Abstract:
A reefing slider for providing improved line management and canopy deployment characteristics of a ram air inflated airfoil type canopy. During initial descent of the parachute the slider, secured by retaining elements, is held against the canopy in the upper reefing position where it mechanically restricts canopy deployment while giving the canopy time to achieve proper orientation following the drop from the launching aircraft. Upon sufficient air flow into the canopy cells, the retaining elements separate, releasing the slider and enabling full opening of the canopy.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of copending application Ser. No. 11/201,186, filed Aug. 11, 2005, issuing as U.S. Pat. No. 7,338,016 on Mar. 4, 2008, and hereby claims the priority thereof to which it is entitled. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates in general to delaying the opening of parachute canopies and, more particularly, to a slider type reefing device that is secured to the canopy during initial parachute deployment. 
         [0004]    2. Description of the Related Art 
         [0005]    A known problem with the use of parachutes to lower personnel and unmanned cargo to the ground from airplanes and other airborne craft is the sudden shock when the parachute opens and fills quickly with air. This is especially serious at high speeds where the canopy fills more rapidly, as may occur during the deployment of parafoils designed to fly at high wing loadings. 
         [0006]    The mechanical reefing of parachute canopies by sliders on the canopy suspension lines for the purpose of delaying canopy opening and/or reducing canopy opening shock is already well known as representatively disclosed in U.S. Pat. No. 5,005,785 to Puskas. According to such prior art arrangement, opening of a ram-air inflated, airfoil gliding parachute canopy (hereinafter “ram air parachutes” or “ram air canopies”) is physically restricted to a decreasing extent as the reefing slider is displaced downwardly from an upper reefing position along converging suspension lines under canopy opening forces. 
         [0007]    The reefing system disclosed in the Puskas patent achieves aerodynamic delay by means of a flow deflecting flap extending from the slider beyond the suspension lines so as to be positioned in alignment with the leading edge portion of the canopy in the upper reefing position. However, because the slider is not physically connected to the canopy, heavier payloads can render the flap insufficient to withstand the force of the air flowing into the canopy upon deployment. Hence, under heavy loading of the parachute canopy, the slider may descend too rapidly such that adequate retarding of the canopy opening process is not achieved. 
         [0008]    One system has been developed by Pioneer Aerospace Corporation that is directed to a large forward-gliding parachute canopy bearing a heavy payload such as spacecraft returning from orbit. This system relies upon pyrotechnic connections between adjacent chords of the canopy which are activated to release one section of the canopy at a time. However, the system is highly complex and very expensive, making it unsuitable for routine and repeated airborne delivery of equipment and supplies such as is needed for troop support during military operations, particularly during periods of war and foreign occupation. 
         [0009]    Therefore, a need exists for a reefing device suitable for large and very large ram air canopies that produces a retarded rate of slider descent while also providing suspension line management capabilities. A need also exists for a reefing device that is released based upon actual forces imposed on the canopy, making it more responsive to dynamic deployment or opening conditions and appropriate for use with heavy payloads being delivered by forward gliding parachute canopies of the ram-air inflated airfoil type. 
       SUMMARY OF THE INVENTION 
       [0010]    In view of the foregoing, and the need to overcome the difficulties of undesirable inflation characteristics in ram air parachutes supporting large payloads, the present invention is directed to a generally rectangular slider type reefing device that is physically secured to the ram air canopy to retard its initial descent along the suspension lines. Retention of the slider prolongs the physical restriction of the ram air canopy opening process, producing delay in the inflation of the canopy by reducing the inflow of inflating air to the cells of the canopy. 
         [0011]    The generally rectangular slider is provided with multiple, appropriately spaced grommets for managed segregation of the suspension lines, and is retained against the canopy by retaining devices positioned adjacent to at least the edge grommets. The retaining devices include slider retaining loops secured adjacent to at least the slider edge grommets, canopy retaining loops secured to the canopy, and breakable fastening elements to secure the slider retaining loops and the canopy retaining loops together in respective pairs. To compensate for varying load on different portions of the canopy, the strength of the breakable fastening elements can vary at each grommet location according to distance from the wing tip so as to preferably obtain a uniformly timed release of the fastening elements and the subsequent even release of the slider retaining loops from their corresponding canopy retaining loops. 
         [0012]    It is therefore an object of the present invention to provide a retained slider system in which the slider is secured to at least the leading edge portion of the ram air canopy with breakaway fastening elements that delay initial descent of the slider from the upper reefing position. 
