Patent Publication Number: US-7713152-B1

Title: Arrowhead with unfolding blades

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority under 35 USC §119(e) to U.S. Provisional Patent Application 60/877,256 filed 26 Dec. 2006 and to U.S. Provisional Patent Application 60/950,449 filed 18 Jul. 2007, the entireties of which are incorporated by reference herein. 

   FIELD OF THE INVENTION 
   This document concerns an invention relating generally to arrowheads used in archery, and more specifically to broadhead-type arrowheads wherein one or more blades extend outwardly from the body of the arrowhead. Even more specifically, the invention relates to broadhead-type arrowheads wherein one or more blades may unfold from the arrowhead (commonly known as “expandable broadheads” or “mechanical broadheads”). 
   BACKGROUND OF THE INVENTION 
   When bowhunters hunt game animals, they seek to hit their targets in such a manner that maximum trauma is inflicted upon their first shot (i.e., so that the first shot is a “killing shot”), since there may not be a chance for a second shot. In those cases where the first shot does not immediately critically wound and bring down the animal, it is at least desirable to have the arrow inflict sufficient trauma that heavy bleeding results, thereby resulting in relatively rapid death via loss of blood, as well as a blood trail which the hunter may follow to retrieve the animal. Otherwise, if the animal is only marginally injured, it may undergo prolonged suffering and may lack the ability to fend for itself in the wild—outcomes which most hunters and conservationists frown upon. 
   In order to maximize trauma, bowhunters often hunt game animals with broadhead-type arrowheads, that is, arrowheads which bear one or more blades extending laterally outwardly from the arrowhead and its trailing arrow shaft. This is in contrast to arrowheads used for recreational archery, which generally have a simple conical/pointed shape with no laterally-extending protrusions. The objective of a broadhead is to increase the effective area of the arrowhead which strikes the target animal, thereby enhancing the size of the inflicted wound and the lethality of the arrow. 
   However, broadheads suffer from the disadvantage that they are more likely to cause undesirable off-trajectory arrow flight than simple conical arrowheads. Since the blades extending outwardly from the broadhead effectively act as forward fletchings or “wings” on the arrow, even minor misalignments and/or other imperfections in one or more blades can cause an arrow to veer from its intended course. Additionally, the blades also make an arrow more susceptible to being blown off course by wind currents, since the blades can effectively define wind-catching “sails” on the broadhead. 
   As a result of the flight inaccuracies demonstrated by broadheads, the development of new broadheads has generally followed two paths. A first path involves “fixed-blade” broadheads, wherein the blades are immovably affixed to the arrowhead. These blades are usually designed to extend only a slight distance laterally outwardly from the arrowhead so as to reduce the aerodynamic effect of the blades. A second path involves “expandable” or “mechanical” broadheads, wherein movable blades affixed to the arrowhead are situated in a closed state close to the arrowhead and shaft when launched, but the blades subsequently move outwardly from the arrowhead during flight (preferably late in their flight) or upon striking a target. In the expandable/mechanical broadhead, the blades in their open state may extend further laterally outwardly from the arrowhead than in a fixed-blade broadhead because the blades, being closed for (preferably) most or all of the arrow flight, have lesser effect on arrow trajectory. Stated differently, by reducing the forwardly-facing blade surface area which is exposed during flight of the arrow, and then maximizing this area during or near impact, the expandable/mechanical broadhead seeks to avoid misflight while maximizing lethality. 
   Despite the foregoing, many prior expandable/mechanical broadheads carry their own unique disadvantages. Several expandable/mechanical broadheads operate by using restraining members (such as rubber O-rings) to hold their blades in place during flight, with the restraining member then being cut or otherwise ejected from the arrowhead at or near impact. The loss of the restraining member then allows the blades to spring open. Such broadheads are inconvenient and/or expensive to use because they require that a hunter obtain and carry a supply of restraining members—which are usually small in size, and easily lost—in order to make continued use of the broadheads in the field. In general, broadheads which do not require any O-rings or other sacrificial members are more conveniently used in the field. 
   Other expandable/mechanical broadheads require that the blades contact the target animal to open the blades. For example, several broadheads incorporate levers on the frontward/leading sides of the blades whereby the levers, upon contact with the target game, are to urge the blades into their open/unfolded state. Such broadheads can be problematic because some blades may contact the target, animal (and thereby open) before others, which can then cause the arrow to deviate from its intended trajectory. Additionally or alternatively, certain blades may open after entry rather than upon entry, thereby causing the entry wound size to be less than it would be had all blades been open upon entry. Further, some blades may be entirely prevented from opening if they are buried in tissue before their levers or other blade-triggering structures are subjected to sufficient opening force. Many of these broadhead designs also require that the levers or other blade-triggering structures be blunt, since a sharp triggering structure may simply penetrate the animal without encountering sufficient tissue resistance that it triggers the opening of the blade(s). These blunt structures can undesirably slow the arrow to such a degree that even if the blades open and a large entry wound is generated, it will not be sufficiently deep to lethally impair the animal. 
