Abstract:
Embodiments of the present invention relate to an adaptable wing having a variable geometry for influencing aerodynamic performance, the wing comprising a jointed leading edge having a main pivot, and a wrist joint, with a wing arm therebetween, 5 and a distal wing hand depending from the wrist joint; the wing being reciprocally actuable, via the main pivot and wrist joint, between a first state having an extended wing planform and a second state having a tucked wing planform.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the present invention relate to a morphing foil or wing and vehicle comprising such a foil or wing. 
       BACKGROUND TO THE INVENTION 
       [0002]    It is well known to change the planform, via wing configuration changes, to achieve varying performance objectives for aircraft. For example, modern combat planes have variable sweep wing geometries that are deployed according to immediate performance requirements such as subsonic cruising, take-off and landing, which will have a corresponding, high-aspect ratio wing geometry, as compared to supersonic flight, which will have a different corresponding geometry, such as fully-swept back wings to mitigate drag. Such combat planes include, for example, the Panavia Tornado, F-14 Tomcat and MiG-27. Being able to make significant geometric changes to an aircraft&#39;s wing during flight increases the flexibility and overall suitability of the aircraft for disparate missions or disparate parts of a mission. However, such wings are very complex, introduce complex control issues and are highly expensive and therefore inappropriate for unmanned air vehicles (UAVs). 
         [0003]    Furthermore, there is significant interest in biologically inspired technologies. Avian and marine biological systems comprising aerodynamic or hydrodynamic surfaces provide useful insights into balancing performance requirements of air and marine vehicles in terms of, for example, the lift/drag ratio, roll, pitch and yaw control and stability. 
       SUMMARY OF INVENTION 
       [0004]    Accordingly, embodiments of the present invention provide an adaptable wing having a variable geometry for influencing aerodynamic performance, the wing comprising a jointed leading edge having a main pivot, and a wrist joint, with a wing arm therebetween, and a distal wing hand depending from the wrist joint; the wing being reciprocally actuable, via the main pivot and wrist joint, between a first state having an extended wing planform and a second state having a tucked wing planform. 
         [0005]    Advantageously, the aerodynamic performance, such as, for example, loading, of the wing can be adapted to different states or phases of flight. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments of the present invention will now be described, by way of example only, in which: 
           [0007]      FIG. 1  is a perspective view of a UAV; 
           [0008]      FIG. 2  shows an exploded view of a wing for the UAV; 
           [0009]      FIG. 3  depicts a view of a wing for the UAV in an extended position; 
           [0010]      FIG. 4  shows a view of a wing for the UAV in a tucked position; 
           [0011]      FIG. 5  illustrates the relative distances between a number of axes associated with the wing; 
           [0012]      FIG. 6  depicts a view of a feather mounted on a feather rib; 
           [0013]      FIG. 7  is a side-sectional view of an alternative embodiment of a feather rib/wing surface element assembly; 
           [0014]      FIG. 8  shows a wing bearing a covert in an extended state; and 
           [0015]      FIG. 9  shows a wing bearing a covert in a tucked state. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    Referring to  FIG. 1 , there is shown a perspective view  100  of a UAV  102 . The UAV  102  comprises a fuselage  104  bearing a propeller  106 , tailerons  108  and a tail  110 , as well as a pair of wings  112  and  114 , coupled to the fuselage  104  via a housing  120 . 
         [0017]    The leading edge of the wings  112  and  114  is jointed. Each wing  112  and  114  comprises a main pivot  116  and a wrist joint  118 . In the illustrated figure, only the right wrist joint is visible due to the wing  112  being in a tucked position or state, while the other wing  114  is in an extended position or state. 
         [0018]    Each wing comprises a wing hand section  122  and  124 , a wing arm section  126  and  128 , and a tip fairing  129  and  130 . Each wing also has a plurality of feathers  135 , such as, for example the distal most feather  132  and  134  relative to the fuselage. In the present embodiment, each wing  112  and  114  has seven lower feathers, which are visible in  FIG. 1  and seven upper feathers. The feathers  135  are arranged to overlap in the tucked state and/or overlap in the extended state to varying degrees. 
