Safety and arming device

A safety and arming device interconnecting a bomb with a target detector ures safe mine laying deployment thereof through a detonation explosive train that is armed in delayed response to payout of a lanyard under enablement control exercised by a hydrodynamic piston in response to water impact during such deployment.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the fail-safe arming of 
explosive weapons, and more particularly to the arming of mines or the 
like deployed into water from an aircraft. 
The provision of safety and arming devices for aircraft delivered explosive 
weapons, is already generally known in the art. Heretofore, such safety 
and arming devices were operated in response to impact so as to restrict 
aircraft delivery speed and altitude as a safety measure. Also, aircraft 
launch conditions and deployment requirements imposed by prior arming 
devices, restricted delivery speed and altitude and imposed water depth 
requirements on underwater mine laying operations. 
It is therefore an important object of the present invention to provide a 
safety and arming device which improves underwater explosive weapon 
deployment by aircraft delivery, with respect to safety, reliability and 
imposition of operational limits. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a safety and arming device is 
installed in an aircraft delivery envelope, such as the casing for a bomb 
and target detector. A lanyard pays out from a winding spool within the 
safety and arming device to store energy in a clock spring during 
deployment. Water impact is detected through a hydrodynamic piston during 
deployment so as to avoid arming in response to dry land impact. The water 
and dry land environments involved in use of the safety and arming device 
accounts for a reduction in altitude and an decrease in flight speed from 
limits heretofore imposed on arming operations. Explosive safety and 
reliability is also improved during arming operations by use of a 
detonator that is both electrically shorted and held in out-of-line 
relation to an explosive train by a time delay driven rotor until 
fail-safe completion of an arming cycle is achieved.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to the drawing in detail, FIG. 1 illustrates a safety and 
arming device, generally referred to by reference numeral 10, which is to 
be utilized for improved delivery of naval weapon mines in accordance with 
one embodiment of the invention. The device 10 is accordingly associated 
with a launch platform on a high speed, low altitude flying aircraft from 
which a bomb is deployed as an underwater mine. Such bomb is associated 
with a aircraft arming unit 14 and a target detection device 16, as 
diagrammed in FIG. 2 and generally known in the naval mine laying art. 
Thus, the device 10 is adapted to be installed in the nose fuse well of 
the bomb casing as an aircraft delivery envelope, also having a tail fuse 
well within which the target detection device 16 is installed. The device 
10 includes a safety section 18 and an arming section 20 interconnected 
therewith by means of a joint ring 22 as shown in FIG. 1. The safety 
section 18 is physically connected to the aircraft arming unit 14 by a 
lanyard 24 and swivel 25 of calibrated strength, while a bomb connector 26 
projects from the arming section 20, as also shown in FIG. 1, for 
communication with the target detector device 16. The operational 
connections between the device 10 and the target detection device 16 are 
diagrammed in FIG. 2. 
As depicted in FIG. 2, a detonation explosive train 28 is provided within 
the arming section 20 of device 10 to establish an explosive path to the 
bomb, such path being selectively rendered discontinuous when device 10 is 
in a "safe" condition and the explosive train maintained electrically 
shorted. The target detection device 16 is also electrically turned on as 
hereinafter explained. When a target is thereafter sensed by the target 
detection device 16, it sends an electrical signal through a bomb fuse 
cable from and the bomb connector 26 to the explosive train 28 to achieve 
detonation. The lanyard 24 connected to the aircraft arming unit 14 
through swivel 25 extends into the lanyard subsystem 34 of the safety 
section 18, from which lanyard movement is transferred by a time delay 
mechanism 36 to the explosive train 28 under safety payout restrictions 
imposed by safe jettison controls 38 through which a water impact 
subsystem 40 is also enabled. Subsystem 40 detects entry of the delivery 
envelope carrying device 10 into the water to provide an output applied to 
the safe jettison controls 38 for payout control of the subsystem 34 of 
device 10 connected to the explosive train 28 through time-delay mechanism 
36 for regulating arming. A safe-enable mechanism 42 is connected to 
subsystem 40 as also diagrammed in FIG. 2. 
