Abstract:
A model airplane, airplane kit, and method of making a model airplane. The kit of the present invention enables children and adults to easily make a well-flying model airplane using recycled plastic foam moldings such as polystyrene food trays well known as 10-S in the food packaging arts.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a division of my earlier U.S. Ser. No. 08/942,378 filed Oct. 1, 1997, now U.S. Pat. No. 6,089,940, which was a continuation-in-part of my earlier U.S. Ser. No. 08/489,805, filed Jun. 12, 1995, now U.S. Pat. No. 5,676,580. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a model airplane and a kit and method for making the same. More particularly, the present invention relates to a model airplane constructed from a polystyrene foam food tray and a kit and method for making the airplane. 
     BACKGROUND OF THE INVENTION 
     Toy airplanes which fly through the air when thrown by hand are well known in the art. Among such toy airplanes designed to fly are model gliders constructed from balsa wood. U.S. Patents describing flying toy airplanes include U.S. Pat. No. 3,590,517 to Regehr; U.S. Pat. No. 4,895,541 to Miller; U.S. Pat. No. 4,103,454 to Stone; and U.S. Pat. No. 4,388,777 to Herman. 
     Plastic foam cutters employing a heated wire are also well known in the art. Such cutters are described in U.S. Pat. No. 3,895,438 to Burkepile et al.; U.S. Pat. No. 3,297,856 to Gershon; and U.S. Pat. No. 3,017,487 to Priestly. Another foam cutter is described and claimed in my earlier U.S. Pat. No. 5,676,580 mentioned above which is hereby incorporated by reference herein in its entirety. 
     Applicant is unaware of the prior use of polystyrene foam trays as a primary material for making a model airplane, nor of any kit or methodology for the construction thereof. 
     SUMMARY OF THE INVENTION 
     The model airplane kit of the present invention includes components to build a well flying model airplane from food trays commonly used to display meat or produce or other food items in a grocery store and generally discarded afterwards. 
     As one embodiment, the present invention provides a method for making a model airplane. As a first step, an airplane wing template is removably secured to a preformed plastic foam molding. As a second step, the wing is cut from the foam molding cutting along an edge of the template. Preferably, a first template is used to cut a leading edge of the wing and a second template is used to cut a trailing edge of the wing. An airfoil is then sanded on the wing. Weights are attached to a nose of the wing. Optionally wheels are cut from the foam molding, attached to a wire and secured to the wings to form landing gear. The wing cutting step preferably includes the step of latching a cutting wire to a U-bend hook to complete an electrical circuit with a battery and heat the wire. The plastic foam molding preferably comprises a polystyrene 10-S food or meat tray commonly found in the grocery store. The wheels are preferably cut from the foam using a tubular die. 
     As another embodiment, the present invention provides a model airplane kit. The kit comprises a preformed plastic foam molding, an optional plastic foam cutter, a template for cutting a wing from the plastic foam molding, sandpaper for sanding an airfoil on the wing, one or more weights for weighting a nose of the wing, an optional die for cutting wheels from the foam sheet, and an optional wire for attaching the wheels to the wing and forming a landing gear for the model airplane. The kit preferably comprises a polystyrene foam molding in the form of a 10-S food or meat tray commonly found in the grocery store. The kit preferably includes a template for making a sanding block from residual foam sheet. 
     As yet a further embodiment, the present invention provides a model airplane made by the steps of: securing a wing template against a preformed plastic foam molding; cutting the wing from the foam molding; sanding an airfoil on the wing; attaching weights to a nose of the wing; and optionally making a landing gear for attachment to an underside of the wing by cutting wheels from the foam molding, attaching the wheels to a wire and securing the wire to the wings. The plastic foam molding preferably comprises a polystyrene 10-S food or meat tray commonly found in the grocery store. The wheels are preferably cut from the foam molding using a tubular die. 
