Methods for aircraft, wings, fixed wings, wingtip devices, and design interfaces

Abstract

The present invention relates to an aircraft (1002) comprising a wing (1001) having a fixed wing (1005) and a wingtip device (1003) movably mounted at the outer end of the fixed wing. The wingtip device (1003) is capable of moving between a flight configuration and a ground configuration about a rotation axis. The wingtip device (1003) abuts the fixed wing (1005) along an interface cut line (1035). The interface cut line (1035) includes a curved portion (1039) centered on the rotation axis (1011), the radius of the curved portion increasing continuously as the cut line moves about the axis (e.g., a spiral shape). The present invention also relates to a method of designing a wing, a fixed wing, a wingtip device, and an interface.

Description

Technical Field

[0001] The present invention generally relates to aircraft, wings of aircraft, fixed wings, wingtip devices, and a method for designing an interface between an outer end portion of a fixed wing for an aircraft and an inner end portion of a wingtip device. Background Art

[0002] There is a trend towards ever larger airliners, for which correspondingly large wingspans are required. However, the maximum aircraft wingspan is actually limited by airport operating rules that govern the various clearances required for maneuvers around the airport (such as the wingspan and / or ground clearance required for entering a stand and using a safety taxiway).

[0003] To address this problem, various devices have been proposed that include movable wingtip devices that specifically enable the wingspan to be reduced in the ground configuration.

[0004] WO2015 / 150835 is an example of a proposed device. In the device of WO2015 / 150835, the wingtip device and the fixed wing are separated along an inclined cutting plane, and the wingtip device is capable of rotating about a rotation axis perpendicular to the cutting plane.

[0005] In the device of WO2015 / 150835, it has been found that sealing the interface between the fixed wing and the wingtip device (when the wingtip device is in the flight configuration) is problematic. More specifically, when the wingtip device rotates between the flight configuration and the ground configuration, relative sliding motion occurs at the interface between the outer end portion of the fixed wing and the inner end portion of the wingtip device. Although a sliding seal can in principle be employed, this solution is sub-optimal since sliding seals tend to be subject to relatively high wear. This can make the sliding seal prone to wear and / or damage and may therefore require frequent inspection and / or replacement of the seal.

[0006] The UK patent application GB1610108.1 of Airbus Operations Limited (filed on June 9, 2016, not yet published) proposes a device in which the outer end of a fixed wing and the inner end of a wingtip device meet along an interface cut line that separates the outer surface of the fixed wing from the outer surface of the wingtip device. The content of GB1610108.1 is incorporated herein by reference. In the embodiment described in GB1610108.1, the interface cut line includes a first length, a second length, and a transition portion. The first length is formed by a cut through the outer surface, but the first length is offset from a main cutting plane in a first direction; the second length is formed by a cut through the outer surface, but the second length is offset from the main cutting plane in a second direction opposite to the first direction; on the transition portion, the interface cut line transitions from the first length to the second length. The wingtip device can contact the fixed wing along the transition portion in a sliding contact manner, but the wingtip device separates from the fixed wing along the first length and the second length. In GB1610108.1, the transition portion can be many possible shapes.

[0007] Aspects of the present invention seek to provide additional improvements to the interface between a fixed wing and a wingtip device. Summary of the Invention

[0008] According to a first aspect of the present invention, there is provided an aircraft comprising a wing having a fixed wing and a wingtip device movably mounted at an outer end of the fixed wing, the wingtip device being movable between: (a) a flight configuration for use during flight; and (b) a ground configuration for use during ground-based operations, in which the wingtip device rotates about a rotation axis away from the flight configuration such that the wingspan of the wing of the aircraft is reduced. When the wingtip device is in the flight configuration, the outer end of the fixed wing meets the inner end of the wingtip device along an interface cut line that separates the outer surface of the fixed wing from the outer surface of the wingtip device. The interface cut line includes a curved portion centered on the rotation axis, and the radius of the curved portion continuously increases as the cut line moves around the axis.

