Patent Description:
VTOL aircraft are capable of take-off and landing vertically, or at some angle which is close to vertical. This style of aircraft includes helicopters and certain fixed wing aircraft, often used for military applications. Advantageously, VTOL aircraft permit take-off and landing in limited spaces, which negates the need for a large runway, and permits take-off and landing in small spaces and such as boat decks and landing pads on buildings and other structures.

Helicopters are a style of aircraft in which lift and thrust are both provided by rotors. There are several issues associated with helicopters which may be problematic in some applications, such as the high levels of noise output. One such disadvantage associated with helicopters concerns the rotor design which is critical for flight. There is generally no redundancy in the design, meaning that operation of the (or each) rotor is critical. This lack of redundancy dictates that large factors of safety must be applied to all components of the rotor and drive train, which adds considerably to the weight and manufacture cost of helicopters.

Electric aircraft are of increasing interest for various commercial and safety reasons. In recent years there has been a large amount of development with respect to drone technologies, which generally utilise a plurality of electric rotors spaced around a pitch circle diameter. Drones generally operate with the electric rotors each rotating about an axis which is generally vertical.

Whist drones are becoming commercially viable for delivering small payloads, they are generally limited to relatively low flight speeds, on account of the vertical axis of rotation of the rotors. Furthermore, they tend to have reasonably low ranges of travel per battery charge.

Tilt wing aircraft are available and generally operate on the principle of a vertical propeller axis for take-off and landing, and the wings are configured to tilt between a configuration in which the propellers have vertical axes for take-off and landing, and a configuration in which the propellers have horizontal axes for forward flight.

The above noted tilt wing arrangement provides the advantage of take-off and landing in areas with limited available clear space, such as aircraft carriers and landing pads. In addition, tilt wing aircraft are able to provide flight speed comparable with conventional propeller driven fixed wing planes.

Tilt wing aircraft generally have electric motors or gas turbine engines which drive propellers or ducted fans directly mounted to the wing. The entire wing rotates between vertical and horizontal to tilt the thrust vector from vertical to horizontal and return.

By way of definition, the "Thrust line" also referred to as the "thrust vector" is the thrust force of the propeller and is approximately the same as axis of rotation of the propeller. The "hinge line" is the axis of the hinge rotation.

There are several inherent disadvantages with existing tilt wing aircraft. One disadvantage concerns the actuators and bearings or other such mechanisms required to control the angle of inclination of the wing between the take-off/landing configuration and the forward flight configuration. The actuators may also serve to lock the wing at the desired inclination during forward flight. However, in practice, the actuators and bearings add significant weight to the aircraft. This results in a reduction of the amount of payload such as personnel or cargo that can be transported. Furthermore, because of the critical nature of the wing tilt actuation system and bearings, that assembly must be designed with a sufficient degree of redundancy to reduce the risk of catastrophic failure.

An electric VTOL jet is currently being designed and tested by Lilium Aviation, under the brand Lilium Jet™. That prototype is intended as a lightweight commuter aircraft for two passengers having two wings and around <NUM> electric motors.

A disadvantage of the Lilium Jet™ type aircraft concerns the electric motors which are encased fan type motors. This arrangement is highly energy intensive, resulting in reduced possible flight range for a given battery size.

Furthermore, the encased fans can only be operated for take-off and landing on hardstand surfaces, such as designated landing pads and runways. This limits the usability of the aircraft, and prevents it from being operated during take-off and landing on non-hardstand surfaces, such as parks, fields and gardens. For military applications, this is undesirable, and does not cater for impromptu landings in remote locations.

Another concept VTOL aircraft is the S2 electric™ by Joby Aviation. This design has fixed wings with a plurality of electric motors, preferably four, mounted to each wing. Four additional motors are mounted to the rear stabiliser or tail. A disadvantage of this concept aircraft is that each electric motor is independently actuated, requiring a separate actuator for each motor. As noted above, this requires significant additional weight for the actuation motor system.

Box wing aircraft also referred to as Prandtl's "Best Wing System" are a wing configuration where there is generally an upper and lower wing separated vertically and connected by winglets that form a closed box when viewed from the front. These wings can also be separated horizontally with one configuration with upper wing forward of the lower wing, and the alternate where the lower wing is forward of the upper wing.

The Box wing has a particular advantage in that it reduces the drag due to lift (induced drag), which is dominant at low speeds and high lift coefficients, with a strong relationship between the height of the wings to the span of the wings. Box wings have not been widely adopted due to more complex aeroelastic design requirements and potential complex stall behaviour.