     In another aspect, the invention provides a model airplane having a wing and symmetrical upturned winglets formed at either end of the wing. The wing has a swept back leading edge and an airfoil with a generally convex upper surface. The wing is symmetrical with respect to a centerline extending rearwardly from the nose at an apex of the leading edge. The winglets each have an upper reflex area having concavity in a horizontal plane and in a vertical plane at a right angle to the wing centerline. A leading portion of each winglet extends rearwardly from the leading edge of the wing with upper, inner and lower, outer surfaces parallel to the wing centerline. The upper, inner surfaces have concavity in said vertical plane. A trailing winglet portion curves inwardly and rearwardly from the leading winglet portion toward said centerline to define said reflex area. The wing preferably has a flat lower surface between the winglets and is sculpted from a 10-S polystyrene foam tray. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first template for cutting the leading edge of the wing according to the present invention. 
     FIG. 2 is plan view of a second template for cutting the trailing edge of the wing according to the present invention. 
     FIG. 3 is a plan view of a wing according to the present invention. 
     FIG. 4 is a side-frontal perspective view of the wing of FIG.  3 . 
     FIG. 5 is a top plan view of a polystyrene foam molding showing the location of pin holes for the location of the reference line in the fabrication of the wing according to the present invention. 
     FIG. 6 is a plan view of the bottom of the polystyrene foam molding of FIG. 5 showing the location of the reference line. 
     FIG. 7 is a close up plan view of the first template placed over the underside of the polystyrene foam molding showing the alignment of the reference line and the centerline locating aid according to the present invention. 
     FIG. 8 is a perspective view of the first template positioned on the underside of the polystyrene foam molding for the fabrication of the wing according to the present invention. 
     FIG. 9 is a side perspective view showing the cutting of the polystyrene foam molding with a hot wire cutter using the first template according to the principles of the present invention. 
     FIG. 10 is a side-front perspective view of a second template positioned on the polystyrene foam molding after the cutting of the leading edge in preparation for the cutting of the trailing edge according to the principles of the present invention. 
     FIG. 11 is a frontal view of a model airplane constructed according to the principles of the present invention showing the raised tips of the wing. 
     FIG. 12 is a bottom view of the model airplane of FIG.  11 . 
     FIG. 13 is a vertical cross-sectional view of the wing span of the model airplane of FIG. 11 showing the particular shape of the airfoil at the wing leading and trailing edges. 
     FIG. 14 is a horizontal cross-section view of the wing tip of the model airplane of FIG.  11 . 
     FIG. 15 is a perspective view of a sanding block according to the principles of the present invention. 
     FIG. 16 is a sectional view of a wheel-cutting die according to the principles of the present invention. 
     FIG. 17 is perspective side view of the wheel-cutting die of FIG. 16 with the pin-plunger shown in the advanced position. 
     FIG. 18 is a plan view of a jig for bending a wheel strut according to the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Recycled materials including old film canisters and disposable Styrofoam meat trays are used to build a well flying model airplane for the amusement of both children and adults. 
     Referring to FIGS. 1-18, a model airplane  10  which can supply long lasting enjoyment for children and adults is cut from a preformed molding of plastic foam  12  using a foam cutter (not shown) and first and second wing templates  14 , 15  for tracing the wing pattern on the foam molding  12 . In the practice of the present invention, the plastic foam molding  12  preferably comprises a size 10-S meat or food tray made of polystyrene foam. 
     The preferred foam cutter is described in and illustrated in my earlier U.S. Pat. No. 5,676,580. This is an optional feature of the present kit which can include the preferred foam cutter, a different type of hot wire foam cutter, a knife or other tool for cutting polystyrene foam sheet, or the cutting tool can be supplied by the user. 
     The model airplane  10  of the present invention has a wing  48  which includes a swept back leading edge  58 , a complementary trailing edge  60  and raised tips or winglets  52  at either end thereof. The wing  48  is made by securing the templates  14 , 15  in turn to the flat surface of the polystyrene tray  12 , e.g. by using double-sided adhesive tape between the templates  14 , 15  and the tray  12 , and then cutting a leading edge  50  and trailing edge  60  using the respective template  14  or  15 . 