[0009] It has been found particularly beneficial to provide an interface having a curved portion in which the radius of the curved portion continuously increases about the rotation axis. In particular, since the radius of the curved portion of the interface cut line increases and the curved portion of the interface cut line is centered on the rotation axis of the wingtip, this means that as the wingtip device rotates away from the flight configuration, the structure of the wingtip device separates from the structure of the fixed wing along the interface cut line. In other words, considering a point P along the interface cut line in the curved portion wt , point P wtis located on the side of the wingtip device and at a position with a radius R1 from the axis of rotation. When the wingtip device is in the flight configuration, the corresponding point P on the fixed-wing side of the cutting line fw will be located at a position with substantially the same radius (R1) from the axis. When the wingtip device rotates away from the flight configuration by an angle α, the point P located on the wingtip device wt will rotate about the axis. This point P wt remains located at a position with a radius R1 from the axis (since it is located on the wingtip device), but due to the increase in the radius of the cutting line as the cutting line moves around the axis, the radially outward point P on the wingtip device fw α (which is located at the same angular position α from the axis as the new position of P wt ) will be located at a position with a greater radius (R2) from the axis due to the characteristics of the curved portion. When the wingtip device moves away from the flight configuration, the wingtip device and the fixed wing will thus necessarily move apart along the interface (and vice versa, when the wingtip device moves to the flight configuration, the wingtip device and the fixed wing will move towards each other). Since this movement tends to avoid relative sliding movement at the interface, this movement is beneficial.

[0010] The radius of the curved portion preferably increases when the cutting line moves around the axis in the following direction: the direction such that when the wingtip device moves from the flight configuration to the ground configuration, the fixed wing and the wingtip device separate along the interface. The radius of the curved portion preferably increases when the cutting line moves around the axis in the rotational direction that moves the wingtip device from the flight configuration to the ground configuration. Correspondingly, the radius of the curved portion preferably continuously decreases when the cutting line moves around the axis in the rotational direction that moves the wingtip device from the ground configuration to the flight configuration.

[0011] The above direction is considered from the perspective of looking along the axis of rotation towards the wing surface where the interface cutting line is located. For example, in an embodiment where the curved portion of the interface cutting line is located on the upper surface of the wing, the direction is considered from the perspective of looking along the axis of rotation to that upper surface. Generally, unless otherwise specified, it will be understood that when observing the cutting line in the direction along the axis of rotation and to the wing surface where the relevant portion of the interface cutting line is located, the shape, radius, or other characteristics of the interface cutting line are referred to. In other words, the characteristics of the curved portion can be considered with reference to the projection of the curved portion on a plane perpendicular to the axis of rotation.

[0012] The wingtip device (preferably the tip of the wingtip device) can be configured to rotate generally upward and backward when moving from the flight configuration to the ground configuration. Therefore, the radius of the curved portion is preferably arranged to increase when the curved portion of the cutting line moves around the axis from a rear position on the wing towards a front position on the wing.

[0013] In principle, embodiments of the invention may include curved portions that follow any shape, as long as the radius of the curved portion increases continuously as the cutting line moves around the axis. More preferably, the curved portion generally follows a spiral centered on the axis of rotation. It has been found that a spiral is a particularly effective way to achieve the desired characteristic of radius variation.

[0014] The wing may include an upper surface extending from the leading edge to the trailing edge above the wing, and the wing may include a lower surface extending from the leading edge to the trailing edge below the wing. The curved portion may be located on the upper surface of the wing.

[0015] The curved portion is preferably only a portion of the entire length of the interface cutting line. The interface cutting line may also include a first length and a second length, the first length extending rearwardly from the curved portion and the second length extending forwardly from the curved portion. The first length and the second length preferably do not form respective curved portions having a radius that increases as the cutting line moves about the axis of rotation. For example, the first length and the second length are preferably not spiral centered about the axis of rotation.

[0016] The curved portion may be a transition portion between the first length and the second length.

[0017] The second length may be formed by a cut through the outer surface, the cut extending in a plane containing the axis of rotation, or in a plane parallel to that plane. It has been found to be particularly beneficial to provide a second length formed by a cut through the outer surface, the cut being in a plane containing the axis of rotation, or in a plane parallel to that plane. It has been recognised that by forming the second length in this way, the orientation of the second length of the interface cut line tends to mean that the fixed wing and the wingtip device are separated in a locally vertical direction (along the second length). As a result, the sealing movement tends to be purely compression.

[0018] The second length is preferably formed by a cut through the outer surface and in a plane containing the axis of rotation. Providing the cut in this orientation enables simultaneous separation of the fixed wing and the wing tip device along the entire length of the second cut line when the wing tip device moves from the flight configuration towards the ground configuration.

[0019] It has been found that the invention is particularly beneficial on devices where the wing tip device can be rotated substantially in the manner described in WO2015 / 150835. Thus, the wing tip device and the fixed wing can be separated along an imaginary main cutting plane, the axis of rotation being oriented normal to the main cutting plane. The main cutting plane can be oriented obliquely.

