GB2580064A

GB2580064A - Wingtip device for an aircraft

Info

Publication number: GB2580064A
Application number: GB1820830.6A
Authority: GB
Inventors: cosentino Enzo; Polimeno Umberto
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2018-12-20
Filing date: 2018-12-20
Publication date: 2020-07-15
Also published as: GB201820830D0

Abstract

An aircraft wing (102 fig 1) includes a closed surface wing tip device (104 fig 1) which includes an element or actuator 330 within the wing tip for deforming/morphing the shape of the wing tip between geometrical configurations having different aerodynamic properties, for example including one with better overall fuel efficiency for a shorter journey and one with overall fuel efficiency better suited for a longer journey. The device 400 includes a lower winglet 406 with an essentially planar portion 410 spaced apart from the main body of the wing by a blended transition region which is shaped such that the curvature of the local dihedral increases in the outboard direction. The device 400 includes an upper aerofoil structure 414 which with the winglet 406 essentially forms the closed surface.

Description

WINGTIP DEVICE FOR AN AIRCRAFT BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to a wingtip device for an aircraft. More particularly, but not exclusively, this invention concerns a closed surface wing tip device for an aircraft. The invention also concerns a method of operating an aircraft, the aircraft including a pair of closed surface wing tip devices.

[0002] The efficiency of a fixed wing aircraft can be improved by the addition of a wingtip device. Such devices typically improve aerodynamic performance by means of reducing induced drag that would otherwise be caused by vortices downstream of the wingtip of the aircraft wing. One such wingtip device is used on the Airbus A320 Neo, the device commonly being referred to as a "sharklet". The extra mass that is added by such a sharklet can exceed 100 kg, yet the addition of a sharklet can still provide significant fuel efficiency advantages despite such extra mass. Much of the mass of the sharklet is dictated by the need for sufficient structural strength over the whole device. [0003] It has previously been proposed that a spiroid shaped wingtip device might provide improved performance. An early proposal concerning a "spiroid tipped wing" was the subject of US 5,102,068.

[0004] US2017/0029094 discloses an aircraft wing having a strut-braced wing tip device.

[0005] US 2017/0073062 purports to disclose a variable geometry wingtip having an upper aerofoil surface and a lower aerofoil surface which, according to the disclosure, change shape according to the flight conditions of the aircraft. For example it is suggested that a ram air effect between the two aerofoil surfaces acts to inflate the structure, leading to increased stability. There are no moving parts in the upper aerofoil structure. The inventors of the present application have doubts over the feasibility of constructing a wingtip device in accordance with US '062.

[0006] It is generally desired to improve the fuel efficiency of an aircraft. This may typically be achieved by a combination of improving aerodynamic efficiency and/or reducing mass. Thus, any devices added to the aircraft in order to improve aerodynamic efficiency should ideally do so in a way that either does not increase mass or provides an overall benefit despite an overall increase in mass. One added complication is that -2 -optimising fuel efficiency for take-off conditions of an aircraft might result in a solution that is not optimised for the aircraft when flying at cruising altitude, and vice versa. [0007] The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved wingtip device for an aircraft. Alternatively or additionally, the present invention seeks to provide a way in which the fuel efficiency of an aircraft might be improved.

SUMMARY OF THE INVENTION

[0008] The present invention provides according to a first aspect of the invention a wing tip device for an aircraft, preferably including a closed surface. The wing tip device includes an element within the wing tip device which is arranged to deform the shape of the wing tip device, for example when the aircraft is stationary and on the ground. There may be more than one such element within the wing tip device. The one or more elements may be configured to deform the shape from a first geometrical configuration to a second geometrical configuration, for example such that the second geometrical configuration has different aerodynamic properties from the first geometrical configuration.

[0009] Embodiments of the present invention, for example an aircraft featuring such wing tip devices, may enable the aerodynamic performance of the aircraft to be adjusted to suit a typical set of flight conditions. On a given occasion, the wing tip device may for example be set to optimise fuel efficiency for a short haul flight where fuel consumption during take-off has a greater effect on overall fuel efficiency than fuel consumption during steady state cruise mode. On a different occasion, the wing tip device may for example be set to optimise fuel efficiency for a longer haul flight where fuel consumption during steady state cruise mode has a greater impact.

