Abstract:
A continuous disreefing apparatus has a sleeve that has a diameter and is made from a flexible, resilient material that allows the sleeve to diametrically contract when the sleeve is under tension and to diametrically relax when such tension is substantially reduced or removed. The sleeve has a portion thereof configured for connection to a parachute suspension line. The continuous disreefing apparatus includes a reefing line that extends through the sleeve and is arranged for movement through the sleeve wherein the rate at which the reefing line moves through the sleeve is controlled by the amount of tension on the sleeve.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by the U.S. Government for Governmental purposes without the payment of any royalties thereon. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a continuous disreefing apparatus for use with parachutes. 
   2. Description of the Related Art 
   Military cargo parachute systems that are used for heavy cargo delivery typically use large diameter parachutes which are reefed to slow their opening, thereby reducing the forces on the entire system. Reefing cargo parachutes typically require the use of expensive pyrotechnic devices, such as cutters, configured with specific time delays. Some systems require multiple stages of reefing and multiple pyrotechnic devices. During each stage of reefing, the partially opened parachute canopy slows the velocity of the payload. Once the pyrotechnic device fires, the canopy will open to the next reefing stage or open fully. When disreefing occurs, a peek force is observed, producing repeated shocks to the parachute delivery system. Referring to  FIGS. 1A and 1B , there is shown a prior art, reefed parachute. The reefed parachute canopy  10  is reefed by reefing line  12  which is attached to parachute skirt  14  by reefing rings  16  located at the attachment point of each suspension line  18 . Reefing line  12  is sized to allow canopy  10  to initially open to some percent of its full, inflated diameter. Canopy  10  will remain in this configuration until pyrotechnic cutter  20  fires and disreefing occurs. This causes canopy  10  to open fully or to the next reefing stage.  FIG. 1C  illustrates the forces on a typical prior art parachute system over time from deployment to full opening without reefing.  FIG. 1D  illustrates the forces on the same type of prior art parachute system with a single stage of reefing. The time at which disreefing occurs is indicated by time TD.  FIG. 1E  illustrates the forces on the same type of prior art parachute system with multi-stage reefing. The times at which disreefing occurs are indicated by times TD 1  and TD 2 . The forces illustrated in  FIGS. 1C-1E  demonstrate peak and repeated shocks to the parachute system even when reefing is employed. 
   What is needed is an apparatus that provides continuous, smooth and consistent disreefing that causes the parachute canopy to open slowly and reduce or minimize peak and repeated shocks on the parachute system. 
   SUMMARY OF THE INVENTION 
   The present invention is a continuous disreefing apparatus that provides continuous, consistent and smooth disreefing while using any one of load bearing suspension lines of the parachute system to provide sensing of forces in the parachute system. The continuous disreefing apparatus of the present invention does not utilize pyrotechnics, electronics or electromechanical systems. The continuous disreefing apparatus of the present invention reduces or minimizes peak and repeated shocks on the parachute system. 
   In one aspect, the present invention is directed to a continuous disreefing apparatus that comprises a sleeve that has a diameter and is made from a flexible, resilient material that allows the sleeve to diametrically contract when the sleeve is under tension and to diametrically relax when such tension is substantially reduced or removed. The sleeve has a portion thereof configured for connection to a parachute suspension line. The continuous disreefing apparatus includes a reefing line that extends through the sleeve and is arranged for movement through the sleeve. The rate at which the reefing line moves through the sleeve is determined by the amount of tension on the sleeve. The amount of tension on the sleeve is determined by the magnitude of the force on the parachute suspension line to which the sleeve is connected. 
   The continuous disreefing apparatus includes a parachute suspension system which has suspension lines, and the suspension system including the suspension lines performs as a mechanical sensing device for automatically controlling the function of continuous disreefing. 
   Other objects, features and advantages of the present invention will be apparent from the ensuing description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the present invention will become more readily apparent and may be understood by referring to the following detailed description of an illustrative embodiment of the present invention, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1A  is a front elevational view of a prior art parachute system; 
       FIG. 1B  is an enlarged view of a portion of the view of  FIG. 1A ; 
       FIGS. 1C-1E  are graphs illustrating forces on prior art parachute systems during the parachute opening process; 
       FIG. 2  is a front elevational view of a parachute system that utilizes the continuous disreefing apparatus of the present invention; 
       FIG. 3  is an enlarged view of a portion of the view of  FIG. 2 ; 
       FIG. 4A  is an elevational view of the continuous disreefing apparatus of the present invention; 
       FIG. 4B  is an elevational view of the continuous disreefing apparatus of the present invention configured to be removably connected to a riser link; 
       FIG. 4C  is an elevational view of the continuous disreefing apparatus of the present invention utilizing an alternate technique for connecting a sensing suspension line to the continuous disreefing apparatus; 
       FIG. 4D  is an elevational view of the continuous disreefing apparatus of the present invention in combination with a device for stowing excess reefing line; 
       FIG. 5  is a graph that illustrates theoretical predicted forces on a parachute system during the opening process wherein the parachute system uses the continuous disreefing apparatus of the present invention; 
       FIG. 6  is a front elevational view of a parachute system that uses multiple continuous disreefing apparatuses of the present invention; and 
       FIG. 7  is a front view, partially in perspective, of a gliding canopy that uses the continuous disreefing apparatus of the present invention. 