The box wing for VTOL applications has the potential to provide a combination of convenient mounting structure for tilting wings and rotors, coupled with a box wing geometry that reduces the drag due to lift during the high powered transition phase of flight.

Different examples of aircraft are described in the following patent documents. <CIT> relates to a VTOL with pivoting rotors and stowing rotor blades. <CIT> discloses an aircraft in which the rotors and motors are mounted to a rotatable leading edge associated with the rear wings. <CIT> relates to a rhombohedral-wing aircraft for vertical take-off and/or landing. <CIT> discloses an aerofoil for an aircraft. <CIT> disclosed aerodynamically actuated thrust vectoring devices.

It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or to provide a useful alternative.

In a first aspect, the present invention provides a vertical take-off and landing (VTOL) aircraft having:.

The vertical take-off and landing (VTOL) aircraft further preferably comprises a mechanical actuator configured to pivot the motor pod and moveable trailing control surface about a hinge point of the fixed leading edge.

The actuator preferably includes a mechanically driven rotating arm and a linkage.

The rotating arm preferably has a proximal end connected to an actuator motor of the motor pod, and the rotating arm has a distal end connected to a proximal end of the linkage, and a distal end of the linkage is pivotally connected to the fixed leading edge.

The vertical take-off and landing (VTOL) aircraft further preferably comprises a leading edge slot located between the fixed leading edge and the moveable trailing control surface.

The vertical take-off and landing (VTOL) aircraft further preferably comprises an upper slot cover hingedly mounted to an upper side of the fixed leading edge,
wherein the upper slot cover generally covers the leading edge slot in a forward flight configuration, and the leading edge slot is at least partially uncovered in a take-off and landing configuration.

The vertical take-off and landing (VTOL) aircraft further preferably comprises a lower slot cover hingedly mounted to an underside of the fixed leading edge, the lower slot cover generally covers the leading edge slot in a forward flight configuration, and the leading edge slot is at least partially uncovered in a take-off and landing configuration.

Preferably a trailing side of the lower slot cover and a trailing side of the upper slot cover are abutment with each other to define an enclosed volume between the fixed leading edge, the upper slot cover and the lower slot cover.

The trailing side of the lower slot cover and the trailing side of the upper slot cover are preferably moveable and configured to slide relative to each other.

The upper slot cover is preferably curved having a concaved surface which is generally downwardly facing in a forward flight configuration.

The lower slot cover is preferably curved having a generally "S" curve profile, having an upwardly facing concave surface adjacent to the leading edge, and a downwardly facing concave surface adjacent to the trailing side in a forward flight configuration.

The upper slot cover is preferably defined by two or more members which are hingedly connected to achieve an articulated connection pivotal about an axis extending generally parallel with a longitudinal axis of the wing.

The upper slot cover is preferably defined by a flexible member and/or connected to the fixed leading edge by a flexible member, the flexible member being fabricated from a material such as a fibreglass composite which is flexible about an axis extending generally parallel with a longitudinal axis of the wing.

Each wing preferably has at least two motor pods having motors, a first motor has rotors having an axis of rotation which is downwardly inclined relative to the control surface, and a second motor has rotors having an axis of rotation which is upwardly inclined relative to the control surface, such that the first and second motors have different thrust lines.

The first and second motors are preferably selectively operable at different rotation speeds to generate a turning moment to rotate the control surface relative to the fixed leading edge.

In a second aspect, the present invention provides a vertical take-off and landing (VTOL) aircraft having:.

Preferably connecting members join tips of each wing located on the same side of the aircraft, the connecting members each being defined by a first arm secured to the forward wing, a second arm secured to the rearward wing and an intermediate elbow located at a junction of the first and second arms.

Preferably connecting members join tips of each wing located on the same side of the aircraft, the connecting members each having a generally linear body portion extending between the forward wing and the rearward wing.

The first arm of the connecting member preferably defines a pod for storage of batteries, fuel or other equipment.

Preferably the pod is selectively removeable and interchangeable.

The pod is preferably a buoyant float configured for water landing and take-off.

A distal motor is preferably located at or near a tip region of each forward wing, the distal motor being positioned generally in front of the connecting member.

The aircraft preferably has a height to span ratio in the range of:.

The moveable trailing control surface preferably has a length in profile of between about <NUM>% to about <NUM>% of a total chord length of the wing.

In a third aspect, the present invention provides a method of controlling a vertical take-off and landing (VTOL) aircraft having a wing structure having right and left side forward wings, and right and left side rearward wings, each of the right side wings being connected, each of the left side wings being connected in a box wing configuration, and each wing having a first motor and a second motor, the motors each being pivotally mounted to a fixed leading edge, and fixedly secured to a moveable trailing control surface, the first and second motors each having rotors having different thrust lines, the method including the steps of:.