[0010] It may be that at least one point on the wing tip device outer surface is displaced by at least lOmm, preferably by at least 50mm, and possibly by more than 100mm, as between the first and second geometrical configurations. There may be many different geometrical configurations of the wing tip device.

[0011] The one or more elements may be arranged to be able to deform actively the overall shape of the wing tip device while the aircraft is in flight. It may be that the -3 -wing tip device is arranged such that the one or more elements deform the shape of the wing tip device while the aircraft is stationary and on the ground. It may for example be the case that a particular configuration of the wing tip device is selected before the aircraft takes off for a particular destination.

[0012] The shape of the wing tip device may be arranged to be deformed with two degrees of freedom. For such a feature, it may be preferred to have more than one independently movable element for deforming the shape of the wing tip device.

[0013] The one or more elements may be arranged to deform the overall shape of the wing tip device by means of an elastic deformation of the wingtip device. The one or more elements may be arranged to deform the overall shape of the wing tip device such that substantially the majority of the outer surfaces, by surface area, are displaced from one configuration to another. The wing-tip device may for example undergo a global, or macroscopic, deformation of substantially its entire shape. The wing-tip device may comprise a morphing surface.

[0014] The element may be arranged to exert a range of forces wherein the difference between the maximum force and the minimum force is greater than 100N. The element may be under tension when exerting the force. The element may for example comprise one or more cables. The element may for example comprise one or more links, chains, hinged portions, or the like. The element may be under compression when exerting the force. The element may for example comprise one or more actuators. The element may for example comprise one or more pistons, rods, or the like. The element may directly exert a force at various positions along the spanwise length of the wing tip device. The element may be substantially enclosed by the outer skin of the wingtip device, for example such that no part of the element is directly exposed to airflow when the device is in use on an aircraft in flight.

[0015] The wing tip device may comprise a lower section and an upper section, for example the lower section being separately discernible from the upper section. There may be a junction between the upper section and the lower section. The upper section and the lower section may together, possibly with other parts, form a closed loop, for example corresponding to the closed surface of the closed surface wing tip device. In some embodiments, the lower section and the upper section may be joined by a blended region, there being no easily discernible single junction between the upper section and the lower section. The upper section and the lower section may be connected at two -4 -separate spaced apart regions, such that together they form the closed surface. It may be that a joint is formed between the upper section and the lower section of the wing tip device. Such a joint may be a fixed joint. Such a joint may be a pivoting joint. The wing tip device may include an overhang portion, for example at the tip of the wing tip device. Thus, in some embodiments, one or both of the upper section and the lower section may form a part of the wing tip device, which is not also a part of the closed surface.

[0016] The lower section of the closed surface of the wing tip device may be in the form of a winglet, for example a blended winglet. In certain embodiments of the invention, the lower section of the wing tip device is designed primarily having in mind the desire to reduce lift-induced drag caused by wingtip vortices. The winglet may for example resemble the overall shape and have substantially the same aerodynamic function as the so-called -sharklets" provided for use on Airbus A320/A320Neo, A330/330Neo and A350 aircraft.

[0017] The winglet (of the lower section) may be in the form of the wing tip device/shape as described and claimed in EP2084059. The contents of that application are fully incorporated herein by reference. The claims of the present application may incorporate any of the features disclosed in that patent application. In particular, the claims of the present application may be amended to include (in relation to the shape and functionality of the aforementioned winglet) features relating to the claimed wing tip shape for a wing as set forth in EP2084059A as published. For example, the winglet may comprise an essentially planar outboard portion and an inboard transition region which is shaped such that the curvature of the local dihedral increases in the outboard direction. It may also be that said curvature characteristic is present at any curve formed by constant chordwi se points in the transition region along the spanwise dimension. [0018] The winglet may have a first portion having a first dihedral angle and a second portion, outbound of the first portion, having a second higher dihedral angle. The first portion of the winglet may account for at least 25% of the winglet's spanwise length. The second portion of the winglet may account for at least 25% of winglet's spanwise length. The second dihedral angle may be at least 30 degrees higher than the first dihedral angle. The first dihedral angle may be greater than -5 degrees. The first dihedral angle may be positive. The first portion of the lower section may have a dihedral angle of less than +20 degrees, for example over a spanwise length of more -5 -than 100mm, preferably more than 250mm and optionally more than 500mm. The second portion may have a dihedral angle of greater than +60 degrees, for example over a spanwise length of more than 100mm, preferably more than 250mm and optionally more than 500mm. (It will be appreciated that the first portion may have a negative dihedral angle, at least in part, which might be referred to as a positive and anhedral angle.) The lower section of the closed surface of the wing tip device may have no portion that has an anhedral angle greater than 5 degrees. The first portion of the lower section may have a dihedral angle of less than +20 degrees over more than 25% of its spanwise length. The second portion may have a dihedral angle of greater than +60 degrees over more than 25% of its spanwise length.

