Abstract:
An extendable sway brace for a rack for an airborne payload. The sway brace is extendable. A mechanism for extending the sway brace includes means for preventing extension of the sway brace when the pressure exerted by the brace on a payload reaches a predetermined pressure. The means for preventing extension of the brace may include, for example, one or more pre-loaded springs. In this case, extension of the brace is prevented when the springs are compressed by a predetermined amount. The invention also provides a rack for an airborne payload comprising a sway brace of the invention.

Description:
FIELD OF THE INVENTION 
     This invention relates to aircraft mounted racks for carrying and releasing a payload from an airborne aircraft. 
     BACKGROUND OF THE INVENTION 
     A payload, such as a bomb, may be suspended from below an aircraft before takeoff and subsequently released from the aircraft when airborne. The payload is provided with one or more lugs on an upper surface. The payload is mounted on the aircraft by engaging the lugs in hooks that are part of a payload rack attached to a bottom surface of the aircraft. The rack includes “sway braces” that extend from the rack and that are affixed firmly to the payload. This reduces or prevents swaying of the payload that would otherwise occur due to vibrations of the aircraft during takeoff and during flight. The payload is released from the rack by activating a release mechanism that opens the hooks. In order to prevent the released payload from coming into contact with the aircraft, the rack may include an ejection mechanism. The ejection mechanism includes a piston that immediately after the opening of the hooks is made to descend rapidly and strike an upper surface of the payload with a sufficiently large force so as to impart to the released payload a large downward momentum. Movement of the piston rod may be caused by a pyrotechnic mechanism in which an explosion is made to occur within the piston, or by a pneumatic source. 
     The rack typically has two pairs of sway braces. One pair contacts the payload at its forward end, while the second pair contacts the payload at its rear end. In order to accommodate payloads of different sizes, both pairs of sway braces are extendable. After mounting the payload, the sway braces are extended from the rack until they are firmly affixed to the upper surface of the payload. The sway braces are then secured in position. 
     SUMMARY OF THE INVENTION 
     The present invention provides an extendable sway brace for use in a rack for an airborne payload. In accordance with the invention, the sway brace is configured so as to prevent the sway brace from exerting excessive pressure on the payload. This is particularly beneficial for light payloads having a thin outer casing. In a preferred embodiment of the invention, the sway brace includes a mechanism for extending the brace comprising one or more preloaded springs. As the sway brace is extended and contacts the payload, the spring or springs start to become compressed. As the pressure exerted by the brace on the payload increases, the compression of the springs also increases. When the compression of the springs reaches a predetermined value, the brace is prevented from being extended further. This is by way of example only, and any mechanism for preventing the sway brace from exerting excessive pressure on the payload may be used in accordance with the invention. For example, excessive pressure may be prevented by means of a friction clutch incorporated into the mechanism that extends the brace. 
     The invention also provides a rack for an airborne payload comprising the sway brace of the invention. The rack of the present invention is particularly suited for light payloads. A rack of the invention intended for carrying a light payload may have only one hook. 
     The rack of the invention may include a pair of extendable sway braces of the invention together with a pair of fixed sway braces. Having one pair of extendable sway braces instead of two shortens the attachment procedure of the payload to the rack, while still allowing the rack to accommodate payloads of different sizes. 
     The rack of the invention may also have an ejection mechanism. The ejection mechanism comprises a piston that is activated by introducing into the piston a pressurized gas such as Nitrogen. 
     The invention thus provides an extendible sway brace for a rack for an airborne payload, the sway brace having a mechanism for extending the sway brace comprising means for preventing extension of the sway brace when the pressure exerted by the brace on the payload reaches a predetermined pressure. 
     The invention also provides a rack for an airborne payload comprising a sway brace of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a pair of extendable sway braces in accordance with the invention; and 
         FIG. 2  shows a rack for an airborne payload comprising a pair of extendable sway braces in accordance with one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an extendable pair  23  of sway braces in accordance with one embodiment of the invention. The sway brace  23  may be used in a rack for an airborne payload. Pads  24   b  have a bulb like extension  41  that are snap fitted into sockets  42  in a cross-arm  43 . The pads  24  are thus attached to the cross-arm  43  in a ball and socket joint. This allows the pads  24  to swivel and adapt their positions so as to accommodate payloads of different shapes. 
