Patent Publication Number: US-2020282662-A1

Title: Method of sealing an airtight bladder for a kite and an airtight bladder for a kite

Description:
FIELD 
     The present invention relates to improved seam construction and finishing techniques for air tight bladders used in inflatable kite frames and more particularly Supported Leading Edge (SLE) Kites. 
     BACKGROUND 
     A pressurized air frame is critical to the function of air inflatable air frame kites, also known as “Supported Leading Edge” (SLE) Kites. SLE Kites will not fly as designed unless inflated to a pressure of between 4 and 12 psi. It is becoming known that a more rigid air frame on SLE Kites can have desirable improvements in turn response input and stability. 
     The bladders used to support these air frames are most commonly made with thin monolithic membranes or films such as Polyurethane (PU), Polyethylene Terephthalate (PETE or PET), High-Density Polyethylene (HDPE), Polyvinyl Chloride (PVC), Low-Density Polyethylene (LDPE), Polypropylene (PP), Polystyrene. In most cases it is desirable to use the lightest membrane possible to reduce kite weight and improve performance while minimizing failures caused by the longitudinal air tight seams and closing end air tight seams. 
     Typically an inflatable SLE kite bladder is made with welded plain seams on all perimeters edges of the bladder to achieve the desired air holding requirement. This process however has limitations with thinner films of 70 microns or less, as welded plain seams are typically the failure point in crashes or in heavy use of SLE kites. 
     SUMMARY 
     According to one aspect, there is provided a method of sealing an airtight bladder for kites. The method involves sealing longitudinal edges of an airtight bladder with a lap seam. The method then involves sealing ends of the bladder by both deforming bladder material and applying an end seam. 
     According to another aspect there is provided an airtight bladder for kites. The bladder includes a body having longitudinal edges sealed with a lap seam and ends sealed by a combination of deforming bladder material and applying an end seam. 
     As will hereinafter be described, laps seams cannot readily be used to seal the ends of the bladder body. However, it is the ends of the bladder body that are most prone to failure. This problem has been addressed by a combination of deforming the bladder material and applying an end seam. 
     After experimentation, it was determined that there are a number of different ways of deforming the bladder material to protect the end seal. There will hereinafter be described various deformations of the bladder material, which include folding, rolling, accordion folding, knotting, or twisting the ends. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a perspective view of an SLE kite. 
         FIG. 2  is a perspective view of an inflatable support structure of the SLE kite illustrated in  FIG. 1 . 
         FIG. 3  is a detailed perspective view of a strut for the inflatable support structure of the SLE kite illustrated in  FIG. 2 . 
         FIG. 4  is a top plan view of a bladder for the strut of  FIG. 3 , laid flat. 
         FIG. 5  is a side elevation view of the bladder for the strut of  FIG. 3 . 
         FIG. 6  is a section view of the bladder taken along section lines A-A of  FIG. 5 . 
         FIG. 7  is a side elevation view, in section, of the bladder of  FIG. 5 , showing a step in constructing a first embodiment of bladder having an end of a bladder  10  finished using a spacer. 
         FIG. 7A  is a top plan view  FIG. 7 . 
         FIG. 8  is a side elevation view, in section, of the bladder of  FIG. 7  showing a folding step in constructing the first embodiment of bladder. 
         FIG. 8A  is a top plan view  FIG. 8 . 
         FIG. 9  is a side elevation view, in section, of the bladder of  FIG. 8  showing a bonding step in constructing the first embodiment of bladder. 
         FIG. 9A  is a top plan view  FIG. 9 . 
         FIG. 10  is a side elevation view of the first embodiment of bladder. 
         FIG. 11  is a side elevation view, in section, of the bladder of  FIG. 5 , showing a step in constructing a second embodiment of bladder having an end of a bladder  10  finished using a spacer. 
         FIG. 11A  is a top plan view  FIG. 11 . 
         FIG. 12  is a side elevation view, in section, of the bladder of  FIG. 11  showing a first folding step in constructing the second embodiment of bladder. 
         FIG. 12A  is a top plan view  FIG. 12 . 
