Aircraft wing and method of operating aircraft wing

Abstract

The invention relates to an aircraft wing and a method of operating an aircraft wing. The invention relates to an aircraft wing comprising: a fixed wing having a tip; a wing tip device rotatably mounted on a hinge at the tip of the fixed wing such that the wing tip device is rotatable about the hinge; and an actuation system for rotating the wing tip device about the hinge wherein the actuation system comprises a motor, at least one geared rotary actuator, a reduction gearbox, a clutch for selectively disconnecting rotation of the motor from rotation of the geared rotary actuator, the geared rotary actuator is drivable by the motor and is arranged to convert a rotary motion into a different rotary motion and to rotate the wing tip device relative to the tip of the fixed wing, a reduction gearbox is disposed between the clutch and the geared rotary actuator along a driveline between the motor and the geared rotary actuator.

Description

Technical Field

[0001] The present invention relates to an aircraft wing having a movable wingtip arrangement. Background Art

[0002] It is known, for example, from WO2017118832 to use movable wingtip devices during flight. The document teaches an aircraft wing having a fixed wing with a wingtip device movably mounted at its tip, wherein the fixed wing has an upper surface and a lower surface, and the wingtip device has an upper surface and a lower surface, and the wingtip device is capable of operating between: (i) a flight configuration for use during flight, in which the upper and lower surfaces of the wingtip device are a continuation of the upper and lower surfaces of the fixed wing; and (ii) a load-relieved configuration for reducing loads during flight, in which the wingtip device moves relative to the fixed wing so that at least one of the upper and lower surfaces of the wingtip device moves away from the corresponding surface of the fixed wing and the load on the wing is reduced; wherein the aircraft includes a restraint assembly capable of operating between a restraint mode and a release mode, in which the restraint force is used to hold the wingtip device in the flight configuration, and in which the restraint force on the wingtip device is released so that the wingtip device can adopt the load-relieved configuration.

[0003] Once the restraint assembly is in the release mode, the wing tip device can be actuated completely passively to the load-relieved configuration. The wing tip device can move under the action of aerodynamic forces urging the wing tip device toward the load-relieved configuration. Combining the restraint assembly with the articulated wing tip device can be referred to as a "semi-aeroelastic" arrangement.

[0004] The wingtip device may be rotatably mounted on a hinge at the tip of the wing so that it can rotate about the hinge between a flight configuration and a load-reduced configuration. The wingtip device is also movable about the same hinge to a ground configuration for use during ground-based operations, in which the wingtip device is moved away from the flight configuration so that the span of the aircraft wing is reduced.

[0005] The actuation system may be arranged to move the wing tip device between the flight configuration and the ground configuration. The actuation mechanism may also be arranged to move the wing tip device from the load-relieved configuration back to the flight configuration.

[0006] It has been found that when in a load-relieved condition, it may be necessary to adjust the movement of the wing tip arrangement. The present invention seeks to address this problem. Summary of the invention

[0007] A first aspect of the present invention is to provide an aircraft wing, the aircraft wing comprising: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing so that the wingtip device can rotate about the hinge; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises a motor, at least one gear-driven rotary actuator, a reduction gearbox, and a clutch for selectively decoupling the rotation of the motor from the rotation of the gear-driven rotary actuator. The gear-driven rotary actuator can be driven by the motor, is arranged to convert a rotary motion into a different rotary motion, and is arranged to rotate the wingtip device relative to the tip of the fixed wing. The reduction gearbox is arranged between the clutch and the gear-driven rotary actuator along the transmission system between the motor and the gear-driven rotary actuator.

[0008] Compared to positioning the clutch adjacent to the geared rotary actuator, arranging the reduction gearbox between the clutch and the geared rotary actuator introduces an increased drag torque (also known as load torque or braking torque) when the clutch is disengaged. This provides passive damping of the movement of the wingtip device relative to the fixed wing about the hinge. Passive damping can achieve flutter margin. Flutter margin is the airspeed margin between the onset of flutter of the aeroelastic part of the aircraft and 115% of the dive speed of the aircraft. Gust response is the reaction of the wingtip device to reduce loads in response to gusts. In this case, the reaction force is the rotation rate of the wingtip device about the hinge to reduce the lift of the wingtip device. The inventors have surprisingly found that even when the reduction gearbox is arranged between the clutch and the geared rotary actuator, good load relief can still be achieved, which increases the passive damping of the actuation system to increase flutter margin without transmitting too much bending load on the hinge.

[0009] The reduction gearbox is back-drivable when the clutch is disengaged to decouple the rotation of the motor from the rotation of the geared rotary actuator when the wing tip device rotates about the hinge. Providing a reduction gearbox that is back-drivable when the clutch is disengaged ensures that the wing tip device can rotate relative to the fixed wing when the clutch is disengaged.

