Abstract:
An aircraft wing is equipped with asymmetric wing folding hinges to achieve a highly compact folded footprint. One or more of the hinges is advantageously placed at angle with respect to an aircraft centerplane such that the wing tips can fold over the centerplane without touching each other. Preferred aircraft have hinge angles that differ by several degrees such that one wing tip lies in front of the other in a folded configuration. Other asymmetries such as asymmetric hinge placement and asymmetric hinge seam length can be used concomitantly to enhance the compactness of the folded aircraft. Special application to wide span aircraft, high aspect ratio aircraft, and flying wing aircraft is contemplated.

Description:
[0001]    This application is a Continuation-in-Part of U.S. application Ser. No. 13/205,870 filed Aug. 9, 2011 which claims priority to U.S. Provisional Application No. 61/372,941 filed Aug. 12, 2010, both of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]    The field of the invention is aircraft. 
       BACKGROUND  
       [0003]    Aircraft comprise lift-generating surfaces to counter the force of gravity and sustain flight. In general, these lifting surfaces must have a sufficiently large planform area to produce adequate lift. Wings are the dominant lifting surface in most aircraft configurations. For a given wing planform area, a wing with a longer span tends to have increased efficiency at the expense of weight and storage footprint. As wing planform area and wing span increase, it becomes harder to store, transport, and otherwise accommodate aircraft on the ground, on a ship, and so forth. 
         [0004]    To better and more compactly accommodate aircraft on the ground, wing folding systems have been developed. Many wing folding systems have been developed for naval fighter aircraft because of the unique requirements for stowage with a small footprint aboard an aircraft carrier or other ship. Most of these aircraft use one or more hinges on each side of the wing to fold or rotate a portion of the wing out of the nominal plane of the wing. Usually, the hinges on the left and right sides of the wing are parallel with the centerline of the aircraft for simplicity of engineering and manufacturing. Examples of this conventional approach include U.S. Pat. No. 2,290,850 to Umschweif, U.S. Pat. No. 2,623,713 to Foster, U.S. Pat. No.  2,712,421to  Naumann, U.S. Pat. No. 2,925,233 to Dunn et al., and more recently U.S. Pat. No. 5,381,986 to Smith. Of all the folding systems, parallel hinges are used on the largest number of operational aircraft, including for example the Boeing F/A-18E/F Super Hornet. Although most folding wing aircraft have wing tips that are quite far apart in the folded configuration, some folding-wing aircraft have wing tips that almost touch over the centerline when folded such as the Hawker Sea Hawk. 
         [0005]    A few aircraft, such as the Douglas F4D Skyray, have fold lines that are not parallel to the aircraft centerline to avoid folding ailerons. However, for engineering and manufacturing simplicity, the left and right sides of the wing and fold system are symmetric about the centerplane of the aircraft. The wing tips also remain quite far apart in the folded configuration. 
         [0006]    A few aircraft, such as the Fairey Gannet, have used a double fold system whereby the wing has two wing fold hinge assemblies per side, allowing the wing to fold twice for additional compactness. This adds additional weight and complexity to the aircraft. Still further, some aircraft, especially those designed to travel on roads as flying cars, incorporate one or more hinges that allow the wing to fold up and back out of the plane of the wing for compactness. Examples of this latter wing folding approach include U.S. Pat. No. 2,572,421 to Abel, U.S. Pat. No. 2,674,422 to Pellarini, U.S. Pat. No. 3,439,890 to Stits, and the Grumman F6F Hellcat and F4F-4 Wildcat. 
         [0007]    Some wing stowage systems have been designed for missiles and munitions, which vary wing sweep without folding hinges to achieve compact stowage. Examples of such systems include U.S. Pat. No. 7,732,741 to Whitham, U.S. Pat. No. D461,159 to Mirales, et al, and the Small Diameter Bomb. For munitions, it is generally desirable to unfold the wings upon deployment. Some aircraft, such as the Bell/Boeing V-22 Osprey and U.S. Pat. No. 5,337,974 to Rumberger rotate the entire wing in the plane of the wing for compact stowage. Because these wings only rotate in plane, and do not fold out of plane, these are not considered wing folding systems. 
         [0008]    Some other aircraft have variable wing sweep, including for example, the Grumman F-14 Tomcat, the General Dynamics F-111 Aardvark, and U.S. Pat. No. 4,569,493 to Burhans, et al. The predominant motivation for the variable sweep is to tailor performance to different flight speeds. As used herein, the term “wing folding system” does not encompass variable wing sweep systems that rotate wings in the plane of the wing during flight. 
         [0009]    These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
         [0010]    What all these prior art wing folding systems have in common is that they are symmetric systems, with symmetric wings and folding systems about the aircraft centerline, resulting a symmetric compact folded configuration. In particular, simple wing fold hinge lines parallel to the centerline are aerodynamically efficient, as they disturb only a small sliver of the airflow over the wing. Such symmetric designs also provide benefits in the form of common engineering processes and parts between left and right wings. 
         [0011]    Even with the use of prior art wing folding systems, aircraft with especially long wing spans and high aspect ratios still have a large on-ground stowage footprint. Thus, there is still a need for a wing fold system that provides for increased compactness as compared with prior art systems. 
