Patent Publication Number: US-6659832-B1

Title: Boomerang for sport

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a boomerang for sport, more particularly to a boomerang made from a flat sheet material of a reduced weight so as to ensure safety. 
     2. Description of the Related Art 
     Boomerangs, which have been used for sport in recent years, are devices capable of being thrown by a user, flying in a continuous path, and returning to the point of launching. Referring to FIGS. 1 to  3 , two conventional boomerangs  5 ,  6  are shown to include two arms  51 , 52  and three arms  61 , respectively. Each arm  51 , 52 , 61  is designed to have an airfoil thickness such that, when the boomerang  5 , 6  is thrown, air flows over its leading edge  511 , 521 , 611  and its trailing edge  512 , 522 , 612  to produce a lift force according to Bernoulli&#39;s law, and the boomerang  5 , 6  continues rotation until it returns to the point of launching. As such, the boomerang  5 ,  6  is required to have a sufficient thickness in order to produce the desired lift, thereby resulting in a greater weight thereof, which in turn results in a larger flight range. Therefore, the conventional boomerangs  5 ,  6  generally cannot be used in a relatively narrow area. 
     To overcome the above problem, referring to FIGS. 4 and 5, another conventional boomerang  7  was proposed. The boomerang  7  is made from a thin plate, and is shown to include four arms  71 , each of which has two bent portions  711 , 712  so as to reduce the overall weight of the boomerang  7 . However, as the flight path of the boomerang  7  is monotonous, the boomerang  7  is not interesting to play with. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a sport boomerang which is capable of adjustable flight patterns and which has an adjustable flight range. 
     According to this invention, the boomerang is made from a flat sheet material, and includes a central body with an outer periphery surrounding a center point. The central body has top and bottom surfaces that are substantially parallel to each other and that are symmetrical relative to a horizontal plane. A plurality of interconnecting portions are integrally formed with the outer periphery of the central body, and are angularly displaced from one another about the center point. Each of the interconnecting portions extends outwardly and along a radial axis, and terminates at a boundary region. A plurality of blades are integrally and respectively formed with the interconnecting portions, and are angularly displaced from one another. Each of the blades includes leading and trailing edges which are opposed to each other in one of clockwise and counterclockwise directions when the blades are turned about an axis that is normal to the horizontal plane and that passes through the center point, and which are symmetrical relative to a middle line. Each of the blades further includes a distal end which is opposed to the boundary region along the middle line and which joins the leading and trailing edges, respectively, at leading and trailing junctures. The middle line intersects the radial axis to form an obtuse included angle therewith, which faces towards the leading edge. Each blade further includes a bent line which extends towards the distal end and which is positioned between the middle line and the trailing edge. A bent portion, which faces towards the leading edge, is defined by the bent line and the trailing edge. The bent portion forms an obtuse included angle with the horizontal plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings, in which: 
     FIG. 1 is a fragmentary perspective view of a conventional boomerang with two arms; 
     FIG. 2 is a top view of a conventional boomerang with three arms; 
     FIG. 3 is a cross-sectional view of the boomerang shown in FIG. 2, taken along lines  3 — 3  thereof; 
     FIG. 4 is a top view of a conventional boomerang with four arms; 
     FIG. 5 is a cross-sectional view of the boomerang shown in FIG. 4, taken along lines  5 — 5  thereof; 
     FIG. 6 is a top view of a preferred embodiment of a boomerang according to this invention; 
     FIG. 7 is a cross-sectional view of the boomerang shown in FIG. 6, taken along lines  7 — 7  thereof; 
     FIG. 8 is a top view illustrating the preferred embodiment in a state of flight; 
     FIG. 9 is a schematic view illustrating how the preferred embodiment is held by the thrower; and 
     FIG. 10 is a top view of another preferred embodiment of the boomerang according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 6 and 7, the preferred embodiment of a boomerang  1  according to the present invention is formed from a thin, flat sheet material of a substantially uniform thickness that is less than 2 mm, and has a single-piece construction. The boomerang  1  is shown to be throwable by a right-handed user, and comprises a central body  10 , three interconnecting portions  21 , and three blades  22 . 
     The central body  10  has an outer periphery surrounding a center point  11 , and top and bottom surfaces that are substantially parallel to each other and that are symmetrical with respect to a horizontal plane. The interconnecting portions  21  are integrally formed with the outer periphery of the central body  10 , and are angularly displaced from one another about the center point  11 . Each of the interconnecting portions  21  extends outwardly and along a radial axis  31 , and terminates at a boundary region. The blades  22  are integrally and respectively formed with the interconnecting portions  21 , and are angularly displaced from one another. Each of the blades  22  includes leading and trailing edges  223 , 224  which are opposed to each other in one of clockwise and counterclockwise directions when the blades  22  are turned about an axis that is normal to the horizontal plane and that passes through the center point  11 . In this embodiment, the leading and trailing edges  223 , 224  are opposed in the counterclockwise direction. The leading and trailing edges  223 , 224  are symmetrical with respect to a middle line  32 . Each of the blades  22  further includes a distal end  221  which is opposed to the boundary region along the middle line  32  and which joins the leading and trailing edges  223 , 224 , respectively, at leading and trailing junctures  2231 , 2241 . 
