Abstract:
A disc-shaped accessory having radially-hinged flaps is adapted to be attached to an aircraft wheel. The flaps open no more than 90° (preferably 45-70°) in an airstream to exert a rotational torque on the wheel, causing the wheel to spin. The rotation helps reduce tire wear and damage during aircraft landing.

Description:
CONTINUITY AND CLAIM OF PRIORITY 
       [0001]    This is an original U.S. patent application that claims priority to U.S. provisional application No. 61/628,746 filed 7, Nov. 2011. 
     
    
     FIELD 
       [0002]    The invention relates to auxiliary equipment for aircraft landing gear. More specifically, the invention relates to wheel-mounted accessories to cause the wheels to begin rotating before they strike the ground during landing. 
       BACKGROUND 
       [0003]    The vast majority of aircraft land on solid—and often paved—surfaces, using three or more wheels (a 747-400, for example, has 18 wheels in four sets of four, with two additional wheels at the nose). The wheels are typically shod with tires of more-or-less conventional heavy-duty construction. 
         [0004]    Aircraft landings place significant stresses on landing-gear tires: a plane may land at a speed of 80-150 mph (128-240 km/h), yet when the tires touch down, they are scarcely turning. Therefore, they must spin up from a standstill to match the landing speed very quickly, and until they do, they skid along the runway, burning off rubber tread, creating flat spots and occasionally destroying a tire. (Runways commonly have a black skid-marked segment at one end where most planes touch down, and photos of planes landing often show clouds of smoke from the skidding tires.) 
         [0005]    A number of devices and systems have been proposed to reduce landing-related wear on tires by accelerating, spinning or pre-rotating the wheels of an aircraft in preparation for landing. However, none of these have achieved significant commercial success, possibly due to excessive mechanical complexity, weight and/or inadequate durability. A new design that helps pre-rotate aircraft tires for landing may offer longer tire life, improved landing safety, reduced parts fatigue and maintenance cost, and other benefits for aircraft owners and operators. 
       SUMMARY 
       [0006]    Embodiments of the invention are resilient disc-shaped accessories, adapted to be secured to an aircraft landing-gear wheel, with passive, automatically retracting flaps or vanes that open when exposed an airstream to apply a rotational force to the wheel. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
           [0008]      FIG. 1  is a perspective view of a basic embodiment of the invention, installed on a sample wheel. 
           [0009]      FIG. 2  is a plan view of an embodiment with a section therethrough. 
           [0010]      FIGS. 3A and 3B  show alternate flap constructions and mechanisms for limiting the maximum opening angle. 
           [0011]      FIGS. 4-6  show alternate flap surface profiles. 
           [0012]      FIG. 7  shows an alternate flap opening-limit construction. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  shows a typical embodiment of the invention, installed on a sample wheel/tire  100 . The embodiment is a generally disc-shaped structure  110 , slightly smaller than the tire (preferably between about 70% and 90% of the tire diameter), and attached to the tire/wheel assembly so that the outer circumference of the embodiment rests firmly against the sidewall of the tire. In many embodiments, the disc has a convex outside shape (and corresponding concave inside shape). This shape causes the embodiment to be “over-fitted” to the tire, so that when the embodiment is attached, the flattening of the resilient disc provides extra spring force to hold the outer circumference against the tire sidewall. The outer circumference of the disc may include a thicker, weighted “ring” to provide a centrifugal force to reset a disc that has been “flipped” (overextended clue to a hard landing, causing the disc to curve away from the tire sidewall, instead of towards it). 
         [0014]    This embodiment has a central opening  120  to provide access to the wheel, bearing, and other parts of the landing gear, and is held against the tire by bolts  130 . In installations where the landing-gear axle does not extend through the embodiment disc, the central opening need not be provided. 
         [0015]    Moveable flaps or vanes  140  are positioned around the perimeter of the disc. The flaps are attached at one side to the disc, but are free to rotate about the attachment point, like a door about a door hinge. The hinge lines are oriented roughly parallel to radii of the disc. Above the horizontal centerline of the wheel, the flap hinge leads the flap into the airstream, so the flaps tend to remain closed. However, below the horizontal centerline of the wheel, air can begin to enter behind the flap and push it open (in this Figure, flap  150  is shown starting to open). At the bottom of the wheel, airflow pushes the flaps fully open, as shown at  160 . Finally, toward the trailing edge of the wheel, the airstream exerts less “opening” force on the flaps, so they return to their closed position ( 170 ). 
         [0016]    Since the open flaps at the bottom of the wheel present greater wind resistance than the closed flaps at the top, the wheel experiences a torque that tends to cause it to rotate in the direction shown. When the wheel does rotate, the flaps continue to open and close automatically as they are exposed to the airstream. The longer a wheel equipped with an embodiment of the invention is exposed to the airstream, the faster it tends to spin (at least until the vanes at the bottom of the wheel approach the speed of the airstream). Thus, an embodiment of the invention can help spin up an aircraft wheel in preparation for landing. 
