Abstract:
A fast acting and low leak rate vent for an impact landing bag in which a vent hole is covered by a gas barrier assembly having a flexible membrane and a low gas permeability layer. A flap assembly positioned around the gas barrier assembly includes flaps that are movable between an open position in which the membrane is exposed and a closed position in which the flaps cover and reinforce the gas barrier assembly. An externally actuated flow initiator is associated with a fastening element that retains the flaps in the closed position. Upon landing, the flow initiator is activated to sever the fastening element and release the flaps and the low gas permeability layer. Thereafter, the internal pressure within the landing bag under landing forces causes the membrane to burst, releasing a flow of gas from within the landing bag to attenuate impact.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to the field of landing bag force attenuation and, more particularly, to a vent system and method for a parachute landing bag. 
         [0003]    2. Description of the Related Art 
         [0004]    Parachute landing bags are well known to those skilled in the art. Such airbags are used to attenuate impact force on the payload upon landing and include an airbag having a control volume of air. Upon impact with the ground, the airbag flattens somewhat to absorb the initial impact, after which a flow of air from the control volume is initiated to continue attenuating the impact. 
         [0005]    According to conventional venting approaches, the airbag is provided with one or more pressure-based burst discs as a passive means of initiating flow from the control volume. Such passive systems are activated by a build-up in pressure so as to burst when a threshold pressure inside the airbag has been reached. When employing such a system, care must be taken to ensure that the airbag itself does not rupture before the discs. 
         [0006]    Passive venting systems perform very poorly in a variable or uncertain landing envelope in which the necessary pressure may build up too soon or not soon enough, resulting in imprecise venting performance. Therefore, unless a consistent landing condition can be established, the performance of passive venting systems in terms of providing the necessary attenuation for the payload can be compromised. 
       SUMMARY OF THE INVENTION 
       [0007]    In order to overcome the known problems associated with conventional passive venting systems for landing bags, the present invention provides a system and method for actively controlling the flow of air from an inflatable control volume as embodied in a parachute landing bag. According to the system, a fast acting and low leak rate vent is provided that incorporates a gas barrier assembly and an externally actuated flow initiator that allows for active venting. The gas barrier assembly includes a flexible membrane for sealing a vent opening in the landing bag, and a sheet of low or near zero gas permeability material that covers and provides strength to the membrane. Overlying both the membrane and the sheet are one or more fabric flaps that are secured in a closed position by fastening elements coupled with the flow initiator. To initiate active venting, the flow initiator is externally actuated to release the one or more flaps which, in turn, releases the cover sheet of low permeability material. Thereafter, the internal pressure within the landing bag under landing forces causes the membrane to burst, releasing a flow of gas from within the landing bag. 
         [0008]    The flow initiator may be controlled by a device such as an accelerometer that measures the gravity force exerted on the airbag as it impacts the ground and triggers activation of the initiator when a predetermined trigger point is reached. Alternatively, and particularly in an configuration having multiple airbags, initiation of flow from specific airbags may be systematically initiated at various stages of the landing to improve the overall performance. 
         [0009]    Accordingly, it is an object of the present invention to provide a fast acting and low leak rate vent for a parachute landing bag. 
         [0010]    Another object of the present invention is to provide a fast acting and low leak rate vent for a landing bag that includes an externally actuated flow initiator for affirmative activation of vented air flow, including active initiation at various stages of the landing sequence for improved landing performance. 
         [0011]    Still another object of the present invention is to provide a fast acting and low leak rate vent covered by a membrane and a fabric flap, the membrane rupturing to initiate air flow and thereafter being replaceable for reuse of the vent and fabric flap. 
         [0012]    A further object of the present invention is to provide a method of constructing a fast acting and low leak rate vent for a landing bag using conventional and commercially available materials. 
         [0013]    Yet a further object of the present invention is to provide a method of constructing a fast acting and low leak rate vent for a landing bag that includes covering the vent opening with a membrane, a layer of low permeability material, and a fabric flap, and securing the fabric flap in a closed position covering the vent opening by fastening elements associated with a flow initiator device. 
