Patent Publication Number: US-6220918-B1

Title: Tossable ring airfoil projectile

Description:
This is a continuation of U.S. application Ser. No. 09/097,727 filed Jun. 12, 1998 now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to ring airfoils. More particularly, this invention relates to tossable ring airfoil projectiles configured to adopt and maintain a flying orientation that generates lift. This lift causes the tossable ring airfoil projectiles to follow a nearly level trajectory having a longer flight time than characterizes standard ballistic motion. 
     BACKGROUND OF THE INVENTION 
     Flying toys are popular amusement devices that include boomerangs, flying discs, kites, model airplanes, and ring airfoils. The popularity of flying toys arises in part because flying toys generate lift as they move through the air, giving them interesting and engaging flight characteristics. 
     Ring airfoils are relatively obscure flying toys that generally resemble hollow cylinders having open ends. The walls of these cylinders may have an airfoil shape. Ring airfoils “fly” when they generate lift by moving through the air in a flying orientation. Lift generated in flying orientations, combined with low aerodynamic drag, causes ring airfoils to follow nearly level trajectories. In contrast, nonflying toys, such as balls, follow parabolic ballistic trajectories. Nearly level trajectories ensure greater flight times than ballistic trajectories, enhancing the fun of playing with ring airfoils. 
     In a preferred flying orientation, a leading end of the ring airfoil points generally forward, in the direction of motion, and a trailing end points generally backward, away from the direction of motion. This orientation may be gyro-stabilized by imparting spin to the ring airfoil about a longitudinal symmetry axis connecting the leading and trailing ends. 
     Although known for many years, ring airfoils have failed to achieve the popularity of other flying toys. This failure may be due in part to difficulties inherent in inducing ring airfoils to move through the air in a flying orientation. In particular, because ring airfoils generally are launched by hand, they typically do not begin their trajectory in a flying orientation. Moreover, even if ring airfoils do begin their trajectory in a flying orientation, they typically do not have sufficient spin to gyro-stabilize that orientation, leaving them susceptible to pitching, yawing, wobbling, and/or tumbling during flight. The skill level necessary to overcome these difficulties effectively may place the use of ring airfoils outside the ability of casual players, or of children in general. 
     Previous attempts to improve the flight characteristics of ring airfoils have included adjusting the dimensions and mass distribution of the ring airfoils to improve lift. Yet, such improved lift cannot be exploited fully unless the ring airfoil is in a flying Orientation. 
     SUMMARY OF THE INVENTION 
     The invention addresses these and other shortcomings by providing tossable ring airfoil projectiles configured to adopt and maintain a flying orientation. The tossable ring airfoil projectiles generally include (i) a ring airfoil having a trailing end, an aperture, and a longitudinal symmetry axis running through the aperture, and (ii) a tail associated with the ring airfoil and extending rearward beyond the trailing end. 
     The ring airfoil is substantially symmetric about the longitudinal symmetry axis and provides lift that allows the tossable ring airfoil projectile to follow a flying trajectory. The ring airfoil may be formed of a variety of materials, including deformable materials, and may be configured to be held in a hand. 
     The tail stabilizes the tossable ring airfoil projectile during flight and may provide a torque that biases the ring airfoil toward a flying orientation. The tail may be formed of a variety of materials, including deformable materials, and may extend substantially parallel to or along the longitudinal symmetry axis. The tail may have various geometries and dimensions. It may be symmetric, it may include at least one fin extending outward from the longitudinal symmetry axis, and it may be substantially at least as long as the ring airfoil. The tail may be movable or may have a substantially fixed orientation relative to the ring airfoil. 
     The tail may be associated with the ring airfoil in various ways. For example, the tail may be associated with the ring airfoil by a connection to the trailing end. Alternatively, the ring airfoil may have an inner surface, and the tail may be associated with the ring airfoil by a connection to the inner surface. The connection may include a plurality of flanges and a structure configured to join the flanges to the trailing end and/or inner surface. These flanges may be aligned with fins in the tail. 
     The nature of the invention will be understood more readily after consideration of the drawings and the detailed description of the preferred embodiment that follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a tossable ring airfoil projectile constructed in accordance with the invention. 