[0019] The upper section of the closed surface of the wing tip device may extend from a region in the first portion of the lower section to a region in the second portion of the lower section. The upper section may be in the form of an aerofoil surface. The overall dimensions of the upper section of the closed surface may be similar to those of the lower section. The upper section of the closed surface may have a maximum dimension in the chordwise direction that is between 50% and 200% (possibly greater than 75%, optionally greater than 80%, possibly less than 150%) of the maximum dimension in the chordwise direction of the lower section. The upper section of the closed surface may be significantly less massive than the lower section however. For example, the upper section of the closed surface may have a mass that is less than two thirds of the mass of the lower section, optionally less than less than half of the mass of the lower section, possibly less than 40% of the mass of the lower section. It may be that the mass is greater than 20% of the mass of the lower section.

[0020] The closed surface may be in the form of a spiroidal wing tip device.

[0021] It will be understood that the dihedral angle is the angle as measured when the aircraft is on the ground at rest with the wing tip device adopting the first geometrical configuration. If the angle of inclination of the wing surface varies according to the chordwise position at which it is measured and/or on which of the upper and lower surfaces of the wing tip device is used to define the angle, then the dihedral angle may be taken as the angle when measured with reference to the surface midway between the upper and lower surfaces of the body concerned and as averaged across the chordwise direction. -6 -

[0022] The upper section of the closed surface of the wing tip device may have a height (e.g. measured as the vertical component of the distance above the root of the wing tip device) which is between 50% and 200% (possibly greater than 75%, optionally greater than 80%, possibly less than 150%) of the height of the lower section. The lower section of the closed surface of the wing tip device may have a height of at least 250mm, preferably at least 500mm and optionally greater than 750mm.

[0023] The upper section of the closed surface of the wing tip device may have a spanwise extent which is between 50% and 200% (possibly greater than 75%, optionally greater than 80%, possibly less than 150%) of the spanwise extent of the lower section.

[0024] The wing tip device may be so shaped that in its first configuration there is a point on the lower surface of the upper section for which the shortest distance to the nearest point on the lower section is greater than 10%, preferably at least 20%, and optionally greater than 30% of the height of whichever is higher of the upper section and the lower section. The wing tip device may be so shaped that in its first configuration there is a point on the lower surface of the upper section for which the shortest distance to the nearest point on the lower section is greater than 10%, preferably at least 20%, and optionally greater than 30% of whichever is longer of the spanwise extent of the upper section and the lower section.

[0025] The wing tip device may be so shaped that in its first configuration there is a point on the lower surface of the upper section for which the shortest distance to the nearest point on the lower section is greater than 250mm away, preferably at least 500mm away, and optionally greater than 750mm away.

[0026] The first portion and the second portion of the lower section may be joined by a blended portion.

[0027] The upper section of the wing tip device may have a portion having a dihedral angle of greater than +30 degrees, and preferably greater than +45 degrees, over a spanwise length of more than 250mm, preferably more than 500mm and optionally more than 750mm.

[0028] Certain embodiments of the present invention may have application where the lower section is provided primarily to perform the function of a winglet (such as for example a sharklet device) whereas the upper section is provided primarily to perform the dual functions of bracing the winglet and actively manipulating the aerodynamic shape of the winglet. The upper section may be actively moveable (by integrated actuators for example) whereas the winglet (lower section) may be a passive structure having a global shape that is adaptable by external forces. This may simplify design and manufacture of a new aircraft wing. The core design may be based on an existing (e.g. passive, but reasonably flexible/elastically deformable) winglet structure which is then modified to reduce its strength and/or mass in view of the bracing that is able to be provided by an upper (e.g. active) section that is added, and which upper section can be controlled / activated to morph the shape of the winglet structure. The benefits of embodiments of the invention can then be provided with greater ease than a complete redesign of the wing. In some embodiments, the upper section could be provided as a retrofitted structure to an existing winglet.

