Wing assembly

Abstract

A wing assembly (1) for an aircraft. The wing assembly (1) comprises a wing (11), a tendon (12) coupled to the wing (11) to transform vibrations of the wing (11) into axial displacement of the tendon (12), and a vibration control unit, VCU, (13) coupled to the tendon (12). The VCU (13) comprises an input element, coupled to the tendon (12) to transform axial displacement of the tendon (12) into rotation of the input element, and at least one rotary damping element configured to be coupled to the input element. The VCU (13) is proximal the root (14) of the wing (11).

Description

[0001] WING ASSEMBLY

[0002] TECHNICAL FIELD

[0003] The present invention relates to a wing assembly for an aircraft, a method of designing a wing assembly for an aircraft, and a method of manufacturing a wing assembly of an aircraft.

[0004] BACKGROUND

[0005] Many structures are subject to vibration in use. There is a need to dampen vibrations in structures to avoid damage and potential structural failure. Slender structures such as high-rise buildings, antennae, masts, and wind turbine blades, are particularly susceptible to vibrations.

[0006] Developments in the design of aircraft wings have led to wings taking the form of a slender structure. For example, traditional aircraft may comprise a fuel tank housed within a wing, but as alternative propulsion means are developed, there is not always a requirement for a wing to house a fuel tank. As such, the wing can be made thinner to enhance aerodynamic efficiency. This results in a slender wing which is more susceptible to potentially damaging vibrations. Traditional methods of controlling vibrations in aircraft wings may not be suitable for slender wings.

[0007] There is therefore a need to control vibrations in slender structures such as slender wings for aircraft.

[0008] SUMMARY

[0009] A first aspect provides a wing assembly for an aircraft. The wing assembly comprises a wing, a tendon coupled to the wing, and a vibration control unit configured to be coupled to the tendon.

[0010] The vibration control unit is preferably proximal to the root of the wing. The vibration control unit may be closer to the root of the wing than the tip of the wing. The vibration control unit may be adjacent the root of the wing. The vibration control unit may be mounted to the wing. The vibration control unit may be mounted on or in the wing. The wing may comprise a box wing and the vibration control unit may be arranged within an internal volume of the box wing. The vibration control unit may be spaced apart fromthe root of the wing in a direction extending from the tip of the wing towards the root of the wing.

[0011] The wing may be a slender wing or a high aspect ratio wing. The wing may have an aspect ratio of greater than 9, 10, 12, 15, 20, 25, 30, or 35, or within a range between any two of these values. The wing may not be configured to house a fuel tank.

[0012] Some wings, in particular, slender wings, may not be suitable for locating vibration control means, such as dampers, on the wing itself. Such wings may not have the space or structural integrity for supporting such vibration control means. The arrangement of the tendon and vibration control unit of the first aspect advantageously provides control of vibrations of the wing without a requirement for locating vibration control means on or inside the wing itself.

[0013] The tendon may be elastic. The tendon may be formed from Kevlar or any other suitable material. The tendon may comprise a cross -section having a diameter or a maximum dimension in the range of 20-90mm, 30-80mm, 40-70mm, 50-60mm, 52-58mm, or 54-56mm. The tendon may comprise a length at least 500, 600, 700, 800, 900, or 1000 times the diameter or maximum dimension of the cross-section of the tendon. The diameter or maximum dimension of the cross -section of the tendon may be substantially constant along the length of the tendon. It will be appreciated that the dimensions of the tendon may vary depending on the application of the vibration control system.

[0014] The tendon may be coupled to the wing to transform vibrations of the wing into motion of the tendon. The motion of the tendon may comprise axial displacement of the tendon. The axial displacement of the tendon may comprise a change in length of the tendon. The axial displacement of the tendon may comprise oscillating axial displacement of the tendon. The tendon may be fixed to the wing at a first location along the span of the wing. The first location may be at the tip of the wing. The first location may be between the tip and the root of the wing. The first location may be adjacent the tip of the wing. The first location may be closer to the tip of the wing than the root of the wing. An end of the tendon may be fixed to the wing at the first location. The tendon may extend between the first location and the root of the wing.The tendon may comprise a first end and a second end. The first end may be fixed to the wing at the first location. The second end may be fixed to the wing at the first location. The first end and the second end may be fixed to a common fixing point at the first location. The second end may be fixed to the wing at a second location. The second end may be fixed at a second fixing point at the second location. The second location may be adjacent the first location. The first location and the second location may be at the same span-wise position of the wing. The second location may be at the tip of the wing. The second location may be between the tip and the root of the wing. The second location may be adjacent the tip of the wing. The second location may be closer to the tip of the wing than the root of the wing. The tendon may extend from the first end of the tendon to the vibration and control unit and from the vibration control unit to the second end of the tendon.

[0015] In use, the vibration control unit may be mounted to the fuselage of an aircraft comprising the wing assembly or any other suitable mounting location on an aircraft comprising the wing assembly. In other examples, the wing assembly may comprise a mounting structure and the vibration control unit may be mounted to the mounting structure. The wing may be arranged to allow vibration of the wing relative to the mounting structure.

[0016] The vibration control unit may comprise an input element configured to be coupled to the tendon to transform movement of the tendon into movement of the input element. The movement of the tendon may comprise oscillating movement of the tendon and the movement of the input element may comprise oscillating movement of the input element. The vibration control unit may comprise at least one damping element configured to be coupled to the input element. The at least one damping element may comprise at least one of: a moveable mass, an elastic element, and a damper.

[0017] The moveable mass may be configured to be coupled to the input element to transform motion of the input element into motion of the moveable mass. The moveable mass may be configured to be coupled to the input element to resist acceleration of the input element. As described herein, a moveable mass may be substituted with an inerter. The at least one damping element may comprise both a moveable mass and an inerter.The elastic element may be configured to be coupled to the input element to absorb kinetic energy of the input element. The elastic element may be configured to be coupled to the input element to resist displacement of the input element.

[0018] The damper may be configured to be coupled to the input element to resist motion of the input element. The damper may be configured to be coupled to the input element to dissipate kinetic energy of the input element.

[0019] The input element may be coupled to the tendon by means of friction between the input element and the tendon. In other examples, the tendon may be fixed to the input element by a fastening means, such as an adhesive, mechanical fastening, or any other suitable fastening means.

[0020] The at least one damping element may comprise a mass-damper comprising a moveable mass and a damper coupled to the moveable mass. The damper may be coupled to the moveable mass to resist movement of the moveable mass. The damper may be coupled to the moveable mass to dissipate kinetic energy of the moveable mass.

[0021] The at least one damping element may comprise a spring-mass comprising a moveable mass and an elastic element coupled to the moveable mass. The elastic element may be coupled to the moveable mass to absorb kinetic energy of the moveable mass. The at least one damping element may comprise a spring -damper comprising a damper and an elastic element coupled to the damper.

[0022] The at least one damping element may comprise a spring-mass-damper comprising a moveable mass, an elastic element coupled to the moveable mass, and a damper coupled to the moveable mass. In some examples of the spring-mass-damper, the elastic element and the damper may be arranged in parallel. In other examples, the moveable mass, the elastic element, and the damper may be arranged in series. The damper may be coupled to the moveable mass to resist movement of the moveable mass. The damper may be coupled to the moveable mass to dissipate kinetic energy of the moveable mass. The elastic element may be coupled to the moveable mass to absorb kinetic energy of the moveable mass. The mass-damper and / or the spring -mass-damper may be realised as a tuned mass damper. The moveable mass, the elastic element, and / or the damper of the mass-damper, the spring-mass, and / or the spring-mass-damper, as applicable, may beconfigured to be coupled to the input element, where applicable, in the same manner as the moveable mass, the elastic element, and the damper as described above.

[0023] In any of the examples described herein, the tendon may act as a spring in a system comprising the at least one damping element of the vibration control unit. For example, where the at least one damping element comprises a mass-damper, the tendon may act as a spring to provide a spring -mass-damper, wherein the spring of the spring -massdamper is provided by the tendon and the moveable mass and damper of the spring -mass-damper are provided by the mass-damper of the at least one damping element. In another example, where the at least one damping element comprises an elastic element, the tendon may act as an additional spring to provide two springs arranged in series or in parallel, wherein one of the two springs is provided by the tendon and the other of the two springs is provided by the elastic element of the at least one damping element.

[0024] The input element may be coupled to the tendon to transform movement of the tendon, i.e., where applicable, axial displacement of the tendon, into rotation of the input element. The rotation of the input element may comprise oscillating rotation of the input element. The at least one damping element may comprise at least one rotary damping element. The at least one rotary damping element may comprise a rotary mass. The rotary mass may be configured to be coupled to the input element to transform rotation of the input element into rotation of the rotary mass. The rotary mass may be configured to be coupled to the input element to resist angular acceleration of the input element. As described herein, a rotary mass may be substituted with a rotary inerter. The at least one rotary damping element may comprise both a rotary mass and a rotary inerter. Where present, the rotary inerter may comprise a planetary gear inerter.

[0025] The at least one rotary damping element may comprise a rotary elastic element. The rotary elastic element may be configured to be coupled to the input element to absorb rotational energy of the input element. The rotary elastic element may be configured to be coupled to the input element to resist angular displacement of the input element.

[0026] The at least one rotary damping element may comprise a rotary damper. The rotary damper may be configured to be coupled to the input element to resist rotation of the input element. The rotary damper may be configured to be coupled to the input element to dissipate rotational energy of the input element.The at least one damping element may be tuned to dampen one or more vibration modes of the wing. The one or more vibration modes may comprise the first bending mode and / or the first torsion mode of the wing. The one or more vibration modes may comprise a vibration mode dominated by the first bending mode of the wing and / or a vibration mode dominated by the first torsion mode of the wing. The one or more vibration modes may comprise a pair of coupled vibration modes of the wing. The pair of coupled vibration modes may comprise a bending mode and a torsion mode. The pair of coupled vibration modes may comprise a first vibration mode dominated by a bending mode and a second vibration mode dominated by a torsion mode. The pair of coupled vibration modes may be activated by wing flutter. The one or more vibration modes may comprise the first two bending modes of the wing. The one or more vibration modes may comprise a first vibration mode dominated by the first bending mode of the wing and a second vibration mode dominated by the second bending mode of the wing. The first two bending modes of the wing may be activated by wind gusts.

[0027] The at least one damping element may comprise a single degree -of-freedom system tuned to dampen one or more vibration modes of the wing. The at least one damping element may comprise a two degree -of-freedom system tuned to dampen one or more vibration modes of the wing. The at least one damping element may comprise a multi degree-of-freedom system tuned to dampen one, two or more vibration modes of the wing. At least one of a mass of the moveable mass or rotary mass, a stiffness of the elastic element or rotary elastic element, a damping coefficient of the damper or rotary damper, and any other applicable property of any other damping element described herein may be selected to dampen one or more vibration modes of the wing. The one or more vibration modes of the wing may comprise a single vibration mode, two vibration modes, or more than two vibration modes of the wing.

[0028] The input element may comprise a pulley. The pulley may comprise a sheave. In other examples, the input element may comprise a belt or chain drive mechanism, or any other component or mechanism configured to transform motion of the tendon, i.e., where applicable, axial displacement of the tendon, into rotation.

[0029] The at least one rotary damping element may comprise a rotary mass -damper comprising a rotary mass and a rotary damper coupled to the rotary mass. The rotary damper maybe coupled to the rotary mass to resist rotation of the rotary mass. The rotary damper may be coupled to the rotary mass to dissipate rotational energy of the rotary mass.

[0030] The at least one rotary damping element may comprise a rotary spring -mass comprising a rotary mass and a rotary elastic element coupled to the rotary mass. The rotary elastic element may be coupled to the rotary mass to absorb rotational energy of the moveable mass. The at least one rotary damping element may comprise a rotary spring -damper comprising a rotary damper and a rotary elastic element coupled to the rotary damper.

[0031] The at least one rotary damping element may comprise a rotary spring -mass-damper comprising a rotary mass, a rotary elastic element coupled to the rotary mass, and a rotary damper coupled to the rotary mass. In some examples of the rotary spring-mass-damper, the rotary elastic element and the rotary damper may be arranged in parallel. In other examples, the rotary mass, the rotary elastic element, and the rotary damper may be arranged in series. The rotary damper may be coupled to the rotary mass to resist rotation of the rotary mass. The rotary damper may be coupled to the rotary mass to dissipate rotational energy of the rotary mass. The rotary elastic element may be coupled to the rotary mass to absorb rotational energy of the rotary mass. The at least one rotary damping element can be realised as a visco-elastic multi-modal system, one degree-of-freedom system, two degree-of-freedom system or multi degree-of-freedom system. The rotary mass-damper and / or the rotary spring-mass-damper may be realised as a rotary tuned mass damper.

[0032] The rotary mass, the rotary elastic element, and / or the rotary damper of the rotary mass-damper, the rotary spring-mass, and / or the rotary spring -mass-damper, as applicable, may be configured to be coupled to the input element, where applicable, in the same manner as the rotary mass, the rotary elastic element, and the rotary damper as described above.