     As best seen in FIGS. 5 and 6, a reference line  20  is drawn transversely across the exact center of the back side  22  of the foam molding  12 . To mark the molding  12 , advantage can be taken of the symmetrical waffle pattern formed by diamonds  24  typically imprinted on the upper surface  25  of the foam molding  12  (see FIG.  5 ). A pin (not shown) is used to poke holes  26  straight through the foam molding  12  at the center of the “X” between the central row of diamonds  24 , typically the ninth row from either longitudinal end of the upper surface  25 . These holes  26  then lie in a straight line visible on the back side  22  of the foam molding  12  which can be used to position the reference line  20  using a suitable straight edge and pen or pencil (not shown). 
     The templates  14 , 15  can be a paper or cardboard form, desirably cut from a pre-printed sheet (not shown). The sheet can also include a sanding block template  80 , preferably printed in the template  14  along a centerline locating aid  84  printed along a centerline of template  14 . If desired, a dotted line  85  an also be printed from a trailing edge  160  of the first template  14  to mark a place to cut into the first template  14  to cut out the sanding block template  80 . This line  85  can be repaired by closing the incision with tape (not shown) to restore the integrity of the first template  14 . 
     As best seen in FIG. 7, the removal of the sanding block template  80  from the first template  14  allows the reference line  20  to be seen when the first template  14  is positioned on the back side  22  of the molding  12  and facilitate alignment of the reference line  20  with the preprinted centerline locating aid  84  which is critical to the ultimate aerodynamics of the wing  48 . The trailing edge  160  of the first template  14  and a bottom  22  of the foam molding  12  are positioned to rest on a flat surface  164  such as a tabletop with the first template  14  held against the back side of the foam molding  12  with the reference line  20  and centerline locating aid  84  in alignment. When the first template  14  and foam molding  12  can be aligned properly with the back side  22  of the foam molding  12  and first template  14  completely vertical at a right angle to the top of the flat surface  164 , the first template  14  can be removably secured in relative position to back side  22  of the foam molding  12  using two or three pieces of two-sided tape between them. 
     The leading edge  58  of the wing  48  is then cut by tracing the cutting tool, preferably a hot wire cutter, as perpendicularly as possible along the leading edge  150  of the first template  14 . Using a hot wire cutter, the cutter should be slid smoothly and evenly throughout the polystyrene foam molding  12  to trace out the leading edge  58 , without forcing or stopping the wire cutter to avoid tearing or melting an unwanted hole or tear in the wing  48 . Some practice may be helpful to keep the cutter perpendicular to the first template  14 , especially in areas of the winglet  52  where the foam molding  12  and first template  14  makes a sharp curve. I have found that it is helpful to hold the foam molding  12  at eye level while cutting and using one eye to line things up as seen in FIG. 9, keeping the other eye closed. It also helps to make two cuts, beginning each at a respective winglet  52  and cutting in toward the centerline  20 . Also, depending on the depth of the throat of the hot wire cutter, it may be necessary to trim off excess foam from the molding  12  to accommodate the hot wire cutter. 
     The trailing edge  60  is then cut in the foam molding  12  using the second template  15  and cutting tool in much the same manner as the first template  14 . As best seen in FIG. 10, the first template  14  is removed and second template  15  is removably secured to back side  22  of foam molding  12  using the two-three pieces of two-sided tape, aligning the leading edge  58  of the foam molding  12  with a leading edge  150   a  of the second template  15  and the reference line  20  with a preprinted centerline locating aid  84   a.    
     The winglets  52  of the wing  48  are formed by the upturned edges of the foam molding  12 . As best seen in FIGS. 3-4 and  11 - 14 , the span portion  50  defines respective top and bottom planar surfaces  54 ,  56  and the respective leading and trailing edges  58 ,  60 . The winglets  52  define planar side surfaces  62 ,  64  and leading and trailing edges  66 ,  67 . 
     An aerodynamically stable cross-section (see FIG. 11) is formed in the winglets  52  by sanding the planar side surfaces  62 ,  64  at the leading edge  66  thereof. A sanding block  170  (see FIG. 15) can be conveniently made from a residual section of the foam molding  12  by cutting a block shape therefrom using the sanding block template  80 , for example. The sanding block  170  is covered with sandpaper  172  which is taped in place around the block  170 . 