   More fundamentally, to expand on issues noted above, many expandable/mechanical broadheads suffer from the disadvantage that the blades are triggered to their open/unfolded state at a less than optimal time—either during flight, or after the blades have entered the animal. As previously noted, blades which are open during flight can cause undesirable arrow trajectory variations. As for blades which open after entry, while these may cause significant internal bleeding and other internal damage, the entry wound itself may be of small size, and it may be effectively “plugged” by the arrow shaft. The smaller entry wound (and the arrow stopping the wound) can inhibit blood loss and potentially allow the animal to flee for long distances before it expires. 
   Another problem experienced by some expandable/mechanical broadheads is the blades may be triggered to open/unfold upon impact and entry with a target animal, but they may then retract to their closed/folded state if the arrow is pulled rearwardly (i.e., the blades open when moving forwardly into a target, but then close when moving in reverse). Such broadheads can be advantageous insofar as they allow easier arrow removal by hunters, but they can be disadvantageous in that the arrows can more easily fall from, or be pulled from, the animal as it flees. An arrow that falls out may allow the animal to more readily bleed out, but it is usually desirable to have the arrow remain in place within the target animal because animals are generally less likely to flee (or to flee as far) when the arrow remains in place. 
   Another problem with many expandable/mechanical broadheads is their ease of preparation. As previously noted, some require the pre-firing installation of O-rings or other consumables to restrain the blades in a closed state until a time at or near impact, and the need to install such consumables can be inconvenient, particularly where a hunter has limited time to prepare an arrow for firing. Many broadheads also or alternatively require the user to grasp and manipulate the blades to place the broadhead in a firing condition, e.g., the user may need to grasp the blades and fold them into the closed state. These arrangements often result in finger cuts, which in turn cause difficulties with bow operation. 
   SUMMARY OF THE INVENTION 
   The invention involves an arrowhead which is intended to at least partially solve the aforementioned problems. To give the reader a basic understanding of some of the advantageous features of the invention, following is a brief summary of preferred versions of the arrowhead, with reference being made to the accompanying drawings to enhance the reader&#39;s understanding. Since this is merely a summary, it should be understood that more details regarding the preferred versions may be found in the Detailed Description set forth elsewhere in this document. The claims set forth at the end of this document then define the various versions of the invention in which exclusive rights are secured. 
   Referring to the exemplary arrowhead depicted in  FIGS. 1A-1D  at the reference numeral  100 , the arrowhead  100  includes a tip  102 , a body  104  extending rearwardly from the tip  102  and terminating in a tail end  106  adapted to mount to an arrow shaft (such a shaft not being shown), and one or more blades  108  on the body  104  which each have a pivot end  110  about which the blade  108  pivots with respect to the body  104 . Here, the arrowhead  100  is shown with three blades  108 , though more or less are possible. Each blade  108  is then pivotable about its pivot end  110  between an open state wherein the blade  108  is folded outwardly from the body  104  (see  FIGS. 1C-1D ) and a closed state wherein the blade  108  is folded inwardly to rest closer to the body  104  (see  FIGS. 1A-1B ). As best seen in  FIGS. 1B and 1D , an actuating member  112 —here provided in the form of a shaft with a protruding nub  114  of lesser diameter, though the actuating member  112  might take other forms—extends rearwardly from the tip  102 , and into the interior of the body  104 . This actuating member  112  is movable within and along the length of the body  104  such that it may travel rearwardly from the position shown in  FIGS. 1A-1B  —wherein the tip  102  and actuating member  112  are in an extended in-flight position, prior to impact with a target—to the position shown in  FIGS. 1C-1D , wherein the tip  102  (and thus the actuating member  112 ) is urged rearwardly within the body  104  upon the impact of the tip  102  with a target. As best seen from a comparison of  FIGS. 1B and 1D , when the actuating member  112  is urged rearwardly into the interior of the body  104 , it urges against the blade pivot ends  110  to move the blades  108  from their closed state ( FIG. 1B ) to their open state ( FIG. 1D ), and thus the blades  108  unfold in the moment after the impact of the tip  102  to increase the cutting area of the arrowhead  100 . 
   First and second springs  116  and  118  are seen in  FIGS. 1B and 1D , wherein only the cross-section of the second spring  118  is visible. The second spring  118  acts as a latching spring when the arrowhead  100  is in its in-flight closed state ( FIGS. 1A-1B ), biasing the blades  108  with respect to the body  104  to urge the blades  108  toward the closed state. More particularly, the latching spring  118  acts against a camming surface  120  on the pivot end  110  of each blade  108 , wherein the camming surface  120  is contoured to store energy within the second/latching spring  118  when the blade  108  is in the open state, and to relieve energy stored within the second/latching spring  118  when the blade  108  is in the closed state. The latching spring  118  thereby attempts to close the blades  108 . In contrast, the first spring  116  constantly biases the actuating member  112  rearwardly with respect to the body  104  to urge the actuating member  112  rearwardly into the interior of the body  104 , and therefore against the pivot ends  110  of the blades  108 , to urge the blades  108  toward the open state. However, the first spring  116 —which may be regarded as a blade opening spring—is defeated by the action of the latching spring  118  until the actuating member  112  begins to move rearwardly owing to impact forces on the tip  102 , at which point the opening spring  116  assists the actuating member  112  in defeating the latching spring  118  and opening the blades  108 . The opening spring  116  therefore plays only a minor role in opening the blades  108 , but it is nonetheless useful in maintaining the actuating member  112  against the pivot ends  110  of the blades  108  when the blades  108  are in their closed state (see  FIG. 1B ), and preventing the actuating member  112  from sliding forwardly within the body  104  and out of contact with the blade pivot ends  110 . 