[0020] In embodiments having a first length and a second length of the interface cut line (extending on either side of the bending portion), the first length may be formed by a cut offset from the main cut plane in a first direction. In some embodiments, the second length may be offset from the main cut plane in an opposite second direction. In a more preferred embodiment, the second length may be formed by a cut passing through the outer surface and lying in a plane containing the axis of rotation.

[0021] In embodiments where the wing tip device can rotate in this way, it has been found beneficial to divide the interface cut line into a first length and a second length located on either side of the bending portion. More specifically, since the first length and the second length do not lie in the main cut plane, when the wing tip device rotates about its axis of rotation, the sliding contact motion along these lengths tends to be restricted or there is no sliding contact motion. Instead, the fixed wing and the wing tip device tend to separate (along the first length and the second length) in the case of local translational motion. Since a non-sliding seal (such as a compression seal) can be employed along these lengths, it is beneficial. In all embodiments, the orientation of the axis is preferably such that the wingspan of the aircraft wing decreases when the wing tip device rotates from the flight configuration to the ground configuration about the axis.

[0022] In embodiments including a main cut plane, the main cut plane preferably extends through the upper and lower surfaces of the wing. The distance along the upper surface of the wing from the root of the wing to the cut plane (i.e., to the position where the cut plane intersects the upper surface) may be less than the distance along the lower surface of the wing from the root of the wing to the cut plane (i.e., to the position where the cut plane intersects the lower surface). Accordingly, the cut plane may produce an overcut with respect to the fixed wing. In other embodiments, the distance along the upper surface of the wing from the root of the wing to the cut plane (i.e., to the position where the cut plane intersects the upper surface) may be greater than the distance along the lower surface of the wing from the root of the wing to the cut plane (i.e., to the position where the cut plane intersects the lower surface). Accordingly, the cut plane may produce an undercut with respect to the fixed wing.

[0023] The main cut plane is preferably an imaginary plane separating the fixed wing from the wing tip device (such as a cut plane generated during the design phase of the wing). It will be understood that the cut plane itself may not necessarily appear as a physical planar surface over the entire wing depth. The main cut plane will be readily identifiable to a person skilled in the art. The main cut plane may be the plane in which the wing tip device rotates. Some embodiments of the present invention may include a bearing for supporting the rotation of the wing tip device, such as a slewing ring. The bearing may be coaxial with the axis of rotation. The main cut plane may extend through the thickness of the bearing and typically through the middle thickness of the bearing (i.e., the middle thickness of the bearing is coplanar with the main cut plane).

[0024] The axis of rotation can be oriented at an angle relative to the longitudinal direction (i.e., excluding parallel or perpendicular to the longitudinal direction). The axis is preferably at an angle relative to the lateral direction (i.e., excluding parallel or perpendicular to the lateral direction). The axis is preferably at an angle relative to the vertical direction (i.e., excluding parallel or perpendicular to the vertical direction). The vertical direction, longitudinal direction, and lateral direction can be perpendicular to each other. In some embodiments, the longitudinal direction, lateral direction, and vertical direction can be in an absolute reference system (i.e., the longitudinal is front - rear, the lateral is port - starboard, and the vertical is perpendicular to the ground). The longitudinal direction can be the chordwise direction; the lateral direction can be the spanwise direction. In other embodiments, it may be appropriate to use the longitudinal direction, lateral direction, and vertical direction in a local reference system of the wing. For example, for a swept wing, the longitudinal direction can alternatively be along the length of the wing, and the lateral direction can be along the width of the wing (i.e., from the leading edge to the trailing edge, measured perpendicular to the longitudinal direction). Alternatively or additionally, for a wing with dihedral, the vertical direction can be perpendicular to the plane of the wing. In all cases, the cutting plane / axis is oriented such that the span of the wing decreases as the wingtip device rotates about the axis.

[0025] The wingtip device is preferably capable of rotating about a single axis of rotation. For example, the rotation of the wingtip device is preferably not the result of a compound rotation (i.e., a net rotation produced by multiple individual rotations about separate axes).

[0026] The axis is preferably at an angle of less than 45 degrees with respect to the vertical, and more preferably at an angle of less than 25 degrees. The axis can be at an angle of 15 degrees with respect to the vertical axis. It has been found that the present invention is particularly beneficial in embodiments where the axis is at a relatively small angle with respect to the vertical because the axis orientation results in a shallow cutting plane and the interface area between the fixed wing and the wingtip device may thus be relatively large.

