Abstract:
A pivoting aircraft wing and associated system and method are provided. The pivoting aircraft wing includes a wing member, a carry-through structure, and a spar box assembly pivotally connected to the carry-through structure. The spar box assembly extends longitudinally within the wing member. The spar box assembly comprises a spar box and a bearing support structure attached to the spar box. The aircraft wing further includes a plurality of bearings disposed within a plurality of bearing races defined by the bearing support structure and carry-through structure. The plurality of bearing races advantageously define an arcuate path of rotation such that the wing member is capable of rotating about a virtual axis of rotation.

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to variable sweep aircraft and, more particularly, to a pivoting aircraft wing capable of varying the sweep angle of an aircraft, as well as an associated system and method. 
   2) Description of Related Art 
   It is well known that wing design plays an instrumental role in optimizing lift and drag during flight in response to various conditions. Wing design becomes especially important depending on whether the wing is subjected to subsonic, transonic, or supersonic speeds. Decreasing drag involves balancing several different parameters, including, for example, speed, altitude, angle of attack, wing dimensions, and the profile of the airfoil. 
   Wings having a high span are preferred for takeoff and landing where drag is substantially lower than wings having a low span. Because the aspect ratio is defined as the ratio of the wing span to the average chord length, longer and narrower wings will have better lift than shorter and wider wings. However, swept wings are preferred over high aspect ratio unswept wings at transonic and supersonic speeds because drag is significantly reduced. Even though swept wings can also maintain the required lift at these higher speeds, swept wings do not perform well at subsonic speeds. Therefore, swept wing aircraft are generally required to have lower sweep angles than would typically be required for transonic and supersonic speeds in order to make takeoff and landing feasible. 
   Therefore, variable sweep aircraft wings have been developed that are able to balance the tradeoffs of using either a high aspect ratio, unswept wing, or a lower aspect ratio, swept wing. Aircraft with variable sweep wings can modify the wing configuration from a high span during takeoff, subsonic cruise, or landing, to an increased sweep during supersonic speeds. Advantageously, aircraft with variable sweep wings are able to decrease weight due to an increase in fuel efficiency and may require smaller engines to accelerate the aircraft to supersonic speed, in addition to being capable of operating over a wide range of speeds, decreasing noise due to decreased drag, and shortening takeoff and landing field lengths. 
   For example, U.S. Pat. No. 4,212,441 to Ascani, Jr. et al (“Ascani”) discloses a wing pivot assembly for a variable sweep aircraft. Ascani discloses a pivot assembly located at the end of each wing adjacent to the fuselage. The pivot assembly includes a pivot pin that utilizes a “pin within a pin” design, where either pin can carry the load limit. A pair of outboard lugs, i.e., plates, located between the wing and the pivot pin acts to carry the wing bending moment loads into the pin, while a second pair of inboard lugs located between the pivot pin and a carry-through structure carry the wing bending moment loads into the carry-through structure. In addition, two bearing assemblies connecting to the outboard lugs facilitate rotating of the pivot pin and also transmit wing bending moment loads from the outboard lugs into the pivot pin. Ascani also employs a shear bearing and the “truss concept,” which includes canting the inboard and outboard lugs at an angle, to counter axial shear loading. 
   However, previous variable sweep aircraft, such as that discussed above, have inherent disadvantages, namely increased weight, which counteracts any advantages associated with varying the sweep of the wings. In addition, the pivot pin design and excess weight offer a poor mechanical advantage and offset load paths. The support structure surrounding the pivot pin may extend quite far out into the outboard wing box in order to direct the loads away from a wide wing box geometry and toward the pin in a way that does not exceed material strength limits. The same is true of the inboard bearing support structure. Therefore, in addition to a potentially large and heavy pivot pin, the supporting structures add even more weight in transferring loading from the wings to the pivot pin and further inboard to a carry-through structure. Furthermore, the thickness of the wing is required to be at least as thick as the pivot pin, and even wider to accommodate the surrounding support structures, which also increases weight and drag, especially for supersonic aircraft. 
