GB2583500A

GB2583500A - Aircraft wing with a moveable wing tip

Info

Publication number: GB2583500A
Application number: GB1906063.1A
Authority: GB
Inventors: Wilson Thomas
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-04-30
Filing date: 2019-04-30
Publication date: 2020-11-04
Also published as: GB201906063D0

Abstract

An aircraft wing 104 with a folding wing tip 108 which rotates about an axis 114, the axis flares outwards in a fore to aft direction 124. The aerodynamic loads on the wing tip during landing can assist in moving the wing tip to a folded position where the span of the wing is reduced. In another aspect the wingtip is rotated between a flight position for use during flight, and a ground position for use during ground-based operations. During the ground position the wing tip is moved away from the flight position in order to reduce the span of the wing. The aft end of the hinge is outboard of the fore end of the hinge and the mean angle of incidence of the wing tip increases as the wing tip rotates about the hinge from the flight position to the ground position. Also provided is an aircraft and method of landing an aircraft. The hinge axis is oriented such that it flares outwards, away from the fuselage, in the fore-to-aft direction. The wing tip can be allowed to rotate about the hinge axis during landing.

Description

AIRCRAFT WING WITH A MOVEABLE WING TIP

IECHNICAL FIELD

10001] The present invention concerns aircraft wings having a movable wing tip.

More particularly, this invention concerns aircraft wings having a wing tip that is foldable in order to reduce the wing span of the aircraft whilst the aircraft is on the ground. The invention also concerns a method of moving the wing tip.

BACKGROUND OF THE INVENTION

[0002] Increasing the wingspan of an aircraft can be beneficial as it can lead to a reduction in the induced drag (induced drag is approximately proportional to 1/span'-). Airport operating rules and gate sizes limit the maximum aircraft wing span when the aircraft are on the ground. It is known to have aircraft with wings having folding wing tips. When the aircraft are on the ground, the wing tips can be moved to a folded position so as to allow the aircraft to conform to airport operating rules and gate sizes. When the aircraft is in flight, the wing tips are extended to take advantage of the aerodynamic efficiencies provided by the longer wing span.

[0003] Prior art wing arrangements typically use an actuator to fold and unfold the wing tips. Typically it is necessary to wait for the aircraft to slow down to a certain speed (for example about 40-50kts) before actuating the actuator to move the wing tips. In some cases this may mean that the wings will not be in a ground configuration (e.g. with the wing tips fully raised such that the wing is within the gate limit) by the time the aircraft comes to leave the runway, which could cause a delay to the progress of the aircraft towards its gate. In order to move the wings to the ground configuration at a higher speed, a more powerful actuator must be used to withstand the aerodynamic loads generated by the wing tips. Typically, the more powerful the actuator, the larger and heavier the actuator is; which may mitigate sonic of the advantages of the movable wing tip.

[0004] US patent application publication number US 2017/0190410 Al teaches of moving control surfaces on the aircraft wing so as to change the airloads (aerodynamic -2 -forces) on the wing tips during a wing tip folding operation. For example, US 2017/0190410 Al teaches that ailerons proximate the wing tips could be moved to a position where they funnel less air onto the wing tips making it easier to fold the wing tips upward. US 2017/0190410 Al also teaches of providing the wing tips with their own control surface, such as an aileron, that can be used to increase the lift generated by the wing tips to help raise the wing tips.

[0005] In practice, it can be difficult to create a net positive lift force sufficient to lift a wing tip by moving only control surfaces on the fixed part of the wing. It can also be difficult to integrate a control surface into a movable wing tip.

[0006] The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved aircraft wing.

SUMMARY OF THE INVENTION

100071 The present invention provides, according to a first aspect, an aircraft wing comprising a fixed wing, and a wing tip mounted to an end of the fixed wing. The wing tip is arranged to rotate relative to the fixed wing about a hinge, the hinge having a hinge axis. The wing tip is rotatable about the hinge between: (i) a flight position for use during flight, and (ii) a ground position for use during ground-based operations. In the ground position, the wing tip is moved away from the flight position such that the span of the wing is reduced. The hinge axis is oriented at an angle to the fore-to-aft direction, such that an aft end of the hinge is outboard of a fore end of the hinge. In other words, the hinge axis is oriented such that it flares outwards, away from the fuselage, in the fore-to-aft direction (i.e. the hinge axis gets further away from the fuselage towards the rear of the aircraft). The hinge is also arranged such that the mean angle of incidence of the wing tip increases as the wing tip rotates about the hinge axis from the flight position to the ground position. In other words, the wing tip is arranged to rotate in an upward direction when moving from the flight position to the ground position. -3 -

