Aircraft wing with movable wingtip device for load alleviation

Abstract

An aircraft (1), the aircraft comprising a wing (5), the wing having a fixed wing (7), the fixed wing having a wingtip device (9) rotatably mounted about a hinge (11) at the tip of the fixed wing. The wingtip device (9) is operable between a flight configuration and a load alleviation configuration for load alleviation during flight. The aircraft (1) comprises a restraint assembly (17) operable between a restraint mode and a release mode, in the restraint mode, the wingtip device is held in the flight configuration by a restraint force, such as by a brake (19), and in the release mode, the force on the wingtip device is released such that the wingtip device (9) can adopt the load alleviation configuration.

Description

[0001] This application is a divisional application of a Chinese patent application filed by Airbus Operations Limited as the applicant on September 29, 2016, with the invention title of "Aircraft Wing with Movable Wing Tip Device for Load Alleviation" and the application number of 201680077908.X. Background Art

[0002] It is known to use movable wing tip devices in particular to provide load alleviation during flight. US 5,988,563 discloses the following arrangement: In this arrangement, a foldable winglet can pivot between a retracted position and an extended position about a hinge that is oriented along the flight line during flight. When the aircraft reaches cruise, the actuator can be powered manually or automatically to pivot the winglet from a vertical position to an extended position. When encountering strong loads (e.g., during a dive), the load (the load on the foldable winglet) overcomes the action of the actuator and pivots the winglet back to its vertical position. This action is used to reduce the bending moment acting on the wing. In US 5,988,563, the winglet is not locked in the extended position, but only remains extended as long as the torque of the actuator that extends the wing is greater than any opposing aerodynamic moment. Since the forces acting on the wing are used to rotate the winglet, this effect is called passive load alleviation, which eliminates the need to command the actuator to return the winglet to its retracted position (i.e., reduce the load).

[0003] Another example of using a movable wing tip device for load alleviation is shown in US 7,275,722. In this arrangement, the wing tip device can be rotatably moved to a load alleviation position using active or passive devices. The axis of rotation of the wing tip device is such that when the wing tip device rotates to the load alleviation configuration, its average inclination angle decreases.

[0004] The paper titled "Preliminary Study of Use of Folding Wing-tips for Loads Alleviation" published by Cooper et al. on March 31, 2013, explored the relationship between the orientation of the hinge line of the movable wing tip device and the magnitude of load alleviation when the wing tip device rotates about this hinge. This study found that compared with a hinge oriented along the airflow direction, a hinge perpendicular to the wing box / average wing chord line enables the shear force and bending moment distributions to be reduced.

[0005] There is a trend for passenger aircraft to become larger, which requires a correspondingly larger wingspan. However, the maximum aircraft wingspan is actually limited by airport operating rules that govern the various clearances required for maneuvers around the airport (e.g., the wingspan and / or ground clearance required for aircraft parking bay entry and safe taxiway use). To address this issue, various arrangements have been proposed that include movable wingtip devices that specifically enable the wingspan to be reduced in the ground configuration. US 2013 / 0099060 and WO 2015 / 150816 are examples of such arrangements.

[0006] Using such movable wingtip devices to provide a larger wingspan during flight is advantageous in terms of induced drag reduction, but it tends to increase the aerodynamic loads on the wing during use and thus tends to require a stronger and heavier wing (the weight of the wing tends to be approximately proportional to the cube of the wingspan (span 3 ). SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention, there is provided an aircraft comprising a wing having a fixed wing with a wingtip device movably mounted at the tip of the fixed wing, 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 operable between the following configurations: (i) a flight configuration for use during flight, in which the upper surface and the lower surface of the wingtip device are continuous with the upper surface and the lower surface of the fixed wing; and (ii) a load alleviation configuration for use during flight for load alleviation, in which the wingtip device moves relative to the fixed wing such that at least one of the upper surface and the lower surface of the wingtip device moves away from the corresponding surface of the fixed wing and the load on the wing is reduced; characterized in that the aircraft comprises a restraint assembly operable between a restraint mode and a release mode, wherein in the restraint mode, the wingtip device is held in the flight configuration by a restraint force, and in the release mode, the restraint force on the wingtip device is released such that the wingtip device can adopt the load alleviation configuration.

[0008] It has been found particularly beneficial to provide a restraint assembly that can be operated in a release mode in which the restraint force is released. For example, the wingtip device can be firmly held in the flight configuration during normal cruise flight, but if the aircraft encounters a gust or other large load event, the restraint force can be released such that the wingtip device can quickly move to the load alleviation configuration. This may mean that the wing can avoid being subjected to large gust loads. This in turn enables the wing to have a relatively large wingspan without having to incur an associated weight penalty, since the wing can be designed for a lower magnitude of maximum load.

[0009] The default (passive) mode of the restraint component is preferably the restraint mode. For example, in an embodiment including a brake, the default (passive) state of the brake is preferably such that it is used to restrain the wingtip device. The restraint component preferably requires activation, for example via an input signal, in order to switch to the release mode. This arrangement has been found to be beneficial because it ensures that moving the restraint component to the release mode will require an "active" step, thereby eliminating the risk of being actuated to the release mode non-commandingly. For example, in an embodiment including a brake, the brake preferably needs to be switched to ON in order to release the brake and release the wingtip device.

[0010] In principle, once the restraint component is in the release mode, the wingtip device can be actuated to the load alleviation configuration completely passively. For example, the wingtip device can move under the action of aerodynamic forces that urge the wingtip device towards the load alleviation configuration. In some embodiments of the present invention, the wing may include a biasing member arranged such that when the wingtip device is in the flight configuration, the biasing member applies a biasing force to urge the wingtip device towards the load alleviation configuration. This arrangement has been found to be beneficial because it tends to reduce the lag between the restraint component in the release mode and the wingtip device that actually moves to the load alleviation configuration (the biasing force helps move the wingtip device into the load alleviation configuration such that the wingtip device moves under the action of both the biasing force and the aerodynamic forces. The combination of the restraint component and the wingtip device equipped with this hinge can be referred to as a "semi-aeroelastic" arrangement).

