The invention relates to an unmanned aerial vehicle (UAV) and particularly, but not exclusively, to a mechanism which allows simultaneous rotor tilting and landing gear deployment.

The design and development of UAVs has been, and continues to be an extremely exciting area of study. While the field was initially advanced for military purposes, it has grown into commercial fields, such as delivery, agriculture, surveying and filmmaking. Although rotary-wing UAVs have received a considerable proportion of the publicity in recent years, fixed-wing UAVs are currently more efficient, especially when travelling over long distances, and tend to be able to achieve higher speeds. The main advantage of rotary wing UAVs is their ability to perform a vertical take-off and landing (VTOL), and hover in a stationary position. A tilt-rotor aircraft aims to achieve the advantages of both aircraft by orientating the rotors vertically during take-off and landing and orienting the rotors horizontally during forward-flight for maximum efficiency and speed.

It is desirable to provide a UAV with an improved tilt-rotor assembly.

In accordance with an aspect of the invention there is provided an unmanned aerial vehicle comprising: a fixed wing; and a pair of nacelles connected to the wing and spaced laterally either side of a centreline of the wing. Each nacelle comprises a stationary portion which is fixed to the wing and a movable portion which is rotatable relative to the stationary portion. A rotor is connected to the movable portion of each nacelle. The movable portion of each nacelle has a first position in which the axis of rotation of the rotor is substantially parallel to a longitudinal axis of the nacelle and a second position in which the axis of rotation of the rotor is substantially perpendicular to the longitudinal axis of the nacelle. The movable portion comprises a strut which in the first position lies against the stationary portion and in the second position extends downwards away from the stationary portion to support the unmanned aerial vehicle during take-off and/or landing.

The stationary portion may comprise a recess which receives the strut of the movable portion in the first position. The stationary portion and the movable portion may have complementary cross- sections which mate with one another in the first position.

The movable portion may be pivotably connected to the stationary portion.

The movable portion may be connected to the stationary portion by a hinge.

The hinge may be formed on an upper surface of the nacelle. The movable portion may be rotated relative to the stationary portion between the first and second positions by an actuator.

The actuator may be disposed within a cavity formed within the nacelle. The actuator may be a linear actuator.

The movable portion of each nacelle may comprise a housing which houses a motor for driving the rotor. The motor and strut may be located on opposite sides of a pivot point of the movable portion.

The rotor may be provided at a front portion of the nacelle and a rear rotor may be provided at a rear portion of the nacelle.

The rear rotor of each nacelle may be connected to a second movable portion which is rotatable relative to the stationary portion of the nacelle between a first position in which the axis of rotation of the rear rotor is substantially parallel to a longitudinal axis of the nacelle and a second position in which the axis of rotation of the rear rotor is substantially perpendicular to the longitudinal axis of the nacelle.

The second movable portion may comprise a strut which in the first position lies against the stationary portion and in the second position extends downwards away from the stationary portion to support the unmanned aerial vehicle during take-off and/or landing. The rear rotor may comprise a propeller having blades which have a deployed position in which they extend radially and a stowed position in which they extend axially along the axis of rotation. The blades may be configured to be in the stowed position when the second movable portion is in the first position and the deployed position when the second movable portion is in the second position.

The rear rotor may be configured to be drawn into a cavity within the nacelle with the blades in the stowed position when the second movable portion is in the first position.

The strut may comprise a wheel or wheels such that the unmanned aerial vehicle can be manoeuvred while on the ground. The unmanned aerial vehicle may further comprise a fuselage connected to the wing, wherein the nacelles are spaced either side of the fuselage.

The unmanned aerial vehicle may further comprise a tailplane provided at a rear portion of the fuselage; wherein the tailplane comprises a horizontal stabilizer and extensions which project downwards from either side of the horizontal stabilizer; wherein the unmanned aerial vehicle is supported by the extensions at its rear and the struts at its front during take-off and/or landing.