         [0014]    A still further object of the present invention is to provide a method of activating a landing bag vent covered by a membrane and a fabric flap that includes externally actuating a flow initiator that releases the fabric flap, allowing the membrane to expand and burst in response to pressure build-up within the landing bag. 
         [0015]    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. While the drawings are intended to illustrate the invention, they are not necessarily to scale. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a cross-sectional view of an airbag vent in accordance with the present invention. 
           [0017]      FIG. 2  is a perspective view of an airbag vent such as that shown in  FIG. 1 , in a pre-deployment readiness configuration. 
           [0018]      FIG. 3  shows the airbag vent of  FIG. 2  with the flaps pulled back prior to installation of the membrane and gas impermeable disc. 
           [0019]      FIG. 4  depicts a textile fabric airbag vent with the flaps closed and secured with a single fastening element in accordance with the present invention. 
           [0020]      FIG. 5  depicts the textile fabric airbag vent of  FIG. 4  with the flaps closed and secured with multiple fastening elements. 
           [0021]      FIG. 6  depicts modification of the flaps to aid in installation of the membrane during construction of the textile fabric airbag vent of  FIGS. 4 and 5 . 
           [0022]      FIG. 7  illustrates a vent opening ready for membrane insertion in accordance with the present invention. 
           [0023]      FIG. 8  shows the step of applying adhesive to the membrane to be installed on the vent opening of  FIG. 7  with the membrane positioned on a suction tool. 
           [0024]      FIG. 9  shows the step of using the suction tool to install the membrane of  FIG. 8  onto the vent opening of  FIG. 7 . 
           [0025]      FIG. 10  depicts removal of the suction and the suction tool following the step shown in  FIG. 9 . 
           [0026]      FIG. 11  shows the resulting installed membrane upon completion of the step shown in  FIG. 10 . 
           [0027]      FIG. 12  illustrates the placement of a Spectra disc on the installed membrane of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    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. 
         [0029]      FIG. 1  illustrates a cross-sectional view of a landing bag vent, generally designated by the reference numeral  10 , in accordance with the present invention. The vent  10  is formed in an airbag or landing bag, generally designated by reference numeral  12 . As used herein, the phrase “landing bag” is intended to include all airbag structures used to attenuate force, whether from landing or other contact conditions in which significant forces are generated. The landing bag described herein is suitable for landing impact attenuation for large payloads including vehicles such as Unmanned Aerial Vehicles (UAVs), unmanned spacecraft, manned spacecraft, etc. 
         [0030]      FIG. 2  provides an exterior view of a landing bag  12  with a landing bag vent  10  of the type shown in  FIG. 1 , in a pre-deployment readiness configuration. The landing bag is typically made of a polyurethane-coated fabric material  78  with strips or lines of Kevlar reinforcement  80  as needed. Silicon may also be used to coat the landing bag fabric. 
         [0031]    The vent  10  includes a vent opening  14  formed in the wall  16  of the landing bag  12 . Optionally, the vent opening  14  may be reinforced by an orifice reinforcing element  60  which is secured around the perimeter  62  of the vent opening, such as by adhesive. As shown in  FIG. 1 , this element may be embodied as a single reinforcing layer  60  on the outside surface  68  of the landing bag. If desired, the reinforcing element could include an additional reinforcing layer (not shown) on the inside surface  58  of the landing bag wall as well such that the landing bag wall is sandwiched between the two layers. The reinforcing element  60  strengthens the perimeter  62  and protects the vent opening  14  from tearing during landing. 
         [0032]    The vent opening  14  is covered by a gas barrier assembly, generally designated by the reference numeral  17 . The gas barrier assembly  17  includes a membrane  18  and a layer of low or near zero gas permeability material  22 . The membrane spans the opening  14  and is sealed at its edges  20  to an exposed vent perimeter region  21  (see  FIG. 3 ) of the landing bag wall  16 . If an orifice reinforcing element  60  is included, the membrane  18  is affixed to the reinforcing element  60  which provides a consistent surface for adherence of the membrane  18 . The membrane  18  is preferably made of a material with a low modulus of elasticity so as to provide a sealed closure of the vent opening  14  with limited flexibility for expansion. 
