GB2584665A

GB2584665A - An aircraft with a moveable wing tip device

Info

Publication number: GB2584665A
Application number: GB1908235.3A
Authority: GB
Inventors: Wilson Thomas
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-06-10
Filing date: 2019-06-10
Publication date: 2020-12-16
Also published as: GB201908235D0

Abstract

A primary aircraft 900 comprises a fixed wing 201 for mounting to a fuselage and a wing tip 202 mounted at an end of the fixed wing which is freely rotatable about a hinge axis under the influence of aerodynamic forces during flight. The wing tip also forms the wing of a secondary aircraft 801 that may be detached from the fixed wing of the primary aircraft. The secondary aircraft 801 carries a propulsion unit 705 and also includes a source of electrical power in the form of batteries (602, fig 3). Electrical interfaces (605, fig 3) are provided on the wing tips and are configured to supply electrical power to a bank of batteries (601, fig 3) in the primary aircraft.

Description

AN AIRCRAFT WITH A MOVEABLE WING TIP DEVICE

BACKGROUND OF THE INVENTION

100011 The present disclosure relates to an aircraft comprising a moveable wing tip device.

[0002] The present invention concerns a primary aircraft portion for use in such an aircraft. The invention also concerns a wing tip device for use in such an aircraft, a secondary aircraft portion for use in such an aircraft, a wing and a fixed wing for use in such an aircraft, a method of operating an electrically-powered aircraft and a composite aircraft comprising primary aircraft and secondary aircraft.

[0003] Aircraft with moveable wing tip devices are known. The wing tip devices may be moved from a flight configuration in which the wing tip contributes to the lift generated by the wing, but also contributes to the forces experienced by the wing inwards of the wing tip device, to a load alleviating configuration in which the wing tip device does not contribute to the load experienced by the wing inwards of the wing tip device. The wing tip device is typically moved to a load-alleviating configuration in response to a high load event caused, for example, by a gust of wind or a particular aircraft manoeuvre. An example of such an arrangement is shown in W02017118832, the content of which is fully incorporated herein by reference. Once the high load event has passed it may be desirable to move the wing tip device back into the flight configuration. This is sometimes achieved using an actuator, for example, to overcome the lift forces experienced by the wing tip device. The provision of an actuator may add to one or more of the weight, complexity and cost of the aircraft.

[0004] Alternatively or additionally the present invention seeks to provide an improved aircraft with moveable wing tip device.

SUMMARY OF THE INVENTION

[0005] According to a first aspect of the invention, there is provided an aircraft comprising (a) a primary aircraft portion, the primary aircraft portion comprising a fixed -2 -wing, and (b) a wing tip device moveably mounted at the tip thereof about a hinge axis, and the wing tip device is moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight,.

wherein the primary aircraft portion is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, the wing tip device is provided with a store of electrical power. and the aircraft is configured so that the store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.

[0006] The store of electrical power (typically a battery or multiple batteries) not only provides electrical power to the primary aircraft portion, but the store of electrical power provides weight to the wing tip device, thereby facilitating recovery of a wing tip device into the first configuration from the second configuration, optionally without an actuator. Furthermore, embodiments of the invention recognise that since the wing tip device generates significant lift, it is beneficial to increase the weight of the wing tip device, preferably to such an extent that a freely rotating hinge can be used. Furthermore, locating a store of electrical power (such as a battery of multiple batteries) on the wing tip device may enable it to be used to control the orientation of the wing tip device.

[0007] The fixed wing may have an upper surface and a lower surface, and the wing tip may have an upper surface and a lower surface. In the first configuration, the upper and lower surfaces of the wing tip device may be continuations of the upper and lower surfaces of the fixed wing. In the first configuration, the trailing edge of the wing tip device is preferably a continuation of the trailing edge of the fixed wing. The leading edge of the wing tip device is preferably a continuation of the leading edge of the fixed -3 -wing. There is preferably a smooth transition from the fixed wing to the wing tip device. It will be appreciated that there may be a smooth transition even when the shape of the wing is such that there are changes in sweep or twist at the junction between the fixed wing and wing tip device. However, there are preferably no discontinuities at the junction between the fixed wing and wing tip device. The position of the wing tip device when the wing is in the first configuration may be referred to as the flight position of the wing tip device.

100081 In the second configuration, the wing tip device may be moved relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is moved away from the respective surface of the fixed wing.

100091 Optionally, the wing tip device is configured to be freely moveable about the hinge axis. In this case, there is nothing apart from the weight of the weighted wing tip device (including the store of electrical power and optional propulsion unit, as mentioned below) preventing movement from the first configuration to the second configuration. Therefore, the wing tip device optionally moves to the second configuration in the event that the lift generated by the wing tip device overcomes the opposing force generated by the weight of the weighted wing tip device. The wing tip device may be described as being freely rotatable about the hinge axis. In this case, the wing tip device typically moves to a second configuration in which the lift generated by the wing tip device balances the counteracting force generated by the weight of the weighted wing tip device (including the weight of the store of electrical power and optionally one or more propulsion units). When the lift generated by the wing tip device balances the counteracting force generated by the weight of the weighted wing tip device, the wing tip device "floats" or "coasts" in a second configuration. If the lift generated by the wing tip device decreases, then the wing tip device will fall back towards the first configuration. If the lift generated by the wing tip device increases, then the wing tip device will tend to move (and usually rotate) to a new equilibrium position.