     FIG. 2 is a front elevation view of the tossable ring airfoil projectile shown in FIG.  1 . 
     FIG. 3 is a rear elevation view of the tossable ring airfoil projectile shown in FIG.  1 . 
     FIG. 4 is a breakaway partially cross-sectional view of the ring airfoil shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND BEST MODE OF CARRYING OUT THE INVENTION 
     FIGS. 1-4 show an embodiment of a tossable ring airfoil projectile  10  .constructed in accordance with the invention. Generally, the invention includes (i) a ring airfoil  12  having a trailing end  14 , an aperture  16 , and a longitudinal symmetry axis S running through aperture  16 , and (ii) a tail  18  associated with ring airfoil  12  and extending rearward beyond trailing end  14 . 
     Ring airfoil. 
     The ring airfoil provides lift that allows the tossable ring airfoil projectile to follow a flying trajectory. The ring airfoil may take a variety of forms, but generally resembles a hollow cylinder open at both ends and substantially symmetric about longitudinal symmetry axis S. Ring airfoil  12  includes a hollow, annular body  20  having an aperture  16 , leading and trailing ends  22 ,  14 , and a wall  24  with inner and outer surfaces  26 ,  28 . Aperture  16  may vary in diameter, but typically will be substantially at least one-half the diameter of body  20 . 
     Walls  24  of ring airfoil  12  may have an airfoil cross section, like that of an airplane&#39;s wing. This cross section may be asymmetric about a longitudinal centerline Q bisecting leading and trailing ends  22 ,  14 . Moreover, this cross section also may be asymmetric about a transverse centerline R bisecting inner and outer surfaces  26 ,  28 . Whether symmetric or asymmetric, ring airfoil  12  has an inherently rounded shape that enhances its safety as a tossable projectile. 
     Particular properties of ring airfoil  12  may be determined by safety considerations. For example, ring airfoil  12  may be formed of a lightweight, deformable material, such as foam, to reduce impact hazards to humans, objects, and the ring airfoil itself. Similarly, ring airfoil  12  may be dimensioned larger than a human eye socket to reduce the likelihood of substantial impact with a human eyeball. In a preferred embodiment, ring airfoil  12  is about 4 inches in length and about 3.5 inches in diameter. 
     Particular properties of ring airfoil  12  also may be determined by functional considerations. For example, ring airfoil  12  may be configured to be held in a hand by including shallow indentations on outer surface  28  for receiving fingertips, or by being dimensioned to grip comfortably in a hand. 
     Tail. 
     The tail stabilizes the tossable ring airfoil projectile during flight and may take a variety of forms. Tail  18  includes a central cylindrical portion  30  extending rearward from trailing end  14  along longitudinal symmetry axis S. A central tail aperture  32  runs the entire length of cylindrical portion  30 . In alternative embodiments, the tail may be solid and may extend parallel or at an angle to longitudinal symmetry axis S, rather than along it. Tail  18  also includes three generally planar, outwardly extending fins  34  attached at equal angles to central cylindrical portion  30  along substantially its entire length. Fins  34  include a curved leading edge  36  and straight outer and trailing edges  38 ,  40 . In alternative embodiments, the tail may have no fins, a different number of fins, or differently shaped fins. Tail  18  is substantially symmetric about longitudinal symmetry axis S. In a preferred embodiment, tail  18  is about 5 inches in length, or substantially at least as long as ring airfoil  12 . In alternative embodiments, the tail may be asymmetric and/or may be shorter or longer than ring airfoil  12 . Tail  18  has a substantially fixed orientation relative to the ring airfoil. In alternative embodiments, the tail may be movable relative to the ring airfoil. For example, the ring airfoil may be able to spin around longitudinal symmetry axis S while the tail does not. 
     Particular properties of tail  18  may be determined by safety and/or functional considerations. For example, tail  18  may be formed of a deformable material to reduce impact hazards. Tail  18  also may be configured to stabilize the projectile during flight. 
     Connection. 