[0010] The gearbox may have a maximum damping value that allows oscillatory flapping motion of the wing tip device rotating about the hinge during normal operation when the clutch is disengaged. The maximum damping value may be selected to prevent the angular velocity of the oscillatory flapping motion of the wing tip device about the hinge from exceeding a threshold value.

[0011] The rotating portion of the clutch may have a speed of no more than about 30,000 rpm when disengaged.

[0012] An aircraft wing may include a plurality of geared rotary actuators arranged along the hinge line of a hinge. Providing a plurality of geared rotary actuators rather than a single geared rotary actuator may allow the diameter of each geared rotary actuator to be made smaller, thereby reducing the effect of the hinge joint on the aerodynamic performance of the aircraft.

[0013] The clutch may have an outer diameter that is substantially the same as the outer diameter of each of the geared rotary actuators. Providing a clutch having an outer diameter that is substantially the same as the outer diameter of each of the geared rotary actuators may allow the clutch and the geared rotary actuators to be arranged along a common axis of an articulated joint having a relatively constant outer diameter, thereby reducing the effect of the articulated joint on the aerodynamic performance of the aircraft.

[0014] The actuation system may also include a brake for preventing movement of the geared rotary actuator when the clutch is engaged. The brake may be used to lock the wing tip device in place relative to the fixed wing, for example during takeoff or when loading the wing tip device on the ground. This may prevent undesired rotation of the wing tip device about the hinge due to external loads.

[0015] The actuation system is capable of operating in the following modes: i) a drive mode in which the clutch is engaged and the motor is driven to rotate the wingtip device about the hinge; ii) a flapping mode in which the clutch is disengaged and the wingtip device can be rotated about the hinge by a force external to the wingtip device; and iii) a braking mode in which the clutch is engaged and the brake prevents rotation of the wingtip device about the hinge. The actuation system can be controlled during flight to change between any of the three operating modes, so that different modes can be selected depending on flight conditions and / or requirements.

[0016] The braking mode may correspond to a zero angle or non-zero angle position of the wing tip device about the hinge, wherein the upper and lower surfaces of the wing tip device form a substantially zero angle or non-zero angle with the upper and lower surfaces of the fixed wing. This mode may be used to lock the wing tip device so that the total span of the fixed wing and the wing tip device is maximized. This condition may help to generate maximum lift, for example, during takeoff.

[0017] The actuation system can also be operated in a target mode in which the clutch is engaged, the brake is disengaged, and the motor actively targets a non-zero angular position of the wingtip device around the hinge, at which the upper and lower surfaces of the wingtip device form a non-zero angle with the upper and lower surfaces of the fixed wing. A closed-loop control system can be used to feedback the angular position of the wingtip device and control the motor based on the feedback. When the brake is not engaged, the system can be used to target a constant zero or non-zero angular position of the wingtip device. For example, operating the wing in a target mode can avoid flutter problems that the wingtip device may suffer from if the brake is applied under those same operating conditions because the motor and drive train increase the damping of the system.

[0018] The geared rotary actuator may have a first knuckle fixed to the fixed wing and a second knuckle fixed to the wingtip device. The first knuckle and the second knuckle may be driven by the geared rotary actuator to rotate relative to each other using a motive force provided by a motor. A system consisting of the first knuckle and the second knuckle may provide a compact system for converting a rotary motion from a motor into a different rotary motion of the wingtip around the fixed wing.

[0019] The clutch may be configured to disengage during flight for a) load relief, or b) when the aircraft is flying at a relatively low speed or altitude and a relatively high roll rate is required. Disengaging the clutch may allow the wing tip device to rotate about the hinge joint in response to external forces under these conditions, thereby reducing the effect of loads on bending and / or twisting the wing.

[0020] The aircraft wing may also include a second reduction gearbox, which is arranged between the clutch and the motor along the transmission system between the motor and the geared rotary actuator. This arrangement may allow the torque from the motor to increase in two stages, i.e., first by the second gearbox in front of the clutch and secondly by the gearbox positioned between the clutch and the geared rotary actuator. This may allow the reduction ratio of the gearbox to be selected based on the desired damping characteristics of the articulated joint when driving in reverse, while still providing enough torque to drive the wingtip device. It may also allow the outer diameter of both the gearbox and the second gearbox to be smaller than the outer diameter of the case of using a single gearbox to provide the same total transmission ratio. Compared with a single gearbox with the same total transmission ratio arranged between the motor and the clutch, the clutch may also be made smaller and lighter due to the lower torque through the clutch.