[0033] The rotary mass of any example described herein may comprise a mass, such as a disc, wheel or bar, configured to rotate about an axis of rotation. The mass may be distributed radially from the axis of rotation. The mass may be distributed about the axis of rotation. The mass may be distributed over more than 180 degrees about the axis of rotation. The mass may be distributed over 360 degrees about the axis of rotation. The mass may be distributed radially from the axis of rotation over more than 180 degrees about the axisof rotation. The mass may be distributed radially from the axis of rotation over 360 degrees about the axis of rotation. The mass may be distributed to substantially maximise the mass moment of inertia of the rotary mass.

[0034] Rotation of the rotary mass may be unconstrained. The rotary mass may be configured to rotate freely through 360 degrees or more about the axis of rotation. The rotary mass may comprise a flywheel. The flywheel may comprise a tungsten composite material.

[0035] The rotary elastic element of any example described herein may comprise a torsion bar, a torsion spring, a flexible coupling, or any other suitable rotary elastic element. Examples of suitable flexible coupling elements are a spider coupling, a jaw coupling, a Bibby coupling, or a bush coupling. The rotary damper of any example described herein may comprise a torsional damper, such as a torsional elastomeric damper, a viscous damper, a fluid damper, a flexible coupling, such as a flexible coupling as described above with built-in damping, or any other suitable damper. Where present, the rotary mass-damper or the rotary spring -mass-damper may comprise a rotary mass partially or fully submerged in a damping fluid such that the damping fluid resists rotation of the rotary mass. The damping fluid may comprise any suitable viscous fluid.

[0036] The use of at least one rotary damping element as described above advantageously helps to minimise the volume of the vibration control unit. For example, a moveable mass configured to move along a linear path requires space not only for the moveable mass itself but also space to allow the moveable mass to move along the linear path. In contrast, a rotary mass comprising a mass configured to rotate about an axis of rotation only requires space for the mass itself.

[0037] The vibration control unit may comprise at least one clutch or brake. The vibration control unit may comprise at least one transmission. The at least one damping element may be at least one first damping element and the vibration control unit may comprise at least one second damping element. The vibration control unit may comprise any number and combination of clutches, brakes, transmissions, and damping elements, as described herein. This advantageously provides a vibration control unit which is adaptable to different operational scenarios involving vibration of the wing, for example under different flight conditions or regimes in use.The vibration control unit may comprise at least one clutch arranged between the input element and the at least one damping element. The or each clutch may be operable in an engaged state to couple the at least one damping element to the input element and a disengaged state to decouple the at least one damping element from the input element. The vibration control unit may be operable in an active state and an inactive state. The or each clutch may be in the engaged state when the vibration control unit is in the active state. The or each clutch may be in the disengaged state when the vibration control unit is in the inactive state.

[0038] The at least one clutch may be configured to vary a magnitude of force transmitted from the input element to the at least one damping element. Where applicable, the or each clutch may be configured to vary a magnitude of torque transmitted from the input element to the at least one rotary damping element. This may be achieved through slipping and / or partially engaging the or each clutch. Advantageously, this may enable the damping effect provided by the at least one damping element to be varied.

[0039] The vibration control unit may comprise at least one transmission. The transmission may comprise an input and an output. The input element may be configured to be coupled to the input of the transmission. The output of the transmission may be configured to be coupled to the at least one damping element. As such, the at least one damping element may be configured to be coupled to the input element via the transmission. The transmission may be configured to transmit force from the input element to the at least one damping element. Where applicable, the transmission may be configured to transmit torque from the input element to the at least one rotary damping element.

[0040] The transmission may be configured to increase a speed of motion of the output of the transmission relative to a speed of motion of the input of the transmission. Where applicable, the transmission may be configured to increase a speed of rotation of the output of the transmission relative to a speed of rotation of the input of the transmission.

[0041] Where present, the moveable mass, the elastic element, or the damper may be configured to be coupled to the output of the transmission. The moveable mass may be configured to be coupled to the output of the transmission to transform motion of the output of the transmission into motion of the moveable mass and / or resist acceleration of the outputof the transmission. The elastic element may be configured to be coupled to the output of the transmission to absorb kinetic energy of the output of the transmission and / or resist displacement of the output of the transmission. The damper may be configured to be coupled to the output of the transmission to resist movement of the output of the transmission and / or dissipate kinetic energy of the output of the transmission. The moveable mass, the elastic element, and / or the damper of the mass -damper, the springmass, and / or the spring -mass-damper, as applicable, may be configured to be coupled to the output of the transmission stage in the same manner.

[0042] The transmission provides the effect of amplifying vibrations of the wing before they are transmitted to the at least one damping element. Amplifying the vibrations of the wing by means of the transmission means that the volume and mass of the moveable mass, elastic element, and / or damper can be reduced compared to if the transmission was not present. The transmission therefore advantageously helps to minimise the volume and mass of the vibration control unit.

[0043] Where present, the rotary mass, the rotary elastic element, or the rotary damper may be configured to be coupled to the output of the transmission. The rotary mass may be configured to be coupled to the output of the transmission to transform motion of the output of the transmission into motion of the rotary mass and / or resist acceleration of the output of the transmission. The rotary elastic element may be configured to be coupled to the output of the transmission to absorb rotational energy of the output of the transmission and / or resist displacement of the output of the transmission. The rotary damper may be configured to be coupled to the output of the transmission to resist rotation of the output of the transmission and / or dissipate kinetic energy of the output of the transmission. The rotary mass, the rotary elastic element, and / or the rotary damper of the rotary mass-damper, the rotary spring-mass, and / or the rotary springmass-damper, as applicable, may be configured to be coupled to the output of the transmission in the same manner.

[0044] The transmission may comprise a gear train. The gear train may comprise a planetary gear train. The use of a planetary gear train advantageously helps to minimise the volume of the vibration control unit. In other examples, the transmission may comprise a spur gear transmission, a hydraulic transmission, an electromagnetic transmission, a continuously variable transmission, or any other suitable transmission.The vibration control unit may comprise a plurality of transmissions. The plurality of transmissions may comprise a plurality of gear trains coupled in series. For example, the transmission may comprise a first gear train and a second gear train. An output of the first gear train may be coupled to an input of the second gear train. An input of the first gear train may be configured to be coupled to the input element. An output of the second gear train may be configured to be coupled to the at least one damping element. The transmission may further comprise at least one intermediate gear train. An input of the or each intermediate geartrain may be coupled to an output of an adjacent geartrain. An output of the or each intermediate gear train may be coupled to an input of an adjacent gear train. At least one of the first gear train, the second gear train, and the at least one intermediate gear trains may comprise a planetary gear train.

[0045] The use of two or more gear trains coupled in series as described above may advantageously increase the amplifying effect of the transmission stage, thereby further helping to minimise the mass and volume of the at least one damping element and therefore the vibration control unit as a whole.

[0046] The at least one clutch arranged between the input element and the at least one damping element may comprise a clutch arranged between the input element and the input of the transmission. The clutch may be operable in an engaged state to couple the input e lement to the input of the transmission and a disengaged state to decouple the input element from the input of the transmission. The clutch may be configured to vary a magnitude of force transmitted from the input element to the transmission. The clutch may be configured to vary a magnitude of torque transmitted from the input element to the transmission. This may be achieved through slipping and / or partially engaging the clutch.

[0047] The at least one clutch arranged between the input element and the at least one damping element may comprise a clutch arranged between the output of the transmission and the at least one rotary damping element. The clutch may be operable in an engaged stat e to couple the at least one damping element to the output of the transmission and a disengaged state to decouple the at least one damping element from the output of the transmission The clutch may be configured to vary a magnitude of force transmitted from the output element of the transmission to the at least one damping element. The clutch may be configured to vary a magnitude of torque transmitted from the outputelement of the transmission to the at least one damping element. This may be achieved through slipping and / or partially engaging the clutch.

[0048] The at least one damping element may be at least one first damping element. The vibration control unit may comprise at least one second damping element. The at least one second damping element may comprise at least one second rotary damping element. The at least one second rotary damping element may comprise one or more of a rotary mass, a rotary elastic element, or a rotary damper, as described herein.

[0049] The at least one second damping element may be configured to be coupled to the input element. The at least one second damping element may be configured to be coupled to the input element via the at least one first damping element. The at least one first damping element and the at least one second damping element may be configured to be independently coupled to the input element. For example, the at least one first damping element may comprise a first rotary mass and the at least one second damping element may comprise a second rotary mass. The first rotary mass may be configured to be coupled to the input element via a first drive shaft. The second rotary mass may be configured to be coupled to the input element via a second drive shaft. The second drive shaft may be a hollow drive shaft. The first drive shaft may be arranged to extend through the hollow drive shaft.

[0050] The vibration control unit may comprise at least one clutch arranged between the at least one second damping element and the input element. The or each clutch may be operable in an engaged state to couple the at least one second damping element to the input element and a disengaged state to decouple the at least one second damping element from the input element. The or each clutch may be configured to vary a magnitude of force transmitted from the input element to the at least one second damping element. Where applicable, the or each clutch may be configured to vary a magnitude of torque transmitted from the input element to the at least one second rotary damping element. This may be achieved through slipping and / or partially engaging the or each clutch.

[0051] In examples comprising the transmission, the at least one second damping element may be configured to be coupled to the output of the transmission. The vibration control unit may comprise at least one clutch arranged between the at least one second dampingelement and the output of the transmission. The or each clutch may be operable in an engaged state to couple the at least one second damping element to the output of the transmission and a disengaged state to decouple the at least one second damping element from the output of the transmission. The or each clutch may be configured to vary a magnitude of force transmitted from the output of the transmission to the at least one second damping element. Where applicable, the or each clutch may be configured to vary a magnitude of torque transmitted from the output of the transmission to the at least one second rotary damping element. This may be achieved through slipping and / or partially engaging the or each clutch.

[0052] The at least one second damping element may be configured to be coupled to the at least one first damping element. The vibration control unit may comprise at least one clutch arranged between the at least one first damping element and the at least one second damping element. The or each clutch may be operable in an engaged state to couple the at least one first damping element to the at least one second damping element of the transmission and a disengaged state to decouple the at least one first damping element from the at least one second damping element. The or each clutch may be configured to vary a magnitude of force transmitted from the at least one first damping element to the at least one second damping element. Where applicable, the or each clutch may be configured to vary a magnitude of torque transmitted from the at least one first damping element to the at least one second rotary damping element. This may be achieved through slipping and / or partially engaging the or each clutch.

[0053] The vibration control unit may comprise at least one transmission arranged between the at least one first damping element and the at least one second damping element in a manner described herein.

[0054] In some examples, the at least one first damping element may comprise a first moveable mass. The at least one second damping element may comprise a second moveable mass. The at least one damping element may comprise an elastic element coupling the first moveable mass and the second moveable mass together. The elastic element may couple the first moveable mass and the second moveable mass together to absorb kinetic energy of each of the first moveable mass and the second. The first moveable mass may comprise a first rotary mass. The second moveable mass may comprise a second rotary mass. The elastic element may comprise a rotary elastic element, such as a torsion bar.In this example, or in any other example described herein, the input element may comprise a hollow pulley and the first rotary mass may be configured to be coupled to a first axial end of the hollow pulley. The torsion bar may extend through the hollow pulley, from the first axial end of the hollow pulley, and beyond a second axial end of the pulley, opposite the first axial end. This may advantageously provide a compact vibration control unit. The hollow pulley may comprise a sheave.

[0055] The at least one first damping element and the at least one second damping element may be configured to dampen different vibrations of the wing. The at least one first damping element and the at least one second damping element may together form a tuneable dynamic system that can interact with multiple different vibrations of the wing simultaneously. The different vibrations may differ in at least one of: vibration mode, frequency, wavelength, amplitude, duration, and any other vibration property.

[0056] The different vibrations of the wing may comprise vibrations caused by flutter, discrete gusts, series of gusts, or shock. Vibrations of the wing caused by flutter, gusts, and shock may differ in mode, frequency, and duration. For example, vibrations caused by flutter are characterised by a pair of coupled modes comprising a first vibration mode dominated by a bending mode and a second vibration mode dominated by a torsion mode. Vibrations caused by gusts are typically characterised by a first vibration mode dominated by the first bending mode of the wing and a second vibration mode dominated by the second bending mode of the wing. Flutter and gusts may both occur during flight. Flutter is an aeroelastic dynamic instability that will be understood by persons skilled in the art and gusts are characterised as at least one sudden or repetitive change in wind speed and / or direction. The frequency of vibrations caused by flutter and vibrations caused by gusts may be different. Shock is a transient excitation of the wing and may occur, for example, during landing as landing forces are transmitted to the wing.

[0057] In some examples, the at least one damping element may be configured to provide damping of vibrations caused by flutter and / or gusts. The at least one damping element may be configured to provide damping of critical vibrations caused by flutter and / or gusts. In contrast, the at least one damping element may be configured to provide a gradually increasing amount of damping in response to shock in order to initially absorb energy rapidly before gradually dissipating the energy in the at least one damping element without returning or reflecting the energy back to the wing.The vibration control unit may comprise at least one brake configured to selectively resist movement of the input element and / or the or each moveable mass. This may provide further adaptability of the vibration control unit to different flight conditions.