[0027] It has been found that embodiments of the present invention are particularly beneficial when a seal needs to be formed between the fixed wing and the wingtip device. The wing can include a sealing assembly for sealing between the fixed wing and the wingtip device when the wingtip device is in a flight configuration. The wing can include an upper surface that extends from the leading edge to the trailing edge above the wing. The wing can include a lower surface that extends from the leading edge to the trailing edge below the wing. The curved portion can be along the upper surface of the wing. The curved portion can be along the lower surface of the wing. The interface cutting line can include a curved portion along the upper surface and a second curved portion along the lower surface. The second curved portion can generally correspond in shape to the first curved portion (i.e., the second curved portion can be centered on the axis of rotation and the radius of the second curved portion continuously increases as the cutting line moves around the axis). Features described with reference to the (first) curved portion can equally apply to the second curved portion.

[0028] The interface cut line extends continuously around the wing. In embodiments where the interface cut line includes a first curved portion on the upper surface, the first length and the second length of the interface cut line are on both sides of the first curved portion. In embodiments where the interface cut line includes a second curved portion on the lower surface, the interface cut line may further include a third length on the lower surface of the wing. The third length may be formed by a cut that passes through the outer surface of the wing but is offset from the main cutting plane. This offset may be in a second direction opposite to the first direction (i.e., in the opposite direction offset from the first length). The second curved portion may be a transition portion where the interface cut line transitions from the third length to the portion of the second length on the lower surface.

[0029] In embodiments including the first length and the second length of the interface cut line, the first length is preferably located behind the axis of rotation; the second length is preferably located in front of the axis of rotation. In embodiments further including the third length, the third length may be located behind the axis of rotation. In embodiments of the present invention, the wingtip device can be configured between: (a) a flight configuration for use during flight, and (b) a ground configuration for use during ground-based operations, in which the wingtip device moves away from the flight configuration such that the wingspan of the aircraft wing is reduced. In the flight configuration, the wingspan may exceed the airport compatibility limit. In the ground configuration, the wingspan can be reduced such that the wingspan (where the wingtip device is in the ground configuration) is less than or substantially equal to the airport compatibility limit. The airport compatibility limit is a wingspan limit (e.g., related to clearances with buildings, signs, other aircraft). The compatibility limit is preferably a stand limit.

[0030] The wingtip device may be a wingtip extension; for example, the wingtip device may be a planar tip extension. In other embodiments, the wingtip device may include a non-planar device such as a winglet, or be constituted by a non-planar device such as a winglet.

[0031] In the flight configuration, the trailing edge of the wingtip device is preferably a continuation of the trailing edge of the fixed wing. The leading edge of the wingtip device is preferably a continuation of the leading edge of the fixed wing. Preferably, there is a smooth transition from the fixed wing to the wingtip device. It will be understood that a smooth transition may exist even if the sweep or twist at the junction between the fixed wing and the wingtip device changes. However, there is preferably no discontinuity at the junction between the fixed wing and the wingtip device. The upper surface and the lower surface of the wingtip device may be continuations of the upper surface and the lower surface of the fixed wing. The wingspan ratio of the fixed wing to the wingtip device may be such that the fixed wing includes 70%, 80%, 90% or more of the total wingspan of the aircraft wing.

[0032] When the wingtip device is in the ground configuration, an aircraft incorporating the wing may not be suitable for flight. For example, the wingtip device may be aerodynamically and / or structurally unsuitable for flight in the ground configuration. The aircraft is preferably configured such that the wingtip device cannot be moved to the ground configuration during flight. The aircraft may include sensors for sensing when the aircraft is in flight. When the sensors sense that the aircraft is flying, the control system is preferably arranged to prohibit the possibility of moving the wingtip device to the ground configuration.

[0033] The aircraft is preferably a passenger aircraft. The passenger aircraft preferably includes a passenger cabin that includes multiple rows and columns of seat units for accommodating a large number of passengers. The aircraft may have a capacity of at least 20, more preferably at least 50, and more preferably more than 50 passengers. The aircraft is preferably a powered aircraft. The aircraft preferably includes engines for propelling the aircraft. The aircraft may include engines mounted to the wings and preferably mounted under the wings.

[0034] According to another aspect of the present invention, there is provided a wing of an aircraft, the wing of the aircraft being used as the wing in the aircraft of another aspect of the present invention. The wing may have a fixed wing and a wingtip device movably mounted at an outer end of the fixed wing, the wingtip device being capable of moving between: (a) a flight configuration for use during flight; and (b) a ground configuration for use during ground-based operations, in which the wingtip device rotates about a rotation axis away from the flight configuration such that the wingspan of the aircraft wing is reduced. When the wingtip device is in the flight configuration, the outer end of the fixed wing abuts the inner end of the wingtip device along an interface cut line that separates the outer surface of the fixed wing from the outer surface of the wingtip device. The interface cut line includes a curved portion centered on the rotation axis, the radius of the curved portion continuously increasing as the cut line moves around the axis.