         [0033]    Once the membrane  18  is sealed in place, the layer of low or near zero gas permeability material  22  is placed over the membrane  18 . Fabrics that have a permeability of less than  5  SCFM/square foot at ½ inch of water pressure are best suited for the present invention. A conventional zero porosity fabric for parachutes is coated with a mixture of polyurethane and silicone and readily available commercially from parachute fabric supplies, such as the “Soar Coat” fabric sold by Performance Textiles of Greensboro, N.C. The specifications for the Performance Textiles “Soar Coat” zero porosity fabric state that it has zero porosity at a differential pressure of 10 inches of water column. Another fabric suitable for the gas barrier assembly of the present invention is referred to as the “F-111” type and is presently available from several sources, including Performance Textiles, and Brookwood Companies, Inc. of New York, N.Y. It is defined in U.S. military specification, MIL-SPECMIL-C-44378. The F-111 type fabric is specified to have a permeability between zero to 5 SCFM at ½ inch water pressure. 
         [0034]    According to a preferred embodiment, the low or zero gas permeability layer is made of Spectra cloth or Vectran. Spectra is light in weight and relatively strong, with a “slick” surface that is well suited to protection of the membrane  18 . The Spectra layer  22 , which is not attached to the membrane  18  but is merely placed thereon, controls the expansion of the membrane  18  and also evenly distributes the load thereon during airbag inflation. 
         [0035]    The Spectra layer  22  is generally cut in the shape of a disc and is placed over the membrane  18 . For ease of reference, this component is hereafter referred to as “Spectra disc”  22  with the understanding that the precise shape and exact material is not necessary to the proper functioning of the invention. Other materials having similar structural and gas permeability characteristics, such as those identified above, and cut or otherwise formed to have other shapes could also be used. 
         [0036]    The membrane  18  and Spectra disc  22  are covered by at least one flap  24  that is secured, preferably by sewing, to the wall  16  of the landing bag  12  along at least one flap edge  26 . The free portion  28  of the flap  24  is able to move between an open position in which the free portion  28  is pulled back toward the secured flap edge  26  to expose the vent opening  14  as shown in  FIG. 3 , and a closed position in which the free portion  28  is laid flat to at least partially cover the vent opening  14  and gas barrier assembly  17  as shown in  FIG. 2 . With the flap in the closed position, the Spectra layer  22  is loosely secured in place by an adhesive such as a piece of fiberglass tape. 
         [0037]    In the preferred embodiments shown in  FIGS. 2-4 , the vent  10  includes a flap assembly generally designated by reference numeral  30  having a plurality of pie-wedge-shaped flaps  24  extending inwardly from the secured flap edges  26  which form a generally circular perimeter  32  around the vent opening  14 . In the closed position shown in  FIG. 2 , each flap  24  covers only a wedge-shaped portion of the vent opening  14 , with the tips  34  of all of the flaps  24  meeting or nearly approaching one another in the center  36  of the vent  10 . Conversely, in the open position shown in  FIG. 3 , the flaps  24  can be folded back to overlap their respective secured edges  26  affixed to the landing bag  12 . While the embodiment shown in  FIGS. 2 and 3  is preferred, it is also possible to cover the vent opening  14  with a single flap, such as a rectangular component that would cover the vent opening like a tent flap. 
         [0038]    With the flaps  24  in their closed position, a fastening element generally designated by reference numeral  38  is used to secure the flap tips  34  together as shown in  FIGS. 4 and 5 . The fastening element  38  is associated with an externally activated flow initiator, generally designated by the reference numeral  40 , that, when activated, severs the fastening element  38  to release the flap tips  34 . 
         [0039]    The externally activated flow initiator  40  includes a measuring component  42 , a controller  44  and a cutting device  46 . The measuring component  42  may be embodied as an accelerometer that measures the force exerted by gravity, or the “gee” level, on the landing bag  12 . When the gee level reaches a predetermined trigger point, the controller  44 , which may be embodied as an onboard sequencer, sends a signal to activate the cutting device  46 . 
