GB2573105A - Apparatus, aircraft comprising an apparatus and method of performing a descent in an aircraft - Google Patents

Abstract

An apparatus 1000 is provided for controlling a movable wing tip device 9 of an aircraft 1, the apparatus comprising a processor 10, a controller (40, figure 3) and an actuator (50, figure 3). The controller 40 is coupled to the actuator 50 to move, or permit to move, the wing tip device 9 in response to receipt of instructions from the processor 10 from a flight configuration to a lift-reducing configuration. This permits the aircraft 1 to descend more effectively. An aircraft 1 comprising such an apparatus and a method of performing a descent in an aircraft 1 are also described.

Description

APPARATUS. AIRCRAFT COMPRISING AN APPARATUS AND METHOD OF PERFORMING A DESCENT IN AN AIRCRAFT

BACKGROUND OF THE INVENTION

[00011 The present disclosure relates to aircraft with moveable wing tip devices. [00021 The present invention concerns aircraft with a fixed wing portion and a movable wing tip device. More particularly, but not exclusively, this invention is an apparatus for controlling a movable wing tip device. The invention also concerns an aircraft comprising a fixed wing portion and a movable wing tip device and a method of performing a descent in an aircraft.

[00031 When performing a descent in an aircraft it is conventional to reduce lift, for example, by varying engine power and angle of attack (pitch) of the aircraft and sometimes by deploying control surfaces, such as spoilers. Spoilers are typically used when it is desired to descend rapidly, for example, during an emergency descent. Airworthiness requirements demand that an aircraft is able to make an emergency descent from its maximum altitude to 25,000 feet within two minutes following a rapid decompression of the fuselage. The use of spoilers reduces the lift to drag ratio enabling the aircraft to descend without increasing forward speed. Wing loads for high speed “air brakes out” conditions can be substantially higher than when no air brakes are deployed.

[0004] Aircraft with moveable wing tip devices attached to fixed wings are known to those skilled in the art. The wing tip devices are typically used to allow load alleviation during flight, for example, in the event of wind gusts. Typically, large loads cause the wing tip device to move from a flight configuration in which the wing tip device is effectively a continuation of the fixed wing portion to a load-alleviating configuration in which the load on the wing is reduced. An example of an arrangement having passive load alleviation by use of a moveable wing tip device is disclosed in WO2017118832.

[0005] The present invention seeks to provide an improved method of performing an aircraft descent and an apparatus and aircraft for controlling the same.

SUMMARY OF THE INVENTION

[00061 The present invention provides, according to a first aspect, an apparatus for controlling a movable wing tip device of an aircraft, the apparatus comprising: a processor configured: to receive a signal indicative of a descent in an aircraft and/or to receive a signal indicative of an impending descent; and to generate an instruction to move, or to permit to move, a wing tip device movably mounted to a fixed wing of the aircraft, in response to the receipt of said signal; a controller; and an actuator, the controller being communicatively coupled to the actuator to move, or permit to move, the wing tip device in response to receipt of the instruction from the processor from a flight configuration (for example in which the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing) to a lift-reducing configuration (for example in which the wing tip device is oriented relative to the fixed wing such that at least one of the upper and lower surface of the wing tip device is positioned away from the respective surface of the fixed wing), and the lift provided by the wing is reduced relative to the flight configuration.

[0007] Those skilled in the art will realise that the wing tip device, the fixed wing and the aircraft are not necessarily parts of the apparatus of the first aspect of the present invention.

[0008] The actuator may be coupled or coupleable to the wing tip device to move the wing tip device from the flight configuration to the lift-reducing configuration. The actuator may be operable to move the wing tip device from the lift-reducing configuration to the flight configuration. In some embodiments, the actuator may only be operable to move the wing tip device from the lift-reducing configuration to the flight configuration. For example, the wing tip device may be passively moveable from the flight configuration to the lift-reducing configuration.

[0009] The apparatus may comprise a restraining assembly operable between a restraining mode in which the wing tip device is held in the flight configuration using a restraining force, and a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device is able to adopt the lift-reducing configuration, the actuator being operable to control operation of the restraining assembly. The restraining assembly may comprise the actuator.

[0010] Once the restraining force on the wing tip device is released, the wing tip device is permitted to move according to the other forces applied to the wing tip device (e.g. aerodynamic forces resulting from flight). If the restraining force is removed, the wing tip device would typically move to the lift-reducing configuration, subject to other forces applied to the wing tip device as described below.

[0011] For example, the restraining assembly may comprise a brake, the operation of which is controlled by the actuator. The actuator will typically be used to release the brake on receipt of a suitable control signal, thereby removing the restraining force.