The mechanical actuation step preferably includes rotating a mechanically driven rotating arm, the rotating arm having a proximal end connected to an actuator motor of one of the first and second motors, and the rotating arm has a distal end connected to a proximal end of the linkage, and a distal end of the linkage is pivotally connected to the fixed leading edge.

A preferred embodiment of the invention will now be described by way of specific example with reference to the accompanying drawings, in which:.

Several embodiments of VTOL aircraft <NUM> are disclosed herein. In common to each embodiment of the aircraft <NUM>, the wing structure is a box wing structure, and the wings <NUM>, <NUM>, <NUM>, <NUM> are each defined by a fixed leading edge <NUM>, and a moveable trailing control surface <NUM>.

Referring to <FIG>, each wing <NUM>, <NUM>, <NUM>, <NUM> has a fixed leading edge <NUM> which is secured to the aircraft chassis or another structural component of the fuselage <NUM>. Each fixed leading edge <NUM> may be a continuous single piece structure which passes through the fuselage <NUM> to define the structural component of corresponding left and right side wings <NUM>, <NUM>, <NUM>, <NUM>.

The fixed leading edge <NUM> may be fabricated with differing cross-sectional profiles. For example, referring to <FIG>, the cross-section of the fixed leading edge has a rounded teardrop like profile, being curved, and having a more acute profile on the upstream side, and a more gently curved profile on the downstream side. However, it will be appreciated that other cross-sections are envisaged, as will be discussed below. Furthermore, the fixed leading edge <NUM> may be hollow. The fixed leading edge <NUM> may be fabricated from carbon fibre or another composite material having suitable strength, rigidity and lightness. The fixed leading edge <NUM> can be manufactured using high volume techniques such as extrusion, composite pultrusion or filament winding as well as using conventional wing construction with aluminium alloys or composites.

Each of the embodiments of the aircraft <NUM> combines a box wing structure with a wing structure having a moveable control surface/flap <NUM> that has a length in profile of about <NUM>-<NUM>% of the wing chord and a fixed leading edge <NUM>.

The trailing control surface <NUM> is moveable relative to the fixed leading edge <NUM> between a forward flight configuration (for example <FIG>) and a take-off and landing configuration (for example <FIG>). Importantly, the fixed leading edge <NUM> does not rotate or otherwise move relative to the fuselage <NUM>. The control surface <NUM> is able to rotate through a range of between about <NUM> and <NUM> degrees, and preferably approximately <NUM> degrees between horizontal flight mode (<FIG>) and vertical flight mode (<FIG>).

The trailing control surface <NUM> is directly connected to a propulsion pod <NUM> having a motor <NUM> and a rotor <NUM> such that tilting the propulsion pod <NUM> deflects the trailing control surface or flap <NUM>.

Referring to <FIG>, the vertical take-off and landing (VTOL) aircraft <NUM> includes a plurality of motors <NUM>, which may be electric motors or gas powered motors. Each motor <NUM> has a propeller or rotor <NUM>. The propulsion pod or housing <NUM> of each motor <NUM> is mounted adjacent to the lower surface of the moveable control surface <NUM>, generally in front of (upstream) the fixed leading edge <NUM>.

The motors <NUM> may be mounted sufficiently forward of the fixed leading edge <NUM> so that the rotor <NUM> blades can fold rearwardly and remain clear of the wing structure. However, a preferred embodiment uses non-folding rotor blades with a variable pitch mechanism. Fixed pitch blades may alternatively be used.

In some embodiments of the invention, as depicted in <FIG>, the wing <NUM>, <NUM>, <NUM>, <NUM> includes an upper slot cover <NUM>. Referring to <FIG>, a leading edge slot <NUM>, is defined by a gap located between the fixed leading edge <NUM> and the trailing control surface <NUM>. The leading edge slot <NUM> increases the coefficient of lift and reduces buffet at high angles of tilt, in descent.

The upper slot cover <NUM> is mounted to the fixed leading edge <NUM> with one or more hinges or some other flexible connection, on the upper side of the fixed leading edge <NUM>. As shown in the top left portion of <FIG>, in a forward flight mode, the slot cover <NUM> generally covers the clearance defined between the fixed leading edge <NUM> and the trailing control surface <NUM>, such that the combination of the fixed leading edge <NUM>, the slot cover <NUM> and the trailing control surface <NUM> together define a generally continuous aerofoil surface on the upper side of the wing <NUM>, <NUM>, <NUM>, <NUM>.