The aforementioned "safe" condition of the device 10 is maintained by 
out-of-line positioning of the detonation explosive train 28 of arming 
section 20 during storage, handling and transportation of device 10 in its 
delivery envelope installation. Only after environmental conditions unique 
to weapon deployment are sensed in the safety section 18 of device 10, is 
it switched to the "armed" condition. Such environmental conditions 
include aircraft launch reflected by deployment of the lanyard 24, 
hydrodynamic pressure reflecting water entry sensed by the water impact 
subsystem 40 as hereinafter described and a time delay imposed by the time 
delay mechanism 36 for fail-safe operational control. Before the delivery 
envelope enclosing the device 10 is dropped from an aircraft, the lanyard 
24 is held retracted within the safety section 18 under a force of 40 
pounds for example, exceeding the pull-out force of the arming unit 14 of 
the aircraft imposed by its deenergized solenoid (not shown), to prevent 
initiation of any arming sequence. Such solenoid in the arming unit 14 is 
energized under selective control of the aircraft pilot to "arm" the 
device 10 before a mine laying operation is initiated, in which case the 
lanyard 24 will be pulled from the device 10 when its delivery envelope is 
dropped. The arming unit solenoid may remain deenergized if the delivery 
envelope is dropped without arming thereof, in which case the lanyard 24 
is not extracted from device 10 as it falls from the aircraft. Upon 
ejection of the delivery envelope from the aircraft after arming, it 
continues to fall a short distance of 30 inches for example, during which 
the lanyard subsystem 34 stores energy transferred thereto by lanyard 
payout to enable the water impact subsystem 40 when deployment is 
subsequently completed. Further payout of the lanyard 24 is then prevented 
so that it separates from the arming unit 14 under a force of about 150 
pounds established by calibration of swivel 25 connecting the lanyard to 
the arming unit. 
During travel of the device 10 through the water in its delivery envelope, 
the hydrodynamic pressure exerted on the water impact subsystem 40 turns 
on the target detection device 16 as hereinafter explained while operation 
of the water impact subsystem 40 continues. Also, the detonation explosive 
train 28 is unlocked to permit operation thereof after an approximately 90 
second time delay imposed by the time delay mechanism 36, as 
aforementioned. At the end of such time delay, electrical shorting of 
detonation is removed, electrical firing circuit connection is made and 
detonation path completed to establish the "armed" condition of device 10 
after a momentary hydrodynamic pressure on the water impact subsystem 40 
subsides. In such "armed" condition, a firing signal from the target 
detection device 16 within the deployed delivery envelope casing, is 
awaited. 
Referring now to FIG. 3, the lanyard 24 extends into a cylindrical housing 
50 of the safety section 18 through a bearing assembly 52 radially offset 
from the axis of housing 50. The lanyard 24 in the retracted storage 
position shown, is wound upon a spool 54 of the lanyard subsystem 34 
aforementioned, which also includes a gear train having a drive gear 56 
fixed to the spool 54 and rotatably mounted therewith in the housing 50 by 
shaft 58. The spool 54 is drivingly connected by the gear train to a 
driven shaft 60 having a pinion gear 62 at one axial end thereof in mesh 
with idler gear 64 also rotatably mounted in the housing and in mesh with 
the drive gear 56. A shear pin 66 constituting one of the safe jettison 
controls 38 extends from a radially outer portion of spool 54 into the 
housing to hold the spool fixed during storage of the lanyard 24 wound 
thereon. In response to the pull exerted on the lanyard by the arming unit 
14 in excess of 40 pounds, the resulting torque applied to the spool 54 
causes shear of the pin 66 to release the spool for rotational payout of 
the lanyard. Such rotational movement is transferred from spool 54 to 
shaft 60 by the gears 56, 64 and 62. 
The shaft 60 is connected to a barrel 68 in the safety section 18 to which 
an energy storage clock spring 70 is fixed at its radially inner end to 
the delay drive mechanism 36 by an arbor 72 on which the barrel 68 is 
rotatably mounted. The rotation imparted to the barrel 68 through shaft 60 
by the gearing 56, 64, 62 in response to lanyard payout, thus causes clock 
spring 70 to be wound within the barrel 68 for storage of mechanical 
energy therein. Such rotation of barrel 68 is also imparted by shaft 60 to 
a threaded tubular shaft 74 extending axially from the barrel 68 as shown 
in FIG. 3. 
While the energy storing clock spring 70 is being wound within barrel 68, 
rotation of the threaded tubular shaft 74 causes axial displacement of a 
nut 76 threadedly mounted thereon, as more clearly seen in FIG. 4, to form 
another one of the safe jettison controls 38. A pin 78 projecting from nut 
76 into an axial guide slot 79 formed in housing 50, limits its rotational 
displacement thereby enabling axial movement of nut 76 as the barrel 
rotates. A shoulder on barrel 68 limits such axial movement of the nut 76, 
to thereby enable the water impact subsystem 40 as hereinafter explained. 
