Aircraft wing, aircraft comprising such a wing and method of reducing aeroelastic flutter in a wing

Abstract

The present disclosure provides an aircraft wing, an aircraft including the same, and a method of reducing aeroelastic flutter in a wing tip, the aircraft wing including a fixed wing (402) having a gull-shaped wing tip (404) rotatably mounted at the tip of the fixed wing, the gull-shaped wing tip (404) extends below a wing plane defined by the end of the fixed wing (402) such that the center of gravity of the gull-shaped wing tip (404) lies below the wing plane. It has been found that the center of gravity of the gull-shaped wing tip (404) is lowered to reduce the occurrence of flutter. The gull-shaped wing tip (404) may be gull-shaped about its articulation axis (406) intersecting the fixed wing (402), or may be otherwise folded or bent to lower the center of gravity of the gull-shaped wing tip (404).

Description

Technical Field

[0001] The present disclosure relates to an aircraft wing including a movable wing tip.

[0002] The present disclosure also relates to an aircraft including a wing with a movable wing tip, a wing tip for use in such an aircraft wing, and a method of reducing aeroelastic flutter. Background Art

[0003] Aircraft with movable wing tips are known. The wing tip can be moved from a flight configuration, in which the wing tip contributes to the lift generated by the wing but also contributes to the forces experienced by the wing inboard of the wing tip, to a load relief configuration, in which the wing tip does not contribute to the loads experienced by the wing inboard of the wing tip. The wing tip is typically moved to the load relief configuration in response to a high load event, such as caused by a gust of wind or a particular aircraft maneuver. In certain circumstances, such a wing tip may experience flutter, which is undesirable.

[0004] WO2017118832 and GB2546246 disclose a device in which the wing tip can move between such a flight configuration and a load mitigation configuration. Flutter is mitigated by providing a biasing member, a damper or selecting a suitable hinge orientation. It has been found that using these methods to mitigate flutter has some disadvantages. For example, springs and dampers may limit the ability of the wing tip to rotate freely, and the hinge orientation is determined in the design stage and is therefore difficult to adjust in a timely manner once it has been set.

[0005] GB2584668 also discloses a device in which the wing tip can move between such a flight configuration and a load relief configuration. In this case, the polar moment of inertia of the wing tip is increased by arranging a balancing mass to alleviate flutter.

[0006] The present invention may solve the above problems.Alternatively or additionally, the present invention seeks to provide an improved aircraft wing with a movable wing tip. Summary of the invention

[0007] According to a first aspect of the invention, there is provided an aircraft wing, the wing comprising: a fixed wing; and a wing tip, the wing tip being mounted at the end of the fixed wing; wherein the wing tip is rotatable relative to the fixed wing about a hinge axis, the wing being operable between: (i) a flight configuration for use during flight, in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight, in which the wing tip is allowed to rotate about the hinge axis towards an equilibrium position under the action of aerodynamic forces applied to the wing tip during flight, so that loads on the wing are reduced. The end of the fixed wing defines a wing plane, and in the flight configuration, the wing tip extends below the wing plane so that the center of gravity of the wing tip is located below the wing plane.

[0008] In the load relief configuration, the equilibrium position of the wing tip - otherwise known as the glide angle - may be arranged at a non-zero angle relative to the fixed wing. In some flight scenarios, it has been observed that there may be a relatively early onset of flutter, which is undesirable. It has now been discovered that by reducing the magnitude of the relative angle, the center of gravity of the wing tip relative to the fixed wing is lowered, thereby reducing the likelihood of flutter occurring (i.e. increasing the flutter speed). Accordingly, aspects of the present invention recognize that it may be beneficial to provide a wing tip that is tilted downwardly, thereby lowering the center of gravity and reducing the likelihood of flutter occurring.

[0009] Unless otherwise stated, the glide angle is measured directly through the hinge axis (i.e., in close proximity to the hinge axis). For example, the glide angle may be measured between a wing plane and a plane containing the root of the wing tip. The plane containing the root of the wing tip may contain a root chord line of the root of the wing tip. Alternatively or additionally, the plane containing the root of the wing tip may contain a second chord line of the wing tip, the second chord line being located outside the root at a distance along the span of the wing tip. The second chord line may optionally be located at least 1%, optionally at least 5%, optionally at least 15% along the length of the wing tip. Typically, the length of the wing tip is measured along the 1 / 4 chord line.

[0010] The end of the fixed wing defines a wing plane. It will be appreciated that the wing plane can therefore maintain an anhedral or dihedral angle of a portion of the fixed wing close to the end of the fixed wing. Therefore, in various embodiments of the present invention, the wing tip can effectively have a lower center of gravity than the case where the wing tip is only an in-plane extension of the fixed wing outside the hinge axis. The wing plane may contain a tip chord line at the end of the fixed wing. Alternatively or additionally, the wing plane may contain a second chord line of the fixed wing, which is located at a distance along the span of the fixed wing inside the end of the fixed wing. The second chord line may optionally be located at least 1% of the length of the fixed wing, optionally at least 5%, optionally at least 15%, optionally at least 25%. In some embodiments, for example, in the case where the fixed wing is generally a plane, the second position may be at least 50% and optionally 100% of the length of the fixed wing. Typically, the length of the fixed wing is measured along the 1 / 4 chord line.