       SUMMARY OF THE INVENTION 
       [0012]    The inventive subject matter provides apparatus, systems and methods in which a wing is equipped with asymmetric left and right wing fold hinge assemblies. 
         [0013]    In a preferred class of embodiments, an aircraft has a wing with left and right sides disposed about a centerplane, and at least one of the left and right sides has a hinge oriented at an angle of at least two degrees with respect to the centerplane. To a non-critical reader, a deviance off the centerplane of only two degrees might seem small, but in aircraft manufacturing tolerance is typically very tight, and a variance of two degrees is actually quite significant. In the inventive subject matter discussed herein, the variance is important because it allows the left and right tips of the wing to fold over the centerplane. Greater variances are also contemplated, including for example at least five, ten, fifteen, twenty or even forty degrees, with the higher variances off centerplane contemplated to be practical for relatively lower wingspan aircraft. 
         [0014]    Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary. 
         [0015]    Although one might expect that hinges for a hinged wing aircraft would be equidistant from the centerplane, it is also contemplated that an asymmetric arrangement would be advantageous to attain increased compactness in folding. This is a function of one the wing tips being disposed forward of the other wing tip in the folded configuration. In preferred embodiments the left and right mean hinge distance from the centerplane can advantageously differ in magnitude by a least one percent, and more preferably at least two percent. This compares with typical aerospace manufacturing tolerance measured in hundredths or thousandths of a percent. 
         [0016]    In theory, the most compacted configuration that a wing can achieve for a single fold on each side is for the compacted configuration to be one third of the unfolded configuration. But with a symmetric configuration and single folds and the wing folding nearly back on itself, one cannot expect the compacted configuration to be less than one half the unfolded configuration. The reason is that the wings tips would touch at the centerplane. Naturally, one could fold the wings such that they are oriented upwards in a compacted configuration, but this incurs a significant height penalty. By orienting the folds away from the centerplane, and concomitantly locating the hinge seams lines at different mean distances from the centerplane, embodiments contemplated herein can approach the theoretical maximum. To point, a right wing folding hinge can be disposed at a right mean hinge distance from the centerplane that is less than 34%, 40%, 45%, 50%, or even 60% of a right wing semi-span. 
         [0017]    Viewed from another perspective, the fold lines can advantageously be disposed to define inboard (non-folding) and outboard (folding) wing portions such that the combined left and right folding planform areas are between 25% and 200% of the combined left and right non-folding planform areas, more preferably between 40% and 120%, and still more preferably between 50% and 90%. In especially preferred embodiments, the combined left and right folding planform areas are at least 60% of the combined left and right non-folding planform areas. 
         [0018]    Although it is might seem optimal to use fold lines that are the same lengths on the left and right sides of the wing, it is contemplated that one could use fold lines having different lengths. For example, it is contemplated than an aircraft could have left and right wing hinge seam with lengths that differ by at least 2%, 5%, 7% or even 10%. 
         [0019]    Many different types of aircraft can take advantage of the teachings herein, but these teachings are contemplated to be especially valuable to long wing span (high aspect ratio), high efficiency aircraft. Some such aircraft could be of the “flying wing” variety having no empennage, and other aircraft could be have an airfoil profile shape configured for natural laminar flow with an upper surface laminar flow extent of at least 30%. It is still further contemplated that system could be assembled comprising a given fuselage and inboard wing portions that could be used with different sets of outboard wing portions. Replacing the outboard wing portions should be relatively easier in aircraft according to the inventive ideas herein than in traditional aircraft because the wing is already divided at the hinge seams. 
         [0020]    Although one could achieve many of the compactness features contemplated herein using multiple wing folding hinges on each side of an aircraft, and possibly with trammel or other compound hinge arrangements, it is contemplated herein that sufficient compactness can be achieved by use of only a single, simple hinge or a hinge with rotational elements in a very small radius for folding on each side of the aircraft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0021]      FIGS. 1A ,  1 B, and  1 C are side, front, and top view illustrations respectively of a folding-wing airplane in an unfolded configuration generally according to the prior art. 
           [0022]      FIGS. 2A ,  2 B, and  2 C are side, front, and top view illustrations respectively of the same folding-wing airplane of  FIGS. 1A-1C  but in a folded configuration. 
           [0023]      FIGS. 3A ,  3 B, and  3 C are side, front, and top view illustrations respectively of a preferred folding-wing airplane configured according to the present teachings in an unfolded configuration. 
           [0024]      FIGS. 4A ,  4 B, and  4 C are side, front, and top view illustrations respectively of the same folding-wing airplane of  FIGS. 3A-3C  but in a folded configuration. 
           [0025]      FIGS. 5A ,  5 B, and  5 C are schematic illustrations of geometrical constructions useful defining descriptive terminology related to symmetric, anti-symmetric, and asymmetric angles, respectively. 
           [0026]      FIG. 6A  is a plan view drawing of an especially preferred folding wing aircraft, while  FIG. 6B  is a plan view drawing of the same aircraft in a folded configuration.  FIG. 6C  is a plan view of a left replacement outboard wing portion for the aircraft of  FIG. 6A .  FIGS. 6A-6C  are drawn to scale. 