         [0013]    Another object of the present invention is to provide a relatively simple, force-activated system for securing and then releasing the edges of a forward gliding parachute canopy of the ram-air inflated airfoil type to regulate the opening thereof. 
         [0014]    A further object of the present invention is to provide a slider system with retaining devices having variable retention strength which is both reliable and effective for modulating the canopy inflation and opening process during chute deployment. 
         [0015]    A still further object of the present invention is to provide a retained slider system that can be readily adapted to fit and work effectively with a wide range of commercially available ram air parachutes while requiring minimal adaptation of the existing parachute structure. 
         [0016]    It is yet another object of the invention to provide a slider type reefing device that is not complex in structure and which will conform to conventional forms of manufacture so as to provide a canopy inflation control system that is economically feasible, long-lasting and relatively trouble free in operation. 
         [0017]    These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of a ram-air inflated airfoil-type parachute with the retained slider reefing system of the present invention installed thereon, shown with the slider in the upper reefing position prior to release from the canopy. 
           [0019]      FIG. 2  is a perspective view of the ram air parachute of  FIG. 1 , shown as fully deployed, with the slider in a lower position. 
           [0020]      FIG. 3  is a more detailed view of a portion of the bottom surface of the parachute taken along line  3 - 3  of  FIG. 2 . 
           [0021]      FIG. 4  is an enlarged view of detail “ 4 ” of  FIG. 1 . 
           [0022]      FIG. 5  is an enlarged view of detail “ 5 ” of  FIG. 1 . 
           [0023]      FIG. 6  is a plan view of the slider of  FIGS. 1 and 2 . 
           [0024]      FIG. 7  is an enlarged view of detail “ 7 ” in  FIG. 6 , showing a corner grommet with adjacent slider retaining loop. 
           [0025]      FIG. 8  depicts a suspension line extending from its attachment point on the canopy through a slider grommet during packing in accordance with the present invention. 
           [0026]      FIG. 9  shows four upper cascaded lines from a suspension line gathered through a slider grommet during packing, with the shortest cascaded line provided with a detachable slider stop and the corresponding canopy portion fitted with a canopy retaining loop. 
           [0027]      FIG. 10  depicts an alternative arrangement in accordance with the present invention in which the slider stop is secured to the canopy and the canopy retaining loop is attached directly to the slider stop. 
           [0028]      FIG. 11A  shows a calibrated break cord with one turn around an aligned pair of slider and canopy retaining loops in accordance with the present invention. 
           [0029]      FIG. 11B  shows the calibrated break cord of  FIG. 11A  with two turns around the aligned pair of retaining loops. 
           [0030]      FIG. 11C  shows the calibrated break cord of  FIGS. 11A and 11B  with three turns around the aligned pair of retaining loops. 
           [0031]      FIG. 12  illustrates the securing of the retaining loops on the slider and canopy with multiple turns of a calibrated break tie in accordance with the present invention. 
           [0032]      FIG. 13  illustrates knotting of the calibrated break tie or cord of  FIG. 12 . 
           [0033]      FIG. 14  is an enlarged view of detail “ 14 ” of  FIG. 2 . 
           [0034]      FIG. 15  shows a first alternative fastening mechanism embodiment using magnetic elements in accordance with the present invention. 
           [0035]      FIG. 16  shows the magnetic elements of  FIG. 15  in a fastened configuration. 
           [0036]      FIG. 17  shows a second alternative fastening mechanism embodiment using a snap fastener in accordance with the present invention. 
           [0037]      FIG. 18  shows the snap fastener elements of  FIG. 17  in a fastened configuration. 
           [0038]      FIG. 19  is another view of the snap fastener elements of  FIG. 16  in a fastened configuration. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
         [0040]    Referring now to the drawings in detail,  FIGS. 1 and 2  illustrate a ram air parachute, generally designated by the reference numeral  10 , in a partially deployed and a fully deployed condition, respectively. The parachute includes a canopy generally designated by the reference numeral  12 , shown fully inflated in  FIG. 2 , from which a payload  15  is suspended by means of a plurality of suspension lines  16  connected at their upper ends to the bottom surface of the canopy at suspension line attachment points  56 , as shown in  FIG. 3 . Groups of adjacent suspension lines  16  are anchored at their lower ends to the airborne guidance unit  20 . A generally rectangular reefing slider device, generally designated by reference numeral  24 , slides or descends from an upper operative reefing position, as shown in  FIG. 1 , to a lower position, as shown in  FIG. 2 . 