[0058] The wing assembly may comprise a controller. The controller may be configured to control any or all of the clutches described above to switch the or each clutch between the respective engaged and disengaged states and / or control the or each clutch to vary the magnitude of transmitted force or torque as described above. The controller may be configured to control the or each clutch to switch the vibration control unit between the active state and the inactive state. The controller may be configured to control the or each clutch to vary the magnitude of transmitted force or torque in dependence on different vibrations of the wing as described herein. The controller may be configured to control the or each brake to selectively resist movement of the input element and / or the or each moveable mass. The controller may be configured to control the or each brake to selectively resist movement of the input element and / or the or each moveable mass in dependence on different vibrations of the wing as described herein.

[0059] Where the vibration control unit comprises at least one first damping element and at least one second damping element each configured to dampen different vibrations of the wing, the controller may be configured to control the at least one clutch arranged between the input element and the at least one first damping element, the at least one clutch arranged between the input element and the at least one second damping element, and / or the at least one clutch arranged between the at least one first damping element and the at least one second element to switch between the respective engaged and disengaged states in dependence on the different vibrations of the wing. In this way, the vibration control unit can be adapted to provide different damping in dependence on different vibrations of the wing, for example during different flight conditions.

[0060] In one example, the at least one first damping element may comprise a moveable mass and the at least one second damping element may comprise a damper. The vibration control unit may be operable in a first configuration in which the or each clutch arranged between the input element and the rotary mass is in the engaged state and the or each clutch arranged between the rotary mass and the rotary damper is in the disengaged state. The vibration control unit may be operable in a second configuration in which at least one of the at least one clutch arranged between the rotary mass and the inputelement is in the disengaged state and the or each clutch arranged between the rotary mass and the rotary damper in the engaged state. The controller may be configured to control each clutch to switch the vibration control unit from the first configuration to the second configuration in response to a shock response of the wing.

[0061] In use, the example described in the preceding paragraph enables the vibration control unit to initially absorb large amounts of kinetic energy from the wing through transfer of the kinetic energy to the moveable mass following a shock response of the wing, for example, during landing of an aircraft comprising the wing assembly. The vibration control unit is then decoupled from the wing, in the second condition described in the preceding paragraph, to allow the remaining kinetic energy of the wing to be further dissipated through inherent damping effects of the wing and tendon, while the kinetic energy of the moveable mass is gradually dissipated through the damper. Decoupling the vibration control unit from the wing allows the kinetic energy of the moveable mass to be dissipated with minimal impact on the wing and at a rate which provides efficient conversion of the kinetic energy to another form of energy such as heat.

[0062] The vibration control unit may comprise the controller. Alternatively, the controller may form part of a flight control system of an aircraft comprising the wing assembly. The controller may be configured to receive at least one input and provide at least one output to the or each clutch to control the or each clutch in dependence on the at least one input. The at least one input may be indicative of different vibrations of the wing and / or a shock response of the wing.

[0063] The at least one input may comprise at least one input indicative of at least one vibration property of the wing. The at least one vibration property may comprise at least one of: a degree of activation of a given vibration mode of the wing, one or more values of one or more frequencies of vibration of the wing, such as the values of the dominant or specific modal frequencies of vibrations of the wing, a wavelength of vibrations of the wing, an amplitude of one or more vibration responses of the wing, variance of one or more vibration responses in a specified frequency interval, a duration of vibrations of the wing, and any other vibration-sensitive response feature. The wing assembly may comprise at least one sensor. The at least one sensor may be configured to determine the at least one vibration property of the wing and provide the at least one input to the controller.The at least one sensor may comprise at least one sensor coupled to the wing, such as at least one accelerometer, at least one strain gauge, or any other arrangement of suitable sensors. The at least one sensor may comprise sensors forming part of a flight control system of an aircraft comprising the wing assembly. For example, the at least one sensor may comprise at least one of an altitude sensor, airspeed sensor, fuel level sensor, weather radar, Doppler radar, LiDAR, electro -optical or optical sensor, gyroscope, and any other suitable situational awareness sensor.

[0064] The at least one input may comprise at least one input indicative of a flight condition of an aircraft comprising the wing assembly. The controller may be configured to receive the at least one input from a flight control system of an aircraft comprising the wing assembly. The flight condition of the aircraft may comprise at least one of takeoff, cruise, and landing. The controller may be calibrated to infer different vibrations of the wing and / or a shock response of the wing in dependence on the at least one input indicative of a flight condition of an aircraft comprising the wing assembly.

[0065] The at least one input may comprise at least one manual inputs provided by a pilot or crew member of an aircraft comprising the wing assembly. In use, a pilot or crew member of an aircraft comprising the wing assembly may assess the flight conditions of the aircraft and provide the at least one input to the controller as required.

[0066] The controller may comprise any suitable combination of at least one processors, at least one memories, and / or any other controller elements. In other examples, the controller may comprise mechanical control means.

[0067] The vibration control unit may comprise a housing configured to house any of the components of the vibration control unit described herein.

[0068] The tendon may be under tension when the wing is at rest. The wing assembly may comprise tension adjusting means configured to adjust tension of the tendon. The tension adjusting means can be manually or remotely and / or automatically operable to increase or decrease the state of tendon tension. The wing assembly may comprise a controller configured to control the tension adjusting means to adjust tension of the tendon. The vibration control unit may comprise the controller. Alternatively, the controller may form part of a flight control system of an aircraft comprising the wingassembly. The controller may be the same controller configured to control the or each clutch as described above, or the controller may be a separate controller.

[0069] The tension adjusting means may comprise a tensioning stage coupled to the tendon. The tensioning stage may be configured to translate to adjust tension of the tendon. The tensioning stage may be configured for rectilinear or curvilinear translation to adjust tension of the tendon. The tension adjusting means may comprise an actuator configured to cause translation of the tensioning stage. The actuator may comprise a manually or remotely and / or automatically operable actuator configured to cause translation of the tensioning stage. The actuator may comprise a fluid, mechanical, electrical, or magnetic actuator. For example, the actuator may comprise a hydraulic actuator, ball-screw mechanism, helical or traditional rack-and-pinion mechanism.

[0070] The tensioning stage may comprise a tensioning rack. The actuator may comprise a pinion configured to drive translation of the tensioning rack, and a motor configured to drive rotation of the pinion.

[0071] The tensioning stage may be configured to translate in a first direction to increase tension of the tendon. The tensioning stage may be configured to translate in a second direction to decrease tension of the tendon. The second direction may be opposite the first direction.

[0072] The tensioning stage may be mounted to the vibration control unit. Where present, the tensioning stage may be mounted to the housing of the vibration control unit. The tensioning stage may be coupled to the tendon via the vibration control unit, for example, via the input element of the vibration control unit. The actuator, for example the pinion where the translation stage comprises a tensioning rack and the actuator comprises a pinion, may be configured to be mounted to the fuselage or other suitable mounting location of an aircraft comprising the wing assembly. Where present, the actuator may be mounted to the mounting structure of the wing assembly. The vibration control unit may be configured to be mounted to the fuselage or other suitable mounting location of an aircraft comprising the wing assembly, or to the mounting structure of the wing assembly, via the tensioning stage.The controller configured to control the tension adjusting means may be configured to receive at least one input and provide at least one output to the tension adjusting means to adjust tension of the tendon in dependence on the at least one input. The controller may be configured to provide the at least one output to the motor of the tension adjusting means described above. The at least one input may comprise an input indicative of a current tension of the tendon. The controller may be configured to determine a difference between the current tension of the tendon and a target tension of the tendon. The controller may be configured to provide the at least one output to adjust the tension of the tendon to meet the target tension in dependence on the difference between the current tension and the target tension. This may advantageously enable the tension of the tendon to be maintained at an optimum value.

[0073] The controller configured to control the tension adjusting means may be configured to receive at least one input indicative of different vibrations of the wing and / or a shock response of the wing, as described above, and provide at least one output to the tension adjusting means to adjust tension of the tendon in dependence on the at least one input. The controller configured to control the tension adjusting means may be configured to receive at least one input indicative of at least one vibration property of the wing, as described above, and provide at least one output to the tension adjusting means to adjust tension of the tendon in dependence on the at least one input. This may advantageously enable the tension of the tendon to be adjusted in dependence on different vibrations and responses of the wing.

[0074] The wing assembly may comprise at least one tendon guide mounted to the wing and configured to guide the tendon along a predetermined path. The predetermined path may extend between the first location, at which the tendon is fixed to the wing, and the vibration control unit. For example, the predetermined path may extend between the tip of the wing and the root of the wing. The tendon is preferably arranged to aggregate and / or amplify vibrations of the wing before the vibrations are transformed to motion of the input element of the vibration control unit. The predetermined path is preferably selected to maximise aggregation and / or amplification of the vibrations of the wing by the tendon. The predetermined path may be selected to maximise aggregation and / or amplification of specific or critical vibrations of the wing by the tendon.The at least one tendon guide may define segments of the tendon. The tendon may comprise a first segment extending between the vibration control unit and an adjacent tendon guide along the predetermined path. The tendon may comprise a final segment extending between the first location, at which the tendon is fixed to the wing, and an adjacent tendon guide along the predetermined path. The at least one tendon guide may comprise a plurality of tendon guides. The tendon may comprise at least one intermediate segment extending between adjacent tendon guides along the predetermined path.

[0075] At least a portion of the tendon along the predetermined path may be angled to a central longitudinal axis of the wing. The central longitudinal axis may extend centrally along the span of the wing. The central longitudinal axis may be equidistant between the upper surface and the lower surface of the wing. The central longitudinal axis may be equidistant between the leading edge and the trailing edge of the wing. The central longitudinal axis may be the neutral axis of the wing.

[0076] At least one of the first tendon segment, intermediate tendon segments, and final tendon segments may be angled to the central longitudinal axis of the wing. The angle between the or each tendon segment and the central longitudinal axis of the wing may be between 0 and 90 degrees. Where the tendon comprises the first segment, at least one intermediate segments, and the final segment, each of the segments may be angled to the central longitudinal axis of the wing. The or each tendon segment may be angled to the central longitudinal axis of the wing in the chordwise direction and / or in the direction of the thickness of the wing. The tendon segments being angled to the central longitudinal axis of the wing in the chordwise direction may be particularly advantageous in damping vibration modes of the wing displaying a torsional component. The tendon segments being angled to the central longitudinal axis of the wing in the direction of the thickness of the wing may be particularly advantageous in damping vibration modes of the wing displaying a bending component.

[0077] The tendon may be arranged above and / or below a central plane of the wing. The central plane may extend in the chordwise direction and the spanwise direction of the wing. The central plane may be equidistant between the upper surface and the lower surface of the wing. The central plane may be the neutral plane of the wing. At least a first portion of the tendon may be arranged above the central plane of the wing and at leasta second portion of the tendon may be arranged below the central plane of the wing. The tendon may pass through the central plane of the wing at one or more locations along the span of the wing.

[0078] The skilled person in the art will be familiar with the chordwise direction, the spanwise direction, and the direction of the thickness of a wing. The chordwise direction extends between the leading and trailing edges of a wing. The spanwise direction extends between the root and the tip of a wing. The direction of the thickness of a wing extends between the upper and lower surfaces of the wing.

[0079] The distance between the tendon guides may vary along the predetermined path. The length of the tendon segments may vary along the predetermined path. The length of the first segment may be greater than the length of the final segment. The length of at least one of the intermediate segments may be less than the length of one or both of the first segment and the final segment. The length of the tendon segments and / or the angle between the tendon segments and the central longitudinal axis of the wing, as described above, may be selected to provide damping of one or more vibration modes of the wing or two or more vibration modes of the wing as described elsewhere herein.

[0080] The at least one tendon guide may comprise at least one pulley, at least one eyelet, at least one linear friction or roller or ball bearing, at least one aperture in at least one structural elements of the wing, or any other element configured to guide the tendon along the predetermined path. The or each pulley may comprise a sheave.

[0081] The tendon may comprise a first branch and a second branch. The first branch may be arranged above and / or below the central plane of the wing. The first branch may be arranged entirely above the central plane of the wing. At least a first portion of the first branch may be arranged above the central plane of the wing and at least a second portion of the first branch may be arranged below the central plane of the wing. The first branch may pass through the central plane of the wing at one or more locations along the span of the wing.

[0082] The second branch of the tendon may be arranged above and / or below the central plane of the wing. The second branch may be arranged entirely below the central plane of the wing. At least a first portion of the second branch may be arranged below the centralplane of the wing and at least a second portion of the second branch may be arranged above the central plane of the wing. The second branch may pass through the central plane of the wing at one or more locations along the span of the wing.

[0083] The first branch of the tendon and second branch of the tendon may be mirrored about a first plane of symmetry lying in the central plane of the wing and / or about a second plane of symmetry perpendicular to the central plane of the wing. The central longitudinal axis of the wing may lie within the second plane of symmetry. With this arrangement, as the wing bends or twists, tension in one of the first or second branches of the tendon will increase while tension in the other of the first and second branches of the tendon will decrease. This has the effect of improving the transformation of movement of the tendon, i.e., where applicable, axial displacement of the tendon, to movement of the input element, i.e., where applicable, rotation of the input element.