         [0019]    Further details regarding the fuselage  104  are available in, for example, UK patent application nos. GB1106617.2 and PCT/GB2012/050856, which are incorporated herein by reference for all purposes. 
         [0020]      FIG. 2  shows an exploded view  200  of an embodiment of the wings  112  and  114 . The wing comprises the housing  120  for coupling the wing  112  and  114  to the fuselage  104 . The housing comprises a main pivot housing  202  for receiving a main pivot hub  204  of the wing arm section  126  and  128 . The main pivot  116  has upper and lower race bearings  206  and  208  and respective upper and lower retaining caps  210  and  212 . Preferably, the race bearings comprise acetyl shells and steel balls to save weight. The bearings  206  and  208  are received by respective recesses  214  and  216  of the main pivot hub  204 . It can be appreciated that only recess  214  is visible. The retaining caps  210  and  212  have complementary formations that cooperate to provide a non-rotating axis about which the wing arm section  126  and  128  can rotate. In the embodiment shown, those complementary formations take the form of recesses  218  that cooperate with respective lugs  220  on the upper and lower outer surfaces  222  of the main pivot housing  202 . The retaining caps  210  and  212  are secured in place via a fastener (not shown). 
         [0021]    The distal end of the wing arm section  126  and  128  comprises the wrist joint  118 . The wrist joint  118  is formed from complementary portions of the wing arm section  126  and the wing hand section  124 . In the embodiment shown, the complementary portions comprise a distal upper wrist joint portion  224  and a proximal lower wrist joint portion  226 . The upper and lower wrist joint portions are arranged to receive a respective race bearing  228  and retaining cap  230 . The race bearing facilitates free rotation of the wrist while holding it together. A race bearing  232  or the like is provided to facilitate smooth operation of the wrist joint  118 . The race bearing is captured within respective tracks of the upper and lower wrist joint portions  224  and  234 ; only the track  234  of the lower wrist joint portion  226  is visible in  FIG. 2 . The wrist joint  118  is held together via a respective fastener (not shown). The distal end of the wing hand section  124  is adapted to cooperate with a complementary formation of the tip fairing  129  (not shown in  FIG. 2 ). 
         [0022]    The wing arm sections  126  and  128  have a number of engagement members. In the embodiment illustrated, the wing arm sections  126  and  128  comprise a pair of engagement members  236 ; although embodiments are not limited thereto. The engagement members  236  in preferred embodiments comprise upper and lower foraminated lugs; only the upper foraminated lugs are shown in  FIG. 2 . The upper and lower foraminated lugs have the same size and separation. The upper and lower lugs are adapted to be able to receive, where appropriate, one or more of a hub  238  of a servo linkage  240  and complementary formations of respective feather ribs  246 . Preferred embodiments realise the complementary formations of respective feather ribs  246  using upper and lower spigots  248  and  250 . Preferably, the spigots  248  and  250  form a snap fit with the upper and lower foraminated lugs. Preferred embodiments also provide nylons bolts that pass through the upper and lower spigots  248  and  250  to retain joint tolerance. In preferred embodiments the servo linkage hub  238  and the actuation linkage hub  240  are captured between the upper and lower spigots and secured in place by complementary recesses adapted to receive the free ends of the upper and lower spigots together with steel bolts passing through the hubs for strength and durability. The wing hand sections  122  and  124  also bear respective engagement members  252  that are identical in form and function to the engagement members  236  of the wing arm sections  126  and  128 . The engagement members  252  are adapted to receive a hub  242  of an actuation linkage  244 . Upper and lower foraminated lugs  254  and  256  of the distal most engagement member  252  are shown. In the illustrated embodiments the wing hand section comprises four such engagement members, but embodiments are not limited to such an arrangement. Embodiments can be realised in which more or fewer engagement members  252  are used. 