As the trailing control surface <NUM> tilts downwardly (<FIG> top centre portion), the slot cover <NUM> also tilts downwardly. The slot cover <NUM> may be free moving or spring biased. Alternatively, the slot cover <NUM> may be actuated by a linkage (not shown) connected with the trailing control surface <NUM>. In still further versions, the slot cover <NUM> may be actuated with a motor or gear train or other actuation mechanism.

The slot cover <NUM> has a length of between about <NUM>% and <NUM>% of the total wing chord length. In one embodiment the slot cover <NUM> trailing edge is located behind the point that laminar flow separation occurs in cruising flight. In a further embodiment the slot cover <NUM> trailing edge has a sawtooth like edge to re-energise and reattach the laminar flow.

In the variation depicted in <FIG>, there is an upper slot cover <NUM> and an additional lower slot cover <NUM>. The lower slot cover <NUM> is also connected by one or more hinges to the fixed leading edge <NUM>. Again, the lower slot cover <NUM> may be free moving, spring biased or otherwise mechanically actuated.

As shown in the top left portion of <FIG>, in a forward flight mode, the upper slot cover <NUM> and lower slot cover <NUM> both cover the clearance, or leading edge slot <NUM> which is defined between the fixed leading edge <NUM> and the trailing control surface <NUM>, such that the combination of the fixed leading edge <NUM>, the slot covers <NUM>, <NUM> and the trailing control surface <NUM> together define generally continuous aerofoil surfaces on both the upper side of the wing and the underside of the wing.

Guide rails may be provided for the slot covers <NUM>, <NUM> to ensure they are kept in the desired relationship to the control surface <NUM>.

The slot covers <NUM>, <NUM> reduce drag in cruise flight conditions and guides the airflow when the control surface <NUM> is deflected to high angles. The fixed leading edge may have a curved or rounded rear such that when the control surface <NUM> is tilted to near vertical the upper surface is relatively smooth. Alternatively, it may have a relatively straight trailing edge.

Referring to <FIG> and <FIG>, a further embodiment is disclosed in which the upper and lower slot covers <NUM>, <NUM> are in abutment with each other on the trailing (downstream) side, to define a downstream apex, and an enclosed volume is defined between the fixed leading edge <NUM>, the upper slot cover <NUM> and the lower slot cover <NUM>. As shown, in this arrangement, the upper slot cover <NUM> has a downwardly facing concave surface. The lower slot cover <NUM> has a profile having an "S" curve profile, having an upwardly facing concave surface adjacent to the leading edge, and a downwardly facing concave surface adjacent to the trailing edge.

Referring to <FIG>, the upper slot cover <NUM> may be defined by two or more members <NUM>, <NUM> which are hingedly connected to achieve an articulated connection, which facilitates the movement of the upper and lower slot covers <NUM>, <NUM> relative to each other during movement of the trailing control surface <NUM>. Alternatively, upper slot cover <NUM> may be attached to the fixed leading edge <NUM> with a hinge that is defined by a flexible section such as a fibreglass composite rather than one or two discrete hinges.

The upper slot cover <NUM> may be mechanically actuated to provide an upper surface spoiler for control purposes during vertical and horizontal flight.

In this arrangement articulation occurs about an axis extending generally parallel with a longitudinal axis of the wing <NUM>, <NUM>, <NUM>, <NUM>. The downstream edges of the upper and lower slot covers <NUM>, <NUM> may be connected to each other, but also free to slide relative to each other, for example with a track and slider or other such mechanical connection that enables translation of the downstream edges relative to each other. <FIG>, depicts how the downstream edges of the upper and lower slot covers <NUM>, <NUM> move relative to each other in the different stages of movement of the control surface <NUM> between forward flight and the take-off and landing configuration.

In the embodiment of <FIG>, the downstream side of the fixed leading edge <NUM> has a channel <NUM> defined by an upper longitudinally extending projection <NUM> and an adjacent, lower, longitudinally extending projection <NUM>. The channel <NUM> can nest the upstream edge of the control surface <NUM> in the forward flight mode, as depicted in <FIG>.

Referring to <FIG>, each wing includes at least one motor <NUM>. The motor <NUM> may be an electric motor. Alternatively, the motor may be an internal combustion engine, such as a turboprop or piston engine. In a still further arrangement, the aircraft <NUM> may have a combination of electric motors and internal combustion engines <NUM>.