[0084] With this geometric arrangement, when the wing bends or twists statically, the tendon mainly experiences the balanced aggregation of the axial tendon displacements between one of the first and one of the second branches of the tendon. The balanced axial aggregation in the two branches of a single tendon is achieved when one branch geometrically shortens by the same amount as the other branch geometrically lengthens. When the wing bends or twists statically in the cyclic manner, this condition leads to the significant cyclic aggregated axial activity of the tendon at the point where the two branches meet and interface with the input element of the vibration control unit. When the wing bends or twists statically, this arrangement uses the natural wing deformations to aggregate their localised effect into the substantially stress -free axial activity of the tendon at the point of interaction with the vibration control unit. The stress -free tendon activation conditions may be substantially perturbed by the consideration of the branch routing patterns that do not maintain mirror symmetry about the central longitudinal axis. Further, the stress-free tendon axial activation conditions may be substantially perturbed during dynamic wing loading conditions and / or when sources of axial tendon displacement activity are introduced along the tendon branches. The dynamically stressed tendon axial activation conditions may be particularly significantly perturbed by the dynamic resistance arising from the damping action of the vibration control unit located between the first and the second branch of the tendon. The statically or dynamically stressed tendon becomes an additional source of the elastic resistance to the primary wing deflections. The exact nature of this elastic resistance is the source ofthe additional stiffness in the augmented wing system. This configuration has the effect of transforming the aggregated wing movement to the axial displacement of the tendon which then transforms to movement of the input element, i.e., where applicable, rotation of the input element.

[0085] It will be appreciated that the terms ‘above’ and ‘below’ refer to the orientation of the wing in normal use, i.e., when an aircraft comprising the wing is on the ground or flying in normal, non-inverted flight.

[0086] In one example, a first end of the tendon may be connected to the wing, adjacent the tip of the wing, above the central plane of the wing. The first branch of the tendon may extend from the first end of the tendon, above the central plane of the wing, to the input element. The second branch of the tendon may extend from the input element, below the central plane of the wing, to a second end of the tendon. The second end of the tendon may be connected to the wing, adjacent the tip of the wing, below the central plane of the wing. In this example, the tendon may loop around the input element between the first and second ends of the tendon. As such, connection between the tendon and the input element may be provided by means of friction between the tendon and the input element.

[0087] In another example, a first end of the tendon may be connected to the wing, adjacent the tip of the wing, and the first branch of the tendon may extend from the first end of the tendon towards the input element. At least a first portion of the first branch may be arranged above the central plane of the wing and at least a second portion of the first branch may be arranged below the central plane of the wing, with the first branch passing through the central plane of the wing at one or more locations along the span of the wing. A second end of the tendon may be connected to the wing, adjacent the tip of the wing, and the second branch of the tendon may extend from the second end of the tendon towards the input element. At least a first portion of the second branch may be arranged below the central plane of the wing and at least a second portion of the second branch may be arranged above the central plane of the wing, with the second branch passing through the central plane of the wing at one or more locations along the span of the wing.A second aspect provides a vibration control system for a wing of an aircraft. The vibration control system comprises a vibration control unit and a tendon. The vibration control unit may comprise any of the features of the vibration control unit of the first aspect. The tendon may comprise any of the features of the tendon of the first aspect.

[0088] A third aspect provides a vibration control unit for a wing of an aircraft. The vibration control unit may comprise any of the features of the vibration control unit of the first aspect.

[0089] A fourth aspect provides an aircraft comprising the wing assembly of the first aspect, the vibration control system of the second aspect, or the vibration control unit of the third aspect. In the fourth aspect, the vibration control unit may be mounted to the fuselage of the aircraft or any other suitable mounting location on the aircraft. Alternatively, the vibration control unit may be mounted on or in the wing. The or each controller may form part of a flight control system of the aircraft.

[0090] In other aspects, the wing assembly may instead be a structural assembly and the wing may be a structure, such as a slender or high aspect ratio structure. The vibration control unit may be arranged adjacent a first end of the structure. The tendon may extend from the vibration control unit to a second end of the structure, opposite the first end. The tendon may be fixed to the structure adjacent or at the second end of the structure. It will be appreciated the examples described with respect to the above aspects may be equally applicable to other aspects as described in this paragraph.

[0091] A fifth aspect provides a method of operating the wing assembly of the first aspect. The method may comprise controlling any or all of the clutches described above to switch the or each clutch between the respective engaged and disengaged states. The method may comprise controlling the or each clutch to vary the magnitude of transmitted force or torque as described above. The method may comprise controlling the tension adjusting means to adjust tension of the tendon as described above. The method may comprise controlling the or each brake as described above.

[0092] A sixth aspect provides a method of designing a wing assembly. The method may be a computer implemented method. The wing assembly comprises a wing, a tendon, and a vibration control unit (VCU). The tendon is coupled to the wing to transform vibrationsof the wing into axial displacement of the tendon. The VCU comprises an input element and at least one damping element. The input element is coupled to the tendon to transform axial displacement of the tendon into movement of the input element. The or each damping element is configured to be coupled to the input element. The at least one damping element comprises one or more of: at least one moveable mass and / or inerter, at least one elastic element, and at least one damper. The VCU is proximal to the root of the wing. The tendon is fixed to the wing at a first location. The wing assembly comprises at least one tendon guide mounted to the wing and configured to guide the tendon along a predetermined path extending between the first location and the VCU. The wing assembly may comprise any of the features of any other wing assembly described herein.

[0093] The wing assembly of the sixth aspect may comprise any features of the wing assembly of the first aspect.

[0094] The method may comprise optimising the predetermined path of the tendon and / or optimising the design of the VCU to dampen at least one vibration mode of the wing. The method may comprise optimising the predetermined path of the tendon and / or optimising the design of the VCU to dampen two or more vibration modes of the wing. The method may comprise determining an optimum predetermined path of the tendon and optimising the design of the VCU in dependence on the optimum predetermined path of the tendon.

[0095] Optimising the predetermined path of the tendon may comprise selecting a predetermined path to maximise aggregation and / or amplification of vibrations of the wing by the tendon. Optimising the design of the VCU may comprise determining properties of the or each damping element of the VCU. The properties of the or each damping element of the VCU may comprise a mass of the or each moveable mass and / or inertance of the or each inerter, a stiffness of the or each elastic element, and / or a damping coefficient of the or each damper.

[0096] Determining the optimum path of the tendon may comprise maximising a tendon routing efficiency factor for at least one vibration mode of the wing. With reference to the relationship between the wing, the tendon and the vibration control unit (VCU), the tendon routing efficiency factor may be defined as a ratio of the square of a tendon-wing coupling factor for a given vibration mode to a tendon-VCU coupling factor for the given vibration mode. The tendon-wing coupling factor may define a coupling factor between the tendon and the wing for the given vibration mode. The tendon-VCU coupling factor may define a coupling factor between the tendon and the VCU for the given vibration mode.

[0097] Optimising the predetermined path of the tendon to dampen two or more vibration modes of the wing may comprise performing a scalarisation of the vector information constituted by the tendon routing efficiency factors for the two or more vibration modes. The scalarisation may comprise applying a weighting factor to the tendon routing efficiency factor for each of the two or more vibration modes of the wing. The scalarisation may comprise determining the sum of the weighted tendon routing efficiency factors. The weighting factors may assign a greater weight to one of the vibration modes than one or more other of the vibration modes. This may enable optimisation of the wing assembly to mitigate responses of the wing during certain operating conditions or scenarios. For example, it may enable optimisation of the wing assembly to mitigate response of the wing to wind gusts, where a first vibration mode may be more dominant than a second vibration mode.

[0098] Optimising the predetermined path of the tendon may comprise performing an optimisation to maximise the sum of the weighted tendon routing efficiency factors. The variables of the optimisation may be defined as the position of each of the tendon guides in the chordwise direction, in the spanwise direction, and in the direction of the thickness of the wing. The optimisation may be performed using any suitable deterministic or heuristic optimisation technique, such as a gradient-based algorithm or a genetic algorithm, each complemented with a suitable set geometry or other relevant constraints.

[0099] Optimising the predetermined path of the tendon to dampen two or more vibration modes of the wing may comprise performing multi-objective optimisation. The multiobjective optimisation may comprise Pareto optimisation. The Pareto optimisation may comprise a Pareto set and Pareto frontier computation to support determination of the Pareto optimal tendon path design. Optimising the predetermined path of the tendon to dampen two or more vibration modes of the wing may comprise determining the tendon routing efficiency factor for each of the two or more vibration modes and performingthe multi -objective optimisation using the tendon routing efficiency factors as optimisation objectives. Other performance, response or discipline -specific characteristics of the predetermined path of the tendon can constitute additional objectives during scalarised single or multi-objective optimisation. Examples of such objectives include but are not limited to the total estimated mass of the tendon and its guiding infrastructure, or the structural performance measures such as the critical stress, strain, strength, stiffness, safety and estimated fatigue life factors. The variables of the optimisation may be defined as the position of each of the tendon guides in the chordwise direction, in the spanwise direction, and in the direction of the thickness of the wing. The multi-objective optimisation may be performed using a multi -objective genetic algorithm, or any suitable optimisation technique.

[0100] Determining properties of the at least one damping element of the VCU in dependence on the optimum predetermined path of the tendon may comprise determining a mass of the or each moveable mass, an inertance of the or each inerter, a stiffness of the or each elastic element, and / or a damping coefficient of the or each damper in dependence on the tendon-wing coupling factor and / or the tendon -VCU coupling factor for the or each vibration mode. The properties of the at least one damping element of the VCU may be determined in dependence on targeted wing dynamics and / or structural characteristics of the tendon.

[0101] Determining properties of the at least one damping element of the VCU may comprise modelling the VCU as a system comprising at least one moveable mass, at least one inerter, at least one damper, and / or at least one elastic element. The at least one damper may be configured to resist movement of the or each moveable mass and / or the or each inerter. The at least one elastic element may be configured to absorb kinetic energy of the or each moveable mass and / or the or each inerter.

[0102] Each damping element of the VCU is configured to produce an effective means of passive vibration control of selected wing vibration modes. The passive vibration control of the wing is achieved using any suitable method of dynamic tuning of the predetermined damping element. Determining the properties of the or each damping element may comprise determining a mass or mass moment of inertia of the or each moveable mass, an inertance of the or each inerter, a damping coefficient of the or each damper, and / or a stiffness of the or each elastic element. For example, one method ofdamping element dynamic tuning may comprise determining a mass or mass moment of inertia of the or each moveable mass, an inertance of the or each inerter, a damping coefficient of the or each damper element, and / or a stiffness of the or each elastic element in dependence on the tendon -wing coupling factor and / or the tendon -VCU coupling factor for the or each vibration mode. Determining the properties may comprise determining the properties in dependence on the inertance of the or each moveable mass, the damping coefficient of the or each damper, and / or the stiffness of the or each elastic element.

[0103] For example, one method of damping element dynamic tuning may comprise determining a mass or mass moment of inertia of the or each moveable mass, an inertance of the or each inerter, a damping coefficient of the or each damper element, and / or a stiffness of the or each elastic element. For example, in a case of two and more degree of freedom damping elements, the tuning procedure may be based on a two-step process which, in its first step, determines an optimal single -mode dynamic tuning for each wing vibration mode of interest individually followed by, in the second step, matching the damping element’s dynamic stiffness function to the optimal parameters determined in the first step. The single -mode tuning stage may require the knowledge of the tendon-wing coupling factor and / or the tendon-VCU coupling factor for the or each vibration mode.

[0104] Determining properties of the at least one damping element of the VCU may comprise modelling the VCU as a single degree of freedom system comprising a moveable mass or an inerter, a damper, and / or an elastic element. The damper may be configured to resist movement of the moveable mass or inerter. The elastic element may be configured to absorb kinetic energy of the moveable mass. The modelled single degree of freedom system may be configured using any method of dynamic tuning to effectively absorb and / or dampen vibrations associated with the critical wing vibration modes.

[0105] Determining properties of the at least one damping element of the VCU may comprise determining the mass or mass moment of inertia of the moveable mass, the inertance of the inerter, the damping coefficient of the damper, and / or the stiffness of the elastic element of the single degree of freedom system. Determining properties of the at least one damping element of the VCU may comprise determining the mass or mass moment of inertia of the moveable mass, the inertance of the inerter, the damping coefficient ofthe damper, and / or the stiffness of the elastic element of the single degree of freedom system in dependence on the tendon-wing coupling factor and / or the tendon-VCU coupling factor for the or each vibration mode and optionally the targeted modal frequency. Determining properties of the at least one damping element of the VCU may comprise determining the properties in dependence on the mass or mass moment of inertia of the moveable mass, the inertance of the inerter, the damping coefficient of the damper, and / or the stiffness of the elastic element of the single degree of freedom system.

[0106] Determining properties of the at least one damping element of the VCU may comprise modelling the VCU as a two degree of freedom system. The two degree of freedom system may comprising a first moveable mass, a first damper coupled to the first moveable mass to resist movement of the first moveable mass, a second moveable mass, a second damper coupled to the second moveable mass to resist movement of the second moveable mass, and an elastic element coupling the first moveable mass and second moveable mass to absorb kinetic energy of the first and second moveable masses. Determining properties of the at least one damping element of the VCU may comprise determining the mass or mass moment of inertia of each of the first and second moveable masses, the damping coefficient of each of the first and second dampers, and / or the stiffness of the elastic element of the modelled preliminary single degree of freedom system. Determining properties of the at least one damping element of the VCU may comprise determining the properties in dependence on the mass or mass moment of inertia of each of the first and second moveable masses, the damping coefficient of each of the first and second dampers, and / or the stiffness of the elastic element of the modelled single degree of freedom system.