           [0027]      FIGS. 7A and 7B  are perspective illustrations of an alternate especially preferred aircraft in unfolded and folded configurations, respectively. 
           [0028]      FIG. 8A  is a side view illustration of a wing folding hinge assembly and its interface with inboard and outboard wing portions.  FIG. 8B  is a detailed side view illustration of the same assembly in a folded configuration, while  FIG. 8C  shows is a side view illustration of the same assembly in an unfolded configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. The explanation and definition of aircraft components, dimensions, and orientations are illuminated through  FIGS. 1A-1C  and  2 A- 2 C, which illustrate a folding-wing airplane generally according to the prior art as described in the background section.  FIGS. 3A-3C  and  4 A- 4 C illustrate how a substantially similar aircraft can achieved increased compactness of a folded configuration in accordance with aspects of the present inventive subject matter. 
         [0030]      FIGS. 1A ,  1 B, and  1 C show side, front, and top views respectively of a folding-wing aircraft  100  in an un-folded configuration generally according to the prior art. The aircraft centerplane  150  defines left and right sides of the aircraft  100  with respect to an observer behind the aircraft facing forward, where forward is the direction of normal aircraft flight. The aircraft  100  comprises a wing  110 , having a right inboard portion  112 , a right outboard portion  114 , a left inboard portion  116 , and a left outboard portion  118 . The extreme right end of the wing defines a right wing tip  170 , while the left end of the wing defines a left wing tip  172 , the tip being the portion of the wing  110  that is farthest away from the aircraft centerplane  150 . The wing  110  has an overall span indicated  180 , defined as the overall length from the left wing tip  172  to the right wing tip  170 . The right wing has a semispan indicated by arrow  182 , which is the length from the aircraft centerplane  150  to the right wing tip  170 . Similarly, the left wing has a semispan indicated by arrow  184 , which is the length from the centerplane  150  to the left wing tip  172 . For conventional symmetric aircraft such as aircraft  100 , the left and right semispans  182 ,  184  are equal and sum to the overall wing span  180 . In this way, aircraft  100  may be viewed as having a single wing  110 , with left and right portions, or equivalently, left and right wings. The two terminologies are used interchangeably in this specification. The right portion of the wing  110  comprises a right inboard portion  112  and a right outboard portion  114 . 
         [0031]    The aircraft  100  further comprises a fuselage  108 , typically configured to carry payload including cargo, fuel, and/or passengers, and often comprising a cockpit  134  that can accommodate a pilot and a flight control system (not shown). The aircraft  100  is powered by a motor  132  coupled to a propeller (not shown) or other propulsive means such as a turbofan, rotor, or jet engine. An empennage  120  comprises a vertical tail  122  with a rudder  124  and a right horizontal tail  126  and left horizontal tail  128 . An elevator  130  is a flapped portion of the horizontal tail  126 , 128 . As used herein, the terms “tail” and “empennage” are used interchangeably. The aircraft control system (not shown) allows flight control of the aircraft  100  through manipulation of the rudder  124 , elevator  130 , and ailerons  190 , 192 , which are flapped portions of the wing  110 . 
         [0032]    The aircraft  100  is also equipped with nose landing gear  142  and main landing gear  144  that cooperate to support the aircraft  100  on the ground  140  when landed, parked, taxiing, or driving on the ground. On the ground, the aircraft has a height indicated by arrow  148  and measured from the ground  140  the highest point on the aircraft  100 . In  FIG. 1A , the highest point on the aircraft is the tip of the vertical tail  122 , but in other aircraft could be a nose, a rudder, a radome, a fuselage, a mission pod, or other component. As shown, aircraft  100  has no additional height penalty relative to the top of the tail  122 . However, there are aircraft (not shown) in the prior art in which folding incurs a substantial height penalty, which might be 5%, 10%, or even 40% or more relative to the overall height of the unfolded aircraft. 
         [0033]    To facilitate folding, the wing  110  has a right folding hinge seam  160  that allows for the rotatable coupling of the wing right outboard portion  114  and right inboard portion  112 . The wing also has a left folding hinge seam  162  that facilitates wing folding through rotation of the wing left outboard portion  118  with respect to the left inboard portion  116 . The wing  110  has a planform area which is defined as the projected area when viewed from above as in  FIG. 1C . The aspect ratio of the wing is defined as the square of the wing span  180  divided by the wing planform area. It can be seem that this prior art aircraft has a symmetrical wing about the centerplane, symmetrical folds, and therefore it has a symmetrical folded configuration 
         [0034]      FIGS. 2A ,  2 B, and  2 C show side, front, and top views respectively of the same prior art folding-wing aircraft  100  of  FIGS. 1A ,  1 B, and  1 C but in a folded configuration. In a folded configuration, the wing outboard portions  114 , 118  are folded up and over the wing inboard portions  112 ,  116 . In this folded configuration, the aircraft  100  has a folded height  248  that may differ from the unfolded height  148 . As shown in  FIG. 1A , the aircraft unfolded height  148  is the distance measured between a substantially flat and level surface or ground  140  and the highest portion of the aircraft, in this case the wing tip  172 , in a wheels down landed configuration. The folded aircraft also has a folded width  280  between the left and right portions of the aircraft  100  farthest outboard of the centerplane  150 . In most cases, this width  280  will be less than the wing span  180  of the unfolded aircraft. 