[0035] According to another aspect of the present invention, there is provided a fixed wing, the fixed wing being used as the fixed wing in other aspects of the invention described herein. The fixed wing is preferably configured to receive a wingtip device that can rotate about a rotation axis. The outer end of the fixed wing is shaped such that it will abut the inner end of the wingtip device along an interface cut line that separates the outer surface of the fixed wing from the outer surface of the wingtip device, the interface cut line including a curved portion centered on the rotation axis, the radius of the curved portion continuously increasing as the cut line moves around the axis.

[0036] According to another aspect of the present invention, there is provided a wing tip device that serves as a wing tip device in other aspects of the invention described herein. The wing tip device is configured to be received on a fixed wing such that the wing tip device can rotate between a flight configuration and a ground configuration about a rotation axis. The inner end portion of the wing tip device is shaped such that it will abut the outer end portion of the fixed wing along an interface cutting line that separates the outer surface of the fixed wing from the outer surface of the wing tip device, the interface cutting line including a curved portion that is centered about the rotation axis and the radius of which continuously increases as the cutting line moves about the axis.

[0037] According to another aspect of the present invention, there is provided a method of designing an interface between an outer end portion of a fixed wing for an aircraft and an inner end portion of a wing tip device, the wing tip device being movable between: (i) a flight configuration for use during flight; and (ii) a ground configuration for use during ground-based operations, in which the wing tip device rotates away from the flight configuration about a rotation axis such that the wingspan of the aircraft wing is reduced, wherein the method comprises the step of defining an interface cutting line that separates the outer surface of the fixed wing from the outer surface of the wing tip device by defining a curved portion that is centered about the rotation axis and the radius of which continuously increases as the cutting line moves about the axis. The method may include the step of manufacturing the wing tip device according to the design.

[0038] According to yet another aspect of the present invention, there is provided an aircraft, which includes a wing having a fixed wing and a wingtip device. The wingtip device is movably mounted at the outer end of the fixed wing and is capable of moving between: (a) a flight configuration for use during flight; and (b) a ground configuration for use during ground-based operations. In the ground configuration, the wingtip device moves away from the flight configuration, such that the wingspan of the aircraft wing is reduced. The wingtip device is capable of rotating between the flight configuration and the ground configuration about an inclined axis of rotation, such that the wingtip device rotates upward and backward when moving from the flight configuration to the ground configuration. When the wingtip device is in the flight configuration, the outer end of the fixed wing abuts against the inner end of the wingtip device along an interface cutting line that separates the outer surface of the fixed wing from the outer surface of the wingtip device. The interface cutting line includes a curved portion having a generally spiral shape centered on the axis of rotation, and the radius of the curved portion continuously increases as the cutting line moves around the axis, such that when the wingtip device moves from the flight configuration toward the ground configuration, the adjacent portions of the fixed wing and the wingtip device on both sides of the interface cutting line separate. The interface cutting line may further include a leading edge portion that passes through the leading edge on the upper surface and reaches the lower surface. The leading edge portion of the cutting line is formed by a cut extending in a plane containing the axis of rotation. The interface cutting line may include an upper surface portion located on the upper surface and behind the axis of rotation, and the upper surface portion is offset inward from the plane containing the axis of rotation. The interface cutting line may include a lower surface portion located on the lower surface and behind the axis of rotation, and the lower surface portion is offset outward from the plane containing the axis of rotation. The leading edge portion and the upper surface portion may be connected by a curved portion, and the other end of the leading edge portion and the lower surface portion may be connected by another curved portion, which is also of a generally spiral shape centered on the axis of rotation, and the radius of the other curved portion continuously increases as the cutting line moves around the axis, such that when the wingtip device moves from the flight configuration toward the ground configuration, the adjacent portions of the fixed wing and the wingtip device on both sides of the interface cutting line separate.

[0039] It will be understood that any feature described with reference to one aspect of the present invention is equally applicable to any other aspect of the present invention, and vice versa. For example, the features described with reference to the aircraft of the first aspect may also be applicable to the wings, wingtip devices, and / or methods of other aspects of the present invention, and vice versa.