[0012] The apparatus may comprise a biasing member, arranged such that when the wing tip device is in the flight configuration, the biasing member exerts a biasing force to urge the wing tip device towards the lift-reducing configuration. Such an arrangement has been found to be beneficial because it tends to reduce the lag between the restraining assembly adopting the releasing mode, and the wing tip device actually moving to the lift-reducing configuration (the biasing force assisting the movement of the wing tip device into the lift-reducing configuration such that it is moved under the action of both the biasing force and aerodynamic forces). Having the restraining assembly in combination with this movable wing tip device may be referred to as a “semi-aeroelastic” arrangement).

[0013] Having the biasing member may be beneficial in reducing flutter (for example in increasing the speed at which flutter may occur).

[0014] When the restraining assembly is in the restraining mode, the biasing force is typically overcome by the restraining force. But, when the restraining assembly is in the releasing mode, the biasing force is typically sufficient to assist in moving the wing tip device into the lift-reducing configuration. In some embodiments, when the restraining assembly is in the releasing mode, the biasing force may be sufficient to move the wing tip device into the lift-reducing configuration. Such an arrangement provides reassurance that the wing tip device can move to the lift-reducing configuration, if needs be, even in the absence of aerodynamic forces acting on the wing tip device. Nevertheless, the wing tip device is more preferably arranged such that it may be moved from the flight configuration to the lift-reducing configuration, at least partially by aerodynamic forces acting on the wing tip device. The biasing member may be elastically-deformable. The biasing member may comprise an actuator for urging the wing tip device into the load-alleviating configuration.

[0015] The biasing member may be able to be selectively disengaged from exerting the biasing force on the wing tip device. For example, the wing may comprise a clutch for selectively disengaging the biasing member from exerting the biasing force on the wing tip device. Such an arrangement has been found to be beneficial because, it may enable the biasing member to be selectively disengaged to enable easier maintenance of the wing tip device.

[0016] The apparatus may comprise a damper arranged to damp movement of the wing tip device. Such an arrangement has been found to be beneficial, especially when the wing tip device is quickly moved to the lift-reducing configuration, as it tends to damp down transient, oscillatory, movements. A damper has also been found to be beneficial because it may mitigate aeroelastic instabilities such as flutter, and/or may limit cycle oscillations.

[0017] In other embodiments, the apparatus need not comprise any damper and/or biasing member. Indeed, in some embodiments the wing tip device may be entirely free to rotate when the restraining assembly is in the releasing mode (i.e. there may be substantially no other resistive forces acting to prevent rotation once the restraining force is removed). When the wing tip device is free to rotate in this manner, it may be referred to as ‘coasting’ or being arranged to ‘coast’. For some embodiments of the invention, having such an arrangement have been found to be especially beneficial. In such embodiments, the centre of gravity of the wing tip device may be positioned such that no substantive shear loads are passed into the wing tip and to ensure the flutter speed is sufficiently high.

[0018] The apparatus may comprise a latching arrangement for holding the wing tip device in the lift-reducing configuration. For example, the aircraft may comprise a ratchet and pawl configured to allow rotation of the wing tip device to the lift-reducing configuration, and to then hold it in that configuration unless or until it is to be reverted to the flight configuration. Such an arrangement may be especially beneficial in embodiments in which there is no biasing member and/or damper because it enables the wing tip device to be ‘caught’ in the lift-reducing configuration (for example, once it has moved under aeroelastic forces once the restraining assembly is in the releasing configuration). The latching arrangement may be controllable to latch and/or release the wing tip device.

[0019] The apparatus may comprise one or more sensors for detecting a descent and/or for detecting an impending descent, for example, by detection one or more conditions indicative of an impending descent. Such sensors may be operable to provide one or more signals indicative of a descent or for providing one or more signals indicative of an impending descent, for example, one or more signals indicative of a condition indicative of an impending descent to the processor.

[00201 The apparatus may comprise one or more sensors for determining whether the wing tip device is in the flight configuration or the lift-reducing configuration.

[00211 The processor may be configured to receive signals indicative of an emergency descent and/or to receive signals indicative of an impending emergency descent. A signal indicative of an impending emergency descent may comprise a signal related to one or more conditions indicative of the requirement for an emergency descent. For example, the apparatus may comprise an altitude sensor or an air pressure sensor configured to sense ambient air pressure external to the aircraft. The apparatus may comprise a sensor configured to sense air pressure in the fuselage. The detection of a fuselage pressure below a pre-determined level may be indicative of a requirement for an emergency descent. The apparatus may comprise one or more of a heat, flame or smoke detector.

[0022] The processor may be configured to transmit instructions to one or more control surface controllers e.g. controllers of one or more spoilers for effecting a descent.

[0023] The apparatus may comprise an actuator configured to move the wing tip device and/or an actuator configured to permit the wing tip device to move. In this connection, the apparatus may comprise an actuator which is configured to move the wing tip device from the flight configuration to the lift-reducing configuration by applying a force to the wing tip device, and/or another actuator which permits the wing tip device to move, for example, by removing a restraining force on the wing tip device.