The motor pod or housing <NUM> is mounted to the fixed leading edge <NUM> at a hinge point <NUM>. The hinge point <NUM> is defined by a lug or other such projection which extends downwardly away from the underside of the fixed leading edge <NUM>. The motor housing <NUM> has a proximal end at which the propeller or rotor blades <NUM> are located (see <FIG>) and a distal end which is mounted to the trailing control surface <NUM>, in a fixed relationship. As such, the trailing control surface <NUM> pivots with the motor housing <NUM>. In one embodiment, the hinge mechanism can be integrated into the motor pod or housing <NUM> structure further reducing structural weight.

The location of the hinge point below and between <NUM>-<NUM>% of the chord of the fixed leading edge <NUM> has the effect of increasing the total wing area and opening up a leading edge slot <NUM> that operates in a similar fashion to a slotted leading edge. This has the effect of increasing the total lift of the wing <NUM>, <NUM>, <NUM>, <NUM>.

The control system for controlling movement of the trailing control surface <NUM> is provided in two distinct ways. Firstly, mechanical actuation is provided by an actuator <NUM>, as shown in <FIG>. The actuator <NUM> is defined by a mechanically driven, rotating arm <NUM> and a linkage <NUM>. The linkage <NUM> is pivotally secured at one end to the rotating arm <NUM>, and also pivotally secured to the fixed leading edge <NUM>. The rotating arm <NUM> is driven by an electric actuator motor <NUM> or other such drive system. When the rotating arm <NUM> is mechanically driven, the angle Φ can be selectively changed. For example, in the embodiment depicted in <FIG>, Φ may be approximately <NUM> degrees, when the trailing control surface <NUM> is in the forward flight configuration.

In contrast, in <FIG>, the angle has been increased to about <NUM> to <NUM> degrees, and in this position, the trailing control surface <NUM> is in the vertical take-off and landing configuration. The rotating arm <NUM> is mechanically driven by the actuator <NUM> to selectively move the trailing control surface <NUM> between the different flight configurations. It will be appreciated that other linkage <NUM> angles may be deployed, with different linkage configurations.

The inclusion of integrated actuators in the motor housing <NUM> permits wing tilt fine control, enabling distribution of weight across the wing, and reduces overall tilt system mass and complexity.

It will be appreciated that whilst one version of the actuator <NUM> has been described above, other arrangements are envisaged such as a gear train or cam and cam follower arrangements. Some such embodiments of actuation devices are described below.

<FIG> show a hinge rotation system based on a curvilinear track mechanism <NUM>. As depicted in <FIG>, the track <NUM> is curved, and provided in the form of a gear rack <NUM>. A gear <NUM> is in meshing engagement with the gear rack <NUM>, and the gear <NUM> is mounted on or otherwise secured to the trailing control surface <NUM> or motor housing. The gear <NUM> is driven by a rotary actuator which rotates the motor pod and trailing control surface <NUM>. The track mechanism <NUM> includes a channel <NUM>, and the channel <NUM> is used to support a pair of roller wheels <NUM>, also mounted to the trailing control surface <NUM> or motor housing. The roller wheels <NUM> cause the trailing control surface <NUM> to follow a curved path when the gear <NUM> moves along the gear rack <NUM>. The assembly of <FIG> can utilise mechanised braking to reduce actuator loads when stationary.

A further embodiment of a linear actuator <NUM> is depicted in <FIG>. The linear actuator <NUM>, such as a hydraulic or pneumatic cylinder, is attached to a lever <NUM>, which is fixed to the leading edge <NUM>. The linear actuator <NUM> drives the trailing control surface <NUM>. This arrangement provides a compact motor-pod assembly and reduces moments from the actuator on the motor-pod assembly.

<FIG> disclose an actuated secondary control surface <NUM>, shown schematically in different positions. This secondary control surface <NUM> is used to expand the effective wing area to maximise lift during transition flight. It is used to deflect flow to maximise lift during transition flight, and is retracted during cruise flight to reduce drag to maximise lift efficiency.

In the embodiment of <FIG>, a rotary actuator rotates a gear <NUM> which meshes with a rack <NUM> connected to a curvilinear track <NUM>. The secondary control surface <NUM> is attached to the track by a set of rollers <NUM>. This mechanism allows the secondary control surface <NUM> to rotate around a large effective hinge location.

This allows larger translation motion during deployment to maximise effective wing area.

<FIG> discloses an embodiment of a double track assembly for controlling the secondary control surface <NUM>. Specifically, in this embodiment, a rotary actuator rotates a gear <NUM> which meshes with a rack <NUM> on a first track <NUM>. The translation of the secondary trailing control surface <NUM> is defined by the first track <NUM>. A fixed link <NUM> is connected to a second track <NUM>, defining the angle of the secondary trailing control surface <NUM>. This arrangement allows optimised position and angle for the secondary trailing control surface <NUM> at any point during deployment.