         [0035]    The right wing inboard portion  112  defines a wing dihedral line  290  with respect to the aircraft front view as shown in  FIG. 2B . For the aircraft of  FIGS. 1B and 2B , the wing right outboard portion  114  lies along this dihedral line in the unfolded configuration, but forms a folded cant line  292  in the folded configuration. Thus, the aircraft wing right outboard portion is rotated or folded through an angle indicated by arrow  294  to convert from the unfolded to folded configurations. It should be noted that the aircraft  100  is symmetric, but that the dihedral line  290  is not necessarily parallel to the plane of the ground  140 . In the folded configuration, the right wing tip  170  lies over the right wing inboard portion  112 , but remains on the right side of the aircraft centerplane  150 . In consideration of the alternate viewpoints of  FIGS. 2B and 2C , it should be noted that the aircraft centerplane  150  is a plane of symmetry. A wing folding hinge assembly  216  mechanically and rotatably couples wing left outboard portion  118  with the wing left inboard portion  116 . 
         [0036]    Viewed from above in  FIG. 2C , the right wing folds or rotates about a folding axis  260 , while the left wing folds about a folding axis  262 . The folding axes  260 , 262  are parallel to each other, are parallel to the aircraft centerplane  150 , and are symmetric about the aircraft centerplane  150 . Further, a right wing folding hinge seam  160  intersects with a point  270  on the wing leading edge  264  and a second point on the wing trailing edge  266 . The projected distance between these points is the hinge seam length  164  (see  FIG. 1C ). 
         [0037]    As used herein, the plane of the wing refers to the plane defined by the dihedral line  290  and the line that runs between points  270 ,  272  at the intersection of the wing folding hinge seam and leading and trailing edges  264 ,  266  of the wing  110 . Also as used herein, a wing that folds “out of plane” is defined as one that rotates about an axis that is within twenty degrees of the axes that define the wing plane. Similarly, a wing that rotates “in the plane” of the wing is defined herein as one that rotates about an axis that is within twenty degrees of perpendicular to the axes that define the wing plane. It is contemplated that left and right wings may define different planes due to dihedral. For typical aircraft, the wing plane is within thirty degrees of being parallel to the ground plane in a parked condition. An aircraft coordinate system that may be useful understanding these concepts is shown in  FIG. 2C , where the x-axis  202  points forward generally in the direction of flight along the aircraft station line, the y-axis  204  points laterally along the aircraft buttline, and a z-axis  206  comes out of the plane of the figure along the aircraft waterline. The lateral plane is defined as the x-y plane, and the longitudinal plane is defined as the y-z plane. 
         [0038]      FIGS. 3A ,  3 B, and  3 C show side, front, and top views respectively of a preferred folding-wing airplane  300  configured according to the teachings herein, in an unfolded configuration on the ground after landing. Other than the wing folding system, preferred aircraft  300  is dimensioned and configured substantially like the aircraft  100  of  FIGS. 1A ,  1 B, and  1 C. In their respective unfolded configurations, aircraft  100  and  300  have identical widths, spans, heights, and lengths. The preferred aircraft  300  is equipped with substantially the same tail  122 , fuselage  108 , cockpit  134 , and landing gear  142 ,  144  as aircraft  100 . The wing  310 , however, is configured to fold in a preferred manner for increased compactness. As shown in  FIG. 3A , the aircraft has a coordinate system with an x-axis  202  pointing forward generally in the direction of flight along the aircraft station line, and a z-axis  206  along the aircraft waterline. When landed and resting on the ground  140 , the unfolded aircraft  300  has a station line that is near parallel to the plane of the substantially flat and level ground surface  140 . 
         [0039]    As shown in  FIG. 3B , an x-z centerplane  350  defines left and right sides of the aircraft  300 . The wing  310  comprises a non-folding right inboard portion  312 , a non-folding left inboard portion  316 , a folding right portion  314 , a folding left portion  318 , a right tip  370 , and a left tip  372 . A first wing folding hinge creates a first folding hinge seam  360  on the right side of the aircraft, while a second wing folding hinge is associated with a second folding hinge seam  362  on the left side of the aircraft. 
         [0040]      FIG. 3C  is a top or plan view of the preferred aircraft  300  in an unfolded or flight configuration, which is bisected by the centerplane  350 . The wing  310  has a planform area defined as the total area of the wing as projected onto the x-y plane as shown in  FIG. 3C . The wing further has a non-folding area defined as the sum of the planform areas of the non-folding right inboard portion  312  and the non-folding left inboard portion  316 . Similarly, the wing has a folding planform area defined as the sum of the planform areas of the folding right outboard portion  314  and the folding left outboard portion  318 . 