   The exemplary arrowhead  100  of  FIGS. 1A-1D  has the useful feature that once the blades  108  are in the open state ( FIGS. 1C-1D ), they are fixed in the open state such that forces exerted on the blades  108  cannot pivot the blades  108  back into the closed state ( FIGS. 1A-1B ), whereby the blades  108  may only pivot into the closed state by movement of the actuating member  112  (e.g., by a user pulling the tip  102  forwardly from the closed state of  FIGS. 1A-1B  to the open state of  FIGS. 1C-1D , so that the latching spring  118  acts to close the blades  108 ). Stated differently, the blades  108  are only moved from the closed state to the opened state by movement of the actuating member  112  in response to forces acting rearwardly on the tip  102  (e.g., impact forces on the tip  102 ), and conversely the blades  108  are only moved from the opened state to the closed state by movement of the actuating member  112  in response to forces acting forwardly on the tip  102  (e.g., forward actuation of the tip  102  by the user). Preferably, this is achieved by having the rearward face  122  of the actuating member  112  (and more specifically, its nub  114 ) bear against the blades  108  (more specifically, against protruding ears  124  on the blade pivot ends  110 ) when the blades  108  are in the closed state (see  FIG. 1B ). When the tip  102  and actuating member  112  are moved rearwardly, as in response to tip impact (and with the assistance of the opening spring  116 ), the actuating member  112  moves rearwardly to more fully rest between the blades  108  (see  FIG. 1D ), with the nub  114  of the actuating member  112  resting between the blade ears  124  and with the latching spring  118  urging the blades  108  and their ears  124  against the circumference of the actuating member  112  and its nub  114 . As a result, the actuating member  112  prevents the blades  108  from rotating to the closed state. When the tip  102  and actuating member  112  are moved forwardly, as by having a user pull the tip  102  forwardly, the nub  114  withdraws from between the blade ears  124  to allow the latching spring  118  to urge the blades  108  into the closed state. 
   In the foregoing arrangement, the resistances (spring constants) of the opening spring  116  and latching spring  118  are chosen to provide the desired opening force (the force needed on the tip  102  to move the blades  108  from the closed state to the opening state), as well as the desired closing force needed to move the tip  102  and actuating member  112  forwardly to close the blades  108 . To some degree, the springs  116  and  118  counteract each others&#39; actions, with the opening spring  116  compressing as the latching spring  118  extends ( FIG. 1B ), and the latching spring  118  compressing as the opening spring  116  extends ( FIG. 1D ). Preferably, the springs  116  and  118  are chosen to require between approximately 6 and 48 ounces of force on the tip  102  before the latching spring  118  yields and allows the actuating member  112  to urge the blades  108  into the open state. 
   The foregoing arrangement is preferably used in conjunction with a preferred tip structure, exemplified in  FIGS. 1A-1D . The tip  102  extends rearwardly from a leading edge  126 , and includes one or more penetrating surfaces  128  which slope outwardly with respect to the axis of the tip  102  as these penetrating surfaces  128  extend rearwardly. The leading edge  126  and penetrating surfaces  128  are intended to initiate and expand an entry wound as the tip  102  penetrates target game. One or more collecting surfaces  130  are then provided which are forwardly exposed on the tip  102  (i.e., at least a portion of the collecting surfaces  130  is situated such that it will directly impact the tissue of the target game about the entry wound during entry), with these collecting surfaces  130  being oriented at least substantially perpendicular to the axis of the tip  102 , and/or being concave with respect to a plane perpendicular to the axis of the tip  102 . In  FIGS. 1A-1D , these collecting surfaces  130  are provided by concave areas defined between the outer perimeter of a cylindrical tip base  132  and a tetrahedral tip head  134 . These collecting surfaces  130  are intended to collect tissue, such that tissue “piles up” behind the collecting surfaces  130  during entry, and so that the collecting surfaces  130  move the tissue forwardly in front of the tip  102  such that an entry wound cannot easily reclose. This effect expands the size of the entry wound, and also helps to generate sufficient rearward force on the actuating member  112  that it almost immediately actuates the blades  108  into their open state upon tip impact (more specifically upon impact of the collecting surfaces  130 ). The collecting surfaces  130  thereby help to fully open the blades  108  before they enter the target game rather than thereafter, and thereby maximize debilitating trauma. 
   Another preferred feature of the tip  102  is to make it “finger-safe” so that a user may grasp it and pull it forwardly to move the blades  108  into the closed state without experiencing finger injury. One way to achieve this is to have the tip  102 , at its region of greatest circumference (in  FIGS. 1A-1D , at the cylindrical tip base  132 ), lack any edges which are sufficiently sharp to cut a user&#39;s finger when grasped by a user. Such an arrangement may be achieved by having a large continuous graspable surface oriented at least substantially parallel to the axis extending through the tip  102  and body  104 . For example, if the tip  102  is regarded as a set of continuous surfaces (e.g., the “facets” of the tip base  132  and head  134 ) bounded by edges, at least one of the continuous surfaces should extend both rearwardly and circumferentially, be aligned at least substantially parallel to the axis extending through the tip  102 , and should have an area which is preferably greater than or equal to at least one-third of the largest continuous surface included on the tip  102 . In the tip  102  of  FIGS. 1A-1D , these conditions are satisfied by the outer perimeter of the tip base  132 . 
