Abstract:
A sling release mechanism for releasing the sling of a drogue parachute from a descending aerially delivered cargo pallet. The sling release mechanism has a body, with which a pivot arm, an inner and outer hinge plate articulate. The inner and outer hinge plates articulate in opposite directions when in use. The inner hinge plate has a cavity or receiver into which the end tip of the pivot arm may engage. The end of a parachute sling is placed over the pivot arm, and the pivot arm and inner hinge plate are articulated to engage the pivot pin end with the receiver of the inner hinge plate. The outer hinge plate is then articulated to engage the inner hinge plate, and is held in place with a releasable retainer. The parachute sling is released by releasing the retainer, allowing the outer and then the inner hinge plates to articulate, thereby releasing the pivot arm to articulate, after which the end of the parachute sling slides off the pivot pin. Other embodiments include multiple mechanisms for releasing a plurality of slings.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 11/733,542 filed on Apr. 10, 2007 and entitled “SLING RELEASE MECHANISM.” U.S. Ser. No. 11/733,542 is a non-provisional of U.S. Provisional No. 60/790,653 filed on Apr. 10, 2006, and entitled “SLING RELEASE MECHANISM.” The entire contents of all of the foregoing applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to release mechanisms for releasing a deployed parachute from a suspended load in a controlled manner. 
     BACKGROUND 
     Aerial delivery is a means frequently used for transporting cargo quickly to areas of limited or hostile access, without the availability of any nearby airports. At times, people in isolated areas, such as jungles, deserts, mountains, polar regions, or combat zones, are in need of essential supplies, including food and medical supplies, but are not within access to an airport at which a supply plane could land. In these instances, aerial delivery of cargo from in-flight aircraft is the sole option. These aerial delivery systems involve the use of parachute systems to slow the descent and gently land the cargo platforms on the ground. 
     Similar parachute systems are further utilized for recovery of aeronautical and astronautical vehicles, including rocket boosters, experimental aircraft and space capsules, returning back to the earth&#39;s surface from flights in the upper atmosphere or outer space. 
     In these aerial delivery or recovery systems, a series of parachute deployments is often used to progressively slow the descent velocity of the payload. Use of a series of parachute deployments is often necessary because the force and impulse on the suspension lines and straps of a main parachute (i.e., one large enough to slow the cargo platform to an acceptable landing velocity) deploying at the terminal, free-fall velocity of the cargo platform would be excessive, causing the parachute system to fail. Instead, the cargo platform is typically slowed in a series of stages using subsequently larger parachutes. 
     A drogue parachute is typically deployed first from the parachute system. The drogue is a small parachute which can be easily deployed from its container by a tether attached to the launching cargo plane or by an easily deployed stored energy means such as a spring launched pilot parachute. As the drogue parachute is deployed and inflated, it moderately decelerates the suspended cargo platform, as well as orientating the cargo platform into its desired upright attitude, without excessive strain on the slings and parachute canopy from which the cargo platform is suspended. After a predetermined time period, the drogue parachute is released from the suspended cargo platform. The drag provided by the released drogue parachute is then utilized to pull and deploy the next, larger parachute. This next parachute may be the final, main parachute, or another intermediary parachute prior to another subsequent deployment of the main parachute, depending upon the size of the cargo platform and the design of the parachute system. 
     To accomplish this release design, the drogue parachute is attached to the suspended cargo platform by a release mechanism. The suspended cargo platform is suspended from the release mechanism typically by a series of suspension slings. The suspension slings maintain the suspended cargo platform in a stable, level attitude. The number of suspension slings is typically four, with one routed to each corner of a square or rectangular cargo platform supporting the suspended cargo. For larger platforms, a greater number of suspension slings may be used. The suspension slings converge at a point above the suspended load to the release mechanism, located at the apex of the pyramid formed by the suspension slings. 
     The drogue parachute may be attached to the release mechanism by a single sling or riser. From the top end of this sling, a number of suspension lines radiate to the perimeter of the drogue parachute canopy. 