[0024] In accordance with the second aspect of the present invention, there is provided an aircraft comprising an apparatus in accordance with the first aspect of the present invention. The aircraft comprises a movably mounted wing tip device which is moveable from a flight configuration to a lift-reducing configuration, the wing tip device being moveably mounted at the tip of a fixed wing of an aircraft, the fixed wing having an upper surface and a lower surface, and the wing tip device having an upper surface and a lower surface. In the flight 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 lift-reducing configuration the wing tip device may be oriented relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is positioned away from the respective surface of the fixed wing, and the lift provided by the wing is reduced relative to the flight configuration.

[00251 The apparatus of the first aspect of the present invention is used to control the movement of the wing tip device in the aircraft of the second aspect of the present invention.

[0026] The wing tip device may be rotatably mounted on a hinge at the tip of the wing, such that it may rotate, about the hinge, between the flight and lift-reducing configurations. In embodiments in which the wing tip device is also moveable to a ground configuration (a configuration to which the wing tip device may be moved when the aircraft is on the ground), the wing tip device is preferably so moveable about this same hinge.

[00271 The hinge is preferably orientated non-parallel to the line-of flight direction. The hinge is preferably orientated such that the hinge at the trailing edge of the wing is further inboard than the hinge at the leading edge of the wing. The hinge is preferably orientated such that in the lift-reducing configuration, the mean incidence of the wing tip device is reduced. The hinge is preferably 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. Such an arrangement has been found to be beneficial in terms of enabling a load reduction (in comparison with a hinge line that is orientated parallel to the line-of flight). Furthermore, such an orientation of hinge has been found to facilitate movement of the wing tip device to a stable lift-reducing configuration. For example, when the hinge is in such an orientation, the wing tip device tends to move to a static-aeroelastically stable position even under purely aerodynamic loading. This orientation of hinge is therefore especially beneficial in combination with the restraining assembly in embodiments of the invention. The orientation of the hinge may be chosen such that it acts to stabilise flutter.

[0028] The wing tip device may be rotatable, from the flight configuration to the lift-reducing configuration, in an upwards direction. The wing tip device may be rotatable, from the flight configuration to the lift-reducing configuration, in a downwards direction. The hinge may be a double hinge enabling both upwards or downward rotation. Providing such a double hinge has been found to be beneficial because it may enable loads from both upwards and downwards events (such as gusts) to be alleviated. Such an arrangement may also ensure the lift-reducing configuration does not inadvertently amplify loads, as might otherwise occur if the wing tip device is allowed to adopt this configuration in response to an event in the opposite direction to that intended.

[0029] The wing tip device may be 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.

[0030] In the flight 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 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 where 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 inner wing and wing tip device.

[0031] When the wing tip device is in the lift-reducing configuration, the aircraft incorporating the wing, is still suitable for flight, but the wing tip device is preferably moved to a position in which the lift provided by the wing is reduced. It will be appreciated that the lift-reducing configuration may encompass the wing tip device being in a range of positions (all of which reduce lift to some degree). The position (for example the magnitude of rotation about the hinge) may be dependent on the magnitude of lift-reduction that is sought. In the lift-reducing configuration the wing tip device remains attached to the fixed wing. The wing tip device may be repeatably moveable between the lift-reducing configuration and the flight configuration.

[0032] In embodiments in which the wing tip device is moveable to a ground configuration, the aircraft incorporating the wing, when the wing tip device is in the ground configuration, may be unsuitable for flight. For example, the wing tip device may be aerodynamically and/or structurally unsuitable for flight in the ground configuration. The aircraft is preferably configured such that, during flight, the wing tip device is not moveable to the ground configuration. The aircraft may comprise a sensor for sensing when the aircraft is in flight. When the sensor senses that the aircraft is in flight, a control system is preferably arranged to disable the possibility of moving the wing tip device to the ground configuration. In the ground configuration, the wing tip device may be rotated about the hinge by an angle greater than the maximum angle about which it is rotated in the load alleviating configuration. In the ground configuration the wing tip device remains attached to the wing. In embodiments of the present invention, in which the wing tip device is configurable between: (a) a flight configuration for use during flight and (b) a ground configuration for use during ground-based operations, in which ground configuration the wing tip device is moved away from the flight configuration such that the span of the aircraft wing is reduced. In the flight configuration, the span may exceed an airport compatibility limit. In the ground configuration the span may be reduced such that the span (with the wing tip device in the ground configuration) is less than, or substantially equal to, the airport compatibility limit. The airport compatibility limit is a span limit (for example relating to clearance restrictions for buildings, signs, other aircraft). The compatibility limit is preferably a gate limit.

[00331 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.

[0034] Those skilled in the art will realise that typically the aircraft will be provided with a moveable wing tip at the end of each fixed wing portion.