   Further advantages, features, purposes, and uses of the invention will be apparent from the remainder of this document in conjunction with the associated drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a perspective view of a first preferred version of an arrowhead  100  which exemplifies concepts of the invention, with the arrowhead  100  having a leading tip  102  having an actuating member  112  extending rearwardly into an arrowhead body  104 , with the body bearing three blades  108  spaced at equal angles about the axis of the arrowhead  100  (one blade  108  having an edge visible in the foreground, and the other two blades being partially shown in the background). Here the blades  108  are depicted in a closed state wherein they may pivot to an open state (seen in  FIG. 1C ) when the arrowhead tip  102  impacts a target and is driven rearwardly (along with the actuating member  112 ) toward the body  104 . 
       FIG. 1B  depicts a partial cross-sectional view of the arrowhead  100  of  FIG. 1A , wherein the body  104  (and more specifically its forward body end  140  and rearward body end  142 ), as well as its associated spring housing  150 , latching spring  118 , and latching member  160 , are all shown sectioned along planes aligned with two of the blades  108 . Here the opening spring  116  urges the actuating member  112  against blade ears  124  situated at the blade pivot ends  110  (with the blades  108  being rotatable about pivots  146 ) in an attempt to pivot the blades  108  into the open state. However, the latching spring  118  urges the blades  108  into the closed state at camming surfaces  120 , defeating the efforts of the opening spring  116 . 
       FIG. 1C  is a perspective view of the arrowhead  100  of  FIGS. 1A and 1B  wherein the arrowhead tip  102  has been driven rearwardly to urge the actuating member  112  into the body  104 , thereby defeating the latching spring  118  of  FIG. 1B  and urging the blades  108  into an open state. 
       FIG. 1D  is a partial cross-sectional view similar to that of  FIG. 1B , but wherein the arrowhead  100  is shown with its blades  108  in the open state, as in  FIG. 1C . 
       FIG. 2A  is a partial cross-sectional view of a second preferred version of an arrowhead  200  which also exemplifies concepts of the invention, wherein its blades  208  are shown in a closed state (similarly to the arrowhead  100  of  FIG. 1B ). Here the latching spring  218  is situated within the rearward body end  242 , unlike the arrowhead  100  of  FIG. 1B , wherein the latching spring  118  is situated within the forward body end  140 . 
       FIG. 2B  is a partial cross-sectional view of the arrowhead  200  of  FIG. 2A , wherein the actuating member  212  has been driven rearwardly from impact of the tip  202  with a target, thereby defeating the latching spring  218  and urging the blades  208  into an open state. 
       FIG. 3A  is a partial cross-sectional view of a third preferred version of an arrowhead  300  which also exemplifies concepts of the invention, wherein its blades  308  are shown in a closed state (similarly to the arrowhead  100  of  FIG. 1B  and the arrowhead  200  of  FIG. 2A ). Here an actuating member  312  may be urged rearwardly by impact forces on a tip  302  (and also by the force of an opening spring  316 ) to defeat a latching spring  318  holding the blades  308  in a closed state, and thereby move the blades  308  to an open state. At the same time, a second opening spring  374  assists in camming the blades  308  open via the action of a second actuating member  376  on second camming surfaces  380 . 
       FIG. 3B  is a partial cross-sectional view of the arrowhead  300  of  FIG. 3A , wherein the blades  308  are shown in their open state. 
   

   DETAILED DESCRIPTION OF PREFERRED VERSIONS OF THE INVENTION 
   To review the arrowhead  100  of  FIGS. 1A-1D  in greater detail, the tip  102  is preferably made removable from the actuating member  112 , as by threading or force-fitting the forward end of the actuating member  112  into a bore (not shown) defined within the tip base  132  along its central axis. This allows the tip  102  to be removed and replaced with other tips if desired, e.g., the tip  202  of  FIGS. 2A-2B  (discussed below), a conventional conical tip, or other tips. Depending on the configuration and weight (and thus the inertia) of the chosen tip, as well as the force of the bow used to launch the arrow, the springs  116  and  118  may need to be chosen to require greater rearward force on the tip before the blades  108  open. Otherwise, the inertia of the tip may cause inadvertent blade opening when the arrow is launched and the shaft of the arrow is thrust forwardly, with the inertia of the tip effectively generating a rearward force on the tip with respect to the body  104 . 
   Referring particularly to  FIGS. 1B and 1D , the actuating member  112 , which is removably or permanently affixed to the tip  102 , is preferably defined by a cylindrical intermediate shaft  136  extending rearwardly from the tip  102 , a cylindrical larger diameter land  138  extending rearwardly from the cylindrical intermediate shaft  136 , and the (cylindrical) smaller diameter nub  114  extending rearwardly from the land  138  (with all of the shaft  136 , land  138 , and nub  114  being coaxially situated along the axis extending rearwardly through the tip  102  and body  104 ). The opening spring  116  may then be fit about the shaft  136  to bear against the land  138  to thereby urge the land  138 , and thus the actuating member  112  and tip  102 , rearwardly to prevent the actuating member  112  and the tip  102  from freely sliding forwardly within the body  104  (and also to provide some assistance in the opening of the blades  108 ). If the opening spring  116  was omitted, the actuating member  112  and tip  102  could freely slide forwardly within the body  104  and “rattle” therein, which can be annoying (particularly when the arrow is being nocked and aimed). To ease in the installation of the opening spring  116 , it is useful to make the land  138  removably affixable to the shaft  136 , e.g., by threading the rearward end of the shaft  136  into an axial bore (not shown) in the land  138 . 
