Abstract:
A parachute having radial slots distributed at regular intervals around the shoulder region to effect boundary flow separation, causing Von Karmen Vortex Street shed vortices to separate in a symmetrical manner from the inflated shape and resulting in an extremely stable aerodynamic decelerator. In addition, pressure vents in the crown region vent high pressure air during the inflation process to contribute to opening load control. Once the parachute is fully inflated, the pressure vents provide energetic airflow that ensures that the shed vortices created by the radial slots do not re-contact the canopy and cause instability.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to round canopy parachutes and, more particularly, to a ring slot parachute having radial slots.  
         [0003]     2. Description of the Related Art  
         [0004]     The use of sails in parachutes is an established technique that is well documented in the ring sail and hybrid classes of parachutes. In the hybrid designs, generally a single row of sails in the shoulder region of the parachute is used to provide a fixed location for flow separation. This fixed location, combined with other features, is often critical to creating a parachute that has good stability while retaining a high drag coefficient.  
         [0005]     Sails have a down side, however, in that they are difficult to pack and thus become impractical in applications with significant packing requirements such as mass parachute assault.  
         [0006]     In addition, high drag canopies tend to either glide or be unstable. Previous efforts to improve stability have included employing slots that are continuous around the entire canopy but this method can cause drag loss and inflation stall. Further, many slotted designs such as those disclosed in U.S. Pat. Nos. 3,298,639 and 3,809,342, are designed to provide forward/horizontal velocity through the incorporation of panels that create “jets” of air. However, forward motion is not desirable in many deployment scenarios and can be dangerous, such as in mass parachute assault, particularly at night, when multiple personnel and/or cargo payloads might easily collide with one another.  
         [0007]     An alternative slot design having what are known as “cat eye” slots is disclosed in U.S. Pat. No. 2,734,706. The cat eye slots, have loose fabric which, upon loading, effectively closes the slots. Hence, radial venting is not constant.  
         [0008]     Therefore, a need exists for a parachute design that is able to provide constant defined flow separation locations comparable to that obtained with sails, while being easier to pack and manufacture, and at the same time provide enhanced stability and high drag without forward speed.  
       SUMMARY OF THE INVENTION  
       [0009]     In accordance with these and other objects, the present invention is directed to a parachute having radial slots distributed at regular intervals around the shoulder region of the parachute and having pressure vents in the crown region. The radial slots provide a mechanism to effect boundary flow separation at the shoulder region, causing Von Karmen Vortex Street (VKVS) shed vortices to separate in a symmetrical manner from the inflated shape. This symmetrical separation of the VKVS shed vortices results in an extremely stable aerodynamic decelerator (parachute).  
         [0010]     The pressure vents in the crown region contribute to opening load control by venting high-pressure air through the crown during the inflation process. Once the parachute is fully inflated, these vents provide energetic airflow that ensures that the shed vortices created by the radial slots do not re-contact the canopy and cause instability.  
         [0011]     Accordingly, it is an object of the present invention to provide a high stability, high drag parachute with improved opening load management.  
         [0012]     Another object of the present invention is to provide a parachute that demonstrates high stability without forward speed.  
         [0013]     A further object of the present invention is to provide a parachute with radial slots designed to provide constant radial venting.  
         [0014]     Yet another object of the present invention is to provide a radially slotted parachute with pressure vents in the crown region for venting high-pressure air during the inflation process.  
         [0015]     A still further object of the present invention is to provide a parachute having radial slots and pressure vents that remain open once the chute is fully inflated, the pressure vents providing energetic flow to ensure that the VKVS shed vortices created by the radial slots do not re-contact the canopy and cause instability.  
         [0016]     Still another object of the present invention is to provide a parachute having radial slots that can be fully open or covered with mesh material, the size of the slot openings being designed to match a desired balance between oscillation and rate of descent.  
         [0017]     A still further object of the present invention is to provide a parachute having radial slots covered with mesh material in which the pattern for the mesh material is shaped to correspond with the radial opening when inflated.  
         [0018]     Yet a further object of the present invention is to provide a parachute that is easier to manufacture and pack than conventional ring sail parachutes while providing good stability and a high drag coefficient.  