[0011] Having a biasing member can be beneficial in terms of reducing flutter (e.g., in terms of reducing the speed at which flutter may occur).

[0012] When the restraint component is in the restraint mode, the biasing force is preferably overcome by the restraining force. However, when the restraint component is in the release mode, the biasing force is preferably sufficient to help move the wingtip device into the load alleviation configuration. In some embodiments, when the restraint component is in the release mode, the biasing force can be sufficient to move the wingtip device into the load alleviation configuration. This arrangement provides assurance that the wingtip device can move to the load alleviation configuration as needed, even in the absence of aerodynamic forces acting on the wingtip device. However, the wingtip device is more preferably arranged such that it can move from the flight configuration to the load alleviation configuration at least partially by aerodynamic forces acting on the wingtip device.

[0013] The biasing member can be capable of selectively disengaging without applying a biasing force to the wingtip device. For example, the wing may include a clutch for selectively disengaging the biasing member without applying a biasing force to the wingtip device. This arrangement has been found to be beneficial because it can enable the biasing member to selectively disengage to make it easier to maintain the wingtip device.

[0014] In the restraint mode, the wingtip device is held in the flight configuration by a restraining force. In the release mode, the restraining force (which has been applied to hold the device in the flight configuration) is released. It will be understood that when the restraint assembly is in the release mode, this does not necessarily preclude the existence of a drag force itself (e.g., the drag force from a damper) between the wing and the wingtip device.

[0015] The wing preferably includes a damping system arranged to damp the movement of the wingtip device. This arrangement has been found to be beneficial, particularly in cases where the wingtip device is rapidly moved to the load alleviation configuration, as this arrangement tends to attenuate transient, oscillatory movements. The damping system has also been found to be beneficial in that it can mitigate aeroelastic instabilities such as flutter and / or can limit periodic oscillations.

[0016] In other embodiments, the aircraft does not need to include any dampers and / or biasing members. In fact, in some embodiments, the wingtip assembly can rotate freely when the restraint assembly is in the release mode (i.e., once the restraining force is removed, there is substantially no other resistance to prevent rotation). When the wingtip device rotates freely in this manner, the wingtip device can be referred to as "skating" or arranged to "skate". This arrangement has been found to be particularly beneficial for some embodiments of the present invention. In these embodiments, the center of gravity of the wingtip device can be positioned such that no significant shear load is transferred into the wingtip and to ensure that the flutter speed is sufficiently high.

[0017] The aircraft may also include a control system configured to control the operation of the restraint assembly between the restraint mode and the release mode. The control system can be part of an electronic flight control system (EFCS).

[0018] The aircraft may include a detector for detecting when the restraint assembly should be switched from the restraint mode to the release mode. In some embodiments, the detector can be configured to detect a force on the aircraft (e.g., a bending force in the wing). The control system can be configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to the detected force exceeding a predetermined threshold. The aircraft may include an alpha detector (the alpha detector is also referred to as an alpha vane or angle of attack detector) for detecting the angle of attack of the aircraft relative to the oncoming flow. The control system can be configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to the detected angle of attack exceeding a predetermined threshold. Thus, the restraint assembly can be placed in the release mode when an event indicating a higher load is detected (e.g., a gust can be recorded using the alpha detector).

[0019] The control system can be set to also respond to an alpha detector to control other load alleviation elements (e.g., elevators or ailerons) located on the aircraft. These elements can provide supplementary load alleviation to the load alleviation provided by the movable wingtip device.

[0020] The alpha detector can be located on the nose of the aircraft such that it is positioned upstream of the wingtip device. It has been found that positioning the alpha detector upstream of the wingtip device is particularly beneficial as it enables an event (e.g., a gust) to be detected before the event encounters the wingtip device. Thus, the wingtip device can be allowed to adopt a load alleviation configuration before the event reaches it.

[0021] It has been found that load alleviation using embodiments of the present invention is particularly beneficial during low-speed operation (e.g., during takeoff, climb, and / or landing). Due to system complexity, it is often difficult to integrate high-lift devices (e.g., slats) into the movable wingtip device. Thus, the wingtip device may be prone to stalling during low-speed operations such as these. What the present invention recognizes is that by moving the wingtip device to a load alleviation configuration, the occurrence of stalling can be reduced (thereby avoiding the associated drag increase). This can help the aircraft meet low-speed requirements, particularly for takeoff and climb. Thus, in some embodiments of the present invention, the control system can be configured to switch the operation of the restraint assembly from a restraint mode to a release mode in response to a speed signal. The speed signal can indicate that the aircraft is operating at a low speed (e.g., the speed signal can indicate a speed below a predetermined threshold).

[0022] In the load alleviation configuration, the load on the wingtip can be reduced and, in some embodiments, the load on the wingtip can be substantially eliminated. It has been found that this arrangement is particularly beneficial when the aircraft is rolling. Specifically, since the lift at the wingtip is alleviated, the lift at the wingtip tends not to resist (i.e., it tends not to damp) the rolling motion. This can enable the aircraft to be more responsive when rolling (or as responsive as an aircraft with a correspondingly shorter wingspan). Thus, in some embodiments of the present invention, the control system can be configured to switch the operation of the restraint assembly from a restraint mode to a release mode in response to a roll signal. The roll signal can indicate that the aircraft is performing a rolling maneuver (e.g., in response to oppositely actuated ailerons on either wing). It has been found that this arrangement is particularly beneficial in embodiments where the wingtip device can "slip" (e.g., embodiments without a biasing member and / or damper).