   Referring also particularly to  FIGS. 1B and 1D , the body  104  is then defined as a generally cylindrical member having a forward body end  140 , a rearward body end  142 , and blade slots  144  extending along the length of the body  104 . The blades  108  are then preferably pivotally mounted within the blade slots  144  at pivots  146 , e.g., threaded or unthreaded pins or other cylindrical members extending through or from the blades  108  and into the body  104  at opposing longitudinal sides of the blade slots  144 . Pin apertures  148  for receiving such pins are visible in  FIGS. 1A and 1C , wherein a pin may be inserted in one of the apertures  148  to extend into the body  104 , then into a blade slot  144  and through a blade  108  therein, and then back into the body  104  within the pin aperture  148  at the opposite side of the blade slot  144 . The forward body end  140  closely receives the land  138  of the actuating member  112  therein, such that the land  138  (and thus the actuating member  112 ) is retrained to slidably translate forwardly and rearwardly within the body  104 . 
   The forward body end  140  also preferably bears external threading whereby a spring housing  150  may be threaded onto the forward end  140 . The spring housing  150  has a forward spring housing end  152  with a shaft aperture  154  sized to closely and translatably receive the intermediate shaft  136  therein, an intermediate spring housing portion  156  which is internally threaded to allow the forward body end  140  to be threaded thereon, and a rearward spring housing portion  158  with internal steps configured to receive the latching spring  118  and a latching member  160 . This latching member  160 , shown in the form of a thrust washer having a T-shaped section, is urged by the latching spring  118  against the camming surfaces  120  of the pivot ends  110  of the blades  108 . 
   The foregoing components can be assembled into the arrangement of  FIGS. 1A-1D  by extending the intermediate shaft  136  of the actuating member  112  within the shaft aperture  154  of the spring housing  150 ; fitting the opening spring  116  about the intermediate shaft  136 , and against the forward spring housing end  152 ; threading or otherwise fitting the land  138  (and nub  114 ) on the rearward end of the intermediate shaft  136 , such that the opening spring  116  is situated between the forward spring housing end  152  and the land  138 ; fitting a forward end of the latching spring  118  within the rearward spring housing portion  158  about the actuating member  112 , and fitting the latching member  160  about the rearward end of the latching spring  118  (and also within the rearward spring housing portion  158 ); and then threading or otherwise fitting the spring housing  150  on the forward body end  140  so that the nub  114  of the actuating member  112  bears against the ears  124  of the (closed) blades  108 , and so that the latching member  160  is urged by the latching spring  118  onto the camming surfaces  120  of the (closed) blades  108 . 
   The rearward body end  142  is then preferably internally threaded or otherwise configured to receive a shaft mount  162 , which extends rearwardly to a threaded tail end  106  adapted to be threaded (or otherwise affixed) within an arrow shaft (not shown). Referring particularly to  FIGS. 1B and 1D , a section of the interior of the body  104  situated forwardly of the shaft mount  162 , and rearwardly of the pivot ends  110  of the blades  108 , is preferably left empty so that a user may insert/install packing weights within the rearward body end  142  if adaptation of the mass of the arrowhead  100  is desired. 
   The blades  108  extend from their pivot ends  110  to outer blade tips  164 , with an outer sharpened blade cutting length  166  and an inner (optionally sharpened) blade edge  168  folding closely adjacent to (or within) the rearward body end  142 . The pivot ends  110  of the blades  108  have abutment surfaces  170  (see  FIGS. 1B and 1D ) which extend inwardly toward the interior of the body  104  from the camming surfaces  120 . Owing to the placement of the ears  124  rearwardly of the pivots  146 , the space between the blades&#39; abutment surfaces  170  defines a pocket which expands to receive the actuating member  112  when the blades  108  move to the open state, with the abutment surfaces  170  receiving the land  138  of the actuating member  112  therebetween when the actuating member  112  is driven rearwardly by tip impact (see  FIG. 1D ). In similar respects, the ears  124  move from the rearward face  122  of the nub  114  to receive the outer circumference of the nub  114  therebetween when the actuating member  112  is driven rearwardly and the blades  108  move to the open state. So long as the ears  124  are urged by the latching spring  118  against the rearward face  122  of the nub  114 , the latching spring  118  assists in maintaining the actuating member  112  and tip  102  in their forwardly-extended position (as shown in  FIGS. 1A-1B ). Otherwise, once the tip  102  and actuating member  112  are urged rearwardly to situate the nub  114  between the ears  124  (and also situate the land  138  between the abutment surfaces  170 ), the blades  108  will be effectively “locked” into the open state against the closing action of the latching spring  118 , such that the blades  108  will only pivot back into the closed state once the actuating member  112  is pulled forwardly (as by the user pulling the tip  102  forwardly). The camming surfaces  120  are configured such that when the blades  108  pivot from their closed states ( FIGS. 1A-1B ) to their open states ( FIGS. 1C-1D ), the latching member  160 —which is biased against the camming surfaces  120  by the latching spring  118 , and which is configured to translate forwardly and rearwardly within the rearward spring housing portion  158 —rides outwardly along the camming surfaces  120 . At the same time, the camming surfaces  120  approach the spring housing  150  and push the latching member  160  forwardly to compress the latching spring  118 . 