         [0041]    The ram air canopy  12  has upper and lower flexible airfoil surfaces  26  and  28  which, together with chordwise extending ribs  32 , form ram air inflated cells  30 . The airfoil shaped surfaces  26  and  28  thus extend chordwise from an open leading edge portion  34  to a trailing edge portion  36  in the direction of forward glide. When the parachute  10  is deployed, the canopy  12  is normally inflated by inflow of air into the cells  30  between ribs  32  at the open leading edge portion  34 , as is already well known in the art. Such inflation causes the canopy  12  to become fully extended in both the chordwise and spanwise directions, the former extending front to back and the latter extending from wing tip  35  to wing tip  35 , to rapidly assume the shape shown in  FIG. 2 . However, in accordance with the present invention, inflation of the canopy  12  is delayed and modulated during initial descent of the parachute  10  by the reefing slider device  24 . 
         [0042]    The slider device  24  is initially retained against the bottom surface  28  of the canopy  12  by retaining devices generally designated by the reference numeral  80 , as shown in  FIGS. 4 and 5 . As will be discussed more fully hereinafter, each retaining device  80  includes a canopy retaining loop  82  secured to the canopy, a slider retaining loop  84  secured to the slider  24 , and a breakable fastening element  86  for securing the two loops together. When the fastening element  86  breaks, the slider is released from the canopy bottom surface  28  so that the slider  24  can descend, relative to the canopy, from its upper retained position as shown in  FIG. 1  to its lower position as shown in  FIG. 2 . 
         [0043]    As evident from  FIG. 2 , the airfoil gliding parachute  10  with which the retained slider  24  of the present invention is intended to operate can be very large, on the order of 3500 square feet with a wing span of about 100 feet. A chute of this size is designed to be able to operate effectively with a payload of up to 30,000 pounds and is greatly benefited by the retained slider of the present invention which reduces the opening force on the payload by delaying the full opening of the chute. 
         [0044]    Somewhat smaller ram air parachutes, but supporting payloads down to about 2,000 pounds, are also benefited by the retained slider of the present invention. Further, even with the smaller design, ram air canopies  12  of this type having the size necessary to support loads of the foregoing magnitude, i.e., of from about 1,000 pounds to about 30,000 pounds, require a large number of suspension lines  16  to distribute the load. As best shown in  FIG. 3 , each suspension line  16  cascades from one lower main line rising from the risers into four upper cascaded lines  40  prior to spaced attachment of the upper cascaded lines  40  to the bottom surface  28  of the canopy  12  at the suspension line attachment points  56 . This multiplication of lines creates a heightened risk, as compared with smaller and simpler chute designs, for crossing and tangling of the suspension lines  16  prior to and during deployment which can produce catastrophic results. 
         [0045]    To address this line management problem, the slider of the present invention includes a plurality of individual grommets  42  through which the suspension lines pass in controlled groups. The number of upper cascaded lines to be passed through each grommet is adjustable according to design choice requirements. As shown in  FIG. 4 , according to a preferred embodiment, the two centermost forward edge grommets  42   a  each accommodate only the four upper cascaded lines from one of the two centermost suspension lines. Limiting the number of upper cascaded lines in the center grommets to four facilitates opening of the center cells, which provides stability to the canopy. Edge grommets closer to the wing tips, by contrast, typically accommodate eight upper cascaded lines each (rising from two lower main suspension lines), as shown in  FIG. 5 . By organizing and spacing the lines in this way, the slider assists in ensuring that the lines remain segregated and unobstructed, and that the canopy material  44  does not become twisted or bunched within a tangle of lines. 
         [0046]    As shown particularly in  FIG. 6 , the slider  24  is constructed as a rectangular sheet  46  made of a relatively low porosity, flexible material. The sheet  46  is bounded on the edges by reinforcing strips or tapes  48 . More specifically, the edges of the sheet  46  are bounded by a forward edge reinforcing tape  48   a , a rear edge reinforcing tape  48   b , and two wing tip edge reinforcing tapes  48   c ,  48   d . These are preferably made of highly rip-resistant nylon fabric as well known in the parachute art. 
         [0047]    Unlike prior art rectangular slider designs which typically included only four corner grommets, each of the edge reinforcing tapes  48   a ,  48   b ,  48   c ,  48   d  includes a plurality of intermediate edge slider grommets  42   a ,  42   b ,  42   c ,  42   d  which are interconnected in spaced relation to each other along the edge tapes  48   a ,  48   b ,  48   c ,  48   d , and bounded by corner grommets  42   e . According to the embodiment shown in  FIG. 6 , and including the corner grommets  42   e  in each of the following totals, the forward edge reinforcing tape  48   a  is provided with a total of ten grommets, the rear edge reinforcing tape  48   b  with a total of six grommets, and each wing tip edge reinforcing tape  48   c ,  48   d  with a total of four grommets. 