     As seen in FIG. 13, the span  50  has an airfoil shape. The airfoil is preferably produced by lightly sanding the span top surface  54  at the leading and trailing edges  58 ,  60  in an acceptable fashion. The span bottom surface  56  is generally not altered. I found it works well to shape the leading edge  58  on the edge of a table top or other flat surface which can be protected from marring by the sandpaper with several thickness of newspaper or other protective coating. The sanding block  170  is desirably moved from side to side to create a gently curved surface which slopes downwardly to the point where the leading edge  58  meets the lower surface  56  of the wing  48 . Generally, the diamonds  24  in the pattern in the first row and part of the second row will be sanded smooth. Special attention should be given to the area where the leading edge  58  meets the winglet  52 . Desirably, the sanding will create a shape here which will direct the air flow smoothly over the top surface  54  of the wing  48  and into the reflex area  53  of the winglet  52 . The reflex area  53  comprises the frontally exposed portion of the surface  62  which extends over the front profile of the leading edge  66 , preferably inwardly concave, outwardly convex, resulting as an artifact from sculpting the winglets  52  from the upward shape of the edge of the original 10-S polystyrene foam tray. I prefer to sand foam out of this transition area using an edge of the sanding block  170  to make a thin-edged miniature air scoop. When the sanding is finished, the sharp leading edge  58  of the wing  48  should form a continuous line with the leading edge  66  of the winglet  52  with a sharp corner formed at the transition between the wing  48  and winglet  52 . 
     The trailing edge  60  is then formed by sanding the top surface  54  in a manner similar to that for forming the leading edge  58 . As best seen in FIG. 13, there is a slope from approximately the middle of the upper surface  64  of the wing  48  back to the trailing edge  60 . Conveniently, the wing is held down on the work surface and sanded over the surface  54  using sanding strokes which are down-and-away or side-to-side. The trailing edge  60  is preferably about 1 mm thick and should slope smoothly up into the reflex area  53  near either winglet  52 . Making the trailing edge  60  paper thin does not seem to improve the flight of the wing  48 , and in some cases seems to actually degrade the sink rate. It also helps to have some stiffness in the trailing edge  60  where one&#39;s thumb pushes on the wing  48  during launching. 
     Desirably, the winglets  52  should be as lightweight and thin as possible to reduce drag. The leading edge  66  should be paper thin, and lower edges of the winglets  52  should be parallel to the reference line  20 . This shape is formed by sanding the winglets  52  using the sanding block  170 . The surface  64  can be conveniently sanded by holding the wing blank in one hand with the upper surface  25  facing downward, and sanding the surfaces  64  with repeated downward strokes. Some strokes can be angled toward the front or back of the wing  48 , but they should all move generally from the lower wing surface  56  toward a tip of the winglet  52 . I prefer to periodically check visually to see how thin the winglet  52  is getting. When the shaping is completed, there should still be some unsanded curved portion of the lower surface  56  at the trailing edges  67  of the winglet  52 . 
     Following the aerodynamic shaping of the wing  48 , the airplane is completed by weighting the nose  51  and attaching a landing gear  72 . The nose  51  can be conveniently weighted by a pair of number one paper clips  74  on either side thereof which are then adjusted fore and aft for best flight characteristics. In addition, the wing  48  can be further sanded to fine tune the glide characteristics. For example, if the wing  48  turns right, sanding off a slight portion of the reflex surface adjacent the right winglet  52  can correct the turning tendency. 
     The landing gear  75  can be made of polystyrene foam wheels  76  of an appropriate size attached to the bottom surface  56  of the wing  48  by steel wires  78  bent to an accommodating shape. The wires  78  can be attached to the wing  48  by adhesive tape. The wheels  76  are conveniently cut from an unused residual portion of the polystyrene sheet  12  preferably using a die comprising a piece of thin walled ½ inch tubing. In a preferred embodiment, the die comprises concentric tubes, including a smaller tube  100  and a larger tube  102  as seen in FIGS. 16 and 17. The smaller tube  100  is slideably received in the larger tube  102 , preferably using spacer elements  104  and  106  secured to an outer surface of the smaller tube  100  along a diameter thereof. 