In the axial limit position of the nut 76, corresponding to complete 
lanyard deployment and full winding of clock spring 70, further rotation 
of the barrel 68 is stopped. Further payout of the lanyard 24 is thereby 
resisted by the barrel 68 with sufficient force so that when the tension 
in the lanyard exceeds about 150 pounds, the swivel 25 fails and the 
lanyard 24 is thus disconnected from the aircraft arming unit 14 with most 
of it retained within the device 10 to avoid the aircraft becoming 
unencumbered by the lanyard. 
The water impact system 40 includes a hydrodynamic piston 80 slidably 
displaceable within an axial bore 82 formed in the housing 50. The piston 
80 is biased by a calibrated spring 84 into abutment with a stop element 
86 in the housing having a passage 88 through which fluid communication is 
established between the piston bore 82 on one axial side of piston 80 and 
an external water entry opening 90 in the housing as shown in FIG. 3. An 
o-ring seal 92 on the piston 80, isolates the piston spring 84 within bore 
82 on the other axial side of piston 80. An elongated piston rod 94 
extends from the piston 80 through a diametrically smaller bore 96 from 
the housing 50 into the arming section 20 of device 10. Accordingly, the 
pressure of water entering opening 90 is exerted through passage 88 on the 
piston 80 causing its displacement against the bias of spring 84 to detect 
the generation of a hydrodynamic pressure during travel of device 10 
through water at a predetermined high velocity characteristic of the low 
altitude, high speed aircraft mine laying operation. 
Initial axial displacement of the piston 80 of the water impact subsystem 
40 toward its armed position, is limited to a short distance by its 
engagement with the nut 76 of the safe jettison controls 38, which also 
includes a lock-out release operated by means of a formation 98 on the 
piston rod 94 when displaced from the safe position shown in FIG. 3. In 
such safe position, the lock-out release formation 98 holds a 
spring-biased jettison detent 100 in its retracted position within the 
housing 50 as more clearly seen in FIG. 5. When released from its 
retracted position, the detent 100 engages and latches the barrel 68 to 
thereby prevent continued winding of the energy storing spring 70 after 
water entry is detected. 
With continued reference to FIG. 3, the piston rod 94 extends from the 
housing 50 of the safety section 18 into the housing 51 of the arming 
section 20 to actuate the turn-on switch 96 by means of a plunger 99 in 
response to displacement of the piston 80 to its armed position. When 
actuated, the switch 96 electrically connects power supply 123 to the 
target detection device 16 to turn it on as diagrammed in FIG. 2. 
Displacement of the piston rod 94 to its armed position moves its reduced 
diameter portion 101 into underlying relations to a lock-out pin 102 which 
is thereby released for axial displacement by a spring 103 as shown in 
FIG. 6. The large diameter end portion 105 of the lock-out pin 102 is then 
moved by spring 103 to a position locking the piston rod 94 in its armed 
position following dissipation of momentary hydrodynamic pressure exerted 
on piston 80. A rotor 104 is also released by the piston rod 94 so that it 
may begin to turn under the torque applied thereto by the energy storing 
spring 70 through arbor 72 and the gearing of the time delay mechanism 36. 
The gearing of the time delay drive mechanism 36 as depicted in FIG. 7 
includes an input gear train 106 of increasing drive ratio connecting the 
low speed arbor 72 to a high speed dynamically unbalanced coupler gear 108 
which is limited to a maximum rotational speed to provide the desired 
arming time. The gearing of the time delay mechanism 36 also includes an 
output gear train 110 of decreasing drive ratio connecting high speed 
coupler gear 108 to a low speed output gear 112 which angularly displaces 
the rotor 104 from a safe position to a position bringing a detonator 114 
carried therein into alignment with lead 116 of the explosive train 28. 
The detonator 114 is thereby actuated to safely complete an explosive path 
to a bomb warhead 117 as diagrammed in FIG. 2, through a booster pellet 18 
as shown in FIG. 3. 
The safe-enable mechanism 42 hereinbefore referred to in connection with 
FIG. 2, includes a safety pin 120 which locks the piston 40 in its 
position engaging the rotor 104 and extending therefrom externally of the 
device 10, as shown in FIG. 1, to signify that the rotor 104 is in its 
safe position physically holding the detonator 114 electrically shorted in 
its out-of-line relationship to the leads 116. Also, a red portion of the 
lanyard 24 located inside of the safety section 18 of device 10 denotes 
that it is in its "safe" condition. The red portion of the lanyard 
therefore becomes visible only after sufficient lanyard payout occurs 
causing rupture of the shear pin 66 as hereinbefore described. Finally, a 
knob 122 is provided as part of the safe-enable mechanism externally 
mounted on housing 50 of device 10 as shown in FIG. 1, to signify that the 
hydrodynamic impact detecting piston 80 is in its safe position. 
Obviously, other modifications and variations of the present invention may 
be possible in light of the foregoing teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.