In an alternative embodiment, <FIG> discloses a hinged link assembly consisting of a rotated arm <NUM> and a lever arm <NUM> for controlling the secondary trailing control surface <NUM>. In this embodiment, the secondary trailing control surface <NUM> is fixed to the rotated arm <NUM>, which pivots about the fixed pin <NUM>, and the lever arm <NUM> drives the rotation of the secondary trailing control surface <NUM>.

<FIG> discloses a spoiler, or upper slot cover <NUM>, which can be mechanically driven, either by a linear or rotary actuator <NUM>. During cruise flight, the upper slot cover <NUM> can be used to spoil lift. Alternatively, it can be used for direct lift control and for flight control (roll pitch) in cruise flight.

In contrast, during transition flight, as depicted in <FIG>, the upper slot cover <NUM> can be used to spoil lift. The upper slot cover <NUM> can also be used to increase lift during transition flight. The upper slot cover <NUM> can also be used to alleviate gust effects during transition flight.

In addition to the mechanical actuation provided by the actuator <NUM>, aerodynamic actuation is also provided to move the control surface <NUM>, as discussed below.

Referring to <FIG>, the axes of rotation of the motors <NUM> are non-parallel. In particular, for each pair of motors <NUM>, each odd motor <NUM> has an axis of rotation XX which is downwardly inclined relative to the control surface <NUM>, and each even motor <NUM> has an axis of rotation YY which is upwardly inclined relative to the control surface <NUM>. That is, each motor <NUM> is mounted having different thrust lines (see <FIG>). In this manner, one of the motors <NUM> has a thrust line that tends to rotate the control surface <NUM> clockwise, and the other motor has a thrust line that tends to rotate the control surface <NUM> counter-clockwise. When the pair of motors <NUM> operate in unison, at a similar rotational speed, the moments cancel out, and stabilisation is achieved in the vertical flight mode.

By rotating each motor <NUM> from each pair of motors <NUM> at different rotations speeds, a turning moment can generate a moment about the hinge point <NUM>, to selectively pivot the control surface <NUM> relative to the fixed leading edge <NUM>. This is referred to herein as aerodynamic actuation of the control surface <NUM>.

This provides aerodynamic control for the control surface <NUM>. The power to move the control surface <NUM> is derived by a combination of one or more of the mechanical actuation and the aerodynamic actuation. This may vary depending on the flight mode.

The control surface <NUM> may be a single surface which extends continuously along the full length of the wing <NUM>, <NUM>, <NUM>, <NUM>. Alternatively, each wing <NUM>, <NUM>, <NUM>, <NUM> may have one or more independently pivotal control surfaces <NUM>, such that the control surfaces <NUM> are capable of pivoting about the leading edge <NUM>, independent of the other control surfaces <NUM>.

There are two possible mounting arrangements for the motors <NUM> and control surfaces <NUM>:.

The aircraft <NUM> can provide a separately regulated power supply to each motor <NUM>. This permits a different voltage and for frequency to be delivered to each motor, and hence variable power output can selectively be generated by each motor <NUM> to achieve desired flight conditions such as turning left and right, and the aforementioned aerodynamic control surface <NUM> actuation.

The fixed leading edge <NUM> forms a continuous structure from the forward wings <NUM>, <NUM> to the rearward wings <NUM>, <NUM> on account of the connection of the wing tips via the connecting members or webs <NUM>. This structural connection provides sufficient rigidity that it enables the design of different fuselage <NUM> configurations, with the potential of using one standard wing configuration for several very different fuselage <NUM> configurations.

This continuous structure provides sufficient stiffness and rigidly such that the aircraft <NUM> can sustain any single engine failure without detrimental elastic deformation. The structure can be designed so that it does not rely on the fuselage <NUM> stiffness to the extent that the fuselage <NUM> structural weight can be reduced.

In the embodiments depicted in the drawings, there are two pairs of wings. Namely, the forward wings <NUM>, <NUM> and the rearward wings <NUM>, <NUM>. Each of the forward wings <NUM>, <NUM> is attached to (or extends through) a laterally opposing region of the fuselage <NUM>. Similarly, each of the rearward wings <NUM>, <NUM> is attached to (or extends through) a laterally opposing region of the fuselage <NUM>. In the embodiments shown in the drawings, the aircraft <NUM> is depicted as a single seat or double seat aircraft <NUM>. However, larger multi-person embodiments are also envisaged. The aircraft <NUM> may be controlled from within by a pilot, or alternatively it may be remotely controlled.