   It would therefore be advantageous to provide a lighter weight pivoting aircraft wing that can vary the wing sweep angle of an aircraft. In addition, it would be advantageous to provide a pivoting aircraft wing that can vary the sweep angle without sacrificing lift and drag. Finally, it would be advantageous to provide a pivoting aircraft wing that enables an aircraft to travel at supersonic speeds without increasing drag. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention addresses the above needs and achieves other advantages by providing a variable sweep aircraft that is able to change the orientation of its wings from an unswept position at low speeds, takeoff, and landing to a swept position at higher speeds. Thus, the variable sweep aircraft is able to pivot its wings about a virtual axis of rotation to any number of sweep angles depending on the speed and other circumstances to reduce drag. The pivoting aircraft wing of the present invention is able to reduce the weight of the variable sweep aircraft relative to conventional variable sweep aircraft, which consequently reduces drag. 
   In one embodiment, the pivoting aircraft wing includes a wing member, a carry-through structure, and a spar box assembly pivotally connected to the carry-through structure. The spar box assembly extends longitudinally within the wing member. The spar box assembly includes a spar box and at least one bearing support structure attached to the spar box. In one variation of the present invention, one end of the spar box tapers to a point proximate to the third bearing and defines a generally triangular shape. The aircraft wing further includes a plurality of bearings disposed within a plurality of bearing races defined by the bearing support structure and carry-through structure. The plurality of bearing races advantageously define an arcuate path of rotation such that the wing member is capable of rotating about a virtual axis of rotation. In variations of the present invention, the aircraft wing is capable of pivoting from an unswept position having about 10 degrees of sweep to a swept position having at least 70 degrees of sweep. An actuator connected to the spar box may be employed to pivot the wing member to various sweep angles. 
   The plurality of bearings may include first, second, and third bearings. The first and second bearings may be attached to the carry-through structure, while the third bearing may be attached to an end of the spar box proximate to the carry-through structure. The spar box assembly may comprise at least a pair of bearing support structures that define respective bearing races in which the first and second bearings are disposed such that the spar box assembly is capable of pivoting about the first and second bearings. Also, a bearing support structure may be attached to the carry-through structure and define at least one bearing race such that the third bearing may be disposed and pivoted within the bearing race. The spar box assembly may advantageously pivot about the plurality of bearings and bearing races to vary the sweep angle of the wing member. 
   In another embodiment of the present invention, a pivoting aircraft wing system includes a pair of wing members, a fuselage member, and a carry-through structure carried by the fuselage member. The aircraft wing system also includes a pair of spar box assemblies that pivotally connect to the carry-through structure and extend longitudinally within each of the wing members. Each spar box assembly includes a spar box and at least one bearing support structure attached to the spar box. Furthermore, the aircraft wing system includes a plurality of bearings disposed within a plurality of bearing races defined by each of the bearing support structures and carry-through structure. The plurality of bearing races defines an arcuate path of rotation such that each of the wing members is capable of rotating about a respective virtual axis of rotation. 
   The present invention further provides a method of pivoting a pair of aircraft wings on a variable sweep aircraft. The method includes first providing a fuselage member, a carry-through structure carried by the fuselage member, and a pair of spar boxes. Each of the spar boxes are pivotally connected to the carry-through structure and extend longitudinally within each of a pair of wing members such that each of the wing members are coupled to each of the spar boxes. The method further includes pivoting each of the wing members about a virtual axis of rotation to predetermined sweep angles. 
   Optionally, the method includes pivoting the wing members about a virtual axis of rotation defined by a plurality of bearings disposed within a plurality of bearing races defined between the carry-through structure and each of the spar boxes. Each of the wing members may be pivoted simultaneously with a respective actuator to predetermined sweep angles, such as a sweep angle of at least 70 degrees. 
   The present invention therefore provides variable sweep aircraft wings that are capable of being oriented at various sweep angles to reduce drag at different speeds. The combination of varying the aspect ratio and reducing the weight of the variable sweep aircraft wings facilitates a decrease in drag. Weight is reduced by maintaining the bending, torsional, and axial loads in the wing spar box structure, rather than focusing the loading through a single small pivot on each wing. Spreading the loading over a larger area results in a reduction in the structural gauges of the wing, which directly results in weight reduction. Reducing drag, in turn, may reduce noise and fuel consumption because of the smaller engine required, and may decrease the runway length needed for takeoff and landing. 
