Abstract:
The present is directed to a specific broadhead configuration for reducing the turbulence generated by a broadhead in flight, thereby reducing the resulting wind noise and aerodynamic drag generated in flight. The aerodynamic improvements to the archery broadhead are accomplished by providing edge treatments on at least one of the leading edges, trailing edges oblique edges or longitudinal edges of the broadhead blades. Specific edge treatments may include a linear tapered profile, a non-linear tapered profile or a radiused or rounded profile. Furthermore, certain edge treatments may be asymmetric so as to impart a rotational moment or spin to the arrow during flight. Such edge treatments are suitable for use on vented and non-vented blades.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/440,289, filed on Jan. 15, 2003. The disclosure of the above application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to archery broadheads and more particularly to the geometric configuration of the broadhead blade that enhances the aerodynamics of the broadhead to reduce the turbulence and noise generated thereby in flight. 
   BACKGROUND OF THE INVENTION 
   Recent developments in the fabrication of archery broadheads by powder injection molding processes have increased the flexibility in broadhead design and enabled better control on the dimensions, weight and variability of the end product. As an example, blade configurations of the broadhead may be thicker and/or may include variable thickness within the cross-section—e.g., taper from the ferrule to the sharpened edge. The use of thicker blade configurations satisfies the desire for stronger archery broadheads. However, it has been determined that thicker blades may also have the adverse effect of increasing the air turbulence and hence the noise of the arrow in flight. 
   When an arrow is shot from a bow at 180 to 350 feet per second, the broadhead, being the leading component, will encounter resistance from the air. With thicker blade designs, the increased frontal area (i.e., the area of the broadhead normal to the apparent wind) tends to exacerbate the turbulence and noise generation which is best described as a swishing or whistling noise. A quiet broadhead is important to a successful hunt because the hunted prey may “duck” or otherwise avoid an arrow if it can hear its approach. The adverse effect of a noisy arrow increases as the shooting distances increase. Therefore, there is a need to improve the aerodynamics of the broadhead to create a quieter arrow during flight. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a broadhead having a reduced aerodynamic drag, thereby decreasing the air turbulence and wind noise generated during flight. The present invention is accomplished by shaping the broadhead, and in particular the blade, such that the leading surfaces are smoothly shaped to the apparent wind. The trailing surfaces may also be shaped to minimize the effects of airflow separation from the broadhead that tend to increase the drag generated thereby. The geometric configurations may also be shaped to impart rotation of the arrow during flight to enhance the flight dynamics thereof. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is an isometric view of an arrow including a vented broadhead in accordance with a first preferred embodiment of the present invention; 
       FIG. 2  is a front view of the broadhead illustrated in  FIG. 1 ; 
       FIG. 3  is a side plan view of the broadhead illustrated in  FIG. 1 ; 
       FIG. 4  is a cross-sectional view taken along line IV—IV shown in  FIG. 2 ; 
       FIG. 5  is a cross-sectional view taken along line V—V shown in  FIG. 3 ; 
       FIG. 6  is a cross-sectional view taken along line VI—VI shown in  FIG. 3 ; 
       FIG. 7  is an isometric view of a non-vented broadhead in accordance with a second preferred embodiment of the present invention; 
       FIG. 8  is an isometric cross-sectional view taken along line VIII—VIII shown in  FIG. 7 ; 
       FIG. 9  is a cross-sectional view taken along line IX- 1 ×shown in  FIG. 7 ; 
       FIGS. 10A–10H  are cross-sectional views similar to that shown in  FIG. 5  illustrating alternate embodiments of present invention; and 
       FIG. 11  is a schematic illustration of a testing configuration of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   With reference now to the drawings and in particular to  FIGS. 1–3 , the present invention is directed to an archery arrow  10  having a fixed blade broadhead  12 , an arrow shaft  14 , fletching feathers  16  secured to the arrow shaft  14  and a nock  18 . The broadhead  12  includes ferrule  20 , cutting blades  22  extending radially outwardly from ferrule  20  and shank  24  extending axially rearwardly from ferrule  20 . As used herein the term blade refers to the portion of the broadhead that extends outwardly from a centerline or central longitudinal axis of the broadhead. Shank  24  has a threaded portion adapted to be received within arrow shaft  14  for releasably securing the broadhead  12  to the arrow shaft  14 . 