         [0017]    The flaps of an embodiment are sized and positioned to prevent excessive speed in pre-rotation, under normal aircraft flight conditions. For example, a large flap located closer to the wheel&#39;s axle might cause the wheel to spin faster than the aircraft&#39;s landing speed. With flaps located closer to the wheel&#39;s outer circumference, this is less likely to happen. (In fact, as the wheel rotates closer and closer to the airspeed, there is less relative airflow to cause the flaps to stand up. Thus, embodiments are self-limiting in speed.) 
         [0018]      FIG. 2  shows a side view and a section (A-A) through another embodiment of the invention. In this figure, an alternate internal opening shape is visible; the main body of the disc is attached to the wheel via four bolts  210 . The dashed outline  220  indicates the outer circumference of the tire. Disc  230  rests against the sidewall of the tire. There are eight (8) flaps  240  in this embodiment, each hinged by a radially-oriented hinge at the counter-clockwise edge of the flap. A wheel flange  250  holds the device to the wheel and against the tire. 
         [0019]    The flaps or vanes of an embodiment impart a rotational torque to the wheel by standing up in the airstream over part of the device&#39;s circumference. The flaps should not be permitted to open beyond 90° (and in many embodiments, a maximum opening of 45-75° is preferred).  FIGS. 3A and 3B  show two different structures that can limit the flap opening as desired. Both figures show flaps in various stages of opening. The view is from the edge of the disc towards the center, as if the outer portion of the disc had been removed to expose the flaps and hinge structures. The Airflow indication refers to airflow across the disc below the wheel axle, so the flaps are being forced open to turn the wheel. Airflow above the wheel axle is in the reverse direction (relative to the flap orientation) so the flaps will be held closed. 
         [0020]    In  FIG. 3A , the disc is formed of a laminate of three layers: a flexible resin plastic base  300  with a Kevlar-type material  305  (the striped layer) bonded thereto. The top layer  310  may be formed of a similar or identical material as the base; it is also bonded to Kevlar  305 . Fins or flaps are formed in the top layer, and the Kevlar layer is cut on three of four sides of each fin, leaving one uncut segment to act as a hinge for the fin. (Only one of these cuts is visible in this view; it is circled at  315 . The other two cuts are either outboard or inboard of the view plane.) In some embodiments, the flaps may be secured to the underlying Kevlar layer with stitching (as well as, or in lieu of, adhesive and/or thermoplastic bonding). 
         [0021]    The cuts around the free (non-hinge) sides of each flap should leave an adequate gap so that the flap does not get stuck in the closed position due to deformation or damage to the apparatus. A gap of at least 3-5 mm is preferred, although a larger gap may be required on heavier-duty embodiments for use on larger wheels. In this figure, left-most fin  320  is closed, middle fin  325  is starting to open, and right-most fin  330  is fully open. The flat, five-sided blocks between the fins (one of which is identified at  335 ) comprise the stationary part of the disc (other parts of which are secured to the wheel). The portion of the block adjacent the trailing edge of a closed fin (e.g.,  340 ) may be angled differently than the trailing edge of the fin to create a gap  345  when the fin is closed. This gap may help the airstream lift the fin. In some embodiments, the trailing edge of each fin may have a convex scallop or scoop formed therein, so that the airstream can enter and force the fins to stand up. (When referring to the flaps or fins, there is a possible ambiguity between the “leading” and “trailing” edges, since the direction of airflow over each flap changes depending on whether the flap is above or below the horizontal centerline of the wheel. In this Specification, the “leading” edge of a flap is specifically defined to be the edge of the flap at the hinge line. This edge also “leads” into the airstream when the wheel rotates so the flap is above the wheel&#39;s centerline. The “trailing” edge of a flap is the edge opposite the leading edge, and is the portion of the flap that opens to catch the airstream below the wheel&#39;s centerline.) 
         [0022]    As the fins rotate below the wheel centerline, the airstream begins to pick them up. The more they stand up, the more force the airstream exerts. Fully-erect fins (e.g.,  330 ) stand up at an angle  350  set by the leading edge of the fin and the trailing edge of the block downwind of the fin. Note that the Kevlar layer functions as a hinge between each fin and its downwind stationary block. 
         [0023]    Some laminated embodiments may include a metal layer for improved strength or reliability. In such implementations, it is preferred that the metal not extend to the edge of the disc, so that it poses less risk of damaging the tire sidewall. It is appreciated that the use of Kevlar-type materials in laminates such as described here offers safety and impact-resistance benefits. For example, an embodiment may provide bullet resistance in military applications. 