[0011] The wing plane may be substantially parallel to the top or bottom surface of the fixed wing at the end of the fixed wing. More preferably, the wing plane includes the chord line of the fixed wing. The center of gravity of the wing tip may be vertically spaced downward from the wing plane by optionally at least 0.05 m, optionally at least 0.1 m, optionally at least 0.5 m, optionally at least 1 m, and optionally at least 2 m. The spacing may be measured from a position vertically aligned with the center of gravity of the wing tip.

[0012] The fixed wing may have an upper surface and a lower surface, and the wing tip may have an upper surface and a lower surface. In the flight configuration, the upper surface and the lower surface of the wing tip may be a continuation of the upper surface and the lower surface of the fixed wing. In the flight configuration, the trailing edge of the wing tip may be a continuation of the trailing edge of the fixed wing. The leading edge of the wing tip may be a continuation of the leading edge of the fixed wing. There may be a smooth transition from the fixed wing to the wing tip. It will be understood that even when the shape of the wing is such that there is a change in sweep or twist at the junction between the fixed wing and the wing tip, there may be a smooth transition. There may be no discontinuity at the junction between the fixed wing and the wing tip. The position of the wing tip when the wing is in the flight configuration may be referred to as the flight position of the wing tip.

[0013] In the load mitigation configuration, the wing tip may be movable relative to the fixed wing such that at least one of an upper surface and a lower surface of the wing tip moves away from a corresponding surface of the fixed wing.

[0014] In the load relief configuration, no bending moment may be transferred from the wing tip to the fixed wing. For example, the wing can be operated to enter the load relief configuration when the wing experiences a flight condition such as high winds or a particular aircraft maneuver that may exert a large lift on the wing tip that would cause a correspondingly large bending moment to be transferred to the fixed wing if the wing was not in the load relief configuration.

[0015] According to various aspects of the invention, the extension of the wing tip below the wing plane may be achieved in a number of alternative or complementary arrangements, as will be described below. These arrangements attempt to increase the airspeed at which flutter occurs.

[0016] In the flight configuration, a portion of the wing tip may gull downwardly about the gull axis relative to the wing plane.

[0017] In this way, the center of gravity of the wing tip can be lowered due to the geometry of the wing tip. The skilled person will be familiar with the "gullification" of wings (also known as "gull-shaped" wings or the like). It will be understood that gull-shaped downward means tilted downward relative to the plane of the wing. In other words, the gullification when defined in the flight configuration can be presented in the following way: part or all of the wing tip presents a downward angle relative to the fixed wing. The gull shape can be between 5 degrees and 20 degrees, such as between 7.5 degrees and 12.5 degrees, such as between 9 degrees and 11 degrees, such as about 10 degrees. The gull-shaped wing tip can also help to reduce the dihedral effect of the wing, otherwise known as C lβ , which can be defined as the amount of rolling moment generated being proportional to the amount of sideslip. This may be more advantageous for wings with higher aspect ratios - the ratio of the wing's span to its average chord.

[0018] A wing tip that is gull-shaped downward at an angle of dihedral in the flight configuration may still exhibit an angle of dihedral relative to the fixed wing in the load relief configuration (due to the wing tip rotating upward about the hinge axis relative to the fixed wing under the action of aerodynamic forces exerted on the wing tip during flight).

[0019] The articulation axis is preferably oriented non-parallel to the longitudinal axis of the aircraft. The articulation axis is preferably oriented non-parallel to a line in the direction of flight. The articulation axis is preferably oriented so that the articulation axis intersects the wing in the trailing edge region inboard of where the articulation axis intersects the wing in the leading edge region. In embodiments, the articulation axis may intersect the trailing edge and / or the leading edge of the wing (e.g. when viewed from above).

[0020] The gull axis is preferably oriented non-parallel to the longitudinal axis of the aircraft. The gull axis is preferably oriented non-parallel to a line in the direction of flight. The gull axis is preferably oriented so that the gull axis intersects the wing in the trailing edge region inboard of where the gull axis intersects the wing in the leading edge region. In embodiments, the gull axis may intersect the trailing edge and / or the leading edge of the wing (e.g. when viewed from above).

[0021] The hinge axis may lie in a vertical first plane, wherein the first plane intersects the trailing edge of the wing and the leading edge of the wing. Preferably, the hinge axis is oriented so that the first plane intersects the trailing edge of the wing inboard of where the first plane intersects the leading edge of the wing.

[0022] The gull axis may lie in a vertical first plane, wherein the first plane intersects the trailing edge of the wing and the leading edge of the wing. Preferably, the gull axis is oriented so that the first plane intersects the trailing edge of the wing inboard of where the first plane intersects the leading edge of the wing.

[0023] The hinge axis is preferably oriented so that the average angle of attack of the wing tip changes as the wing tip rotates about the hinge axis. More preferably, the hinge axis is oriented so that the average angle of attack of the wing tip decreases as the wing tip rotates away from the flight configuration.

[0024] The hinge axis may be oriented substantially perpendicular to the swept mean chord axis of the wing. The swept mean chord axis may be parallel to the longitudinal direction of the wing box. The orientation of the hinge axis may be selected so that the direction of the airflow over the wing in the wing tip region remains non-parallel to the hinge axis during flight. The orientation of the hinge axis may be selected so that for a given direction of the wing tip, the airflow direction remains incident on the same side of the wing tip despite the yaw of the aircraft.

