Abstract:
Flying devices which can ride up and down along a vertical elongate guide member in response to air flow over an airfoil portion of the device. Strings and wires can be used for elongate guide members in some embodiments. Some embodiment flying devices have an adjustable angle of attack. Some devices include an angle of attack lock to lock in a negative angle of attack at a top stop and/or lock in a positive angle of attack at a bottom stop, and a lock, release to release the lock at the opposite travel extreme. Kits having hardware for securing the elongate guide members to buildings are also provided.

Description:
RELATED APPLICATIONS 
     The present application is a non-provisional of U.S. Provisional Patent Application No. 60/767,418, filed Mar. 27, 2006, titled WIND POWERED VERTICALLY FLYING OBJECT, hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention is related generally to flying ornamental objects. More specifically, the present invention is related to flying objects that can ride up and down on a vertical guide in the presence of a sufficiently strong air current. 
     BACKGROUND 
     People have always been fascinated with flying objects, including birds and other flying objects. Such fascination has been captured in early flying machine designs, airplanes, kites, hang gliders, model planes, model birds, remote control planes, wind up flying bird toys, and realistic looking fabric, bird-like objects which flutter in the wind. Artificial birds, flying machines and flying toys have found use as sport and amusement objects, hunting decoys, and scarecrows. 
     What would be desirable are improved bird and plane replicas or flying objects that can be made to fly and do tricks in a controlled area, with or without assistance, using moving air, either natural wind or artificially created breeze. 
     SUMMARY 
     Some embodiments of the present invention provide a flying object kit including an elongate guide member and a body having a front portion, a rear portion, an airfoil portion, and a channel having a substantially vertical region formed through the body and sized to slidably receive the elongate guide member. The kit may also have an upper stop adapted to couple to the elongate guide member which limits upward travel of the body along the elongate guide member and a lower stop adapted to couple to the elongate guide member which limits downward travel of the body along the elongate guide member. 
     Some embodiment kits include a weight for securing to the elongate guide member to apply tension to the elongate guide member, where the weight may include a bird feeder, and/or be made of a clear material such glass or plastic. The clear material may include a cavity for receiving a material such as a liquid. Some weights include batteries and/or electronics. The weight may form the lower stop in some embodiments. 
     Some embodiment kits also include means for securing the elongate guide member to a stationary object, for example rigid brackets, resilient brackets, hooks, loops, rings, and the like. 
     Some kits according to the present invention include means for adjusting the angle of attack of the air foil by adjusting the disposition of the elongate guide member in the channel. Some embodiments also include means for decreasing the airfoil angle of attack responsive to the object reaching the upper stop and means for increasing the airfoil angle of attack responsive to the object reaching the lower stop. Some elongate guide member embodiments are a string. 
     In some embodiments, a flying object kit is provided which includes an elongate guide member and a body having a front portion, a rear portion, a wing portion, and a channel having a substantially vertical region formed through the body and sized to slidably receive the elongate guide member. The kit may also include a lower support securing the elongate guide member and a blower for blowing air toward the wing portion to urge the body to rise upward along the elongate guide member. In some embodiments, the elongate guide member has strength in compression and the elongate guide member is freestanding, being unsupported in the elongate guide member upper region. Some blowers are adapted to be powered by a computer USB port. The output of the blower changes with time in some embodiments, such that the body rises and falls along the elongate guide member responsive to the varying blower output. 
     Some embodiments provide a flying object kit including a body having a front portion, a rear portion, a wing portion, and a channel having a substantially vertical region formed through the body and sized to slidably receive an elongate guide member, wherein the wing portion enables the body to rise upward along the elongate guide member when subjected to air flow. The kit may also include an angle of attack selector coupled to the body which allows the angle of attack of the wing to be fixed in more than one angle. The kit may also include the elongate guide member, in which the elongate guide member has strength in tension and essentially no strength in compression, for example, a string or wire. Some kit embodiments may include a lower travel limiter and an upper travel limiter which limit travel of the body along the elongate guide member. 
     In some embodiments, the channel can receive the elongate guide member in a first position in which the wing has a positive angle of attack providing lift, in a second position in which the wing has a more negative angle of attack than the first position, and in various positions in between the first and second positions. The channel may include an upper portion and a lower portion, in which the lower portion has a longer longitudinal extent than the upper portion, such that the angle of attack can be varied by varying the longitudinal position of the elongate guide member within the channel lower portion. In some embodiment kits, channel includes an upper portion and a lower portion, in which the upper portion has a longer longitudinal extent than the lower portion, such that the angle of attack can be varied by varying the longitudinal position of the elongate guide member within the channel upper portion. 