       FIG. 8  is a graph that illustrates actual forces on a parachute system during the opening process wherein the parachute system uses the continuous disreefing apparatus of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 2 and 3 , there is shown a parachute system that utilizes continuous disreefing apparatus  100  of the present invention. The parachute system includes canopy  102 , suspension lines  104  and reefing rings  106 . Canopy  102  has canopy skirt  108 . Each reefing ring  106  is attached to canopy skirt  108  at the attachment point of a corresponding suspension line  104 . The parachute system also includes reefing line  110  that passes through reefing rings  106 . The ends of reefing line  110  are joined together at junction  112  to form single reefing line  114 . 
   Referring to  FIG. 4A , there is shown continuous disreefing apparatus  100  of the present invention. Continuous disreefing apparatus  100  comprises sleeve  120 . In a preferred embodiment, sleeve  120  is configured as a coarse braided, generally cylindrical sleeve. In one embodiment, this coarse braided sleeve is fabricated from high-strength, flexible, resilient material that is capable of withstanding high temperatures. Suitable flexible materials include steel wire, cable, aramid or coated materials that provide the required high-strength and high-temperature characteristics. 
   As shown in  FIGS. 2 and 4A , load  124  is attached to risers  126  and  128 . Risers  126  and  128  are connected to links  130  and  132 , respectively. Risers  126  and  128  and riser links  130  and  132  are well known in the art and therefore, are not discussed in detail. Continuous disreefing apparatus  100  is connected to link  132 . 
   Referring to  FIG. 4A , in accordance with the invention, one of the suspension lines  104 , indicated by reference number  104 A, functions as a sensing suspension line for sensing a force, i.e., tension. Said sensing suspension line  104 A may be any one of the suspension lines  104 . This characteristic is explained in detail in the ensuing description. Suspension line  104 A is relatively shorter than the other suspension lines  104  and is connected to sleeve  120  in such a manner that tension on suspension line  104 A causes the diameter of sleeve  120  to contract. This contraction produces friction on single reefing line  114  thereby increasing the force needed to pull single reefing line  114  through sleeve  120 . Conversely, a relaxation of the tension on suspension line  104 A allows relaxation and expansion of sleeve  120  which decreases the force needed to pull single reefing line  114  through sleeve  120 . In an alternate embodiment, reefing line  114 A is integral with sleeve  120 . As shown in  FIG. 4A , loop  104 B is formed at the end of suspension line  104 A. Loop  104 B passes through the upper end of sleeve  120 . 
     FIG. 4A  shows a normal attachment of sleeve  120  to riser link  132  and suspension line  104 A to the opposite end of sleeve  120 . This configuration is suitable when the parachute system is manufactured with continuous disreefing apparatus  100 .  FIG. 4B  shows an alternate technique for attaching sleeve  120  to riser link  132 . Link  140  is removably connected to riser link  132 . Sleeve  120  is removably connected link  140 . This configuration shown in  FIG. 4B  is suitable for a retrofit-type situation wherein an existing parachute system is modified to use the continuous disreefing apparatus  100  of the present invention.  FIG. 4C  shows an alternate technique for attaching a sensing suspension line to sleeve  120 . In this configuration, suspension line  144  functions as a sensing suspension line. Suspension line  144  is attached to loop  146 . Loop  146  is attached to sleeve  120 . The end of suspension line  144  is connected to riser link  132  in the standard fashion. Suspension line  144  is relatively longer than the other suspension lines  104  so that continuous disreefing apparatus  100  operates freely without constraint. This configuration makes certain that the sensing suspension line  144  is always connected to riser link  132 . In one embodiment, loop  146  is stitched to sensing suspension line  144 .  FIG. 4D  shows the configuration of  FIG. 4A  with the addition of stowage device  150  that allows excess reefing line  114  to be stowed. Device  150  includes a body of fabric  152  having ends  152 A and  152 B. Body of fabric  152  is attached to riser  128 . In one embodiment, fabric  152  is stitched to riser  128 . Device  150  further includes stow loops  154  and  156  that are attached to body of fabric  152 . The excess portion  114 A of reefing line  114  is wrapped around stow loops  154  and  156 . Body of fabric  152  includes a hook and pyle fastening system that is comprised of portion  158  and complementary portion  160 . This type of fastening system allows ends  152 A and  152 B of body of fabric  152  to be removably attached together so as to cover the stowed excess portion  114 A of reefing line  114 . 