[0025] The angle between the articulation axis and the longitudinal axis of the aircraft may be referred to as the "deployment angle". The deployment angle may be between 10 and 20 degrees. An example deployment angle is 17 degrees. The deployed axis of rotation may refer to an axis of rotation of the wing tip that is not parallel to the longitudinal axis of the aircraft.

[0026] The rotation of the wing tip about the hinge axis may be referred to as flapping of the wing tip. The hinge axis may be a flapping axis.

[0027] The gull axis may be parallel to the articulation axis, and more preferably is coaxial with the articulation axis.

[0028] In the flight configuration, the wing tip may present a nose-down twist relative to the end of the fixed wing. This arrangement may be particularly advantageous in an arrangement in which the gull axis is parallel to the hinge axis or more preferably coaxial with the hinge axis, and in which the hinge axis is oriented so that the average angle of attack of the wing tip decreases as the wing tip rotates upward away from the flight configuration. A wing tip presenting a nose-down twist may present a reduced angle of attack relative to the fixed wing, thereby resulting in a loss of lift. This loss of lift may be compensated by the wing tip being gull-shaped downward relative to the wing plane. In a preferred embodiment of the invention, the size of the nose-down twist and the size of the gull are complementary, so that there is substantially no net change in lift relative to an arrangement without a gull and twist. The nose-down twist may be a geometric twist. The nose-down twist of the wing tip may be between 1 and 5 degrees, for example between 2 and 3 degrees, for example 2.5 degrees. In some embodiments, the nose-down twist may be an aerodynamic twist rather than a geometric twist.

[0029] In this arrangement, the wing tip tends to present a lower glide angle / equilibrium position (compared to a non-gull-shaped / non-twisted wing tip) in a load-mitigated configuration. It has been found that this reduction in glide angle is associated with an increase in flutter speed. In some embodiments, a nose-down twist can be introduced at the hinge axis and extend over a portion or all of the wing tip. In other embodiments, a nose-down twist can be introduced close to the outside of the hinge axis and extend over a portion or most of the wing tip. Introducing a nose-down twist close to the outside of the hinge axis (but not at the hinge axis) may be beneficial because the resulting geometry tends to mean that greater aerodynamic forces are required to move the wing tip to a high glide angle, such as greater than 70 degrees, or even up to 90 degrees. This can reduce the load on any stopper used to prevent movement beyond a high glide angle, and thus reduce the size of any stopper. In some embodiments, the gull axis can be located outside the hinge axis.

[0030] Gull-shapeding the wing tip about a gull axis outboard of the hinge axis may facilitate structural simplification of the wing tip in the region adjacent the hinge axis.

[0031] The gull axis may be parallel to the articulation axis. In some embodiments, the gull axis may be parallel to the flight line. The orientation of the gull axis may depend on the location of the gull axis. For example, once it has been decided to position the gull axis outside the articulation axis, it is often beneficial to orient the gull axis parallel to the flight line because the size of the gull portion has become independent of the glide angle measured directly through the articulation axis.

[0032] The wing tip may present an abrupt change in inclination substantially at the gull axis. Folding the wing tip at the gull axis may simplify the structure of the wing tip.

[0033] The wing tip may be curved. Curving the wing tip may allow for better control of the degree of gullification of the wing tip over the span. Curving the wing tip may reduce or avoid the need for joints on the wing tip. The curvature of the wing tip is preferably in a direction out of the plane of the wing, such as a curvature of the wing tip at an anhedral angle.

[0034] The wing tip may include a downwing. The downwing may enable a reduction in the span of the aircraft wing and improve gate clearance when the wing tip is in the flight configuration compared to a gull-shaped portion on a large portion of the wing tip.

[0035] The wing may be provided with a restraint assembly for preventing the wing tip from moving from the flight configuration to the load relief configuration. The restraint assembly is operable between a restraint mode, in which a restraining force is used to hold the wing tip in the flight configuration, and a release mode, in which the restraining force on the wing tip is released so that the wing tip can adopt the load relief configuration. Such a restraint assembly is described in GB2546246. The restraint assembly may incorporate any of the features of the restraint assembly described in GB2546246, the contents of which are incorporated herein.

[0036] Optionally, the wing may be provided with an actuator for moving the wing tip from the load relief configuration to the flight configuration.

[0037] The wing tip is operable to a ground configuration in which the wing tip moves away from the flight configuration such that the span of the aircraft wing is reduced. Optionally, the wing includes an actuator for moving the wing tip to the ground configuration. The actuator may be used to move the wing tip from the load relief configuration to the flight configuration.

[0038] The angle of rotation of the wing tip between the load relief configuration and the ground configuration may optionally be at least 10 degrees, optionally at least 20 degrees, optionally at least 30 degrees, optionally at least 45 degrees, optionally at least 60 degrees, and optionally up to 90 degrees. The angle will depend on the aerodynamic forces exerted on the wing tip during flight.

[0039] The wing tip length defined along the midpoint of the wing can be optionally at least 10%, optionally at least 15%, optionally at least 20%, optionally at least 25%, optionally at least 30%, optionally at least 35%, and optionally at least 40% of the wing length.

[0040] The length of the wing tip defined along the midpoint of the wing may be no more than 60%, optionally no more than 50%, optionally no more than 40%, and optionally no more than 30% of the wing length.