     The middle line  32  intersects the radial axis  31  to form an obtuse included angle  0   1  therewith, which faces towards the leading edge  223 . In other words, each of the blades  22  curves toward an adjacent one of the blades  22  that is disposed forwardly thereof in turns of the direction of a spin. Each of the blades  22  includes a bent line  222  which extends towards the distal end  221 , which is in parallel to the middle line  32 , and which is positioned between the middle line  32  and the trailing edge  224 . Thus, a bent portion  226 , which faces towards the leading edge  223 , is defined by the bent line  222  and the trailing edge  224 . Referring to FIG. 7, the bent portion  226  forms an obtuse included angle θ2 with the horizontal plane. In addition, a plane portion  225  is defined between the bent line  222  and the leading edge  223 . The central body  10 , the interconnecting portions  21  and the blades  22  are of substantially the same thickness. 
     With reference to FIG. 9, in combination with FIGS. 7 and 8, the thrower can hold the plane portion  225  of one of the blades  22 , and then throw the boomerang  1  in a direction indicated by arrow (I). The boomerang  1  will rotate about the axis passing through the center point  11  in a direction indicated by arrow (II), and then return to the point of launching. 
     In particular, when the boomerang  1  is thrown with a spin in an almost vertical state (i.e. the axis passing through the center point  11  is parallel to the ground) so as to rotate through the air, due to the presence of the included angle θ2 between the bent portion  226  and the horizontal plane, a thrust is generated by airflow to act upon one side of the bent portion  226 , thereby creating a lift at the other side of the bent portion  226  from right to left (as viewed by the thrower). Since there is more lift at the top of the spin than that at the bottom, the difference in lift forces results in a first torque that acts upon the substantially vertical boomerang  1  to cause it to fly leftward in a curve path. At the same time, as more lift is generated in front of the center point  11  (center of mass of the boomerang  1 ) than behind the center point  11 , a second torque results to cause the boomerang  1  to lay down horizontally and rightwardly in a gradual manner while the boomerang  1  climbs to a highest point. Thereafter, the boomerang  1  will returns to the point of launching by virtue of residual rotational inertia. Therefore, the flight range of the boomerang  1  is in a direct proportion to the rotational inertia, and is in an inverse proportion to the lift. 
     Accordingly, referring to FIG. 8, since the bent line  222  of each blade  22  is offset from the center point  11  by an offset distance (X), and since the offset distance (X) can decrease the second torque, the height of flight of the boomerang  1  can be varied by adjusting amount of the offset distance (X). Besides, the flight range can be varied by adjusting length and width of the bent portions  226  and the included angle θ2. 
     Moreover, since the boomerang  1  according to this invention is made from a thin flat sheet material, it has a smaller rotational inertia so that a relatively small lift force is required for rotation thereof. Therefore, the boomerang  1  of this invention is lighter and safer. 
     Referring to FIG. 10, another preferred embodiment of the boomerang  1  according to this invention is shown to be similar to the aforesaid embodiment in construction, except that the top surface of the central body  10  has a circular through hole  12  which extends through the bottom surface of the central body  10  and which surrounds the axis passing through the center point  11 . As such, the weight of the boomerang  1  is decreased, and the gyration stability of the boomerang  1  is increased. It is noted that the through hole  12  can have a rectangular or triangular shape. 
     Further, the boomerang  1  of this invention can be configured to have four interconnecting portions and four blades which are angularly displaced from one another so as to achieve similar flight characteristics. 
     The advantages of the boomerang  1  of this invention are as follows: 
     1. Since the blades  22  are provided with the bent portions  226  that are defined by the bent lines  222  and the trailing edges  224  so as to create lift during flight of the boomerang  1 , compared to the conventional boomerang with the complicated airfoil structure, the boomerang  1  of this invention is easy to fabricate, and can be manufactured at a relatively low cost. Besides, the boomerang  1  has a reduced weight to ensure safety of the thrower and bystanders. 
     2. The offset distance (X) can be determined according to the thickness and material of the boomerang  1  so as to vary the height of flight of the boomerang  1 . In addition, the length and width of the bent portion  226  and the included angles θ2 can be varied to change the flight range of the boomerang  1 . Thus, the boomerang  1  can be designed to perform different flight patterns, and is suitable for use in spatial and narrow spaces. 
     While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.