[0040] Unless the context otherwise requires, the term "or" shall be construed as "and / or". BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Embodiments of the present invention will now be described, by way of example only, with reference to the schematic drawings, in which:

[0042] Figure 1a and Figure 1b shows a wing with a movable wingtip device of the prior art;

[0043] Figure 2 is a top - down front view of a proposed embodiment in unpublished application GB1610108.1, which shows a fixed - wing / wingtip device interface, an interface cut - line, and a cutting plane;

[0044] Figure 3a shows a simplified plan view of a wing on an aircraft of a first embodiment of the present invention, the wing being shown with wingtip devices in both a flight configuration and a ground configuration;

[0045] Figure 3b is a front view of an aircraft with a wing incorporating Figure 3a ;

[0046] Figure 4 is a top - down front view of the wing in the first embodiment of the present invention near the fixed - wing / wingtip device interface, and Figure 4 is taken from a viewpoint similar to the viewpoint used in Figure 2 ;

[0047] Figure 5a is another top - down front view of the wing near the fixed - wing / wingtip device interface, which shows the interface cut - line and the cutting plane;

[0048] Figure 5b is a plan view observed in the direction along the Figure 5a axis of rotation of the wingtip device in

[0049] Except that the wingtip device is in the ground configuration rather than the flight configuration, Figure 6a and Figure 6b is the same as Figure 5a and Figure 5b ;

[0050] Figure 7 is a front view along the arrow A in Figure 6a ;

[0051] Figure 8 is another plan view observed in the direction along the axis of rotation of the wingtip device;

[0052] Figures 9a to 9c shows a close - up view of the transition region (circled in Figure 8 ) when the wingtip device moves from the flight configuration to the ground configuration; and

[0053] Figure 10 is another plan view observed in the direction along the axis of rotation of the wingtip device, and shows the interface cut - line located on the lower surface of the wing. DETAILED DESCRIPTION

[0054] Figure 1a FIG. 1 is a perspective view of a fixed wing 1 and a wingtip device 3 on an aircraft shown in WO2015 / 150835. In summary, the wingtip device 3 can be in a flight configuration ( Figure 1a ) and ground configuration ( Figure 1b ). In the flight configuration, the leading edge 5' and the trailing edge 7' of the wingtip device 3 are the continuation of the leading edge 5 and the trailing edge 7 of the fixed wing 1. In addition, the upper surface and the lower surface of the wingtip device 3 are the continuation of the upper surface and the lower surface of the fixed wing 1.

[0055] The wingtip device 3 is arranged in a flight configuration for flying. In the flight configuration, the wingtip device 3 thus increases the wingspan of the aircraft (thereby providing a beneficial aerodynamic effect, for example, reducing the component of induced drag and increasing lift). In principle, it is desirable to always maintain such a large wingspan and only have large fixed wings. However, the maximum aircraft wingspan is actually limited by airport operating rules, which govern the various clearances required when maneuvering around the airport (such as the wingspan and / or ground clearance required for stand access and safe taxiway use). Therefore, the wingtip device 3 can be moved to a ground configuration for use when on the ground.

[0056] In the ground configuration ( Figure 1b ), the wingtip device 3 is folded from the above-mentioned flight configuration by rotating the wingtip device 3 about the rotation axis 11. By folding the wingtip device 3 in this way, the wingspan of the aircraft 2 is reduced. When the wingtip device 3 is in the ground configuration, the aircraft 2 thus complies with the above-mentioned airport clearances, etc.

[0057] The movement of the wingtip device is determined by the type of joint about which the wingtip device rotates relative to the fixed wing. To achieve the above movement, the wingtip device 3 and the fixed wing 1 are separated along an inclined cutting plane 13 passing through the upper and lower surfaces of the wing. The wingtip device 3 can rotate about an axis 11, which extends in a direction perpendicular to the inclined cutting plane 13. The axis 11 is oriented at an acute angle relative to all three mutually perpendicular axes X, Y and Z (i.e., chord-wise, span-wise and vertical).

[0058] When the movable wing tip device is in the flight configuration, a small gap, step or other mismatch at the interface between the outer end of the fixed wing and the inner end of the wing tip device can produce aerodynamically adverse consequences (such as drag and pressure leakage). Figure 1a and Figure 1bIn the described movable wing tip devices, it is difficult to provide an interface that eliminates these features. For example, in some devices, it has been found difficult to control the tolerances near the interface. It has also been found difficult to provide an effective sealing device to inhibit leakage flow through the interface.