[0041] The wing tip length defined along the midpoint of the wing may optionally be at least 1.0 m, optionally at least 2.5 m, optionally at least 3.0 m, optionally at least 4.0 m, optionally at least 5.0 m, optionally at least 6.0 m, optionally at least 7.0 m, and optionally at least 20.0 m.

[0042] The wing tip length defined along the midpoint of the wing may be no more than 20.0 m, optionally no more than 15.0 m, optionally no more than 10.0 m, optionally no more than 8.0 m, optionally no more than 7.0 m, optionally no more than 6.0 m, and optionally no more than 5.0 m.

[0043] The length of the wing from root to tip measured along the midpoint of the wing (particularly, but not limited to, a twin-engine aircraft) may be at least 5 m, optionally at least 15 m, optionally at least 20 m, optionally at least 25 m, optionally at least 30 m, optionally at least 35 m, optionally at least 40 m, optionally at least 45 m, and optionally at least 60 m. It is envisaged that the aircraft wing of the present invention may facilitate the use of a longer and optionally larger area movable wing tip.

[0044] The aircraft wing may be for use in an aircraft optionally having an operational empty weight of at least 20,000 kg, optionally at least 25,000 kg, optionally at least 30,000 kg, optionally at least 40,000 kg, optionally at least 100,000 kg, and optionally at least 300,000 kg.

[0045] As mentioned above, the wing can be optionally operated to enter and leave (iii) ground configuration, which is used for the aircraft to operate on the ground. In the ground configuration, the wing tip is positioned away from the flight configuration so that the wingspan of the aircraft wing is reduced. For example, if the wing tip can be operated to enter the ground configuration, the rotation angle of the wing tip around the hinge axis between the flight configuration and the ground configuration is optionally at least 60 degrees, optionally at least 80 degrees, optionally at least 90 degrees and optionally at least 110 degrees. In the first configuration, the wingspan can exceed the airport compatibility gate limit. In the ground configuration, the wingspan is reduced to make the wingspan (wherein the wing tip is in the ground configuration) less than or substantially equal to the airport compatibility gate limit. In the ground configuration, the wing tip can be positioned so that the wing has the shortest wingspan. In the ground configuration, the wing tip can be oriented to be substantially vertical. The wing tip may be moved from a flight configuration or a load relief configuration to a ground configuration by rotating the wing about the hinge axis. The position of the wing tip when the wing is in the ground configuration may be referred to as the ground position.

[0046] In the ground configuration, if the wing tip comprises an upper surface and a lower surface, at least one of the upper surface and the lower surface of the wing tip is optionally moved further away from a corresponding surface of the fixed wing than when the wing is in the load relief configuration. The effective length of the wing is reduced in the ground configuration compared to when the wing is in the flight configuration and in the load relief configuration.

[0047] The wing tip may be a wing tip extension; for example, the wing tip may be a planar tip extension. In other embodiments, the wing tip may include or consist of a non-planar device, such as a winglet.

[0048] According to a second aspect of the present invention, there is provided an aircraft comprising a wing according to the first aspect.

[0049] According to a third aspect of the invention there is provided a method of reducing aeroelastic flutter in a wing tip which is attached at the end of a fixed wing for rotational movement, the method comprising providing a wing tip which extends below a wing plane defined by the end of the fixed wing, whereby the centre of gravity of the wing tip is lowered a first distance below the wing plane, the first distance being defined when the wing tip forms an extension of the fixed wing.

[0050] The method may include those features described above in relation to the aircraft wing of the first aspect of the invention.

[0051] According to a fourth aspect of the invention, there is provided an aircraft wing, the wing comprising: a fixed wing; and a wing tip mounted at the end of the fixed wing; wherein the wing tip is rotatable relative to the fixed wing about a hinge axis, the wing being operable between: (i) a flight configuration for use during flight, in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight, in which the wing tip is allowed to rotate about the hinge axis towards an equilibrium position under the action of aerodynamic forces applied to the wing tip during flight, so that the load on the wing is reduced; wherein, in the flight configuration, the wing tip is gull-shaped downward relative to the fixed wing, so that flutter is reduced in the flight configuration and / or the load relief configuration.

[0052] According to a fifth aspect of the invention, there is provided an aircraft wing, the wing comprising: a fixed wing; and a wing tip mounted at the end of the fixed wing; wherein the wing tip is rotatable relative to the fixed wing about a hinge axis, the wing being operable between: (i) a flight configuration for use during flight, in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight, in which the wing tip is allowed to rotate about the hinge axis toward an equilibrium position under the action of aerodynamic forces applied to the wing tip during flight, so that the load on the wing is reduced; wherein, in both the flight configuration and the load relief configuration, a portion of the wing tip is arranged at an angle of dihedral or anhedral different from that of the fixed wing.