         [0040]    The fastening element  38  may be embodied as one or more ties or cords  39 , while the cutting device is embodied as a conventional electrical or pyro-initiated cutter  46  known to those skilled in the art. At least one portion of the cord  39  is threaded through an opening  48  in the cutting device  46 . Upon activation thereof, the cutting device  46  severs the portion of the cord  39  threaded through the opening  48  to release the flap assembly  30  and allow the flaps  24  to move to the open position. According to the preferred embodiment shown in  FIG. 2 , two such cutting devices  46  are included in the routing of the cord, with each cutter having its own activation wire  50 , so as to act as redundant flow initiators  40 . 
         [0041]    As shown in  FIGS. 4 and 5 , each flap tip  34  is provided with a loop  52  through which the fastening element  38 , preferably a spectra cord  39 , is passed. Each flap tip may be secured with a direct line connection to the cutting device such that the fastening element is routed back and forth from each of the flap tips back to the cutting device, as shown in  FIG. 5 . Alternatively, the fastening element may be serially threaded through each of the flap loops to interconnect all of the flap tips before passing through the cutting device at only one point, in the manner shown in  FIG. 4 . The back and forth routing configuration shown in  FIG. 5  is preferred as activation of the cutting device cuts the cord  39  in multiple places. This latter configuration immediately releases all of the flaps with no need for the cord  39  to have to slip back through each of the loops  52  in series as is required in the configuration shown in  FIG. 4 . In both embodiments, a preferred material for the cord  39  is Spectra which, because of its smooth surface, aids in removal of the fastening element from the loops upon vent actuation. 
         [0042]    As also shown in  FIGS. 4 and 5 , the cutting device  46  of the flow initiator  40  is preferably secured against the flap assembly  30  by a sleeve  54  secured to one of the flaps  24 . While the sleeve  54  is shown as being generally cylindrical, other shapes could also be used as needed to accommodate other cutting devices. 
         [0043]    In use, the relatively low modulus membrane  18  acts as a gas barrier, while the Spectra disc  22  which is placed over the membrane controls the expansion of the membrane and also evenly distributes the load on the membrane  18  during airbag inflation. As the landing bag  12  is inflated to design pressures, the membrane expands, transfers the load to the disc  22  which, in turn, subsequently transmits the load to the flaps  24 . Upon impact with the ground, the accelerometer  42  measures the gee level on the landing bag and, when the level reaches the predetermined trigger point, the controller  44  signals the firing of the cutting device  46  to cut the ties  39  holding the flaps in their closed position. Once the flaps are free to open, the Spectra disc  22  flies off and the internal pressure in the landing bag causes the membrane  18 , now unsupported by the disc and the flaps, to burst, releasing the gas inside the bag. 
         [0044]    If there are multiple airbags, actuation of the vents in the respective bags can be set to happen at the same time on all airbag vents or can be set to occur at different times, i.e., pressures, depending on the desired performance required of each airbag. As an example of the latter, in the case of two airbags, the trigger point of the vent in the first airbag may be set to occur at a lower gee level than the trigger point of the vent in the second airbag so that the first vent is opened earlier than the second, i.e., the forward bag has a different trigger gee than the aft bag. 
         [0045]    The force required to break the membrane  18  is a function of the size of the vent  10  and the material from which it is made. A preferred material for the membrane is latex, although nylon or rubber could also be used. The latex material is an off-the-shelf component and can be purchased in varying thicknesses. The best thickness will depend upon the intended application of the landing bag and the area or diameter of the vent. The number of vents in a given airbag is also a consideration, as the presence of multiple vents in the landing bag will typically change, e.g., reduce, the desired size of each of the vents such that the total vent area is not increased. For example, if an airbag has a vent of a certain diameter defining a vent area A, if that vent is to be split into two vents, each vent is made smaller so that the total vent area A remains substantially the same. 
         [0046]    A method for constructing the vent according to the present invention, is set forth in various stages in  FIGS. 3-12 . First, a precision-cut hole is made in the landing bag to form the vent opening  14  as shown in  FIG. 3 . Once the vent opening  14  is made, and prior to the subsequent steps of gluing as will be hereinafter described, a removable disk  56  (see  FIGS. 6 and 7 ) may be temporarily inserted on the inside surface  58  of the landing bag  12  to protect the inside of the landing bag from contact with the adhesives. An orifice reinforcing element  60  may also be secured around the perimeter  62  of the vent opening, if desired. 