   In addition, the variable sweep aircraft wing of the present invention may decrease the effects of sonic booms on commercial flights, as well as facilitate over-land supersonic commercial flights. Commercial flights traveling at supersonic speeds have been generally limited to flights over water due to the effects of sonic booms on humans; however, the configuration of the variable sweep aircraft wing of the present invention may make low-boom flight more achievable. This feature is due to the unswept and swept positions the aircraft wing may obtain, which permits the aircraft to takeoff and land at low speeds with reasonable field lengths, as well as pivot to a more swept position during higher speeds than fixed wing supersonic aircraft can achieve because of their low speed requirements. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
       FIG. 1  is a top view of a variable sweep aircraft according to one embodiment of the present invention, illustrating the wings in an unswept position; 
       FIG. 1A  is another top view of the variable sweep aircraft of  FIG. 1 , illustrating the wings in a swept position. 
       FIG. 2  is an enlarged section view taken through line  2 — 2  illustrating the virtual axis of rotation of the variable sweep aircraft shown in  FIG. 1 ; 
       FIG. 3  is an enlarged exploded view of one end of a spar box assembly shown in  FIG. 1 ; 
       FIG. 3A  is an enlarged cross-sectional view of a bearing race shown in  FIG. 3 ; 
       FIG. 4  is an enlarged perspective view of a spar box, bearing support structures, and bearings according to another embodiment of the present invention; 
       FIG. 5  is a cross-sectional view of the spar box shown in  FIG. 4 , with the section taken through bearings A, B, and the view facing inboard; and 
       FIG. 6  is another cross-sectional view of the spar box shown in  FIG. 4  in an unswept position, with the section taken through bearing C, and the view facing aft. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
   Referring now to the drawings and, in particular to  FIG. 1 , there is shown a variable sweep aircraft  10 . The term “variable sweep aircraft” is not meant to be limiting and may be any aircraft capable of varying the sweep angle of the wings such that the aspect ratio may be increased and decreased depending on the flight speed and other desired parameters. Thus, variable sweep aircraft could be a variable geometry aircraft, or any aircraft that includes wings that may pivot, rotate, swivel, or otherwise change the orientation of the wings to various sweep angles. As a result, the variable sweep aircraft  10  is capable of flying from subsonic to supersonic speeds with improved lift and drag properties over a wide range of speeds. 
   In one embodiment of the present invention  FIG. 1  illustrates a variable sweep aircraft  10  including a fuselage  11  and a pair of wings  12  extending in opposite directions from the fuselage. Each of the wings  12  is carried by, or otherwise attached to, a structural spar box  14 . The spar boxes  14  are pivotally attached to a carry-through structure  16 . Bearings, generally indicated at  18 , and races, generally indicated at  19 , are located between each of the spar boxes  14  and the carry-through structure  16  and define a virtual axis of rotation  20 , as will be explained more fully below. Each of the wings  12  rotates about a respective virtual axis of rotation  20 . As shown in  FIG. 1A , actuators  22  are connected to each of the spar boxes  14  and are operable to rotate the wings about the virtual axis of rotation  20  to various sweep angles θ. 
   The actuators  22  could be any hydraulic, pneumatic, or similar mechanism that is capable of providing sufficient force to pivot each of the wings  12 . Thus, the actuators  22  could be electrically, mechanically, or electro-mechanically controlled, and are capable of closely controlling the sweep angles θ to pivot the wings  12  to predetermined sweep angles. Preferably the actuators  22  are capable of pivoting each of the wings  12  simultaneously to maintain the stability of the variable sweep aircraft  10  during flight. 