[0053] Of course, it will be appreciated that features described with respect to one aspect of the invention may be incorporated into other aspects of the invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings in which:

[0055] Figure 1 A front view of a known aircraft is shown;

[0056] Figure 2 The wing tip is shown in the flight configuration. Figure 1 A plan view of the aircraft;

[0057] Figure 3 Shows Figure 1 A close-up schematic diagram of the wing tip of an aircraft;

[0058] Figure 4 An example of an embodiment of an aircraft having a gull-shaped wing tip is shown;

[0059] Figure 5 shows a graph demonstrating the effect of gull-forming a wing tip on the glide angle / equilibrium position of the gull-shaped wing tip;

[0060] Figure 6 An example of an embodiment of an aircraft having a wing tip that is gull-shaped outboard of the hinge axis is shown;

[0061] Figure 7 An example of an implementation of an aircraft having a curved wing tip is shown; and

[0062] Figure 8 An example of an implementation of an aircraft having a wing tip with a downdraft is shown. DETAILED DESCRIPTION

[0063] exist Figures 1 to 3 An example of a known aircraft is shown in FIG. The aircraft is generally indicated by reference numeral 100 and comprises two aircraft wings 200, 300. Each wing 200, 300 comprises a fixed wing 201, 301 and a wing tip 202, 302 mounted at the end of the fixed wing 201, 301. Each wing tip 202, 302 is rotatable relative to the respective fixed wing 201, 301 about a hinge axis 205, 305. Figure 1 , each wing 200, 300 is capable of operating between: (i) a flight configuration (FC) for use during flight, in which the wing tip 202, 302 forms an extension of the fixed wing 201, 301; and (ii) a load relief configuration (LAC) for load relief during flight, in which the wing tip 202, 302 is allowed to rotate about the hinge axis 205, 305 towards an equilibrium position under the action of aerodynamic forces applied to the wing tip 202, 302 during flight, so that the load on the wing 200, 300 is reduced.

[0064] Lowering the center of gravity of the wing tip has been considered desirable in order to reduce the wing tip flapping frequency relative to the wing bending frequency, thereby reducing aeroelastic flutter, particularly when the wing tip is in a lightened state.

[0065] Those skilled in the art will be familiar with aeroelastic flutter, see, for example, https: / / en.wikipedia.org / wiki / Aeroelasticity#Flutter .

[0066] As described above, each wing 200, 300 is operable between a flight configuration FC and a load relief configuration LAC. In the flight configuration FC, each wing tip 202, 302 is a continuation of the fixed wing 201, 301, and each wing tip 202, 302 is effectively rigidly coupled to the respective fixed wing 201, 301, so that any lift generated by the wing tip 202, 302 during flight exerts a bending moment on the wing. In certain flight-related events (e.g., gusts of wind or when the aircraft performs certain maneuvers), the lift and associated bending moment generated by the wing tip 202, 302 may become undesirably large, and in such circumstances, the wing 200, 300 is operable to a load relief state (LAC), in which the wing tip is allowed to rotate about the hinge axis towards a balance position under the action of aerodynamic forces exerted on the wing tip during flight, so that the load on the wing is reduced. Operation into the load relief configuration LAC is discussed below.

[0067] Each wing 200, 300 is provided with a restraint assembly 350 operable to allow the wing tip 201, 301 to rotate about the hinge axis 205, 305. Examples of restraint assemblies are described in detail in WO2017118832 and GB2546246, and for convenience, an example is also described here.

[0068] Reference Figure 3 , the aircraft 100 is provided with a restraint assembly 350. The restraint assembly 350 includes a brake 351 and a clutch 352, and will now be described in more detail.

[0069] Brake 351 includes two pads configured to selectively clamp against shaft 342 to limit rotation of shaft 342. Limiting assembly 350 is operable between a limiting mode in which brake 351 is deployed to brake rotation of shaft 342 and a release mode in which brake 351 is released by pulling the pads away from shaft 342 to allow free rotation of shaft 342 (and thus rotation of wing tip 302).

[0070] The default (passive) mode of the restraint assembly 350 is a restraint mode in which the shaft 342 is braked. When the wing tip 302 is in the flight configuration, the power to the restraint assembly 350 is switched OFF (i.e., the assembly is passive) and the restraint assembly 350 is in a state in which the shaft 342 is braked. This arrangement is attractive because it ensures that an active command (e.g., an ON signal) is required to move the wing tip device.

[0071] The restraint assembly 350 including the brake 351 is controlled by a control module 343 of an electronic flight control system (EFCS). The control module 343 Figure 3 It is shown as a box-shaped object in the schematic diagram of .

[0072] Module 343 is configured to receive measurements of the local angle of attack from an alpha vane (not shown) on the nose of aircraft 100. During cruise flight, limiter assembly 350 is OFF, and brake 351 brakes shaft 342. However, when measurements from the alpha detector indicate an oncoming gust (i.e., a significant change in the angle of attack), control module 343 switches limiter assembly ON, which releases brake 351.

[0073] This arrangement enables the wing tip 302 to be securely held in the flight configuration during normal cruise flight, but by releasing the brake 351 by switching the release assembly to ON, the wing tip 302 can be quickly moved to the load relief configuration. This means that the wing can be protected from high gust loads. This in turn enables the wing 300 to have a relatively large wingspan without having to incur an associated weight penalty, as the wing can be designed for a lower magnitude of maximum loads.

[0074] The wing tip 302 is at least partially movable to the load relief configuration only under the influence of aerodynamic forces acting thereon during flight or under gust loads.

[0075] The restraint assembly also includes a clutch 352 located on the hinge 305. The clutch 352 is used to selectively engage / disengage with the opposite end of the hinge 305. This arrangement has been found to be beneficial because the clutch 352 enables undesired movement of the wing tip 302 to be prevented in the event of a malfunction of the restraint assembly 350.