[0029] In certain embodiments of the invention, the upper section of the wing tip device is designed primarily having in mind one or more of (i) a desire to reduce mass of the lower section, by providing structural strength by using the upper section as a support strut and (ii) a desire to provide a means of controllably deforming the shape of the lower section by means of one or more elements contained in the upper section. In certain embodiments, the one or more elements may be contained only within the upper section. This arrangement may simplify the aircraft wing design process. The upper section may have a mass greater than 10Kg.

[0030] The upper section of the wing tip device may be a morphing structure, the shape to which the upper section is morphed being controllable by the one or more elements contained within the upper section. The shape adopted by the lower section of the wing tip device may depend on and be controlled by the shape to which the upper section is morphed. The lower section of the wing tip device may be a morphing structure, the shape to which the lower section is morphed being controllable by the one or more elements contained within the lower section. There may be elements for deforming the shape of the wing tip device in both the upper and the lower sections. The upper section of the wing tip device may have a spanwise length that can be controllably changed (increased or decreased) by the one or more elements contained within the upper section.

[0031] The wing tip device may be so arranged that when installed on an aircraft and viewed in the direction of the longitudinal axis of the aircraft, there is a first notional straight line joining (a) the region of the (inboard) junction between the lower section

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and the upper section (i.e. at the region in the first portion of the lower section) and (b) the region of the (outboard) junction between the lower section and the upper section (i.e. at the region in the second portion of the lower section. There may also be a second notional line which defines the average extent and overall shape of the lower section. The first notional line may form at one end a first included angle with the second notional line, the included angle for example being greater than 20 degrees, for example greater than 30 degrees. The first notional line may additionally form at the opposite end a second included angle with the second notional line, the second included angle for example being greater than 20 degrees, for example greater than 30 degrees. [0032] According to a second aspect of the invention there is provided a closed surface morphing winglet for an aircraft (for example a non-planar winglet). The shape of the morphing winglet is preferably internally reconfigurable, for example by mean of (re-)configuring something inside the winglet. The shape of the morphing winglet may be controlled by means of an internal mechanism, for example one or more elements as described above in relation to the first aspect of the invention.

[0033] According to a third aspect of the invention there is provided an aircraft wing comprising a main body, a winglet at an outboard end of the wing, an upper aerofoil structure, and a closed loop at the wing tip formed at least in part by at least part of the winglet and at least part of the upper aerofoil structure, the upper aerofoil structure having an actively controllable shape and/or length, which acts in use to manipulate the shape of the winglet by loading the winglet to cause elastic deformation of the winglet from a first aerodynamic configuration suitable for a short-haul flight over a first distance to a second different aerodynamic configuration better suited for a flight over a second distance different from the first difference. One of the first and second distances may be more than twice the other. The winglet may have an outboard portion, for example an essentially planar portion, spaced apart from the main body by a blended transition region. The dihedral of the outboard portion of the winglet may be higher than a dihedral of the transition region. The transition region may be shaped such that the curvature of the local dihedral increases in the outboard direction. The upper aerofoil structure may extend between a position outboard of a location between the outboard (e.g. essentially planar) portion and the blended transition region to a position inboard of that location. -9 -

[0034] According to a fourth aspect of the invention there is provided an aircraft wing incorporating or otherwise comprising a wing tip device according to the first aspect, a winglet according to the second aspect of the invention, or a wing according to the third aspect of the invention There is also provided an aircraft comprising such a wing The aircraft may be a single aisle aircraft. The aircraft may be a passenger aircraft, for example an aircraft configured to carry more than 50 passengers, for example more than 100 passengers.