         [0024]      FIG. 3B  shows an embodiment with a different flap configuration. There may be a base substrate  355  (of a material like that discussed above, or of metal). Left flap  360  is shown in the closed position. The flap has a spur or spine  365  formed into its outside surface, and the stationary part of the disc has a complementary spine  370 . The perspective-view inset drawing shows how these spines may be arranged on the flap and adjacent surface. For example, there may be a plurality of interleaved spines. It is preferred to have two or more spines. 
         [0025]    The spines may extend toward the free end of the flap to provide support for the flap, and the spine end near the hinge limits the maximum opening angle of the flap. Right-hand fin  375  is shown in the open position, and the action of the spines in preventing further opening is apparent in the second perspective-view inset drawing. In this embodiment, the hinge is formed with the flaps and the rest of the disc surface by scoring or thinning the material along the hinge line. The position of the hinge (seen end-on) is shown by the black clot at  380 . The actual material that forms the hinge, seen from this angle, is much smaller than the clot. 
         [0026]      FIG. 4  shows three flaps of another embodiment in various stages of opening. Left flap  410  is closed, while flap  420  is partly open, and flap  430  is fully open. The hinge of each flap is straight  440  and oriented roughly parallel to a radius of the disc. In this embodiment, a separate hinge structure  450  is used to attach each flap to the disc. The flaps in this embodiment have a curved, airfoil-shaped profile  460  so that airflow over the flap creates a low-pressure region or “lift” to help the flap stand up. 
         [0027]      FIGS. 5 and 6  show each show two flaps of other embodiments. One flap ( 510 ,  610 ) is closed, while the other ( 520 ,  620 ) is open. As with most embodiments, the hinge line of a flap ( 530 ,  630 ) is straight (and oriented roughly parallel to a radius of the disc). However, in the embodiment of  FIG. 5 , the trailing edge of the flap is cupped or scalloped as indicated at  540  to help it catch air and open over the portion of the disc where the airstream is flowing from the trailing edge of the flap towards its leading edge or hinge line. In this Figure, the axis of curvature for the scallop is perpendicular to the hinge line. 
         [0028]      FIG. 6  shows another two flaps of an embodiment. As in  FIG. 5 , one flap  610  is closed, while the other  620  is open. Again, the hinge line  630  is straight, while the trailing edge of the flap is raised ( 640 ). In this embodiment, the axis of curvature of the flap is roughly parallel to the hinge line. 
         [0029]    In some embodiments, each flap will have the same profile, while in other embodiments, a mixture of profiles may be used. The arrangement of dissimilar-profiled flaps around the circumference of the disk is preferably symmetrical. For example, every other flap could have either a first or a second different profile; or every third flap could have one of a first, second or third different profile. It is preferred that all the flaps, regardless of surface profile, be distributed symmetrically around the circumference of the disc. 
         [0030]      FIG. 7  shows another embodiment of the invention. In the perspective view (generally at  700 ) the disc, flaps, and a flap restraining structure are visible. Flap  710  is starting to open; flap  720  is open further, and flap  730  is fully open. 
         [0031]    At  740 , a profile section at A-A is shown. Dashed lines  750  show the trailing edge of a flap at various openings (less than fully open), while heavier dashed line  760  shows the trailing edge of a fully-open flap. In this embodiment, further opening of a flap is prevented by a restraining or limiting structure  770 ; note that a portion of the structure interferes with and prevents further opening of the flap (see  780 ). The maximum opening permitted by the structure is controlled by the height of the structure or the distance  790  between the surface of the disc and the blocking part of the restraining structure. In geometrical terms, the maximum angle of flap opening is roughly equal to the arcsine of the length of the flap (from leading or hinged edge to trailing edge) divided by the height of the restraining structure. 
         [0032]    The embodiments depicted in  FIGS. 1 and 2  attach to an aircraft wheel using bolts, but other embodiments may be secured using clips, cams or other fastening mechanisms. Since the embodiments apply torque to the wheel in only one direction, one potential fastening system is clips that secure in one rotational direction (the same direction as the force that the embodiment applies to the wheel). If the embodiment is turned in the opposite direction, the clips disengage and the embodiment can be removed from the wheel. In bolt-attached embodiments, it is not necessary for every wheel bolt to pass through the disc also. Some embodiments may be attached using bolts that serve only to attach the embodiment (i.e., separate and distinct bolts may secure the wheel to the landing gear). 
         [0033]    The features and characteristics of the present invention have been described largely by reference to specific examples and in terms of particular physical embodiments. However, those of skill in the art will recognize that aircraft tire pre-rotation can also be achieved by devices of different arrangements that nevertheless comprise the novel features described herein. Such variations and different implementations are understood to be captured according to the following claims.