         [0048]    Spaced between the forward edge reinforcing tape  48   a  and the rear edge reinforcing tape  48   b , and generally parallel therewith, are two longitudinally extending inner reinforcing tapes  49   a ,  49   b . Each of these tapes corresponds with the forward edge tape  48   a  in having a total of eight internal grommets  43   a ,  43   b  spaced equivalently therealong, with the outermost grommets on either end of such longitudinally extending inner tapes  49   a ,  49   b  being the intermediate grommets  42   c ,  42   d  on the wing tip edges  48   c ,  48   d , for a total of ten grommets along each inner reinforcing tape  49   a ,  49   b.    
         [0049]    Similarly, spaced between the wing tip edge reinforcing tapes  48   c ,  48   d  and generally parallel therewith are eight laterally extending inner reinforcing tapes  49   c ,  49   d ,  49   e ,  49   f ,  49   g ,  49   h ,  49   i ,  49   j . These tapes cross over the longitudinally extending inner tapes  49   a ,  49   b  at respective internal grommet locations  43   a ,  43   b  therealong and similarly join the forward and rear edges  48   a ,  48   b  at aligned grommet locations  42   a ,  42   b.    
         [0050]    The laterally extending inner reinforcing tapes  49   c - 49   j  are preferably not equidistantly spaced, but are preferably closer to one another nearest the wing tip edges  48   c ,  48   d . This spacing generally corresponds with the narrowing of the cells nearest the wing tips of the ram air canopy as compared with the wider center cells. The center cell is widest to encourage its initial opening, while the wing tip cells are narrower to rigidify the wing and thereby prevent inadvertent collapse when incoming air is reduced during turning maneuvers. 
         [0051]    The ratio of the span to the chord length of the slider  24  is generally the same as that of the wingspan to chord length of the corresponding canopy  12 . In terms of absolute size, if the slider is too big it will not be efficient as the canopy will be allowed to spread too much at the outset, negating the effectiveness of the slider reefing function. Conversely, if the slider is too small, it will produce insufficient drag. For use with a ram air parachute canopy of the type shown in  FIGS. 1 and 2 , being on the order of 100 feet in wingspan with a chord length of about 30 feet, the slider is preferably about 20 feet spanwise and 7 feet chordwise. Hence, the ratio of the wingspan of the canopy to the span of the slider is about 5:1. With smaller parachutes of the same style construction, the ratio of the wingspan of the canopy to the span of the slider should remain substantially the same. 
         [0052]    When the slider  24  is functioning with the parachute  10 , the suspension lines  16  respectively extend slidably through the grommets  42 ,  43  to guide the slider upon its descent following the release of the fastening elements  86 . The number of suspension lines  16  passing through each grommet  42 ,  43  depends upon the number of grommets, which can be used to effect the desired opening behavior of the canopy. For example, as the number of grommets is increased, the number of suspension lines and corresponding upper cascaded lines  40  per grommet is reduced while the force necessary to release the slider from the canopy is increased, assuming all of the grommets are retained. 
         [0053]    As previously noted, the number of upper cascaded lines  40  per grommet  42 ,  43  depends upon the particular outcome desired. For example, if fewer total grommets are provided in the slider, the number of cascaded lines per grommet may be increased to twelve, or even more. However, this can make line management somewhat unwieldy and is ultimately limited by the size of the grommet. Conversely, if the total number of grommets is increased, then each grommet is required to retain fewer cascaded lines, such as only four cascaded lines per grommet throughout the slider. However, as the number of grommets is increased, the complexity of the slider is also increased, as is the time required to pack the parachute in preparation for air drop, as will be discussed more fully hereinafter. 
         [0054]    As shown particularly by the corner grommet  42   e  of  FIG. 7 , each grommet of the slider that is to be secured to the canopy has a corresponding slider retaining loop  84 , or  84   e  in  FIG. 7 . If not all grommets are to be retained, then the unretained grommets do not have to have an associated retaining loop. As used herein, “retaining” a grommet means securing the slider retaining loop adjacent such grommet to a corresponding canopy retaining loop on the canopy; similarly, the slider is “retained” in that it is secured to the canopy. 