[0035] The wingspan of the aircraft with the wing tip in the flight configuration is optionally no less than 52m and optionally greater than 65m. The wingspan of the aircraft with the wing tip in the lift-reducing or ground configuration is optionally no less than 52m and no more than 65m. The length of the wing tip device (measured along the longitudinal axis of the fixed wing portion) is optionally at least 1,0m, optionally at least 1.5m, optionally at least 2.0m, optionally at least 2.5m and optionally at least 3.0m. The length of the wing tip device is optionally no more than 5.0m, optionally no more than 4.5m, optionally no more than 4.0m, optionally no more than 3.5m, optionally no more than 3.0m and optionally no more than 2.5m. The span ratio of the fixed wing relative to the wing tip device may be such that the fixed wing comprises 70%, 80%, 90%, or more, of the overall span of the aircraft wing.

[0036] The aircraft may optionally comprise one or more control surfaces deployable to change aircraft lift. For example, the aircraft may comprise one or more spoilers.

The movement of the one or more control surfaces into a lift-reducing configuration may be controlled by the processor. The one or more control surfaces may be deployed into a lift-reducing configuration so that both the wing tip device and the one or more control surfaces are in a lift-reducing configuration at the same time.

[0037] In accordance with a third aspect of the present invention, there is provided a method of performing a descent in an aircraft comprising a movably mounted wing tip device which is moveable from a flight configuration to a lift-reducing configuration during flight, the wing tip device being moveably mounted at the tip of a fixed wing of an aircraft, the fixed wing having an upper surface and a lower surface, and the wing tip device having an upper surface and a lower surface. In the flight configuration the upper and lower surfaces of the wing tip device may be are continuations of the upper and lower surfaces of the fixed wing. In the lift-reducing configuration the wing tip device may be oriented relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is positioned away from the respective surface of the fixed wing, and the lift provided by the wing is reduced relative to the flight configuration. The method may comprise moving, or permitting movement of, the wing tip device from the flight configuration to the lift-reducing configuration during or immediately before a descent.

[0038] The moving, or permitting movement of, the wing tip device may be manually-activated, for example, in response to an input provided by a person, typically a flight operative, such as a pilot or co-pilot.

[0039] The moving, or permitting movement of, the wing tip device may be automatic. For example, the moving, or permitting movement, of the wing tip device may be in response to a signal indicative of a descent and/or a signal indicative of an impending descent, for example, a signal indicative of one or more conditions indicative of the requirement for a descent.

[0040] The method may comprise moving, or permitting movement of, the wing tip device from the flight configuration to the lift-reducing configuration during or immediately before an emergency descent.

[0041] The movement, or permitting movement, of the wing tip device, may be in response to a signal indicative of an emergency descent and/or in response to a signal indicative of an impending emergency descent, for example, a signal indicative of one or more conditions indicative of a requirement for an emergency descent. The one or more conditions indicative of a requirement for an emergency descent may, for example, comprise one or more of fuselage decompression or fire.

[0042] A signal indicative of an emergency descent may comprise a signal indicative of a rate of descent above a predetermined value.

[00431 Permitting movement of the wing tip device optionally comprises removing a restraining force from the wing tip device, the restraining force inhibiting movement of the wing tip device from the flight configuration to the lift-reducing configuration. The restraining force may be provided by a restraining assembly, such as that described above in relation to the apparatus of the first aspect of the present invention. [00441 A biasing member may be provided to exert a biasing force to urge the wing tip device towards the lift-reducing configuration. A clutch may be provided to selectively disengage the biasing member from exerting the biasing force. A damper may be provided to damp movement of the wing tip device.

[0045] The method may comprise latching the wing tip device once in the lift-reducing configuration. The method may also comprise unlatching the wing tip device to facilitate movement of the wing tip device from the lift-reducing configuration to the flight configuration.

[0046] A processor may be provided, the processor being configured: to receive a signal indicative of a descent in an aircraft, a signal indicative of an impending descent and/or a signal indicative of an impending descent; and to generate an instruction to move, or to permit to move, a wing tip device movably mounted to a fixed wing of the aircraft, in response to the receipt of said signal.

[0047] A controller and an actuator may be provided, the controller being communicatively coupled to the actuator to move, or permit to move, the wing tip device in response to receipt of the instruction from the processor [0048] The method may comprise moving the wing tip device from the lift-reducing configuration to the flight configuration subsequent to moving, or permitting movement of, the wing tip device from the flight configuration to the lift-reducing configuration. For example, the wing tip device may be moved back into the flight configuration once the descent has been completed, or once a significant proportion of the descent has been completed. An actuator may be used to move the wing tip device back to the flight configuration. Moving the wing tip device back into the flight configuration may be instigated automatically (for example, in response to a certain control condition associated with completion or near-completion of the descent e.g. attaining a pre-determined altitude or retraction of spoilers) or may be instigated by a signal provided manually, for example, by a crew member.