[0008] The aerodynamic forces (e.g. lift and drag) acting on the wingtip due to the oncoming airflow may be used during landing to create a moment about the hinge which urges the wing tip away from the flight position towards the ground position. By virtue of the orientation of the hinge axis described herein, and the fact that angle of incidence increases as the wing tip rotates, the aerodynamic forces (e.g. lift and drag) acting to move the wing tip upwards, towards the ground position, may increase, and continue to increase, as the wing tip rotates about the hinge axis and more surface area of the wing tip is exposed to the oncoming airflow. As compared to prior art in which the hinge axis is oriented in the for-to-aft direction, or in which the hinge axis flares inwards in the fore-to-aft direction, this may help increase the speed at which the wing tips may move towards the ground configuration, allow the wing tip to be moved at higher aircraft speeds (e.g. up to 100kts), and/or allow the wing tip fold actuator to be made smaller and/or lighter. Preferably, this may be achieved without the need to employ control surfaces on the wing tip itself or manipulate control surfaces on the fixed wing; although, in embodiments, control surfaces may be provided on the wing tip itself and/or control surfaces on the fixed wing may be moved to further increase the aerodynamic forces acting to move the wing tip to the folded position.

[0009] The fore-to-aft direction may be a direction that is parallel to the longitudinal axis of the aircraft, and which runs from forward of the aircraft to behind the aircraft. The inboard-to-outboard direction may be perpendicular to the fore-to-aft direction, and run from the longitudinal axis outwards.

[0010] The hinge axis may intersect the wing in a leading edge region and/or trailing edge region of the wing. The hinge axis may intersect the leading edge region inboard of where the hinge axis intersects the trailing edge region. In some embodiments, the hinge axis passes directly through the leading edge and/or trailing edge. There may be an interface between the fixed wing and the wing tip. The interface at the leading edge may be inboard of the interface at the trailing edge. The hinge axis may be provided in a vertical plane that intersects the leading edge of the wing inboard of where the vertical plane intersects the trailing edge of the wing. -4 -

[0011] Rotation of the wing tip about the hinge axis may be referred to as folding of the wing tip. For example, it may be that rotation of the wing tip about the hinge axis results in the wing tip moving towards a position in which, if such movement were sufficiently continued, the wing tip would overlay the fixed wing.

[0012] The angle between the longitudinal axis of the aircraft and the hinge axis may be referred to as the "flare angle". The flare angle may be measured with the hinge axis projected onto a horizontal plane. In other words, the flare angle may be the angle between the longitudinal axis of the aircraft and the hinge axis when viewed from above. The flare angle may be chosen to provide an appropriate wing tip raising speed for a particular aircraft, and to ensure that the wing tips will still rise given a strong and steady cross wind. For example, assuming 100kts aircraft speed when the wing tip is moved and accounting for 40kts cross wind, the flare angle may be in excess of 20 degrees.

[0013] In the flight position, the wing span of the aircraft may be extended by the position of the wing tip. The wing may have its greatest span when the wing tip in the flight position. In the flight position, the span may exceed an airport compatibility gate limit.

[0014] 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 flight position, the upper and lower surfaces of the wing tip may be continuations of the upper and lower surfaces of the fixed wing.

[0015] In the flight position, the trailing edge of the wing tip is preferably a continuation of the trailing edge of the fixed wing. The leading edge of the wing tip is preferably a continuation of the leading edge of the fixed wing. There is preferably a smooth transition from the fixed wing to the wing tip. 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 the wing tip. However, there are preferably no discontinuities at the junction between the inner wing and wing tip.

100161 In the flight position, the line of 50% chord (i.e. the line which connects the 50% chord positions) of the fixed wing and the line of 50% chord of the wing tip may be substantially aligned. -5 -

[0017] In the ground position, the wing tip is positioned away from the flight position such that the span of the aircraft wing is reduced (in comparison to the flight configuration). In the ground position, the span may be reduced such that the span is less than, or substantially equal to, the airport compatibility gate limit. In the ground position, the wing may have its shortest span.

