Abstract:
The present invention is a turbine tip arrowhead, used either strictly as a field point or as the forwardmost tip in conjunction with any prior art broadhead assembly. The key feature of this turbine tip is the geometry, which includes a tapered tip and a plurality of helical rifles, consisting of either grooves or ridges, beginning at the tip of the field point and spiraling back towards the aft end. All rifles spiral in the same rotational direction giving the appearance of a turbine. This turbine tip design provides excellent rotation of the arrow shaft during flight without producing a large amount of aerodynamic drag. The invention is compatible with all contemporary arrow shafts and with all contemporary broadhead assemblies. A novel broadhead assembly utilizing the turbine tip and deployable blades to produce axial rotation is also described.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the field of archery. Specifically, the invention relates to arrowheads found on arrow devices.  
         [0003]     2. Description of the Prior Art  
         [0004]     Arrowheads and their associated aerodynamics are a key element for predictable flight of arrow assemblies. Prior art arrowheads can be broadly divided into two groups: those with little or no aerodynamic effect, such as the common field point, and those that do have a pronounced aerodynamic effect, whether intended or not, such as broadhead arrowheads.  
         [0005]     Field point arrowheads are very simple devices that are commonly used for target practice. Field point arrowheads taper from a maximum diameter, equal to approximately the diameter of the arrow shaft, down to a point at the forwardmost end. Some variations of the simple field point geometry include three or four scallops in the field point surface. However these scallops are meant to provide a sharper point for penetration, not influence the aerodynamics of the arrow assembly. This simple point in all its prior art embodiments disturbs the air very little as the arrow assembly flies towards its intended target. A considerable drawback of the prior art field point is that the arrow assembly flight is governed entirely by the aerodynamics of the vanes at the aft end of the arrow. The arrow is essentially pushed through the air. This pushing can cause the flight path of the arrow to wander as the arrow is affected by random influences such as crosswind, oscillating vibration of the arrow shaft, and asymmetries between the arrow vanes. What the prior art lacks is a field point that is itself capable of stabilizing the flight of the arrow assembly.  
         [0006]     Broadhead arrowheads were invented to increase effective hunting penetration and success potential. Typically two to four flat, triangular blades are arranged around the forward pointed tip. As the arrowhead enters the intended target, the blades slice a region much greater than a simple field point and increase the probability of inflicting mortal damage upon the intended target. These broad, flat blades have a pronounced aerodynamic effect that can radically affect the overall stability of the arrow in flight and significantly reduce the precision of flight. The forwardmost tip of such broadheads is typically either the flat blade itself, such as in the patents of Newnam (U.S Pat. No. 5,636,845) or Musacchia (U.S. Pat. No. 4,621,817); or the forwardmost tip is a field point-like cap that provides no aerodynamic effect, such as in the patents of Adams, jr. (U.S. Pat. No. 6,077,180) or Martinez, et. al. (U.S. Pat. No. 6,319,161). One recent improvement is the broadhead of Kuhn (U.S. Pat. No. 6,663,518) which employs blades whose geometry imparts an axial rotational spin on the arrow assembly during flight. However, the forwardmost tip of this broadhead is still basically a field point.  
         [0007]     Mechanical broadhead arrowheads were developed to address problems associated with traditional bladed broadheads. Mechanical broadheads include deployable bladed or spiny bleeder appendages that remain closely attached to the main body of the arrowhead from release until impact. This reduces the overall aerodynamic effect of large, bladed structures during flight. Upon deployment, such appendages provide greater cutting surfaces and or means for lodging within the wounded target than a simple flat blade. Again, the forwardmost tip of such prior art broadheads is typically a field point-like cap, such as in the patents of Liechty, II (U.S. Pat. No. 6,171,206) and Maleski (U.S. Pat. No. 6,217,467), which provides no aerodynamic effect.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is a turbine tip arrowhead, used either strictly as a field point or as the forwardmost tip in concert with any prior art broadhead assembly. The key feature of this turbine tip arrowhead is the geometry, which includes a tapered tip and a plurality of helical rifles, consisting of either grooves or ridges, beginning at the tip of the field point and spiraling back towards the aft end. All rifles spiral in the same rotational direction giving the appearance of a turbine. This turbine tip design provides excellent rotation of the arrow shaft during flight without producing a large amount of aerodynamic drag. The invention is compatible with all contemporary arrow shafts.  