[0059] Figure 2 It is a top elevation view of a proposed embodiment in the unpublished application GB1610108.1. Figure 2 The wing 101 is shown in the vicinity of the joint between the fixed wing 105 and the wing tip device 103. The wing 101 has an upper surface 131 and a lower surface 133. The fixed wing 105 and the wing tip device 103 are separated along an imaginary main cutting plane 113, which is perpendicular to the axis of rotation.

[0060] The main cutting plane 113 is Figure 2 The first and second planes 113a and 113b (see below) are offset and parallel at the point indicated by the dashed line where the main cutting plane 113 intersects the wing. Figure 2 The planes intersect the wing at these dashed lines. Portions of the interface cutting line 135 extend within these planes, and the interface cutting line 135 extends in the planes. Figure 2 The outer end of the fixed wing 105 and the inner end of the wing tip device 103 meet along an interface cut line 135 that separates the outer surface of the fixed wing 105 from the outer surface of the wing tip device 103. As will now be described, the interface cut line 135 is stepped and is formed by a series of different lengths:

[0061] The interface cut line 135 includes a first length 137 extending from the trailing edge to the start of a transition portion 139 in the upper rear quadrant (UA). The first length 137 of the interface cut line lies in a plane 113a parallel to the main cutting plane 113 but offset in the medial direction.

[0062] The interface cutting line 135 also includes a second length 141 extending from the leading edge to the other end of the transition portion 139 in the upper front quadrant (UF). The second length 141 of the interface cutting line is also located in a plane 113b that is parallel to the main cutting plane 113 but offset in the lateral direction (i.e., in the opposite direction to the other plane 113a).

[0063] It will be appreciated from the above that the first length 137 and the second length 141 therefore both lie in inclined planes that are parallel to the main cutting plane 113 , but in planes that are offset in opposite directions from the main cutting plane.

[0064] Between a first length 137 and a second length 141 is a transition portion 139. The transition portion 139 includes a first part 139a and a second part 139b. The first part 139a lies in the same plane 113a as the first length 137, and at the second part 139b the interface cutout jumps from the first plane 113a to a second plane 113b. The transition portion 139 thus transitions the interface cut line 135 from the first length 137 to the second length 141.

[0065] It has been found Figure 2 that the devices in Figures 3a to 10 are beneficial, particularly in being able to seal the interface between the wing and the wingtip device. However, as will become apparent with reference to

[0066] Figure 3a A plan view of a wing 1001 on an aircraft 1002 showing a first embodiment of the present invention ( Figure 3b the aircraft is shown in Figure 3a ). In Figure 3a the wing 1001 is shown with wingtip devices 1003 in both a flight configuration and a ground configuration. The flight configuration is shown shaded, and it goes without saying that Figure 3a shows the reduction in wingspan that occurs when the wingtip device 1003 is rotated to the ground configuration. For the purposes of

[0067] the interface cut line between the fixed wing and the wingtip device is shown in a simplified form - its actual shape is shown in subsequent figures further referenced below. Figures 1a to 1b and Figure 2 Figure 4 In general, the wingtip device 1003 of the first embodiment can rotate in a manner similar to that shown in ). That is, the wingtip device 1003 can rotate about an axis 1011 that is oriented normal to a hypothetical main inclined cutting plane 1013 (see

[0068] As Figure 7 in Figure 5a and Figure 6a is apparent when comparing ), which separates the outer end of the fixed wing 1005 from the inner end of the wingtip device 1003. The axis 1011 is at an acute angle with respect to all three mutually perpendicular axes X, Y, and Z (i.e., chordwise, spanwise, and vertical). The wing includes an annular slewing bearing (not shown) for guiding the rotation and reacting the loads into the fixed wing. The hypothetical main cutting plane 1013 passes through the middle of the slewing bearing.

[0068] As Figure 7 in Figure 5a and Figure 6a it is apparent when comparing ), the nature of the movement is such that when the wingtip device 1003 rotates about the axis 1011, the upper and lower surfaces of the wingtip device in front of the axis 1011 move downward; while the upper and lower surfaces behind the axis move upward.