     Conveniently, the spacer element  104  can be a piece of adhesive loop material, and the spacer element  106  an adhesive-backed hook material, as in a VELCRO® fastener. The large tube  102  preferably has a distal end which is sharpened for cutting the wheel shape from the polystyrene foam. A proximal end of the small tube  100  has a rubber stop secured thereto which has an outside diameter at least as large as an inside diameter of the large tube  102 . The distal end of the small tube  100  has a concentric pin protruding axially outwardly from an anchor  114  secured in the tube  100 , for example, with glue or welding. The pin  112  passes through a disk of polystyrene foam  118  secured, for example, with glue, to the distal end of the small tube  100 . The disk  118  has an outside diameter matching an inside diameter of the large tube  102 . When the small tube  100  is inserted completely into the large tube  102  so that the distal end of the large tube  102  abuts the stop  110 , as shown in FIG. 17, the distal end of the disk  118  is flush with the distal end  108  of the large tube  102  and a portion of the pin  112  extends therefrom. 
     In using the die, a clear area on a piece of scrap polystyrene foam is found. The small tube  100  is retracted from the large tube  102  so that the pin plunger will not stick into the polystyrene foam which is being cut to shape the wheel  76 . The cutting edge  108  of the outer tube  102  is placed against the foam and moved circularly against the polystyrene foam sheet  12  with a gentle twisting motion with the larger tube  102  held generally perpendicular to the polystyrene foam. When the wheel  76  is cut through the polystyrene foam, the pin  112  is slowly advanced into the disk while holding the disk flush with the opening in the cutter. When the wheel  76  is pushed out of the end of the cutter, it can be pulled gently off the pin  112 . With proper technique, the wheel  76  can be well cut with good roundness, edges which are crisp and square, and a hole formed in the exact center of the disk. 
     If desired, from time to time, the cutter can be kept sharp with a file by using upward strokes parallel with the beveled edge  108  on the outside of the large tube  102 , and a little circular motion around the inside edge of the bevel  108 . 
     A bushing can be constructed for the axle by stripping a short length of plastic off of a plastic coated paper clip, trimming one end of the stripped plastic at an angle, for example with a scissors. The plastic tube is then stuck carefully through the hole in the wheel. If polystyrene foam breaks out on the end of the plastic tubing when poked through the hole, the wheel may not function properly and should be discarded in favor of a newly constructed wheel. The ends of the bushing protruding from either side of wheel can be trimmed off with a small scissors, for example. The wheel can be mounted on a strut wire by sliding the wheel onto a strut wire, preferably made using a strut wire bending jig as described in more detail below. Holding the axle wire with the smallest tip of a needlenose pliers right up against the plastic bushing, a bend is made in the wire and excess wire trimmed using a wire cutter. The strut can then be taped to an underside of the wing in an appropriate position. If desired, a little tab of tape can be wrapped around the top of the strut wire and pressed flat to make it easier to secure the strut to the wing. It is also preferred to bend the nose wheel strut wire to rake forward to make the wing  48  sit slightly nose down to facilitate landing. Care should be exercised to fasten the wheels  76  to the wing  48  so that they are positioned to roll straight ahead upon landing. If the wing  48  experiences a turning tendency on landing, this can be corrected by repositioning the nose wheel. 