   As illustrated in the  FIGS. 1–6 , a vented broadhead  12  includes three blades  22  equiangularly disposed about ferrule  20 . Cutting blades  22  have a cutting edge  26  formed along the lateral leg  32  thereof. A generally triangular aperture or vent  28  is formed in the body of each cutting blade  22  to reduce the overall weight of the broadhead and distribute the mass of the blade around its perimeter. Thus, each blade  22  includes a medial leg  30 , a lateral leg  32  having the distal cutting edge  26  formed thereon and radial leg  34  extending between the medial leg  30  and lateral leg  32 . The broadheads illustrated in the figures represent a monolithic fixed blade design in which the medial leg  30  is defined by a portion of the ferrule  20 . However, one skilled in the art will readily recognize that the present invention may be adapted for use with a broadhead having multiple components such as a broadhead having blades releasably secured to a ferrule. In this configuration, each blade would itself include a medial leg. As presently preferred, blade  22  has a tapering cross section from the medial leg  30  adjacent the ferrule  20  to the distal cutting edge  26  as best seen in  FIGS. 2 and 6 . 
   As illustrated in  FIGS. 7–9 , a non-vented broadhead  112  includes a pair of cutting blades  122  extending outwardly from ferrule  120 . Each blade  122  includes a medial legs  130  adjacent the ferrule  120 , a lateral leg  132  having the distal cutting edge  126  formed thereon and a radial leg  134  extending between the medial leg  130  and the lateral leg  132 . As compared with the vented broadhead  12  illustrated in  FIGS. 1–6 , the interior of blade  122  is not vented but includes a web structure between the medial leg  130 , the lateral leg  132  and the radial leg  134 . As illustrated in  FIGS. 7–9 , blade  122  is provided with a recessed area defining a generally triangular web  128 . This recessed area provides means to distribute the mass of the blade around its perimeter while increasing the stiffness of the blade  122  as a whole. The intersection of the web  128  with the lateral leg  132  defines an oblique edge  138 . The intersection of the web  128  with the radial leg  134  defines a leading edge  136 . The intersection of web  128  with the medial leg  130  defines a longitudinal edge  142 . As presently preferred, blade  122  has a tapering cross-section from the medial leg  130  adjacent the ferrule  120  to the distal cutting edge  126  as best seen in  FIG. 8 . The web  128  is formed within the area circumscribed by legs  130 ,  132 ,  134 . Alternately, the thickness of the web structure may be generally equal to the legs  130 ,  132 ,  134  to provide a planar blade configuration in which an edge treatment in accordance with the present invention is formed on a trailing edge of the radial leg  134 . 
   Broadhead  112  further includes a pair of secondary cutting blades  144  extending generally perpendicular to the cutting blades  122 . As best seen in  FIGS. 7 and 8 , the secondary cutting blade  144  tapers from the forward point of the broadhead rearward towards the shank  124 . As best seen in  FIG. 8 , the size of secondary blade  144  is significantly smaller than the size of the cutting blade  122 . 
   In conventional broadheads, the leading surfaces such as the interior edges formed at the window  28  or web  128  have blunt faces which induce turbulence and thus wind-generated noise during the flight of the arrow. To minimize this effect, a broadhead in accordance with the present invention includes formed edges that are smoothly shaped to the apparent wind. Specifically, the broadhead  12 ,  112  may include contoured interior edges such as leading edge  36 ,  136  of the radial leg  34 ,  134  and oblique edge  38 ,  138  of lateral leg  32 ,  132  and the longitudinal edge  42 ,  142  of the medial leg  30 ,  130 . Likewise, the broadhead  12 ,  112  may include a contoured trailing edge  40 ,  140  of the radial leg  34 ,  134 . As shown in  FIGS. 5 and 9 , the leading edge  36 ,  136  of the radial leg  34 ,  134  is forwardly tapered and the oblique edge  38 ,  138  of the lateral leg  32 ,  132  is rewardly tapered to minimize the air disturbance of the broadhead in flight. The leading edge  36 ,  136  and the oblique edge  38 ,  138  are provided with a linear taper. Such a treatment of the leading edge  36 ,  136  and oblique edge  38 ,  138  smoothes the air flow of the broadhead in flight, thereby minimizing the wind noise generated thereby. Likewise, a treatment of the trailing edge  140  of radial leg  134  minimize separation from the broadhead  122 , thereby reducing wind drag and noise. The range of the included angle (α) of the linear taper is between 20° and 120°, more preferably between 20° and 90°, and most preferably between 30° and 60°. 