[00491 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 third aspect of the present invention may incorporate any of the features described with reference to the apparatus of the first aspect of the present invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[00501 Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0051] Figure la shows a plan view of an aircraft according to a first embodiment of the invention comprising an apparatus according to a further embodiment of the invention; [0052] Figure lb shows a close-up view of the tip of the wing of the aircraft in Figure la; [0053] Figure 2a shows a front view of the aircraft of Figure la with the wing tip device a flight configuration, a lift-reducing configuration and a ground configuration; [0054] Figures 2b-d show a plan view of the aircraft of Figure 2a with the wing tip device in respective close-up views [0055] Figure 3 shows a close-up of the tip of the wing of the aircraft of Figure la, together with the restraining assembly; [0056] Figure 4 shows a method of performing a descent in an aircraft in accordance with an embodiment of the present invention; [0057] Figure 5 shows a method of performing a descent in an aircraft in accordance with another embodiment of the present invention; [0058] Figure 6 is a graph showing lift distribution across the wing of the aircraft of Fig. la during lg flight (i) with the wing tip device in the flight configuration and spoilers not deployed, (ii) with the spoilers deployed and the wing tip device in the flight configuration and (iii) with the spoilers deployed and the wing tip device in the lift-reducing configuration.

DETAILED DESCRIPTION

[0059] Figure la is a plan view of an aircraft 1 according to a first embodiment of the invention. The aircraft comprises a central fuselage 3 and two main wings 5 extending outwardly from respective wing roots 5’.

[0060] Each wing 5 comprises a fixed wing 7 extending from the root 5’ to the tip 7’ (shown in close up in Figure lb). At the tip 7’ of the fixed wing 7, the wing 5 also comprises a moveable wing tip device 9, in the form of a planar wing tip extension. The wing tip device 9 is rotatable mounted about a hinge 11 that is orientated perpendicular to the swept mid-chord axis 13. This hinge 11, is thus non-parallel to the line of flight direction (the line of flight direction being shown in Figure lb for comparison).

[0061] Referring now to Figures 2a to 2d, the wing tip device 9 is rotatable about the hinge 11 from a flight configuration to a lift-reducing configuration, to a ground configuration.

[0062] In the flight configuration, the wing tip device 9 is an extension of the fixed wing. Accordingly the upper 7u and lower 71 surfaces of the fixed wing 7 are continuous with the upper 9u and lower 91 surfaces of the wing tip device 9 (see Figure 2b and the lowermost position in Figure 2a). The leading 71e and trailing 7t edges of the fixed wing 7 are also continuous with the respective leading 91e and trailing 9t edges of the wing tip device 9 (see Figure la and lb). Such an arrangement is beneficial as it provides a relatively large wing span, thereby providing an aerodynamically efficient aircraft. However a large span can result in correspondingly large loads on the wing 5, particularly a large wing root bending moment, especially during high load events such a gusts or extreme manoeuvres. The wing 5 must be sized to cope with these maximum loads, which can result in a relatively heavy wing. The ability of the wing tip device 9 to move to the load alleviating configuration (see Figures 2a and 2c) seeks to address that problem.

[0063] As shown in Figure 2c and the middle position in Figure 2a, the wing tip device 9 is rotatable, upwards, such that the lower surfaces 71, 91 between the fixed wing 7 and the wing tip device 9, are no longer continuous with one another. Furthermore, since the hinge 11 is angled with respect to the airstream-wise direction, when the wing tip device 9 rotates upwardly its mean incidence is reduced. In this configuration the lift generated by the wing 5 is significantly reduced. The wing tip device 9 is moveable to this configuration during flight (described in more detail below). By providing this lift-reducing function during flight, the descending properties of the aircraft may be improved, as will be described below.

[00641 The wing tip device 9 is also configurable to a ground configuration in which the wing tip device 9 is rotated yet further, to a substantially upright position (shown in Figures 2a and 2d). The wing tip device is moveable to this configuration when it is on the ground (described in more detail below). Once rotated to such a position, the span of the aircraft 1 is sufficient to meet airport compatibility gate limits. Thus, the aircraft 1 of the first embodiment can have a large span (exceeding gate limits) during flight, but is still able to comply with gate limits when on the ground.

[00651 Load alleviation using moveable wing tip devices is known per se. Providing moveable wing tip device to meet airport compatibility gate limits is also known per se. The first embodiment of the invention relates to the control of the moveable wing tip to facilitate better descending characteristics of the aircraft.

[0066] Referring to Figures la and 3, the aircraft 1 comprises an apparatus 1000 for controlling the wing tip device 9. The apparatus 1000 comprises a processor 10 configured to receive a signal indicative of a descent in the aircraft 1 and/or to receive a signal indicative of an impending descent; and to generate an instruction to move, or to permit to move, wing tip device 9 in response to the receipt of said signal. The apparatus 1000 also comprises a controller 40 and an actuator 50, the controller 40 being communicatively coupled to the actuator 50 to permit the wing tip device 9 to move in response to receipt of the instruction from the processor 10. The signal is, in this case, provided by altitude sensor 12.