   Because the actuating member  112  (and its associated intermediate shaft  136 , land  138 , and nub  114 ) are cylindrical, it (and the attached tip  102 ) may be rotated by a user about the axis of the arrowhead  100  into any desired orientation, which may be useful if a user believes that certain features of the tip  102  (e.g., the edges of the penetrating surfaces  128  of the tip head  134 ) are preferentially aligned with the blades  108 , and/or with arrow fletchings, for better aerodynamic performance. It is noted that the angular orientation of the tip  102  depicted in  FIGS. 1A-1D  is not believed to have any significant impact on flight. However, if the tip  102  was replaced with an alternative tip—e.g., one with fixed extending blades, and/or one which is configured to impart rotation to the tip upon launching the arrow—the ability to align the tip into some desired angular orientation (or the ability for the tip to freely rotate about the axis of the arrowhead  100  into an orientation of least resistance) may be useful. If rotation of the tip  102  with respect to the body  104  is regarded as being undesirable, this could be avoided, for example, by forming the actuating member  112  with a non-cylindrical cross-section (and similarly forming the interior of the body  104  with a complementarity-shaped cross section wherein the actuating member  112  may translate), so that the actuating member  112  (and its affixed tip  102 ) cannot rotate with respect to the body  104 . 
   In some cases, it may be desirable to disable the ability of the blades  108  to transition from the closed to the open state (for example, when target shooting). In this case, referring to  FIGS. 1A and 1B , a disabler (not shown)—e.g., a split ring which is preferably made of rubber or some other flexible material—can be fit onto the intermediate shaft  136  of the actuating member  112  between the tip base  132  and the body  104 . The disabler can prevent rearward motion of the tip  102  and actuating member  112  to such an extent that actuation of the blades  108  to the open state is prevented. Alternatively, if a user wishes to shoot an arrow with the blades  108  of the arrowhead  100  in the open state, the user only needs to push the tip  102  rearwardly to move the blades  108  to the open state (and lock them into this state), and the arrow may be launched thereafter. 
   In testing, the arrowhead  100  has been found to work exceedingly well. Since the springs  116  and  118  can be configured to dependably open the blades  108  only at the end of flight—i.e., immediately after the tip  102  strikes the target, with the blades  108  fully deploying to the open state before entering the target—the wound induced by the arrowhead  100  is exceedingly large, with exceedingly deep penetration by the arrowhead  100 . Wound size and penetration is believed to be enhanced by the aforementioned preferred configuration for the tip  102 . 
   Arrowheads conforming to the concepts of the invention need not take the form of the arrowhead  100 , and a wide variety of other configurations is possible. One example is shown in  FIGS. 2A-2B , which includes, as in the arrowhead  100 , a tip  202  with a rearwardly extending actuating member  212 , and a body  204  into which the actuating member  212  extends to actuate one or more blades  208  into an open state ( FIG. 2B ) from a closed state ( FIG. 2A ) when the tip  202  and actuating member  212  are driven rearwardly. However, the arrowhead  200  has several notable differences from the arrowhead  100 . 
   First, whereas the opening spring  116  of the arrowhead  100  is at least partially situated within the latching spring  118 , with both the opening spring  116  and latching spring  118  resting within the forward body end  140 , the arrowhead  200  situates the latching spring  218  within the rearward body end  242 , between the shaft mount  262  and a latching member  260  engaging the blade ears  224 . As in the arrowhead  100 , the opening spring  216  and latching spring  218  are still coaxially aligned along the axis of the arrowhead  200 . Note that since the opening spring  216  is not fit within the latching spring  218 , the body  204  and spring housing  250  might be formed with a smaller diameter than the corresponding body  104  and spring housing  150  of the arrowhead  100 . The central aperture of the latching member  260  does not encircle the opening spring  216  as does the latching member  160  of the arrowhead  100 , and instead it receives the nub  214  of the actuating member  212  when the blades  208  are in the open state. 
   Second, the tip  202  has penetrating surfaces  228  and collecting surfaces  230  as in the arrowhead  100 , but additional collecting surfaces  272  are defined within the collecting surfaces  230  (with the collecting surfaces  272  being defined at the rearward sides of notches defined at the corners of the tetrahedral tip head  234 ). 