[0010] The hinge axis is preferably oriented non-parallel to the longitudinal axis of the aircraft. The hinge axis is preferably oriented non-parallel to the line of flight direction. The hinge axis is preferably oriented such that the hinge axis intersects the wing in a -4 -trailing edge region inboard of where the hinge axis intersects the wing in a leading edge region. In embodiments, the hinge axis may intersect the trailing edge and/or leading edge of the wing (for example when viewed from above).

[0011] The hinge axis may be located in a vertical first plane, wherein the first plane intersects the trailing edge of the wing and the leading edge of the wing. Preferably, the hinge axis is oriented such that the first plane intersects the trailing edge of the wing inboard of where the first plane intersects the leading edge of the wing.

100121 The hinge axis is preferably oriented such that the mean angle of incidence of the wing tip changes when the wing tip device is rotated about the hinge axis. More preferably, the hinge axis is oriented such that the mean angle of incidence of the wing tip is reduced as the wing tip device rotates away from the first configuration.

100131 The hinge axis may be orientated substantially perpendicular to the swept mean chord axis of the wing. The swept mean chord axis may be parallel to the longitudinal direction of the wing box. The orientation of the hinge axis may be chosen such that the direction of airflow over the wing in the region of the wing tip remains non-parallel to the first axis during flight. The orientation of the hinge axis may be chosen such that, for a given orientation of the wing tip device, the direction of airflow remains incident on the same side of the wing tip device despite the yaw of the aircraft.

[0014] The angle between the hinge axis and the longitudinal axis of the aircraft may be referred to as the "flare angle". The flare and may be between 10 and 20 degrees. An example flare angle is 17 degrees. A flared axis of rotation may refer to an axis of rotation of the wing tip device that is non-parallel to the longitudinal axis of the aircraft. [0015] Rotation of the wing tip device about the hinge axis may be referred to as folding of the wing tip. The hinge axis may be a fold axis.

[0016] In preferred embodiments of the invention, the wing tip device may be arranged such that substantially no bending moment is transferred across the hinge between the wing tip device and the fixed wing; thereby the lift loads generated by the wing tip device are preferably not transferred to the fixed wing.

100171 Optionally, the aircraft may be provided with a restraining mechanism for resisting movement of the wing tip device from the first configuration to the second -5 -configuration. In such an arrangement, the second configuration may be considered as a load-alleviating configuration because it is only adopted when the restraining mechanism is released and the no bending moment can be transferred across the hinge (thus alleviating any loads on the fixed wing). In preferred embodiments of the invention, there may be no restraining mechanism; the need for the restraining mechanism may be mitigated by the presence of the store of electrical power with the wing tip device because the aerodynamic loads needed to overcome the combined weight of' the wing tip device and store of electrical power are sufficiently large that no restraining mechanism is required (the aerodynamic load instead being used to 'carry' the weight of the store of electrical power).

100181 The primary aircraft portion optionally comprises more than one propulsion unit. For example, the primary aircraft portion optionally comprises two or four propulsion units. The aircraft may optionally be configured so that electrical power may be supplied from the store of electrical power provided with the wing tip device to more than one and optionally each propulsion unit. 'The aircraft may optionally be configured so that electrical power may be supplied from the electrical storage unit to one, optionally more than one and optionally each propulsion unit.

[0019] At least one, optionally more than one and optionally each propulsion unit may be an electrically-powered aero engine, such as a hybrid aero engine.

[0020] The wing tip device is optionally provided with one or more propulsion units configured to receive electrical power from the store of electrical power. For example, the wing tip device may be provided with an electrical engine or a hybrid engine that is in part at least configured to receive electrical power from the store of electrical power. The provision of one or more propulsion units with the wing tip device adds further weight to the weighted wing tip device, which may be advantageous in helping to return the wing tip device to the first configuration from the second configuration.

100211 Those skilled in the art will realise that the aircraft of the first aspect of the present invention may be electrically powered or may be a hybrid aircraft i.e. partially electrically powered.

100221 The fixed wing and wing tip device are optionally both swept. -6 -

[0023] The fixed wing may be provided with the propulsion unit, and is optionally provided with more than one propulsion unit. The fixed wing may also optionally be provided with the electrical storage unit for powering the propulsion unit.

[0024] The fixed wing may optionally be provided with an electrical connection interface for facilitating electrical connection to a corresponding electrical connection interface provided to the wing tip device to facilitate supply of electrical energy from the store of electrical energy of the wing tip device to the electrical storage unit of the primary aircraft portion and/or at least one propulsion unit [0025] The wing tip device may be detachable from the fixed wing. This facilitates removal of the wing tip device from the primary aircraft portion at a desirable point in time, for example, when the wing tip device's store of electrical power has been depleted. Another wing tip device may then be attached to the primary aircraft portion.