         [0019]     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  
       [0020]      FIG. 1  shows a side view of an inflated parachute (with only the top portion of the suspension lines shown) having radial slots and pressure vents in accordance with the present invention.  
         [0021]      FIG. 2  illustrates a gore portion of a parachute canopy having radial slots that follow the cloth weave.  
         [0022]      FIG. 3  illustrates a gore portion of a parachute canopy having radial slots that are parallel to the radial.  
         [0023]      FIG. 4  is a top view of a parachute canopy as laid flat and having mid-gore radial slots of the cloth weave type as shown in  FIG. 2 .  
         [0024]      FIG. 4A  depicts a single gore from the parachute canopy of  FIG. 4 .  
         [0025]      FIG. 5  is a top view of a parachute canopy as laid flat and having multiple radial slots of the parallel radial type as shown in  FIG. 3 .  
         [0026]      FIG. 5A  depicts a single gore from the parachute canopy of  FIG. 5 .  
         [0027]      FIG. 6  is a top view of a parachute canopy as laid flat and having long radial slots of the parallel radial type as shown in  FIG. 3 .  
         [0028]      FIG. 6A  depicts a single gore from the parachute canopy of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     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.  
         [0030]     As shown in  FIG. 1 , the present invention is directed to a parachute generally designated by the reference numeral  10 . The parachute  10  includes a canopy  12  constructed from a plurality of gores, generally designated by the reference numeral  14 , that meet together at the peak vent  16  of the canopy and extend to the lower edge  18  thereof. Suspension lines  20  are secured to the lower edge  18  in a manner known in the art. The canopy fabric can have a range of porosities. For example, a cloth enabling an airflow of about 0-3 cubic feet per minute (CFM) may be appropriate in some applications while a different cloth having a much greater porosity, on the order of 30-50 CFM for example, may be used in other applications.  
         [0031]     The gores  14  include a plurality of panels  22  that are stitched or otherwise connected to one another along their circumferential seams  21  as well as along their radially extending edges or radials  24 . Radial slots  26  are formed in the slotted gore panels  22   a , positioned adjacent the radials  24 , and spaced around the shoulder region, generally designated by the reference numeral  28 , of the canopy  12 . According to the embodiment shown in  FIG. 1 , the basic canopy has been shaped with an extended skirt, as is known in the art, such that the shoulder region  28  has a greater diameter than the lower edge  18 .  
         [0032]     Each gore  14  has two slots  26   a ,  26   b  that are aligned with one another circumferentially so as to, together with the slots of adjacent gores, form a slot ring  30 . However, any number of slots, including none, may be included in any particular gore. Thus, the slots may be placed on every gore or on only some of the gores and in any pattern, such as only on alternating gores, on every third gore, etc.  
         [0033]     The radial. slots  26  may be constructed to follow the cloth weave of the panels, as shown by the cloth weave slots  126  in  FIG. 2 , or to be parallel with the radials  24  as shown by the parallel radial slots  226  depicted in  FIG. 3 . As referenced herein, slot  26  is used generally to refer to either the cloth weave slots or the parallal radial slots when either could be used. In addition, slots of other shapes could also be used and are intended to be included within the general designator of reference numeral  26 .  
         [0034]     When made to follow the cloth weave, the slots  126  have a truncated rectangular or trapezoidal shape that, compared with the consistent width of the parallel radial slots  226  which are rectangular, extend further into the panel  22  of the gore  14 . Because of this deeper extension and the resulting increase in slot size, the cloth weave radial slots  126  allow for a greater airflow and thus faster descent. The parallel radial slots  226 , by contrast, have a slower rate of descent, and hence a better drag coefficient, than the cloth weave slots.  
         [0035]     When constructing a parachute  10  according to the present invention, design decisions relating to the inclusion of cloth weave slots versus parallel radial slots depend upon the aerodynamic performance requirements of the canopy. Optimally, the slots  26  are sized, shaped and positioned to ensure that symmetrical vortex shedding is achieved at a magnitude sufficient to achieve the desired stability for each specific canopy shape, e.g., flat, conical, polyconical, hemi-spherical, extended skirt, etc.  