         [0023]      FIG. 2  also shows a servo  258  having a servo arm  260 . The servo arm  260  is arranged to rotate about a respective axis (not shown), in response to a received command, to move the wings between the extended and tucked positions via the servo linkage  240 . In a preferred embodiment, the servo linkage hub  238  is coupled to wing arm section  126  and  128  via one of the engagement members  236 . In the illustrated embodiment, the servo linkage hub  238  is coupled to the second or outer-most engagement member  236 . Preferably, the servo arm  260  is biased, via a biasing member (not shown), towards first and second positions corresponding to the tucked and extended wing states. The servo arm biasing is provided, for example, by a spring (not shown) operable to provide tension either side of the axis (not shown) of the servo arm  260 . The servo  258  is secured in position within the housing  120 . In the illustrated embodiment, the servo  258  is secured in position within the housing by a number of housing columns  262  that cooperate with respective snap-fit jaws  264  of the servo  258 . 
         [0024]    The actuation linkage  244  bears, at a proximal end, a further boss  266  arranged to be received within the housing  120  and to pivot with respect to an axis (not shown) defined by respective housing fastenings  268 . In the embodiment shown, the housing fastenings  268  are realised using frustoconical projections that are arranged to capture the actuation linkage  244  via a snap fit with complementary recesses within the further boss  266 . Steel through bolts are also provided to secure the actuation linkage  244 . Preferred embodiments of the actuation linkage  244  are non-linear. Preferably, the actuation linkage  244  is shaped to avoid contact with any other parts of the wing other than where intended, which is at the hubs  224  and  226 . Still further, a preferred embodiment of the actuation linkage  244  is s-shaped. The actuation linkage  244  is coupled to a predetermined engagement member  252  of the wing hand section  122  and  124 . In preferred embodiments, the actuation linkage  244  is coupled to the proximal most engagement member  252 . 
         [0025]    Each feather rib  246  has a cephalically disposed open end  270 , bearing the spigots  248  and  250 , that transitions, via upper and lower cambered sections  272  and  274 , to a caudally disposed pointed section  276 . The upper and lower cambered sections  272  and  274  are separated by a supporting strut  278 . The upper and lower cambered sections  272  and  274  are arranged to receive respective feathers (described in detail hereafter with reference to  FIG. 6 ) to define the shape of the upper and lower surfaces of the wings. Preferably, the upper  272  and lower  274  cambered sections are foraminated to save weight. The open end  270  is arranged, in use, to bias the spigots towards one another. 
         [0026]    Referring to  FIG. 3 , there is shown a plan view  300  of one of the wings. The servo  258 , servo linkage  240  and actuation linkage  244  cooperate to urge the wing into the extended position shown in  FIG. 3 . As the servo pulls the wing arm towards servo  258 , or towards the fuselage  104  to provide a positive, reduced, sweep-back angle, Λ 1 , (measured relative to a lateral axis of the vehicle), the actuation linkage  244  urges the wing hand section outwards away from the fuselage  104 , that is, in such a manner as to provide a positive, increased, sweep-back angle, Λ 2 . In a preferred embodiment, the sweep-back angle of the wing arm section and the sweep-back angle of the wing hand section are the same in the extended position. However, embodiments are not limited thereto. Embodiments can be realised in which the sweep angles are different, that is, wherein the wing, in its extended position, is a compound sweep wing. For example, the sweep-back angle of the wing arm section can be less than the sweep-back angle of the wing hand section in the extended position. As the servo  258  pushes the wing arm section away from the fuselage  104 , that is, increases the sweep-back angle, Λ 1 , the actuation linkage  244  operates to pull the wing hand section towards the fuselage  104 , that is, reduces the sweep-back angle, Λ 2 . It can be appreciated in the tucked position the sweep-back angle Λ 1  of the wing arm section may not be positive, that is, the wing arm section may be swept forward, as wing arm section  126  is depicted in  FIG. 1 . 