[0023] Some embodiments of the present invention have been found to be beneficial in reducing the flutter speed. Specifically, it has been found that in some embodiments, when the restraint assembly is in the release mode and the wingtip device is in the load alleviation configuration, the onset of flutter may be delayed. This is thought to be due to the oscillatory motion that the wingtip device may adopt when the restraint assembly is in the release mode. There are the following EASACS25 requirements: the aircraft does not flutter at 115% times the dive speed (Vd) for nominal conditions or at 100% times Vd for failure conditions. Some embodiments of the present invention can be used to help suppress flutter in this region between Vd and 1.15Vd. For example, the control system can be configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to a speed signal indicating that the dive speed has been exceeded. This arrangement has been found to be particularly beneficial in embodiments where the wingtip device may "slip" (e.g., in the absence of a biasing member and / or damper).

[0024] The aircraft may include a corresponding fixed wing, wingtip device, and restraint assembly on the other side of the aircraft fuselage. The control system can be configured to switch the operation of the other restraint assembly from the restraint mode to the release mode in response to an input indicating that one of the restraint assemblies has been switched to the release mode. This arrangement is beneficial because it can prevent the asymmetric deployment of the wingtip device (e.g., asymmetric deployment in the case where the restraint assembly is switched to the release mode non-commandingly).

[0025] Embodiments of the present invention are particularly beneficial in an arrangement where the wingtip device is arranged to be movable to achieve load alleviation and such that the wingspan is relatively large during flight but reduced when on the ground to comply with the stand limits. Thus, in some embodiments of the present invention, the wingtip device can also be operated to: (iii) a ground configuration used during ground-based operations, in which the wingtip device is moved away from the flight configuration such that the wingspan of the aircraft wing is reduced. In the flight configuration, the wingspan may exceed the airport compatibility stand limits. In the ground configuration, the reduced wingspan results in a wingspan (when the wingtip device is in the ground configuration) that is less than or approximately equal to the airport compatibility stand limits.

[0026] The aircraft preferably includes an actuator for moving the wingtip device between the flight configuration and the ground configuration. The actuator can also be arranged to move the wingtip device back from the load alleviation configuration to the flight configuration. When the restraint assembly is in the restraint mode, the actuator can be in a passive state such that it does not actively act on the restraint force. These embodiments of the present invention have been found to be beneficial because they enable the restraint function of the wingtip device (during flight) to be separated from the function of the actuator (which can be reversed to move the wingtip device between the flight configuration and the ground configuration).

[0027] The actuator can be a motor, such as an electric motor. The actuator can be a hydraulic actuator.

[0028] The restraint assembly can be associated with a fuse, preferably a mechanical fuse. The restraint assembly can be arranged such that failure of the fuse causes the restraint assembly to assume a release configuration. The fuse can be arranged to fail in response to a load on the wingtip device exceeding a threshold level. The threshold level is preferably higher than the load that would otherwise overcome the restraining force. In other words, the fuse is preferably arranged to fail in response to an excessive load on the wingtip device, where the excessive load may occur in the case where the restraint assembly fails to assume the release configuration.

[0029] The aircraft can include a latching device for holding the wingtip device in the load alleviation configuration. For example, the aircraft can include a ratchet and a pawl configured to allow the wingtip device to rotate to the load alleviation configuration and then hold it in that configuration, unless or until the wingtip device is returned to the flight configuration. Such an arrangement can be particularly beneficial in embodiments without a biasing member and / or damper, as such an arrangement enables the wingtip device (when the restraint assembly moves under aeroelastic forces and the restraint assembly is in the release configuration) to be "captured" in the load alleviation configuration. The latching device can be controlled by a control unit to latch and / or release the wingtip device.

[0030] The wingtip device can be rotatably mounted on a hinge located at the tip of the wing such that it can rotate about the hinge between the flight configuration and the load alleviation configuration. In embodiments where the wingtip device can also move to a ground configuration, the wingtip device preferably can also move about the same hinge.

[0031] The hinge is preferably oriented such that it is not parallel to the flight direction line. The hinge is preferably oriented such that the hinge is more inwardly located at the trailing edge of the wing than at the leading edge of the wing. The hinge is preferably oriented such that the average inclination angle of the wingtip device in the load alleviation configuration is reduced. The hinge is preferably oriented substantially perpendicular to the swept mean chord axis of the wing. The swept mean chord can be parallel to the longitudinal direction of the wing box. It has been found that such an arrangement (compared to a hinge line oriented parallel to the flight line) is beneficial in achieving load reduction. In addition, it has been found that such an orientation of the hinge is beneficial for the wingtip device to move to a stable load alleviation configuration. For example, when the hinge is in such an orientation, the wingtip device tends to move to a static aeroelastically stable position even under aerodynamic loads only. Therefore, such an orientation of the hinge is particularly beneficial when combined with the restraint assembly in embodiments of the present invention. The orientation of the hinge can be selected such that it is used to stabilize flutter. [[ID=1,5]]

[0032] The wingtip device can rotate from a flight configuration in an upward direction to a load alleviation configuration. The wingtip device can rotate from a flight configuration in a downward direction to a load alleviation configuration. The hinge can be a double hinge capable of both upward rotation and downward rotation. It has been found beneficial to provide such a double hinge as it can enable the alleviation of loads from both upward events and downward events such as gusts. This arrangement can also ensure that the load alleviation configuration does not inadvertently amplify the load, which could occur if the wingtip device were allowed to assume the configuration in response to an event in the direction opposite to the expected direction.

[0033] The wingtip device can be a wingtip extension; for example, the wingtip device can be a planar tip extension. In other embodiments, the wingtip device can include or consist of a non-planar device, such as a winglet.