         [0036]     The slots  26  can be entirely open areas, defining a gap such that air flow through the slots is unimpeded. Alternatively, the slots can be covered or partially covered with a partially occluding material  32  such as mesh that continues to allow air flow but which also reduces the risk of entanglement in the event that another jumper were to collide with the canopy, i.e., the partially occluding material prevents the other jumper from “putting his boot through the hole” and endangering both himself and the jumper whose canopy has been entangled.  
         [0037]     According to one preferred embodiment, the partially occluding material is a mesh cloth  32 , but any type or combination of mesh, tapes, cloth with holes or with partially covered holes or openings, may be used. For ease of description, the partially occluding material used to cover the slots will be referred to herein as “mesh”, but with the understanding that this term includes other materials that are able to provide the same or comparable function.  
         [0038]     In addition to protecting against jumper entanglement, the mesh also serves to control the geometry of the slot, ensuring that the slot does not change shape as a function of dynamic pressure. This shape-retaining function is best achieved when the pattern shape  34  of the mesh  32  is adjusted to correspond with the inflated shape of the slots. As shown in  FIGS. 2 and 3 , when inflated, the slots  26  demonstrate a curvature along their edges  36  which is created by the upward force of air against the underside of the canopy, creating a “bulge” in the fabric adjacent the slot edge  36 . To utilize this shape, the mesh  32  is not cut precisely to match the truncated rectangular shape of the slot  126  shown in  FIG. 2  or the rectangular shape of the slot  226  shown in  FIG. 3 . Instead, the mesh is sized to include additional material so as to allow the slot edges  36  to bulge or expand to an extent and shape generally corresponding to that created by inflated slot edges in the absence of a mesh covering.  
         [0039]     Because the mesh partially occludes the slot opening, some attenuation of the air flow through the slot does occur, degrading the performance of the slot in terms of flow. However, this can be effectively compensated through an appropriate increase in the size of the slots when designing a canopy to have mesh-covered slots.  
         [0040]     In addition to the slots, the gores of the canopy according to the present invention are further provided with one or more pressure vents  40  positioned between the peak vent  16  of the chute and the shoulder region  28 . Like the slots  26 , the vents  40  in adjacent gores are aligned circumferentially so that together they form a pressure vent ring, generally designated by the reference numeral  42 .  
         [0041]     The pressure vents  40  serve two primary purposes. First, they provide for an outflow of air that re-energizes the boundary flow from the slots  26 . The outflow precludes the airflow that is initially attached to the canopy from the skirt at the lower edge  18  to the base of the slots, from re-attaching to the upper surface  44  of the canopy. This serves to maintain the stability of the parachute by eliminating asymmetric vortex shedding. Second, during the inflation process, the control of air outflow afforded by the vents  40  enables the parachute designer to tailor the size of the slots  26  to accomplish desired load management. More particularly, the position and width of the vents  40  controls the early shape formation during inflation and ensures that early drag growth is arrested at the most suitable point to realize acceptable parachute opening loads.  
         [0042]     As shown in  FIG. 1 , when multiple pressure vent rings  42   a ,  42   b  are included, they are spaced from one another and may be of different widths. The size and position of the ring or rings is selected based on the performance requirements and airflow characteristics of the canopy.  
         [0043]     The arrangement and number of the slots  26  and pressure vents  40  may be varied according to various designs. In the embodiment shown in  FIGS. 4 and 4 A, each gore has a pair of cloth weave radial slots  126  positioned generally midway along the panels in the shoulder region  28  of the canopy. Above the shoulder region  20   28  in each gore are two pressure vents  40   a ,  40   b  of different widths and spaced from one another according to the design requirements.  
         [0044]     An alternative embodiment having multiple radial slots  26  and a single pressure vent ring  42  is shown in  FIGS. 5 and 5 A. Each gore has an upper set of radial slots, generally designated by the reference numeral  46 , and a lower set of radial slots, generally designated by the reference numeral  48 , with the “upper” and “lower” designations being relative to the peak of the canopy. The sets of slots  46 ,  48  are radially spaced from one another by a mid-gore panel  50 . When the gores are attached to one another along their radials  24  in the constructed canopy  12 , the slots  226  as arranged around the canopy form two concentric rings  30   a ,  30   b , separated by an intervening cloth ring, generally designated by the reference numeral  52 , formed by the adjoining mid-gore panels  50 .  