[0018] In the ground position, the wing tip may have a substantially upright orientation. In the ground position, the free end of the wing tip may be directly above the end of the wing tip that is mounted to the fixed wing.

[0019] In the ground position, at least one of the upper and lower surfaces of the wing tip may be moved away from the respective surface of the fixed wing. In the ground position, at least one of the leading and trailing edges of the wing tip may no longer be a continuation of the respective edge of the fixed wing. In the ground configuration, the line of 50% chord of the fixed wing and the line of 50% chord of the wing tip may have moved out of alignment.

[0020] In the ground position, the wing tip may be referred to as being folded, being in a folded position, or being in a folded state. In the flight position, the wing tip may be referred to as being extended, being in an extended position, or being in an extended state.

[0021] The range of motion of the wing tip about the hinge axis may be restricted. The wing may comprise one or more stop arranged to restrict the range of motion of the wing tip about the hinge axis. The stop may include a damper. The damper may dissipate the kinetic energy and slow the wing tip until stationary at the limits of its range of motion.

[0022] The wing tip may be rotatable only so far as the flight position in one direction and/or the ground position in the other direction. The flight position and/or the ground position therefore may define end positions of the wing tip.

[0023] It may be that the wing tip does not, in its flight positon at the aircraft speeds experienced during landing, generate sufficient aerodynamic forces to initiate movement of the wing tip towards the ground position. The wing tip may need to be moved a certain amount towards the ground positon, and possibly be moved through an equilibrium position, before the aerodynamic forces are sufficient to urge the wing tip to rotate about the hinge axis towards the ground position. The wing may comprise an actuator for this -6 -purpose. The equilibrium position may be a position where the aerodynamic forces (e.g. lift and drag) and weight of the wing tip are all balanced and there is zero net turning moment about the hinge axis due to these forces.

[0024] The actuator may be arranged to rotate the wing tip about the hinge axis. The actuator may be used, upon landing, to initiate and/or assist the movement of the wing tip. The actuator may be used to move the wing tip to a position in which the net areodynamic force on the wing tip is sufficient to urge the wing tip to the ground position without assistance of the actuator. Said position may be a position in which the moment about the hinge (in the direction of the ground position) due to the net aerodynamic force on the wing tip overcomes the opposing moment about the hinge due to the weight of the wing tip.

100251 It may be that most, or all, of the force necessary to move the wing tip to the ground configuration can be provided by aerodynamic forces. The actuator may be provided as a back-up in the event the wing tip fails (e.g. due to a systems failure or strong cross-wind) to move to the ground position under the action of aerodynamic forces during landing. In the event of such a failure, the wing tips may be raised after landing with the plane moving at taxiing speed or being stationary, at which point the aerodynamic loads on the wing tips are much lower than during landing. It may therefore be possible for the (back-up) actuator to be smaller/less powerful than would otherwise be required to raise the wing tips during landing and under aerodynamic load.

[0026] It is possible that a gust of wind may cause aerodynamic loads on the wing tip sufficient to temporarily stop or reverse the motion of the wing tip from the flight position towards the ground position (or vice versa). The wing tip may comprise a ratchet arranged to prevent movement of the wing tip towards the flight position whilst the wing tip is being moved to the ground position (or vice versa). The ratchet is preferably selectively en gageble so as to allow the wing tip to be moved in the opposite direction (e.g. from the ground position to the flight position) when required (e.g. prior to take off).

100271 The wing may be operable between: (i) a flight configuration for use during flight, wherein the wing tip is in the flight position, and (ii) a ground configuration for use during ground-based operations, wherein the wing tip is in the ground position.

[0028] Preferably, in the flight configuration, the position of the wing tip is restrained so as to restrict rotation of the wing tip about the hinge axis. It may be that, in the flight configuration, the wing tip is prevented from rotating about the hinge axis, for example by being locked in the flight position. In the flight configuration, the wing tip may act as an extension of the fixed wing. It may be that, in the flight configuration, lift generated by the wing tip is transferred to the fixed wing. Lift generated by the wing tip in the flight configuration may thereby contribute to the overall lift generated by the wings of the aircraft.

[0029] The wing may comprise a restraining assembly arranged to restrain the wing tip. The restraining assembly may be operable between a restraining mode and a releasing mode. In the restraining mode, the wing tip may be prevented from rotating about the hinge axis. The wing tip may be prevented from rotating about the hinge axis by a restraining force. In the restraining mode, the wing tip may be arranged to hold the wing tip in the flight position and/or the ground position. In the releasing mode, the restraining force on the wing tip may be released. In the releasing mode, the wing tip may be able to move away from the flight position and/or the ground position by rotating about the hinge axis.