         [0009]     When used as a replacement for the common field tip-like caps found on prior art broadhead assemblies, the turbine tip of the present invention again provides stabilizing, axial rotation of the arrow regardless of whether or not the broadhead main blades provide any axial rotation themselves. The rifling also inflicts additional damage while augering into the target upon impact. The invention is compatible with all contemporary broadhead assemblies.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows an oblique view of the rifled turbine tip arrowhead of the present invention.  
         [0011]      FIG. 2  shows an exploded view of the rifled turbine tip arrowhead of the present invention used in concert with a mechanical broadhead arrowhead.  
         [0012]      FIG. 3  shows a side view of the rifled turbine tip of the present invention used in concert with a mechanical broadhead arrowhead in the closed position.  
         [0013]      FIG. 4  shows a front and sectional view of the rifled turbine tip of the present invention used in concert with a mechanical broadhead arrowhead.  
         [0014]      FIG. 5A  shows an oblique view of the rifled turbine tip of the present invention used in concert with a mechanical broadhead arrowhead in the closed position.  
         [0015]      FIG. 5B  shows an oblique view of the rifled turbine tip of the present invention used in concert with a mechanical broadhead arrowhead in the open position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     With reference to  FIG. 1 , field point  1  of this invention comprises a typically cylindrical body  2  with a maximum diameter approximately equal to the maximum diameter of an arrow shaft. Body  2  is typically symmetrical about a longitudinal axis. A portion of body  2  tapers to a point  3  at one end. A plurality of helical rifles  4 , consisting of either grooves or ridges, begin at point  3  of the field point  1  and spiral down the longitudinal axis of body  2 . Rifles  4  may spiral down the entire axial length of body  2  or may terminate partially down a portion of the axial length of body  2 . All rifles  4  spiral in the same rotational direction giving the appearance of a turbine. In the preferred embodiment, rifles  4  are placed close together around body  2  so that they contact each other down their entire helical length.  
         [0017]     In the preferred embodiment there are between about three and about ten rifles  4  located symmetrically about the longitudinal axis of body  2 . There are optimally about eight rifles  4  located symmetrically about the longitudinal axis of body  2 . Too few rifles  4  will not provide enough rotational torque to produce the desired axial flow turbine aerodynamic effect. Too many rifles  4  must be so narrow or small that their aerodynamic effect becomes inconsequential as their aggregate surface approaches that of a smooth field point.  
         [0018]     Rifles  4  are defined as grooves if the maximum diameter of the rifled portion of body  2  does not exceed the nominal maximum diameter of body  2 . In other words, body  2  is tapered continuously from aft to point  3  and rifles  4  are cut into this otherwise smoothly tapered point. Rifles  4  are defined as ridges if the maximum diameter of the rifled portion of body  2  exceeds the nominal maximum diameter of body  2 . Typically, rifles  4  will be V-shaped in cross section although other geometries would be obvious to one of ordinary skill in the art.  
         [0019]     Field point  1  also includes an attachment means  5  used to mount field point  1  on a contemporary arrow shaft. Typically, attachment means  5  comprises a male-threaded post that is received by a female-threaded socket in the arrow shaft. However, attachment to an arrow shaft may comprise any method common in the art such as a press-fitting or gluing. In these embodiments, attachment means  5  of field point  1  may be a smooth socket or other means for mechanical engagement of the arrow shaft. Field point  1  may be made of any suitable material, such as, but not limited to, steel, aluminum, plastic, etc.  