[0021] Another aspect of the invention provides a method of operating an aircraft wing, the aircraft wing having: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises: a motor; at least one geared rotary actuator arranged to convert a rotary motion into a different rotary motion; a reduction gearbox; a clutch for selectively decoupling the rotation of the motor from the rotation of the geared rotary actuator; and a brake for preventing movement of the geared rotary actuator when the clutch is engaged, wherein the reduction gearbox is disposed between the clutch and the geared rotary actuator along a drive train between the motor and the geared rotary actuator, the method comprising operating the actuation system in the following modes:

[0022] i) a drive mode, in which the clutch is engaged and the motor is used to drive the geared rotary actuator to rotate the wing tip device about the hinge;

[0023] ii) A flapping mode in which the clutch is disengaged and the gearbox is reverse driven as the wing tip device rotates about the hinge due to forces external to the wing tip device.

[0024] Another aspect of the invention provides a method of operating an aircraft wing having: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises: a motor; at least one geared rotary actuator arranged to convert a rotary motion into a different rotary motion; a clutch for selectively decoupling the rotation of the motor from the rotation of the geared rotary actuator; and a brake for preventing movement of the geared rotary actuator when the clutch is engaged, the method comprising operating the actuation system in the following modes:

[0025] 1) a drive mode, in which the clutch is engaged and the motor is used to drive the geared rotary actuator to rotate the wing tip device about the hinge;

[0026] 2) a flapping mode, in which the clutch is disengaged to allow the wing tip device to rotate about the hinge due to forces external to the wing tip device;

[0027] 3) a braking mode corresponding to a zero or non-zero angle position of the wing tip device about the hinge, in which the upper and lower surfaces of the wing tip device form a substantially zero or non-zero angle with the upper and lower surfaces of the fixed wing; and

[0028] 4) a target mode in which the clutch is engaged, the brake is disengaged and the motor actively targets a non-zero angular position of the wing tip device about the hinge in which the upper and lower surfaces of the wing tip device form a zero or non-zero angle with the upper and lower surfaces of the fixed wing.

[0029] Operating the wing in the target mode may avoid flutter problems that the wing tip device may otherwise suffer if the braking mode is used under those same aircraft wing operating conditions, due to the added damping of the motor and drive train of the actuation system.

[0030] Another aspect of the invention provides an aircraft wing, the aircraft wing comprising: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing so that the wingtip device can rotate about the hinge; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises a motor, at least one geared rotary actuator, a clutch for selectively decoupling the rotation of the motor from the rotation of the geared rotary actuator, the geared rotary actuator being drivable by the motor and arranged to convert a rotary motion into a different rotary motion and arranged to rotate the wingtip device relative to the tip of the fixed wing, wherein the aircraft wing is operable in the following modes:

[0031] 1) a drive mode, in which the clutch is engaged and the motor is used to drive the gear-driven rotary actuator to rotate the wing tip device about the hinge;

[0032] 2) a flapping mode, in which the clutch is disengaged to allow the wing tip device to rotate due to a force external to the wing tip device;

[0033] 3) a braking mode corresponding to a zero or non-zero angle position of the wing tip device about the hinge, in which the upper and lower surfaces of the wing tip device form a substantially zero or non-zero angle with the upper and lower surfaces of the fixed wing; and

[0034] 4) a target mode in which the clutch is engaged, the brake is disengaged and the motor actively targets a non-zero angular position of the wing tip device about the hinge in which the upper and lower surfaces of the wing tip device form a zero or non-zero angle with the upper and lower surfaces of the fixed wing. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0036] Figure 1 A plan view of an aircraft having wings and folding wingtip devices is shown;

[0037] Figure 2 Shows Figure 1 A front view of an aircraft with the wing tip device in various configurations;

[0038] Figure 3a , Figure 3b , Figure 3c and Figure 3d Shown in detail Figure 2 wingtip devices;

[0039] Figure 4a Schematically illustrates an actuation system for moving a wingtip device according to the invention;

[0040] Figure 4b More generally shown in block diagram form is Figure 4a Actuation system;

[0041] Figure 4c Shows Figure 4a Detailed views of sections of an actuation system;

[0042] Figure 5 A mechanical actuator according to the invention is shown;

[0043] Figure 6a schematically illustrates a wing tip device operating in a driven mode of operation;

[0044] Figure 6b shows a representation of an actuation system configured to operate in a drive mode;

[0045] Figure 7a schematically illustrates a wingtip device operating in a flapping wing operation mode;

[0046] Figure 7b shows a representation of an actuation system configured to operate in a flapping wing mode;

[0047] Figure 8a schematically illustrates a wing tip device operating in a braking mode of operation;

