Abstract:
An unmanned aerial vehicle  2  comprising: a fuselage  4 ; and a wing  6  comprising a central wing section  12  pivotably mounted to the fuselage  4  and a pair of outer wing sections  14   a,    14   b  pivotably mounted to the central wing section  12 ; wherein the wing  6  has a folded configuration in which the central wing section  12  and the outer wing sections  14   a,    14   b  are stacked on top of one another and are aligned with a longitudinal axis of the fuselage  4 ; and a deployed configuration in which the central wing section  12  is substantially perpendicular to the fuselage  4  and the outer wing sections  14   a,    14   b  extend from the central wing section  12  away from the fuselage  4.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to GB 1514386.0 filed on 13 Aug. 2015, which is hereby incorporated by reference in its entirety for any and all purposes. 
     BACKGROUND 
     The disclosure relates to an unmanned aerial vehicle (UAV) and a folding mechanism of aerofoil components for an unmanned aerial vehicle. 
     The design of UAVs has seen great advancement in recent years. The field grew mainly out of military development, where UAVs are commonly used for surveillance, but has expanded further into commercial uses, such as in delivery and filmmaking, which enforces a position at the forefront of technological research. UAVs have been developed in various forms, such as single- or multi-rotor helicopters or fixed wing aircraft. With the evolution of ever decreasing electronic and mechanical components, micro- and even nano-versions of UAVs continue to be developed. 
     One issue with the development of UAVs is that there are advantages to having large wingspans or sizeable rotors in comparison to their fuselage length. These advantages include the ability to create low drag fixed wing aircraft, which allow for long flight times. Any aircraft with a large span will cause problems when it comes to transportation, which has led to disassemblable and foldable designs. 
     It may be useful to transport the UAV in existing available storage, which in military uses, may be on larger aircraft, ships or submarines. Another problem arises when it comes to launch procedure. While launch devices are available for missiles and other munitions, they may not be available for specific UAV designs and it may not necessarily be possible to perform a horizontal takeoff. 
     It is therefore desirable to provide a UAV which overcomes some or all of the disadvantages associated with existing designs. 
     SUMMARY 
     In accordance with an aspect there is provided an unmanned aerial vehicle comprising: a fuselage; and a wing comprising a central wing section pivotably mounted to the fuselage and a pair of outer wing sections pivotably mounted to the central wing section; wherein the wing has: a folded configuration in which the central wing section and the outer wing sections are stacked on top of one another and are aligned with a longitudinal axis of the fuselage; and a deployed configuration in which the central wing section is substantially perpendicular to the fuselage and the outer wing sections extend from the central wing section away from the fuselage. 
     The unmanned aerial vehicle may further comprise a second pair of outer wing sections pivotably mounted to the first pair of outer wing sections. 
     At least one of the outer wing sections may move vertically during a transition from the folded configuration to the deployed configuration such that the outer wing sections are aligned with one another when in the deployed configuration. 
     The outer wing sections may move vertically during a transition from the folded configuration to the deployed configuration such that the outer wing sections are aligned with one another and the central wing section when in the deployed configuration. 
     The outer wing elements may be angled relative to the central wing section when in the deployed configuration such that the wing has a dihedral or anhedral angle. 
     The wing may be biased towards the deployed configuration. 
     The central wing section may be biased by means of a torsion spring. 
     The fuselage may comprise a stop which limits rotation of the central wing section relative to the fuselage. 
     Each of the outer wing sections may be biased by means of a tension spring. 
     The tension spring may be connected at one end to the central wing section and at the other end to the outer wing section via a pulley such that rotation of the outer wing section relative to the central wing section extends the tension spring. 
     The unmanned aerial vehicle may further comprise a latch which holds the wing in the folded configuration against the bias and which is released so as to allow the wing to be deployed. 
     The latch may be released remotely or automatically (e.g. immediately after launch or after a fixed time from launch). 
     The vehicle may housed within a tube which retains the wing in the folded configuration. 
     The wing may be unfolded into the deployed configuration when released from within the tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:— 
         FIG. 1  is a perspective view of a UAV according to an embodiment; 
         FIG. 2  is a perspective view showing the outer wing pivoting mechanism; 
         FIG. 3  is a perspective view showing a central wing pivoting mechanism within the fuselage; and 
         FIG. 4  is a front view of the UAV with the wings in a retracted position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a UAV  2  according to an embodiment. The UAV  2  generally comprises a fuselage  4  on which is mounted a wing  6 . 
     As shown, the fuselage  4  comprises a semicylindrical front section  8  and a cylindrical rear section  10 . At least part of the fuselage  4  may be hollow so as to house the electronics and the engine of the UAV  2 . 
     The wing  6  is mounted to the front section  8  of the fuselage midway along the length of the front section  8 . The wing  6  comprises a central wing section  12  and first and second outer wing sections  14   a ,  14   b . The central wing section  12  and the outer wing sections  14   a ,  14   b  each have an aerofoil profile to provide lift to the UAV  2 . The outer wing sections  14   a ,  14   b  are also provided with ailerons  16  to allow for control of the UAV  2 . 
     The central wing section  12  is pivotably connected at its centre to the front section  8  of the fuselage  4 . In turn, the outer wing sections  14   a ,  14   b  are pivotably connected to the central wing section  12 . Specifically, the first outer wing section  14   a  is connected via one of its ends to the central wing section  12  at or near a distal, free end of the central wing section  12 . Similarly, the second outer wing section  14   b  is connected via one of its ends to the central wing section  12  at or near an opposing distal, free end of the central wing section  12 . 