100301 The restraining assembly may comprise a lock and/or a latch. The lock and/or latch may be engageble to prevent rotation of the wing tip away from the flight position and/or the ground position. For example, the restraining assembly may comprise a latch member, for example a latch pin, carried by the fixed wing that is arranged to engage with the wing tip, or vice versa, to restrain the wing tip. The restraining assembly may comprise a brake arranged to hold the wing tip.

[0031] The wing tip may be allowed to move away from the flight position (e.g. by releasing the restraining assembly) automatically during landing, for example on the basis of aircraft speed. The holding of the wing tip when it reaches its ground position may also be automatic. Confirmation that wing tips on both wings of the aircraft are securely held (e.g. in the ground position) may be made available to the pilot via an indicator in the cockpit.

100321 The releasing of the wing tips prior to take off, such that they move to the flight position, may be manually instigated by the pilot or automatically controlled. The wing -8 -tips may be moved from the ground position to the flight position when the aircraft is stationary. The restraining assembly may be configured to the restraining mode, so as to hold the wing tip in the flight position, automatically prior to take off Confirmation that wing tips on both wings of the aircraft are restrained may be made available to the pilot via an indicator in the cockpit.

[0033] The wing tip may be arranged such that it can move from the ground position to the flight position under its own weight. In the ground position, the centre of mass of the wing tip may be such that the wing tip may, if not securely held in position, rotate about the hinge axis towards the flight position under its own weight without an impulse from the actuator. I.e. in the ground position, the centre of mass of the wing tip may be outboard of the hinge axis. In alternative arrangements, the actuator may be provided to initiate movement of the wing tip from the ground position to the flight position. For example, in the ground position, the centre of mass of the wing tip may be above or inboard of the hinge axis, and the actuator may be used to move the wing tip such that the centre of mass is outboard of the hinge axis so that the wing tip will begin to rotate toward the flight position under its own weight.

100341 The wing tip may be mounted to the fixed wing via a joint. The joint may comprise the hinge. The hinge may define a hinge line about which the wing tip rotates. The orientation of the hinge line may define the orientation of the hinge axis. A forward part of the hinge line may be inboard of an aft part of the hinge line.

[0035] The wing may comprise an aileron. On the wing (i.e. not considering a notional extension of the hinge axis beyond the wing), the aileron may at least partially overlap the hinge axis in a chordwise direction. On the wing, the aileron may at least partially overlap the hinge axis in the fore-to-aft direction. The aileron position may be moved during landing to change the airflow over the wing tip in a way that increases the lift generated by the wing tip. This may help initiate movement of the wing tip towards the ground position.

100361 In embodiments, the wing tip may be provided with a control surface, for example an aileron. The control surface may be used to increase the aerodynamic forces urging the wing tip to the ground position. -9 -

[0037] The wing tip may be a wing tip extension; for example the wing tip device may be a planar tip extension. In other embodiments, the wing tip may comprise, or consist of, a non-planar device, such as a winglet.

[0038] The present invention provides, according to a second aspect, an aircraft comprising a wing in accordance with the first aspect of the invention. The aircraft preferably comprises two wings according to the first aspect of the invention, a wing being provided on each of the port and starboard side of the aircraft.

100391 The aircraft may comprise a control system arranged to control operation of the wing between the flight configuration and the ground configuration. The control system may be part of the Electronic Flight Control System (EFCS).

100401 The control system may be arranged to determine whether the speed of the aircraft is below a threshold speed for initiating movement of the wing from the flight configuration to the ground configuration. The control system may be configured to, when the speed has been determined to be below the threshold speed, allow the wing tip to rotate about the hinge axis towards the ground position.

[0041] The control system may control operation of the restraining assembly between the restraining mode and the releasing mode. The control system may be arranged to instruct the restraining assembly to release the wing tip when the speed has been determined to be below the threshold speed.

[0042] The aircraft is preferably a passenger aircraft. The passenger aircraft preferably comprises a passenger cabin comprising a plurality of rows and columns of seat units for accommodating a multiplicity of passengers. The aircraft may have a capacity of at least 20, more preferably at least 50 passengers, and more preferably more than 50 passengers. The aircraft is preferably a powered aircraft. The aircraft preferably comprises an engine for propelling the aircraft. The aircraft may comprise wing-mounted, and preferably underwing, engines.