[0035] According to a fifth aspect of the invention there is provided a method of operating an aircraft, the aircraft including a pair of closed surface wing tip devices on opposite sides of the aircraft, wherein the method includes deforming the shape of each wing tip device from a first geometrical configuration in which the wing tip devices are set up in a manner to suit a first flight profile, for example in accordance with a given planned destination and route, to a second geometrical configuration in which the wing tip devices are set up in a manner to suit a second flight profile, different from the first flight profile (for example having a different route, planned flight time, distance or the like) In certain embodiments, it may be possible for the fuel efficiency of the aircraft if set up in the second configuration to be worse for the first flight than when set up in the first configuration, and for the fuel efficiency of the aircraft if set up in the first configuration to be worse for the second flight than when set up in the second configuration. For example, the first configuration may suit short-haul flights over particularly short distances, whereas the second configuration may suit longer distance flights.

[0036] The aircraft may be one incorporating any other aspect of the invention as described or claimed herein.

[0037] It may be that the step of deforming the shape of the wing tip device includes exerting a force sufficient to elastically deform the shape an outboard portion of the wing, for example of the wing tip device or of the winglet as described above, such that at least one point on the outer surface is displaced by at least lOmm.

[0038] There may be features of the above described invention that have benefit separately from the ability to change the shape of the wing tip device There may for example be beneficial embodiments of the invention not including any internal elements actuators or the like for morphing the shape of the wing tip device.

-10 - [0039] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa

DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows an aircraft of a type suitable for use with a wing tip device a according to a first embodiment of the invention; Figure 2 shows a side view of a wing tip according to the first embodiment; Figure 3 shows a perspective view of a wing tip device similar to that shown in Figure 2, but in accordance with a second embodiment; Figure 4 shows a side view of a wing tip according to a third embodiment; Figure 5 shows a perspective view of the wing tip device shown in Figure 4 set up in a first configuration; Figure 6 shows a perspective view of the wing tip device shown in Figure 4 set up in a second configuration; Figure 7 shows a perspective view of the wing tip device shown in Figure 4 set up in a third configuration; and Figure 8 shows a flowchart of the steps of a method according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

[0041] Figure 1 shows an aircraft 100 comprising two wings 102. A wing tip device 104 is arranged at the tip of each wing 102. The wing tip device may be in accordance -11 -with the first embodiment of invention, the second embodiment of the invention described below, or variations thereof [0042] Figure 2 shows a wing tip device 200, of a first embodiment, viewed in the longitudinal axis of the aircraft. The device 200 has a root 202 at its inboard end and a tip 204 at its outboard end. The device 200 comprises a lower section 206 which has the general profile of a blended winglet. The lower section 206 in this case has a shape corresponding generally to that of a "sharklet" for the Airbus A320 Neo. Thus the section 206 comprises a generally horizontal inbound portion 208 that is joined to a canted outbound portion 210, via a blended region 212. The dihedral angle of the canted outdone portion is about 70° for at least 1,000 mm of its extent. The height, h, of the tip 204 above the horizontal position of the inbound portion 208 is at least 2,000 mm. Each lower section 206 has a mass of the order of at least 80 kg.

[0043] The device 200 comprises an upper section 214 which acts as a strut extending from a location at or directly adjacent to the root 202 of the device to a location at or directly adjacent to the tip 204 of the device 200. The upper section 214 and the lower section 206 thus define, at least in part, a closed surface. In this embodiment, the upper section 214 is generally planar and is shown in Figure 2 as having a dihedral angle of about 45° for substantially the entirety of its extent in the spanwise direction. Each upper section 214 has a mass of the order of 25 kg (optionally, in the range of 20 kg to 301(g).

[0044] It will be noted that the upper section 214 extends from an outboard position set slightly inward from the extreme end of the tip 204 of the device 200 to an inboard position set slightly outward from the root 202 of the device 200. There is thus a slight overhang at the tip 204 of the device 200 which does not form a part of the closed surface.

[0045] The device shown in Figure 2 thus comprises a blended winglet device 206 (in the form of a sharklet) which is strengthened by means of an upper section 214, which also presents an aerofoil surface. It is believed that substantially the same, or better, aerodynamic benefits may be provided by the lower section 206 as a conventional sharklet structure but as a result of the strengthening provided by the upper section the lower section can be constructed so as to have a lower mass than the conventional sharklet structure, by possibly greater than 25 kg of mass saving per wing tip device. The wing tip device of the first embodiment may therefore be substantially mass neutral -12 -as compared to the same aircraft when fitted with a sharklet wingtip device. The angle formed between the lines of the upper section 214 and the lower section 206 in the region of the root 202 is about 50°. The angle formed between the lines of the upper section 214 and the lower section 206 in the region of the tip 204 is about 25°. The region at which the upper section 214 joins the lower section 206 in the region of the root 202 coincides with a rib (not shown separately in Figure 2). There may be at least one further rib outboard of the rib to which the upper portion 214 so attaches.