     The tail may be associated with the ring airfoil in various ways. For Example, tail  18  is associated with ring airfoil  12  by a connection  42  to inner surface  26 . Connection  42  includes three generally planar, outwardly extending flanges  44  having leading and trailing flange edges  46 ,  48 . Flanges  44  are attached to one another at 120° angles along longitudinal symmetry axis S. A central connection aperture  51  runs the entire length of connection  42  and meets with central tail aperture  32 . Connection  42  also includes a cylinder  50  having inner and outer cylinder surfaces  52 ,  54 . 
     Connection  42  functions as follows. A leading end  56  of tail  18  is joined to flanges  44  at trailing flange edges  48 , so that flanges  44  are aligned with fins  34 . In turn, flanges  44  are joined to cylinder  50  at inner cylinder surface  52 . Finally, cylinder  50  is joined to ring airfoil  12  at inner surface  26 . These pieces may be joined by suitable adhesive means, such as glue, or they may be formed as single unitary elements. 
     In alternative embodiments, connection  42  may have no flanges, a different number of flanges, or differently shaped flanges. Alternatively, tail  18  and ring airfoil  12  may be formed as a unitary structure without a connection. Alternatively, tail  18  may be associated with ring airfoil  12  by a connection to trailing end  14 . 
     Methods of Use. 
     Tossable ring airfoil projectile  10  may be used to play catch or may be launched for accuracy and/or distance, among other applications. For example, launching for accuracy might involve trying to hit a target. Launching for distance might involve trying to travel a long distance by optimizing the launch angle. Maximum range generally is obtained at a smaller launch angle for a tossable ring airfoil projectile than for a nonflying projectile. 
     Tossable ring airfoil projectile  10  is launched as follows. A direction of flight is selected, ring airfoil  12  is grasped in a hand with tail  18  extending away from the direction of flight, the hand grasping ring airfoil  12  is moved in the direction of flight, and ring airfoil  12  is released. The hand may be moved so that tossable ring airfoil projectile  10  spins about longitudinal symmetry axis S in addition to moving forward, thereby gyro-stabilizing the projectile and helping it to maintain lift. 
     If tossable ring airfoil projectile  10  is launched in certain orientations, it will “fly” along a nearly level trajectory rather than fall along a parabolic ballistic trajectory. This flight characteristic is a consequence of lift generated by air moving over the surfaces of the ring airfoil in a way that reduces air pressure on upper surfaces and/or increases air pressure on lower surfaces of the ring airfoil. In a preferred flying orientation, leading end  22  of ring airfoil  12  points generally forward, in the direction of motion, and trailing end  14  points generally backward, away from the direction of motion. In addition, leading end  22  may tilt upward slightly relative to trailing end  14 , such that longitudinal symmetry axis S through ring airfoil  12  makes a small angle relative to the horizontal. This angle will remain largely unchanged throughout the ring airfoil&#39;s trajectory. 
     Tail  18  helps tossable ring airfoil projectile  10  adopt and maintain a flying orientation. In the preferred flying orientation, tail  18  trails ring airfoil  12 , presenting a minimum surface area in the direction of travel. If tossable ring airfoil projectile  10  pitches or yaws, tail  18  will present a larger surface area to the air. Air hitting this larger surface area will create a torque on the projectile that biases it back into the preferred flying orientation. 
     The nearly level trajectories followed by flying tossable ring airfoil projectiles are characterized by longer flight times than characterize standard ballistic trajectories, enhancing the fun of playing with ring airfoils. For example, the flight time t associated with an initially horizontal ballistic trajectory is given by the expression t=[2 h/g] ½ , where h is the vertical distance through which the projectile falls before impact, and g is the acceleration due to gravity, or approximately 9.8 meters per second squared. The flight time for a nonflying projectile launched horizontally from a height of about 1.2 meters (4 feet) will be about 0.50 seconds, according to this formula. The flight time for a tossable ring airfoil projectile launched horizontally from the same height will be at least this long, because lift forces effectively will reduce g in the above expression for flight time. 
     Accordingly, while the invention has been disclosed in its preferred form, the specific embodiment thereof as disclosed and illustrated herein is not to be considered in a limiting sense, because numerous variations are possible and no single feature, function, or property of the preferred embodiment is essential. The invention is to be defined only by the scope of the issued claims.