[0076] The aircraft 100 also includes a motor 341. When the wing 300 is in the flight configuration FC, the motor 15 is in a passive state so that it does not actively contribute to restraining the wing tip 302 in the flight configuration (other than the drag due to rotational inertia). However, when the wing tip 302 has moved to the load relief configuration LAC, the motor 341 can be enabled so that the motor 341 rotates the wing tip 302 back to the flight configuration FC. Once in this position, the restraint assembly 350 is switched back to the restraint mode so that the brake 351 is applied and the motor 341 is again returned to its passive state. Thus, the motor 341 is used to move the wing tip 302 between the flight configuration and the load relief configuration.

[0077] The wing 300 is also operable to a ground configuration GC in which the wingspan of the aircraft 100 is reduced so that the aircraft can comply with airport gate restrictions. The motor 341 is arranged to rotate the wing tip 302 between the flight configuration FC and the ground configuration by actuation of the motor 341 .

[0078] Of note is the orientation of the articulation axes 205, 305. Each of the axes 205, 305 is aligned with the longitudinal axis of the aircraft and the longitudinal axis of the aircraft. Figure 2 The wing tip is oriented at an angle of about 17 degrees to the flight direction indicated by "F" in FIG. The flight direction F corresponds to the longitudinal axis of the aircraft 100. This so-called "deployment" of the articulation axis away from the flight direction F means that the average angle of attack of the wing tip changes when the wing tip device rotates about the articulation axis. The articulation axis is oriented so that the average angle of attack of the wing tip decreases as the wing tip device rotates away from the flight configuration.

[0079] Now only reference Figures 4 to 8 Examples of aircraft wings and aircraft according to embodiments of the invention are described by way of example.

[0080] exist Figure 4 , a front view of an aircraft is shown, which is similar to the examples discussed previously and may include Figures 1 to 3 The aircraft has a fixed wing 402, wherein a gull-shaped wing tip 404 is mounted at the end of the fixed wing 402, and the gull-shaped wing tip 404 can rotate relative to the fixed wing 402 about a hinge axis 406. The hinge axis 406 is referenced Figures 1 to 3 404 is 'deployed' in the manner shown in FIG. 404 and is not directly on the flight line. However, for simplicity, the change in angle of the gull-shaped wing tip 404 is shown from the perspective of the flight line, and the change in orientation of the upper and lower surfaces of the wing tip is not shown. For clarity, only one wing of the aircraft is shown.

[0081] The flight configuration (FC) and load alleviation configuration (LAC) of the non-gull wing tip according to the previous example are shown in thin lines, which reflect the style of the fixed wing. The gull wing tip 404 according to an embodiment of the present invention is shown in a gull flight configuration (GLAC) and a gull load alleviation configuration (GLAC) in thicker lines.

[0082] Overlying the fixed wing 402 and extending outside the root of the fixed wing 402 is a wing plane 405, which is shown in dashed lines with a white outline. The wing plane 405 substantially follows the same dihedral angle as the fixed wing 402, which is generally planar in the example shown. It will be appreciated that in other embodiments where the fixed wing 402 has a variable dihedral angle, the wing plane 405 may follow an angle of the outer portion of the fixed wing 402, for example the outer 10%.

[0083] To lower the center of gravity of the wing tip in both configurations, the wing tip gulls downward relative to the wing plane 405 to form a gull-shaped wing tip 404 having a gull-shaped flight configuration (GFC) and a gull-shaped load alleviation configuration (GLAC), which is shown as a wide rectangular line extending outward from the hinge axis 406. The gull-shaped flight configuration (GFC) and the gull-shaped load alleviation configuration (GLAC) are both rotated downward (clockwise) by a fixed angle relative to the corresponding flight configuration (FC) and load alleviation configuration (LAC). In this way, the gull-shaped wing tip 404 not only continues the upper angle of the fixed wing (402) in the gull-shaped flight configuration (GFC), but also forms a downward angle relative to the end of the fixed wing 402. In this case, the gull-shaped portion of the gull-shaped wing tip 404 is located at and about the hinge axis 406 (ie the gull-shaped axis and the hinge axis are coaxial), and thus the gull-shaped wing tip 404 itself has a generally planar form.

[0084] Figure 4 A graph is shown above the aircraft 400 in FIG. The x-axis of the graph represents the span of the aircraft wing and is aligned horizontally with the aircraft wing to represent a particular point along the span of the wing. The y-axis of the graph represents the twist of the aircraft wing and intersects the x-axis at a twist value of zero. The graph will be described from the minimum x-axis value to the maximum x-axis value, thereby following the span of the wing from its root to its tip.

[0085] Solid line 406 schematically illustrates the relationship between span and twist for a known aircraft wing, i.e., a wing tip that exhibits a normal flight configuration (FC) without a gull-shaped wing tip 404. Solid line 406 has a positive twist value, i.e., nose-up twist, at a minimum x-axis value near the root of the aircraft wing. The first portion of solid line 406 has a negative gradient to indicate that the twist of the aircraft wing changes from a positive value (nose up) to a negative value (nose down) at approximately 25% of the wing span. At this point, the twist of the aircraft wing reaches its lowest (i.e., negative maximum, nose down) value. From this point on, solid line 406 has a positive gradient to indicate that the fixed wing 402 and the wing tip then exhibit a gradual twist change, from a more severe nose-down twist to a slight nose-down twist at the maximum span near the end of the wing tip. There is no discernible gradient change at a point on the graph horizontally aligned with the hinge axis 406, indicating that this change in twist is substantially continuous across the transition between the fixed wing 402 and the wing tip.