[0067] The actuator 50 forms part of a restraining assembly 17 which is operable between a restraining configuration in which the wing tip device 9 is in the flight configuration and in which the wing tip device 9 is restrained from moving from the flight configuration, and a releasing configuration in which the restraining force on the wing tip device 9 has been removed and the wing tip device 9 is free to move, subject to other forces on the wing tip device 9 as described below.

[0068] The restraining assembly 17 also comprises a brake 19, a clutch 21, a rotational spring 23 and a rotational damper 25. The actuator 50 is coupled to the brake 19, and controls operation of the brake 19.

[0069] The brake 19 comprises two pads configured to selectively clamp against the shaft 18 to restrain its rotation. As mentioned above, the restraining assembly 17 is operable between a restraining mode (in which the brake 19 is deployed to brake the rotation of the shaft 18), and a releasing mode (in which the brake 19 is released by pulling the pads away from the shaft 18 to allow its free rotation (and thus the rotation of the wing tip device 9)).

[00701 The default (passive) mode of the restraining assembly 17 is the restraining mode in which the shaft 18 is braked. When the wing tip device 9 is in the flight configuration, the power to the restraining assembly 17 is switched OFF (i.e. the assembly is passive) and the restraining assembly 17 is left with the shaft 18 braked. Such an arrangement is attractive as it ensures an active command (e.g. an ON signal) is required to move the wing tip device). When power is supplied to the restraining assembly 17 via control 40, the control 40 activates the actuator 50 which releases brake 19.

[0071] In the present embodiment, sensor 12 is configured to sense the altitude of the aircraft 1. In the event of a descent, the altitude sensed by sensor 12 will decrease. The processor 10 is configured to receive signals from the sensor 12. The signals received by processor 10 from sensor 12 are indicative of a descent, because altitude is decreasing. The processor 10 is configured to generate an instruction which is sent to controller 40 which transmits a signal to actuator 50 to release brake 19, thereby releasing the restraining assembly from the restraining mode, permitting movement of the wing tip device 9.

[0072] The wing tip device 9 may, at least partially, be moveable to the lift-reducing configuration purely under the action of aerodynamic force acting on it during flight. However, in the first embodiment of the invention, the restraining assembly comprises a rotational spring 23 and damper 25 arrangement to assist this movement. The rotational spring 23 and damper 25 are located at one end of the hinge 11. The rotational spring 23 is preloaded such that when the wing tip device 9 is in the flight configuration, it exerts a biasing force that urges the wing tip device 9 towards the lift-reducing configuration. That biasing force is unable to overcome the restraining force exerted by the brake 19 when it is deployed. However, when the brake 19 is released, the biasing force (in addition to aerodynamic forces acting on the wing tip device) acts to rotate the wing tip device 9 about the hinge 11. The rotational spring 23 is sized such that it rotates the wing tip device 9 by around 30 degrees of rotation (shown in Figure 2c), but once the wing tip device 9 has rotated that far, the spring 23 is fully unwound and does not urge any further rotation. Providing a pre-loaded spring 23 in this manner has been found to be beneficial as it quickly moves the wing tip device 9 to the load alleviated configuration, as soon as the brake 19 has been released.

[00731 The damper 25 is configured to damp movement of the wing tip device 9 as it rotates under the action of the spring 23 (and any aerodynamic forces). Such an arrangement has been found to be beneficial, especially when the wing tip device 9 is quickly moved to the lift-reducing configuration, as it tends to damp down transient, oscillatory, movements. The spring damper may also assist in reducing or eliminating flutter and/or load cycle oscillations.

[00741 The restraining assembly also comprises a clutch 21 located on the hinge 11. The clutch 21 serves to selectively engage/disengage opposing ends of the hinge, such that the spring 23 can be selectively chosen to exert the biasing force on the wing tip device 9. Such an arrangement has been found to be beneficial because it may enable the spring 23 to be selectively disengaged to enable easier maintenance of the wing tip device 9.

[0075] The aircraft 1000 also comprises a motor 15 connected to a drive shaft 18 that forms the shaft of the hinge 11. The wing tip device 9 is connected to the shaft 18 by a connecting piece 20. The motor 15 is arranged to rotate the wing tip device 9 between the flight configuration (see Figure 2b) and the ground configuration (see Figure 2d) by actuation of the motor 15. This typically occurs shortly after landing to enable the aircraft to comply with airport gate limits. This movement also happens in reverse before take-off, once the aircraft has cleared the gate.

[0076] When the aircraft is flying and the wing tip device is in the flight configuration, there tends to be a significant force on the wing tip (typically upwards). It has been recognised that using the motor 15 to actively hold down the wing tip device in the flight configuration, by applying a reverse torque, is undesirable; if using such an approach it would typically be necessary to also provide locks to permanently lock the wing tip device in that flight position during flight.

[0077] In the first embodiment, the motor 15 does not provide a reverse torque.

Instead it is in a passive state such that it does not actively contribute to restraining the wing tip device 9 in the flight configuration, the apparatus 1000 instead being provided with the restraining assembly 17.