In the embodiment shown in the drawings, distal portions of the forward wings <NUM>, <NUM> and the rearward wings <NUM>, <NUM> are connected with connecting members or webs <NUM>, such that the two pairs of wings <NUM>, <NUM>, <NUM>, <NUM> define a boxed wing or closed wing structure. That is, there is a connecting member <NUM> at the wing tips between the front <NUM>, <NUM> wings and rear wings <NUM>, <NUM> and when viewed from the top and the front it has an enclosed profile. In some embodiments, such as <FIG> and <FIG>, the connecting member <NUM> may be a generally straight member. In contrast, in the embodiment of <FIG> and <FIG>, the connecting member <NUM> is non-linear.

In another embodiment (not shown), the forward wings <NUM>, <NUM> and the rearward wings <NUM>, <NUM> may be strut braced wings, connected with tie bars or struts.

The VTOL aircraft <NUM> described herein is a boxed wing or strut braced aircraft <NUM>.

In the embodiment depicted in <FIG>, the rear wings <NUM>, <NUM> are located above the fuselage <NUM>, meaning that the length of the rear wings <NUM>, <NUM> is increased, and hence the available lift which can be generated in forward flight mode is increased. A central portion <NUM> of the rear wing span is fixed, and does not include a moveable control surface.

The forward wings <NUM>, <NUM> and the rearward wings <NUM>, <NUM> are vertically separated, such that the forward wings <NUM>, <NUM> are vertically positioned below the rearward wings <NUM>, <NUM>. In particular, the forward wings <NUM>, <NUM> are positioned below and in front of the rearward wings <NUM>, <NUM>. This provides several advantages and ensures that the wing location provides an efficient mounting for the vertical lift and propulsion motor <NUM> and rotor <NUM> combination.

As depicted in <FIG> having the forward wings <NUM>, <NUM> low (and rearward wings <NUM>, <NUM> high) means that the height to span ratio increases as the rotors rotate from horizontal to vertical. Box wings with a higher height to span ratio have a lower induced drag which can be utilised effectively for VTOL aircraft. The height to span ratio is in the range of:.

As depicted in the embodiment of <FIG>, the tip portion <NUM> of the rearward wings <NUM>, <NUM> extends downwardly and rearwardly. This wing tip portion, or winglet <NUM>, assists to reduce wing tip vortices. The winglets <NUM> may include one or more wheels for supporting the aircraft <NUM> when stationary, and during take-off and landing. The aircraft <NUM> of <FIG> also has a further wheel or set of wheels which are located beneath the fuselage <NUM>, generally near the front of the fuselage <NUM>. In this way, the rear wheels and front wheels are positioned at the vertices of an isosceles triangle. By locating the rear wheels on the winglets <NUM>, the width of the aforementioned isosceles triangle is maximised, thereby increasing the stability of the aircraft <NUM>.

In the embodiment depicted in <FIG> and <FIG>, at least one of the wings <NUM>, <NUM>, <NUM>, <NUM> has a first and a second motor <NUM> which are longitudinally offset relative to each other about an axis of rotation of the rotors <NUM>.

The wing adjustment, depicted in <FIG>, shows the change of inclination of the motors <NUM> and control surface <NUM> when transitioning between the take-off wing position (<FIG>) and the forward flight wing position (<FIG>). As shown in those figures, the leading edges <NUM> are stationary, and non-pivoting. In contrast, the motors <NUM> and control surfaces <NUM> pivot in unison.

Referring to <FIG>, when the control surface <NUM> reaches the final, horizontal position, for forward flight, engagement may occur between the fixed leading edge <NUM> and the control surfaces <NUM> to prevent the control surface <NUM> from pivoting further. Alternatively, the motor pod or housing <NUM> may engage with the underside of the fixed leading edge <NUM>.

In the embodiments depicted in <FIG>, there are two motors <NUM> mounted to each wing <NUM>, <NUM>, <NUM>, <NUM>. However, additional motors <NUM> may be mounted to the aircraft <NUM>, for example on the wings <NUM>, <NUM>, <NUM>, <NUM>, the nose of the fuselage <NUM> or the wing connecting members <NUM>.

By employing lower numbers of motors <NUM>, the rotor <NUM> diameter can be increased. The rotor blade <NUM> diameters may overlap with adjacent rotor <NUM> blades when viewed from the front. In order to accommodate the overlap, the motors <NUM> are mounted such that each set of rotor blades <NUM> is longitudinally offset relative to the adjacent set of rotor blades (relative to an axis of rotation), thereby preventing contact between the adjacent rotors <NUM>, whilst permitting large diameter rotors to be deployed.