[0086] Also shown in the graph is a dashed line 408, which represents the different torsional characteristics exhibited by the gull wing tip 404 in an embodiment of the present invention. At an x-axis point directly aligned with the hinge axis 406, the dashed line 408 has a substantially vertical portion that represents an abrupt change in torsion at the hinge axis 406 at the transition between the fixed wing 402 and the gull wing tip 404. The dashed line 408 then reflects the gradual positive gradient of the solid line 406, indicating that the gull wing tip 404 also exhibits a gradual change in torsion, from a more severe downward twist to a slight downward twist at the maximum span near the end of the gull wing tip 404. At the maximum span along the x-axis, the dashed line 408 is vertically displaced downward from the solid line 406. This y-axis displacement indicates that the gull wing tip 404 exhibits an increased nose-down twist compared to the wing tip in the known arrangement.

[0087] Importantly, in the first embodiment of the invention, the change in the magnitude of the nose-down twist (i.e., the reduction in the effective angle of attack) is complementary to the magnitude of the gullwing (i.e., the increase in the effective angle of attack due to the deployed orientation of the articulation / gull axis) such that there is essentially no net change in lift of 1 g relative to an arrangement without gullwing and twist. This means that the glide angle / equilibrium position of the wing tip in the load-mitigated configuration becomes lower (compared to the non-twisted / non-gullwing wing tip of the prior art). Thus, and with reference to Figure 5 , the arrangement of the first embodiment thus provides improved flutter performance while minimizing changes in lift distribution.

[0088] Figure 5A graph demonstrating the effect of gull-forming the gull wing tip 404 on the glide angle / equilibrium position of the gull wing tip 404 is shown. The x-axis of the graph represents the aircraft airspeed, while the y-axis represents the tuck angle of the gull wing tip 404 at the hinge axis (i.e., the relative angle between the fixed wing 402 and the gull wing tip 404). The dashed line 500 in the form of an open simple upward curve represents the flutter velocity trajectory. In other words, the dashed line 500 shows the tuck angle of the gull wing tip 404 that is experiencing flutter as a function of airspeed.

[0089] A solid line 502 in the form of an open simple upward curve represents the tuck angle employed in the load mitigation configuration as a function of the aircraft airspeed for a non-gull wing tip. Vertically displaced downward from the solid line 502 is a dash-dot line 504 representing the tuck angle employed in the load mitigation configuration as a function of the aircraft airspeed for a gull wing tip 404 according to the first embodiment of the invention. The solid line 502 intersects the dashed line 500 at two points 506, 508 because the dashed line 500 exhibits a greater curvature than the solid line 502. For all tuck angles in the airspeed window between the two points 506, 508 for a given wing tip, the wing tip may be susceptible to flutter.

[0090] Since the dotted line 504 (showing the behavior of the gull wing tip 404 of the first embodiment of the present invention) is vertically displaced downward from the solid line 502, the dotted line 504 does not intersect the dashed line 500. This illustrates how flutter is mitigated for the gull wing tip 404 over a conventional airspeed range. This can be the case in both the gull flight configuration (GFC) and the gull load alleviation configuration (GLAC). It will be appreciated that for other load factors from handling or gusts, there will be similar relationships to those shown in the graph.

[0091] This behavior is believed to be due to the center of gravity of the gull-shaped wing tip being lowered, for example moved below the plane of the fixed wing in the flight configuration. In a first embodiment of the invention, this is achieved by gull-shaped wing tips about an axis coaxial with the hinge line. However, other embodiments of the invention may achieve this effect in different ways, as will now be described with reference to Figures 5 to 8 Give a description.

[0092] Figure 6 Another example of an aircraft having a gull-shaped wing tip 404 is shown. In this case, the gull-shaped wing tip 404 is gull-shaped about a gull axis 410, such as Figure 4, gull axis 410 is not coaxial with hinge axis 406, but is located outside hinge axis 406. In other words, gull wing tip 404 gulls downward at a point along the span of wing tip 404 outside hinge axis 406. In this example, the glide angle / equilibrium position of gull wing tip 404 directly through hinge axis 406 (i.e., the portion of the wing tip inboard of gull axis 410) is not substantially affected because that portion of the wing tip remains planar with the wing plane in the flight configuration. In this sense, in Figure 5 There is a fixed behavior of the flap angle versus speed in the graph of . However, the center of gravity of the gull tip 404 is still lowered by the gull tip, and this changes the flutter speed trajectory, causing it to Figure 5 , and thus increase the vibration speed.

[0093] Figure 7 Another embodiment of an aircraft having a gull-shaped wing tip 404 is shown. In this case, the gull-shaped wing tip 404 is gull-shaped by curvature of the gull-shaped wing tip 404. The illustrated curve is substantially constant over the length of the gull-shaped wing tip 404, but other curves are also contemplated. In this example, the glide angle / equilibrium position of the gull-shaped wing tip 404 directly through the hinge axis 406 (i.e., in the immediate vicinity of the hinge axis) is substantially unaffected, and the center of gravity of the gull-shaped wing tip 404 is still lowered due to the curvature.