[0034] In the flight configuration, the trailing edge of the wingtip device is preferably continuous with the trailing edge of the fixed wing. The leading edge of the wingtip device is preferably continuous with the leading edge of the fixed wing. Preferably, there is a smooth transition from the fixed wing to the wingtip device. It will be understood that a smooth transition can be achieved even in the case where there are variations in sweep or twist at the junction between the fixed wing and the wingtip device. However, there is preferably no interruption at the junction between the inner wing and the wingtip device.

[0035] When the wingtip device is in the load alleviation configuration, the aircraft including the wing is still suitable for flight, but the wingtip device preferably moves to a position where the load on the wing is alleviated. It will be understood that the load alleviation configuration can include the wingtip device being in a range of positions (all of which alleviate the load to some extent). The position (e.g., the amplitude of rotation about the hinge) can depend on the magnitude of the load to be alleviated. In the load alleviation configuration, the wingtip device remains attached to the fixed wing. The wingtip device can move repeatedly between the load alleviation configuration and the flight configuration.

[0036] In embodiments where the wingtip device can move to a ground configuration, the aircraft including the wing may not be suitable for flight when the wingtip device is in the ground configuration. For example, in the ground configuration, the wingtip device may be aerodynamically and / or structurally unsuitable for flight. The aircraft is preferably configured such that the wingtip device cannot move to the ground configuration during flight. The aircraft can include a sensor for sensing when the aircraft is in flight. When the sensor senses that the aircraft is in flight, the control system is preferably set to prohibit the possibility of moving the wingtip device to the ground configuration. In the ground configuration, the wingtip device can rotate about the hinge by an angle greater than the angle by which the wingtip device rotates about the hinge in the load alleviation configuration. In the ground configuration, the wingtip device remains attached to the wing.

[0037] The aircraft is preferably a passenger aircraft. The passenger aircraft preferably includes a passenger cabin which includes multiple rows and columns of seat units for accommodating a plurality of passengers. The capacity of the aircraft can be at least 20, more preferably at least 50 and more preferably more than 50 passengers. The aircraft is preferably a powered aircraft. The aircraft preferably includes an engine for propelling the aircraft. The aircraft can include wing-mounted engines and preferably includes under-wing engines.

[0038] According to another aspect of the present invention, there is provided an aircraft wing for use as the wing in any of the preceding claims, the wing including a fixed wing having wingtip devices movably mounted at the tip of the fixed wing, wherein the fixed wing has an upper surface and a lower surface, and the wingtip devices have an upper surface and a lower surface, and the wingtip devices are capable of operating between the following configurations: (i) a flight configuration used during flight, in which the upper surface and the lower surface of the wingtip devices are continuous with the upper surface and the lower surface of the fixed wing; and (ii) a load mitigation configuration used during flight for load mitigation, in which the wingtip devices move relative to the fixed wing such that at least one of the upper surface and the lower surface of the wingtip devices moves away from the corresponding surface of the fixed wing and the load on the wing is reduced; characterized in that the wing includes a restraint assembly capable of operating between a restraint mode and a release mode, wherein, in the restraint mode, the wingtip devices are held in the flight configuration by a restraining force, and in the release mode, the restraining force on the wingtip devices is released such that the wingtip devices can adopt the load mitigation configuration.

[0039] According to another aspect of the present invention, there is provided a restraint assembly for use as the restraint assembly in any of the preceding claims, the restraint assembly being arranged to be mounted on an aircraft wing and capable of operating between a restraint mode and a release mode, wherein, in the restraint mode, the wingtip devices are held in the flight configuration by a restraining force, and in the release mode, the restraining force on the wingtip devices is released such that the wingtip devices are capable of adopting the load mitigation configuration.

[0040] According to another aspect of the present invention, there is provided a method for controlling load mitigation on a wing having a fixed wing, the fixed wing having wingtip devices movably mounted at the tip of the fixed wing, the method including the following steps: (a) holding the wingtip devices in a flight configuration by a restraining force, in which the upper surface and the lower surface of the wingtip devices are continuous with the upper surface and the lower surface of the fixed wing; and (b) releasing the restraining force to allow the wingtip devices to adopt a load mitigation configuration used during flight for load mitigation, in which the wingtip devices move relative to the fixed wing such that at least one of the upper surface and the lower surface of the wingtip devices moves away from the corresponding surface of the fixed wing and the load on the wing is reduced.

[0041] The method of the above aspect of the invention may include the step of performing a roll maneuver while the restraint assembly is in the released mode. The method may be performed at low speeds, where the ability to achieve maximum roll rate is often most challenging (compared to higher speeds, where maximum roll rate is less of an issue and achieving suitable drag performance is a higher priority). It will be understood that any features described with reference to one aspect of the invention are equally applicable to any other aspect of the invention, and vice versa. For example, features described with reference to the aircraft of the first aspect can also be applied to the wings, restraint assemblies, and / or methods of the other aspects of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] Figure 1a shows a top view of an aircraft according to a first embodiment of the present invention;

[0044] Figure 1b Shown Figure 1a an enlarged view of the tip of the wing of the aircraft in FIG;

[0045] Figure 2a Shown Figure 1a A front view of an aircraft with the wingtip device in a flight configuration and a load relief configuration and a ground configuration;

[0046] Figures 2b to 2d Shown Figure 2a A top view of the aircraft, wherein the wingtip device is in a corresponding enlarged view;

[0047] Figure 3 Shows the limiting components and Figure 1a an enlarged view of the tip of a wing of an aircraft;

[0048] Figure 4 Figure 2 shows the time during 1g cruise and maximum gust conditions. Figure 1a a graph showing lift distribution on a wing of an aircraft having the embodiment of the present invention and lift distribution of an equivalent aircraft without the movable wingtip device of the first embodiment during maximum gust conditions;

[0049] Figure 5 Figure 2 shows the time during 1g cruise and maximum gust conditions. Figure 1a a graph of the wing root bending moment of an aircraft having the movable wing tip device of the first embodiment and the wing root bending moment of an equivalent aircraft not having the movable wing tip device of the first embodiment during maximum gust conditions;

[0050] Figure 6 To show Figure 1aGraph showing the performance of the wingtip device in an aircraft during gust conditions and the performance of an equivalent aircraft without the movable wingtip device of the first embodiment.