     In particular, as shown in  FIG. 2 , the outer wing sections  14   a ,  14   b  are each provided with a shaft  18  which projects from an underside of the outer wing section  14   a ,  14   b . The shaft  18  is received by a bearing  20  located within the central wing section  12  which allows for rotation of the outer wing section  14   a ,  14   b  relative to the central wing section  12 . The shaft  18  is connected to a bias mechanism located within the central wing section  12 . The bias mechanism comprises a tension spring  22  which is fixed at one end to a bracket  24  located within the central wing section  12 . The other end of the tension spring  22  is coupled to a pulley disposed on the shaft  18  via a string  26  (see  FIG. 4 ). Accordingly, rotation of the shaft  18  causes the tension spring  22  to be extended and thus placed under tension. 
     As shown in  FIG. 3 , the central wing section  12  comprises a shaft which extends into the interior of the front section  8  of the fuselage  4  where it passes through a boss  28 . The free end of the shaft located within the front section  8  of the fuselage  4  is connected to a mount  30  which in turn is connected to a torsion spring (not shown). The mount  30  has the form of a circular sector having a pair of radial surfaces connected by an arcuate surface. The torsion spring is attached to the mount  30  via the arcuate surface. The boss  28  has a flange  32  from which a stop  34  projects into the plane of the mount  30 . The stop  34  limits rotation of the mount  30  (through contact with one of the radial surfaces of the mount  30 ) and thus of the central wing section  12 . 
     As described previously, the central wing section  12  is pivotably connected to the fuselage  4  and the outer wing sections  14   a ,  14   b  are in turn pivotably connected to the central wing section  12 . As a result, the wing  6  can be folded such that the outer wing sections  14   a ,  14   b  are rotated so that they overlap with the central wing section  12  and the central wing section  12  can then be rotated so as to align its longitudinal axis with that of the fuselage  4 . As shown in  FIG. 4 , the central wing section  12  and the outer wing sections  14   a ,  14   b  are thus stacked on top of one another. To allow this, the outer wing sections  14   a ,  14   b  are offset vertically from the central wing section  12  by different distances, at least when in the folded configuration. The pivotable connection between the outer wing sections  14   a ,  14   b  and the central wing section  12  may be arranged such that the outer wing sections  14   a ,  14   b  are vertically level with one another when deployed. The outer wing sections  14   a ,  14   b  may also be level with the central wing section  12  when in the deployed configuration. For example, the opposing ends of the outer wing sections  14   a ,  14   b  and the central wing section  12  may be angled so as to cause the outer wing sections  14   a ,  14   b  to ride up over the central wing section  12  when folded. 
     As shown in  FIG. 4 , the central wing section  12  and the outer wing sections  14   a ,  14   b  combined with the semicylindrical front section  8  of the fuselage  4  occupy a substantially cylindrical domain when in the folded configuration. 
     The torsion spring and tension spring  22  bias the central wing section  12  and the outer wing sections  14   a ,  14   b  towards the deployed configuration where they are aligned with one another and perpendicular to the longitudinal axis of the fuselage  4  (as depicted in  FIG. 1 ). Therefore, the central wing section  12  and the outer wing sections  14   a ,  14   b  must be restrained in order to retain the wing in the folded configuration. For example, the UAV  2  may be housed within a tube which prevents the wing  6  from being deployed. However, once released, the wing automatically unfolds into the deployed configuration. Specifically, the central wing section  12  is rotated 90° about the fuselage  4  and the outer wing sections  14   a ,  14   b  are rotated 180° relative to the central wing section  12 . The unfolding of the wing  6  can thus be performed post-launch, extending in mid-air and transitioning to the flight phase. 
     Although the outer wing sections  14   a ,  14   b  have been described as being aligned with the central wing section  12  when in the deployed configuration, they may instead be swept backward. The wing  6  may be arranged so as to provide a dihedral or anhedral angle with respect to the fuselage  4 . This may increase stability in sideslip conditions. This may be created by the central wing section  12  or from the outer wing sections  14   a ,  14   b . In particular, the outer wing sections  14   a ,  14   b  may be deflected upwards (dihedral) or downwards (anhedral) as they pivot relative to the central wing section  12 , such that they are parallel with the central wing section  12  when folded and angled when deployed. 
     In other embodiments, the wing  6  may comprise additional wing sections in order to increase the length of the wing  6  relative to the folded dimensions of the UAV  2 . 
     Although the fuselage  4  has been described as comprising a semicylindrical front section  8  and a cylindrical rear section  10 , it will be appreciated that the shape of the fuselage  4  may vary. In particular, the cross-section of the fuselage  4  may be constant (i.e. the same shape and/or dimensions) along its entire length. It also need not be curved. The UAV  2  may therefore be stored and/or deployed within a non-circular housing. 
     The unfolding of the wing  6  need not be automatic and may instead be triggered electronically, either by timing after launch or by a remote user. For example, the UAV  2  may comprise a latch which fixes the wing  6  in the folded configuration against the bias of the torsion spring and tension spring  22 , and is released to allow the wing  6  to unfold. Further, the wing  6  may be deployed using any power source and is not limited to the use of springs. In particular, the wing  6  may be actuated using solenoids, gas springs, pyrotechnics, electric motors, etc. The deployment of the wing  6  may also be initiated through aerodynamic or inertial forces. 
     The wing  6  may have an aerofoil cross-section only over part of its length. In particular, only a portion of the central wing section  12  may have an aerofoil cross-section and outer wing sections  14   a ,  14   b    
     The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.