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings showing a nacelle with the landing-gear mechanism, in which:-

Figure 1 is a perspective view of a UAV according to an embodiment of the invention in a forward flight configuration;

Figure 2 is a perspective view of a tilt-rotor assembly of the UAV when in the forward flight configuration; Figure 3 is a perspective view of the UAV in a Vertical Take-Off and Landing (VTOL) configuration; Figure 4 is a perspective view of the tilt-rotor assembly when in the VTOL configuration; Figure 5 is a cross-sectional view of the tilt-rotor assembly when in the VTOL configuration showing the internal mechanism; and

Figure 6 is a perspective view showing both front and rear tilt-rotor assemblies. Figure 1 shows an unmanned aerial vehicle (UAV) 2 according to an embodiment of the invention. The UAV comprises a fuselage 4 and a fixed wing 6 attached to a central portion of the fuselage and extending perpendicularly to a longitudinal axis of the fuselage 4 such that it extends laterally either side of the fuselage 4. A tailplane (or horizontal stabilizer) 8 is provided at a rear portion of the fuselage 4. At least part of the fuselage 4 may be hollow so as to house the electronics and/or power source of the UAV 2.

The wing 6 has an aerofoil cross-section so as to provide lift to the UAV 2. As shown, the wing 6 tapers in a chordwise direction towards its ends, although it will be appreciated that other forms of wing may be used.

The wing 6 carries a pair of nacelles 10 which are affixed to the underside of the wing 6 at either side of the fuselage 4 (i.e. either side of a centreline of the wing 6). The longitudinal axes of the nacelles 10 are substantially parallel to that of the fuselage 4 and thus the nacelles extend perpendicularly to the wing 6. As shown, the nacelles 10 are generally cylindrical and hollow. The nacelles 10 are connected to the wing 6 partway along their length such that they project forward of the wing 6 and also rearward of the wing 6 towards the tailplane 8. Each nacelle 10 carries a rotor 12 at its front end. The rotor comprises a propeller which rotates relative to the nacelle 10. The nacelle 10 and rotor 12 may form a tilt- rotor assembly, as described in detail below.

The nacelle 10 is formed by a stationary portion 14 which is affixed to the wing 6 and a movable portion 16 which is movable relative to the stationary portion 14 and the wing 6. The movable portion 16 of the nacelle carries the rotor 12. Specifically, the movable portion 16 is connected to the stationary portion 14 via a hinge 18. The hinge 18 is provided on an upper surface of the nacelle 10 and is arranged such that its axis of rotation is substantially horizontal and parallel with the longitudinal axis of the wing 6 (i.e. perpendicular to the longitudinal axis of the nacelle 10 itself). The hinge 18 thus allows the movable portion 16 to rotate between a horizontal orientation, as shown in Figure 2, to a vertical orientation, as shown in Figure 3.

As best shown in Figure 4, the movable portion 16 comprises a housing 20 and a strut 22 which extends from the housing 20. The movable portion 16 is connected to the stationary portion 14 via the hinge 18 such that the hinge 18 is positioned between the housing 20 and the strut 22. In other words, with the movable portion 16 in a vertical orientation, the housing 20 is above the hinge 18 and the strut 22 is below the hinge 18, and in a horizontal orientation, the housing 20 is forward of the hinge 18 and the strut is rearward of the hinge 18.

The housing 20 houses a motor 24 (see Figure 5) which is configured to drive the rotor 12. The strut 22 extends from the housing 20 at a position which is spaced from the hinge 18. The strut 22 is spaced from the hinge by a distance which is greater than the thickness of the stationary portion 14 of the nacelle 10 so that the stationary portion 14 does not foul the rotation of the movable portion 16.

The stationary portion 14 of the nacelle 10 comprises a recess 26 which is shaped to receive the strut 22 when it is in the horizontal orientation. The strut 22 therefore lies flush with the stationary portion 14 when in the horizontal orientation to provide the nacelle 10 with a streamlined profile, thereby reducing the unfavourable aerodynamic effect of the strut 22.

As shown in Figure 5, a linear actuator 28 is provided within the nacelle 10. The linear actuator 28 is connected at one end to the interior of the stationary portion 14 via a bracket 30. The opposing end of the linear actuator 28 is connected to the movable portion 16 within or adjacent to the housing 20. The linear actuator 28 is configured to move between a retracted position having a first length and an extended position having a second length which is greater than the first length. In the retracted position, the linear actuator causes the movable portion 16 to rotate about the hinge 18 into the horizontal orientation with the strut 22 stowed against the stationary portion 14 within the recess 26. When the linear actuator 28 is extended, it forces the movable portion 16 to rotate about the hinge 18 into the vertical orientation.