   Referring to  FIGS. 2 and 4A , during packing of the parachute system, a predetermined length of single reefing line  114 , indicated by reference number  114 A, is drawn through sleeve  120  in the direction of riser link  132  so as to establish an initial reefing position. This initial reefing position allows parachute canopy  102  to open to a predetermined initial diameter prior to the start of the continuous disreefing process. When parachute canopy  102  begins to open, tension is produced in suspension line  104 A which causes sleeve  120  to contract diametrically. This diametric contraction of sleeve  120  impedes the movement of single reefing line  114  in the direction of canopy  102 . As a result, the movement of reefing line  110  is impeded which, in turn, impedes or retards inflation of canopy  102 . Once the initial deceleration of payload  124  occurs due to the initial, predetermined reefed canopy size, the tension in suspension line  104 A begins to decrease which causes a decrease or relaxation of the forces that caused the diametrical contraction of sleeve  120 . This relaxation or decrease in these forces allows single reefing line  114  to start sliding through sleeve  120  more rapidly. The greater the rate of deceleration, the faster single reefing line  114  slides through sleeve  120 . The rate at which single reefing line  114  slides through sleeve  120  depends on the tension forces, created by deceleration of payload  124 , transmitted through suspension line  104 A to link  132 . If single reefing line  114  accelerates through sleeve  120 , then reefing line  110  is able to quickly move thereby allowing canopy  102  to expand and inflate at an accelerated rate. This in turn increases the deceleration on the entire parachute system and payload  124  thereby causing an increase in the suspension line forces and in particular, the forces on suspension line  104 A. This increase in the force or tension on suspension line  104 A diametrically contracts sleeve  120  thereby slowing or impeding the movement of single reefing line  114  through sleeve  120  so as to slow or impede the opening of canopy skirt  108 . This self-regulating process is continuous throughout the entire parachute-opening process and ends when the parachute canopy  102  is fully opened. 
   Continuous disreefing apparatus  100  acts essentially as a linear brake device using the force in a suspension line  104 A to control the breaking function of continuous disreefing apparatus  100 . The implementation of the braking function of continuous disreefing apparatus  100  depends on several factors including the length of sleeve  120 , the diameter of single reefing line  114 , and the friction coefficients between the materials used to fabricate continuous disreefing apparatus  100  and of single reefing line  114 . For example, the degree of coarseness in the braid of sleeve  120  is a factor that affects the braking function of continuous disreefing apparatus  100 . 
   The continuous disreefing apparatus of the present invention takes advantage of the fact that each parachute suspension line carries an equal portion of the peak opening forces during symmetrical parachute openings. Each suspension line acts as a load bearing structural member and mechanical load sensor. Thus, as shown in  FIG. 4A , suspension line  104 A functions as a load sensor that controls sleeve  120  to either impede the movement of single reefing line  114  or to allow single reefing line  114  to move toward canopy  102  unimpeded.  FIG. 5  illustrates the theoretical opening force trace of a parachute that utilizes the continuous disreefing apparatus of the present invention. This force trace shows the parachute system opening with a relatively lower (than without the present invention) but constant force throughout deceleration until final, steady state descent is attained. 
     FIG. 8  shows the results of an instrumented test showing the actual opening force versus opening time trace of a parachute that is opening with the continuous disreefing apparatus of the present invention. The overload, payload weight is six hundred and twenty five pounds. The system was dropped and allowed to fall for twenty one seconds reaching a velocity of over two hundred twenty five miles per hour vertically, at which time the parachute was deployed to recover the payload. The parachute has a constructed diameter of twenty eight feet with twenty eight gores and twenty eight suspension lines. It was initially reefed to a diameter of four feet. This type of parachute normally takes less than two seconds to open under these deployment conditions with a two hundred twenty five pound payload. As shown in  FIG. 8  this parachute required more than ten seconds to fully open with the continuous disreefing apparatus. This translates to lower opening forces on the entire parachute/payload system and a recovery with no damage to the parachute. When  FIG. 8  is compared to the predicted, theoretical opening force versus opening time in  FIG. 5 , the results are similar. 
   The continuous disreefing apparatus includes a parachute suspension system which has suspension lines, and the suspension system including the suspension lines performs as a mechanical sensing device for automatically controlling the function of continuous disreefing. 
   Although the foregoing description has been in terms of a parachute system using one continuous disreefing apparatus of the present invention, it is to be understood that a pair of apparatuses  100  can be used wherein one apparatus  100  is connected to riser link  132 , as shown, and the other apparatus  100  is connected riser link  130 . Such an embodiment is explained in the ensuing description. 