[0046] Figure 3 shows (with a highly schematic diagram) a perspective view of a device 300 according to a second embodiment, which has substantially the same shape and configuration as the device of Figure 2. The reference numerals as used in Figure 3 will refer to the same parts as the reference numerals used in Figure 2, but will start with a "3' instead of starting with a "2". The upper section 314 of the device 300 includes two elements 330, which are arranged to exert varying forces within the structure of the upper section 314 in a direction substantially parallel with the spanwi se direction Ds of the wing, when viewed in plan. (It will be understood that in the present context the spanwise direction at a given location is taken as the mean direction of the leading and trailing edges of the wing when viewed in plan, and not necessarily perpendicular to the longitudinal direction of the aircraft). In this embodiment, the elements 330 may be in the form of hydraulic actuators. By means of varying the force exerted by each element 330 in the upper section 314, it is possible to change the global shape of the upper section 314 and consequently also change the global shape of the lower, winglet, section 306. In use, it is then possible to morph the aerodynamic shape of the lower, winglet, section 306 to suit a particular flight plan. For example for a 1/2 hour flight, the optimum shape of the winglet part of the wing may be different from the optimum shape of the winglet part for a three hour flight. The elements 330 are independently operable and therefore are able to manipulate the shape of the upper and lower sections 306, 314 with two degrees of freedom. If both elements 330 are contracted, the tip 304 of the device is moved inboard. If one element 330 is extended and the other element 330 is contracted then a twisting stress is induced in the upper and lower sections 306, 314. The hydraulic elements 330 can be controlled from within the aircraft, for example by the pilot of the aircraft, during flight, but it is envisaged that the hydraulic elements 330 would typically be set up in advance of takeoff and not adjusted again until landing. However, in more sophisticated embodiments of the -13 -present invention, the hydraulic elements 330 could be controlled during flight so as to improve the aerodynamic performance of the wing as between, for example, takeoff and cruise conditions.

[0047] Figure 4 shows a wing tip device 400, of a third embodiment, viewed in the longitudinal axis of the aircraft. The reference numerals as used in Figure 4 will refer to the same parts as the reference numerals used in Figure 2, but will start with a "4" instead of starting with a "2". The device 400 has a root 402 at its inboard end and a tip 404 at its outboard end. The device 400 comprises a lower section 406 which has the general profile of a blended winglet. The lower section 406 has a shape which is substantially the same as the lower section 206 of the first embodiment of the invention. Thus the section 406 comprises a generally horizontal inbound portion 408 that is joined to a canted, essentially planar, outbound portion 410, via a blended transition region.

[0048] The device 400 comprises an upper section 414 extending from a location at or directly adjacent to the root 402 of the device to a location in the region of the tip 404 of the device 400. It will be noted that the upper section 414 extends from an outboard position set slightly inward from the extreme end of the tip 404 of the device 400. In this embodiment, the tip of the upper section 414 extends to an outboard position beyond the tip of the lower section 410 [0049] In this embodiment, the upper section 414 is generally curved, such that its upper surface 428 is substantially convex. The upper section 414 thus has a dihedral angle that varies along the spun way is extent of the upper section from a value of about 700 to a value of about 30°. It will be seen that the gap between the upper and lower sections of the wingtip can be several orders of magnitude bigger than the thickness of either the upper or lower section. For example, the length represented by the arrow labelled / (such a length representing the shortest distance between the lower surface of the upper section 414 to the upper surface of the lower section 406 at the location of the arrow)) is greater than 500 mm.