[0051] Figure 7 Shows an alternative embodiment with a double hinge that allows the wingtip device to rotate up and down. Figure 7a and Figure 7b Show enlarged views of the wingtip device in different configurations respectively. Figure 7a Shows the wingtip device in the flight configuration. Figure 7b Shows the wingtip device in the load alleviation configuration; and

[0052] Figure 8 Is a schematic front view showing the different contributors to the lift distribution along the wingspan of an aircraft of the third embodiment of the present invention. Detailed Description

[0053] Figure 1a Is a top view of an aircraft 1 according to the first embodiment of the present invention. The aircraft includes a central fuselage 3 and two main wings 5 extending outward from respective wing roots 5'.

[0054] Each wing 5 includes a fixed wing 7 extending from the root 5' to the tip 7' (shown in enlarged view in Figure 1b ). At the tip 7' of the fixed wing 7, the wing 5 further includes a movable wingtip device 9 in the form of a flat wingtip extension. The wingtip device 9 is rotatably mounted about a hinge 11 oriented perpendicular to the swept intermediate wing chord axis 13. Thus, the hinge 11 is not parallel to the flight direction line (the flight direction line is shown in Figure 1b for comparison).

[0055] Now referring to Figures 2a to 2d , the wingtip device 9 is capable of rotating from the flight configuration to the load alleviation configuration about the hinge 11.

[0056] In the flight configuration, the wingtip device 9 is an extension of the fixed wing. Thus, the upper and lower surfaces of the fixed wing 7 are continuous with the upper and lower surfaces of the wingtip device 9 (see the lowermost positions in Figure 2b and Figure 2a ). The leading and trailing edges of the fixed wing 5 are also continuous with the corresponding leading and trailing edges of the wingtip device 9 (see Figure 1a and Figure 1b ))。 This arrangement is beneficial as it provides a relatively large wingspan, thus providing an aerodynamically efficient aircraft. However, the relatively large wingspan correspondingly results in a large load on the wing 5, especially a large wing root bending moment, particularly during large load events such as gusts or extreme maneuvers. The wing 5 must be sized to withstand these maximum loads, which results in a relatively heavy wing. In a first embodiment of the present invention, the ability of the wingtip device 9 to move to a load alleviation configuration (see Figure 2a and Figure 2c ) attempts to address this problem.

[0057] As Figure 2c shown in the intermediate position in Figure 2a and

[0058] , the wingtip device 9 is capable of rotating upwards such that the lower surfaces between the fixed wing 7 and the wingtip device 9 are no longer continuous with each other. In addition, since the hinge 11 is angled with respect to the airflow direction, its average inclination angle decreases when the wingtip device 9 rotates upwards. In this configuration, the load generated by the wingtip device 9 on the wing 5 is significantly reduced. The wingtip device 9 is capable of moving to this configuration during flight (which will be described in more detail below). By providing such a load alleviation function during flight, the maximum load for which the wing needs to be designed can be reduced, and thus, the wing 5 can be manufactured relatively lightly. Figure 2d and Figure 2a 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 (shown in the upright position in

[0059] ). The wingtip device can move to this configuration when it is on the ground (which will be described in more detail below). Once rotated to such a position, the wingspan of the aircraft 1 is sufficient to meet the apron compatibility bay restrictions. Thus, although the aircraft 1 of the first embodiment can have a relatively large wingspan during flight (the relatively large wingspan exceeding the bay restrictions), it can still comply with the bay restrictions when located on the ground. Figure 3 Load alleviation using a movable wingtip device is known per se. Providing a movable wingtip device to meet apron compatibility bay restrictions is also known per se. The first embodiment of the present invention combines these two functions in a symbiotic manner. In addition, the first embodiment provides a novel restraint assembly to enable such movement as will now be described with reference to

[0060] Referring to Figure 3 , the aircraft 1 includes a motor 15, and the motor 15 is connected to a drive shaft 18 that forms the axis of the hinge 11. The wingtip device 9 is connected to the shaft 18 by a connecting member 20. The motor 15 is arranged to cause the wingtip device 9 to actuate through the motor 15 to a flight configuration (see Figure 2b) rotates with respect to the ground configuration (see Figure 2d ). This typically occurs immediately after landing to enable the aircraft to comply with airport stand limits. This movement also occurs in the opposite direction before takeoff, once the aircraft leaves the stand.

[0061] When the aircraft is flying and the wingtip device is in the flight configuration, there are often significant forces (usually upwards) on the wingtips. It has been recognized that it is not desirable to actively depress the wingtip device in the flight configuration using the motor 15 by applying a reverse torque; if this method is used, it will generally also be necessary to provide a lock to permanently lock the wingtip device in this flight position during flight.

[0062] In the first embodiment, the motor 15 does not provide a reverse torque. Instead, the motor 15 is in a passive state such that it does not actively contribute to restricting the wingtip device 9 to the flight configuration. The aircraft 1 is alternatively provided with a restricting assembly 17.

[0063] The restricting assembly 17 includes a brake 19, a clutch 21, a rotary spring 23, and a rotary damper 25, and will not be described in more detail.

[0064] The brake 19 includes two pads configured to selectively clamp the shaft 18 to restrict its rotation. The restricting assembly 17 is operable between a restricting mode (in which the brake 19 is deployed to brake the rotation of the shaft 18) and a release mode (in which the brake 19 is released by pulling the pads away from the shaft 18 to allow the shaft 18 to rotate freely (and thus allow the wingtip device 9 to rotate)).