[0026] The wing tip device may be detachable from the fixed wing in flight. In this connection, the wing tip device may be jettisoned from the fixed wing and may be collected. Alternatively, the wing tip device may be provided as part of a secondary aircraft portion that is flyable independent of the primary aircraft portion. The secondary aircraft portion is optionally unmanned. The aircraft may therefore comprise a secondary aircraft portion comprising the wing tip device, the secondary aircraft portion comprising a propulsion unit for powering the secondary aircraft portion. In this case, the wing tip device optionally provides a wing for the secondary aircraft portion. Optionally, this wing is asymmetric relative to the secondary aircraft portion.

[0027] The secondary aircraft portion may comprise a lift-providing tail portion, such as a horizontal tail plane. The secondary aircraft portion may comprise a direction-controlling tail portion, such as a vertical tail plane.

100281 The secondary aircraft portion may comprise a single propulsion unit comprising a single propeller. In this case, it is preferred that the secondary aircraft portion comprises a direction-controlling tail portion. The secondary aircraft portion may comprise two counter-rotating propellers. This reduces the need for a direction-controlling tail portion.

[0029] The secondary aircraft portion may comprise a fuselage. The fuselage may be provided with batteries for providing power to the propulsion unit(s), especially for when the secondary aircraft portion is detached from the primary aircraft portion.

[0030] The second aircraft portion may be provided with landing gear. Such landing gear may optionally comprise one or more of a float, a wheel and a skid.

[0031] The wing tip device may optionally be detachable when the aircraft is on the ground. The wing tip device may optionally only be detachable when the aircraft is on the ground. In this case, the wing tip device is not detachable when the aircraft is in the air. [0032] The wing tip device may be rotatable between the first configuration and the second configuration, optionally about a wing tip device rotational axis.

100331 The wing tip device may be moveable to a ground configuration for movement on the ground, optionally rotationally moveable, optionally about the wing tip device hinge axis. The ground configuration is not limited to use on the ground, but is typically used when the aircraft is on the ground.

[0034] In the ground configuration, the wing tip device is positioned away from the first configuration such that the span of the aircraft wing is reduced. In the first configuration, the span may exceed an airport compatibility gate limit. In the ground configuration the span is reduced such that the span (with the wing tip in the ground configuration) is less than, or substantially equal to, the airport compatibility gate limit. In the ground configuration, the wing tip device may be positioned such that the wing has its shortest span. In the ground configuration, the wing tip device may be oriented substantially vertically. The wing tip device may be moved from the first configuration to the ground configuration by rotating the wing about the hinge axis. The position of the wing tip device when the wing tip device is in the ground configuration may be referred to as the ground position. In the ground configuration, at least one of the upper and lower surfaces of the wing tip device are optionally moved further away from the respective surface(s) of the fixed wing than when the wing is in the second configuration.

[0035] If the wing tip device is moveable to a ground configuration, the wing optionally comprises a lock for locking the wing in the ground configuration. The lock may be -8 -configured to release the wing tip device when in the ground configuration to facilitate movement of the wing tip device from the ground configuration to the first configuration. [0036] If the wing tip device is moveable to a ground configuration, then the fixed wing may comprise an actuator for urging the wingtip device into, and/or out of, the ground configuration.

[0037] If the wing tip device is movable to a ground configuration, in the ground configuration, at least one of the upper and lower surfaces of the wing tip device is moved further away from the respective surface(s) of the fixed wing than when the wing is in the second configuration.

[0038] Optionally, there is nothing apart from the weight of the weighted wing tip device preventing movement from the first configuration to the second configuration so no bending moment is exerted on the fixed wing by the wing tip device. Therefore, the wing tip device optionally moves to the second configuration in the event that the lift generated by the wing tip device overcomes the opposing force generated by the weight of the weighted wing tip device. In this case, the wing tip device typically moves to the second configuration in which the lift generated by the wing tip device balances the counteracting force generated by the weight of the weighted wing tip device. When the lift generated by the wing tip device balances the counteracting force generating by the weight of the wing tip device and associated features, the wing tip device "floats" or "coasts" in a second configuration. If the lift generated by the wing tip device decreases, then the wing tip device will fall back towards the first configuration. If the lift generated by the wing tip device increases, then the wing tip device will tend to move (and usually rotate) to a new equilibrium position.

[0039] Given the weight of the weighted wing tip, there need be no actuator for moving the wing tip device from the second configuration to the first configuration. Crudely speaking, the weight of the weighted wing tip device may be sufficient to return the wing tip device to the first configuration in the event that the weight of the weighted wing tip device is more than the lift generated by the wing tip device. The aircraft may therefore be devoid of an actuator for moving the wing tip device from the second configuration to the first configuration. -9 -

[0040] The length of the wing tip device as defined along a midpoint of the wing may optionally be at least 5% of the length of the wing, optionally at least 10% of the length of the wing, optionally at least 15% and optionally at least 20% of the length of the wing. [0041] The length of the wing tip device as defined along a midpoint of the wing may be no more than 40% of the length of the wing, optionally no more than 30% and optionally no more than 20% of the length of the wing.

[0042] The length of the wing tip device as defined along a midpoint of the wing may optionally be at least 1.5m, optionally at least 2.0m, optionally at least 2.5m, optionally at least 3.0m and optionally at least 4.0m.