100431 The span ratio of the fixed wing relative to the wing tip may be such that the fixed wing comprises at least 70%, 80%, 90%, or more, of the overall span of the aircraft wing.

-10 - [0044] The present invention provides, according to a third aspect, a control system for an aircraft according to the second aspect of the invention.

[0045] The present invention provides, according to a fourth aspect, a method of landing an aircraft, for example an aircraft according to a second aspect of the invention. The aircraft has a wing, the wing comprising a fixed wing and a wing tip mounted at an end of the fixed wing. The wing tip is arranged to rotate relative to the fixed wing about a hinge, the hinge having a hinge axis. The wing tip is rotatable about the hinge between: (i) a flight position for use during flight, and (ii) a ground position for use during ground-based operations, wherein the wing tip is moved away from the flight position and the span of the wing is reduced. The hinge axis is oriented at an angle to the fore-aft direction, such that an aft end of the hinge is outboard of a fore end of the hinge. The hinge is arranged such that a rotation of the wing tip away from the flight position increases the mean angle of incidence of the wing tip. The method comprises a step of determining whether the speed of the aircraft is below a threshold speed for initiating movement of the wing from the flight configuration to the ground configuration. The method comprises a step of, when the speed has been determined to be below the threshold speed, allowing the wing tip to rotate about the hinge axis towards the ground position. The method may comprise a step of holding the wing tip in the ground position.

[0046] The upper aircraft speed (threshold speed) at which the wing tip may be moved away from its flight position may be dictated by the speed below which a touch and go landing is not possible. In embodiments, it may be possible to move the wing tip away from the flight position at aircraft speeds of approximately I OOkts.

[0047] The step of allowing the wing tip to rotate about the hinge axis towards the ground position may comprise configuring a restraining assembly, acting to prevent rotation of the wing tip about the hinge axis, into a releasing mode in which wing tip is allowed to rotate about the hinge axis. For example, the restraining assembly may comprise a lock, and the step of allowing the wing tip to rotate about the hinge axis may comprise releasing/disengaging the lock.

100481 The method may comprise a step of using an actuator to initiate movement of the wing tip towards the ground position by moving the wing tip away from the flight position to an intermediate position at which the net aerodynamic force is sufficient to urge the wing tip to the ground position without assistance of the actuator.

[0049] The aircraft may comprise a main landing gear and a nose landing gear. The method may comprise a step of braking the wheels of the main landing gear. The brakes of the main landing gear may be applied before the nose landing gear has touched down.

[0050] The method may comprise a step of moving an aileron on the wing tip a position which increases the lift generated by the wing tip.

100511 It will be appreciated that any features described with reference to one aspect of the invention are equally applicable to any other aspect of the invention, and vice versa. For example, features described with reference to the wing of the first aspect may also be applicable to the aircraft, control system and/or method of the other aspects of the invention.

[0052] The term 'or' shall be interpreted as and/of unless the context requires otherwise.

DESCRIPTION OF THE DRAWINGS

100531 Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 100541 Figure 1 shows a plan view of an aircraft comprising a wing according to a first embodiment of the invention, the wing having a wing tip in a flight position; 100551 Figure 2 shows a plan view of the wing tip shown in Figure 1; [0056] Figure 3 shows a front view of the aircraft comprising the wing according to the first embodiment of the invention, the wing tip being in the flight position; [0057] Figure 4 shows a front view of the wing tip shown in Figure 3; [0058] Figure 5 shows a plan view of the aircraft comprising the wing according to the first embodiment of the invention, the wing tip being in a ground position; 100591 Figure 6 shows a plan view of the wing tip shown in Figure 5; [0060] Figure 7 shows a front view of the aircraft comprising the wing according to the first embodiment of the invention, the wing tip being in the ground position; and -12 - 100611 Figure 8 shows a front view of the wing tip shown in Figure 7.

DETAILED DESCRIPTION

[0062] Figures 1, 3, 5 and 7 show an aircraft 100 comprising a fuselage 102 and two wings 104 according to a first embodiment of the invention. The wings 104 are swept backwards with respect to the fuselage 102. Each wing 104 comprises a fixed wing 106 and a wing tip 108. The fixed wing 106 is mounted to the fuselage 102 at the wing root 110. The wing tip 108 is rotatably mounted to the outboard end of the fixed wing 106 via a joint in the form of a hinge 112. The aircraft 100 has a longitudinal axis 122 running in the for-to-aft direction.