   As shown in the embodiment of  FIG. 2 , an engine inlet  24  is located below each of the wings  12  to direct air into the engine to thrust the variable sweep aircraft  10 . In one embodiment of the present invention, a turbojet engine with air inlets on both sides of the fuselage  11  could be incorporated with the variable sweep aircraft  10  to provide the aircraft with adequate thrust to reach supersonic speed. In addition, a wing strake  26  extends approximately orthogonal to the fuselage  10  and aft towards each of the wings  12  and carry-through structure  16 . Thus, the strake  26  is aligned in the direction of airflow and is generally aligned with each of the wings  12  when the wings  12  are fully swept, as shown in  FIG. 1A . 
   The structural spar boxes  14 , as known to those skilled in the art, include a front spar  28  and a rear spar  30 , both of which extend vertically within each of the wings  12 . The front  28  and rear  30  spars are connected by a pair of horizontal members to form a hollow “box.” The spar boxes  14  extend substantially along the length of each of the wings  12  to provide the main structural support for the wings  12  and to increase the torsional rigidity of the wings. At one end of the spar boxes  14 , the spar boxes include a tapered end  44  having a generally triangular shape, as shown in  FIG. 3 . Thus, each of the front  28  and rear  30  spars converge and intersect at bearing C. Because each of the spar boxes  14  are connected to the respective wings  12 , as the spar boxes are rotated each of the wings are also rotated to vary the sweep angle θ. As a result, the wings  12  follow an arcuate path of rotation about their respective virtual axis of rotation  20 . 
   Generally, an upper skin  32  and a lower skin  34  are carried, or otherwise attached to, each of the spar boxes  14 , as shown in  FIG. 2 . Internal skin stiffeners, stringers, and ribs are typically arranged between the upper  32  and lower  34  skins and along the wings  12  for reinforcement and to define the contour of the airfoil, as known to those skilled in the art. Generally, the stiffeners and stringers extend spanwise within the wings  12 , while the ribs extend chordwise. It is understood that any arrangement of spars, skin stiffeners, stringers, or ribs could be used within each of the wings  12  to provide varying amounts of support, wing shapes, or airfoils. For example, the spar boxes  14  could also include a middle spar located between the front  28  and rear  30  spars. Similarly, the spar box  14  could have a shape other than triangular at the end proximate to bearing C, such as a semi-circular or even rectangular. 
   The carry-through structure  16 , as known to those skilled in the art, bridges between the wings  12  and attaches to, or is integral with, the fuselage  11 . Thus, the carry-through structure  16  is a major structural element that transfers loading from the wings  12  and spar boxes  14  to, or across, the fuselage  11 . The carry-through structure  16  is shown in  FIG. 1  as having a curvature that conforms to each virtual axis of rotation  20 , and also lies adjacent to the upper  32  and lower  34  skins, as shown in  FIG. 2 .  FIG. 1  also illustrates that the carry-through structure  16  is generally aligned spanwise with the leading edge of the wings  12  when in an unswept position. It is understood that the carry-through structure  16  could be any shape or size to accommodate different sized fuselages  11 , wings  12 , or spar boxes  14 , as well as conform to a variety of virtual axes of rotation. 
   Referring now to  FIGS. 1–3 , one advantageous embodiment of the present invention is shown and is described in detail for purposes of example and not of limitation. The variable sweep aircraft  10  of this embodiment is about 155 feet in length, and has a span of approximately 120 feet in an unswept position. The front  28  and rear  30  spars are spaced about 6 feet apart. Also, the variable sweep aircraft  10  has a sweep angle θ of about 10 degrees when unswept, and may rotate to a sweep angle of about 70 degrees. 
   It should be noted that the aforementioned features of the exemplary embodiment of the variable sweep aircraft  10  may change as they depend on many factors. For example, the fuselage  11  could be various cross sections and sizes depending on the type of aircraft desired. Additionally, the profile of the airfoil could be any suitable airfoil, symmetric or asymmetric, having any number of chord lengths, leading edge radii, trailing edge angles, and thicknesses, as known to those skilled in the art, depending on the drag and lift properties desired. Although it is preferred that the wings  14  assume a sweep angle θ ranging from about 10 to 70 degrees, it is understood that any specified angle could be employed with the variable sweep aircraft  10  in alternative embodiments of the present invention to achieve a desired drag coefficient. 