     For affixing the pads  24   b  on a payload, a wrench or other suitable tool is used to turn a cap  54 . Sleeve  60  is attached and secured to cap  54 , so that rotation of the cap  54  causes rotation of the threaded sleeve  60 . Sleeve  60  rotates in a cylindrical passageway  61  having a matching threaded surface, so that rotation of the sleeve  60  is coupled with descent of the sleeve  60  in the cylindrical passageway  61 . 
     Preloaded springs  58  are attached at an upper end  90  to an upper surface  91  of the sleeve  60 . A control rod  55  extends from the upper surface  91  in order to maintain the springs  58  in the correct position inside the sleeve  60 . The downward movement of the sleeve  60  causes downward movement of the preloaded springs  58  which press upon an extension element  57  so as to cause downward movement of the extension element  57 . Downward movement of the extension element  57  causes, in turn, downward movement of the cross arm  43  causing the pads  24  to contact the payload. 
     At this point, further rotation of the cap  54  increases the pressure of the pads  24   a  and  24   b  on the payload and when this pressure exceeds a pre-set value, the springs  58  become compressed beyond their preloaded length, and no longer cause further downward movement of the extension element  57 . In this way, the pressure of the pads  24   b  does not exceed a predetermined limit. 
       FIG. 2  shows a rack  1  for an airborne payload comprising the extendable sway brace of the invention. The rack  1  includes holes  40  for attachment of the rack to an aircraft. The rack  1  includes a hook  2  from which a payload (not shown) may be suspended. The hook  2  is pivotable around a pivot  95  between a closed position shown in  FIG. 2 , and an open position (not shown). 
     Bell-crank  4  and bell-crank  70  are pivotable around a common pivot  5 . Bell-crank  4  drives the hook  2  mechanism, and has 2 extensions:  11  and  72 . Bell-crank  70  drives a locker  13  mechanism, and has 2 extensions:  7  and  71 . When bell-crank  70  rotates in the direction of arrow  8 , extension  71  of bell-crank  70  pushes extension  72  of bell-crank  4  causing the bell-crank  4  to rotate about a pivot  5  in the direction of the arrow  8   
     A link  9  is attached at one end at a pivot  10  to an extension  11  of the bell-crank  4 . At another end, the link  9  is attached at a pivot joint  12  to the hook  2 . 
     Extension  72  of Bell-crank  4  is attached to a spring  73  by means of a pivot joint  76 . Another end of the spring  73  rotates around a pivot  74 . The spring  73  supplies a toggling feature to the hook  2  between it&#39;s opened and closed positions, and secures the hook mechanism in its open position and in its closed position. 
     A locker  13  is pivotable around a pivot  6 . The locker  13  has one extension connected by a pivot joint  14  on an end of a link  15 . At another end, the link  15  is attached at a pivot joint  75  to the extension  71  of bell-crank  70 . Another extension of the locker  13  is attached to a spring  16  by means of a pivot joint  17 . Another end of the spring  16  rotates around a pivot  18 . The spring  16  prevents rotation of the locker  13  in the direction of the arrow  80  when the piston  3  is in its up position. This in turn prevents inadvertent rotation of the bell-crank  70  in the direction of the arrow  8  (hook opening), so as to prevent inadvertent opening of the hook  2  when the hook is in the closed position shown in  FIG. 2 . 
     Movement of the hook  2  between its open and closed positions is regulated by means of an actuating mechanism. The actuating mechanism includes a piston  3  having an up position shown in  FIG. 2  corresponding to the closed position of the hook  2 . Actuation of the piston  3  by the introduction of pressurized gas into the piston  3  causes the piston to move from its up position to a down position (not shown)  2  corresponding to the open position of the hook  2 . 