     The flying object may include a lock mechanism to lock the elongate guide member to impart a negative angle of attack to the flying object. Some lock mechanisms unlock the angle of attack responsive to the flying object having downward travel along the elongate guide member stopped or stop. Some flying objects also include an elastic member coupled to the body and configured for bearing against the elongate guide member to provide spring action to store energy from downward angle of attack airfoil movement, and to urge the airfoil angle of attack further positive when the angle of attack does go towards negative. The flying object may include a spring configured and shaped to be disposed between the body and the elongate guide member which stores energy to urge the airfoil angle of attack further positive. 
     Some embodiments of the invention provide a method for making a vertically flying object (VFO) fly, the method including slidably disposing the VFO over an elongate guide member, the VFO having a body and at least one wing portion coupled to the body. The body may have a guide channel therethrough for receiving the elongate guide member therethrough, the VFO having a user adjustable angle of attack, in which the adjustable angle of attack is adjustable between the body and the elongate guide member. The method can also include establishing an upper travel limit on the elongate guide member and a lower travel limit on the guide member, and orienting the elongate guide member in at least a somewhat vertical position. The method may further include allowing the VFO to rise and fall along the elongate guide member in response to the wind, in some embodiment methods, the VFO has a natural positive angle of attack caused by the guide channel being located forward of the VFO center of gravity, and the method includes allowing the VFO to rise to the upper travel limit and attain a more negative angle of attack than the natural angle of attack, and also includes allowing the VFO to fall to the lower travel limit and attain a more positive angle of attack than the more negative angle of attack. 
     Some methods can include suspending the elongate guide member from a building or other structure, and may include using a bottom weight secured to the elongate guide member to orient the elongate guide member in a substantially vertical orientation. The method may include suspending the elongate guide member and flying object between two elements secured to a structure secured to the earth, or suspending the elongate guide member and flying object between two brackets secured to a building. In some methods, the vertical flying object resembles a waterfowl decoy. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of one embodiment of the invention in which the vertical flying object (VFO) has a tubular guide channel support passing through the vertical flying object body. 
         FIG. 2  is a top view of another embodiment of the invention, having a guide channel top opening. 
         FIG. 3  is a rear, perspective view of one embodiment of the invention having a clamp style upper stop on the elongate guide member, which passes through the guide channel. 
         FIG. 4  is a side view of one embodiment of the invention having a translucent container securing the vertical elongate guide member at the bottom. 
         FIG. 5  is a perspective view of one embodiment of the invention mounted outside of a building window and having the vertical elongate guide member top and bottom secured to the building with brackets. 
         FIG. 6  is a side view of one embodiment of the invention having a bird-like flying object riding on a translucent vertical elongate guide secured at bottom by weighted artificial grass and at top by a suspended hummingbird feeder. 
         FIG. 7  is a perspective view of another embodiment of the invention having a bird-like flying object riding on a vertical elongate guide member secured at bottom by a hummingbird feeder and at top by a stationary building cave. 
         FIG. 8  is a fragmentary perspective view of the flying object of  FIG. 7 , in which the flying object has an adjustable angle of attack. 
         FIG. 9  is a side view of yet another embodiment of the invention having a bird-like flying object riding on a vertical elongate guide member secured at top and bottom by tension brackets secured to a stationary building. 
         FIG. 10  is a fragmentary side view of an embodiment of the invention for guiding a vertical flying object riding on a vertical elongate guide member secured at top and bottom by brackets secured to a stationary building, in which one bracket includes a take up spool to keep a portion of the flexible elongate guide member. 
         FIG. 11  is a perspective view of a VFO system having a powered blower and a platform. 
         FIG. 12  is a perspective view of a bird VFO system having an artificial air current source and a bird cage. 
         FIG. 13  is a perspective view of a bird VFO having adjustable ailerons, rudder, and elevators. 
         FIGS. 14A-14C  are schematic, front views of a VFO having segmented, folding wings. 
         FIGS. 15A-B  are perspective views of a lock and lock release mechanism being made. 
         FIGS. 16A-D  are schematic, side views of a VFO system, showing the body and bottom slot structure in varied vertical angle of attack positions. 
         FIGS. 16E-H  are schematic top views of the VFO system of  FIGS. 16A-D  respectively, showing the bottom slot structure having the elongate guide member in the corresponding varied positions within. 