[0043] The length of the wing tip device as defined along a midpoint of the wing may be no more than 10m, optionally no more than 8.0m, optionally no more than 7.0m, optionally no more than 6.0m, optionally no more than 5.0m and optionally no more than 4.0m.

[0044] The length of the wing from the root of the fixed wing to the tip of the wing tip device in the first configuration (in particular, but not, exclusively for a two-engine aircraft) as measured along the midpoint of the wing may be at least 15m, optionally at least 20m, 25m, optionally at least 30m, optionally at least 35m, optionally at least 40m and optionally at least 45m. It is envisaged that the aircraft of the present invention may facilitate the use of longer and optionally larger area movable wing tip devices.

[0045] The wing may comprise one or more means for limiting the movement of the wing tip device relative to the fixed wing.

[0046] The wing may comprise means for limiting the movement of the wing tip device in a direction that is substantially the same as that in which the wing tip device is displaced when in the second configuration. Such a means inhibits over-rotation of the wing tip device. Said means for limiting the movement of the wing tip optionally limits movement to no more than 120 degrees from the first configuration, optionally no more than 110 degrees from the first configuration and no more than 100 degrees from the first configuration.

100471 The wing may comprise means for limiting the movement of the wing tip device in a direction opposite from that in which the wing tip device is displaced when in the -10 -second configuration. Such a means may be configured to inhibit the end of the wing tip device from contacting the ground.

[0048] The wing tip device may be provided with landing gear, optionally located at or proximate to an end of the wing tip remote from the fixed wing.

[0049] As mentioned above, the wing tip device may be movable to a ground configuration for movement on the ground, optionally rotationally moveable, optionally about the hinge axis. The ground configuration is not limited to use on the ground, but is typically used when the aircraft is on the ground. In the ground configuration, one or both of the upper and lower surfaces of the wing tip device are optionally moved further away from the respective surface(s) of the fixed wing than when the wing is in a second configuration. In the ground configuration, the effective length of the wing from the root of the fixed wing to the tip is reduced compared to when the wing is in the first configuration and when in the second configuration. When in the ground configuration, the rotational displacement about the hinge axis relative to the first configuration is optionally at least 60 degrees, optionally at least 75 degrees, optionally at least 90 degrees and optionally at least 105 degrees. Said rotational displacement may optionally be no more than 120 degrees, optionally no more than 105 degrees and optionally no more than 90 degrees.

[0050] If the wing tip device is movable to a ground configuration, the wing optionally comprises a locking mechanism for locking the wing in the ground configuration. The locking mechanism may be configured to release the wing when in the ground configuration to facilitate movement of the wing tip device from the ground configuration to the first configuration.

[0051] If the wing tip device is movable to a ground configuration, then the wing may comprise an actuator for urging the wing tip device into, and/or out of, the ground configuration.

100521 The aircraft optionally has an operating empty weight of at least 20,000kg, optionally at least 25,000kg, optionally at least 30,000kg and optionally at least 40,000kg. 100531 The wing tip device may comprise a wing tip extension; for example, the wing tip device may be a planar tip extension. In other embodiments, the wing tip device may comprise, or consist of, a non-planar device, such as a winglet. It will be appreciated that in the context of the present invention, the terms 'wing tip' and 'wing tip device' may be used interchangeably.

[0054] The aircraft may comprise two wings substantially as described above. The aircraft may therefore comprise (a) a primary aircraft portion, the primary aircraft portion comprising two fixed wings, and (b) two wing tip devices, one of which is moveably mounted at the tip of each fixed wing about a hinge axis, each wing tip device being moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight, . wherein the primary aircraft portion is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, each wing tip device is provided with a store of electrical power; and the aircraft is configured so that each store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.

100551 According to a second aspect of the present invention, there is provided a primary aircraft portion for use in the aircraft of the first aspect of the present invention. In particular, the primary aircraft portion comprises an electrical connection interface for facilitating electrical connection to a corresponding electrical connection interface provided to a wing tip device, the fixed wing being configured for attachment to a wing tip device to form an aircraft in accordance with the first aspect of the present invention. The attachment permits movement of the wing tip device relative to the fixed wing, as indicated above in relation to the aircraft of the first aspect of the present invention.

[0056] According to a third aspect of the present invention, there is provided a wing tip device for use in the aircraft of the first aspect of the present invention. In particular, the -12 -wing tip device is provided with a store of electrical power and is provided with an electrical connection interface facilitating electrical connection to a corresponding electrical connection provided on a fixed wing. The wing tip device is configured to be attached to a fixed wing to permit movement of the wing tip device relative to the fixed wing as indicated above in relation to the aircraft of the first aspect of the present invention.

[0057] In accordance with a fourth aspect of the present invention, there is provided a secondary aircraft portion for use in the aircraft of the first aspect of the present invention. The secondary aircraft portion may optionally have those features described above in relation to the aircraft of the first aspect of the present invention.

100581 In accordance with a fifth aspect of the present invention, there is provided an group of aircraft comprising a primary aircraft portion in accordance with the second aspect of the present invention and a plurality of secondary aircraft portions in accordance with the fourth aspect of the present invention. The group of aircraft may comprise more than two secondary aircraft portions, and optionally one or more of the secondary aircraft portions is not attached to the primary aircraft portion.