         [0020]     One of the features of the field point arrowhead of this invention is its ability to produce stabilized arrow flight without the use of fletching or tail fins (or feathers). The rotation induced in the arrow by the aerodynamically designed turbine tip is sufficient to stabilize the arrow in flight. Eliminating or reducing the size of the fletching in fact improves flight characteristics because the rotational drag normally induced by the fletching is avoided. It should be noted, however, that all embodiments of the arrowhead of the invention can be used with fletched arrow shafts as well.  
         [0021]     The standalone point described above may be used in concert with any conventional broadhead. A conventional broadhead, as broadly defined, includes a ferrule, at least one blade coupled to the ferrule, a means for attachment of the broadhead to an arrow shaft, and a tip. In such a case, the cylindrical, pointed tip common on many contemporary broadheads is replaced by a tip having the same rifled geometry as the standalone point of the present invention.  
         [0022]     One such novel broadhead, incorporating the turbine tip of the present invention, is described in  FIGS. 2 through 5 B, broadhead arrowhead assembly  100  includes a rifled tip  101  as an alternate embodiment of the invention. Analogous to the stand-alone field point  1 , tip  101  is typically cylindrical in geometry with a maximum diameter at its aft end  104  approximately equal to the mating diameter of the first end portion  108  of broadhead body  107 . A portion of tip  101  tapers to a point  102  at one end. A plurality of helical rifles  103 , consisting of either grooves or ridges, begin at point  102  of tip  101  and spiral down the longitudinal axis of tip  101 . Rifles  103  may spiral down the entire axial length of tip  101  or may terminate partially down the axial length of tip  101 . All rifles  103  spiral in the same rotational direction giving the appearance of a turbine. In the preferred embodiment, rifles  103  are placed close together around tip  101  so that they contact each other down their entire helical length. The aft end  104  of tip  101  includes a smooth, hollow socket capable of accepting a tensioner  105  and capable of fitting over part of first end portion  108  in an integral assembly. Mating surfaces of aft end  104  and first end portion  108  may be assembled by press-fitting, swaging, gluing, by complementary threads on the mating surfaces, or by any other means common in the art.  
         [0023]     Broadhead arrowhead  100  further comprises a body or ferrule  107 . At a first, or proximal, end, ferrule  107  incorporates a first end portion  108 . First end portion  108  typically tapers to a reduced diameter at its most proximal end. Ferrule  107  also has a second, or distal, end portion  113 . Second end portion  113  is of reduced diameter so that it may fit within the hollow end of a conventional arrow shaft. The aft portion of ferrule  107  may be slightly flared outwardly. It is not necessary that the aft portion of ferrule  107  be flared outwardly, however. As shown in the embodiment of  FIGS. 2 through 5 B, the aft portion of body  107  may continue substantially straight along its length until the reduced diameter of second end portion  113 . Ferrule  107  is typically symmetrical about a longitudinal axis between first end portion  108  and second end portion  113 . Arrowhead body  107  may be made of any suitable material, such as, but not limited to, steel, aluminum, plastic, etc.  
         [0024]     A mounting stub  114  extends rearwardly from second end portion  113  of arrowhead body  107 . Typically, stub  114  is symmetrical about and coaxial with a longitudinal axis. Mounting stub  114 , along with second end  113 , is intended to fit into a mating recess typically located at one end of a standard arrow shaft. Stub  114  may be threaded to mate with matching threads in the arrow shaft recess or it may be seated in the recess in a press fit arrangement. Alternatively, mounting stub  114  may be glued or otherwise sealed into the mating recess of the arrow shaft.  
         [0025]     In other variations of mounting means, instead of a stub  114 , second end  113  of body  107  may be of diameter equal to or greater than that of an arrow shaft. Second end  113  may then be hollowed out to fit over said arrow shaft. In such an arrangement, the inside of hollow second end  113  may be threaded to mate with threads on the outer surface of the arrow shaft; or distal second end  113  may be press fit over the arrow shaft. Alternatively, second end  113  may be fitted over the end of the arrow shaft and glued or otherwise sealed to the arrow shaft.  