[0065] The default (passive) mode of the restricting assembly 17 is the restricting mode in which the shaft 18 is braked. When the wingtip device 9 is in the flight configuration, the power of the restricting assembly 17 is cut off (i.e., the assembly is passive), and the restricting assembly 17 is in a state where the shaft 18 is braked. This arrangement is attractive because it ensures that an active command (e.g., an ON signal) is required to move the wingtip device.

[0066] The restricting assembly 17 including the brake 19 is controlled by a control module 20 of an electronic flight control system (EFCS). The control module 20 is shown as a box in the Figure 3 schematic diagram.

[0067] The module 20 is configured to receive a measurement of the local angle of attack from an alpha vane (not shown) located on the nose of the aircraft 1. During cruise flight, the restricting assembly 17 is OFF and the brake brakes the shaft 18. However, when the measurement from the alpha detector indicates an oncoming gust (i.e., a significant change in the angle of attack), the control module 20 switches the restricting assembly to ON, thereby releasing the brake 19.

[0068] Although this arrangement enables the wingtip device 9 to be firmly held in the flight configuration during normal cruise flight, by switching the release assembly to ON to release the brake 19, the wingtip device 9 can be quickly moved to the load alleviation configuration. This means that the wing can avoid being subjected to large gust loads. This in turn enables the wing 5 to have a relatively large wingspan without having to incur an associated weight penalty, since the wing can be designed for a lower magnitude of maximum load.

[0069] The wingtip device 9 can move at least partially to the load alleviation configuration only under the action of the aerodynamic forces acting on it during flight or under gust loads. However, in a first embodiment of the present invention, the restraint assembly includes a torsion spring 23 and a damper 25 arranged to assist this movement. The torsion spring 23 and the damper 25 are located at one end of the hinge 11. The torsion spring 23 is preloaded such that when the wingtip device 9 is in the flight configuration, the torsion spring 23 exerts a biasing force that urges the wingtip device 9 towards the load alleviation configuration. This biasing force cannot overcome the restraining force exerted by the brake 19 when it is deployed. However, when the brake 19 is released, the biasing force (along with the aerodynamic forces acting on the wingtip device) is used to rotate the wingtip device 9 about the hinge 11. The torsion spring 23 is sized such that it rotates the wingtip end device 9 by up to approximately 30 degrees of rotation (as Figure 2c shown), but once the wingtip device 9 has rotated beyond approximately 30 degrees, the spring 23 is fully extended and does not urge any further rotation. It has been found advantageous to provide the preloaded spring 23 in this way, since the spring 23 causes the wingtip device 9 to quickly move to the load alleviation configuration as soon as the brake 19 is released.

[0070] The damper 25 is configured to damp the movement of the wingtip device 9 as the wingtip device 9 rotates under the action of the spring 23 (and any aerodynamic forces). This arrangement has been found to be beneficial, especially in cases where the wingtip device 9 is quickly moved to the load alleviation configuration, since the damper 25 tends to attenuate transient, oscillatory movements. The spring-damper system can also help to reduce or eliminate flutter and / or load cycle oscillations.

[0071] The restraint assembly further includes a clutch 21 located on the hinge 11. The clutch 21 is used to selectively engage / disengage the opposite ends of the hinge such that the spring 23 can be selectively chosen to exert a biasing force on the wingtip device 9. This arrangement has been found to be beneficial since it enables the spring 23 to be selectively disengaged to facilitate the maintenance of the wingtip device 9.

[0072] As described above, when the wingtip device 9 is in the flight configuration, the motor 15 is in a passive state such that it does not actively contribute to restricting the wingtip device 9 to the flight configuration (except for the drag caused by rotational inertia). However, when the wingtip device has been moved to the load alleviation configuration, the motor 15 can be activated such that the motor 15 rotates the wingtip device 9 back to the flight configuration and recompresses the spring 23. Once in this position, the restraint assembly is switched back to the restraint mode such that the brake is applied and the motor is returned to its passive state again. Thus, the motor can be used not only to move the wingtip device between the flight configuration and the ground configuration, but also to move the wingtip device from the load alleviation configuration to the flight configuration (but not to move the wingtip device from the flight configuration to the load alleviation configuration).

[0073] Reference will now be made to Figures 4 to 6 explain the advantages of the present invention in terms of wing loading:

[0074] Figure 4 A graph showing the variation of the lift coefficient (Y-axis) of the wingspan (x-axis) of the wing with the wingtip device in the load alleviation configuration during 1g cruise flight and during gusts. For comparison, the graph also shows the variation of the lift coefficient of a conceptual wing with the wingtip device fixed (i.e., the wingtip device effectively remains in the flight configuration) during the gusts.

[0075] Figure 5 A graph showing the variation of the wing bending moment (Y-axis) of the wingspan (x-axis) of the wing with the wingtip device in the load alleviation configuration during 1g cruise flight and during gusts. For comparison, the graph also shows the variation of the wing bending moment of a conceptual wing with a fixed wingtip device (i.e., the wingtip device effectively remains in the flight configuration) during the gusts.

[0076] As can be seen by comparing the performance with the wingtip device in the load alleviation configuration during gusts or the performance with the wingtip device fixed in the flight configuration, load alleviation causes the lift of the wing to be significantly reduced near the tip and on the far side of the wingtip device (the hinge line 11 is marked on the x-axis). This results in a corresponding reduction in the wing bending moment (including the reduction in the wing root bending moment).

[0077] Figure 6 Four sets of data are shown. The top line shows the variation of the alpha value detected by the alpha vane located at the nose of the aircraft with time (x-axis). This can be considered a measure of the magnitude of the gust experienced by the aircraft.

[0078] The second line from the top shows the angle by which the wingtip device is away from the flight configuration when the wingtip device is configured to be in the load alleviation configuration.