         FIG. 13  is a side elevation view, in section, of the bladder of  FIG. 11  showing a second folding step in constructing the second embodiment of bladder. 
         FIG. 13A  is a top plan view  FIG. 13 . 
         FIG. 14  is a side elevation view, in section, of the bladder of  FIG. 13  showing a gluing step in constructing the second embodiment of bladder. 
         FIG. 14A  is a top plan view  FIG. 14 . 
         FIG. 15  is a side elevation view, in section, of the bladder of  FIG. 5 , showing a step in constructing a third embodiment of bladder having an end of a bladder finished using a welded seam. 
         FIG. 15A  is a top plan view  FIG. 15 . 
         FIG. 16  is a side elevation view, in section, of the bladder of  FIG. 15  showing a positioning of a fold line in constructing the third embodiment of bladder. 
         FIG. 16A  is a top plan view  FIG. 16 . 
         FIG. 17  is a side elevation view, in section, of the bladder of  FIG. 16  showing a folding step in constructing the third embodiment of bladder. 
         FIG. 17A  is a top plan view  FIG. 17 . 
         FIG. 18  is a side elevation view, in section, of the bladder of  FIG. 17  showing a securing with a tape fastener in constructing the third embodiment of bladder. 
         FIG. 18A  is a top plan view  FIG. 18 . 
         FIG. 19  is a side elevation view of a variation on the third embodiment finished using a welded seam, by rolling the ends of the bladder. 
         FIG. 20  is a side elevation view of a variation on the third embodiment finished using a welded seam, by using an accordion fold at the ends of the bladder. 
         FIG. 21  is a side elevation view of a variation on the third embodiment finished using a welded seam, by tying the ends of the bladder into a knot. 
         FIG. 22  is a side elevation view of a variation on the third embodiment finished using a welded seam, by tying the welded seam into a knot. 
         FIG. 23  is a side elevation view of a variation on the third embodiment finished using a welded seam, by using twisting and securing the ends of the bladder. 
         FIG. 24  is a side elevation view of a variation on the third embodiment finished using a welded seam, bunching the ends of the bladder. 
     
    
    
     DETAILED DESCRIPTION 
     A method of sealing an airtight bladder for a kite will now be described with reference to  FIG. 1  through  FIG. 24 . 
     Structure and Relationship of Parts: 
     Referring to  FIG. 1 , there is illustrated an inflatable kite  2  used for kiting traction sports. Referring to  FIG. 2 , the support structure of kite  2  is shown with leading edge  4 , struts  6  and valves  8  that inflate the bladders inside the leading edge  4  and struts  6 . The struts  6  have strut ends  36  and the leading edge tube has leading edge tube ends  38 . 
     Referring to  FIG. 3 , there is illustrated how the bladder  10  fits inside of the strut  6  with the bladder end is against the strut end  36 . Referring to  FIG. 4 , there is shown a view with an unassembled bladder  10  lying flat. Valve  8  is affixed to the bladder  10  near one end. A seam allowance  12  borders the edges of the bladder material  10 . A fold line  14  extends along the lengthwise midline of bladder material  10 . 
     We have reached the conclusion that the reason for the failures of SLE kite bladders is directly related to the quality of the weld. When a bladder with a welded plain seam is pressurized, the resulting force on the seam causes a stress concentration at the juncture of the films. Under pressure this stress concentration tears apart the bladders halves which propagates the stress concentration through the entirety weld eventually resulting in a failure. 
     We attempted to address the problem with laminated films. Laminated films provide advantages in bladder construction as stronger films can be combined with those which have favourable heat sealing properties or other various properties. Unfortunately, plain seams limit the use of laminated films in bladder construction as the glues used to bond multiple layers of film are particularly susceptible to delamination under this type of loading. In addition to the stress concentration created when loading a plain seam the geometry of this bladder construction method is such that the glued layers of the lamination are pulled directly apart where the adhesion strength is significantly less than that of the shear direction. 