         [0026]     A second key feature of broadhead arrowhead  100  is the inclusion of mechanically deployable blades  121  including an inertial trigger mechanism that both inhibits premature deployment during release and flight yet also facilitates deployment during impact with the intended target. Such a trigger is also found in the pending application of Kuhn (U.S. patent application Ser. No. 10/766,664). Each deployable blade  121  comprises an elongated third blade portion  123  that is sharpened on the side adjacent to body  107  when in the closed position. Integral to a first end of third blade portion  123  is a semi-circular, cam-shaped fourth blade portion  120 . Integral to a second end of third blade portion  123  is a flag-shaped fifth blade portion  124 . Fifth blade portion  124  comprises between about  20 % and  50 % of the total length of deployable blade  121 .  
         [0027]     Both elongated third blade portion  123  and integral cam-shaped fourth blade portion  120  are disposed in a plane at least substantially parallel to a longitudinal axis of body  107 . Flag-shaped fifth blade portion  124  extends from third blade portion  123  at an angle thereto. Fifth blade portion  124  is preferably continuously curved, with a radius of curvature optimally between about 0.2″ and 0.5″, giving the blade the characteristics of an airfoil. The radius of curvature may vary over the surface of the blade. In the preferred embodiment, fifth blade portion  124  curves out of the plane of third blade portion  123  at a constant radius of curvature. The resultant leading edge region of fifth blade portion  124  is disposed at an angle to body  107  and also at an angle to third blade portion  123 . This angle may be as great as 45 degrees or more, but optimally it is the range between approximately 5 and 5 degrees and most optimally in the range between approximately 5 and 25 degrees. In the closed position, fifth blade portion  124  resembles a swept forward wing.  
         [0028]     Broadhead assembly  100  includes at least one associated deployable blade  121  and preferably three deployable blades  121 . Cam-shaped fourth blade portion  120  fits into a deployable blade slot  110 , which is cut into the side of ferrule body  107 . Deployable blade slot  110  is substantially coplanar with a longitudinal axis of body  107  and is of a depth and geometry that permits deployable blade  121  to rotate freely about a pivot shaft  112  between the open position and the closed position as shown particularly in  FIG. 5A  and  FIG. 5B . In the preferred embodiment, pivot shaft  112  is a removable screw that permits easy replacement of deployable blade  121 . Pivot shaft  112  is preferably perpendicular to the major plane of cam-shaped fourth blade portion  120 . Deployable blades  121  and pivot screws  112  may be made of any suitable material, such as, but not limited to, steel, aluminum, plastic, etc.  
         [0029]     As shown in the preferred embodiment in  FIG. 4 , deployable blade slots  110  and their associated deployable blades  121  are preferrably disposed substantially symmetrically around body  107  at an angle θ from each other when broadhead assembly  101  is viewed from the front.  
         [0030]     Each of the fifth blade assembly portions  124  are angled out of the plane of their respective third blade portion  123  in the same rotational direction as shown in  FIG. 4 . Fifth portions  124  of deployable blades  121 , acting together with rifles  103  of tip  101 , form an axial-flow turbine. It will be understood by those skilled in the art that all rifles  103  and fifth blade assembly portions  124  are preferably angled in the same rotational direction to promote stable flight.  
         [0031]      FIG. 4  shows rifles  103  and fifth portions  124  of deployable blades  121  angled clockwise when viewed from the front. Alternatively, rifles  103  and fifth portions  124  of deployable blades  121  can be angled counterclockwise when viewed from the front.  
         [0032]     Ferrule  107  further comprises an inertial trigger mechanism that both inhibits premature deployment of deployable blades  121  during release and flight, yet also promotes deployment of deployable blades  121  during impact with a target. Cylindrical cavity  109  begins at the leading face of the first end  108  of body  107  and continues down the longitudinal axis of body  107  to a depth approximately equal to the location of pivot shafts  112 . The diameter of cylindrical cavity  109  is preferably in the range of 20% and 80% of the diameter of tip  101  and most preferably in the range of 25% and 50% of the diameter of tip  101 . Cylindrical cavity  109  is symmetrical about the longitudinal axis of body  107 .  