[0050] Figure 5 shows the wingtip device 400 of the third embodiment in a highly schematic manner. The upper section 414 comprises two integrally formed cable systems 430 which are arranged within the structure of the upper section 414 in such a way as to enable the shape of the upper section 414 to be deformed elastically under the control of the cable systems 430. In this embodiment, the integrated cable systems 430 are designed to be adjusted by ground crew when attending to the aircraft when on -14 -the ground and a stationary. Once the geometry of the wingtip device 400 has been set up by ground crew by means of making adjustments to the integrated cable systems 430 and the aircraft is moving, the setup of the wingtip device, in so far as its global geometry is concerned, is a fixed and cannot be altered or controlled by the pilot during flight. Figure 5 shows the wingtip device 400 in a first configuration, in which the tension in each cable system is approximately equal, at about 250 N. [0051] Figures 6 and 7 show the wingtip device 400 in a second configuration and a third configuration, respectively. In both Figures 6 and 7, the position of the upper section 414 when in its first configuration is shown in broken line (labelled as 414') the position of the lower section 406 when in its first configuration is shown in dotted line (labelled as 406'). Figure 6 shows the cable systems both under increased tension for example each exerting a tension of about 500 N, resulting in the tip of the upper section 414 being drawn more inboard with a consequent movement of the tip of the lower section 406 inboard also.

[0052] Figure 7 illustrates a case where one of the cable systems 430 has a tension (for example 100 N) significantly lower than the tension in the other of the cable systems 430 (for example 700 N). Tn this case the upper section 414 and the lower section 406 are twisted from the position of the first configuration. There are portions on the wingtip device which moved by more than 50 mm as between the first configuration and the second configuration. Similarly, there are portions on the wingtip device which move by more than 50 mm as between the first configuration and the third configuration. The movement from the first to the second configurations (and the movement from the first to the third configurations), is such that the wingtip device is deformed elastically and is thus able to return to its previous shape, as and when the internal stresses are returned to their previous values. It will be seen that the extent of the cable systems 430 in the upper section 414 follows a path that curves, and that the curvature of that path can change as between the various configurations of the wingtip device. Such a curvature, and changes in curvature, can be accommodated by means of the cable passing via channels, pulleys, wheels or the like.

[0053] Figure 8 illustrates a flowchart of 500 illustrating a method according to a fourth embodiment of the invention. The aircraft may be one as shown in Figure 1 incorporating wingtip devices of an embodiment of the invention. As a first step 501 the wingtip devices are set up so as to be suitable for a short haul flight, in which the -15 -time the aircraft is expected to fly at cruising altitude is around 30 minutes. The aircraft undertakes the flight (step 502). When back on the ground, the wingtip devices are adjusted by means of changing the geometry of the wingtip devices (as in step 503) so as to be more suited to a longer flight. This step may include imparting a twisting force in the wingtip device to provide a different aerodynamic profile at the wingtip. The aircraft then undertakes a further flight (step 504), in which the aircraft flies at cruising aptitude for three hours or longer. The fuel efficiency of the aircraft when set up in the first configuration is better for the first flight and it would be for the second flight if retained in that first for configuration. Likewise, the fuel efficiency of the aircraft when set up in the second configuration is better for the second flight than it would be for the first flight if retained in that second configuration.

[0054] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0055] It will be appreciated that the wingtip device shown in the Figures might include fairings and/or additional fairing services in order to smooth out any sharp changes in curvature. The wingtip device may be a closed service wingtip device without any other parts protruding from the smoothly faired structure that provides the closed surface.

[0056] There may be features of the above described embodiments that have benefit independently of a wing tip device with an upper aerofoil surface forming a closed loop blended wing tip device (in which the upper and lower aerofoil surfaces are similarly dimensioned). For example, there may be embodiments of the invention where a (for example, sharklet-type) winglet has a shape which can be morphed using a moveable bracing structure (with associated integrated actuators for example) that extends from an inboard portion of the winglet to an outboard portion of the winglet. Such a bracing structure may be so shaped that it has a maximum chordwise dimension at a location immediately above a portion of the winglet structure which has a chordwise dimension at least twice the size. Additionally or alternatively, such a bracing structure may be so shaped that its chordwise dimension at the midpoint along its spanwise length, is less than half of the chordwise dimension of the winglet structure at the location immediately below. Additionally or alternatively, such a bracing structure may have -16 -an average chordwise dimension (along its spanwise length) which is less than half the average chordwi se dimension (along its spanwi se length) of the wi ngl et structure. [0057] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[0058] The term 'or' shall be interpreted as 'and/or' unless the context requires otherwise.