[0107] The wing assembly of the first aspect may be designed using the method of the sixth aspect. In other examples, the wing assembly of the first aspect may be designed using any other suitable method. For example, the predetermined path of the tendon and / or the properties of the VCU of the first aspect may be designed using any other suitable optimisation method or any suitable method based on trial and error.

[0108] A seventh aspect provides a method of manufacturing a wing assembly of an aircraft. The method comprises producing a design of the wing assembly using the method of the sixth aspect and manufacturing the wing assembly according to the design.Any feature of any of the examples described above may be combined with any other feature of any other of the examples described above.

[0109] BRIEF DESCRIPTION OF THE DRAWINGS

[0110] Implementations will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0111] Figure la shows a wing assembly for an aircraft;

[0112] Figure lb shows a close-up view of a portion of the wing assembly of Figure la;

[0113] Figure 1c shows an alternative configuration of the wing assembly of Figure la;

[0114] Figure Id shows a close-up view of a portion of the wing assembly as shown in Figure 1c;

[0115] Figure 2 shows a vibration control unit (VCU) for a wing assembly for an aircraft; Figure 3 shows a VCU according to another example;

[0116] Figure 4 shows a VCU according to another example;

[0117] Figure 5 shows a VCU according to another example;

[0118] Figure 6 shows a VCU according to another example; and

[0119] Figure 7 illustrates a method of designing a wing assembly.

[0120] DETAILED DESCRIPTION

[0121] Figure la shows a wing assembly 1 for an aircraft. The wing assembly 1 comprises a wing 11, a tendon 12 coupled to the wing 11, and a vibration control unit (VCU) 13 coupled to the tendon 12. The wing 11 comprises a root 14 and a tip 15. The VCU 13 is proximal the root 14 of the wing 11 and spaced apart from the root 14 of the wing 11 in a direction di extending from the tip 15 of the wing 11 towards the root 14 of the wing 11.

[0122] The wing 11 is a high aspect ratio slender wing which does not house a fuel tank. In this example, the wing 11 is a box wing 11 and the tendon 12 is housed within the internal volume of the box wing 11. Figure 1 a shows an upper panel of the box wing 11 removed. In other examples, the wing 11 may take any other suitable form.

[0123] The tendon 12 is elastic and, in this example, formed from Kevlar. The tendon 12 has a diameter of 56mm which is constant along the length of the tendon 12. In otherexamples, the tendon 12 may be formed from any other suitable material and may comprise any suitable cross-section and dimensions.

[0124] Figure la shows the neutral axis anof the wing 11. The neutral axis anextends in a direction extending between the root 14 and the tip 15 of the wing. The neutral axis anlies within the neutral plane of the wing 11, the neutral plane extending in the spanwise and chordwise directions of the wing 11.

[0125] A first end 16 of the tendon 12 is connected to the wing 11, adjacent the tip 15 of the wing 11. The tendon 12 comprises a first branch 17 extending from the first end 16 of the tendon 12 to the VCU 13. The tendon 12 comprises a second branch 18 extending from the VCU 13 to a second end 19 of the tendon 12. The second end 19 of the tendon 12 is connected to the wing 11, adjacent the tip 15 of the wing 11. In other examples, the first end 16 and / or the second end 19 of the tendon 12 may be connected to the wing 11 at any other location between the root 14 and the tip 15 of the wing 11.

[0126] The wing assembly 1 comprises a plurality of tendon guides 110a-e, 111a-e mounted to the wing 11. In this example, the tendon guides 110a-e, 111a-e are mounted to spars or ribs of the wing 11, but in other examples the tendon guides 110a-e, 111a-e may be mounted to any suitable structural elements of the wing 11. Between the tendon guides 110a-e, 111a-e, the tendon 12 extends through apertures in the spars or ribs. In this example, each tendon guide 110a-e, 111a-e takes the form of a pulley and the tendon 12 extends around a portion of the circumference of each pulley. In other examples, the tendon guides 110a-e, 111a-e may take another suitable form, such as eyelets.

[0127] The plurality of tendon guides 110a-e, 111a-e comprises a first set of tendon guides 110a-e configured to guide the first branch 17 of the tendon 12 along a predetermined path between the first end 16 of the tendon 12 and the VCU 13. The plurality of tendon guides 110a-e, 111a-e comprises a second set of tendon guides 111a-e configured to guide the second branch 18 along a predetermined path between the VCU 13 and the second end 19 of the tendon 12. In this example, each of first set of tendon guides 110a-e and the second set of tendon guides 111a-e comprises five tendon guides 110a-e, 111a-e; however, in other examples the first set of tendon guides 110a-e and / or the second set of tendon guides 111a-e may comprise a different number of tendon guides. Thepaths of the first branch 17 and second branch 18 are mirrored about a first plane of symmetry lying in the neutral plane of the wing 11.

[0128] The plurality of tendon guides 110a-e, 111a-e defines segments of the tendon 12. The first branch 17 of the tendon 12 comprises a first segment 112 extending between the VCU 13 and an adjacent tendon guide 110a. The second branch 18 of the tendon 12 comprises a first segment 113 extending between the VCU 13 and an adjacent tendon guide 111a. The first branch 17 of the tendon 12 comprises a final segment 114 extending between the first end 16 of the tendon 12 and an adjacent tendon guide 110e. The second branch 18 of the tendon 12 comprises a final segment 115 extending between the second end 19 of the tendon 12 and an adjacent tendon guide 111e. The first branch 17 of the tendon 12 comprises intermediate segments 116a-d extending between adjacent tendon guides 110b-d. The second branch 18 of the tendon 12 comprises intermediate segments 117a-d extending between adjacent tendon guides 111b-d. As shown in Figure la, intermediate segments 116b, 117b of the first and second branches 17, 18, respectively, of the tendon 12 pass through the neutral plane of the wing 11.

[0129] Each ofthe segments 112, 113, 114, 115, 116a-d, 117a-d are angled to the neutral axis anof the wing 11 in the chordwise direction and / or in the direction of the thickness of the wing 11. The distance between the tendon guides 110a-e, 111a-e, and therefore the length of the segments 112, 113, 114, 115, 116a-d, 117a-d of the tendon 12, varies along the path of the tendon 12. In other examples, the arrangement of the tendon guides 110a-e, 111a-e, and therefore the arrangement of the segments 112, 113, 114, 115, 116a-d, 117a-d of the tendon 12, may take any other suitable form. In practice, the tendon guides 110a-e, 111a-e, and therefore the segments 112, 113, 114, 115, 116a-d, 117a-d of the tendon 12, may be arranged depending on the application of the VCU 13 and the tendon 12, for example depending on the or each vibration mode of the wing 11 the VCU 13 and the tendon 12 are required to dampen. The arrangement of the tendon guides 110a-e, 111a-e, and therefore the arrangement of the segments 112, 113, 114, 115, 116a-d, 117a-d of the tendon 12, may be determined using an optimisation method or any other suitable design method known to those skilled in the art.

[0130] Figure lb shows a close-up view of a portion of the wing assembly 1 of Figure la. Figure lb shows the VCU 13 and an adjacent portion of the wing 11. The VCU 13 comprises an input element 118 in the form of an input pulley 118. The tendon 12extends around a portion of the circumference of the input pulley 118 such that the first segment 112 of the first branch 17 of the tendon 12 and the first segment 113 of the second branch 18 of the tendon 12 extend either side of the input pulley 118. In this way, the tendon 12 extends from the first end 16 of the tendon 12, around the input pulley 118, and to the second end 19 of the tendon 12.

[0131] The input pulley 118 is coupled to the tendon 12 by means of friction between the input pulley 118 and the tendon 12. In other examples, the input pulley 118 may be coupled to the tendon 12 by additional or alternative means, such as at least one mechanical fastening. In Figures la and lb, the wing 11 is shown at rest. In other words, the wing 11 is not subject to any excitation which may cause vibration of the wing 11. In this configuration, the tendon 12 is under tension. In use, the VCU 13 is fixed to the fuselage of an aircraft comprising the wing assembly 1 or any other suitable mounting location on an aircraft comprising the wing assembly 1. In other examples, the wing assembly 1 may comprise a mounting structure and the VCU 13 may be mounted to the mounting structure. In such examples, the wing 11 is arranged to allow vibration of the wing 11 relative to the mounting structure.

[0132] In operation, movement of the wing 11, relative to the structure to which the VCU 13 is mounted, will cause axial displacement of the tendon 12, which in turn will cause rotation of the input pulley 118. Vibrations of the wing 11 will cause oscillating axial displacement of the tendon 12, which in turn will cause oscillating rotation of the input pulley 118.

[0133] The VCU 13 further comprises a drive shaft 119 coupled to the input pulley 118 for rotation with the input pulley 118. As such, oscillating rotation of the input pulley 118 in use will cause oscillating rotation of the drive shaft 119. The VCU 13 comprises a plurality of rotary damping elements 120a, 120b, 120c coupled to the drive shaft 119 to dampen oscillating rotation of the drive shaft 119, thereby damping oscillating rotation of the input pulley 118. By damping oscillating rotation of the drive shaft 119, the plurality of rotary damping elements 120a, 120b, 120c are configured to dampen vibrations of the wing 11 by means of the coupling to the wing 11 via the drive shaft 119, the input pulley 118, and the tendon 12. The plurality of rotary damping elements 120a, 120b, 120c may be tuned to dampen two or more vibration modes of the wing 11.Alternatively, the plurality of rotary damping elements 120a, 120b, 120c may be tuned to dampen a single vibration mode of the wing.

[0134] In the example of Figure lb, the plurality of rotary damping elements 120a, 120b, 120c comprises three rotary damping elements 120a, 120b, 120c. In other examples, the plurality of rotary damping elements may comprise more or fewer damping elements or may instead comprise a single rotary damping element.

[0135] Figure 1c shows the wing assembly 1 of Figure la but with a different routing of the tendon 12. The same reference numerals are used to refer to the same features in Figures la and 1c. In the example of Figure 1c, the first branch 17 of the tendon 12 is arranged above the neutral plane of the wing 11 and the second branch 18 of the tendon 12 is arranged below the neutral plane of the wing 11,

[0136] Figure Id shows a close-up of a portion of the wing assembly 1 as shown in Figure 1c. The same reference numerals are used to refer to the same features in Figures lb and Id.

[0137] Figure 2 shows a vibration control unit (VCU) 2 for a wing assembly of an aircraft. The VCU 2 has features in common with the vibration control unit of the wing assembly of Figures la and lb. Common features are labelled in Figure 2 with the prefix ‘2’ in place of the prefix ‘ 1 ’ in Figures la and lb. In some examples, the VCU 2 of Figure 2 may be provided in place of the VCU of the wing assembly of Figures la and lb.

[0138] In the example of Figure 2, the VCU 2 comprises a single damping element 220 coupled to the drive shaft 219. The vibration control unit 2 comprises a housing 221, shown in cross-section in Figure 2, which houses the input pulley 218, the drive shaft 219, and the damping element 220. In this example, the damping element 220 is a rotary damper 220. The rotary damper comprises a damper vane 222 and a damper housing 223. The damper vane 222 is coupled to the drive shaft 219 for rotation with the drive shaft 219. The damper vane 222 is sealed within the damper housing 223. The drive shaft 219 extends from the damper vane 222, through the damper housing 223, and out of the damper housing 223 to the input pulley 218. The portion of the drive shaft 219 extending through and out of the damper housing 223 is sealed with a suitable arrangement of one or more seals and bearings (not shown) familiar to those skilled in the art. The damperhousing 223 is filled with a damping fluid which resists rotation of the damper vane 222, therefore resisting rotation of the drive shaft 219 and the input pulley 218. In other examples, an alternative rotary damper, such as a flexible coupling between the drive shaft 219 and the input pulley 218, may be provided.

[0139] The VCU 2 further comprises a clutch 224 arranged between the input pulley 218 and the rotary damper 220. The drive shaft 219 comprises a first drive shaft potion 219-I and a second drive shaft portion 219-II. The input pulley 218 is coupled to a first end of the first drive shaft portion 219-1. The clutch 224 is coupled between a second end of the first drive shaft portion 219-1, opposite the first end of the first drive shaft portion 219-1, and a first end of the second drive shaft portion 219-II. The damper vane 222 is coupled to a second end of the second drive shaft portion 219-II, opposite the first end of the second drive shaft portion 219-II.

[0140] The clutch 224 is operable in an engaged state to couple the rotary damper 220 to the input pulley 218 and a disengaged state to decouple the rotary damper 220 from the input pulley 218. In the engaged state, the first drive shaft potion 219-I is coupled to the second drive shaft portion 219-II, such that torque can be transmitted between the first drive shaft potion 219-I and the second drive shaft portion 219-II, and therefore torque can be transmitted between the input pulley 218 and the damper vane 222. In the disengaged state, the first drive shaft potion 219-I is decoupled from the second drive shaft portion 219-II, such that zero or negligible torque can be transmitted between the first drive shaft potion 219-I and the second drive shaft portion 219-II, and therefore zero or negligible torque can be transmitted between the input pulley 218 and the damper vane 222. The VCU 2 is operable in an active state, in which the clutch 224 is in the engaged state, and an inactive state, in which the clutch 224 is in the disengaged state.