         [0027]    Each wing contains a biasing member  302  that extends through the inside of at least one of the wing hand section and the wing arm section. Primarily, the biasing member is coupled to the tip fairing  129  and  130 , or the outer most feather rib  246 , and biased to urge the wing, in particular, the tip fairing  129  and  130 , towards the extended position. This arrangement allows the wing tip to sweep passively in a rearward direction during, for example, an impact. Preferred embodiments use an elongate elastic member under tension to bias the tip fairing towards the extended position. In one embodiment, the biasing member is arranged to be under greater tension when the wing is in the tucked position as compared to the extended position. Embodiments can be realised in which the biasing member is coupled, and operable, between the wing hand section and the tip fairing. However, embodiments can be realised in which the biasing member passes through the wing hand section and is coupled at a point that is closer to the fuselage than the wrist joint  118  such that the biasing member, as well as urging the tip fairing towards the extended position, also acts on the wrist joint to urge it in a caudal direction, which, in turn, assists in urging the wing into the extended position. 
         [0028]    Each of the feather ribs  246  is coupled to an adjacent feather rib, where appropriate, by a travel limiter that is arranged to limit the travel of the feather ribs towards the extended position. Preferred embodiments use a relatively inextensible nylon cord to realise the travel limiters. In the embodiment illustrated, seven travel limiters are shown  304  to  316 . Preferably, the travel limiters  304  to  316  and  318  to  330  are disposed at predetermined corresponding positions relative to the wing chord. In preferred embodiments, the travel limiters  304  to  316  and  318  to  330  are disposed at substantially the half chord position. As the outer most feather rib is urged towards the extended position, it will be appreciated that the travel limiters also urge the other feather ribs towards the extended position. The relative increase in spacing between the feather ribs ceases when each travel limiter is fully extended. Each of the feather ribs  246  is also provided with feather rib biasing members  318  to  330  that are arranged to urge the feather ribs towards the fuselage. Preferred embodiments of the feather rib biasing members are realised using elongate resiliently deformable elastic members  318  to  330  arranged to be under increasing tension as the wing moves towards the extended position. Preferably, the feather rib biasing members  318  to  330  are also under tension when the wing is in the tucked position. Although embodiments have been described as using an inextensible chord to realise the travel limiters, embodiments are not limited to such an arrangement. Embodiments can alternatively use an elastic member that is arranged under tension to urge the feather ribs towards the extended position. 
         [0029]    As the wing moves between the extended and tucked positions, the feather ribs will pivot about their respective axes defined by the engagement members  236  and  252  and the spigots  248  and  250  of the feather ribs. 
         [0030]      FIG. 4  shows a plan view  400  of the wing in the tucked position. It can be appreciated that the feather rib biasing members  318  to  330  are still under tension. It can be appreciated that the travel limiters  304  to  316  are not under tension. The servo arm  260  is visible and shown pushing the wing arm section towards the tucked position. 
         [0031]      FIG. 5  provides a view  500  of the relative spacing and dimensions of the elements of the wings. In the following, all ratios are expressed for the wing in the fully extended position. The ratio, A:B, of the distance between the first  502  and second  504  axes of the actuation linkage  244  to distance between the first axis  502  of the actuation linkage  244  and the axis  506  of the wrist joint  118  is between 1:0.2 and 1:0.7 and is preferably 1:0.25. The ratio, A:C, of the distance between the first  502  and second  504  axes of the actuation linkage  244  to distance between axis of the wrist joint  506  and the axis  508  of the main pivot is between 1:0.1 and 1:0.8 and is preferably 1:0.71. The ratio, A:D, of the distance between the second axis  504  of the actuation linkage  244  and the axis  508  of the main pivot  116  is between 1:0.1 and 1:1.25 and is preferably 1:0.48. The ratio, F+E:E, of the sum of the distances E between a first normal  510 , depending from the main pivot axis  508 , to an axis  512  running parallel to the leading edge of the wing arm section  126  and a second normal  514 , depending from the wrist joint axis  506 , to the axis  512  and F between the second normal  514  to a third normal  516 , depending from the tip fairing tip  518  to the axis  512  to the distance between the second normal  514  and the third normal measured along the axis  512  is between 1:0.1 and 1:0.6 and is preferably 1:0.21. 