         [0055]    The slider retaining loops  84  are preferably made of reinforced nylon, although any lightweight, high-strength material could be used. The loops  84  are sewn or otherwise secured to the reinforcing tapes  48 ,  49 , or  48   b  and  48   d  in  FIG. 7 . 
         [0056]    Whether or not all of the grommets are to be retained will depend upon design requirements. Any number of grommets may be retained. For example, every grommet can be retained, or only those grommets on the edges of the slider, or alternate grommets, or any other combination of grommets. According to a preferred embodiment, the grommets  42  located at the periphery or edges of the slider are retained while the center or internal grommets  43 , which are used to segregate and organize the corresponding suspension lines stemming from the center areas of the canopy, are not necessarily retained and, if not, do not have associated retaining loops. 
         [0057]    The suspension line attachment points  56  where the upper cascaded lines  40  are secured to the canopy typically are placed along the chord ribs as can be seen in  FIG. 3 . At each suspension line attachment point  56 , the cascaded line is secured to the canopy in accordance with conventional line attachment techniques. When the canopy is being packed, or prepared for air drop, the four upper cascaded lines of each suspension line are gathered together to be run through an appropriate grommet. When the lines are gathered and passed through the grommet, they will have slightly different lengths according to their individual attachment points on the canopy, as depicted in  FIG. 9 . To prevent the canopy fabric  44  from being drawn through the grommet  42  with the lines, the shortest line  58  within each grommet group of lines is provided with a slider stop  60 . The canopy retaining loops  82  are also placed adjacent the shortest suspension lines as shown. 
         [0058]    The slider stop  60  is an element that is sized so as to be unable to fit through the grommets and is preferably made of reinforced nylon although other lightweight materials could also be used. The material itself, or the material in combination with a contained object or other material, must be sufficiently rigid to prevent folding or crushing thereof that would allow the slider stop to be pulled through the grommet. 
         [0059]    As shown in  FIGS. 8 and 9 , the slider stop  60  is preferably a separate component that can be tied to the desired line and then, if necessary, untied and retied to a different line. This allows adjustments to be made to the canopy while in the field, as no sewing is required to secure the slider stop and no damage occurs to the chute upon removal of the slider stop. In the embodiment shown in  FIG. 9 , the slider stop is constructed with a hard object, such as a rigid disc  62 , encased within a nylon sleeve  64 . An attachment loop  66 , used to secure the slider stop  60  to the cascaded suspension line  40 , is sewn to the nylon sleeve  64 . Any sufficiently rigid and lightweight object could be encased within the nylon sleeve  64  to provide the slider stop function. 
         [0060]    In an alternative embodiment, the slider stop  60  may be sewn into the fabric  44  of the canopy  12  at the suspension line attachment point  56 , as shown in  FIG. 10 . With this configuration, the canopy retaining loop  82  can be advantageously secured to the slider stop itself as shown. As with the embodiment of  FIGS. 8 and 9 , the slider retaining loop  84  adjacent the grommet  42  and the canopy retaining loop  82  on the shortest associated suspension line  58  are then secured together by the fastening element  86  as shown in  FIGS. 4 and 5 . As with the slider retaining loops, the canopy retaining loops  82  are preferably made of reinforced nylon or other lightweight, high-strength material. 
         [0061]    As already discussed, the number of grommets provided on any given slider will depend on the canopy size and construction, as well as the degree of canopy opening restriction that is desired. However, for the purposes of explanation, the particular slider embodiment of  FIG. 6 , in conjunction with a parachute of the type shown in  FIGS. 1 and 2 , will be described in the following explanation of the process for packing a parachute with a retained slider according to the present invention. 
         [0062]    Returning to the specific construction of the slider  24  illustrated in  FIG. 6 , according to the preferred embodiment shown, the grommets  42  along the periphery of the slider are retained. Therefore, counting so as to include the corner grommets  42   e  in each total, there are ten leading edge grommets  42   a , eight wing tip grommets  42   c ,  42   d , and six rear edge grommets  42   b  which must be secured to the canopy. This equates to an absolute total of twenty grommets to be retained. 