[0141] The clutch 224 is also operable to vary the magnitude of torque transmitted between the first drive shaft potion 219-I and the second drive shaft portion 219-II, and therefore between the input pulley 218 and the damper vane 222, when the clutch 224 is in the engaged state. The clutch 224 may take any suitable form known to those skilled in the art. For example, the clutch 224 may comprise a first plate coupled to the first drive shaft potion 219-I and a second plate coupled to the second drive shaft portion 219-II. The magnitude of torque transmitted between the first drive shaft potion 219-I and thesecond drive shaft portion 219-II may be varied by partially engaging the first and second plates, i.e., by allowing the first and second plates to slip relative to each other.

[0142] A controller 225 is arranged in communication with the clutch 224. In this example, the controller 225 is separate from the VCU 2 and forms part of a wing assembly comprising the VCU 2, for example the wing assembly of Figures la and lb, or part of a flight control system of an aircraft comprising the wing assembly. In other examples, the controller 225 may form part of the VCU 2. The controller 225 is configured to switch the clutch 224 between the engaged state and the disengaged state. The controller 225 is also configured to control the clutch 224 to vary the magnitude of torque transmitted between the first drive shaft potion 219-I and the second drive shaft portion 219-II, and therefore between the input pulley 218 and the damper vane 222, as described above.

[0143] A plurality of sensors 226 is arranged in communication with the controller 225. The plurality of sensors 226 is coupled to a wing of a wing assembly comprising the VCU 2, for example the wing of the wing assembly of Figures la and lb. The sensors of the plurality of sensors 226 are configured to determine at least one vibration property of the wing, such as a frequency of vibrations of the wing, a wavelength of vibrations of the wing, an amplitude of vibrations of the wing, or a duration of vibrations of the wing, and provide at least one input to the controller 225 indicative of the or each vibration property of the wing. The plurality of sensors 226 may comprise at least one accelerometer, at least one strain gauge, or any other arrangement of suitable sensors. In some examples, the plurality of sensors 226 may alternatively or additionally comprise at least one sensor forming part of a flight control system of an aircraft comprising the wing assembly. For example, the at least one sensor may comprise at least one of an altitude sensor, airspeed sensor, fuel level sensor, and weight sensor.

[0144] The controller 225 is configured to provide at least one output, in dependence on the or each input received from the plurality of sensors 226, to the clutch 224 to switch the clutch 224 between the engaged state and the disengaged state or control the clutch 224 to vary the magnitude of torque transmitted between the input pulley 218 and the damper vane 222 via the drive shaft 219. In some examples, the controller 225 may alternatively or additionally be configured to receive at least one manual input provided by a pilot or crew member of an aircraft comprising the wing assembly and provide at least oneoutput, in dependence on the or each manual input, to the clutch 224 to control the clutch 224 as described above.

[0145] Figure 3 shows a vibration control unit (VCU) 3 for a wing assembly of an aircraft. The VCU 3 has features in common with the vibration control unit of Figure 2. Common features are labelled in Figure 3 with the prefix ‘3’ in place of the prefix ‘2’ in Figure 2. In some examples, the VCU 3 of Figure 3 may be provided in place of the VCU of the wing assembly of Figures la and lb.

[0146] The VCU 3 comprises a transmission 327 in the form of a planetary gear train 327. The planetary gear train 327 comprises a transmission input 328 and a transmission output 329. In this example, the transmission input 328 is provided by the gear carrier of the planetary gear train 327 and the transmission output 329 is provided by the sun gear of the planetary gear train 327. The input pulley 318 is coupled to the transmission input 328 via a first drive shaft 319a. The damper vane 322 of the rotary damper 320 is coupled to the transmission output 329 via a second drive shaft 319b.

[0147] The housing 321, a portion of which is shown in Figure 3, houses the input pulley 318, the planetary gear train 327, and the rotary damper 320. The input pulley 318, the transmission input 328, the transmission output 329, and the damper vane 322 are arranged to rotate relative to the housing 321 by means of a suitable arrangement of bearings.

[0148] The VCU 3 comprises a clutch 324 arranged between the transmission output 329 and the damper vane 322. For clarity, in Figure 3, the clutch 324 is shown spaced apart from the transmission output 329 and the damper vane 322. The second drive shaft 319b comprises a first drive shaft potion 319b-I and a second drive shaft portion 319b-II. The transmission output 329 is coupled to a first end of the first drive shaft portion 319b-I. The clutch 324 is coupled between a second end of the first drive shaft portion 319b-I, opposite the first end of the first drive shaft portion 319b-I, and a first end of the second drive shaft portion 319b-II. The damper vane 322 is coupled to a second end of the second drive shaft portion 319b-II, opposite the first end of the second drive shaft portion 319b-II.The clutch 324 is operable in an engaged state to couple the rotary damper 220 to the transmission output 329 and a disengaged state to decouple the rotary damper 320 from the transmission output 329. In the engaged state, the first drive shaft potion 319b-I of the second drive shaft 319b is coupled to the second drive shaft portion 319b-II of the second drive shaft 319b, such that torque can be transmitted between the first drive shaft potion 319b-I and the second drive shaft portion 319b-II, and therefore torque can be transmitted between the transmission output 329 and the damper vane 322. In the disengaged state, the first drive shaft potion 319b-I is decoupled from the second drive shaft portion 319b-II, such that zero or negligible torque can be transmitted between the first drive shaft potion 319b-I and the second drive shaft portion 319b-II, and therefore zero or negligible torque can be transmitted between the transmission output 329 and the damper vane 322.

[0149] The clutch 324 is also operable to vary the magnitude of torque transmitted between the first drive shaft potion 319b-I of the second drive shaft 319b and the second drive shaft portion 319b-II of the second drive shaft 319b, and therefore between the transmission output 329 and the damper vane 322, when the clutch 324 is in the engaged state. The clutch 324 may take any suitable form known to those skilled in the art. For example, the clutch 324 may comprise a first plate coupled to the first drive shaft potion 319b-I and a second plate coupled to the second drive shaft portion 319b-II. The magnitude of torque transmitted between the first drive shaft potion 319b-I and the second drive shaft portion 319b-II may be varied by partially engaging the first and second plates, i.e., by allowing the first and second plates to slip relative to each other.

[0150] The controller 325 and the plurality of sensors 326 are configured to control the clutch 324 in the same manner as described above with respect to the clutch of the VCU of Figure 2.

[0151] The VCU 3 further comprises tension adjusting means comprising: a tensioning stage comprising a tensioning rack 330 coupled to the housing 321, an actuator comprising a pinion 331 configured to drive translation of the tensioning rack 330, and a motor 332 configured to drive rotation of the pinion 331. The components housed within the housing 321 are fixed relative to the housing 321 to translate with the housing 321 and the tensioning rack 330. The pinion 331 is fixed in translation relative to the fuselage of an aircraft comprising the VCU 3 or a mounting structure of a wing assemblycomprising the VCU 3, as applicable. In use, the input pulley 318 is coupled to a tendon and the tendon is fixed to a wing, for example as described above with respect to the wing assembly of Figures la and lb. As such, translation of the tensioning rack 330, driven by the pinion 331, causes translation of the input pulley 318, which in turn causes adjustment of the tension of the tendon.

[0152] The controller 325 is arranged in communication with the motor 332. The controller 325 is configured to provide at least one output to the motor 332, in dependence on the or each input received from the plurality of sensors 326, to control translation of the rack 330 and therefore adjust the tension of the tendon in use. In some examples, the plurality of sensors 326 alternatively or additionally comprises at least one sensor configured to determine a current tension of the tendon. In such examples, the controller 325 may be configured to determine a difference between the current tension of the tendon and a target tension of the tendon. The controller 325 may be configured to provide the at least one output to the motor 332 to control translation of the rack 330 to adjust the tension of the tendon to meet the target tension in dependence on the difference between the current tension and the target tension. In this way, the tension adjusting means may be configured to maintain a predetermined target tension of the tendon in use.

[0153] In some examples, the controller 325 may not be arranged to control the tension adjusting means and instead a separate controller may be provided to control the tension adjusting means as described above.

[0154] Figure 4 shows a vibration control unit (VCU) 4 for a wing assembly of an aircraft. The VCU 4 has features in common with the vibration control unit of Figure 3. Common features are labelled in Figure 4 with the prefix ‘4’ in place of the prefix ‘3’ in Figure 3. In some examples, the VCU 4 of Figure 4 may be provided in place of the VCU of the wing assembly of Figures la and lb.

[0155] In the example of Figure 4, the VCU 4 comprises a first damping element in the form of a first rotary mass-damper 420a. The first rotary mass-damper 420a comprises a first rotary mass 433a, in the form of a first flywheel 433a, and a first damper housing 434a. The first flywheel 433a is sealed within the first damper housing 434a. The VCU 4 comprises a hollow drive shaft 434. The first flywheel 433a is coupled to the hollowdrive shaft 434 for rotation with the hollow drive shaft 434. The hollow drive shaft 434 extends from the first flywheel 433a, through the first damper housing 434a, and out of the first damper housing 434a between first and second ends of the hollow drive shaft 434. The portions of the hollow drive shaft 434 extending through the first damper housing 434a are sealed with a suitable arrangement of one or more seals and bearings (not shown) familiar to those skilled in the art. The first damper housing 434a is filled with a fluid which resists rotation of the first flywheel 433a, therefore resisting rotation of the hollow drive shaft 434.

[0156] The VCU 4 further comprises a second damping element in the form of a second rotary mass-damper 420b. The second rotary mass-damper 420b comprises a second rotary mass 433b, in the form of a second flywheel 433b, and a second damper housing 434b. The second flywheel 433b is sealed within the second damper housing 434b. The mass moment of inertia of the second flywheel 433b is less than the mass moment of inertia of the first flywheel 433a.

[0157] The VCU 4 comprises a main drive shaft 419 comprising a first drive shaft portion 419-I and a second drive shaft portion 419-II. The first drive shaft portion 419-I comprises a first end and a second end, opposite the first end. The transmission output 429 is coupled to the first end of the first drive shaft portion 419-I. The first drive shaft portion 419-I extends through the hollow drive shaft 434 between the first and second ends of the first drive shaft portion 419-I. The hollow drive shaft 434 is fixed axially relative to the first drive shaft portion 419-1 and configured to rotate relative to the first drive shaft portion 419-1 by a suitable arrangement of one or more bearings (not shown).

[0158] The VCU 4 comprises a first clutch 424a arranged between the transmission output 429 and the first rotary mass-damper 420a. The first clutch 424a is coupled between the first drive shaft portion 419-1 of the main drive shaft 419 and the first end of the hollow drive shaft 434. The first clutch 424a is operable in an engaged state to couple the hollow drive shaft 434 to the transmission output 429, via the first drive shaft portion 419-1, and a disengaged state to decouple the hollow drive shaft 434 from the first drive shaft portion 419-1, and therefore from the transmission output 429. In the engaged state, the hollow drive shaft 434 is coupled to the first drive shaft portion 419-1, such that torque can be transmitted between the hollow drive shaft 434 and the first drive shaft portion 419-1, and therefore torque can be transmitted between the transmissionoutput 429 and the first flywheel 433a. In the disengaged state, the hollow drive shaft 434 is decoupled from the first drive shaft portion 419-1, such that zero or negligible torque can be transmitted between the hollow drive shaft 434 and the first drive shaft portion 419-1, and therefore zero or negligible torque can be transmitted between the transmission output 429 and the first flywheel 433a.

[0159] The second drive shaft portion 419-11 of the main drive shaft 419 comprises a first end and a second end, opposite the first end. The second flywheel 433b is coupled to the second end for rotation with the second drive shaft portion 419-11. The VCU 4 further comprises a second clutch 424b arranged between the first rotary mass -damper 420a and the second rotary mass -damper 420b. The second clutch 424b is coupled between the second end of the first drive shaft portion 419-1 of the main drive shaft 419 and the first end of the second drive shaft portion 419-II of the main drive shaft 419.

[0160] The second clutch 424b is operable in an engaged state to couple the second rotary mass-damper 420b to the transmission output 429 and a disengaged state to decouple the second rotary mass-damper 420b from the transmission output 429. In the engaged state, the first drive shaft potion 419-1 of the main drive shaft 419 is coupled to the second drive shaft portion 419-11 of the main drive shaft 419, such that torque can be transmitted between the first drive shaft portion 419-1 and the second drive shaft portion 419-11, and therefore torque can be transmitted between the transmission output 429 and the second flywheel 433b. In the disengaged state, the first drive shaft portion 419-I is decoupled from the second drive shaft portion 419-II, such that zero or negligible torque can be transmitted between the first drive shaft portion 419-I and the second drive shaft portion 419-II, and therefore zero or negligible torque can be transmitted between the transmission output 429 and the second flywheel 433b.

[0161] In other examples, the VUC 4 may comprise a further damping element in the form of an elastic element, such as a spring or torsional coupling, arranged to couple the first flywheel 433a to the hollow drive shaft 434, couple the second flywheel 433b to the second drive shaft portion 419-11 of the main drive shaft 419, and / or couple the first flywheel 433a to the second flywheel 433b.

[0162] The first clutch 424a and the second clutch 424b therefore provide four configurations of the VCU 4: a first configuration in which both of the first clutch 424a and the secondclutch 424b are in the respective disengaged states, a second configuration in which the first clutch 424a is in the engaged state and the second clutch 424b is in the disengaged state, and third configuration in which the first clutch 424a is in the disengaged state and the second clutch 424b is in the engaged state, and a fourth configuration in which both of the first clutch 424a and the second clutch 424b are in the respective engaged states.