[0079] The bottom two lines show the estimated wingtip loads over time for an embodiment (solid bottom line) where the wingtip device moves to a load alleviation configuration during gusts and a conceptual wing (dashed line) where the wingtip device is fixed (i.e., the wingtip device effectively remains in the flight configuration).

[0080] As can be observed, at t = 2, the aircraft encounters an upward gust. This gust exceeds a predetermined threshold magnitude (which is stored in the storage device of control module 20). In response to the gust, restraint assembly 17 is switched from the restraint mode to the release mode. As a result, brake 19 is released from hinge shaft 18, allowing wingtip device 9 to rotate freely upward. Under the action of spring 23 and the aerodynamic forces of the gust, the wingtip device rotates upward about the hinge to a maximum angle at approximately t = 3. Figure 6

[0081] Damper 25 is used to attenuate flutter or other oscillatory motion such that the rotation of the wingtip device stabilizes between t = 3 and t = 8 and assumes a fixed angle of approximately 30 degrees relative to the flight configuration. In this configuration, the upward load experienced by the wingtip is much lower than the upward load that would occur if the wingtip device were fixed (see the bottom two lines of the graph). Although the downward load experienced by the wingtips of the present invention is actually higher than the downward load that a fixed wingtip would experience, this is not a problem because the wing is typically sized to handle the maximum upward load.

[0082] After t = 16, the gust returns below the threshold level. Accordingly, the control system energizes motor 15, which then pulls the wingtip device downward and reloads spring 23. At t = 20, the wingtip device has returned to the flight configuration. Accordingly, control module 20 switches the restraint assembly back to the restraint mode such that hinge shaft 18 is braked and motor 15 is de-energized.

[0083] In an alternative embodiment, as shown in Figure 7 hinge 111 can be a double hinge that allows the wingtip device 109 to rotate both upward to a load alleviation configuration and downward to a load alleviation configuration (only the downward rotation is illustrated in Figure 7b and the upward rotation is as shown in the first embodiment in Figure 2c ). This arrangement alleviates both positive g and negative g loads. Figure 7a shows the wingtip device 109 in the flight configuration with the upper and lower surfaces of the fixed wing 107 being continuous with the upper and lower surfaces of the wingtip device 109.

[0084] In Figure 8 ​Figure 3 schematically shows a third embodiment of the present invention. The third embodiment is the same as the first embodiment except for the features described below. Features corresponding to similar features in the first embodiment of the present invention in the third embodiment of the present invention are denoted by the same reference numerals as in the first embodiment, but with the prefix '2' added (or the prefix '20' added where appropriate).

[0085] Figure 8 Fig. 4 is a schematic front view of an aircraft 201 having a fuselage 203 and wings 205. Each wing 205 has a wingtip device 209 that can move from a flight configuration in which the wingtip device is held in the wing plane to a load mitigation configuration in which the wingtip device moves freely to mitigate the load. The mechanism and control system are the same as those shown in Figure 3 ( Figure 3 for the first embodiment), except that there are no springs and dampers. Thus, when the brakes are released, the wingtip device 209 rotates freely about its hinge line (in a so-called "taxiing" arrangement).

[0086] In the third embodiment, the restraint assembly adopts a release mode during a roll maneuver to mitigate the roll damping effect caused by the wingtips. This can be observed from Figure 8 the following: Line C L -1g represents the 1g flight lift distribution when the restraint assembly is in the restraint mode and the wingtip device is in the flight configuration. Line C L -roll represents the lift distribution when the restraint assembly is in the restraint mode and the wingtip device is in the flight configuration, but the ailerons 210 are actuated in the opposite direction to achieve a roll maneuver. Line C L -aileron represents the lift distribution caused by the ailerons 210. The dash-dot line C L -roll-load-mitigation represents the lift distribution when the restraint assembly is in the release mode and the wingtip device is in the load mitigation configuration. Line C L -roll rate represents the change in the lift coefficient caused by the local roll rate along the wing.

[0087] From the comparison of line C L -roll and C L -roll-load-mitigation, it can be seen that once the tip is in the load mitigation configuration, the outer lift of the ailerons is substantially eliminated. This results in the overall lift distribution being restricted to the inner side, and any roll damping effect from the load on the tip can be largely eliminated.

[0088] In a second embodiment of the present invention, a control module of an electronic flight control system (EFCS) places a restraint assembly in a release mode when it detects that a roll is being performed (e.g., in response to opposite movement of ailerons 210). The control module of the EFCS is also configured to receive signals related to the speed of the aircraft and when the aircraft is at a relatively low speed (e.g., during a climb).

[0089] Although the invention has been described and illustrated with reference to specific embodiments, those of ordinary skill in the art will appreciate that the invention itself has many different variations not specifically set forth herein. By way of example only, in other embodiments (not shown), the wingtip device may include a hydraulic actuator for actuating the wingtip device between a flight configuration and a ground configuration. In such a case, the hydraulic device may also function as a damper when the wingtip device is in a load alleviation configuration.

[0090] If, in the foregoing description, reference has been made to known, obvious or foreseeable equivalents of a whole or an element, such equivalents are incorporated herein as if set forth individually. The true scope of the invention should be determined with reference to the claims, which should be construed to include any such equivalents. The reader will also appreciate that the wholes or features of the invention described as preferred, advantageous, convenient, etc. are optional and do not limit the scope of the independent claims. Further, it will be understood that although these optional wholes or features may be beneficial in some embodiments of the invention, they may not be desirable in other embodiments and may therefore be omitted in other embodiments.