[0078] When the wing tip device has been moved to the lift-reducing configuration, the motor 15 may, however, be activated such that it rotates the wing tip device 9 back to the flight configuration and re-compresses the spring 23. This would typically occur on completion of the descent or close to the completion of the descent, typically as indicated by the altitude sensor 12. Once back in the flight configuration, the restraining assembly 17 is switched back into restraining mode such that the brake 19 is applied, and the motor 15 is again returned to its passive state. Thus the motor 15 can be used not only to move the wing tip device between the flight and ground configurations, but also from the load alleviating configuration to the flight configuration (albeit not from the flight configuration to the load alleviating configuration).

[0079] Those skilled in the art will realise that the processor 10 will be configured to differentiate between a descent for which movement of the wing tip device 9 is desired (typically a prolonged descent) and a descent for which movement of the wing tip device 9 is not desired (typically a descent of short duration, such as that associated with turbulence).

[0080] A further method 100 of performing a descent will now be described with reference to Figs. 1A, 3 and 4. Processor 10 receives 101 a signal from a sensor which indicates that the aircraft is descending. Processor 10 transmits a signal to controller 40 which activates actuator 50, causing brake 19 to be released, thereby permitting 102 movement of the wing tip device 9 to the lift-reducing position. Once in the lift-reducing position, the wing tip device is latched 103, thereby securing the wing tip device 9 in the lift-reducing position. The wing tip device 9 is then unlatched 104 in response to a signal indicative that the descent has been completed. Motor 15 is then used to move 105 the wing tip device to the flight configuration. Once in the flight configuration, the brake 19 is re-engaged, ensuring that the wing tip device is in a restrained 106 configuration.

[0081] Another method 200 of performing a descent, in this case, an emergency descent, will now be described with reference to Figs. 1 A, 3 and 4. Processor 10 receives 201 a signal from a sensor which indicates that the aircraft is undergoing an emergency descent. Processor 10 transmits a signal to controller 40 which activates actuator 50, causing brake 19 to be released, thereby permitting 202 movement of the wing tip device 9 to the lift-reducing position. Once in the lift-reducing position, the wing tip device is latched 203, thereby securing the wing tip device 9 in the lift- reducing position. The wing tip device 9 is then unlatched 204 in response to a signal indicative that the descent has been completed. Motor 15 is then used to move 205 the wing tip device to the flight configuration. Once in the flight configuration, the brake 19 is re-engaged, ensuring that the wing tip device is in a restrained 206 configuration.

[0082] The advantages of the present invention with respect to wing lift, will now be explained with reference to Figure 6.

[0083] Figure 6 is a graph showing lift distribution across the wing of the aircraft of Fig. la during lg flight (i) with the wing tip device in the flight configuration and spoilers not deployed, (ii) with the spoilers deployed and the wing tip device in the flight configuration and (iii) with the spoilers deployed and the wing tip device in the lift-reducing configuration.

[0084] It is clear from plots (i) and (ii) of Figure 6 that the wing tip device generates considerable amounts of lift when the wing tip device is in the flight configuration, irrespective of whether or not the spoilers are deployed. Line (iii) shows that when the wing tip device is in the lift reducing configuration, then the wing tip device generates very little lift. This reduced lift at the wing tip facilitates the method of the present invention.

[0085] 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.

[0086] Whilst the examples above use the retraining assembly described in WO2017/118832, those skilled in the art will realise that this is not necessary.

[0087] The examples above describe how movement of the wing tip device can be controlled based on signals indicative that a descent has started. It is, of course, entirely possible to control movement of the wing tip device based on signals indicative that a descent is im8minent. For example, a signal may be generated in response to an aircraft condition which is indicative that a descent is imminent, for example, a decrease in aircraft attack angle or deployment of aircraft control surfaces which are typically used in descents, such as spoilers. In the case of an emergency descent, it may be possible to control movement of the wing tip device based on a signal indicative of a condition indicative of the requirement for an emergency descent (for example, a signal indicative of reduced cabin pressure or a signal indicative of a fire).

[00881 The examples above describe how the wing tip device may be permitted to move (for example, under the influence of aerodynamic loading) from the flight configuration to the lift-reducing configuration. The apparatus and aircraft of the present invention may comprise an actuator configured to move the wing tip device by providing a movement force which moves the wing tip device from the flight configuration to the lift-reducing configuration. Indeed, the apparatus and actuator may comprise an actuator for providing a movement force for moving the wing tip device, in addition to an actuator for releasing the wing tip device from a restraining configuration.

[00891 The examples above relate to twin engine aircraft. Those skilled in the art will realise that the present invention may be used on other aircraft, such as four engine aircraft.

[0090] The examples above relate to relatively large aircraft, for example, those having a wing span of about 50-70 metres. Those skilled in the art will recognise that the present invention may be used on other aircraft.