100591 In accordance with a sixth aspect of the present invention, there is provided a wing for use in the aircraft of the first aspect of the present invention, the wing comprising a fixed wing and a wing tip device.

[0060] In accordance with a seventh aspect of the present invention, there is provided a fixed wing for use in the aircraft of the first aspect of the present invention. The fixed wing of the seventh aspect of the present invention may comprise those features described above in relation to the primary aircraft portion of the second aspect of the present invention and in relation to the aircraft of the first aspect of the present invention.. 100611 In accordance with an eighth aspect of the present invention, there is provided a method of operating an electrically-powered aircraft, the method comprising: Providing electrical power from a wing tip device that is mounted for movement about a hinge axis to a fixed wing to an electrical storage device and/or an aircraft propulsion unit located inboard of the moveable wing tip device.

-13 - [0062] The wing tip device is moveable between (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight.

[0063] The movement of the wing tip device may comprise those features described above in relation to the aircraft of the first aspect of the present invention.

[0064] The aircraft may comprise one or more features of the aircraft of the first aspect of the present invention. The aircraft may be an aircraft in accordance with the first aspect of the present invention.

[0065] The wing tip device may have an upper surface and a lower surface. The fixed wing may have an upper surface and a lower surface.

100661 In the first configuration, the upper and lower surfaces of the wing tip device may be continuations of the upper and lower surfaces of the fixed wing. In the second configuration, at least one of the upper and lower surfaces of the wing tip portion may be moved away from the respective upper and lower surfaces of the fixed wing.

[0067] The method may optionally comprise separating the wing tip device from the fixed wing.

[0068] Separating the wing tip device from the fixed wing may take place in the air. [0069] The wing tip device may be provided as a secondary aircraft portion, the wing tip device forming a wing of the secondary aircraft portion. The secondary aircraft portion may comprise a propulsion unit for powering the secondary aircraft portion. The wing tip device and the secondary aircraft portion may comprise those features described above in relation to the aircraft of the first aspect of the present invention.

[0070] Separating the wing tip device from the fixed wing may take place on the ground. For example, separating the wing tip device may take place prior to arrival at a disembarking or embarking gate. Removal of the wing tip device may enable the aircraft to use the gate.

[0071] The method may comprise replacing the wing tip device with a replacement wing tip device. This may comprise removing a first wing tip device and attaching a second wing tip device. The first wing tip device may comprise a depleted store of electrical -14 -power. The second wing tip device may comprise a replete store of electrical power. The replacement of the wing tip device may take place in the air, for example. In this case, a first secondary aircraft portion may separate from the aircraft, to be replaced by a second secondary aircraft portion. The replacement of the wing tip device may take place on the ground, for example. For example, a first wing tip device may be removed on the ground e.g. before the aircraft approaches a gate. A second wing tip device may be attached on the ground e.g. after the aircraft has left a gate.

100721 In accordance with a ninth aspect of the present invention, there is provided a composite aircraft comprising (a) a primary aircraft comprising two fixed wings, and (b) two secondary aircraft, each of which comprises a wing tip device, a wing tip device being moveably mounted at the tip of each fixed wing about a hinge axis, each wing tip device being moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight, . wherein the primary aircraft is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, each secondary aircraft is provided with a store of electrical power; and the composite aircraft is configured so that each store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.

[0073] According to a further aspect of the invention, there is provided a primary aircraft comprising a fixed wing for mounting to a fuselage, a wing tip mounted at an end of the fixed wing; wherein wing tip is freely rotatable about a hinge axis under the influence of aerodynamic forces during flight, and wherein the wing tip is also the wing of a secondary aircraft that may be detached from the fixed wing of the primary aircraft. The secondary aircraft is provided with a battery for providing electrical power to the primary aircraft. The wing tip preferably forms an extension of the fixed wing of the primary -15 -aircraft when the aerodynamic lift forces acting on the wing tip are less than the weight of the secondary aircraft, but the wing tip preferably rotates upwards about the hinge when the aerodynamic forces exceed the weight of the secondary aircraft.

[0074] It will, of course, be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0075] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0076] Figure I shows a schematic plan view of an example of an aircraft according to a first embodiment of the invention; [0077] Figure 2 shows a schematic front-on view of the aircraft of Fig. I, showing the wing tip device in the first configuration and in the second configuration; 100781 Figure 3A shows a schematic plan view of the secondary aircraft used in the aircraft of Figs. 1 and 2; 100791 Figure 3B shows a schematic plan view of an example of an alternative secondary aircraft; 100801 Figure 4 shows a schematic representation of an example of a method of operating an aircraft according to an embodiment of the invention; and [0081] Figure 5 shows a schematic representation of the an example of a further method of operating an aircraft according to a further embodiment of the invention.