         [0063]    In preparation for securing the slider  24  to the canopy  12 , the canopy must be equipped with sufficient canopy retaining loops  82  to correspond with the slider retaining loops  84  on the slider  24 . Hence, ten canopy retaining loops  82  are attached to the leading edge  34  of the canopy, four to each wing tip  35 , and six to the trailing edge  36  of the canopy  12 . As with the slider, the corner retaining loops on the leading edge  34  of the canopy are the same as the forward-most corner retaining loops of the canopy wing tips  35 . Similarly, the corner retaining loops on the canopy trailing edge  36  of the canopy are the same as the rear corner retaining loops of the wing tips  35 . Accordingly, the total number of retaining loops  82  on the canopy is twenty. 
         [0064]    The process by which the slider is retained against the canopy is undertaken as follows. First, the ten forward edge slider retaining loops  84   a ,  84   e  are secured to the ten leading edge canopy retaining loops  82 ; the retaining loops on the corners are designated  84   e  for clarity given their shared membership with the group of wing tip retaining loops  84   c ,  84   d.    
         [0065]    Starting from either the left or the right slider wing tip with loop  84   e  and working toward the center, corresponding pairs of slider and canopy retaining loops  84   a ,  82  are brought into alignment with one another. Upon reaching the center, the aligning process is repeated beginning from the opposite wing tip corner loop  84   e . Once all of the retaining loop pairs of slider loops  84   a ,  84   e  and canopy loops  82  are aligned, the loops of each pair are secured to one another using appropriate fastening elements  86 . 
         [0066]    The fastening elements can include string, cord, cable-tie type fasteners, etc. Any fastening element  86  having a set or calibrated break strength within a required range and a configuration making it suitable to join two loops of fabric may be used. According to a preferred embodiment as shown in  FIGS. 11A ,  11 B,  11 C,  12  and  13 , the fastening element  86  is embodied as a calibrated break tie or cord  78  such that each aligned pair of retaining loops is fastened together by tying. 
         [0067]    To tie each aligned pair of loops, the calibrated break tie or cord  78  is passed through each of the two retaining loops  82 ,  84  at least once, i.e., for one turn, as shown in  FIG. 11A , and then tied. For increased tie strength, the cord  78  is passed through the two retaining loops  82 ,  84  a second time, i.e., for two turns, as shown in  FIG. 11B , and then tied. Similarly, the cord  78  may be passed through the two retaining loops  82 ,  84  a third time, i.e., for three turns, as shown in  FIG. 11C ; this process may be continued with as many turns as desired. The turns are pulled tightly, as shown in  FIG. 12 , and then a knot  79  is formed with the cord ends to complete the tie, as shown in  FIG. 13 . When fastened in this manner, the slider  24  is retained against the canopy  12  as in  FIG. 1 . 
         [0068]    Using calibrated break ties or cord, it has been determined that desirable chute opening performance is achieved with an incremental pattern of tie strength beginning from the wing tips  35  and edge tapes  48   c  and  48   d  and increasing toward the center. More particularly, and still referring to the forward edge  48   a  of the slider, the process of tying the aligned loops begins from either the left or the right slider wing tip  48   c ,  48   d  and working toward the center. First, the wing tip corner loops are secured together using one turn of the cord. The next pair of loops is secured using two turns of cord, the next pair using three turns of cord, and the next pair using four turns of cord. Finally, the centermost pair of loops is secured using four turns of cord. Upon completing this centermost pair of loops, the process is repeated beginning from the opposite wing tip. 
         [0069]    Once the ten pairs of retaining loops  82 ,  84  on the forward and leading edges  48   a ,  34  of the slider and canopy, respectively, have been retained in the manner just described, the eight wing tip retaining loops on the slider, which include four intermediary loops  84   c ,  84   d  and four corner loops  84   e , are secured to the corresponding eight wing tip retaining loops on the canopy (not shown). Since the loops  84   e  on the forward corners of the wing tips  48   c ,  48   d  have already been secured as part of the securing of the retaining loop pairs on the forward/leading edges of the slider/canopy, there remain only six pairs of wing tip retaining loops  84   c ,  84   d ,  84   e  to be secured, three on each side. 
         [0070]    Beginning on either side and working front to rear, the wing tip retaining loops  84   c ,  84   d ,  84   e  on the slider are aligned with the corresponding wing tip retaining loops on the canopy. Once aligned, each pair is secured by one turn of the calibrated break cord, as shown in  FIG. 11A , and knotted, as shown in  FIG. 13 . The process is repeated on the opposite wing tip. 