[0091] The examples above demonstrates an emergency descent triggered by rapid decompression of the fuselage. While this is the most common reason for making an emergency descent, other conditions indicative of the need for an emergency descent may trigger an emergency descent (such as a fire).

[0092] 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.

[0093] The term ‘or’ shall be interpreted as ‘and/or’ unless the context requires otherwise.

Claims (17)

1. An apparatus for controlling a movable wing tip device of an aircraft, the apparatus comprising: a processor configured: to receive a signal indicative of a descent in an aircraft and/or to receive a signal indicative of an impending descent; and to generate an instruction to move, or to permit to move, a wing tip device movably mounted to a fixed wing of the aircraft, in response to the receipt of said signal; a controller; and an actuator, the controller being communicatively coupled to the actuator to move, or permit to move, the wing tip device in response to receipt of the instruction from the processor from a flight configuration in which the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing to a lift-reducing configuration in which the wing tip device is oriented relative to the fixed wing such that at least one of the upper and lower surface of the wing tip device is positioned away from the respective surface of the fixed wing, and the lift provided by the wing is reduced relative to the flight configuration.

2. An apparatus according to claim 1 wherein the actuator is coupled or coupleable to the wing tip device to move the wing tip device from the flight configuration to the lift-reducing configuration, the actuator being operable to move the wing tip device from the lift-reducing configuration to the flight configuration.

3. An apparatus according to claim 1 or claim 2 comprising a restraining assembly operable between a restraining mode in which the wing tip device is held in the flight configuration using a restraining force, and a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device is able to adopt the lift-reducing configuration, the actuator being operable to control operation of the restraining assembly. The restraining assembly may comprise the actuator

4. An apparatus according to claim 3 when dependent on claim 2, wherein the restraining assembly comprises a brake, the operation of which is controlled by the actuator.

5. An apparatus according to any preceding claim comprising a biasing member, arranged such that when the wing tip device is in the flight configuration, the biasing member exerts a biasing force to urge the wing tip device towards the lift-reducing configuration.

6. An apparatus according to any preceding claim comprising a damper arranged to damp movement of the wing tip device.

7. An apparatus according to any preceding claim comprising a latching arrangement for holding the wing tip device in the lift-reducing configuration.

8. An apparatus according to any preceding claim comprising one or more sensors for detecting a descent and/or for detecting an impending descent.

9. An apparatus according to any preceding claim comprising one or more sensors for determining whether the wing tip device is in the flight configuration or the lift-reducing configuration.

10. An apparatus according to any preceding claim wherein the processor is configured to receive signals indicative of an emergency descent and/or to receive signals indicative of an impending emergency descent.

11. An apparatus according to any preceding claim wherein the processor is configured to transmit instructions to one or more control surface controllers.

12. An aircraft comprising an apparatus according to any preceding claim, the aircraft comprising a movably mounted wing tip device which is moveable from a flight configuration to a lift-reducing configuration, the wing tip device being moveably mounted at the tip of a fixed wing of an aircraft, the fixed wing having an upper surface and a lower surface, and the wing tip device having an upper surface and a lower surface, wherein in the flight configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and in the lift-reducing configuration the wing tip device is oriented relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is positioned away from the respective surface of the fixed wing, and the lift provided by the wing is reduced relative to the flight configuration.

13. A method of performing a descent in an aircraft comprising a movably mounted wing tip device which is moveable from a flight configuration to a lift-reducing configuration during flight, the wing tip device being moveably mounted at the tip of a fixed wing of an aircraft, the fixed wing having an upper surface and a lower surface, and the wing tip device having an upper surface and a lower surface, wherein in the flight configuration the upper and lower surfaces of the wing tip device are continuations of the upper and lower surfaces of the fixed wing; and in the lift-reducing configuration the wing tip device is oriented relative to the fixed wing such that at least one of the upper and lower surfaces of the wing tip device is positioned away from the respective surface of the fixed wing, and the lift provided by the wing is reduced relative to the flight configuration, the method comprising moving, or permitting movement of, the wing tip device from the flight configuration to the lift-reducing configuration during or immediately before a descent.

14. A method according to claim 13 in which the moving, or permitting movement of, the wing tip device is manually-activated.

15. A method according to claim 13 in which the moving, or permitting movement of, the wing tip device is automatic.

16. A method according to any of claims 13 to 15 in which the moving, or permitting movement, of the wing tip device is in response to a signal indicative of a descent and/or a signal indicative of an impending descent.

17. A method according to any of claims 14 to 16 in which the method comprises permitting movement of the wing tip device, and permitting movement of the wing tip device comprises removing a restraining force from the wing tip device, the restraining force inhibiting movement of the wing tip device from the flight configuration to the lift-reducing configuration.

18 . A method according to any of claims 13 to 17 comprising moving the wing tip device from the lift-reducing configuration to the flight configuration subsequent to moving, or permitting movement of, the wing tip device from the flight configuration to the lift-reducing configuration.