[0163] For clarity, in Figure 4, the first clutch 424a and the second clutch 424b are shown spaced apart from the main drive shaft 419. In some examples, one or both of the first clutch 424a and the second clutch 424b may be configured to vary the magnitude of torque transmitted between the first drive shaft potion 419-1 of the main drive shaft 419 and the hollow drive shaft 434 and between the first drive shaft potion 419-1 of the main drive shaft 419 and the second drive shaft potion 419-11 of the main drive shaft 419, respectively, in the manner described above with reference to the clutch of the VCU of Figure 3.

[0164] The controller 425 and the plurality of sensors 426 are configured to control each of the first clutch 424a and the second clutch 424b in the same manner as described above with respect to the clutch of the VCU of Figure 3.

[0165] Figure 5 shows a vibration control unit (VCU) 5 for a wing assembly of an aircraft. The VCU 5 has features in common with the vibration control unit of Figure 4 and the vibration control unit of Figure 3. Common features are labelled in Figure 5 with the prefix ‘5’ in place of the prefix ‘4’ in Figure 4 or the prefix ‘3’ in Figure 3. In some examples, the VCU 5 of Figure 5 may be provided in place of the VCU of the wing assembly of Figures la and lb.

[0166] In the example of Figure 5, the first damping element comprises a rotary mass 533 in the form of a flywheel 533. The second damping element comprises a rotary damper 520. The VCU 5 comprises a drive shaft 519 comprising a first drive shaft portion 519-I, a second drive shaft portion 519-11, and a third drive shaft portion 519-III. Each of the first drive shaft portion 519-1, the second drive shaft portion 519-11, and the third drive shaft portion 519-III comprises a first end and a second end, opposite the first end. The transmission output 529 is coupled to the first end of the first drive shaft portion 519-1. The flywheel 533 is coupled to the second drive shaft portion 519-11 forrotation with the second drive shaft portion 519-11. The damper vane 522 is coupled to the third drive shaft portion 519-III for rotation with the third drive shaft portion 519-III. The third drive shaft portion 519-III is sealed with respect to the damper housing 523 in the manner described above with respect to the rotary damper of Figure 3.

[0167] The VCU 5 comprises a first clutch 524a arranged between the transmission output 529 and the flywheel 533. The first clutch 524a is coupled between the second end of the first drive shaft potion 519-1 and the first end of the second drive shaft portion 519-11. The first clutch 524a is operable in an engaged state to couple the flywheel 533 to the transmission output 529 and a disengaged state to decouple the flywheel 533 from the transmission output 529. In the engaged state, the first drive shaft potion 519-1 is coupled to the second drive shaft portion 519-11, such that torque can be transmitted between the first drive shaft portion 519-1 and the second drive shaft portion 519-11, and therefore torque can be transmitted between the transmission output 529 and the flywheel 533. In the disengaged state, the first drive shaft portion 519-1 is decoupled from the second drive shaft portion 519-11, such that zero or negligible torque can be transmitted between the first drive shaft potion 519-1 and the second drive shaft portion 519-11, and therefore zero or negligible torque can be transmitted between the transmission output 529 and the flywheel 533.

[0168] The VCU 5 comprises a second clutch 524b arranged between the transmission output 529 and the rotary damper 520. The second clutch 524b is coupled between the second end of the second drive shaft potion 519-11 and the first end of the third drive shaft portion 519-III. The second clutch 524b is operable in an engaged state to couple the rotary damper 520 to the transmission output 529 and a disengaged state to decouple the rotary damper 520 from the transmission output 529. In the engaged state, the second drive shaft potion 519-11 is coupled to the third drive shaft portion 519-III, such that torque can be transmitted between the second drive shaft portion 519-11 and the third drive shaft portion 519-III, and therefore torque can be transmitted between the transmission output 529 and the damper vane 522. In the disengaged state, the second drive shaft potion 519-11 is decoupled from the third drive shaft portion 519-III, such that zero or negligible torque can be transmitted between the second drive shaft portion 519-II and the third drive shaft portion 519-III, and therefore zero or negligible torque can be transmitted between the transmission output 529 and the damper vane 522.The first clutch 524a and the second clutch 524b provide a first configuration of the VCU 5, in which the first clutch 524a is in the engaged state and the second clutch 524b is in the disengaged state, and a second configuration of the VCU 5 in which the first clutch 524a is in the disengaged state and the second clutch 524b is in the engaged state. The controller 525 is configured to control each of the first clutch 524a and the second clutch 524b to switch the vibration control unit from the first configuration to the second configuration in response to a shock response of the wing. The controller 525 is configured to detect a shock response of the wing of the wing, based on the or each input provided to the controller 525 by the plurality of sensors 526, and provide at least one output to the first clutch 524a and the second clutch 524b to switch the vibration control unit from the first configuration to the second configuration in response to the shock response of the wing.

[0169] In some examples, one or both of the first clutch 524a and the second clutch 524b may be configured to vary the magnitude of torque transmitted between the first drive shaft portion 519-1 and the second drive shaft portion 519-11 and between the second drive shaft portion 519-11 and the third drive shaft portion 519-III, respectively, in the manner described above with reference to the clutch of the VCU of Figure 3. The controller 525 and the plurality of sensors 526 are configured to control each of the first clutch 524a and the second clutch 524b in the same manner as described above with respect to the clutch of the VCU of Figure 3.

[0170] The VCU 5 further comprises a brake 535 coupled to the first drive shaft potion 519-1. The brake 535 is configured to selectively resist rotation of the first drive shaft potion 519-1, and therefore selectively resist rotation of the flywheel 533 when the first clutch 524a is in the engaged state. The controller 525 is in communication with the brake 535 and is configured to control the brake 535 to selectively resist rotation of the first drive shaft potion 519-1. The controller 535 is configured to provide at least one output to the brake 535, in dependence on the or each input received from the plurality of sensors 526, to control the brake 535 to selectively resist rotation of the first drive shaft potion 519-1. In some examples, the controller 525 may not be arranged to control the brake 535 and instead a separate controller may be provided to control the brake 535 as described above.In other examples, any of the VCU of Figures 3, 4, and 5 may comprise an additional clutch arranged between the input pulley and the transmission input and / or between the transmission output and the adjacent damping element as applicable. In such examples, the controller may be configured to control the or each additional clutch in the same manner as described above with reference to the clutch of the VCU of Figure 2.

[0171] Figure 6 shows a vibration control unit (VCU) 6 for a wing assembly of an aircraft. The VCU 6 has features in common with the vibration control unit of Figure 3. Common features are labelled in Figure 6 with the prefix ‘6’ in place of the prefix ‘3’ in Figure 3. In some examples, the VCU 6 of Figure 6 may be provided in place of the VCU of the wing assembly of Figures la and lb.

[0172] The VCU 6 comprises a rotary elastic element 636, in the form of a torsion bar 636, coupling the first flywheel 633a and the second flywheel 633b together. In use, the torsion bar 636 absorbs rotational energy of the first flywheel 633a and the second flywheel 633b as the first flywheel 633a and the second flywheel 633b rotate relative to each other.

[0173] In this example, input pulley 618 takes the form of a hollow input pulley 618. The first flywheel 633a is coupled to a first axial end of the hollow input pulley 618, for rotation with the hollow input pulley 618. The second flywheel 633b is not coupled to the hollow input pulley 618, to allow rotation of the second flywheel 633b relative to the hollow input pulley 618. The torsion bar 636 extends through the hollow input pulley 618, from the first axial end of the hollow input pulley 618, and beyond the second axial end of the hollow input pulley 618.

[0174] For reference, a portion of a tendon 62, for example the tendon of the wing assembly of Figures la and lb, is shown in cross-section extending around a portion of the circumference of the hollow input pulley 618.

[0175] It will be appreciated that the example VCUs of Figures 3 to 6 are merely illustrative and that any other example VCU may be provided comprising any number and combination of clutches, transmissions, damping elements, and brakes as described herein.Figure 7 illustrates a method 700 of designing a wing assembly. The wing assembly comprises a wing, a tendon, and a vibration control unit (VCU). The tendon is coupled to the wing to transform vibrations of the wing into axial displacement of the tendon. The VCU comprises an input element and at least one damping element. The input element is coupled to the tendon to transform axial displacement of the tendon into movement of the input element. The or each damping element is configured to be coupled to the input element. The at least one damping element comprises one or more of: at least one moveable mass or inerter, at least one elastic element, and at least one damper. The VCU is proximal to the root of the wing. The tendon is fixed to the wing at a first location. The wing assembly comprises at least one tendon guide mounted to the wing and configured to guide the tendon along a predetermined path extending between the first location and the VCU.

[0176] The wing assembly may comprise any of the features the wing assembly of Figure 1. The VCU may comprise any of the features of the VCU of any of Figures 2 to 6.

[0177] The method 700 begins by determining 701 a tendon-wing elastic coupling factor, Fxx, and determining 702 a tendon-VCU elastic coupling factor, Fxx, for a first vibration mode of the wing. The tendon-wing elastic coupling factor, Fxx, and the tendon-VCU elastic coupling factor, Fxx, are defined as follows:

[0178]

[0179] lTi~xo x0)’xx%0(Zz- x0)

[0180] where:

[0181]

[0182] —%A{m) (dq Qm> ^B(m) |) Qm where:

[0183] Tt= the tension of the tendon;

[0184] a = strain of the tendon as a result of the tension, FT;

[0185] ly = the total length of the tendon, including the first and second branches, when the tendon is at rest, i.e., when the wing as at rest;

[0186] xo = the unstrained length of the tendon subtended in the first branch when the wing is at rest,qm= the mass normalised shape vector of the first vibration mode;

[0187] X, |47|=the sum of the lengths of the vectors of the tendon segments in the first branch of the tendon;

[0188] X, |^B7|= the sum of the lengths of the vectors of the tendon segments in the second branch of the tendon;

[0189] dq= the vector of partial derivative operations, and

[0190]

[0191] T = the matrix transposition operation.

[0192] A tendon routing efficiency factor is then determined 703 for the first vibration mode. The tendon routing efficiency factor is defined as:

[0193] O _ F / ? LxX

[0194] ~ -T~

[0195]

[0196] 1XX

[0197] A tendon-wing elastic coupling factor, Fxx, and a tendon-VCU elastic coupling factor, Fxx, for a second vibration mode of the wing are then determined and used to determine a tendon routing efficiency factor for the second vibration mode as described above. This process may be repeated for any number of vibration modes of the wing.

[0198] The method then comprises performing 704 an optimisation using the tendon routing efficiency factors as the optimisation objective. In some examples, the optimisation comprises performing a scalarisation of the tendon routing efficiency factors by applying a weighting factor to each of the tendon routing efficiency factors and determining the sum of the weighted tendon routing efficiency factors, as follows:

[0199]

[0200] & - ■ ■ +FN^mN

[0201] where pmN is the tendon routing efficiency factor for vibration mode N. The objective function of the optimisation is defined as:

[0202] maxpEp)

[0203] peDwhere p and D define the constraints of the objective function, where p is a parameterisation vector depending on given constraints, such as the number of tendon segments in each branch of the tendon, and D is a permissible set from which the parameterisation vector is drawn. D may be limited by constraints such as the mass and / or volume of the wing. The optimisation is then performed using a genetic algorithm, such as a genetic algorithm available in Matlab (RTM).

[0204] The variables of the optimisation are defined as the position of each of the tendon guides in the chordwise direction, in the spanwise direction, and in the direction of the thickness of the wing. As such, the output of the optimisation is the position of each of the tendon guides on the wing.

[0205] In another example, the tendon routing efficiency factors are used as the optimisation objectives in a multi -objective optimisation. The constraints and variables of the multiobjective optimisation are as defined above, such that the output of the multi -objective optimisation is the position of each of the tendon guides on the wing. The multi -objective optimisation is performed using a multi -objective genetic algorithm available in Matlab (RTM).

[0206] Once the optimum path of the tendon is determined, as defined by the position of each of the tendon guides on the wing, the design of the VCU is then optimised in dependence on the optimum path. The design of the VCU is optimised by determining 705 the properties of the damping elements to optimise the design of the VCU.

[0207] The VCU exerts a force on the tendon, which resists the differential tensions between the first segment of the first branch and the first segment of the second branch. This force originates from the damping elements in the VCU, such that the force is a function of the tendon’s displacement across the VCU (i.e., the tendon transfer of the tendon from the first branch to the second branch, or vice versa). As such, this force can be described using a dynamic stiffness function in the frequency domain, imposed on the afore-mentioned displacement of the tendon. Such a dynamic stiffness function can be used to describe the afore describe interaction with the differential tensions as follows:

[0208] K") = -

[0209]

[0210] x{a>)where:

[0211] / (&>) = is the dynamic stiffness function;

[0212] TAB= adifference in tension between the first segment of the first branch of the tendon and the first segment of the second branch of the tendon;

[0213] x = the axial displacement of the tendon, from one of the first of second branches to the other;

[0214] a> = is the vibratory frequency.