         [0041]    The right portion of the wing  310  folds about a first folding axis  380 , which has a first hinge angle  384  with respect to the aircraft centerplane  350 . Equivalently, the folding axis  380  has this same angle  384  relative to any line parallel to the centerplane in the plan view. The left portion of the wing  310  folds about a second folding axis  382  which has a second hinge angle  386  with respect to the aircraft centerplane  350 . In preferred embodiments, these angles are advantageously configured to be in anti-symmetric directions with different magnitudes. It is contemplated that well-chosen hinge folding axis angles allow the aircraft to fold into an especially compact configuration such that the left wing tip is at least partially disposed on the right side of the aircraft centerplane in a folded configuration. 
         [0042]    To fold the aircraft wing, it is contemplated that a seam is needed that runs around the wing. In the plan view of  FIG. 3C , the right folding hinge seam  360  runs parallel to the right folding axis  380 . The right folding axis  380  intersects the wing leading edge  364  at a right leading point  392 , while the same right folding axis  380  intersects the wing trailing edge  366  at a right trailing point  394 . In the plan view, the right leading point  392  is positioned at a right leading distance  352  from the aircraft centerplane  350  whole the right trailing point  394  is positioned at a right trailing distance  354  from the aircraft centerplane. The average of these two values is defined as the right wing hinge mean spanwise location. The straight line distance between the right leading point  392  and the right trailing point  394  in the plan view defines the right wing hinge seam length. 
         [0043]    The same general arrangement is found on the left side of the aircraft, although angles and distances differ for preferred aircraft configurations. The left outboard folding portion  318  is separated from the left inboard portion  316  of the wing by a left folding hinge seam  362 . A left folding axis  382  intersects the wing leading edge  364  at a left leading point  396  while the same left folding axis  382  intersects the wing trailing edge  366  at a left trailing point  398 . In the plan view, the left leading point  396  is positioned at a left leading distance  356  from the aircraft centerplane  350  while the left trailing point  398  is positioned at a left trailing distance  358  from the aircraft centerplane  350 . The average of these two values is defined as the left wing hinge spanwise location. The straight line distance between the left leading point  396  and the left trailing point  398  in the plan view defines the left wing hinge seam length. 
         [0044]    In preferred aircraft, the wing folding geometry is configured in an asymmetric manner. Preferably, the left leading distance  356  differs from at least one of the right leading distance  352  and the left trailing distance  358 . Likewise, the right trailing distance  354  is preferably configured to be different from at least one of the left trailing distance  358  and the right leading distance  352 . The first and second (right and left) folding axes  380 ,  382  are preferably configured to have angles  384 ,  386  with respect to the centerline that differ in magnitude by at least 1°, 2°, 3°, 4°, 5°, 8°, 10°, 15°, 20°, 30°, 45 or even more degrees. When the angles  384 ,  386  differ in a wing of otherwise symmetric planform layout, the left and right wing hinge seam lengths will differ. These lengths can be advantageously configured to differ by 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, or even more in preferred aircraft. Further, it can be seen that aircraft advantageously configured according to these teachings will have a planform areas of the folding right outboard portion  314  and the folding left outboard portion  318  that are different, preferably by 0.25%, 0.5%, 0.75%, 1%, 2%, 5%, or even more. In preferred aircraft, the folding planform area is configured to be 25%, 50%, 100%, 150%, or 200% of the non-folding planform area. 
         [0045]      FIGS. 4A ,  4 B, and  4 C show side, front, and top views respectively of the same folding-wing airplane  300  of  FIGS. 3A ,  3 B, and  3 C but in a folded configuration.  FIG. 4A  shows that the preferred aircraft  300  has a height  348  in a folded configuration. Preferred aircraft have a folded height  348  that is not more than 1%, 5%, 20%, 50%, 55%, or 60% greater than the unfolded height. Also, the left wing folding axis  382  has an orientation in the x-z plane with respect to the x-axis  202 , and is preferably configured to be within 5°, 10°, or even parallel with the aircraft station line. 
         [0046]      FIG. 4B  is a front view of the aircraft  300  in the folded configuration, showing that the aircraft  300  has a folded width  480 . This folded width  480  is the sum of a right folded width  482  measured from the centerplane  350  the furthest right extent of the aircraft  300  and a left folded width  484  measured from the centerplane  350  the furthest left extent of the aircraft  300 . In preferred aircraft, these widths  482 ,  484  are different in magnitude by at least 0.5%, 1%, 2%, 5%, 10%, or even more. 
         [0047]    In the folded configuration, the folding right outboard portion  314  of the wing  310  is rotated about a hinge assembly  416 . All suitable means for rotation are contemplated including internal electrical actuation, internal hydraulic actuation, manual rotation, and external actuation. Simple hinges are preferred, in which points on a pivoted body traces out circular paths, although trammel or other compound pivots are also contemplated, in which points on a pivoted body traces out non-circular arced paths. 
         [0048]    For preferred aircraft, in the folded configuration, the right wing tip  370  is at least partly disposed on the left side of the aircraft centerplane  350 . The right folding portion  314  of the wing  310  is at least partially disposed over the right inboard portion  312  and the left inboard portion  316 . Similarly, on the other side, in the folded configuration the left wing tip  372  is at least partly disposed on the right side of the aircraft centerplane  350 . This configuration allows for increased compactness as compared with prior art aircraft folding schemes. 