The horizontal orientation of the movable portion 16 represents a forward-flight configuration of the UAV, as shown in Figure 1. In this configuration, the axis of rotation of the rotor 12 is oriented horizontally and so the rotor 12 provides propulsive force which moves the UAV 2 forward and thus may be used as a cruise mode. The vertical orientation of the movable portion 16 represents a vertical take-off and landing (VTOL) configuration. In this configuration, the axis of rotation of the rotor 12 is oriented vertically and so the rotor 12 provides propulsive force which moves the UAV 2 vertically. In the VTOL configuration, the movable portion 16 is oriented vertically with the strut 22 extending downwards from the stationary portion 14 of the nacelle 10. The struts 22 of the nacelles 10 may therefore be used to support the UAV 2 during landing and take-off. Although not shown, the struts 22 may be provided with wheels or other similar means in order to aid movement when the UAV 2 is on the ground. Such wheels could be driven via power or mechanically.

As shown in Figures 1 and 3, the tailplane 8 may comprise a horizontal stabilizer portion 32 and a pair of extension portions 34 which project downwardly from either end of the horizontal stabilizer portion 32. The extension portions 34 project below the level of the fuselage 4. In conjunction with the struts 22 towards the front of the UAV 2, the extension portions 34 may support the UAV 2 at the rear.

As shown in Figure 6, each nacelle 10 may also carry a rotor 36 at its rear end. As per the front rotors 12, the rear rotors 36 each comprise a propeller which rotates relative to the nacelle 10. Each rear rotor 36 is driven by a motor which is housed within a housing 38. The housing 38 is also hinged to the nacelle 10 so as to allow the rotor 36 to rotate from a horizontal orientation where the axis of rotation of the rotor 36 is aligned with the nacelle 10 and a vertical orientation where the axis of rotation is vertical and perpendicular to the longitudinal axis of the nacelle 10. As shown, the housing 38 may be hinged so that the rear rotor 36 rotates downwards when moving from the horizontal orientation to the vertical orientation, rather than upwards as per the front rotors 12. The front and rear rotors thus rotate in the same direction (i.e. clockwise or anticlockwise when viewed from one side). Alternatively, the rear rotors 36 may be mounted on a movable portion having an integral strut, as per the front rotors 12 and rotates upwards when moving from the horizontal orientation to the vertical orientation so that the strut is deployed downwards. The struts associated with the front and rear rotors 12, 36 may therefore support the fuselage 4 of the UAV 2 off the ground during landing and take-off. In the forward-flight configuration, the rear rotors 36 may not be used and so may be moved to a stowed position to reduce drag. Specifically, the blades of the propellers may be hinged so that they extend parallel to the longitudinal axis of the nacelles 10, as shown in Figure 1 , during forward flight. The blades may automatically rotate into this configuration when the rear rotors 36 are not rotating and under the force of the oncoming air flow as the UAV 2 moves forwards. In contrast, the blades may be forced outwards under the centrifugal forces generated as the rear rotors 36 rotate. The rear rotors 36 may also be drawn into the hollow interior of the nacelles 10 so that the propellers are partially or fully concealed within the nacelles 10. In the VTOL configuration, with the front and rear rotors 12, 36 arranged so that their axes of rotation are vertical, the UAV 2 assumes a quad-copter configuration. The reason for using two propellers in forward-flight and four in the VTOL configuration is due to the larger power requirements during take-off and landing. Using a nacelle 10 which has a stationary portion 14 that does not rotate with the rotor 12 during the transition between VTOL and forward-flight configurations enables the rotor 12 to be positioned forward of the fixed wing in both the VTOL and forward-flight configurations. Although the movable portion 16 has been described as being hinged to the upper surface of the stationary portion 14, this need not be the case. The stationary portion 14 and the movable portion 16 also may be arranged such that the movable portion 16 is able to sit alongside the stationary portion 14 when in the horizontal orientation, rather than below.

The strut 22 of the movable portion 16 may cooperate with the stationary portion 14 to complete a desired cross-section of the nacelle 10. For example, the cross-section of the strut 22 may be a segment of a circle (e.g. semi-circular) or other shape and the stationary portion 14 may have a complementary cross-section forming the remainder of the shape (e.g. also semi-circular) such that when the strut 22 and stationary portion 14 are brought together they form a complete shape. It will be appreciated that the use of terms relating to the orientation or position of features, such as upper, vertical, horizontal, forward, rear, refer to the normal orientation of the UAV when on level ground and to the normal direction of travel of the UAV.

In other embodiments, the UAV need not have a fuselage and may instead house all motors, power sources, electronics and ancillary equipment in the wing and/or nacelles.

Although the movable portion 16 has been described as being rotated using a linear actuator, it will be appreciated that other forms of actuator may be used. The actuator may also be external to the nacelle 10 rather than housed within it. 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.