     Referring to  FIG. 5 , the preferred method involves folding bladder material in half along fold line  14  and the seam allowances  12  have been over lapped and bonded with a welded lap seam  16  to form bladder  10 . Referring to  FIG. 6 , this section view shows the partially assembled bladder  10  of  FIG. 5  with seam allowances  12  over lapped and bonded with a welded lap seam  16 . 
     Typically air holding bladders are designed to be the same size or slightly larger than the outer strut and spar envelope they are inflating. During a perfect inflation, the bladder will fill the entire void of the leading edge tube and strut envelopes, with the outer envelopes restraining the pressurized forces rather than the fragile bladder material taking any high pressure loads. The most common fail point in air holding bladders is at the end or tip of the inflated leading edge tube or strut. For if a bladder is not correctly fitted before inflation, the bladder film can be overstressed, in particular if the end does not come in contact with the ends of the outer envelope during the inflation process. This typically results in the aneurysm and failure of the film at the leading edge or strut end. This is undesirable as the SLE Kite will now deflate, losing its aerodynamic shape, making the kite uncontrollable while in use. Unfortunately, the geometry of a bladder with a welded longitudinal lap seam makes a regular lap seam on bladder ends impossible which create a weak point. For this reason, having welded lap seam  16  alone is not sufficient unless an effort is made to reinforce the ends. There will now be described some approaches that have been developed to reinforce the ends. 
       FIG. 7  through  FIG. 10  show steps in constructing a first embodiment of bladder  10  with reinforced ends. Referring to  FIG. 7 , a spacer material  18 , that doesn&#39;t bond to the bladder material  10 , is inserted between the layers of the bladder  10 . There is a fold line  14  at the edge of the spacer material  18 . Referring to  FIG. 7A , this figure provides a top plan view of spacer material  18  with fold line  14  at the edge of the spacer material  18 . Referring to  FIG. 8 , there is shown a folding step with bladder  10  being folded along fold line  14  such that folded bladder  20  lays over spacer material  18 . Referring to  FIG. 8A , this figures provides a top plan view of bladder  10  folded along fold line  14  such that folded bladder  20  lays over spacer material  18 . Referring to  FIG. 9 , there is shown a bonding step with folded bladder  20  being bonded to bladder  10  with a welded lap seam  16 . Referring to  FIG. 9A , this top plan view shows folded bladder  20  being bonded to bladder  10  with a welded lap seam  16 . Spacer material  18  prevents the internal surfaces of bladder  10  from bonding together. Referring to  FIG. 10 , the first embodiment of bladder  10  is shown completed with welded lap seams  16  along the ends and lengthwise edge. 
       FIG. 11  through  FIG. 14  show steps in constructing a second embodiment of bladder  10  with reinforced ends. Referring to  FIG. 11 , a spacer material  18 , that doesn&#39;t bond to the bladder material  10 , is inserted between the layers of the bladder  10 . A separate bladder end piece  22  has a fold line  14 . Referring to  FIG. 11A , this top plan view shows spacer material  18 , bladder end piece  22  and fold line  14 . Referring to  FIG. 12 , the bladder end piece  22  positioned on one side of the end of bladder  10  in line with spacer material  18 . Referring to  FIG. 12A , this top plan view shows the bladder end piece  22  positioned on one side of the end of bladder  10 , in line with spacer material  18 , such that the fold line  14  is in line with the end of the bladder  10 . Referring to  FIG. 13 , bladder end piece  22  is folded over the end of the bladder  10  such that both ends of the bladder end piece cover the spacer material  18 . Referring to  FIG. 13A  this top plan view shows the bladder end piece  22  folded over the end of the bladder  10  such that both ends of the bladder end piece cover the spacer material  18 . Referring to  FIG. 14 , the bladder end piece  22  is folded over the end of the bladder  10  and then bonded in place with a welded lap seam  16 . Referring to  FIG. 14A , this top plan view shows the bladder end piece  22  folded over the end of the bladder  10  and then bonded in place with a welded lap seam  16 . Spacer material  18  prevents the internal surfaces of bladder  10  from bonding together. 