         FIG. 17  is a perspective view of a pusher arm and bottom slot support disposed near the bottom of an elongate guide member shown in a positive angle of attack configuration, with the pusher arm relaxed. 
         FIG. 18  is a perspective view of the pusher arm and bottom slot support of  FIG. 17 , disposed near the top of an elongate guide member, having a more negative angle of attack than that of  FIG. 17 , with the pusher arm being flexed. 
         FIGS. 19A-19C  are perspective views of a bottom slot support having a lock and lock release mechanism. 
         FIG. 20  is a perspective view of a VFO having several bushings above the VFO to receive the elongate guide member at various angles, to adjust the angle of attack. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a vertical flying object (VFO)  20  having a body  22 , an airfoil portion  24 , and an alignment fin  26 . The alignment fin  26  can point the VFO into the wind. The view of  FIG. 1  is from the bottom and side, showing the underside and a guide tube  30  having a guide channel within for receiving an elongate guide member therethrough. In various embodiments, the elongate guide member can be a string, a cable, a ribbon, a wire, a tube or a rod. The vertical axis is indicated at  32 , the horizontal axis at  34 , and the angle of attack at  36 . Guide tube  30  can be inserted through a channel  28  formed through VFO body  22 . Guide tube  30  acts as but one type of guide channel structure. This guide channel structure can be used to vary the angle of attack of the VFO. When VFO  20  is mounted on an elongate guide member, the VFO can rise and fall along the elongate guide member. 
     The VFO can be constructed out of lightweight materials, for example, foam, paper, plastic, balsa wood, fabric, spars, or frames. Low density foam (polystyrene) works well in some embodiments, VFOs can have a body and a wing or airfoil portion, where the wing or airfoil portion can be integral with the body or be a separate component secured to the body. The airfoil portion can provide the lift for the VFO. Some VFOs are kite or hang glider shaped VFOs, having a lightweight framework covered with fabric or plastic. Many materials, for example, molded foam, paper, fabric, metal, wood, fiberglass, carbon fiber, plastic, and the like may be used to construct some VFOs. Some VFO embodiments may have built-in, add-on, or removable parts such as spars, wings, tails, propellers, wind alignment fins or vanes, streamers, on-board electronics, computer chips, lights, payloads, and many different coverings. 
     The elongate member or elongate guide member can include a string, line, wire, cable, rod, pole, or tube. The guide channel for receiving the elongate guide member can be located forward of the center of gravity in many embodiments, to provide a naturally positive angle of attack caused by the rear being heavier than the front. Near the top extent of travel, where the VFO may have reached the top stop, the normally descending tail may be forced up, causing the VFO to descend or flutter, in various embodiments. The channel for receiving the elongate guide member may include a guide channel support structure in some embodiments. This guide channel support structure can provide a lock and lock release mechanism for changing the angle of attack of the VFO in some embodiments. The angle of attack can vary, but some embodiments provide a range of between about 10 degrees negative and 30 degrees positive. 
       FIG. 2  illustrates another VFO  40  having a line of symmetry  42  extending through an alignment fin or tail  46  and an alignment guide channel  48 , VFO right side  43  and VFO left side  44  are disposed on either side of line of symmetry  42 . In some embodiments, channel  48  has a small hole at top lengthening to a longer longitudinal slot at bottom. In other embodiments, the hole at bottom is smaller than the slot at top. In still other embodiments, the channel is smallest at the middle in a throat region located between the top and bottom. 
       FIG. 3  illustrates another VFO  50  in the shape of a bird, VFO  50  has a guide channel tube  54  slidably receiving an elongate guide member  52  which is a string secured to an upper support element  56 , which is a hook in this embodiment. An upper stop  58  is secured to elongate guide member  52  to limit the upward travel of VFO  50 . 
       FIG. 4  illustrates a VFO system  60  including a VFO  62  traveling along an elongate guide member  64  which is coupled to an upper support member  70  at top and a bottom weight  71 . In this embodiment, a supporting device  66  is anchored to the ground at  68 . In some embodiments, the lower weight also serves as a lower stop; while in other embodiments a separate element serves as the lower stop. In this embodiment, bottom weight  71  is translucent or transparent, to reduce visibility. Some such bottom weights include a cavity which can be filled with water or other media. 