   While  FIGS. 5 and 9  illustrates generally linear edge treatments, the present invention contemplates a variety of edge treatments which may function to minimize turbulence generated by the broadhead in flight. Specifically, as illustrated in  FIGS. 10A–10D , the treatment of leading edge  36  may vary. For example, as illustrated in  FIG. 10A , the leading edge  36  is provided with a linear taper similar to that shown in  FIGS. 5 and 9 . As illustrated in  FIG. 10B , the leading edge  36  is provided with a radiused edge treatment. As illustrated in  FIG. 10C , the leading edge  36  is provided with a non-linear tapered treatment. As illustrated in  FIG. 10D , the leading edge  36  is provided with an asymmetric linear taper. An asymmetric edge treatment such as that illustrated in  FIG. 10D  may be utilized to induce a rotational moment of the arrow during flight. In this manner, such an edge treatment can be utilized alone or in combination with a helical fletching to enhance the accuracy and flight dynamics of the arrow assembly during flight. The oblique edges  38  and the trailing edges  40  illustrated in  FIGS. 10A–10D  are not provided with an edged treatment. While the various edge treatments discussed above are shown for a vented broadhead, one skilled in the art will recognize that such edge treatments are equally suitable for use on a non-vented broadhead. 
   As noted above, the present invention further contemplates other edge treatments on the broadhead to minimize the effects of air flow separation over the broadhead during flight which tends to increase the drag generated thereby. For example, as illustrated in  FIGS. 10E–10G , various edge treatments may be utilized on the trailing edge  40  of radial leg  34 . Specifically, as illustrated in  FIG. 10E , the trailing edge  40  includes a linear taper similar to that formed on the leading edge  36 . As illustrated In  FIG. 10F , the trailing edge  40  includes a rounded or radiused edge treatment similar to that as shown on leading edge portion  36 . As illustrated in  FIG. 10G , the trailing edge  40  includes a “boat-tail” treatment having a linear taper portion transitioning to a rounded or curved portion. The present invention further contemplates an edge treatment formed on the oblique edge  38 , that is to say the inner edge of the lateral leg portion  32 . As illustrated in  FIGS. 10F–10H , the treatment of the oblique edge  38  may take various configurations including a rounded or radiused configuration as illustrated in  FIGS. 10F and 10H , a non-linear tapered configuration as illustrated in  FIG. 10G , or a linear tapered configuration as illustrated in  FIG. 5 . While the various edge treatments discussed above are shown for a vented broadhead, one skilled in the art will recognize that such edge treatments are equally suitable for use on a non-vented broadhead. 
   A powder injection molding (PIM) process is particularly well suited for fabrication of the present invention. Specifically, the PIM manufacturing process affords great flexibility and adaptation for fabricating complex shapes. A more detailed description of the PIM manufacturing process as applied to archery broadheads is set forth in U.S. Pat. No. 6,290,903 issued Sep. 18, 2001 entitled “Archery Broadhead and Method of Manufacture” and U.S. Pat. No. 6,595,881 issued Jul. 22, 2003 entitled “Expanding Blade Broadhead”, the disclosures of which are expressly incorporated by reference herein. However, the present invention is not limited to PIM-fabricated broadheads but includes broadheads fabricated using any of a variety of known technologies which permit the shaping or machining of the various edges to provide an edge treatment such as, but not limited to, machining, investment casting or fine blanking. Thus, broadheads fabricated by any of the above technologies are considered to be within the scope of the present invention. 
   The present invention further contemplates a simple test stand for qualitatively evaluating the effectiveness of specific edge treatments of the broadhead blade for imparting rotation to the arrow during flight such as illustrated in  FIG. 10D . In this regard, the test standard is not intended to provide precise quantification of the broadhead aerodynamics. With reference now to  FIG. 11 , the test stand configuration  200  includes an arrow support cradle  202  having a pair of V-blocks or roller blocks  204  spaced apart to support an arrow shaft  14 , while allowing the free rotation thereof. A stop  206  is disposed at the nock end  18  of the arrow  10  to prohibit axial sliding of the arrow shaft relative to the support cradle. A ball bearing  20 B is interposed between the stop block  206  and the arrow  10  to further facilitate free rotation of the arrow in the test fixture. An air flow generator  210  such as a source of compressed air or a fan is located forward of the arrow to generate an apparent wind or air flow generally indicated at  212  over the broadhead  12 . Specifically, the compressed air source  212  is configured to provide an apparent wind speed between approximately 180 and 350 feet per second. In this configuration, the test stand  200  illustrated in  FIG. 11  has proved suitable evaluating an edge treatment on the broadhead blade  22  such as that illustrated in  FIG. 10D  for inducing a rotational moment on the arrow. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. For example, the broadheads described and illustrated herein as preferred embodiments are shown to have specific blade configurations; however the present invention may be readily adapted for use on broadheads having other blade configurations. These and other such variations are not to be regarded as a departure from the spirit and scope of the invention.