[0063] Figures 2, 4, 6 and 8 show a close up view of the outboard end of the port wing 104 (circled in Figures 1, 3, 5 and 7). The hinge 112 defines a hinge axis 114. The wing tip 108 rotates relative to the fixed wing 106 about the hinge axis 114.

[0064] A forward end of the hinge 112 is inboard of an aft end of the hinge 112. The hinge axis 114 therefore flares outwards in the fore-to-aft direction. The fore-to-aft direction is indicated by arrow 124 in Figure 1. When viewed from above, the hinge axis 114 intersects a trailing edge 118 of the wing 104 outboard of where the hinge axis 114 intersects a leading edge 120 of the wing. The inboard-to-outboard direction is indicated by arrow 125 in Figure 1. The angle between the hinge axis 114 and longitudinal axis 122 of the aircraft 100, which is parallel to the fore-to-aft direction 124, is termed the flare angle 126. In this embodiment, the flare angle 126 is approximately 20 degrees (the Figures are not to scale).

[0065] An aileron 116 is provided on the fixed wing 106. On the wing (i.e. not considering a notional extension of the hinge axis 114 beyond the wing), the aileron 116 partially overlaps the hinge axis 114 in the fore-to-aft direction 124.

100661 The wing 104 also comprises a restraining assembly, shown schematically as a box 128. The restraining assembly 128 is operable between a restraining mode and a releasing mode. When the restraining assembly is in the restraining mode, the wing tip 108 -13 -is prevented from rotating about the hinge axis 114. When the restraining assembly 128 is in the releasing mode, the wing tip 108 may rotate about the hinge axis 114.

[0067] In embodiments, the restraining assembly 128 may comprise a latch and/or lock, for example using a latch pin which engages with both the fixed wing 106 and wing tip 108 to prevent rotation of the wing tip 108 about the hinge axis 114. In other embodiments, the restraining assembly 128 may be a brake which acts to hold a part of the wing tip 108 in place.

100681 The wings 104 are operable between a flight configuration and a ground configuration.

[0069] Figures 1 to 4 show the wings 104 in the flight configuration wherein the wing tip 108 is in a flight position. In the flight configuration the wing tip 108 is an extension of the fixed wing 106. The upper and lower surfaces of the fixed wing 106 are continuous with the upper and lower surfaces of the wing tip 108. Similarly, the leading and trailing edges of the fixed wing 106 are continuous with the leading and trailing edges of the wing tip 108. The wing span of the aircraft 100 is maximised. At the interface between the fixed wing 106 and the wing tip 108, the mean chord line of the fixed wing 106 is aligned with the mean chord line of the wing tip 108. When the wings 104 are in the flight configuration, the aircraft 100 exceeds airport compatibility rules and gate limits.

[0070] In the flight configuration, the wing tip 108 is restrained by the retraining assembly 128 (the restraining assembly 128 is in the restraining mode) so as to prevent rotation of the wing tip 108 about the first axis 114. The wing tip 108 is therefore held in the flight position.

[0071] Figures 5 to 8 show the wings 104 in the ground configuration wherein the wing tip 108 is in a ground position. In the ground position, the wing tip 108 is in an upright orientation. The free end of the wing tip 108 is directly above the mounted end of the wing tip 108. The wing span of the aircraft 100 is reduced as compared to when the wing tips are in the flight position. When the wings 104 are in the ground configuration, the wing span of the aircraft 100 is sufficient to meet airport compatibility rules and gate limits.

100721 The wing tip 108 moves between the flight position and the ground position by rotating, via hinge 112, about the hinge axis 114. Due to the hinge axis 114 being flared -14 -outwards in the fore-to-aft direction 124, the angle of incidence of the wing tip 108 increases (i.e. the wing tip rotates in a nose-up direction and the pitch angle increases) as the wing tip 108 rotates about the hinge axis 114 from the flight position to the ground position. The further the wing tip 108 rotates away from the flight position, the greater the angle of incidence becomes and the more the lower surface of the wing tip 108 is exposed to the oncoming airflow. In use, the further the wing tip 108 rotates about the hinge axis, the greater the turning moment becomes about the hinge axis 114 due to the aerodynamic forces (e.g. lift and drag) acting on the wing tip 108.