         [0071]    The remaining six rear edge slider retaining loops and trailing edge canopy retaining loops are then similarly secured using the same tying technique. Beginning on either side and working from the wing tip corner loops  84   e  on the rear corner toward the center, the respective pairs of loops are aligned with one another. Since the wing tip corner loops  84   e  by the rear corner grommets  42   e  have already been secured as part of the securing of the retaining loop pairs on the wing tip edges  48   c ,  48   d  of the slider/canopy, there remain only four pairs of rear edge retaining loops  84   b  to be secured. The next inward pair is secured by two turns of the calibrated break cord, as shown in  FIG. 11B , and knotted, as shown in  FIG. 13 . Finally, the innermost pair is secured by three turns of the cord, as shown in  FIG. 11C , and knotted. The process is repeated on the opposite side working from the opposite wing tip inward. 
         [0072]    To help prevent the possibility of a “line over”, a situation in which the suspension lines attached to the trailing edge of the canopy get crossed over to the leading edge prior to deployment, often with serious results upon deployment, the process of retaining the slider may conclude with the final step of gathering the rear edge slider stops together and securing them in a bundle with a single turn of calibrated tie cord. The cord is passed through each of the trailing edge retaining loops, which are located adjacent the slider stops, with the ends of the cord then being drawn snugly together, but without drawing up the canopy material, and then knotted as with the other ties. 
         [0073]    As is evident from the example just given, the higher stress to which the center of the canopy is subjected necessitates that the fastening elements retaining the centermost edge grommets be stronger than those used to retain the wing tip grommets. The goal in defining the different strengths of the fastening elements is to have all of the fastening elements break simultaneously in response to air flow forces encountered during parachute descent. Simultaneous breaking of the fastening elements releases the canopy evenly so that its pressurization is regular across the span. The rear edge also needs to break evenly with the front edge and thus is secured with weaker tie strength reflective of the lower level of stress imposed on the rear edge relative to that on the front. 
         [0074]    A range of other fastening materials may be used to retain the slider as has already been stated. The calibrated break cord used in the representative example is preferably one that is readily available to military users from existing supply stocks such as, for example, MIL-T-5660-Style A Ticket 5. Use of such a standard supply stock material, with varying strength obtained through variation in the number of turns, allows a single material supply source to be used to secure all of the retaining loops, increasing the efficiency of military operations by simplifying the equipment requirements and avoiding complexity in the packing procedure. However, any connecting element or combination of connecting elements may be used. For example, cable ties of different strengths may be secured to different retaining loop pairs, i.e., with stronger cable ties in the center and weaker cable ties on the wing tips. Alternatively, cords of different strengths could be used for specific retaining loop pairs. 
         [0075]    Other fastening mechanisms of various types that will release when subjected to a specified amount of force may also be used while retaining the advantages already described in connection with the break ties. For example, magnets, snaps, calibrated wires, clips, etc. could all be effectively adapted to retain the slider until sufficient force is applied thereto in accordance with the present invention. 
         [0076]    A first alternative embodiment using magnetic retaining devices is set forth in  FIGS. 15 and 16 . As shown in  FIG. 15 , a magnet  100  is positioned within a fabric housing  102  that is sewn onto or otherwise secured to the slider  24 ; preferably, the fabric housing is adjacent a slider grommet  42 . A mating magnet  104  is secured within a similar fabric housing  106  that is sewn or otherwise connected to the canopy  12  at the point where the slider stop  60  comes in contact with the slider grommet  42 . The fabric housings protect and secure the magnets against the respective slider or canopy portion to which they are attached. 
         [0077]    During the packing process, the two magnets  100 ,  104  are coupled to one another as shown in  FIG. 16  and thereby hold the slider  24  against the canopy  12 . When the canopy deploys, the slider is retained against the bottom of the canopy by the magnetic force until enough pressure builds up inside the canopy to pull the two magnets  100 ,  104  apart. Once the magnets are separated, the slider is free to move down the suspension lines  16 . 
         [0078]    A second alternative embodiment using snap fasteners  110  as retaining devices is set forth in  FIGS. 17 ,  18  and  19 . As shown in  FIG. 17 , each snap fastener  110  includes a stud  112  and a mating socket  114 . The stud  112  is preferably positioned on the slider  24  adjacent to a grommet  42 , while the socket  114  is installed on a piece of webbing  116  that is sewn or otherwise connected to the canopy  12  at the point where the slider stop  60  comes in contact with the slider grommet  42 . As would be understood by persons of ordinary skill in the art, the positions of the stud  112  and socket  114  could be reversed, and a material other than webbing could be used to hold the socket  114 . 