Claims

CLAIMS1. A dosed surface wing tip device for an aircraft, wherein the wing tip device includes an element within the wing tip device which is arranged to deform the shape of the wing tip device from a first geometrical configuration to a second geometrical configuration with different aerodynamic properties from the first geometrical configuration.
2. A device according to claim I, wherein the element is arranged to deform the overall shape of the wing tip device by means of an elastic deformation
3. A device according to claim 1 or claim 2, wherein the element is arranged to exert a range of forces wherein the difference between the maximum force and the minimum force is greater than 100N.
4. A device according to any preceding claim, wherein the closed surface of the wing tip device comprises a lower section being in the form of a winglet having a first portion having a first dihedral angle and a second portion, outbound of the first portion, which has a second dihedral angle which is at least 30 degrees more than the first positive dihedral angle, and an upper section which extends from a region in the first portion of the lower section to a region in the second portion of the lower section, and which forms with the lower section the closed surface.
A device according to claim 4, wherein the first portion of the lower section has a dihedral angle of less than +20 degrees and the second portion has a dihedral angle of greater than +60 degrees over a spanwise length of more than 500mm
6. A device according to claim 4 or claim 5, wherein the winglet forming the lower section of the closed surface of the wing tip device has a height of at least 500mm.-18 -
7. A device according to any of claims 4 to 6, wherein the upper section includes a portion having a dihedral angle of greater than +45 degrees over a spanwise length of more than 500mm
8. A device according to any of claims 4 to 7, wherein there is a point on the lower surface of the upper section for which the shortest distance to the nearest point on the lower section is greater than 500mm away.
9. A device according to any of claims 4 to 8, wherein when the wing tip device is installed on an aircraft and viewed in the direction of the longitudinal axis of the aircraft, there is a first notional straight line joining said region in the first portion of the lower section and said region in the second portion of the lower section, between which regions the upper section extends, and a second notional line which defines the average extent and overall shape of the lower section, the first notional line forming at one end a first included angle with the second notional line and at the other end a second included angle with the second notional line, each of the first and second included angles being greater than 20 degrees.
10. A device according to any of claims 4 to 9, wherein the upper section has a mass of greater than 10Kg.
11. A device according to any of the preceding claims, wherein the element comprises an actuator.
12 A device according to any of the preceding claims, wherein the shape of the wing tip device is arranged to be deformed with two degrees of freedom
13. A closed surface internally reconfigurable morphing w nglet for an aircraft.-19 -
14. An aircraft wing comprising a main body, a winglet at an outboard end of the wing, the winglet having an essentially planar portion spaced apart from the main body by a blended transition region which is shaped such that the curvature of the local dihedral increases in the outboard direction and an upper aerofoil structure extending between a position outboard of a location between the essentially planar portion and the blended transition region to a position inboard of the location between the essentially planar portion and the blended transition region, and a closed loop at the wing tip formed at least in part by at least part of the winglet and at least part of the upper aerofoil structure, the upper aerofoil structure having an actively controllable shape and/or length, which acts in use to manipulate the shape of the winglet by loading the winglet to cause elastic deformation of the winglet from a first aerodynamic configuration suitable for a short-haul flight over a first distance to a second different aerodynamic configuration better suited for a flight over a second distance different from the first difference.
15. An aircraft wing Incorporating or otherwise comprising a wing tip device according to any of claims Ito 12 or a winglet according to claim H.
16. An aircraft comprising a wing according to claim 14 or claim 15.
17 A method of operating an aircraft, the aircraft including a pair of closed surface wing tip devices on opposite sides of the aircraft, wherein the method includes deforming the shape of each wing tip device from a first geometrical configuration in which the wing tip devices are set up in a manner to suit a first flight to a second geometrical configuration in which the wing tip devices are set up in a manner to suit a second flight, different from the first flight, such that the fuel efficiency of the aircraft if set up in the second configuration would be worse for the first flight than when set up in the first configuration, and -20 -the fuel efficiency of the aircraft if set up in the first configuration would be worse for the second flight than when set up in the second configuration.
18. A method according to claim 17, using an aircraft according to claim 16.