[0048] Figure 8b shows a representation of an actuation system configured to operate in a braking mode;

[0049] Figure 9a schematically illustrates a wingtip device operating in a target operating mode;

[0050] Figure 9b showing a representation of a braking system configured to operate in a target mode;

[0051] Fig.10a Schematically shows another actuation system for moving a wingtip device according to the present invention;

[0052] Fig.10b More generally shown in block diagram form is Fig.10a Actuation system;

[0053] Fig.11a Schematically shows another other actuation system for moving a wingtip device according to the present invention;

[0054] Fig.11b More generally shown in block diagram form is Fig.11a Actuation system;

[0055] Fig.11c Shows Fig.11a Exploded view of the brake system; DETAILED DESCRIPTION

[0056] Figure 1 is a plan view of an aircraft 1. The aircraft comprises a central fuselage 3 and two main wings 5 ​​extending outwardly from respective wing roots 5'.

[0057] Each wing 5 comprises a fixed wing 7 extending from a root 5' to a tip 7'. At the tip 7' of the fixed wing 7, the wing 5 further comprises a movable wingtip device 9 in the form of a flat wingtip extension. The wingtip device 9 is rotatably mounted around a hinge 11. The hinge 11 can be oriented non-parallel to the flight direction line F (or outwardly flared relative to the flight direction line F). The hinge 11 can alternatively be parallel to the flight direction line F.

[0058] In the fixed flight configuration, the wingtip device 9 is fixed relative to the fixed wing 7. The wingtip device 9 may be an extension of the fixed wing. Thus, the upper surface 7a and the lower surface 7b of the fixed wing 7 may be continuous with the upper surface 9a and the lower surface 9b of the wingtip device 9 (see Figure 3a and Figure 2The leading edge and trailing edge of the fixed wing 7 may also be continuous with the corresponding leading edge and trailing edge of the wing tip device 9. This arrangement is beneficial because it provides a relatively large wing span, thereby providing an aerodynamically efficient aircraft.

[0059] However, a larger wingspan may result in correspondingly larger loads on the wing 5, particularly larger wing root bending moments, especially during high load events such as gusts or extreme maneuvers. Such large wing root bending moments are a problem for relatively large span wings. The wing 5 must be sized to handle these maximum loads which may result in a relatively heavy wing, which may not be acceptable.

[0060] The wing tip device 9 is in the mobile flight configuration (see Figure 2 , Figure 3b and Figure 3d ) attempts to address this problem. In this configuration, the wing tip device 9 is substantially able to rotate freely about the hinge 11 with passive damping, as will be described further below.

[0061] like Figure 3b In Figure 2 In the second position from the uppermost position in FIG. 1 , the wingtip device 9 can be rotated upwards so that the lower surfaces between the fixed wing 7 and the wingtip device 9 are no longer continuous with each other. In addition, if the hinge 11 is angled relative to the direction of the airflow (i.e., opposite to the line of the flight direction F), the average angle of attack of the wingtip device decreases when the wingtip device 9 rotates upwards.

[0062] like Figure 3d In Figure 2 As shown in the lowermost position in FIG. 1 , the wingtip device 9 can also be rotated downward so that the upper surfaces between the fixed wing 7 and the wingtip device 9 are no longer continuous with each other.

[0063] In the moving flight configuration and the other moving flight configuration, the loads on the wing 5 generated by the wing tip device 9 are significantly reduced. The wing tip device 9 can be released to any of these configurations during flight (described in more detail below). By providing this load relief function during flight, the maximum load that the wing needs to be designed for can be reduced, and therefore the wing 5 can be made relatively light.

[0064] The wingtip device 9 can also be configured in a ground configuration, in which the wingtip device 9 is further rotated to a substantially upright position (in Figure 3c In Figure 21. The wingtip device is shown in an upright position in FIG. 1. The wingtip device can be moved to this configuration when it is on the ground (described in more detail below). Once rotated to such a position, the wingspan of the aircraft 1 is sufficient to meet the airport compatibility gate restrictions. Thus, the aircraft 1 can have a large wingspan (exceeding the gate restrictions) during flight, but still be able to meet the gate restrictions when on the ground.

[0065] like Figure 3d As shown in FIG, the hinge 11 allows the wing tip device 9 to rotate upward and downward in the mobile flight configuration. This arrangement enables both positive and negative g loads to be mitigated.