DETAILED DESCRIPTION

[0082] An example of an aircraft according to an embodiment of the present invention will now be described by way of example only with reference to Figs. Ito 4. The aircraft is denoted generally by reference numeral 100 and a primary aircraft portion is denoted generally by reference numeral 900. The primary aircraft portion 900 comprises two -16 -fixed wings 201, 301. Each wing tip device 202, 302 is rotatably attached by a hinge (not shown) to a respective fixed wing 201, 301 to provide a hinge axis 205, 305. Each wing 200, 300 is dihedral and swept. The aircraft 100 comprises two secondary aircraft portions 801, 802, each of the secondary aircraft portions 801, 802 comprising a respective wing tip device 202, 302. Each of the secondary aircraft portions 801, 802 is therefore rotatably mounted about a hinge axis 205, 305 to a respective fixed wing 201, 301. Primary aircraft portion 900 is provided with four propulsion units 701, 702, 703, 704, each of which is a hybrid engine, configured to run on two types of power, in this case, aviation fuel and electrical power. Aircraft 100 is provided with a bank of batteries 601 for providing power to the propulsion units 701, 702, 703, 704. Each secondary aircraft portion 801, 802 is provided with a source of electrical power in the form batteries 602, 603. The wing tip devices 202, 302 are provided with electrical interfaces 604, 605 for forming electrical connections with corresponding electrical interfaces 606, 607 provided at the outboard end of each fixed wing 201, 301. The electrical interfaces 604, 605, 606, 607 are configured so that the batteries 602, 603 in the secondary aircraft portions can provide electrical power to the bank of batteries 601 located in the primary aircraft portion 900. Each secondary aircraft portion 801, 802 is provided with a propulsion unit 705, 706 in the form of a hybrid aero engine. The engines 705, 706 are used to help power the aircraft 100 when the secondary aircraft portions 801, 802 are attached to the primary aircraft portion 900 and are used to help power the secondary aircraft portions 801, 802 when the secondary aircraft portions 801, 802 are detached from the primary aircraft portion 9000, as is discussed below.

[0083] The wing tip devices 202, 302 are movable from a first configuration in which the upper 210, 310 and lower 211, 311 surfaces of the wing tip devices 202, 302 are continuations of the upper 212, 312 and lower 213, 313 surfaces of the fixed wings 201, 301 to a second configuration in which at least the upper or lower surface of the wing tip devices are moved away from the corresponding surface of the fixed wing.

[0084] In Fig. 1 and in the continuous line configuration labelled FC in Fig. 2, each wing tip device is in the first configuration in which the wing tip device 202, 302 forms an extension of the fixed wing 201, 301. In this first configuration FC, upper surface 210, -17 - 310 of the wing tip device is continuous with the upper surface 212, 312 of the fixed wing 201, 301 and in which the lower surface 211, 311 of the wing tip device 202, 302 is continuous with the lower surface 213, 313 of the fixed wing 201, 301. The wing tip devices 202, 302 are moveable between the first configuration and a second configuration, in which configuration in which each wing tip device 202, 302 is rotated about the hinge axis 205, 305 under the action of aerodynamic forces exerted on the wing tip device 202, 302 during flight. In this second configuration, the upper surface 210, 310 of the wing tip device 202, 302 is moved away from the upper surface 210, 310 of the fixed wing 201, 301 and the lower surface of the wing tip device 211, 311 is moved away from the lower surface 213, 313 of the fixed wing 201, 301.

100851 In the second configuration, shown as SC in Fig. 2, is achieved in flight when the lift exerted on the wing tip device 202, 302 exceeds the counteracting force resulting from the weight of the secondary aircraft portion 801, 802. The wing tip device 202, 302 is rotatably attached at the hinge axis 205, 305 to the respective fixed wing 201, 301 so no bending force is transferred from the wing tip device 202, 302 to the fixed wing 201, 301; the wing tip device 202, 302 merely rotates about the hinge axis 205, 305 relative to the fixed wing 201, 301 when the lift exerted on the wing tip device 202, 302 exceeds the counteracting force associated with the weight of the secondary aircraft portion 801, 802. Such movement may occur, for example, when the aircraft experiences a particularly strong gust of wind or when the aircraft is undertaking a particular manoeuver. When the event that causes the wing tip device to move to the second configuration is over, the weight of the secondary aircraft portion 801, 802 causes the wing tip device 202, 302 to move back to the first configuration FC.

[0086] It is worth noting the orientation of the hinge axis 205, 305. Each of said axes 205, 305 is at an angle of about 17 degrees to the flight direction of the aircraft, denoted by "F" in Fig. 1. The flight direction F corresponds to the longitudinal axis of the aircraft 100. This so-called "flaring" of the hinge axis away from the flight direction F means that the mean angle of incidence of the wing tip changes when the wing tip device is rotated about the hinge axis. The hinge axis is oriented such that the mean angle of incidence of the wing tip is reduced as the wing tip device rotates away from the first configuration.