       FIG. 5  illustrates another VFO system including a VFO  82  traveling along an elongate member  84  which is coupled between an upper rigid bracket  86  and a lower rigid bracket  88 . Brackets  86  and  88  are secured to a building having a window  89  for viewing the VFO. An upper stop  83  and a lower stop  81  are fixed to elongate member  84  to limit the upper and lower travel of the VFO. In some embodiments, a tension spring is coupled in-line with the elongate guide member to maintain tension in the line. 
       FIG. 6  illustrates yet another VFO system  90  in which a VFO  92  resembling a hummingbird travels up and down on an elongate guide member  94  hanging downward from a hummingbird feeder  96 . Elongate guide member  94  can be a fishing line, for example, a nearly invisible four pound translucent monofilament, in some embodiments. Elongate guide member  94  includes a bottom stop  100  and a bottom weight  102 , which is a weighted clump of artificial grass in this embodiment. A shepherds hook or crook  98  is driven into the ground and supports hummingbird feeder  96  in this embodiment. 
       FIG. 7  shows another VFO system  120  having VFO  122 , which is an artificial hummingbird, where the elongate member  124  is suspended from a building cave by a hook  126 . A bottom weight, here a hummingbird feeder  128 , maintains elongate member  124  in a substantially vertical orientation. 
       FIG. 8  illustrates the VFO system of  FIG. 7 , showing hummingbird  122  and elongate member  124 . Elongate guide member  124 , which can be a string, passes through a guide channel  132  passing through the hummingbird. Guide channel  132  has a longitudinally oriented long bottom slot and a smaller top opening  130 , in the embodiment shown. Top opening can be formed through a bead or bushing in some embodiments. A bottom structure, here a slotted guide support  134  can be used to vary the angle of attack of the VFO. In some embodiments, the slotted guide support can be used to fix the elongate guide member in a variety of angular positions, for example, using lateral engagement teeth or a friction fit, to maintain a desired angle of attack once selected. 
       FIG. 9  illustrates still another VFO system  140  having a top bracket  142 , a bottom bracket  144 , VFO  122  and elongate guide member  124 . In this embodiment, a take up spool  14 S stores extra elongate guide member line and a reel or pulley  145  is disposed at the end of bottom bracket  144  to provide fine tension adjustment. A tension spring can be coupled between elongate guide member  124  and top bracket  142  to maintain tension in the elongate guide member. In some embodiments, the top and bottom brackets are tension brackets which can maintain tension in the elongate member even without a spring. In such embodiments, the tension brackets can themselves include resilient arms to provide tension. In other embodiments, having rigid support brackets, another tension providing mechanism, such as spring  147 , may be used. 
       FIG. 10  illustrates yet another system  160  having an upper resilient rod or tension bracket  160  having a notch  170  at one end. A wood screw  168  having a shoulder in the middle can be used to secure upper rod  166  to a pole, tree, or other structure  162 . A bottom tension bracket or rod  172  is shown already secured to the pole, tree, or structure  162 . A flexible elongate guide member  164  is shown wound around a bottom notch  163  for fine tension adjustment and around a take up spool  174 . 
       FIG. 11  illustrates another system  200  having a platform  202  including a blower or fan  205  which provide an updraft. A VFO  206  is guided by an elongate guide member  204  coupled at bottom to platform  202  and at top to a support device  208  secured to platform  202 . Blower  204  can be a rotary fan or squirrel cage fan, etc, depending on the embodiment. In some embodiments, the fan is an electric fan powered by the USB port of a computer, providing desktop amusement. Some embodiments of the invention obtain an artificial air current from another source, such as a forced air duct or external fan, and do not include a fan with the kit. 
       FIG. 12  illustrates a variation on the system of  FIG. 11 , in a system  210 . System  210  has platform  212 , blower  205 , VFO  206 , and elongate member  204 . System  210  also has a wire cage or bird cage  214 . Some embodiments use the air from a building forced air heating system in place or in addition to blower  204 . 
       FIG. 13  illustrates another embodiment of the invention in VFO  220  having a body  222  and airfoil portion  224 . Airfoil  224  includes adjustable ailerons  226 , adjustable elevators  230 , and an adjustable rudder  228 . A guide channel enters at a small opening  232  at top and exits through a longer bottom slot  234 . 
       FIG. 14A  illustrates another embodiment in VFO  240  having a body  242  and wings  244 , where the wings are hinged at  246  and  248 , allowing for more lifelike movement of the wings.  FIG. 14B  shows the wings extended upward while  FIG. 14C  shows the wings in a downward position. 