[0073] Stops (not shown) are provided to limit the range of motion of the wing tip 108 about the hinge axis I 14. The stops prevent the wing tip 108 for rotating upwards beyond the ground position, and downwards beyond the flight position. The stops comprise dampers arranged to dissipate the kinetic energy of the wing tip and slow the wing tip until stationary at the limits of its range of motion.

[0074] The wing tip 108 and the stops are arranged such the centre of mass of the wing tip 108 is on an outboard side of the hinge axis 114 when the wing tip 108 is in the ground position. Thus the wing tip 108 may tend to move from the ground position to the flight position under its own weight. In embodiments, the restraining assembly 128 is additionally operable to hold the wing tip 108 in the ground position. In alternative embodiments, a further holding assembly, such as a latch, lock or movable stop, is provided to hold the wing tip 108 in the ground position.

[0075] In embodiments, the wing 104 is additionally provided with an actuator arranged to generate a force that urges the wing tip 108 to rotate about the hinge axis. The actuator has at least sufficient power/force output so as to move the wing tip 108 from the ground configuration to the flight configuration when the aircraft is stationary or taxiing. The load capacity of the is, however, less than is required to move, under the aerodynamic loads experienced during landing, equivalent sized wing tips, on an equivalent aircraft, but where the wing tips are not flared outwards in the fore-to-aft direction.

[0076] The aircraft 100 further comprises a control system 130 arranged to control operation of the wing 104 between the flight configuration and the ground configuration. The control system 130 is arranged to operate the restraining assembly 128 and configure -15 -the restraining assembly 128 between the restraining mode and the releasing mode. Sensors are provided to determine the position of the wing tip 108 about the hinge axis 114. The sensors are coupled to the control unit 130. A speed sensor (not shown) is also provided to determine the aircraft speed and relay the speed to the control system 130.

[0077] The present invention is of particular use when configuring the wing 104 from the flight configuration to the ground configuration during landing.

[0078] A method of landing the aircraft 100 will now be described. The aircraft is initially in flight with the wing 104 in the flight configuration with the restraining assembly 128 in the restraining mode so as to hold the wing tip 108 in the flight position. The aircraft 100 subsequently touches down and decelerates. The speed of the aircraft 100 is monitored by the control unit 130. When the aircraft 100 speed is determined to be below a threshold level, the control unit 128 instructs the restraining assembly 128 to move to the releasing mode. The threshold level is the speed below which a touch and go landing is no longer possible, i.e. the speed at which the aircraft is committed to landing and cannot perform a go-around. In an example, the threshold speed is 100kts.

[0079] Once the restraining assembly 128 is released, the wing tip 108 is free to rotate about the hinge axis 114. Provided the aircraft is travelling at a sufficient speed, the aerodynamic forces (e.g. lift and drag) on the wing tip 108 create a net turning moment about the hinge axis 114 in a direction which rotates the wing tip 108 upwards and towards the ground position. The wing tip 108 thereby begins to rotate about the hinge axis 114 towards the ground position. As the wing tip 114 rotates, the angle of incidence of the wing tip 108 increases (i.e. the wing tip 108 is moved in a nose up direction and the pitch angle increases). The aerodynamic forces acting to urge the wing tip 108 towards the ground position therefore tend to increase. The opposing turning moment due to the weight of the wing tip 108 will also reduce as the horizontal distance between the centre of mass of the wing tip 108 and the hinge axis 114 decreases. Therefore, once rotation about the hinge axis has begun, it tends to continue.

[0080] When the wing tip 108 has reached the ground position, for example as determined by sensors connected to the control unit 128, the wing tip 108 is held in place -16 -by a holding assembly to prevent the wing tip 108 from returning to the flight position. The wing 104 has thus completed its transition to the ground configuration.

[0081] In embodiments, an actuator may initiate and/or assist movement of the wing tip 108 away from the flight position and towards the ground position. This may, for example, be required in the case where, in the flight position, the angle of incidence of the wing tip 108 is insufficient to generate enough lift to rotate the wing tip 108 about the hinge axis 114; and where, after sonic upward movement, the angle of incidence is such that sufficient lift is generated to rotate the wing tip 108 the remainder of the way to the ground position.