         [0033]     Trigger  106  comprises a solid cylinder of outer diameter slightly less than the inner diameter of cylindrical cavity  109  such that trigger  106  can slide freely within cylindrical cavity  109  without binding or becoming cocked. Trigger  106  includes a trailing surface that interfaces with ledges  122  on both cam-shaped fourth blade portions  120  when deployable blades  121  are in the closed position. In the preferred embodiment, trigger  106  is a normal, right cylinder with walls perpendicular to its flat trailing surface. In this embodiment, ledges  122  are also flat so that they contact trigger  106  along their entire length when deployable blades  121  are rotated into the closed position. Trigger  106  may be made of any suitable material, such as, but not limited to, steel, aluminum, plastic, etc. Trigger  106  may also be coated with a lubricant, such as graphite, silicone oil, mineral oil, polytetrafluoroethylene, etc., in order to inhibit friction or binding along the inner surface of cylindrical cavity  109 .  
         [0034]     A mechanical tensioner  105  is located between the leading face of trigger  106  and the socketed aft end  104  of tip  101  and within cylindrical cavity  109 . When tip  101  is integrated into broadhead assembly  100 , the socketed aft end  104  of tip  101  compresses tensioner  105 , which in turn urges trigger  106  in the aft direction and down upon ledges  122  of deployable blades  121 . Tensioner  105  may comprise a coiled spring, a plug of reversibly compressible material, such as solid silicone, a collapsible volume filled with a compressible fluid, or any other means for storing mechanical energy that would be apparent to one of ordinary skill in the art.  
         [0035]     During release and flight, inertial forces act to relieve compression on tensioner  105 , thereby further urging trigger  106  in the aft direction and firmly retaining deployable blades  121  in the closed position by pressing firmly upon ledges  122 . In the closed position, third blade portions  123  of deployable blades  121  are in close contact with the sides of ferrule body  107 . Flag-shaped fifth blade portions  124  are disposed at angles laterally outward away from the sides of body  107 .  
         [0036]     During impact, flag-shaped fifth portions  124  of deployable blades  121  are forced laterally outward by contact with the surface of the target. At the same time, as rapid deceleration of the broadhead is occurring, trigger  106  is urged forward away from ledges  122  thereby compressing tensioner  105 . The combination of torque applied by fifth blade portions  124  contact with the target and relieved rearward pressure applied by trigger  106  permits deployable blades  121  to overcome the engagement between ledges  122  and trigger  106  and rotate about pivot screws  112  toward the rear as shown in  FIG. 4  and  FIG. 5B .  
         [0037]     The angle of deployment is limited by eventual contact between deployable blades  121  with ring  115 . In the preferred embodiment, the maximum angle of deployment for blades  121  is preferably in the range of approximately 90 degrees and 170 degrees and more preferably in the range of approximately 100 degrees and 135 degrees as measured from the closed position. In the closed position, third blade portions  123  lie alongside body  107  and parallel to the longitudinal axis of body  107 .  
         [0038]     In the embodiment shown, ring  115  comprises a flat, annular device with an inner diameter equal to the outer diameter of second end  113  of body  107  and an outer diameter equal to the outer diameter of body  107 . Ring  115  is placed over second end  113  prior to attaching second end  113  to an arrow shaft. Alternatively, ring  115  can be mechanically attached to body  107  by any means common in the art such as welding or adhesive bonding. Ring  115  may also be integrally formed along with body  107 . Ring  115  may be made from any material such as steel, aluminum, plastic, etc., although metal is used in the preferred embodiment.  
         [0039]     One of the features of the arrowhead of this invention is its ability to produce stabilized arrow flight without the use of fletching or tail fins (or feathers). The rotation induced in the arrow by the aerodynamically designed turbine tip used in combination with the deployable blades is sufficient to stabilize the arrow in flight. Eliminating or reducing the size of the fletching in fact improves flight characteristics because the rotational drag normally induced by the fletching is avoided. It should be noted, however, that all embodiments of the arrowhead of the invention can be used with all fletched arrow shafts as well.  
         [0040]     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.