   Another version of the invention, shown in  FIGS. 3A-3B , involves an arrowhead  300  which is similar in certain respects to the arrowheads  100  and  200 . Here, the arrowhead  300  includes an actuating member  312 , opening spring  316 , and latching spring  318  within the forward body end  340 , and these act similarly to the corresponding components in the arrowhead  100 . However, a second opening spring  374  is provided within the rearward body end  342  (similar to the latching spring  218  of the arrowhead  200 ), and it urges a second actuating member  376 —here simply provided in the form of a sphere—toward second ears  378  on the blades  308 , with the second ears  378  being located rearwardly of the first ears  324 ). Second camming surfaces  380  also extend between the second ears  378  and the inner blade edge  368 , and these second camming surfaces  380  are angled (see  FIG. 3A ) such that the spherical second actuating member  376 , as driven by the second opening spring  374 , will tend to attempt to urge the blades  308  into their open state (with the actuating member  312  and opening spring  316  simultaneously attempting to urge the blades  308  into their open state via the (first) ears  324 . As with the arrowheads  100  and  200 , the latching spring  318  is chosen with a spring force such that the first and second opening springs  316  and  374  are defeated (and blade opening is deterred) until tip impact occurs and the actuating member  312  is driven rearwardly. When this happens, the actuating member  312  urges the blades  308  open via their (first) ears  324 , and the nub  314  and land  338  of the actuating member  312  move between the ears  324  and abutment surfaces  370  of the blades  308 , to lock the blades  308  in the open state (as in the arrowhead  100 ). At the same time, the second actuating member  376 —which is urged forwardly by the second opening spring  374 , and also by its forward momentum upon target impact—assists in urging the blades  308  toward the open state, and it will move between the second camming surfaces  380  to continue forwardly past the second ears  378 , and into a pocket  382  defined between the first and second ears  324  and  378 , to also help lock the blades  308  in the open state. Note that here, the second ears  378  move in the opposite direction from the second actuating member  376 —with the second ears  378  moving rearwardly as the second actuating member  376  moves forwardly—whereas the first ears  324  move in the same direction (rearwardly) as the first actuating member  312 . The arrowhead  300  thus includes two means of urging the blades  308  toward the open state, and locking them into this state. This arrangement can be useful to further ensure near-instantaneous deployment of the blades  308  into the open state when the tip  302  impacts the target: even if the force of tip entry fails to immediately drive the actuating member  312  sufficiently far rearwardly to open the blades  308 , the second actuating member  376  may assist in opening the blades  308  so that they are fully opened before entering the target, thereby maximizing trauma. Note that the arrangement of the arrowhead  300  can be particularly useful where tips  302  are used which may not immediately generate appreciable rearward impact forces, e.g., where an elongated conical tip or other tip without collecting surfaces is used. Also note that depending on the configuration of the second ears  378  and pocket  382 , the second actuating member  376  may continue to lock the blades  308  in the open state even if the tip  302  is pulled forwardly (an action which, in the arrowheads  100  and  200 , would be sufficient to unlock the blades and move them to the closed state). Thus, it can be useful to slope the walls of the pocket  382  such that when the tip  302  and actuating member  312  are pulled forwardly, the walls of the pocket  382  will cam the second actuating member  376  rearwardly out of the pocket  382  via the force of the latching spring  318 . 
   Yet another version of the invention, one not shown in the drawings, involves an arrowhead similar to that of  FIGS. 3A-3B , but wherein the second opening spring  374  is omitted and momentum alone is used to drive the second actuating member  376  forwardly to assist with opening and locking of the blades  308 . In this case, omission of the second opening spring  374 , and use of a spherical second actuating member  376 , might allow the second actuating member  376  to freely roll and “rattle” within the rearward body end  342  as the user lifts and nocks the arrow (which is annoying and undesirable). Thus, in this case it is useful to extend the sloped second camming surfaces  380  along at least a substantial portion of the inner blade edge  368 , such that the second camming surfaces  380  and inner blade edges  368  restrain the second actuating member  376  at the rear of the rearward body end  342  and against the shaft mount  362  when the blades  308  are in the closed state. In other words, when the blades  308  are in the closed state, the second actuating member  376  is held between the second camming surfaces  380 /inner blade edges  368 , and is also held against the shaft mount  362  by the second camming surfaces  380 /inner blade edges  368 ). 
   It is emphasized that the invention encompasses a wide variety of other arrowheads other than those discussed above. As previously noted, the invention may utilize tips  102 / 202 / 302  with configurations other than those shown and described. This includes tips  102 / 202 / 302  with other than tetrahedral heads  134 , and/or cylindrical bases  132 , with or without collecting surfaces  130 / 272 , and with or without blades (these blades being distinct from those blades  108 / 208 / 308  on the arrowhead body  104 / 204 / 304 ). 
   As another example, the invention may use fewer or more blades  108 / 208 / 308 , and the blades  108 / 208 / 308  may have configurations other than those shown and described. For example, apart from having different blade lengths, widths, and/or thicknesses, blades  108 / 208 / 308  could be configured to be curved, notched/barbed, or could incorporate other design variations. Further, blades  108 / 208 / 308  (and their blade slots  144 ) need not be thin/planar, and blades  108 / 208 / 308  can take the form of any members which bear sharp edges and/or tips. Different blades  108 / 208 / 308  on the same arrowhead  100 / 200 / 300  could have different characteristics, and fixed blades might be installed on an arrowhead  100 / 200 / 300  as well as pivotable blades  108 / 208 / 308 . Additionally, while the preferred versions of the arrowheads  100 / 200 / 300  discussed above have the blades  108 / 208 / 308  pivot outwardly toward the tips  102 / 202 / 302 , blades  108 / 208 / 308  could instead or additionally unfold away from the tip  102 / 202 / 302 , rather than toward it (i.e., the pivots may be situated rearwardly on the arrowhead  100 / 200 / 300 , with the outer blade tips  164 / 264 / 364  being situated forwardly). Further, while this document describes blades  108 / 208 / 308  pivoting about “pivot ends”  110 / 210 / 310 , it should be understood that a pivot end  110 / 210 / 310  need not necessarily be directly on or adjacent to a terminal boundary of a blade  108 / 208 / 308 , i.e., a pivot end  110 / 210 / 310  can be located on an intermediate portion of the length of the blade  108 / 208 / 308  such that the blade  108 / 208 / 308  extends from opposing sides of the pivot end  110 / 210 / 310  for some distance along the length of the blade  108 / 208 / 308 . 