         [0032]      FIG. 6  is a view  600  of a feather rib  246  bearing upper  602  and lower  604  feathers, that is, wing surface elements. Preferred embodiments use sheets of polyester film to realise the wing surface elements. The wing surface elements are arranged so that there is an overlapping relationship with adjacent wing surface elements when the wing is in the extended position. It will be appreciated that the degree of overlap will increase when the wing is in the tucked position. Embodiments can be realised in which a selectable edge, preferably, the trailing edge, of the wing surface elements are porous or foraminated to allow pressure leakage between the upper and lower surfaces of the wing, which serves to urge the feathers together in regions where there is an overlapping relationship between wing surface elements. Embodiments can be realised in which the porosity or foraminations to allow pressure leakage are adapted to vary in at least one of density and size to create a variable predetermined or intentional pressure leakage profile across the wing. The wing surface elements  602  and  604  have substantially the same length as the feather rib  246  and are between 4 and 7 times, preferably 5 to 6 times, as wide as the feather ribs  246 . The upper and lower spigots  248  and  250  are clearly visible. 
         [0033]      FIG. 7  is a side-sectional view  700  of an alternative embodiment of a feather rib/wing surface element assembly. It can be appreciated that a primary difference between the assembly shown in  FIG. 6  and that shown in  FIG. 7  is that the latter has a single wing surface element  702 . The wing surface element  702  is coupled to the leading edge of the wing  704 , which can be at least one of either the wing arm section or wing hand section, via a hinge  706  that has an axis  708 . The wing surface element  702  can pivot about the axis  708  in substantially the same manner as described above with respect to the feather ribs  246 , it will be appreciated that a wing containing such single surface elements can be made lighter and can use a thinner wing section, which will reduce form or section drag. 
         [0034]    Furthermore, the reduced thickness of the wing surface element  702  allows tailoring of the passive aeroelasticity, which allows it to be made more plastically deformable when operating at high angles of attack or during contact with other objects. 
         [0035]    Embodiments of such an element  702  can be realised in which reinforcement for the wing is provided in the form of a composite or metal spar  710  because of the reduction in strength following from employing a thinner surface element. 
         [0036]    It can also be appreciated that embodiments can be realised in which the coverts around the hinge  706  may be part of the same component that forms the leading edge of the wing 
         [0037]      FIG. 8  is a view  800  of a wing having a leading edge covert  802 . The covert  802  performs at least one, and preferably both, of improving or smoothing airflow over the wing and controlling pressure leakage between the lower and upper wing surfaces. The overlapping wing surface elements  602  and  604  exhibit gaps that form through-holes or vias between the wing surfaces. The sizes of the through-holes differ as between the tucked and extended positions. The covert  800  is adapted to influence any pressure leakage attributable to or associated with those through-holes, particularly those that manifest themselves in the extended position. Furthermore, it will be appreciated that the coverts are position in the area of the wing that produces the most lift. Therefore, it is preferable that they are secured in place so as to conform with or match the profile of the wing. Embodiments of the invention use clips, such as, for example steel clips, to secure the coverts in place. Preferably, the covert  800  has a profiled trailing edge  804 . The profiled trailing edge  804  preferably has extensions or protrusions  806  to  812  arranged in registry with or to correspond to any such through-holes or other regions of adverse pressure leakage. It can be appreciated from  FIG. 9 , which shows a view  900  of the wing in a tucked position, that the leading edge covert  800  comprises two parts; the first part  902  forms a covert for the wing arm section and the second part  904  forms a covert for the wing hand section. It will be appreciated that a wing is an embodiment of a foil and that the term foil can encompass one or more of a wing, blade and/or sail; all for use in fluids such as gases and liquids. The terms foil, wing, blade and sail are used synonymously. 
         [0038]    Although embodiments of the present invention have been described with reference to the wings having only tucked and extended positions, embodiments are not limited thereto. Embodiments can be realised in which the tension imparted by biasing member  302  is balanced by the tension imparted by biasing members  318  to  330  to maintain the wing in one or more intermediate positions between the fully tucked and fully extended positions. Additionally, or alternatively, although embodiments have been described in which the servo is operable to move the wing between fully extended and fully tucked positions, embodiments are not limited to such an arrangement. Embodiments can be realised in which the servo  258  positions the servo arm  260  at one or more intermediate positions between those that correspond to the fully tucked and fully extended positions.