       FIG. 15  through  FIG. 18  show steps in constructing a third embodiment of bladder  10  with reinforced ends. Referring to  FIG. 15 , bladder  10  has a welded plain seam  24  near the end. Referring to  15 A, this top plan view shows bladder  10  has a welded plain seam  24  near the end. Referring to  FIG. 16 , bladder  10  has a welded plain seam  24  near the end and a fold line  14 . Referring to  FIG. 16A , this top plan view shows bladder  10  with a welded plain seam  24  near the end and a fold line  14 . Referring to  FIG. 17 , bladder  10  with a welded plain seam  24  is folded over  20  and then the folded bladder  20  is affixed to the bladder  10  with tape  26  between the folded bladder  20  and bladder  10 . Referring to  FIG. 17A , this top plan view shows bladder  10  with a welded plain seam  24  folded over  20  and then the folded bladder  20  is affixed to the bladder  10  with tape  26  between the folded bladder  20  and bladder  10 . Referring to  FIG. 18 , bladder  10  with welded plain seam  24  is folded over  20  and then the folded bladder  20  is affixed to the bladder  10  with tape  26  on the outside of folded bladder  20  and bladder  10 . Referring to  FIG. 18A , this top plan view shows bladder  10  with welded plain seam  24  folded over  20  and then the folded bladder  20  is affixed to the bladder  10  with tape  26  on the outside of folded bladder  20  and bladder  10 . 
     Variations: 
     There are different manners of folding and securing the ends. A few of which will hereinafter be described. Referring to  FIG. 19 , the third embodiment of bladder  10  with a welded plain seam  24  could be rolled or have multiple folds  28 . Referring to  FIG. 20 , the third embodiment of bladder  10  with a welded plain seam  24  could have an accordion fold  30 . Referring to  FIG. 21 , the third embodiment of bladder  10  with a welded plain seam  24  could have bladder  10  tied in a knot  32 . Referring to  FIG. 22 , the third embodiment of bladder  10  could have that section of the bladder  10  that has the welded plain seam  24  tied in a knot  32 . Referring to  FIG. 23 , the third embodiment of bladder  10  with a welded plain seam  24  could be secured with twists  32 . Referring to  FIG. 24 , the third embodiment of bladder  10  with a welded plain seam  24  could be secured with the end bunched  34 . 
     Operation: 
     Referring to  FIG. 7 through 10 , the airtight bladder for kites resulting from following the teachings of the method has a bladder body  10  having longitudinal edges sealed with a lap seam and ends sealed by a combination of deforming bladder material and applying an end seam. There has been illustrated the various ways that the bladder material may be deformed to shelter and protect the end seal. They include folding, rolling, accordion folding, knotting, or twisting the ends. 
     When in use bladder  10  is inserted into the protective soft envelope of the struts or leading edge. During inflation the ends are forced onto an inner surface of the protective soft envelope by the inflating bladder. However, this force holds the plain seam of the end in its folded configuration which prevents the film from opening under pressure and creating a stress concentration at the seam. 
     In the event of a high impact crash on an inflated SLE kite, impact forces typically move outward toward the tips of the leading edge, spars and struts, resulting in ruptures at the ends of the air tight bladder. By deforming the ends of the air tight bladder by folding, rolling, accordion folding, knotting, or twisting as described above, the chance of bladder failure is reduced. 
     This approach allows the use of lighter films, less than 70 microns and other light air holding laminated materials. The primary seam failure points, at the ends of the bladders, are enhanced by folding, rolling, accordion folding, knotting, or twisting. These deformations serve to help absorb pressure on the end. 
     Folding, rolling, accordion folding, knotting, or twisting, enables the ends to hold more pressure, with lighter films, allowing for higher PSI levels for SLE kites while reducing weights. Higher pressure leading edges, spars and struts deliver improved performance to the user. Light weight is always desirable on SLE Kites for improved handling and performance in all conditions. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
     The scope of the claims should not be limited by the illustrated embodiments set forth as examples, but should be given the broadest interpretation consistent with a purposive construction of the claims in view of the description as a whole.