[0082] 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.

[0083] In embodiments, the aileron 116 is moved to a position that creates an airflow that increases the lift load on the wing tip 108 after touchdown. In embodiments, the airflow generated by the aileron helps initiate the raising of the wing tip 108 towards the ground position.

[0084] In embodiments, the landing procedure comprises touching down the main landing gear, and applying the main landing gear brakes, before the nose landing gear touches down (referred to as nose up braking).

[0085] 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

-17 -CLAIMS1. An aircraft wing comprising: a fixed wing, and a wing tip mounted to an end of the fixed wing, the wing tip being arranged to rotate relative to the fixed wing about a hinge, having a hinge axis, between: (i) a flight position for use during flight, and (ii) a ground position for use during ground-based operations, wherein the wing tip is moved away from the flight position such that the span of the wing is reduced; wherein the hinge axis is oriented at an angle to the fore-to-aft direction, such that an aft end of the hinge is outboard of a fore end of the hinge; and wherein the mean angle of incidence of the wing tip increases as the wing tip rotates about the hinge axis from the flight position to the ground position.
2. An aircraft wing according to claim 1, wherein the wing tip, when in the flight position, is prevented from rotating about the hinge axis in a direction that decreases the angle of incidence of the wing tip.
3. An aircraft wing according to claim I or 2, wherein the wing comprises a ratchet assembly, the ratchet assembly being configured to allow rotation of the wing tip from the flight position to the ground position, and prevent return movement of the wing tip towards the flight position.
4. An aircraft wing according to any preceding claim, comprising a restraining assembly operable between a restraining mode in which the wing tip is prevented from rotating about the hinge axis, and a releasing mode in which the restraining force on the wing tip is released.
5. An aircraft wing according to claim 4, wherein the restraining assembly comprises a lock and/or a latch engagable to prevent rotation of the wing tip.
-18 - 6. An aircraft wing according to any preceding claim, comprising one or more stops arranged to restrict the range of motion of the wing tip about the hinge axis.
7. An aircraft wing according to any preceding claim, comprising an aileron at least partially overlapping the hinge axis in a fore-to-aft direction.
An aircraft comprising a wing according to any preceding claim.
9. An aircraft according to claim 8, the aircraft comprising a control system, the control system being arranged to: determine whether the speed of the aircraft is below a threshold speed for initiating movement of the wing tip from the flight position to the ground position; when the speed has been determined to be below the threshold speed, allow the wing tip to rotate about the hinge axis towards the ground position.
10. A method of landing an aircraft, wherein the aircraft has a wing, the wing comprising a fixed wing and a wing tip mounted at an end of the fixed wing, the wing tip being arranged to rotate relative to the fixed wing about a hinge, having a hinge axis, between: (i) a flight position for use during flight, and (ii) a ground position for use during ground-based operations, wherein the wing tip is moved away from the flight position such that the span of the wing is reduced; wherein the hinge axis is oriented at an angle to the fore-to-aft direction, such that an aft end of the hinge is outboard of a fore end of the hinge; and wherein a rotation of the wing tip away from the flight position increases the mean angle of incidence of the wing tip; the method comprising the steps of: determining whether the speed of the aircraft is below a threshold speed for initiating movement of the wing tip from the flight position to the ground position; -19 -when the speed has been determined to be below the threshold speed, allowing the wing tip to rotate about the hinge axis towards the ground position, the wing tip rotating towards the ground configuration at least partly under the action of a net aerodynamic force urging the wing tip towards the ground position; and holding the wing tip in the ground position.
11. A method of landing an aircraft according to claim 10, wherein the step of allowing the wing tip to rotate about the hinge axis towards the ground position comprises configuring a restraining assembly, acting to restrain rotation of the wing tip about the hinge axis, into a releasing mode in which wing tip is allowed to rotate about the hinge axis.
12. A method of landing an aircraft according to claim 10 or 11, comprising a step of using an actuator to initiate movement of the wing tip towards the ground position by moving the wing tip away from the flight position to an intermediate position at which the net aerodynamic force is sufficient to urge the wing tip to the ground position without assistance of the actuator.
13. A method of landing an aircraft according to any of claims 10 to 12, further comprising a step of braking the wheels of a main landing gear before touching down of a nose landing gear.
14 An aircraft wing with a folding wing tip which is configured to rotate about an axis that flares outwards in a fore-to-aft direction.