     A wheel strut  78  is preferably made using a bending jig supplied with the model airplane kit of the present invention. The jig comprises a base B, a plurality of pins P 1 , P 2 , P 3 , P 4 , P 5  and P 6  protruding from the base B along a predetermined pattern, and a lever arm L rotatably secured to the base B. The base B can be made of composite materials such as, for example, thin pieces of cardboard sandwiched alternatingly with polystyrene foam sheets of like length and width. The base materials can be taped or glued together into a solid piece. The pins P 1  through P 6  are preferably formed in a pattern leading inwardly from an outer edge of the base B. The pins P 1 -P 6  are preferably formed by inserting a steel pin into the base B in the desired position, and cutting the head of the respective pin to leave a desired amount of pins P 1 -P 6  extending upwardly from the base B. The pins P 1 -P 6  are preferably arranged in an alternating pattern on opposite sides of the desired configuration of the wire. For example, pins P 1 , P 2  and P 3  are arranged to the right, to the left, and then to the right, respectively, of a line for receiving a first length of the wire to be bent. Pin P 4  forms an apex, on the left side of the wire to allow the wire to be bent 90° around pin P 4 . Pins P 5  and P 6  are then aligned along a right angle to the direction of pins P 1 , P 2 , P 3 , P 4 , pin P 5  being on the outside of the wire away from the edge of the base B, pin P 6  being disposed just to side of the wire toward the edge of the base B. The wire is then bent around pin P 6  to form a U-shape in the wire. 
     The lever arm L is secured to a shaft positioned laterally approximately half way between the pins P 4  and P 6 , just to the side of the line defined by pins P 4 , P 5 , and P 6  so that a trailing edge of the lever arm L can be positioned parallel adjacent the line defined by the pins P 4 , P 5  and P 6 . The lever arm L has a width of a dimension suitable for forming a V in the wire in a plane perpendicular to the plane defined by the upper surface of the base B. The lever arm L can be made of a piece of plastic, such as plastic from a used surgical tray. The lever arm L is attached to the base B by forming a bore through the base B with a relatively large nail, and securing the lever arm L to the base B by passing a brass fastener through a hole formed toward on end of the lever arm L and the bore formed through the base B. Ends of the brass fastener are spread open and conveniently covered with tape. 
     In making the wire struts, the bending jig is preferably fastened to a table top, for example, using double stick tape or adhesive-backed hook-and-loop VELCRO® fasteners. Using an appropriate wire, such as, for example, 0.015-inch diameter guitar string wire, the wire strut is made by placing the wire along the pins P 1 -P 4  and allowing the free end to extend a little beyond the edge of the base B. The wire is then bent around pin P 4 , making a 90° bend. The wire is then placed between pins P 5  and P 6  and a second 90° bend is made around pin P 6 , preferably holding the wire down against the base B with a thumb or finger nail and pushing the free end down toward the edge. The lever arm L is then rotated over the wire below pin P 6  so that the lever arm L is generally parallel to the wire extension between pins P 4  and P 6 . Holding the lever arm L down with a finger, the wire is lifted up and back away from the edge to form a V shape. Excess wire is cut off at the V. 
     In addition, the underside  56  of the wing  48  can include a launching tab (not shown) so that the plane can be launched by gripping the tab (not shown). 
     The airplane  10  is launched by holding it above one&#39;s head with the wing  48  level, moving the airplane  10  forward through the air and releasing with the nose  51  falling forward. Throwing too hard causes nose-up and stalls; left wingtip low creates a left-turning flight, and likewise with the right tip low. A hard downward throw with the wingtips level can cause a loop; hard throws to the left or right can cause a boomerang flight path. 
     A kit for making the model airplane  10  preferably comprises one or more 10-S polystyrene trays  12 , the templates  14 , 15  and written instructions (not shown) for putting the whole thing together. In addition, the kit can optionally include a spool of high gauge steel wire (not shown), a hot wire cutter (not shown), and the tubular wheel die. Suitable wire comprises high pitch guitar wire. 
     In addition, one or more associated building materials can be included although such materials are generally found in most households. Among associated building materials are paper clip nose weights  74 , sandpaper, adhesive tape (not shown), and a C-cell battery (not shown). 
     The present model airplane and kit therefor is illustrated by way of the foregoing description and examples. The foregoing description is intended as a non-limiting illustration, since many variations will become apparent to those skilled in the art in view thereof. It is intended that all such variations within the scope and spirit of the appended claims be embraced thereby.