Claims

1. An aircraft, the aircraft comprising a wing having a fixed wing, the fixed wing having a wingtip device movably mounted at the tip of the fixed wing, Among them, the fixed wing having an upper surface and a lower surface, and the wingtip device having an upper surface and a lower surface, and the wingtip device being operable between the following configurations: (i) A flight configuration used during flight, in which the upper surface and the lower surface of the wingtip device are continuous with the upper surface and the lower surface of the fixed wing; and (ii) A load mitigation configuration used during flight for load mitigation, in which the wingtip device moves relative to the fixed wing such that at least one of the upper surface and the lower surface of the wingtip device moves away from the corresponding surface of the fixed wing and the load on the wing is reduced; characterized in that the aircraft comprises a restraint assembly operable between a restraint mode and a release mode, wherein, in the restraint mode, the wingtip device is held in the flight configuration by a restraining force, and in the release mode, the restraining force on the wingtip device is released such that the wingtip device can adopt the load mitigation configuration, and when the restraint assembly is in the release mode, the wingtip device rotates completely freely, wherein the aircraft further comprises a control system configured to control the operation of the restraint assembly between the restraint mode and the release mode; wherein the aircraft further comprises a detector configured to: detect a force on the aircraft, and / or detect a gust encountered by the aircraft, and / or detect a roll maneuver of the aircraft; and wherein the control system is configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to the detected gust exceeding a predetermined threshold, or the detected force exceeding a predetermined threshold, or the detected roll signal indicating that the aircraft is performing a roll maneuver.

2. The aircraft according to claim 1, wherein, The detector includes an alpha detector for detecting the angle of attack of the aircraft relative to the oncoming flow to detect a gust encountered by the aircraft, and wherein the control system is configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to the detected angle of attack exceeding a predetermined threshold.

3. The aircraft according to claim 2, wherein, The alpha detector is located at the nose of the aircraft such that the alpha detector is upstream of the wingtip device.

4. The aircraft according to any one of claims 1 to 3, wherein, The control system is further configured to switch the operation of the restraint assembly from the restraint mode to the release mode in response to an input indicating that the aircraft is in a landing phase and / or a takeoff phase.

5. The aircraft according to any one of claims 1 to 3, wherein, The aircraft includes a corresponding fixed wing, wingtip device, and restraint assembly on the other side of the fuselage of the aircraft, And wherein, the control system is further configured to switch an operation of the other restraint component from the restraint mode to the release mode in response to an input indicating that one of the restraint components has been switched to the release mode.

6. The aircraft according to any one of claims 1 to 3, wherein, The wingtip device is further operable to: (iii) A ground configuration used during ground-based operation, in which the wingtip device moves away from the flight configuration such that the wingspan of the wing of the aircraft is reduced.

7. The aircraft according to claim 6, wherein, The aircraft includes an actuator configured to move the wingtip device between the flight configuration and the ground configuration.

8. The aircraft according to claim 7, wherein, The actuator is further configured to move the wingtip device back from the load mitigation configuration to the flight configuration.

9. The aircraft according to claim 7, wherein, When the restraint component is in the restraint mode, the actuator is in a passive state such that the actuator does not actively contribute to the restraint force.

10. The aircraft according to any one of claims 1 to 3, wherein, The wingtip device is rotatably mounted on a hinge located at the tip end of the wing such that the wingtip device can rotate about the hinge between the flight configuration and the load mitigation configuration.

11. The aircraft according to claim 10, wherein, The hinge is oriented not parallel to the flight direction line.

12. The aircraft according to claim 11, wherein, The hinge is oriented substantially perpendicular to the swept mean chord axis of the wing.

13. The aircraft according to claim 10, wherein, The hinge is a double hinge to allow the wingtip device to rotate upward and downward.

14. An aircraft wing, the aircraft wing being used as the wing of an aircraft according to any one of claims 1-13, the wing including a fixed wing having a wingtip device movably mounted at the tip end of the fixed wing, Among them, 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 operable between the following configurations: (i) A flight configuration used during flight, in which the upper surface and the lower surface of the wingtip device are continuous with the upper surface and the lower surface of the fixed wing; and (ii) A load mitigation configuration used for load mitigation during flight, in which the wingtip device moves relative to the fixed wing such that at least one of the upper surface and the lower surface of the wingtip device moves away from the corresponding surface of the fixed wing and the load on the wing is reduced; Characterized in that The wing includes a restraint component operable between a restraint mode and a release mode, wherein, in the restraint mode, the wingtip device is held in the flight configuration by a restraint force, and in the release mode, the restraint force on the wingtip device is released such that the wingtip device can adopt the load mitigation configuration, and When the restraint component is in the release mode, the wingtip device is completely free to rotate.

15. A restraint component, the restraint component being used as the restraint component of the aircraft according to any one of claims 1-13, the restraint component being arranged to be mounted on the aircraft wing and capable of operating between a restraint mode and a release mode, wherein, In the restraint mode, the wingtip device is held in the flight configuration by a restraint force, and in the release mode, the restraint force on the wingtip device is released such that the wingtip device is completely free to rotate and the wingtip device can adopt the load mitigation configuration.

16. A method for controlling load alleviation on a wing with a fixed wing of an aircraft, the fixed wing having a wingtip device movably mounted at the tip of the fixed wing, The method includes the following steps: (a) Holding the wingtip device in a flight configuration with a restraining force, in which the upper and lower surfaces of the wingtip device are continuous with the upper and lower surfaces of the fixed wing; and (b) Releasing the restraining force to allow the wingtip device to adopt a load alleviation configuration for load alleviation during flight, in which the wingtip device rotates completely freely and moves relative to the fixed wing, such 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, Among them, The method further includes the following steps: Detecting a force on the aircraft and / or detecting a gust encountered by the aircraft and / or detecting a roll maneuver of the aircraft; and Releasing the restraining force in response to the detected force exceeding a predetermined threshold, or the detected gust exceeding a predetermined threshold, or the detected roll signal indicating that the aircraft is performing a roll maneuver, to allow the wingtip device to adopt the load alleviation configuration.

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