         [0047]    After the orifice reinforcing element is installed, if such element is included, the flap assembly  30  having a plurality of flaps  24  is attached to the exposed vent perimeter  21  on the outside surface  68  of the landing bag wall around the vent opening. As can be seen in  FIG. 6 , the flap assembly may be embodied as a generally circular fabric component generally designated by reference numeral  70  formed through the joinder of a plurality of pie-shaped wedges  72 . The flaps  24  are secured to one another around the circumference  32  of the assembly  30 , but are unattached at their inward tips  34  such that they can be folded back toward the circumference  32  as shown. If the free portion  28  of the flaps is not large enough, part of the side seams  74  joining adjacent flaps may be cut an additional distance, as indicated at  76  in  FIG. 6 , to aid in proper installation of the membrane. The generally circular fabric component  70  is preferably sewn onto the airbag fabric, although other attachment methods could be used if and as appropriate. 
         [0048]    Rather than textile fabric  70  as shown in  FIG. 6 , the flaps can be constructed of the polyurethane-coated airbag fabric  78  itself, with a Kevlar reinforcement pattern  80  around the edges as shown in  FIG. 2 . Flaps with this construction may be affixed to the airbag material by sewing or through a combination of a weld and a stitching pattern. In forming the weld, heat and pressure are applied to the joint until the polyurethane coating on the two fabric articles fuses. 
         [0049]    Preparatory to installing the gas barrier assembly  17 , the flaps  24  are folded back to their open position as shown in  FIGS. 3 and 7 . The flaps can be secured with tape  82 , as shown in  FIG. 3 , or a flap retention tool  84  may be used such as that shown in  FIG. 7 . The flap retention tool  84  is preferred as it is not susceptible to unexpected release of one or more flaps  24  as can occur with tape  82 . 
         [0050]    A vent opening  14  ready to receive the gas barrier assembly  17 , as well as the membrane  18  and Spectra disc  22  to be inserted, are shown in  FIG. 7 . The membrane  18  is installed using an adhesive  86 . When using a two-part adhesive, the first component is applied to the outer surface  88  of the reinforcing element and, as shown in  FIG. 8 , the second component of the adhesive  86  is applied to the membrane  18 . 
         [0051]    To facilitate application of the adhesive  86  to the membrane  18 , a suction tool  90  having a hose  92  for drawing in air may be used which pressurizes the membrane  18  against a fine wire mesh  94  to ease the manipulation of the membrane material. Once the adhesive  86  has been activated, the membrane as held by the tool  90  is pressed against the exposed vent perimeter  21 , or the reinforcing element  60  if present, as shown in  FIG. 9 . Once the adhesive has set, the suction is removed,  FIG. 10 , leaving the membrane installed as shown in  FIG. 11 . 
         [0052]    After the adhesive has been given time to fully cure, a Spectra disc  22  is placed over the membrane  18  as shown in  FIG. 12 . As the disc is not attached to the membrane  18 , an adhesive material such as double-sided tape is preferably provided on the interfacing surface  96  of one or more of the flaps  24  to loosely secure the disc in place during packing and deployment of the landing bag. According to a preferred embodiment, the Spectra disk is secured to only one flap. 
         [0053]    Closure of the vent opening is completed by securing the tips  34  of the flaps to one another and/or to the cutting device  46  of the flow initiator  40  as shown in  FIGS. 2 ,  4  and  5 . In both the fabric embodiment of  FIGS. 4 and 5 , and the Kevlar reinforced pattern on the polyurethane-coated airbag fabric of  FIG. 2 , the fastening element or cord  39  is threaded through the loops  52  on the tips  34  of the flaps as shown in  FIG. 5 . Threading the cord in this manner ensures that no cord  39  will become caught in the loops  52 . 
         [0054]    When deployed, the relatively high modulus of the flap assembly  30  as secured by the fastening element  38  in the closed position carries the majority of the inflation load. Once the vent  10  is opened by the externally actuated flow initiator  40  and the Spectra disc  22  released, the membrane  18  will expand and burst to provide the desired landing performance. The vent  10  may thereafter be refurbished by replacing the membrane, allowing for reuse of the landing bag  12 . 
         [0055]    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.