-18 - [0087] The secondary aircraft portions 801, 802 provide electrical power to the engines of the primary aircraft portion 900, optionally by charging the bank of batteries 601 located in the primary aircraft portion 900. Furthermore, the secondary aircraft portions 801, 802 are replaceable. For example, once a secondary aircraft portion 801 has transferred an appropriate amount of electrical power to the primary aircraft portion 900, the secondary aircraft portion 801 can be detached from the primary aircraft portion 900. The wing tip device 201, 202 acts as a wing to the secondary aircraft portion 801, 802 when the secondary aircraft portion 801, 802 is detached from the primary aircraft portion 900. Those skilled in the art will realise that this wing is asymmetric. It is anticipated that two secondary aircraft portions 801, 802 detach from the primary aircraft portion 900 at about the same time to maintain symmetry. Detachment of the secondary aircraft portions 801, 802 may be actuated from the primary aircraft portion 900 or may be automated. The detached secondary aircraft portions 801, 802 then fly to a nearby recharging facility (not shown for convenience). It is anticipated that the secondary aircraft portions 801, 802 would retain sufficient electrical power to facilitate flight from the primary aircraft portion to the recharging facility. Replacement secondary aircraft portions 801, 802 may then be attached to the fixed wings 201, 301, so that those replacement secondary aircraft portions may provide electrical power to the primary aircraft portion. Those replacement secondary aircraft portions may themselves be replaced in due course. In this manner, electrical power may be provided to the primary aircraft portion over an extended period of time and the range of the primary aircraft portion may be extended significantly.

[0088] Those skilled in the art will realise that the wingspan of the primary aircraft portion 900 without the wing tip devices will be sufficiently large to maintain flight.

100891 Figure 3A shows a schematic plan view of the secondary aircraft portion 802 that has been described above. It should be noted that secondary aircraft portion 802 has a single propulsion unit 706 and a single propeller 707. Secondary aircraft portion 802 comprises a vertical tail plane 650 to inhibit the yaw that is associated with the use of a single propeller. Figure 3B shows a schematic plan view of an example of a different secondary aircraft portion 802'. The secondary aircraft portion 802' comprises a wing tip -19 -device 302' that can be coupled to the fixed wing 301 of aircraft 100. Wing tip device 302' comprises an electrical interface 605' for forming electrical connections with a corresponding interface 607 provided on the fixed wing. The secondary aircraft portion 802' is provided with a battery 603' that can provided electrical power to the bank of batteries 601 located in the primary aircraft portion 900 once the secondary aircraft portion 802' is coupled to the primary aircraft portion 900. Secondary aircraft portion 802' comprises two hybrid aero engines 706', 706-, each of which is provided with a propeller 707', 707". The propellers 707', 707" are configured to counter-rotate the secondary aircraft portion should not have a tendency to yaw, once detached from the primary aircraft portion 900. Secondary aircraft portion 802' is not provided with a vertical tail plane in light of this lesser tendency to yaw.

100901 An example of a method of operating an aircraft will now be described by way of example only with reference to Fig. 5. The examples in denoted generally by reference numeral 3000. The method 3000 comprises providing 30W electrical power from a secondary aircraft portion 801, 802 that is moveably mounted on a fixed wing 201, 301 to an electrical storage device 601 located inboard of the moveable wing tip device. After discharge of an appropriate amount of electrical power from the secondary aircraft portions 801, 802 to the primary aircraft portion 900, the secondary aircraft portions 801, 802 are detached 3002 from the primary aircraft portion 900. Replacement secondary aircraft portions are then attached 3003 to the fixed wing of the primary aircraft portion. The replacement secondary aircraft portions then provide 3004 electrical power to the primary aircraft portion 900.

[0091] The method 3000 described above with reference to Fig. 4 involves the detachment and attachment of secondary aircraft portions from the primary aircraft portion when the aircraft is in flight. It is possible for the secondary aircraft portions 801, 802 to be by detached from the primary aircraft portion 900 when the aircraft is on the ground.

[0092] Furthermore, the wing tip devices 202, 302 need not be provided as part of a flyable secondary aircraft portion. In this case, the wing tip device 202, 302 may be attached to the fixed wings for the time in which the aircraft is airborne, the wing tip -20 -devices 202, 302 only being detached from the aircraft when the aircraft is on the ground. An example of such a method will now be described with reference to Fig. 5. In this connection, the method of operating an aircraft is denoted generally by reference numeral 4000. The method 4000 may comprise providing 4001 electrical power from a battery provided to a wing tip device 202, 302 that is moveably mounted on a fixed wing 201, 301 to an electrical storage device 6W located inboard of the moveable wing tip device. This may optionally take place at least partly when the aircraft is airborne. Once the aircraft has landed, the method 4000 may comprise detaching 4002 the wing tip device 202, 302 from the fixed wing 201, 302, and moving 4003 the wing tip device, optionally to a charging facility (not shown). The removal of the wing tip device 202, 302 also reduces the effective wing span of the aircraft, which may facilitate approach of the aircraft to a gate.

[0093] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

100941 The example of the aircraft described above in relation to Figs. 1 to 3 describes a wing tip device that is movable to a second configuration. Those skilled in the art will realise that the aircraft may have a wing tip device that is also movable to a ground configuration.

[0095] The example of the aircraft described above in relation to Figs. 1 to 3 describes a wing tip device which is attached to a fixed wing with a freely rotating hinge, without a restraining mechanism for resisting movement of the wing tip device from the first configuration to the second configuration. Such a restraining mechanism is described in W02017118832, the content of which is fully incorporated herein by reference.

100961 The example of the aircraft described above in relation to Figs. 1 to 3 shows the engines positioned below the lower surfaces of the wing tip. Those skilled in the art will realise that the engines may be positioned above the upper surface of the wing tip device.