[0215] When the wing is at rest, TAB= 0. As the wing bends or twists, tension in one of the first segment of the first branch or the first segment of the second branch of the tendon will increase while tension in the other of the first segment of the first branch or the first segment of the second branch will decrease, resulting in axial displacement of the tendon.

[0216] The effect of the dynamic stiffness function, which drives the tension in the tendon’s branches, results in a control force that is transferred to the structure / wing. Considering an example where the intermediate guides of the tendon are assumed to pose minimal / zero resistance to the tendon’s axial movement, the passively transmitted control force which originates under the displacement of a vibratory mode can be given as follows,

[0217] fc<^ r. zrz \ i

[0218]

[0219] FxxG(") + Fxx)

[0220] where:

[0221] fc(co) = the modal control force exerted on the structure by the VCU, transmitted through the tendon; and

[0222] Xm(co) = the modal coordinates for a given vibration mode of the wing, m.

[0223] In one example, the VCU may comprise damping elements in the form of a first moveable mass, a first damper coupled to the first moveable mass to resist movement of the first moveable mass, a second moveable mass, a second damper coupled to the second moveable mass to resist movement of the second moveable mass, and an elastic element coupling the first moveable mass and second moveable mass to absorb kinetic energy of the first and second moveable masses. To determine the properties of the damping elements to optimise the design of the VCU, the damping elements are firstmodelled as a single degree of freedom system comprising a single moveable mass and a damper configured to resist movement of the movable mass. The single degree of freedom system to target vibration mode i reads as follows:

[0224] / (&>) = — a)2bi + ja> Ci

[0225] where j imaginary unit (square root of -1) and, based on an example tuning criteria involving the objective of minimising the resonant responses in frequency domain, the inertia and viscous factors are generated to satisfy,

[0226] a)i 1 3 / z

[0227] = 7^- ^" = 2^

[0228]

[0229] where,

[0230] _ l^xx7_ci _ > J bi 2a)vcubi Fxx

[0231]

[0232] where:

[0233] tOi = the natural frequency of vibration mode i;

[0234] bL= the inertance of the moveable mass; and

[0235] cL= the damping coefficient of the damper.

[0236] The above equations are reduced to two simultaneous equations which are then solved to determine the variables bLand ctfor each of the vibration modes for which the tendonwing elastic coupling factor, FXx, and the tendon-VCU elastic coupling factor, Fxx, were determined as described above.

[0237] The VCU is then modelled as a two degree of freedom system comprising a first moveable mass, a first damper coupled to the first moveable mass to resist movement of the first moveable mass, a second moveable mass, a second damper coupled to the second moveable mass to resist movement of the second moveable mass, and an elastic element coupling the first moveable mass and second moveable mass. The two degree of freedom VCU in this example is used to target two structural vibratory modes. Thedynamic stiffness of the two degree of freedom system can be modelled as follows, at frequencies near that of the resonant frequency of a vibration mode i

[0238] /

[0239]

[0240] (&)) « — &)2beyy(&)j) +

[0241] where:

[0242] 1! b2 / brbeff(ci>i) b-y Ceff&d =ci 1 + - - -2

[0243] 1 - rf(b2 / kint) \ (l - rf(b2 / kint))

[0244]

[0245] where:

[0246] b_eff(ω_i) = b̄_i, c_eff(ω_i) = c̄_i

[0247] where:

[0248] bi = the inertance of the first moveable mass;

[0249] b2 = the inertance of the second moveable mass;

[0250] Ci = the damping coefficient of the first damper;

[0251] C2 = the damping coefficient of the second damper; and

[0252] kint = the stiffness of the elastic element coupling the first moveable mass and second moveable mass.

[0253] The above equations provide four simultaneous equations (for two selected modes, i.e: i=il, i2, for each of which b̄_i, c̄_i are determined as per the previous 1 DOF VCU modelling) which are then solved to determine the variables bi, b2, Ci, C2, and kint. The variables bi, b2, Ci, C2, and kint are then used to determine 705 properties of the damping elements of the VCU.

[0254] In one example, the VCU may comprise an input element in the form of a pulley, a transmission, wherein the pulley is coupled to the input of the transmission, a first rotary mass, wherein the rotary mass is coupled to the output of the transmission, a second rotary mass, and an elastic element in the form of a torsional bar coupling the first and second rotary masses to absorb rotational energy of the first and second rotary masses.

[0255] The properties of the pulley can be defined as:θ_in = x / r_pul

[0256] where:

[0257] θ_in = the angular displacement of the pulley;

[0258] x = the axial displacement of the tendon; and

[0259] r_pul = the radius of the pulley.

[0260] The properties of the transmission can be defined as:

[0261]

[0262] where:

[0263] g = the transmission ratio of the transmission; and

[0264] 0i = the angular displacement of the output of the transmission for a given angular displacement of the pulley.

[0265] The properties of the first rotary mass can be defined as:

[0266] I_rot1 = b_1 r²_pul / g²

[0267] where:

[0268] I_rot1 = the rotational inertia of the first rotary mass.

[0269] The properties of the torsion bar can be defined as:

[0270] GJ = k_int r²_pul / g²

[0271] where:

[0272] G = the modulus of rigidity of the torsion bar; and

[0273] J = the torsional constant of the torsion bar.

[0274] Finally, a multi-objective Pareto optimisation is then performed using the properties of the damping elements as defined above as the optimisation objectives. The variables of the optimisation are defined as the total physical mass of the damping elements and thecritical dimensions of the damping elements. The critical dimensions of the damping elements are defined as follows:

[0275] max(2R_1, 2R_2, H + 0.5

[0276]

[0277] + h2)

[0278] where:

[0279] Ri = the radius of the first rotary mass;

[0280] R2 = the radius of the second rotary mass;

[0281] H = the height of the torsion bar, as measured between the first and second rotary masses;

[0282] hi = the thickness of the first rotary mass; and

[0283] h_2 = the thickness of the second rotary mass.

[0284] It will be appreciated that the examples described herein are merely illustrative and that any modifications of any of the examples described herein may be covered within the scope of the appended claims.

Claims

CLAIMS1. A wing assembly for an aircraft, the wing assembly comprising:a wing;a tendon coupled to the wing to transform vibrations of the wing into axial displacement of the tendon; anda vibration control unit comprising:an input element coupled to the tendon to transform axial displacement of the tendon into rotation of the input element; andat least one rotary damping element configured to be coupled to the input element; whereinthe vibration control unit is proximal to the root of the wing.

2. The wing assembly of claim 1, wherein the at least one rotary damping element comprises at least one of: a rotary mass or rotary inerter, a rotary elastic element, and a rotary damper.

3. The wing assembly of claim 1 or claim 2, wherein the vibration control unit comprises at least one clutch and / or at least one transmission, and / or wherein the at least one rotary damping element is at least one first rotary damping element and the vibration control unit comprises at least one second rotary damping element.

4. The wing assembly of any preceding claim, wherein the vibration control unit comprises at least one clutch arranged between the input element and the at least one rotary damping element and operable in an engaged state to couple the at least one rotary damping element to the input element and a disengaged state to decouple the at least one rotary damping element from the input element.

5. The wing assembly of any preceding claim, wherein the vibration control unit comprises a transmission comprising an input and an output, wherein the input element is configured to be coupled to the input of the transmission and the at least one rotary damping element is configured to be coupled to the output of the transmission, wherein the transmission is configured to increase a speed of rotation of the output of the transmission relative to a speed of rotation of the input of the transmission.

6. The wing assembly of claim 5, wherein the transmission comprises a planetary gear train.

7. The wing assembly of claim 5 or claim 6, when dependent on claim 4, wherein the at least one clutch arranged between the input element and the at least one rotary damping element comprises a clutch arranged between the input element and the input of the transmission and operable in an engaged state to couple the input e lement to the input of the transmission and a disengaged state to decouple the input element from the input of the transmission.

8. The wing assembly of claim 7, or claim 5 or claim 6, when dependent on claim 4, wherein the at least one clutch arranged between the input element and the at least one rotary damping element comprises a clutch arranged between the output of the transmission and the at least one rotary damping element and operable in an engaged state to couple the at least one rotary damping element to the output of the transmission and a disengaged state to decouple the at least one rotary damping element from the output of the transmission.

9. The wing assembly of any preceding claim, wherein the at least one rotary damping element is at least one first rotary damping element, and wherein the vibration control unit comprises at least one second rotary damping element.

10. The wing assembly of claim 9, wherein the at least one second rotary damping element is configured to be coupled to the input element.

11. The wing assembly of claim 10, wherein dependent on any of claims 5 to 8, wherein the at least one second rotary damping element is configured to be coupled to the output of the transmission.

12. The wing assembly of any of claims 9 to 11, wherein the at least one second rotary damping element is configured to be coupled to the at least one first rotary damping element.

13. The wing assembly of any of claims 9 to 12, wherein the at least one first rotary damping element and the at least one second rotary damping element are configured to dampen different vibrations of the wing.

14. The wing assembly of claim 13, wherein the different vibrations differ in at least one of: vibration mode, frequency, wavelength, amplitude, and duration.

15. The wing assembly of claim 10, or any of claims 11 to 14 when dependent on claim 10, wherein the vibration control unit comprises at least one clutch arranged between the at least one second rotary damping element and the input element and operable in an engaged state to couple the at least one second rotary damping element to the input element and a disengaged state to decouple the at least one second rotary damping element from the input element.

16. The wing assembly of claim 15, when dependent on claim 11, or any of claims 12 to 14 when dependent on claim 11, wherein the at least one clutch arranged between the at least one second rotary damping element and the input element comprises a clutch arranged between the at least one second rotary damping element and the output of the transmission and operable in an engaged state to couple the at least one second rotary damping element to the output of the transmission and a disengaged state to decouple the at least one second rotary damping element from the output of the transmission.

17. The wing assembly of claim 12, or any of claims 13 to 16 when dependent on claim 12, wherein the vibration control unit comprises at least one clutch arranged between the at least one first rotary damping element and the at least one second rotary damping element and operable in an engaged state to couple the at least one second rotary damping element to the at least one first rotary damping element and a disengaged state to decouple the at least one second rotary damping element from the at least one first rotary damping element.

18. The wing assembly of any of claims 15 to 17, when dependent on claim 13 or claim 14, comprising a controller, wherein the controller is configured to control the or each clutch to switch between the respective engaged and disengaged states in dependence on the different vibrations of the wing.

19. The wing assembly of claim 17, or claim 18 when dependent on claim 17, when dependent on claim 4, or any of claims 5 to 8 when dependent on claim 4, wherein the at least one first rotary damping element comprises a rotary mass and the at least one second rotary damping element comprises a rotary damper, and wherein the vibration control unit is operable in:a first configuration in which the or each clutch arranged between the input element and the rotary mass is in the engaged state and the or each clutch arranged between the rotary mass and the rotary damper is in the disengaged state; anda second configuration in which at least one of the at least one clutch arranged between the rotary mass and the input element is in the disengaged state and the or each clutch arranged between the rotary mass and the rotary damper in the engaged state; whereinthe wing assembly comprises a controller configured to control each clutch to switch the vibration control unit from the first configuration to the second configuration in response to a shock response of the wing.

20. The wing assembly of any preceding claim, wherein the tendon is under tension when the wing is at rest.

21. The wing assembly of any preceding claim, comprising tension adjusting means configured to adjust tension of the tendon.

22. The wing assembly of any preceding claim, comprising at least one tendon guide mounted to the wing and configured to guide the tendon along a predetermined path.

23. The wing assembly of claim 22, wherein at least a portion of the tendon along the predetermined path is angled to a central longitudinal axis of the wing.

24. The wing assembly of any preceding claim, wherein the tendon is fixed to the wing at a location adjacent the tip of the wing.

25. The wing assembly of any preceding claim, wherein the tendon comprises a first branch and a second branch, wherein the first branch extends from a first end of the tendon to the input element and the second branch extends from the input element to a second end of the tendon.

26. An aircraft comprising the wing assembly of any preceding claim.

27. A computer implemented method of designing a wing assembly, the wing assembly comprising:a wing;a tendon fixed to the wing at a first location and coupled to the wing to transform vibrations of the wing into axial displacement of the tendon; anda vibration control unit comprising:an input element coupled to the tendon to transform axial displacement of the tendon into rotation of the input element; andat least one damping element configured to be coupled to the input element and comprising one or more of: at least one moveable mass or inerter, at least one elastic element, and at least one damper; whereinthe vibration control unit is proximal to the root of the wing; and at least one tendon guide mounted to the wing and configured to guide the tendon along a predetermined path extending between the first location and the vibration control unit;the computer implemented method comprising:optimising the predetermined path, wherein optimising the predetermined path comprises:determining a tendon-wing coupling factor for at least one vibration mode of the wing;determining a tendon-VCU coupling factor for the or each vibration mode of the wing;determining a tendon routing efficiency factor in dependence on the tendon-wing coupling factor and the tendon-VCU coupling factor; and performing an optimisation to maximise the tendon routing efficiency factor for the or each vibration mode of the wing; anddetermining a mass of the or each moveable mass, a stiffness of the or each elastic element, and / or a damping coefficient of the or each damper in dependence on the tendon-wing coupling factor and the tendon-VCU coupling factor for the or each vibration mode.

28. A method of manufacturing a wing assembly of an aircraft, the method comprising:producing a design of the wing assembly using the method of claim 27; and manufacturing the wing assembly according to the design.

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