     One common release mechanism is a pyrotechnic cord cutter powered by an explosive or pyrotechnic charge. This mechanism utilizes the detonation of a small explosive charge to drive a cutting blade through the suspension sling. For example, Norton, U.S. Pat. No. 4,493,240, disclosed a pyrotechnic cord cutter comprising an elongated cylindrical body with a lateral aperture proximate to one end of the body, through which passes the suspension line or other support line in the parachute system. A chamber is located at the other end of the body, containing an explosive charge. An opening is provided in the medial end of the chamber, into which is registered the rear end of a cutting blade. Upon detonation of the explosive charge in the chamber, the cutting blade is propelled through the aperture, severing the cord within. 
     The pyrotechnic cord cutters are typically usable only for relatively small-diameter cords. As the weight of a platform and payload increases, the size of the cord or strap between the parachute and payload platform increases. A pyrotechnic cord cutter for payloads above a moderate size becomes too large for practical handling and would incorporate an explosive charge too large and powerful for safe handling by personnel. 
     SUMMARY 
     A sling release mechanism is provided for installation between an aerially descending cargo platform and its drogue parachute. The sling release mechanism is disposed on the platform or pallet supporting the delivery load. The parachute release mechanism has a body with a connection means located at its upper portion for connection to the sling of a drogue parachute. The release mechanism has one or more pivot arms. Each pivot arm is situated within the body and pivots about a common axle or pivot pin located in the body. Each pivot arm has a free end section with a shaped end section which engages with a latch apparatus. 
     In one embodiment, the latch mechanism is comprised of an inner and an outer hinge plate, each having a flat plate section with parallel inner and outer flat faces which articulate with the body. The inner face of the inner hinge plate has a receiver defined therein, which is shaped and adapted to receive the shaped end section of the pivot arm. The inner hinge plate will typically articulate with the body at its lower end, while the outer hinge plate will conversely hinge from its upper end. The two hinge plates are adapted and disposed on the body such that the inner latch plate can articulate to a point where its receiver is engaged by the shaped end section of the pivot arm, after a sling end loop has been placed thereon, and, in this position, the outer hinge plate can articulate to have its inner face lie flush against the outer face of the inner hinge plate. The outer hinge plate is then secured to the body with a retainer, and the retainer is provided with a release means. 
     In this configuration, the leverage provided by the two hinge plates allows the retainer to exercise a significantly augmented force to hold the shaped end section of the pivot arm in place within the receiver of the inner latch plate. This significantly reduces the necessary size of the retainer and the means to release the retainer from the outer hinge plate. In one embodiment, the retainer is a cut loop and the release means is a cord cutter. Because the cut loop in this invention needs only to be sufficiently strong to resist the torque on the outer hinge plate imparted by the pivot arm, which is only a small fraction of the weight of the platform, and not the entire weight of the payload platform, a much smaller cord, and thus a much smaller cord cutter may be used than in conventional release means. 
     The following detailed description is not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of the preferred embodiment of the sling release mechanism. 
         FIG. 2  is another isometric view of the preferred embodiment. 
         FIG. 3  is a plan view of the preferred embodiment. 
         FIG. 4  is a plan view of the preferred embodiment, illustrating the operation of the sling release mechanism. 
         FIG. 5  is of another embodiment of the invention, showing an alternate torsion means, retainer and release means. 
         FIG. 6  is an elevational view of another embodiment of the invention, showing an alternate retainer and release means. 
         FIG. 7  is an illustration of an alternate embodiment of the invention, illustrating multiple pivot arms. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , a preferred embodiment of a sling release mechanism is comprised, first, of a body  10 , which serves as the base or foundation upon which all other components are assembled. The base can be fabricated of any commonly known, structurally strong material, such as metal, including but not limited to steel, stainless steel, cast iron, aluminum, aluminum alloys, titanium or titanium alloys. 
     Attached to the body is a pivot arm  12 . The pivot arm  12  has an elongated section  14 . At one end of the elongated section  14  is a shaped end section  16  and at the other, a means for articulating with the body  10 . This means for articulating with the body  10  comprises, preferably, an aperture  18 . A first pin  20  or the like passes through the aperture  18  with minimal clearance and conjoins at one or both of its ends with the body  10 . The pivot arm  12  can then freely articulate around the first pin  20 . The shaped end section  16  is disposed at the opposite end of the elongated section  14  from the aperture  18 . 