[0066] Figure 4a and Figure 4b An example of an actuation system 20 for rotating the wing tip device 9 about the hinge 11 is shown. The actuation system 20 comprises a motor 22, at least one geared rotary actuator 24 and a gearbox 26. In the case where the actuation system 20 comprises a plurality of geared rotary actuators 24, the geared rotary actuators 24 are arranged along the hinge line of the hinge 11. The motor 22 may form part of a power drive unit (PDU) incorporating a brake, or may be a gearbox 26. Figure 4a and Figure 4b The illustrated arrangement is provided with a separate brake 23. The geared rotary actuator 24 is a rotary actuator arranged to convert a first rotary motion into a different second rotary motion, for example at a different angular rotation rate and / or torque and / or direction.

[0067] In the illustrated example, there are three geared rotary actuator (GRA) "slices" 24 arranged along the articulation line of the hinge 11. Figure 4c As shown in FIG, the three GRAs can be driven by a common shaft 26a connected via a gearbox 26, which is a reduction gearbox. The shaft 26a can have a rotation axis coaxial with the hinge line of the hinge 11. The motor 22 (or PDU) is arranged at one end of the three GRA slices. The GRAs 24 are each arranged on the hinge line of the hinge 11.

[0068] exist Figure 4a The fairing 30 is shown in phantom in FIG. 1 and is sized to accommodate the actuation system 20. Figure 4c As illustrated in , the clutch 28 may have the same outer diameter as each of the GRAs 24 and the optional gearbox 26 so that the front surface area of ​​the actuation system 20 , and therefore the fairing 30 , is minimized.

[0069] The GRAs 24 each have a first steering knuckle 24a (or a pair of first steering knuckles) coupled to the fixed wing 7 and a first steering knuckle 24a (or a pair of first steering knuckles) coupled to, for example, the fixed wing 7. Figure 524. The second knuckle 24b (or a pair of second knuckles) of the wing tip device 9 shown in FIG. Each of the GRAs 24 is substantially identical and includes an internal gear transmission device for applying a gear ratio to the torque applied to the GRA via the common shaft 26a. When the motor 22 is enabled to drive the common drive shaft 26a via the gearbox 26, the second knuckle 24b rotates relative to the first knuckle 24a of the GRA 24. This drives the articulation of the wing tip device 9 about the hinge 11 relative to the fixed wing 7. The rotation can be a positive rotation or a negative rotation.

[0070] A clutch 28 is provided between the gearbox 26 and the motor 22. In this way, the clutch 28 can be designed to handle lower torques because it is arranged before the gear ratio is applied to the torque from the motor 22 by the gearbox 26. This can reduce the size, weight, cost and complexity of the clutch 28. Engaging the clutch 28 enables the motor 22 to drive the GRA 24 in the drive mode to rotate the wingtip device 9 about the hinge 11. By Figure 6a An example of a schematic representation of the actuation system 20 operating in a drive mode is illustrated, with the curved arrow indicating the direction in which the motor 22 rotates the wingtip device 9 (e.g., counterclockwise when looking backwards). It should be noted that the motor 22 may alternatively rotate the wingtip device 9 about the hinge 11 in the opposite (e.g., clockwise) direction. Figure 6b It is illustrated how the clutch 28 and brake 23 are configured to allow the motor 22 to drive the wingtip device 9 .

[0071] Disengaging the clutch 28 enables the GRA 24 to rotate substantially freely, thereby allowing the wingtip device 9 to rotate substantially freely about the hinge 11 (with passive damping due to the actuation system) relative to the fixed wing 7 when in the flapping wing operating mode. Once the brake 23 and clutch 28 are released, the wingtip device 9 can be actuated completely passively in the flapping wing mode. For example, the wingtip device can move under the influence of aerodynamic forces and / or gravity. The option of braking or releasing the wingtip device can be referred to as a "semi-aeroelastic" arrangement. By Figure 7a A schematic representation of the actuation system 20 operating in flapping mode is illustrated, with the curved arrows indicating the permissible rotation of the wingtip device 9 . Figure 7b It is illustrated how the clutch 28 and the brake 23 are configured to allow the wing tip device 9 to rotate freely about the hinge 11 .

[0072] When the clutch 28 is disengaged, the gearbox 26 can be driven in reverse so that the gearbox 26 can be operated by the movement of the wing tip device 9 rotating about the hinge 11. This can introduce mechanical damping into the system, optionally wherein the gearbox 26 has a maximum damping value that allows an oscillating flapping movement of the wing tip device 9 rotating about the hinge 11 when operating in the flapping mode. The maximum damping value of the gearbox 26 can be about 500Nm / rad / s. Once disengaged, the rotating part of the clutch 28 can be limited to a speed of no more than about 30,000rpm, preferably less than 25,000rpm.

[0073] Operating the actuation system 20 in flapping mode requires due consideration of the flutter mode. Flying at certain aircraft speeds, such as the flutter speed of the wing 5, may result in flutter instabilities, which may damage the wing 5. By introducing passive damping into the actuation system 20 using a gearbox 26 as described above, the flutter margin of the fixed wing / wingtip arrangement is increased.