     The distal end of the shaft  60  of the piston  3  contacts the extension  7  of the bell-crank  70 . Activation of the piston  3  into its lowered position depresses the extension  7  of the bell-crank  70  so as to cause the bell-crank  70  to rotate about pivot  5  in the direction of the arrow  8 . As the bell-crank  70  rotates in the direction of the arrow  8 , the following happens:
         a. Link  15  causes locker  13  to rotate about the pivot  6  in the direction of the arrow  81  from its closed position shown in  FIG. 2  to its open position (not shown), enabling the hook to rotate to its opened position   b. Extension  71  of bell-crank  70  causes bell-crank  4  to rotate about the pivot  5  in the direction of the arrow  8     c. Link  9  causes the hook  2  to rotate about the pivot  95  from its closed position shown in  FIG. 2  to its open position (not shown).       

     A hole  19  in the frame is configured to receive a safety pin (not shown) which, when inserted in the hole  19 , prevents rotation of the bell-crank  4  in the direction of the arrow  8  so as to lock the hook  2  in its closed position. The pin can only be inserted into the hole  19  when the hook  2  is in its closed position. 
     A hub  20  over the pivot  5  has a square protrusion  21 . The square protrusion  21  may be grasped by a wrench (not shown) and rotated in the direction of the arrow  8 , so as to rotate the control arm  4  in the direction of the arrow  8  for manual opening of the hook  2 . The rack also has a sensor  28  for generation of an electrical signal indicative of the state of the hook  2  (open or closed). 
     The rack also includes two pairs of sway braces  22  and  23  for stabilizing a payload suspended from the hook  2 . (Only one sway brace is visible in each of the pairs  22  and  23  in the perspective shown in  FIG. 2 ). The sway brace pair  22  is positioned in the rack as required for the dimensions of the payload, and is then clamped in this position. The sway brace pair  23  is extendable, as explained above in reference to  FIG. 1 , and serves to perform payload preloading. As the pads  24   b  press upon the payload, the payload may swing in the hook  2  until the pads  24   a  on the pair  22  of fixed sway braces contact the payload. The position of the adjustable pair  23  of sway braces is determined so that pads  24   a  attached to the tips of the pair  22  of sway braces, and pads  24   b  attached to the tips of the pair  22  of sway braces are in firm contact with the payload. 
     The rack  1  also includes an ejector  30  for ejecting the payload immediately after the opening of the hook  2 . The ejector  30  reduces the risk of the released payload coming into contact with the aircraft after release. The ejector  30  includes a piston  31  having an upper position shown in  FIG. 2 , in which a pad  32  located at the exposed end of the piston shaft is not in contact with the payload. The piston  31  is bought from its upper position to lowered position by means of a pressurized gas such as Nitrogen that is conducted from a reservoir (not shown) into the ejector  30  via a connecting hose  33 . The ejector  30  is activated immediately after the opening of the hook  2 , so as to cause the piston  31  to descend rapidly and strike an upper surface of the payload with a sufficiently large force so as to impart to the released payload a large downward momentum. The piston  31  is positioned to strike the payload close to its center of gravity. 
     The use of a pressurized gas such as Nitrogen to activate the ejector  30  prevents the formation of soot and other impurities that are formed during a pyrotechnic reaction. Such impurities in the piston may cause the piston  31  to become stuck and may cause corrosion inside the piston. For a light payload, an ejector activated by a pressurized gas such as Nitrogen is more suitable than an ejector that is activated by a pyrotechnic explosion. Another advantage in using a pressurized gas is that the behavior of the ejector is more predictable. When using a pyrotechnic unit, for example, the presence of moisture may affect the behavior of the pyrotechnic device. 
     For suspension of a payload on the rack, the payload is moved upwards, in a way that a lug firmly attached to the top of the payload is pushed against the extension  80  of the hook  2 , causing the hook to close spontaneously and latch closed under the influence of the spring  73 . 
     At this point, the payload is suspended on the hook  2 . The hook is secured by two means:
         a. Geometric locking: the pivot  10  is over-centered relative to the line between pivots  12  and  5 .   b. Locker  13  is in its closed position