   The bearings  18  and bearing races  19  advantageously define a virtual axis of rotation  20  for each of the wings  12 . As illustrated in the embodiment shown in  FIG. 3 , bearing support structure  36  is attached to the vertical face of the front spar  28 , while bearing support structure  38  is attached to the vertical face of the rear spar  30 . Each of the bearing support structures  36 ,  38  defines a race  42  in its outer surface, i.e., the surface facing away from the spar box  14 , as shown in  FIGS. 2 ,  3 A, that engages a respective one of bearings A, B. Bearing A is a single ball attached to the carry-through structure  16  that fits within the bearing race  42  defined in bearing support structure  36  such that each of the spar boxes  14  may pivot when rotated to a specified sweep angle θ. Similarly, bearing B is a ball that is attached to the carry-through structure  16  that allows the spar boxes  14  to pivot along the races within the bearing race  42  defined in bearing support structure  38 . Thus, the bearing support structures  36 ,  38  provide a smooth radial path in which each of the bearings A, B ride when the spar box is rotated. It should be noted that bearings A, B and bearing support structure  38  are shown on  FIG. 2  in dashed lines for illustrative purposes only, as the view of section  2 — 2  would not otherwise depict bearings A, B and bearing support structure  38 . Bearings A, B could be attached to the carry-through structure  16 , and bearing support structures  36 ,  38  attached to the spar boxes  14 , by any suitable means, such as by welding, fastening, riveting, and the like, that is capable of withstanding the loads endured during flight. 
   Bearing C is shown in  FIGS. 2–3  as having two adjacent balls that are attached to the tapered end  44  of the spar boxes  14 . A bearing support structure  48  is attached to the carry-through structure  16 , and bearing C may be positioned with a ball in each of a pair of races  40  defined by the bearing support structure such that bearing C may pivot within the pair of races when the spar boxes  14  are rotated. Bearing C pivots to position C 1  while in a fully swept position, and thus follows an arcuate path of rotation, as shown in dashed lines on  FIG. 1A . Bearing C could be attached to the spar boxes  14 , and bearing support structure  48  attached to the carry-through structure  16 , by any suitable means, such as by welding, fastening, riveting, and the like, that is capable of withstanding the loads endured during flight. 
   Thus, the bearings  18  and bearing races  19  define a virtual axis of rotation  20  for each of the wings  12  in one advantageous embodiment of the present invention. The term “virtual” axis of rotation  20  is used because there is no actual bearing, bearing race, or other device at the specific point about which the wings  12  pivot. However, each of the wings  12  pivots about its respective virtual axis of rotation  20 , which acts to distribute loading away from a single pivot point. 
     FIGS. 4–6  illustrate another embodiment of the present invention. Each of the spar boxes  14  includes a bearing C that is integrally formed with the spar box. Bearing C includes several teeth  46  that extend outwardly and engage bearing races  40  defined in a bearing support structure  48 . The bearing support structure  48  is attached to the carry-through structure  16 . As shown in  FIG. 4 , bearing C is located proximate to a tapered end  44 , wherein the tapered end extends from the end of the spar box  14  to bearing C. Bearing support structures  36 ,  38  are attached to the spar box  14  and also include several bearing races  42  that may engage the teeth  52  extending from bearings A, B. As before, bearings A, B are attached directly to the carry-through structure  16 , as shown in  FIG. 5 . As a result, the bearing support structures  36 ,  38 ,  48  define respective bearing races  40 ,  42  that are arranged in an arc so that the teeth  46 ,  52  of each of the respective bearings may slide within the bearing races to rotate the spar boxes  14  about a respective virtual axis of rotation  20 . 
   The wings  12  generally experience shear, torsional, and bending loading during flight. Bearings A, B, C transfer loading to the carry-through structure  16  and fuselage  11  and vice versa. Specifically, bearings A, B transfer shear loading due to drag and lift, as well as torsional loading due to the wing pitching moment. The lever arm of the torsional load in the unswept and swept positions would be equivalent to the distance between bearings A, B in approximately a chordwise direction. Bearing C transfers the bending moment caused by lift and the lift distribution along each of the wings  12 . The bending moment arm would be reacted over the spanwise distance from a line between bearings A and B to bearing C when the wings  12  are in an unswept position, while the moment arm would be reacted over a longer arm from position C 1  to bearing B in a swept position. The bending moment in bearing C is generally much higher than the loading experienced at bearings A, B. The configuration of bearings A, B, C distributes the loading so that no single bearing or pivot point experiences all of the loading at any given instant. 