     The sling release mechanism further comprises an inner hinge plate  22 . The inner hinge plate  22  generally is of the shape of an elongated flat plate  26  having one enlarged end section. The enlarged end section has an aperture  24  defined within it, the axis of the aperture  24  normal to the longitudinal axis of the flat plate and parallel to the width dimension of the flat plate. A second pin  28  registers with the inner hinge plate aperture  24  and secures with the body  10 , permitting articulation of the inner hinge plate  22  about the second pin  28 . The longitudinal axis of the second pin  28  is parallel to that of the first pin  20 , so that the pivot arm  12  and the inner hinge plate  22  articulate within the same plane, with the inner hinge plate  22  inner face proximate to the pivot arm  12 . 
     In the inner hinge plate  22  inner face is or is defined a receiver  30  for the shaped end section  16  of the pivot arm  12 . The shaped end section  16  and the receiver  30  are complementarily shaped so that the shaped end section  16  registers with the receiver  30  when the inner hinge plate  22  is articulated towards the pivot arm  12 . Once the shaped end section  16  registers with the receiver  30  and the inner hinge plate  22  is restrained in place, the pivot arm  12  is likewise secured in place and precluded from any further articulation until the inner hinge plate  22  is released and allowed to articulate. In one embodiment, the complementary shapes are simply a rounded, convex hemispherical tip on the shaped end section and a concave, hemispherical cavity in the inner face of the inner hinge plate  22 . In another embodiment, the complementary shapes are of a conical frustrum. Other shapes to the shaped end section  16  and receiver  30  are within the scope of the invention, including but not limited to one or more tongue-and-groove slots disposed parallel to the axes of the pivot arm  12  and inner hinge plate  22 , so long as the shaped end section  16  and the receiver  30  can freely engage and disengage with little force to the inner hinge plate  22 , but, when engaged, will restrain articulation of the pivot arm  12 . 
     The sling release mechanism further comprises an outer hinge plate  36 . The outer hinge plate  36  is constructed similar to the inner hinge plate  22 , being again in the preferred embodiment a flat plate  38  with an expanded end section and an aperture  40  defined in the expanded end section normal to the longitudinal axis and parallel to the width dimension of the flat plate  38 . A third pin  42  registers with the outer hinge plate aperture  40  and is secured to the body  10 , permitting articulation of the outer hinge plate  36  about the axis of the third pin  42 . The axis of articulation of the outer hinge plate  36 , the inner hinge plate  22  and the pivot arm  12  are parallel, and the three components articulate substantially within the same plane. 
     The third pin  42 , about which the outer latch plate  36  articulates is disposed on the body  10  at a point where an imaginary line through the third pin  42  and the second pin  28  is parallel to the longitudinal axis of the inner hinge plate  22 , when the shaped end section  16  of the pivot arm  12  has registered with the inner latch plate receiver  30 . The inner and outer hinge plates  22 ,  36  are constructed such that, when the pivot arm  12  has engaged with the receiver  30  in the inner face of the inner hinge plate  22 , the inner face of the outer hinge plate  36  can engage flush with the outer face of the inner hinge plate  22 . 
     As shown in  FIG. 3 , the sling release mechanism further comprises a first torsion means, provided on the inner hinge plate  22 , which applies a torque to the inner hinge plate  22  about the axis of its articulation in a direction away from the pivot arm  12 . In the preferred embodiment, the first torsion means is a compression spring  32  which is disposed within a cavity or well  34  in the body  10 . The depth of the cavity  34  is slightly less than the length of the compression spring  32 , such that, when inserted into the well  34 , one end of the compression spring  32  protrudes slightly beyond the edge of the well  34 . A foot  35  is provided on the inner hinge plate  22  to engage and compress the protruding end of the compression spring  32  when the inner hinge plate  22  rotates to a position of engagement with the pivot arm  12 . The first torsion means facilitates disengagement of the receiver in the inner hinge plate  22  from the shaped end section  16  of the pivot arm  12 , when the inner latch plate  22  is intentionally released and allowed to articulate. 