         [0045]     While both sets of slots  46 ,  48  shown in  FIGS. 5 and 5 A are of the parallel radial type  226 , the sets may be advantageously of different types. For example, parallel radial slots  226  may be used for the upper set  46  nearest the peak  16  to maximize drag while cloth weave slots  126  are arranged in the lower set  48  to improve vortex shedding. By tailoring slot type to canopy position in this way, the performance benefit obtained from each type can be maximized.  
         [0046]     A further alternative is illustrated in  FIGS. 6 and 6 A in which a single set, generally designated by the reference numeral  54 , of long radial slots  326  and a single pressure vent ring  42  are provided. When using long slots  326  such as those shown, parallel radial slots  226  with their better drag coefficient are generally preferable to cloth weave slots.  
         [0047]     While cloth weave slots and parallel radial slots have been specifically set forth in the disclosed embodiments, the slots according to the present invention are intended to include slots of any width, height or shape along or within about eight inches of the radial, and in any position along the radial. With particular reference to the cloth weave slots, further variability in shape may be introduced by changing the orientation or weave direction of the cloth in the slotted panels  22   a . By adjusting the weave direction in these panels  22   a , the width of the base of the trapezoidal cloth weave slot can be increased or decreased relative to the width of the parallel side.  
         [0048]     As an example, in the preferred embodiments shown in  FIGS. 2 and 4 A, the cloth weave of panels  22  as well as slotted panel  22   a  is oriented such that for all the panels in the canopy the cloth warp and weft are respectively perpendicular and parallel to the lower edge  18  of the gore. This is known as a block construction. To vary the shape of the slots while retaining the block construction baseline performance, the weave direction in the slotted panel  22   a  is angled so that the warp and weft are no longer perpendicular and parallel, respectively, to the gore lower edge  18 ; the block construction is retained in the remainder of the canopy panels  22 .  
         [0049]     The size of the slot openings can range from only a slit in the cloth to an excised portion taken from the cloth having a selected shape such as the truncated rectangular (trapezoidal) area  60 , or the generally rectangular area  62 , shown in  FIGS. 2 and 3 , respectively. These areas  60 ,  62  can have a width up to one third the width of the gore and can be on both sides thereof as shown, leaving the center one third of the gore (or more) cloth. This range of slot sizes is applicable to both open slots and mesh-covered slots.  
         [0050]     The positioning of the radial slots relative to the pressure vents is dependent upon the type and number of slots, and the desired performance characteristics of the canopy. According to one preferred embodiment shown in  FIGS. 4 and 4 A, the radial slots  126  are positioned so as to be down approximately 64% of the radius of the canopy from the vent center  70 , where the vent center  70  represents the point at which all the vent lines cross. Vent lines (not shown) span the opening in the peak vent  16  of the parachute and attach to opposite radials at the top of each gore where the fabric ends, as is well known in the art.  
         [0051]     The relationship of the total area of the slots to the reference diameter of the canopy, Do, varies according to slot style. Assuming the “canopy reference area” is the area of a single gore, including the slots and vents, multiplied by the number of gores, the reference diameter is the diameter of a circle determined from this reference area. By calculating the area of all of the slots and assuming this area to be the area of a second circle, this second circle corresponds with the percentage diameters shown in  FIGS. 2 and 3 . Therefore, the cloth weave slots shown in  FIG. 2  have an area of approximately 5.5% of the reference diameter, Do, of the canopy. The parallel radial slots of  FIG. 3 , on the other hand, have an area of approximately 6.0% of the reference diameter.  
         [0052]     As just described, the radial slots provide constant radial venting while the pressure vents provide energetic flow to ensure that the VKVS shed vortices created by the radial slots do not re-contact the canopy and cause instability. Furthermore, the parachute according to the present invention does not have a forward speed component, making it suitable for a variety of deployment scenarios requiring precise drop zones. This absence of forward speed is achieved by symmetric placement of the radial slots.  
         [0053]     The parachute according to the present invention may be used for both personnel and payload deployment. For personnel, the preferred size range of the diameter of the canopy is between about 25-45 feet. For cargo applications, the canopy size can be much larger or smaller depending upon the cargo and the parachute performance requirements. The ratio between payload weight and the canopy size is also adjustable according to specific application requirements.  
         [0054]     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.