         [0049]      FIG. 4C  is a plan view of a preferred folded aircraft  300 . In this figure, it can be readily observed that the right wing tip  370  lies on the left side of the aircraft centerplane  350  for compact folding. Folding hinge assemblies  416 ,  418  are configured on the right and left sides of the aircraft, respectively. The generally asymmetrical aircraft arrangement is also apparent, including the different angles of the folding hinge axes  380 ,  382  with respect to the centerplane  350 . 
         [0050]      FIG. 5A  is an illustration of a geometrical construction useful for explaining the descriptive terminology of aircraft folding arrangements. In  FIG. 5A , a centerline  550  runs longitudinally along the station line and defines first and second sides. A first line  540  defines a first angle  560  with respect to the centerline as shown. On the opposite side, a second line  542  defines a second angle  570  with respect to the centerline  550 . As drawn in  FIG. 5A , the angles  560 ,  570  are equal in magnitude and opposite in sign. This is defined as a symmetric arrangement because the first and second sides are mirror images of each other reflected about the centerline. It can also be stated that the first angle  560  and second angle  570  are symmetrically disposed because they are opposite in sign. 
         [0051]      FIG. 5B  is an illustration of an alternate geometric construction with a centerline  550 , first line  540 , and first angle  560  as in  FIG. 5A . A second line  544  has a second angle  572  with respect to the centerline  550 . As drawn in  FIG. 5A , the angles  560 ,  570  are equal in magnitude and equal in sign. This is defined as anti-symmetric arrangement. It can also be stated that the first angle  560  and second angle  570  are anti-symmetrically disposed because they are equal in sign. 
         [0052]      FIG. 5C  is an illustration of yet another geometric construction with a centerline  550 , first line  540 , and first angle  560  as in  FIG. 5A . A second line  546  is oriented to be parallel to the centerline  550 . This is to say that the second line  546  has an angle of zero degrees with respect to the centerline  550 . This is an example of an asymmetric arrangement because the first and second lines  540 ,  546  have angles that differ in magnitude. 
         [0053]    Preferred folding aircraft have wing planforms which are substantially symmetric in design but are equipped with asymmetric wing folding features to allow folding portions of the wing to cross the aircraft centerline for increased compactness. In especially preferred aircraft, the wing folding axes angles are symmetrically disposed but asymmetric. One preferred aircraft has one wing folding axis parallel to the aircraft centerline and another that makes an angle with respect to the centerline. 
         [0054]      FIG. 6A  is a plan view of an especially preferred folding wing aircraft  600 , while  FIG. 6B  is a plan view of the same aircraft  600  in an asymmetrical folded configuration. The aircraft  600  is a tailless, flying-wing configuration comprising a wing having a right inboard portion  612  rotatably coupled to a folding right outboard portion  614 . A right folding hinge seam  660  separates these wing portions  612 ,  614 . Likewise, a left inboard portion  616  is rotatably coupled to a folding left outboard portion  618  at a left holding hinge seam  662  by a hinge assembly (not shown). The right wing outboard portion  614  terminates in a right wing tip  670 , while the left outboard portion terminates in a left wing tip  672 . The aircraft  600  has a substantially symmetrical planform and layout which advantageously creates symmetrical aerodynamic and inertial properties. However, the provisions for wing folding are asymmetric in nature. 
         [0055]    The aircraft  600  further comprises a centerplane  650  which defines left and right sides of the aircraft, and about which plane the wing planform is symmetric although the wing folding provisions are not symmetric. The aircraft has a means for propulsion  632  and a fuselage or other provision for payloads  608 . The aircraft  600  also comprises a fuel tank  622  shown here disposed inboard of the wing folding seam. 
         [0056]    The wing right outboard portion  614  folds about a first hinge axis  690  which has a first hinge angle with respect to the centerplane  650  in the plan view as shown. Similarly, the wing left outboard portion  118  folds about a second hinge axis  692  which has a second hinge angle with respect to the centerplane  650 . For the preferred aircraft  600  of  FIGS. 6A and 6B , the first and second hinge angles have different magnitudes, and thus are asymmetric but symmetrically disposed because they are opposite in sign. The angles are advantageously selected to allow the aircraft to fold compactly as shown in  FIG. 6B . A first hinge angle magnitude is advantageously selected to be between 0° and 50°, 0° and 15°, or 1° and 5° of the centerplane. A second hinge angle has a larger magnitude than the first, between 5° and 50°, 5° and 15°, or 10° and 15° of the centerplane. 
         [0057]    In normal sustained cruising flight, the aircraft  600  flies forward substantially along the x-axis, such that far-field streamlines are parallel to the aircraft centerplane  650 . A consequence of orienting the wing folding hinge seams  660 ,  662  at a nonzero angle with respect to the aircraft centerplane  650  is that increased turbulent separation will occur as air passing over the seam can trip the boundary layer into turbulence. This degrades aircraft performance by increasing drag, and this performance degradation can be larger when the airfoils selected for the aircraft wing are natural laminar flow airfoils designed to achieve at least 5%, 10%, 20%, 30%, 40%, or even 50% of upper surface natural laminar flow at an aircraft cruise condition. One skilled in the art would not normally combine an airfoil profile shape configured for natural laminar flow with an upper surface laminar flow extent of at least 30% with an oblique seam, because the oblique seam will trip flow over a larger spanwise slice of the streamwise airflow, creating turbulent drag. 
