cannot release flywheel  34  until a high rpm threshold has been reached. Flywheel  34  has a central center of gravity so that its release does not cause it to begin rotation. Drive gear  36 , however, has a center of gravity eccentric to its axis of rotation about pivot shaft  46 . Accordingly, as round  10  experiences high rpms, drive gear  36  is urged by centrifugal forces to rotate about said pivot shaft  46 . However, by highly novel insight, drive gear  36  cannot respond to such centrifugal forces because drive gear teeth  36   a  are meshingly engaged with the teeth of pinion gear  48  which is secured to a central hub of flywheel  34 . When flywheel  34  is released by flywheel centrifugal lock spring  52 , drive gear  36  rotates instantaneously because it is already under bias to rotate as aforesaid. Rotation of drive gear  36  thus causes rotation of pinion gear  48  and conjoint rotation of flywheel  34  and timing post  50  that depends therefrom. Timing post  50  strikes second end  60   b  of rotor release lock spring  60  from slot  62  formed in zip rotor  56  and this frees said zip rotor to pivot quickly to the armed position due to its center of gravity  56   a  being eccentric from its axis of rotation as defined by rotor shaft  58 . 
         [0081]    The weight and CG of the drive gear are designed such that the torque generated by the rotation of the drive gear rotates the flywheel in a predetermined amount of time. The weight and inertia of the flywheel is designed such that the torque transferred through the pinion gear rotates the flywheel at a predetermined speed such that the zip rotor will not be released until the round has traveled to the desired arm distance. By not having the detonator located in the flywheel, the weight of the flywheel is kept to a minimum, thereby enabling the drive gear to be very small. Even though the drive gear is eccentrically pivoted, its low weight reduces the friction resulting from the spin of the projectile to a tiny fraction of what would be experienced in prior art fuzes. This lack of significant friction enables the fuze to perform consistently and have very little variation in arm time and said arm time can be accurately predicted and set by the design of the flywheel and drive gear. 
         [0082]    It will thus be seen that the objects set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
         [0083]    It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.