-21 - [0097] The example of the aircraft described above in relation to Figs. 1 to 3 shows that the wing tip devices are provided with propulsion units. Those skilled in the art will realise that it is not essential for the propulsion units to be provided.

[0098] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-22 -CLAIMS1. An aircraft comprising: (a) a primary aircraft portion, the primary aircraft portion comprising a fixed wing, and (b) a wing tip device moveably mounted at the tip thereof about a hinge axis, wherein the wing tip device is moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight,.wherein the primary aircraft portion is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, the wing tip device is provided with a store of electrical power; and the aircraft is configured so that the store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.
2 An aircraft according to claim 1 wherein the wing tip device is configured to be freely moveable about the hinge axis.
3 An aircraft according to claim I wherein the aircraft is provided with a restraining mechanism for resisting movement of the wing tip device from the first configuration to the second configuration.
4 An aircraft according to any preceding claim wherein the hinge axis is oriented non-parallel to the longitudinal axis of the aircraft.
-23 -An aircraft according to any preceding claim wherein the hinge axis is oriented such that the mean angle of incidence of the wing tip device is reduced as the wing tip device rotates away from the first configuration.
6 An aircraft according to any preceding claim comprising more than one propulsion unit.
7 An aircraft according to any preceding claim in which the wing tip device is provided with one or more propulsion units configured to receive electrical power from the store of electrical power.
8 An aircraft according to any preceding claim wherein the fixed wing is provided with an electrical connection interface for facilitating electrical connection to a corresponding electrical connection interface provided to the wing tip device to facilitate supply of electrical energy from the store of electrical energy of the wing tip device to the electrical storage unit of the primary aircraft portion and/or at least one propulsion unit.
9 An aircraft according to any preceding claim wherein the wing tip device is detachable from the fixed wing.
10. An aircraft according to claim 9 wherein the wing tip device is detachable from the fixed wing in flight.
11. An aircraft according to claim 9 comprising a secondary aircraft portion that is flyable independent of the primary aircraft portion, the secondary aircraft portion comprising the wing tip device and a propulsion unit for powering the secondary aircraft portion.
12. An aircraft according to any preceding claim comprising (a) a primary aircraft portion, the primary aircraft portion comprising two fixed wings, and (b) two wing tip devices, one of which is moveably mounted at the tip of each fixed wing about a hinge axis, -24 -each wing tip device being moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight; wherein the primary aircraft portion is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, each wing tip device is provided with a store of electrical power; and the aircraft is configured so that each store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.
13. A primary aircraft portion for use in the aircraft of any preceding claim.
14. A primary aircraft portion according to claim 13 comprising a fixed wing which fixed wing comprises an electrical connection interface for facilitating electrical connection to a corresponding electrical connection interface provided to a wing tip device, the fixed wing being configured for attachment to a wing tip device to form an aircraft in accordance with any one of claims 1 to 12.
15. A wing tip device for use in the aircraft of any of claims 1 to 12.
16. A wing tip device according to claim 15 provided with a store of electrical power and an electrical connection interface facilitating electrical connection to a corresponding electrical connection provided on a fixed wing.
17. A secondary aircraft portion for use in the aircraft of claim 11.
18. A group of aircraft comprising a primary aircraft portion in accordance with claim 13 or claim 14 and a plurality of secondary aircraft portions in accordance with claim 17.
19. A wing for use in the aircraft of any of claims 1 to 12, the wing comprising a fixed wing and a wing tip device.
-25 - 20. A fixed wing for use in the aircraft of any of claims 1 to 12.
21. A method of operating an electrically-powered aircraft, the method comprising: providing electrical power from a wing tip device that is mounted for movement about a hinge axis to a fixed wing to an electrical storage device and/or an aircraft propulsion unit located inboard of the moveable wing tip device.
22. A method of operating an electrically-powered aircraft according to claim 21, the wing tip device being moveable between (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight.
23 A method according to claim 21 or claim 22, comprising separating the wing tip device from the fixed wing.
24. A composite aircraft comprising (a) a primary aircraft comprising two fixed wings, and (b) two secondary aircraft, each of which comprises a wing tip device, a wing tip device being moveably mounted at the tip of each fixed wing about a hinge axis, each wing tip device being moveable during flight between: (i) a first configuration in which the wing tip device forms an extension of the fixed wing; and (ii) a second configuration, in which second configuration the wing tip device is rotated about the hinge axis under the action of aerodynamic forces exerted on the wing tip device during flight, wherein the primary aircraft is provided with a propulsion unit which is at least partially electrically powered and an electrical storage unit for powering the propulsion unit, each secondary aircraft is provided with a store of electrical power and -26 -the composite aircraft is configured so that each store of electrical power can provide electrical power to the electrical storage unit and/or said propulsion unit.A primary aircraft comprising a fixed wing for mounting to a fuselage, a wing tip mounted at an end of the fixed wing, wherein wing tip is freely rotatable about a hinge axis under the influence of aerodynamic forces during flight, and wherein the wing tip is also the wing of a secondary aircraft that may be detached from the fixed wing of the primary aircraft.