   The wings  12  could be any suitable material, but is preferably a lightweight yet high strength aluminum or composite suitable for aircraft wings. Similarly, the spar boxes  14 , carry-through structure  16 , bearings  18 , and bearing races  19  are preferably all lightweight and manufactured from a composite, ceramic, or metallic material. The composite material could be any suitable particle-reinforced, sandwiched, laminated composite, or fiber-reinforced material, such as a carbon-fiber reinforced plastic. In one embodiment, the bearings  18  include a metallic or ceramic backing and have a Teflon™ material (commercially available from E.I. du Pont de Nemours and Company) surface where the bearings engage the bearing races  19 . However, it is understood that various composites, including metals and their alloys, could be incorporated in additional embodiments of the present invention. 
   Although the wings  12  are illustrated in one embodiment of the present invention as having three pivot points about bearings A, B, C to define the virtual axis of rotation  20 , it is understood that alternative configurations could be employed and still be within the scope of the present invention. For example, any number of bearings  18 , bearing races  19 , and bearing support structures  36 ,  38 ,  48  could be used to define the virtual axis of rotation  20 . In addition, the bearings  18 , bearing races  19 , and bearing support structures  36 ,  38 ,  48  could be arranged such that the virtual axis of rotation  20  may be located in any desirable location between the spar box  14  and carry-through structure  16 . 
   Although various elements, such as the bearings  18  and bearing supports structures  36 ,  38 ,  48 , are described as being “attached” in various embodiments, it is understood that the bearings  18 , bearing races  19 , and bearing support structures  36 ,  38 ,  48  could be integrally molded, machined, or otherwise formed as discrete elements, in either or both of the spar boxes  14  and carry-through structure  16 , and still be “attached” for purposes of the present invention and still be capable of withstanding the loading imposed on the variable sweep aircraft  10  during flight. For example, the bearing support structures  36 ,  38  could be integral with the spar boxes  14 , or bearings A, B could be integral with the carry-through structure  16 . Additionally, it is understood that in alternative embodiments the spar box  14  could carry all of the bearings  18 , while the carry-through structure could define all of the bearing races  19 , and vice versa. 
   Furthermore, although the bearings  18  are shown in  FIGS. 1–3  as being spherical, the bearings could be any type or dimension of bearing, such as tapered, cylindrical, or the like, that enable the spar boxes  14  and wings  12  to pivot. It is also understood that the bearings  18  illustrated in  FIGS. 4–6  could include any number and dimension of respective teeth  46 ,  52  to accommodate any number of respective bearing races  19  defined in the respective bearing support structures  36 ,  38 ,  48 . Similarly, the bearing races  19  could be any type or dimension to accommodate each of the corresponding bearings  18 , and could be lubricated in alternative embodiments. It is also understood that each of the bearings  18  and corresponding bearing races  19  could also be different, so that at least one bearing and corresponding bearing race are different than the others. 
   Advantageously, the configuration of the bearings  18  and bearing races  19  act to distribute the loading about a virtual axis of rotation  20  for each of the wings. This distribution ensures that the weight of the carry-through structure  16  and spar box  14  can be reduced. In addition, because the loading is distributed, the thickness of the wing may also be reduced, which allows for small thickness-to-chord ratios to be employed. For example, in one embodiment of the present invention, the thickness-to-chord ratio is about 0.08 in an unswept position and about 0.025 at about 70 degrees of sweep, which are typical values for aircraft traveling at supersonic speeds. Furthermore, the variable sweep aircraft  10  of the present invention is also capable of traveling at supersonic speeds, and the decreased weight and drag would improve all aspects of performance and make a low-boom configuration more achievable. 
   Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.