   Referring to  FIG. 6 , there is shown a parachute system that utilizes more than one continuous disreefing apparatus of the present invention. For purposes of facilitating understanding of this embodiment, these continuous disreefing apparatuses are indicated by reference numbers  100 A and  100 B. Each continuous disreefing apparatus  100 A and  100 B is identical in construction to continuous disreefing apparatus  100  described in the foregoing description. Continuous disreefing apparatus  100 A comprises sleeve  120 A which is identical in construction and function to sleeve  120  described in the foregoing description. Similarly, continuous disreefing apparatus  100 B comprises sleeve  120 B which is identical in construction and function to sleeve  120  described in the foregoing description. In this configuration, the parachute system includes canopy  200 , canopy skirt  202 , and parachute suspension lines  204 . For purposes of simplicity in describing this embodiment, not all suspension lines  204  are shown. This parachute system also includes a reefing line that is divided into two parts: reefing line  206  and reefing line  208 . Reefing line  206  is positioned on the front half of parachute canopy  200  and reefing line  208  is positioned on the rear half of parachute canopy  200 . One end of reefing line  206  is joined to one end of reefing line  208  at junction  210  to form single reefing line  212 . Similarly, the opposite ends of reefing lines  206  and  208  are joined at junction  214  to form single reefing line  216 . Continuous disreefing apparatus  100 A is connected to link  218 . Riser  220  is connected to and between link  218  and payload  222 . Similarly, continuous disreefing apparatus  100 B is connected to link  224 . Riser  226  is connected to and between link  224  and payload  222 . Suspension lines  204 A and  204 B are connected to sleeves  120 A and  120 B, respectively, in the same manner in which suspension line  104 A is connected to sleeve  120  (see  FIG. 4A ). Reefing lines  212  and  216  extend through sleeves  120 A and  120 B, respectively, in the same manner in which single reefing line  114  extends through sleeve  120  (see  FIG. 4A ). Continuous disreefing apparatuses  100 A and  100 B function in exactly the same manner as continuous disreefing apparatus  100  discussed in the foregoing description. Tension on suspension line  204 A causes sleeve  120 A to diametrically contract which impedes movement of single reefing line  212  through sleeve  120 A. As deceleration decreases, tension on parachute suspension line  204 A decreases thereby allowing relaxation of the diameter of sleeve  120 A. This relaxation allows single reefing line  212  to move unimpeded in the direction of canopy  200 . Similarly, tension on suspension line  204 B causes sleeve  120 B to diametrically contract which impedes movement of single reefing line  216  through sleeve  120 B. As deceleration decreases, tension on parachute suspension line  204 B decreases thereby allowing relaxation of the diameter of sleeve  120 B. This relaxation allows reefing line  216  to move unimpeded in the direction of canopy  200 . The movement of single reefing lines  212  and  216  directly affect the movement of reefing lines  206  and  208  which control the rate at which canopy  200  opens. 
   Although two continuous disreefing apparatuses are shown in  FIG. 6 , it is to be understood that more than two continuous disreefing apparatuses  100  may be required depending on deployment velocities of the parachute, altitude, canopy design and the mass of the payload. 
   Referring to  FIG. 7 , there is shown a front view of a rectangular gliding canopy  300  that uses the continuous disreefing apparatus of the present invention, indicated by reference number  302 . It is to be understood that continuous disreefing apparatus  302  has the same structure and functions in the same manner as continuous disreefing apparatus  100  shown in  FIGS. 4A-4D . This view is of the opening phase of gliding canopy  300  and shows leading edge  304  as cells  306  inflate. Suspension lines  307  extend downward from canopy  300 . Reefing lines  308  and  310  pass through reefing rings  312  on the lower surface of canopy  300  and are joined together at junction  314  to form single reefing line  316 . Single reefing line  316  extends through continuous disreefing apparatus  302 . Lines or lanyards  320  and  322  connect continuous disreefing apparatus  302  to links  324  and  326 , respectively. Risers  328  and  330  are connected between links  324  and  326 , respectively, and payload  340 . Force in suspension line  307 A is the sensing or control force for continuous disreefing apparatus  302  in the same manner in which suspension line  104 A is the sensing or control force for continuous disreefing apparatus  100  (see  FIG. 4A ). Continuous disreefing takes place from the center of canopy  300  toward its tips in a spanwise direction. 
   Multiple continuous disreefing apparatuses of the present invention can also be used on rectangular, flexible wing-type gliding parachutes. However, the actual number of continuous disreefing apparatuses used depends on the same variables as round parachutes, namely, deployment velocity, altitude, canopy design and mass of payload. 
   The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. This invention should not be construed as limited to the particular forms disclosed, as these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, the foregoing detailed description should be considered as exemplary in nature and not limiting the scope and spirit of the invention as set forth in the attached claims.