     A second torsion means is further provided on the outer hinge plate  36 , applying a torque to the outer hinge plate  36  about the axis of articulation in a direction away from the pivot arm  12 , similar to the first torsion means on the inner hinge plate  22 . However, since the outer hinge plate  36  is oriented inversely from the inner hinge plate  22 , the second torsion means will apply a torque to the outer hinge plate  36  in a direction opposite from the first torsion means. If the inner hinge plate  22  is disposed as shown in  FIG. 1 , with its axis of articulation to the left and below the pivot arm  12 , the first torsion means will apply an anticlockwise torque to the inner hinge plate  22 , while the second torsion means will apply a clockwise torque to the outer hinge plate  36 . 
     Like the first torsion means, the second torsion means in the preferred embodiment is a compression spring  44 , which is disposed in a cavity or well  46  in the body  10 , which protrudes slightly from the well  46 , and which engages with part of the outer hinge plate  36  as the outer hinge plate  36  contacts the inner hinge plate  22 , while the inner hinge plate  22  has been engaged by the pivot arm  12 . 
     Once the inner hinge plate  22  has engaged the pivot arm  12 , and the outer hinge plate  36  has engaged the inner hinge plate  22 , a releasable retainer is provided to temporarily secure the outer hinge plate  36  in place against the torque applied to the outer and inner hinge plates  22 ,  36 , as well as any force applied to the pivot arm  12  from a sling disposed thereon. However, because of the lever arms provided by both the outer and inner hinge plates  22 ,  36 , the force on the retainer is significantly less than the external force applied on the pivot arm  12 . 
     In the preferred embodiment, again shown in  FIG. 3 , the retainer is an explosive bolt  48  securing the end of the outer hinge plate  36 , distal from its aperture  40 , to the body  10 . This can be accomplished by drilling aligned holes in the outer hinge plate  36  and the body  10  and tapping the hole in the body  10  to accept the threads of an explosive bolt  48 . An explosive bolt  48  is well known in the art of aerial parachute delivery systems, and is comprised of a frangible bolt with an embedded explosive charge which, when ignited, severs the bolt laterally. The explosive charge may be ignited by a remote or an automatic controller, which delivers an igniting electrical charge or current to the explosive at a predetermined time for release of the outer hinge plate  36 . 
     Once the release means releases the retainer securing the two hinge plates to the body, the two are free to articulate. As shown in  FIG. 4 , upon detonation of the explosive bolt (not shown), the outer hinge plate  36  is free to articulate clockwise, assisted in part by the force provided by the compressed compression spring  44 . The outer hinge plate  36  then articulates, in the case in the layout shown in  FIG. 4 , clockwise. This then releases the inner hinge plate  22 , which then articulates anti-clockwise, propelled in part by the force exercised by the compression spring  32  against the foot  35 . Once the inner hinge plate begins to articulate, the receiver  30  disengages from the shaped end section  16  of the pivot arm  12 , and the pivot arm  12  is then free to articulate, in this case, clockwise. Once the pivot arm has sufficiently articulated, a sling secured onto the pivot arm  12  is free to slide off and release from the mechanism. 
     In other embodiments of the present invention, alternative devices may be used for the first and second torsion means. As shown in  FIG. 5 , torque may be provided by torsion springs  62 ,  64  disposed coaxially on the second and third pins  28 ,  42  respectively, with one end secured to the respective hinge plate  22 ,  36  and the other to the pin  28 ,  42  or body  10 . However, this embodiment is less desirable because the spring would not unload and would continue to impart a torque to the respective hinge plate even after the engagement with the pivot arm  12  was released. 
       FIG. 5  also shows another embodiment of the retainer and release means. Here, the retainer comprises a piece of cord in a loop, commonly called a “cut loop”  50  in the art, which circumscribes the outer and inner hinge plates  22 ,  36  and, optionally, part or all of the body  10 . A pyrotechnic cord cutter  52 , well known in the art, is disposed on the cut loop  50 . The cord cutter  52  has an aperture through which passes the cord of the cut loop  50 . Within the cord cutter  52  is a knife edge which is propelled by a small pyrotechnic charge. The charge can be detonated by an electric signal sent automatically or remotely. When an electric signal is provided to the cord cutter  52 , the pyrotechnic charge ignites, propelling the knife edge through the cord and severing the cut loop  50 . The two hinge plates  22 ,  36  are then free to articulate away from engagement with the pivot arm  12 . 