[0074] This passive damping of the movement of the wingtip device relative to the fixed wing about the hinge can increase the flutter margin of the fixed wing / wingtip device and reduce the gust response of the wingtip device when the wingtip device is released due to the disengagement of the clutch. When the reduction gearbox is arranged between the clutch and the geared rotary actuator, good load relief can still be achieved, which increases the flutter margin to avoid potential flutter problems. Passive damping can have the effect of increasing the flutter stability of the wingtip device when it is released in the flapping mode and also reduces the flapping frequency in the flapping mode. This can have a beneficial effect on several types of flutter associated with the hinge. For example, i) the coupling of the flapping mode and the first wing bending mode, and ii) the coupling of the flapping mode (or the outer wing bending mode in the case where the wingtip device is braked) and the higher frequency of the outer wing twist / forward and backward mode, which is sensitive to the angle between the fixed wing 7 and the wingtip device 9. Thus, passive damping may allow an increase in the angle of deployment of the hinge line without compromising the mitigation of type i) flutter, which in turn may reduce the glide angle (the static equilibrium angle between the fixed wing 7 and the wingtip device 9 when the wingtip device 9 is operating in a flapping mode). Reducing the glide angle of the wingtip device 9 may increase the stability of type ii) flutter. Increasing the flutter margin of the folding wingtip device 9 by adding damping to the hinge 11 may also affect the flutter response of other aircraft movable parts, such as aircraft ailerons. Increased damping about the hinge may also reduce the amplitude of the flapping oscillations of the wingtip device when released at lower aircraft speeds, which may avoid the need for stops (or reduce the size of the stops and therefore reduce their weight) to prevent over-rotation of the folding wingtip device (e.g., stopping at approximately plus or minus 90 degrees).

[0075] Alternatively, the clutch 28 may be configured to be disengaged during flight. In other words, the wing tip device 9 may be operated in a flapping mode at aircraft speeds at which flutter instabilities do not occur.

[0076] The clutch 28 may be disengaged during flight for a number of reasons. Allowing the wing tip device 9 to rotate substantially freely may be used to reduce the loads acting on the wing 5 due to external forces. Thereby, the maximum load for which the wing 5 needs to be designed may be reduced, and the wing 5 may therefore be made relatively light. Alternatively, the wing tip device 9 may be allowed to rotate freely so that the span of the wing 5 is effectively reduced. Reducing the span of the wing 5 may be beneficial, for example, during relatively low speed or low altitude flight where high lift levels are not required, or when relatively high roll rates are required.

[0077] When the brake 23 (optionally the brake 23 of the PDU) is engaged and the clutch 28 is also engaged, the actuation system 20 operates in a braking mode in which the brake 23 is used to prevent the wingtip device 9 from rotating relative to the fixed wing 7 about the hinge 11. The braking operating mode may correspond to a zero angular position or a non-zero angular position of the wingtip device 9 about the hinge 11. In the zero position, the upper surface 9a and the lower surface 9b of the wingtip device 9 form a substantially zero angle with the upper surface 7a and the lower surface 7b of the fixed wing 7, so that the overall span of the wing 5 is maximized, or alternatively, in a non-zero position, the upper surface 9a and the lower surface 9b of the wingtip device 9 form a non-zero angle with the upper surface 7a and the lower surface 7b of the fixed wing 7. By Figure 8a A schematic representation of the actuation system 20 operating in a braking mode is illustrated. Figure 8b It is illustrated how the clutch and brake are configured to prevent the wing tip device 9 from rotating about the hinge 11 .

[0078] The actuation system 20 is also capable of operating in a target mode in which the clutch 28 is engaged and the brake 23 is disengaged so that the motor 22 can drive rotation of the wingtip device 9 about the hinge 11. The motor 22 can be configured to actively target a zero angle or non-zero angle position of the wingtip device 9 relative to the fixed wing 7 so that the upper surface 9a and the lower surface 9b of the wingtip device 9 form a zero angle or a non-zero angle with the upper surface 7a and the lower surface 7b of the fixed wing 7. The angular position of the wingtip device 9 can be fed back to the motor 22 using a closed-loop control system so that the motor 22 is driven to change the angular position of the wingtip device 9 to match the target position. This "target" operating mode may be useful, for example, when a braking mode used to achieve the same angular position of the wingtip device may otherwise be subject to flutter issues under the same aircraft operating conditions or when the clutch is in a fail-safe mode. By Figure 9aA schematic diagram of the actuation system 20 operating in a target mode is illustrated, with the dashed line indicating a non-zero target position of the wingtip device 9 and the curved arrow indicating the direction in which the motor 22 drives the wingtip device 9 to achieve the target position. Figure 9b It is illustrated how the clutch and brake are configured to allow the motor 22 to drive the wingtip device 9 .