         [0058]    In the folded configuration, the aircraft  600  has a right wing tip  670  that lies on the left side of the centerplane  650  and a left wing tip  672  that lies on the right side of the centerplane  650 . The wing folding hinges and folding hinge seams  660 ,  662  are advantageously configured such that the right first mean hinge distance  682  from the centerline is between 20% and 80%, 30% and 50%, or 33% and 40% of the aircraft wing right semispan  680 . For maximum compactness, it will be seen that the left and right outboard wing portions do not touch or overlap in the folded configuration. Further, the left wing tip is forward of the right wing tip in the folded configuration. For the preferred aircraft of  FIG. 6B , during folding, the wings rotate through an angle of at least 60°, 70°, or 80°. 
         [0059]      FIGS. 6A ,  6 B, and  6 C are drawn to scale with respect to each other. It can be observed that the left hinge seam length is 4.1% greater than the right hinge seam length. Further, the left and right mean hinge distances differ by 1%. The right wing mean hinge distance from the centerplane is 36.5% of the right wing semi span. The left and right folding hinge angles are asymmetric but symmetrically disposed. The right hinge angle magnitude is 3.45 degrees and the left hinge angle is 12.5 degrees. The wing left outboard portion has a projected planform area that is 0.88% greater than that of the right outboard portion. The total folding area is 65% of the non-folding planform area. 
         [0060]      FIG. 6C  is a plan view of an alternate replaceable left outboard wing  619  that can replace the wing left outboard portion  618 . In especially preferred aircraft, the outboard wing portions  614 ,  618  are replaceable and can be uncoupled from inboard wing portions  612 ,  616  along the folding hinge seams  660 ,  662  at the hinge assemblies. In this manner, alternate outboard wings can be substituted allowing the aircraft to better perform across multiple roles and missions. It is contemplated that outboard wing replacement could be rapidly performed by ground crews. It is further contemplated that a system could be assembled comprising the aircraft  600 , with a first left outboard wing portion  618  having a first planform, and also a second left replacement outboard wing portion  619  having a second planform that differs from the first planform as shown. 
         [0061]    As shown in  FIG. 6A , the aircraft  600  is advantageously configured with one or more control surfaces  620  on the wing outboard folding portion  618 . A replaceable left outboard wing  619  can have an alternate control surface  621 . It is contemplated that such control surfaces can be configured to be controlled by a flight control system, and can receive commands and power through lines that traverse the wing folding hinge. All suitable means for transmitting electrical or hydraulic power and signals across the wing fold hinge are contemplated including flexible wiring and tubing, sliprings, and other means. 
         [0062]      FIG. 7A  is a perspective view of an alternate especially preferred aircraft  700  in an unfolded configuration stationary on the ground after landing and before takeoff in accordance with the inventive concepts herein. The aircraft  700  is shown resting on a substantially flat and level landing surface (not shown) support but aft landing gear  744  and nose landing gear  742 . An optional fuselage  708  or other payload accommodation sits on the upper surface of the wing and optionally protrudes on the lower surface. To accommodate a pilot, it is contemplated that the fuselage  708  could be configured to include a cockpit and means for controlling the aircraft. The aircraft  700  has no tail, empennage, rudder, horizontal stabilizer, or vertical stabilizer. As viewed from another perspective, the aircraft  700  has no control surfaces aft of the wing. 
         [0063]    The aircraft  700  is bisected by a centerplane  750  oriented in the plane defined by the x-axis  702  and z-axis  706 . The y-axis  704  extends in the spanwise or buttline direction. The orientation of objects can be referred to these axes. 
         [0064]    The aircraft  700  has a wing comprising non-folding or fixed right and left inboard portions  712 ,  716  and replaceable folding right and left outboard portions  714 ,  718  having tips  770 ,  772 . The upper and lower skin surfaces of inboard and outboard portions of the wings are separated by folding hinge seams  760 ,  762 . In the folded configuration at its gross weight, aircraft  700  has a folded height that is 52% greater than the unfolded height. 
         [0065]    In a preferred embodiment, to fold the aircraft, a pilot, operator, or automatic algorithm generates a folding command signal. Based on this signal, one or more actuators displace to rotate and fold the wing on one side of the aircraft. After the first wing has successfully been folded in place, actuators commence the folding of the second wing. Alternate embodiments are also contemplated in which the folding is entirely manual, in which the command is external to the aircraft, in which the motive power source is external or internal to the aircraft, and in which the actuation is external to the aircraft. Hydraulic, electrical, stored energy, and other actuation means are contemplated. Simultaneous folding of left and right wings is also contemplated. 