       FIG. 5  further shows a sling  58  secured to the pivot arm  12  by a loop  60  at the end of the sling  58 . 
     In another embodiment, shown in  FIG. 2 , the first and second torsion means are found in and as part of the second and third pins  28 ,  42 , wherein the second and third pins  28 ,  42  are rigidly secured to the respective inner and outer hinge plates  22 ,  36  and are fabricated of an elastic material, such as a polymeric elastomer or spring steel, in part or in toto, which can elastically twist and provide a torque on the respective hinge plates as those hinge plates are articulated on the two pins  28 ,  42 . This is commonly referred to in the art as a torsion bar. This torsion bar has a similar disadvantage of the other alternative embodiments, in that a torque is still applied even when the respective hinge plates  22 ,  36  rotates at angles beyond that sufficient to disengage the pivot arm  12  from the inner hinge plate  22 , but the torsion bars  28 ,  42  have the advantage of providing the capability of holding the two hinge plates  22 ,  36 , after release, at a fixed angle away from the pivot arm  12 , rather than freely flapping and articulating uncontrolled after release from the pivot arm  12 . This can be provided by securing the two torsion bars  28 ,  42  to the body with the respective hinge plates  22 ,  36  at a desired angle after release. The torsion bars  28 ,  42  will provide the necessary torque when the two hinge plates  22 ,  36  are articulated to the position of engagement with the pivot arm  12  but, when released, will only articulate sufficiently to release the pivot arm  12 . Any further articulation of either of the hinge plates  22 ,  36  will be corrected by the reverse torque imposed by the torsion bar  28 ,  42  twisted in the reverse direction. 
     In another embodiment, shown in  FIG. 6 , the retainer is a sliding pin  54  which engages a hasp  55  mounted on the outer hinge plate  36  with either the body  10  or the inner hinge plate  22 . The sliding pin  54  is translationally operated by an electric solenoid  56 . When the inner hinge plate (hidden from view) and outer hinge plates  36  are positioned to engage the pivot arm (hidden from view), the solenoid  56  is de-energized to register the sliding pin  54  with the outer hinge plate  36 . When the pivot arm (hidden from view) is desired to be released, the electrical power to the solenoid  56  is energized on, the sliding pin  54  withdraws from the hasp  55  and the outer hinge plate  36  is released. 
     Another embodiment of the invention comprises a plurality of the single sling mechanism described above. In this embodiment, shown in  FIG. 7 , a body  10  has a plurality of pivot arms  12  disposed therein, preferably on a common or concentric axis. A set of inner and outer hinge plates  22 ,  36  as described above, can be provided for each of the plural pivot arms  12 . Each outer hinge plate  36  may have its own, dedicated retainer and release means, such as a separate explosive bolt. This would allow release of each pivot arm  12  and its associated sling independently. Alternatively, one set of inner and outer hinge plates  22 ,  36  may be provided. The single inner hinge plate  22  would have multiple receivers disposed in its inner face, the number of which equaling the number of pivot arms  12 . 
     Another alternative of this plural sling embodiment is one having a plurality of pivot arms  12 , capable of securing and then releasing multiple slings. This may find use where several drogue parachutes may be deployed and then released in series, to decelerate a cargo incrementally. The plurality of pivot arms may be secured by a plurality of inner and outer hinge plates  22 ,  36  operating in a similar manner as a single sling release mechanism, in which each inner hinge plate has one receiver  30  securing one pivot arm  12 , and each outer hinge plate  36  secures one inner hinge plate  22 . Alternatively, large inner and outer hinge plates  22 ,  36  can be provided which can individually secure multiple pivot arms  12  or inner hinge plates  22 , respectively. As shown in  FIG. 7 , one embodiment has two pivot arms  12  articulating on a common first pin  20 . The pivot arms  12  each engage with an individual inner hinge plate  22  with a single receiver  30 . However, as shown, the two inner hinge plates  22 , shown in hidden view, would be secured by a single outer hinge plate  36 . This outer hinge plate  36  can be held in place with the various retainers and release means described in the other embodiments. 
     While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit, scope or application of the invention. This is especially true in light of technology and terms within the relevant art that may be later developed. Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should only be defined in accordance with the appended claims and their equivalents.