[0079] The actuation system 20 is capable of operating in any combination of the above-described operating modes and can change between operating modes during flight.

[0080] Fig.10a Another embodiment (combinable with any of the previous disclosures) is shown, in which the actuator mechanism 20 includes a second gearbox 27, which is arranged between the clutch 28 and the motor 22. Providing the gearbox 26 and the second gearbox 27 allows the torque from the motor 22 to be increased in two stages, first by the second gearbox 27 and then by the gearbox 26 before the torque is transmitted through the clutch 28. Therefore, the gear ratio and therefore the size of each of the gearbox 26 and the second gearbox 27 can be made smaller than that of the embodiment shown in FIG. Figure 4a and Figure 4b 26 is used as shown in the figure. This can be advantageous in reducing the overall size of the actuation system 20 and therefore the size of any fairing 30 arranged around the braking system 20. In addition, this can allow the reduction ratio of the gearbox 26 to be selected based on the desired damping characteristics of the articulated joint when being backdriven, while still using the second gearbox 27 to provide sufficient torque to drive the wing tip device 9. Fig.10b This arrangement is shown more generally in a block diagram.

[0081] The actuation system 20 may alternatively be configured as follows Fig.11a and Fig.11b As shown in FIG. 1 , the motor 22 is arranged on the opposite side of the gear-driven rotary actuator 24 from the clutch 28 and the gearbox 26. This arrangement can position the clutch 28 and the gearbox 26 in front of the leading edge of the wing 5, such as Fig.11a As shown in , this is useful, for example, for packaging components within a fairing 30. Although shown as including a second gearbox 27, this configuration can also be applied to an actuation mechanism that includes only a single gearbox 26. Fig.11c An example of an actuation system 20 configured in this manner is shown in an exploded view in FIG. In this example, a drive shaft 27a connected to a second gearbox 27 transfers torque to a clutch 28, but does not act on the gear-driven rotary actuator 24. Once engaged, the clutch 28 transfers torque to the gearbox 26, which in turn uses, for example, Figure 4c The common shaft 26a shown in FIG. 2 drives the geared rotary actuator 24 .

[0082] Where the word "or" appears, this will be interpreted as meaning "and / or" such that the referred items are not necessarily mutually exclusive and can be used in any appropriate combination.

[0083] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An aircraft wing, the aircraft wing include: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing so that the wingtip device can rotate about the hinge; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises a motor, at least one gear-driven rotary actuator, a reduction gearbox, a clutch for selectively disconnecting the rotation of the motor from the rotation of the gear-driven rotary actuator, the gear-driven rotary actuator being drivable by the motor and arranged to convert a rotational motion into a different rotational motion and being arranged to rotate the wingtip device relative to the tip of the fixed wing, wherein the reduction gearbox is arranged between the clutch and the gear-driven rotary actuator along a transmission system between the motor and the gear-driven rotary actuator, wherein the reduction gearbox is capable of reverse driving when the clutch is disengaged to disconnect the rotation of the motor from the rotation of the gear-driven rotary actuator when the wingtip device rotates about the hinge.

2. The aircraft wing according to claim 1, in, The gearbox has a maximum damping value that allows oscillatory flapping motion of the wing tip device rotating about the hinge during normal operation when the clutch is disengaged.

3. An aircraft wing according to any one of claims 1 to 2, in, The rotating portion of the clutch has a speed of no more than about 30,000 rpm when disengaged.

4. An aircraft wing according to any preceding claim, further comprising a plurality of said geared rotary actuators arranged along a hinge line of said hinge.

5. The aircraft wing according to claim 4, in, The clutch has an outer diameter that is substantially the same as an outer diameter of each of the geared rotary actuators.

6. An aircraft wing according to any preceding claim, in, The actuation system also includes a brake for preventing movement of the geared rotary actuator when the clutch is engaged.

7. An aircraft wing according to claim 6, in, The actuation system is operable in the following modes: i) a drive mode in which the clutch is engaged and the motor is driven to rotate the wingtip device about the hinge; ii) a flapping mode in which the clutch is disengaged and the wingtip device is able to rotate about the hinge by a force external to the wingtip device; and iii) a braking mode in which the clutch is engaged and the brake prevents the wingtip arrangement from rotating about the hinge.