         [0079]    During the packing process, the stud  112  and socket  114  are snapped together to hold the slider  24  against the canopy  12 , as shown in  FIGS. 18 and 19 . When the canopy deploys, the slider is retained against the bottom of the canopy by the mechanical connection of the snap fastener elements  112 ,  114  until enough pressure builds up inside the canopy to pull the socket  114  from the stud  112  and unfasten the snap. Once the socket and stud have been pulled apart, the slider is free to move down the suspension lines. 
         [0080]    Clips having a determined strength may also be used to secure a portion of the canopy to the slider, preferably adjacent a grommet location. The clips may be attached with a string tie or other mechanism to either the slider or the canopy so that, once they have been forced to release the fabric they were holding, the clips will be retained and can be reused. However, clips represent a less preferred embodiment as the clip structure tends to be bulky and can become caught on other portions of the canopy or slider during the packing process. 
         [0081]    In addition to the use of different fastening mechanisms, tie materials and related methods, the relative strength of the ties or other fastening mechanisms used to secure the center retaining loop pairs as opposed to the wing tip pairs may also be varied to suit the particular size parachute and payload. For example, as the weight of the payload is reduced within a moderate range, the fastening elements will take slightly longer to break release, whether by breaking as in the case of ties or calibrated wires, or by element separation as in the case of magnets or snaps, but the delay will not be unduly extended. When the weight of the payload is substantially reduced, as from 10,000 pounds to 5,000 pounds, however, a different fastening element arrangement may be necessary to ensure timely fastening element breakage release. 
         [0082]    In addition to varying the strengths of a particular fastening mechanism to accommodate the varying loads placed upon different areas of the canopy during deployment, more than one type of fastening mechanism may be utilized on the same canopy. For example, in certain parachute payload conditions, break ties may be used in the center of the canopy where the force is greatest, while magnets are used on the wing tips where a reduced force is experienced. This is advantageous in that the ease of the magnetic closure is obtained in those areas of the canopy where the retaining power of smaller magnets is sufficient, while avoiding the use of large heavier magnets as would otherwise be needed to accommodate the greater center loading were only magnetic fastening mechanisms to be used. 
         [0083]    Any of the fastening mechanisms discussed herein, as well as other comparable fastening mechanisms that are structured to release when subjected to a level of force as described herein, may be used together in various combinations on a single canopy to best suit the particular load and force requirements thereof. In accommodating these combinations, the canopy may be equipped with both a magnetic and a retaining loop device at a particular grommet, or with both a snap fastener and retaining loops at a particular grommet. In this way, the magnetic connection (or the snap fastener) can be used when their retaining force is sufficient, as with a smaller payload, reducing the time needed for packing of the parachute. The same canopy configuration can thereafter be used with a heavier payload by securing the retaining loop device, which is at the same grommet formerly secured by the magnets or snap fastener, with appropriate break ties. This use of alternate fastening mechanisms provides significant versatility and variability in load capability using a single canopy. 
         [0084]    The speed at which the chute is to be deployed must also be taken into consideration when planning fastening element strength. Stronger fastening elements are needed to withstand the greater opening forces experienced at higher altitudes where higher air drop speeds are required to sustain lift. Weaker fastening elements may be advisable at lower altitudes to ensure adequate flight time for the parachute. 
         [0085]    The retained slider according to the present invention requires only conventional materials, making it cost-effective and relatively simple to employ. Upon chute deployment, the fastening elements break or are separated when sufficient force is created by the inflow of air into the cells of the canopy, allowing the slider  24  to descend to the position shown in  FIG. 2 . However, in the case of the break ties, the canopy retaining loops  82  remain secured to the canopy  12 , as shown in  FIG. 14 , just as the slider retaining loops  84  are still affixed to the slider  24 , thus enabling both loops to be reused with only a new fastening element being required. In the case of magnets or snaps, or course, the fastening mechanism elements remain respectively secured to one of the canopy and slider and can be reused almost indefinitely; all that is required is to refasten the mating components during the packing process. 
         [0086]    The slider retention design according to the present invention also facilitates chute preparation. As compared with prior art designs for the controlled opening of large canopies which could take multiple persons several days or more to pack preparatory to air drop, the retained slider system of the present invention can be folded and packed by two people in about four hours using conventional parachute packing techniques. 
         [0087]    In sum, the retained slider according to the present invention provides not only for greater regularity in the expansion of the chute through delay in the opening thereof, the duration of which is directly responsive to actual forces on the chute, but also provides improved line management capability through segregation and retention of groups of lines within the plurality of individual grommets for greater organization and increased deployment safety. 
         [0088]    The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.