[0094] Figure 8 Another embodiment of an aircraft having a gull-shaped wing tip 404 is shown. In this case, the gull-shaped wing tip 404 is gull-shaped by providing a downwing at the end of the gull-shaped wing tip 404. In other words, the gull-shaped wing tip 404 includes an abrupt change in inclination at about 60% of its span, and the outboard portion of the gull-shaped wing tip 404 gulls downward. In this example, the glide angle / equilibrium position of the gull-shaped wing tip 404 directly through the hinge axis 406 (i.e., inboard of the downwing) is substantially unaffected, and the center of gravity of the gull-shaped wing tip 404 is still lowered due to the downwing.

[0095] Although the present invention has been described and illustrated with reference to specific embodiments, it will be appreciated by those skilled in the art that the invention lends itself to many different variations not specifically described herein. Some possible variations will now be described by way of example only.

[0096] The above about Figures 1 to 3 The examples of aircraft described describe wing tips that are movable to a load relief configuration and a ground configuration. Those skilled in the art will recognize that an aircraft may have wing tips that are movable from a flight configuration to a load relief only configuration.

[0097] Where reference is made in the foregoing description to wholes or elements that have known, obvious or foreseeable equivalents, such equivalents are incorporated herein as if set forth individually. Reference should be made to the claims to determine the true scope of the invention, which should be interpreted as including any such equivalents. The reader will also understand that wholes or features of the invention described as preferred, advantageous, convenient, etc. are optional and do not limit the scope of the independent claims. Furthermore, it will be understood that such optional wholes or features, while potentially beneficial in some embodiments of the invention, may be undesirable and therefore may not be present in other embodiments.

Claims

1. An aircraft wing, the wing comprising: Fixed wing, and a wing tip mounted at the end of the fixed wing; in, The wing tip is rotatable relative to the fixed wing about a hinge axis, The wing is capable of operating between: (i) a flight configuration for use during flight in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight in which the wing tip is allowed to rotate about the hinge axis towards an equilibrium position under the effect of aerodynamic forces acting on the wing tip during flight, so that loads on the wing are reduced; wherein the end of the fixed wing defines a wing plane, and wherein, in the flight configuration, the wing tip extends below the wing plane such that the center of gravity of the wing tip is located below the wing plane.

2. The aircraft wing according to claim 1, wherein: In the flight configuration, a portion of the wing tip gulls downwardly about a gull axis relative to the wing plane.

3. The aircraft wing according to claim 1, wherein: In the flight configuration, the wing tip exhibits a nose-down twist relative to the end of the fixed wing.

4. An aircraft wing according to claim 2 or claim 3, wherein: The gull axis is coaxial with the hinge axis.

5. An aircraft wing according to claim 2 or claim 3, wherein: The gull axis is located outside the hinge axis.

6. The aircraft wing according to claim 5, wherein: The wing tip exhibits an abrupt change in inclination substantially at the gull axis.

7. The aircraft wing according to claim 1, wherein: The wing tip is curved.

8. The aircraft wing according to claim 1, wherein: The wing tip includes a downlink wing.

9. The aircraft wing according to claim 1, wherein: The wing is provided with a restraint assembly for preventing the wing tip from moving from the flight configuration to the load relief configuration.

10. An aircraft wing according to claim 9, wherein: The restraint assembly is operable between a restraint mode, in which a restraining force is used to hold the wing tip in the flight configuration, and a release mode, in which the restraining force on the wing tip is released so that the wing tip can adopt the load relief configuration.

11. The aircraft wing of claim 1, wherein: The articulation axis is non-parallel to the longitudinal axis of the aircraft.

12. An aircraft wing according to claim 1, capable of being operated to enter and exit (iii) a ground configuration for the aircraft to operate on the ground, in which the wing tip is positioned away from the flight configuration so that the wingspan of the aircraft wing is reduced.

13. An aircraft comprising the wing according to claim 1.

14. A method of reducing aeroelastic flutter in a wing tip attached at the end of a fixed wing for rotational movement, the method comprising providing a wing tip extending below a wing plane defined by the end of the fixed wing, whereby the centre of gravity of the wing tip is lowered a first distance below the wing plane, the first distance being defined when the wing tip forms an extension of the fixed wing.

15. An aircraft wing, the wing comprising: Fixed wing, and a wing tip mounted at the end of the fixed wing; in, The wing tip is rotatable relative to the fixed wing about a hinge axis, The wing is capable of operating between: (i) a flight configuration for use during flight in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight in which the wing tip is allowed to rotate about the hinge axis towards an equilibrium position under the effect of aerodynamic forces acting on the wing tip during flight, so that loads on the wing are reduced; Therein, in the flight configuration, the wing tip is gull-shaped downward relative to the fixed wing, so that flutter is reduced in the flight configuration and / or the load relief configuration.

16. An aircraft wing, the wing comprising: Fixed wing, and a wing tip mounted at the end of the fixed wing; in, The wing tip is rotatable relative to the fixed wing about a hinge axis, The wing is capable of operating between: (i) a flight configuration for use during flight in which the wing tip forms an extension of the fixed wing; and (ii) a load relief configuration for load relief during flight in which the wing tip is allowed to rotate about the hinge axis towards an equilibrium position under the effect of aerodynamic forces acting on the wing tip during flight, so that loads on the wing are reduced; wherein, in both the flight configuration and the load relief configuration, a portion of the wing tip is arranged at an anhedral angle or dihedral angle that is different from an anhedral angle or dihedral angle of the fixed wing.

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