8. An aircraft wing according to claim 7, in, The braking mode corresponds to a zero or non-zero angle position of the wingtip device about the hinge, in which the upper and lower surfaces of the wingtip device form a substantially zero or non-zero angle with the upper and lower surfaces of the fixed wing.

9. An aircraft wing according to claim 7 or claim 8, in, The actuation system is also operable in a target mode in which the clutch is engaged, the brake is disengaged and the motor actively targets a non-zero angular position of the wing tip device about the hinge in which the upper and lower surfaces of the wing tip device form a non-zero angle with the upper and lower surfaces of the fixed wing.

10. An aircraft wing according to any preceding claim, in, The geared rotary actuator has a first knuckle fixed to the fixed wing and a second knuckle fixed to the wingtip device, wherein the first knuckle and the second knuckle are driven by the geared rotary actuator to rotate relative to each other using a motive force provided by the motor.

11. An aircraft wing according to any preceding claim, in, The clutch is configured to be disengaged during flight for a) load relief, or b) when the aircraft is flying at a relatively low speed or altitude and a relatively high roll rate is required.

12. An aircraft wing according to any preceding claim, further comprising a second reduction gearbox disposed between the clutch and the motor along a drive train between the motor and the geared rotary actuator.

13. A method of operating an aircraft wing, the aircraft wing comprising: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing ； and an actuation system for rotating the wing tip device about the hinge, wherein: The actuation system comprises: a motor; at least one geared rotary actuator arranged to convert a rotary motion into a different rotary motion; a reduction gearbox; a clutch for selectively decoupling the rotation of the motor from the rotation of the geared rotary actuator; and a brake for preventing movement of the geared rotary actuator when the clutch is engaged, wherein the reduction gearbox is disposed between the clutch and the geared rotary actuator along a drive train between the motor and the geared rotary actuator, the method comprising operating the actuation system in the following modes: i) a drive mode in which the clutch is engaged and the motor is used to drive the geared rotary actuator to rotate the wing tip device about the hinge; ii) a flapping mode in which the clutch is disengaged and the gearbox is reverse driven when the wing tip device rotates about the hinge due to forces external to the wing tip device.

14. A method of operating an aircraft wing, the aircraft wing comprising: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing ； and an actuation system for rotating the wing tip device about the hinge, wherein: The actuation system comprises: a motor; at least one geared rotary actuator arranged to convert a rotary motion into a different rotary motion; a clutch for selectively decoupling rotation of the motor from rotation of the geared rotary actuator; and a brake for preventing movement of the geared rotary actuator when the clutch is engaged, the method comprising operating the actuation system in the following modes: 1) a drive mode in which the clutch is engaged and the motor is used to drive the geared rotary actuator to rotate the wing tip device about the hinge; 2) a flapping mode in which the clutch is disengaged to allow the wing tip device to rotate about the hinge due to a force external to the wing tip device; 3) a braking mode, the braking mode corresponding to a zero angle or non-zero angle position of the wing tip device about the hinge, in which the upper and lower surfaces of the wing tip device form a substantially zero angle or non-zero angle with the upper and lower surfaces of the fixed wing; and 4) a target mode in which the clutch is engaged, the brake is disengaged and the motor actively targets a non-zero angular position of the wing tip device about the hinge in which the upper and lower surfaces of the wing tip device form a zero or non-zero angle with the upper and lower surfaces of the fixed wing.

15. An aircraft wing, the aircraft wing include: a fixed wing having a tip; a wingtip device rotatably mounted on a hinge at the tip of the fixed wing so that the wingtip device can rotate about the hinge; and an actuation system for rotating the wingtip device about the hinge, wherein the actuation system comprises a motor, at least one geared rotary actuator, a clutch for selectively decoupling the rotation of the motor from the rotation of the geared rotary actuator, the geared rotary actuator being drivable by the motor and arranged to convert a rotary motion into a different rotary motion and arranged to rotate the wingtip device relative to the tip of the fixed wing, wherein the aircraft wing is operable in the following modes: 1) a drive mode, in which the clutch is engaged and the motor is used to drive the geared rotary actuator to rotate the wing tip device about the hinge; 2) a flapping mode in which the clutch is disengaged to allow the wing tip device to rotate about the hinge due to a force external to the wing tip device; 3) a braking mode, the braking mode corresponding to a zero angle or non-zero angle position of the wing tip device about the hinge, in which the upper and lower surfaces of the wing tip device form a substantially zero angle or non-zero angle with the upper and lower surfaces of the fixed wing; and 4) a target mode in which the clutch is engaged, the brake is disengaged and the motor actively targets a non-zero angular position of the wing tip device about the hinge in which the upper and lower surfaces of the wing tip device form a zero or non-zero angle with the upper and lower surfaces of the fixed wing.

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