       FIG. 15A  illustrates a structure  250  which can be used in conjunction with a long slot in the guide channel through a VFO body to receive the elongate guide member. Structure  250  in  FIG. 15A  is shown during manufacture, in a flat configuration, having a first flat portion  252  having a first slot  255 . A bending line  256  is shown, as is a second slot  258  and a second portion  254 . A lock or tooth  259  is also shown. 
       FIG. 15B  shows structure  250  after being bent about line  256  and attached to the bottom of a VFO  251 . Lock or tooth  259  has been bent in a horizontal position to capture the elongate guide member, such as a string or wire. The elongate guide member can be received through first slot  255 , and temporarily held by lock  259 . Structure  250  can be inserted within the bottom slot of the guide channel in the VFO body in some embodiments. In other embodiments, structure  250  can be inserted near the top of the VFO, or in the middle. A small member coupled to trigger the lock release may extend from the VFO in some embodiments. 
       FIGS. 16A-D  show side schematic views of a VFO having a body  260  carrying a slotted guide structure  262  for receiving an elongate guide member  264  through the body and structure. An upper stop  266  and a lower stop  268  are also shown. In  FIG. 16A , VFO body  262  has just reached upper stop  266 , the body can no longer translate upward, and begins to rotate or pitch forward in response to the continued wind pressure, which acts at  261  on the VFO. 
       FIG. 16B  shows VFO body  260  rotating or pitching forward to a negative angle of attack in response to the wind and the upper stop. The wind pressure is beginning to push the VFO downward. 
       FIG. 16C  shows VFO body  260  after the VFO has fallen due to the negative angle of attack, and hit the bottom stop  268 .  FIG. 16D  shows VFO body  260  with gravity pulling the VFO rear downward to impart a positive angle of attack, which will carry the VFO upward again in response to the positive angle of attack and the wind. 
       FIGS. 16E-16H  show a top view of slot structure  262  including a slot  263  and elongate guide member  264  corresponding to  FIGS. 16A-16E , respectively. In a VFO where the elongate guide member (for example, a string or wire) enters through a small opening at top and exits through an elongate slot at bottom, the position of the elongate guide member will vary with the angle of attack. When the angle of attack is positive, the elongate guide member will be located toward the rear of the slot, and when the angle of attack is negative, the elongate guide member will be located toward the front of the slot. This may be seen in  FIGS. 16E-16H , where the varied position of elongate guide member  264  is intended to qualitatively illustrate one embodiment of the present invention. Note that an engagement member or lock near the slot could be used to temporarily lock the elongate guide member in a forward and/or rearward position in the slot. This would force the VFO to remain in a positive and/or negative angle of attack longer than would be the case without the lock. 
     In one such embodiment, a clip type lock can be added near the front of the slot, to lock in a negative angle of attack. When the VFO strikes the lower stop, this action can splay the clip to the side to free the locked elongate guide member, allowing the elongate guide member to travel rearward to attain a positive angle of attack. 
       FIG. 17  illustrates a substantially vertical elongate guide member  280  having a bottom or lower stop  282 . A guide channel structure  284  is shown, which can be inserted into an aperture in a VFO to receive elongate guide member  280 . Guide channel structure  284  can be made of resilient sheet metal or plastic, in some embodiments. Guide channel structure  284  includes an upper portion  286  having a rear receiving hole  288  and a front receiving hole  290 , where elongate guide member  280  has been inserted through front receiving hole  290 . Some embodiments have more than two receiving holes, where the various holes can be used to vary the angle of attack of the VFO. Guide channel structure  284  further includes a pusher arm  292 , which can be elastically resilient to provide a spring force, explained further below. Pusher arm  292  is shown in a relaxed, unstressed state, disposed near the rear of slot  298 . A pair of side arms  294  are coupled to or built into the bottom of pusher arm  292 , extending rearward on either side of elongate member  280  to trap elongate member  280 . A bottom, slot guide  296  having a slot within is shown disposed beneath pusher arm  292 , receiving elongate member  280  near the rear of slot  298 , indicating that the angle of attack is positive. The positive angle of attack can cause the VFO to rise until the top stop is reached. This positive angle of attack is also shown at  299 . 