         [0066]      FIG. 7B  is a perspective illustration of the same especially preferred aircraft  700  after folding according to preferred methods. It can be readily observed that in this folded configuration, the a part of the right outboard wing, namely the right wing tip  770 , is at least partially disposed on the left side of the aircraft  700  as defined by a centerplane  750 . Similarly, the left wing tip  772  is at rest disposed over the right inboard wing  712  and supported by a left hinge assembly  722 . The left hinge assembly  722  is configured and oriented along a left hinge axis  782  that has an orientation with respect the x-axis  702 , y-axis  704 , and z-axis  706 . The left hinge axis is advantageously configured to have an oblique angle with respect to the x-axis  702  to allow for especially compact folding of a wing over an aircraft centerline. 
         [0067]      FIG. 8A  is a side view illustration of a wing folding hinge assembly  722  and its interface with a wing inboard portion  716  and a folding wing outboard portion  718 . The seam has a length indicated by arrow  802 . In this preferred aircraft, the hinge assembly  722  is positioned chordwise along the wing at a position centered  37 % of the seam length back from the wing leading edge as indicated by arrow  804 . It is contemplated that by appropriate choice of materials and dimensions that wing folding could be mechanized using only a single hinge assembly  722  with a width  806  that is not more than 20% of the seam length and more preferably 11.5% of the seam length. In order to react the considerable bending moments that may result during folding or in the folded configuration, prior art systems have tended to use either multiple hinge assemblies in the chordwise direction or use very wide hinge assemblies. Preferred aircraft according to teachings herein use only a single hinge assembly  722  coupled to the wing with a titanium rib interface  808  to react these bending moments. 
         [0068]      FIG. 8B  is a detailed side view illustration of the same assembly in a folded configuration. Eight spar-pin attachments  810 ,  811 ,  812 ,  814 ,  815 ,  816 , and  817  on the inboard and outboard wing portions  716 , 718  couple the wing in the unfolded (flight) configuration and transfer and react bending moments and other loads. In preferred embodiments, a spar-pin attachment  810  allows the coupling a wing spar cap  818  to an expanding pin  842 , and is constructed of a metal such as titanium or steel. In this manner, the wing structure is allowed to carry loads across a folding joint. 
         [0069]    Folding operations are mechanized by an outer actuator  822  comprising an outer actuator link  823  and coupled to the wing outboard portion  718  and an inner actuator  820  with an inner actuator link  821  and coupled to the wing inboard portion  716 . The actuator links  821 , 823  are coupled to a wingfold truss  824  with pin joints. When powered and commanded, the actuators  820 ,  824  can drive the wing between folded and unfolded configurations through rotation about the hinge assembly  722 . 
         [0070]    The hinge itself comprises an inboard attachment plate  828  that is coupled to structure of the wing inboard portion  716  and an outboard attachment plate  829  coupled to the wing outboard portion  718 . These plates are coupled to the wingfold truss  824  by a torque tube  834 . A preferred hinge assembly has inboard and outboard hinge pins  830 ,  832  spaced in close proximity. As used herein, a “basic hinge” is defined as a hinge that has two hinge pins and, during rotation, the pins remain inside of an imaginary cylinder centered at the mean hinge pin location, the imaginary cylinder having a radius that is less than five times the diameter of the largest hinge pin. In this manner, it is seen that the operation of a “basic hinge” is similar to that of a simple hinge, in that it traces out a nearly-circular path during operation. A simple hinge is one in which the object moves in a circular pattern; while complex hinge has displacement also. 
         [0071]    A retractable expanding pin  842  can be inserted in the interleaving portions of spar-pin attachments  816 ,  810  to lock the wing into the unfolded position. A pin actuator  844  drives an arm  846  coupled to the expanding pin  842  with an articulated joint. This is referred to as a wingfold locking assembly  840 . 
         [0072]      FIG. 8C  is a side view illustration of the same hinge assembly in an unfolded configuration. The actuators  820 ,  822  are in fully retracted positions, and spar-pin attachments  811 ,  817  are mated and ready to be locked in place by an expanding pin. 
         [0073]    While the subject matter disclosed herein allows for more compact folding of an aircraft, it also entails certain complications not found in prior art systems. In general, an engineer will strive to design and build systems of low complexity and high strength. The presently disclosed wing folding systems are asymmetric which can increase considerably the engineering and manufacturing work required. Also, an engineer would normally place seams or joints either in a streamwise direction or normal to structural surfaces because loads are devolved in one of those two directions and because they usually result in lower seam lengths and thus lower structural masses. It is contemplated that when oblique, asymmetric seams are used, additional structure may be required for strength and stiffness as compared to simple streamwise joints. 
         [0074]    Viewed from another perspective, the material herein provides a method of folding an aircraft having a wing with left and right wing hinges. Preferred wings have spans of 40, 60, 80, 100, 120, 140, or even 160 feet although other spans are also contemplated in the range of 1 to 300 feet. Folding comprises folding the wing at the wing hinges such that at least one of the left and right tips of the wing each pass over a centerline of the aircraft. 
         [0075]    It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. For example, the teachings regarding folding can be applied to rotorcraft and helicopter rotors. Alternately, this could be applied to folding wings of aircraft having more than one each left and right wings, or to folding tails or other surfaces. Some embodiments are contemplated in which the wings at least partially overlap in the folded configuration, and still others are contemplated where only the right or left wing has a folding hinge. Where folding of oblique wings is desired, folding may be performed parallel to far-field streamlines for compactness to achieve the same effect. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.