   The configuration of the body  104 / 204 / 304  of an arrowhead  100 / 200 / 300  may also be altered. As examples, apart from varying the length and/or internal/external diameters of the body  104 / 204 / 304 , the body  104 / 204 / 304  may have a polygonal cross-section (and the blade slots  144  may then be situated on the sides or the corners of the polygon), or another differently-shaped cross-section; the blade slots  144  (and thus the blades  108 / 208 / 308 ) may be at angles with respect to the axis of the arrowhead  100 / 200 / 300 , rather than being parallel to it; the blades  108 / 208 / 308  need not be symmetrically spaced about the perimeter of the body  104 / 204 / 304 ; and so on. 
   The various mechanisms used to effect the opening and closing of the blades  108 / 208 / 308  may also be varied. As one example, the opening spring  116 / 216 / 316  and/or latching spring  118 / 218 / 318  need not take the form of conventional helical/coil springs, and could take the form of other springs, e.g., elastomeric springs (as by forming a spring of an elastic tube or ring, an elastic plug, a rubber band, or the like); pneumatic springs (as by forming the actuating member as a piston biased by a compressible/expandable pocket of air, and/or by forming a latching spring as a toroidal or other compressible bladder), or other springs (e.g., leaf springs, cantilever springs, Belleville springs, etc.). As illustrated by a comparison of the arrowhead  300  with the arrowheads  100  and  200 , it is possible for additional springs to be incorporated, or for their roles to be changed. As an example, consider that the second opening spring  374  and second actuating member  376  of the arrowhead  300  could be reconfigured into a second latching spring and second latching member by having them take the form of the latching spring  218  and latching member  260  of the arrowhead  200 . It is notable that an opening spring  116 / 216 / 316  is not required, particularly where the actuating member  112 / 212 / 312  (more specifically its land  138 / 238 / 338  and/or nub  114 / 214 / 314 ) lock the blades  108 / 208 / 308  in the open state once the open state is achieved. As noted previously, the opening spring  116 / 216 / 316  is nonetheless useful to prevent the actuating member  112 / 212 / 312  and tip  102 / 202 / 302  from freely sliding and “rattling” within the body  104 / 204 / 304 . However, if the configuration of the actuating member  112 / 212 / 312  is changed—e.g., if the cylindrical nub  114 / 214 / 314  was replaced with a conical nub, such that the nub does not lock the blades  108 / 208 / 308  into their open state—the opening spring  116 / 216 / 316  is of greater use to help maintain the blades  108 / 208 / 308  in their open state upon and after tip impact. (The same is true if the configuration of the blades  108 / 208 / 308  is altered in certain respects, e.g., by moving the blade ears  124 / 224 / 324  forwardly of the pivot, and altering the configuration of the actuating member nub  114 / 214 / 314  and land  138 / 238 / 338 , such that the interaction of the blade pivot ends  110 / 210 / 310  and actuating member  112 / 212 / 312  does not lock the blades  108 / 208 / 308  in the open state.) The actuating member  112 / 212 / 312  may also be provided with configurations vastly different from the cylindrical shaft-like shape shown in the drawings. As examples, it may have a cross-section which is polygonal rather than circular, or might even have a more complex cross-section (e.g., it might incorporate a hollow interior and/or a side slot wherein a spring or pin might be fit); it need not have a nub  114 / 214 / 314  or other variations in its cross-section (or alternatively it could include numerous variations in its cross-section along its length); it could be formed of an articulated linkage or other interconnected parts; and so forth. 
   All other components of an arrowhead  100 / 200 / 300  can similarly undergo a variety of changes in configuration. For example, the latching member  160 / 260 / 360  can assume the form of a thrust washer having a T-shaped section (as in the arrowhead  100 ) or an L-shaped cross-section (as in the arrowheads  200  and  300 ), or it need not take the form of a thrust washer at all. To illustrate, the latching member  260  of  FIGS. 2A-2B  could take the form of a cylindrical plug which is driven by the latching spring  218  onto the blade ears  224 . As another example, the shaft mount need not take the form of the illustrated shaft mounts  162 ,  262 , and  362 , and it might bear an internal front bore into which the rearward body ends  142 ,  242 , and  342  are received, and/or it might bear an internal rear bore (rather than a threaded tail end  106 / 206 / 306 ) for receiving an arrow shaft therein, rather than being received within an arrow shaft. Other modes of attaching an arrowhead  100 / 200 / 300  to an arrow are also possible, e.g., the shaft mount  162 / 262 / 362  might be entirely eliminated, and the arrow shaft might be directly received within the rearward body end  142 / 242 / 342 . 
   It should be understood that the versions of the invention described above are merely exemplary, and the invention is not intended to be limited to these versions. Rather, the scope of rights to the invention is limited only by the claims set out below, and the invention encompasses all different versions that fall literally or equivalently within the scope of these claims.