       FIG. 18  again illustrates guide structure  284  of  FIG. 17 , this time having upper portion  286  pushing against top stop  283 . The wind direction is indicated at  281 . The wind pressure against the rear of the airfoil, indicated at  295  can cause the VFO to pivot or pitch downward from the previous positive angle of attack, with the angle of attack shown as horizontal at  297 . This downward change in the angle of attack also causes elongate member  280  to move forward within slot  298 . The downward pitch of the airfoil while the VFO is still pinned against top stop  283  can cause pusher arm  292  to flex, bowing rearward, and storing some force which may later urge the airfoil to a more positive angle of attack when the VFO is no longer pinned against the top stop. In this way, after the VFO begins to move downward, the angle of attack may be urged upward, to an angle in which the descent of the VFO is not as rapid. Thus, an angle of attack sufficiently negative to begin the descent of the VFO can be attained, followed by an angle of attack less negative or even positive, providing a gentle descent, flapping, or a fluttering motion. 
       FIGS. 19A-19C  illustrate an elongate guide member locking support structure  300  slidably disposed on elongate guide member  302 . A top aperture guide for receiving elongate member  280  near the top of the VFO body (not shown in  FIGS. 19A-19C ) and bottom stop  282  are also shown. Slot support structure  300  includes a substantially planar, downward facing bottom surface, indicated at  301  in several positions for clarity. Tooth  307  may be understood to lie between the viewer and bottom surface  301  in this embodiment, not interrupting the bottom surface. A bottom slot  304  is formed in a rear portion of bottom surface  301  for receiving elongate guide member  280 . With bottom surface  301  facing vertically downward, a first finger region  303  can be bent downward part way (or all of the way in some embodiments) towards vertical along bend line  306  in some embodiments. A second finger region can be bent along a second bend line  308  to bring tooth  307  across the region that is vertically below slot  304 . Tooth  307  is bent substantially perpendicular to second finger region  305  in some embodiments, along a bend line. 
     In one example, first finger region  303  is bent 90 degrees along bend line  306 , making first finger region  303  a vertical plane extending forward to backward. In this example of the invention, second finger region  305  is also a vertical plane, bent to approach the region that is vertically beneath slot  304 . Finally, tooth  307  can be bent 90 degrees from second finger region  305  to form a horizontal surface to capture elongate guide member  280 , locking it toward the front of slot  204  to maintain a negative angle of attack. 
     Many other examples of the invention are within the scope of the invention. In some of these embodiments, first finger region  303  is not bent to be vertical, but bent only part of the way toward vertical. Second finger region  305  may then be already splayed away from vertical, such that when second finger region  305  strikes a bottom stop of other object, it may be moved away from the elongate member to release the elongate guide member from the tooth or other lock mechanism being used. 
     When second finger region  305  strikes bottom stop  282 , second finger region  305  splays away from elongate member  280 , taking tooth  307  with it, thereby freeing elongate guide member  280  to travel rearward in slot  304 , allowing the VFO to assume a more positive angle of attack, and begin to rise again in the presence of wind. In this way, tooth  307  acts as a lock, and second finger  305  acts as a lock release. A wide variety of bends, curves, and elements can be used to form the lock and the lock release. Numerous embodiments of this mechanism are possible and are within the scope of the present invention. 
       FIG. 20  illustrates another VFO embodiment in VFO  320 , having a right wing  322 , a left wing  324 , and a tail  326 . A slot  334  for receiving an elongate guide member is shown, as are a pair of spaced apart rails  328 , located above slot  334 . Bushings  330  may be located in a variety of locations along rails  328  and then fixed in position to the rails. The angle of attack for the VFO may be determined by both adjusting the position of a bushing before fixing the bushing position, and by selecting which bushing to use to receive the elongate guide member. In one embodiment of the invention, the forward and rearward limits to travel within the rails may be fixed by using the bushings or other objects and stops. In one example, the two bushings  330  may be fixed in the positions shown in  FIG. 20 , and the elongate guide member inserted through space  332  located between the two bushings or stops. In this way, the angle of attack can vary from positive to negative through action at the top of the VFO. A similar structure may be used underneath the VFO, in addition to the structure at top or in place of the structure at top. The angle of attack can be forced negative at one vertical travel extreme and forced positive at the opposite vertical travel extreme, in one embodiment a small sliding weight or even fluid may be used for lock, in the angle of attack to positive and/or negative. In one such example, a BB, several BBs, metal shot, or liquid in a tube may be used to lock in the angle of attack until changed by outside forces, such as the wind action or striking a travel stop on the elongate guide member. 
     Various embodiments and examples have been illustrated and described to illustrate, not limit the present invention. The scope of the present invention is defined in the claims which follow.