Referring to <FIG>, an embodiment of the aircraft is depicted for possible water landing and take-off applications, for example in the form of a military aircraft <NUM> for deployment at sea. In these embodiments, the pads <NUM> have the potential to allow water landings, by acting as stabilising floats. This may be useful for some applications for normal water landings and emergencies. In particular applications where landing on the water is useful such as picking up and dropping off people, areas where water is the best landing site or for roles where picking up and dropping of equipment or people from the water or deploying sensors or equipment such as dipping sonar.

In these embodiments, the landing pads <NUM> may be used to house energy storage systems that may include more batteries, fuel cells, such as hydrogen fuel cells, with hydrogen fuel tanks, and turbogenerators with fuel tanks.

In the embodiment of <FIG>, battery/fuel pods <NUM> are located within the connecting members or webs <NUM> which join the forward wings <NUM>, <NUM> and the rearward wings <NUM>, <NUM>. Furthermore, in this embodiment, the outermost motors <NUM> on the forward wings <NUM>, <NUM> are located at or near the wing tips, in a low drag manner, in front of the battery/fuel pods <NUM>, such that the fuel pod <NUM> is positioned behind and within the rotor <NUM> area during forward flight.

This arrangement of <FIG> provides reduced drag in high speed cruise flight as the wing tip drag and motor pod drag of an integrated unit are less than a separate wing tip and motor pod <NUM>. Furthermore, the arrangement of <FIG> reduces rotor blockage in vertical flight mode, as the outboard propellers are only pushing high pressure air onto a smaller wing area.

This arrangement also reduces structural weight, as the mass in the wing tips can be used to reduce the bending moment on the wing structure in flight, hence providing a lighter overall structure.

This arrangement also has the potential to allow hot swappable batteries on the wing tips that will reduce down time between flights. Alternatively, the aircraft <NUM> can be reconfigured for different energy storage options such as battery in one configuration and hydrogen fuel cell, (with hydrogen tank with <NUM> or <NUM> Bar gaseous hydrogen tank) as another configuration. This may be a model choice at the factory or an operational choice by the end user.

Furthermore, the embodiment of <FIG> increases passenger safety in an emergency as the fuel/energy is located at the wing tips, and in the event of a fire it is remote from occupants, and in the event of an emergency landing the high mass objects are also remote from the cabin.

Advantageously, a box wing structure is more aerodynamically efficient than a conventional wing of the same size and can be more structurally efficient (therefore lighter).

Advantageously, the boxed wing structure provides additional rigidity.

Advantageously, the aircraft <NUM> reduces the weight of the bearings and tilt structure required when compared to a conventional tilt wing aircraft. This is because a conventional tilt wing requires a single, large bearing pair (one on either side of the aircraft fuselage) with a stiff structure that rotates.

Advantageously, the aircraft <NUM> provides a simple, low cost VTOL aircraft <NUM> for transport and aerial surveillance applications. The aircraft <NUM> reduces weight and complexity of similar systems. It can be manufactured at lower cost due to the use of simple continuous wing structure and the simplicity of the distributed tilt bearings/hinges. It is lower cost to develop different configurations as the structure does not require a torsionally stiff fuselage. This allows it to be designed so that the same basic wing and propulsion system could have several configurations with significantly different fuselage pods. Structural connection of the wingtips in a box-wing formation reduces the need for fuselage <NUM> torsional rigidity and simplifies the fuselage <NUM> structure. In practice, this allows different configuration fuselages <NUM> with the same, or very similar, wing <NUM>, <NUM>, <NUM>, <NUM> structure.

Advantageously, the aircraft <NUM> allows the structure to have a lower weight for a given payload.

Claim 1:
A vertical take-off and landing (VTOL) aircraft having:
a wing structure having right and left side forward wings (<NUM>, <NUM>); and
right and left side rearward wings (<NUM>, <NUM>), each of the right side wings (<NUM>, <NUM>) being connected, and each of the left side wings (<NUM>, <NUM>) being connected in a box wing configuration;
characterized in that each wing (<NUM>, <NUM>, <NUM>, <NUM>) has a fixed leading edge (<NUM>) and at least one moveable trailing control surface (<NUM>),
further wherein each wing (<NUM>, <NUM>, <NUM>, <NUM>) has at least one motor pod (<NUM>) having a motor (<NUM>), the motor pod (<NUM>) being pivotally mounted to an underside of the fixed leading edge (<NUM>), and fixedly secured to the moveable trailing control surface (<NUM>).