[0069] The aspects of the present invention are particularly characterized by the shape of the interface cut line between the fixed wing and the wing tip device, and reference will now be made to Figures 4 to 10 Describing it in more detail:

[0070] First refer to Figure 4 , Figure 5a and Figure 5b , these figures show views of the area surrounding the fixed wing / wingtip device interface. The wingtip device 1003 is a planar wingtip extension (its distal end is not visible in these figures). Figure 2 In a similar manner to the above, the wing 1001 has an upper surface 1031 and a lower surface 1033. The outer end of the fixed wing 1005 and the inner end of the wingtip device 1003 meet along an interface cut line 1035, which separates the outer surface of the fixed wing 1005 from the outer surface of the wingtip device 1003. The interface cut line 1035 is arranged so that when the wingtip device 1003 rotates from the flight configuration to the ground configuration, a specific type of relative movement occurs between the outer end of the fixed wing 1005 and the inner end of the wingtip device 1003. The interface cut line 1035 is formed by a series of different lengths, which will be described in more detail below.

[0071] The fixed wing 1005 and the wing tip device 1003 are separated along an imaginary main cutting plane 1013 (which is perpendicular to the axis of rotation). The main cutting plane 1013 is Figure 4 , where the primary cutting plane 1013 intersects the wing, but the primary cutting plane 1013 itself does not appear as a physical cut in the wing skin. Instead, and with Figure 2 Similar to the device in FIG. 1 , the interface cutting line 1035 includes a first length 1037 located in the upper rear quadrant, and the first length 1037 is offset from the main cutting plane 1013. However, Figure 2 Unlike the device in FIG. 1 , the first length does not lie in parallel planes; rather, the first length is curved so that it does not lie in any single plane. It has been found that giving the first length such a curved shape is beneficial in terms of relative movement between the fixed wing and the wingtip device along the interface (when the wingtip device rotates about the axis). In addition, giving the first length such a curved shape can achieve a first length 1037 and a third length 1045 (located on the underside of the wing - see FIG. 1 ) in the trailing edge region. Figure 10 ) because the ends of these lengths can be brought relatively close together.

[0072] The interface cutting line 1035 also includes a second length 1041 located in front of the rotation axis 1011. Figure 2Unlike the device in [reference], the second length does not deviate outwardly; instead, the second length 1041 extends along the upper surface 1031 of the wing, passes through the leading edge, and extends onto the lower surface 1033 of the wing. The second length 1041 lies within a plane P (schematically indicated by a dashed line in some figures) that contains the axis of rotation 1011, and this plane is also substantially perpendicular to the front spar (not shown) of the wing. This is best shown in Figure 5b , Figure 6b and Figure 7 .

[0073] It has been found that it is particularly beneficial to arrange the second length 1041 within the plane containing the axis of rotation 1011. It has been recognized that by forming the second length in this way, when the wingtip device 1003 moves from the flight configuration towards the ground configuration, the fixed wing 1005 and the wingtip device 1003 separate simultaneously along the entire length of the second cut line 1041. Additionally, the orientation of the second length 1041 of the interface cut line 1035 tends to mean that the fixed wing 1005 and the wingtip device 1003 separate in a locally perpendicular direction (along the second length 1041). Thus, the sealing motion tends to be pure compression.

[0074] In other embodiments (not shown), the second length need not lie within the plane containing the axis of rotation - instead, it can lie within a plane parallel to this plane. Such an arrangement does not necessarily result in simultaneous separation between the fixed wing and the wingtip device, but it still tends to exhibit a perpendicular relative motion between the two sides of the interface cut line, which is beneficial for sealing.

[0075] Another advantageous feature of the first embodiment of the present invention is the shape of the transition portion 1039 between the first length 1037 and the second length 1041. In the first embodiment of the present invention, the transition portion 1039 is generally in the form of a helix, as will now be explained with reference to Figure 8 and Figures 9a to 9c :

[0076] Figure 8 is a view looking from above the wing along the axis of rotation 1011 of the wingtip device 1003 and towards the upper surface 1031 of the wing, where the interface cut line 1035 is located on the upper surface 1031 of the wing. Superimposed on Figure 8 are some radii R1 - R4 from the axis 1011 to the interface cut line 1035.

[0077] When the cut line 1035 rotates about the axis 1011 as the wingtip device moves from the flight configuration to the ground configuration (indicated by Figure 8When moving in the rotational direction shown by the curved arrow (in [FIGURE]), the radius of the curved portion 1039 continuously increases. Therefore, when moving from the rear position adjacent to the first length 1037 of the cutting line to the front position adjacent to the second length 1041 of the cutting line, the radii are such that R1 < R2 < R3 < R4.

[0078] It has been found particularly advantageous to provide an interface cutting line having a curved portion 1039, wherein the radius of the curved portion increases continuously about the axis of rotation 1011. In particular, since the radius of the curved portion 1039 of the interface cutting line 1035 increases and the curved portion of this interface cutting line is centered about the axis of rotation 1011 of the wing tip, this means that when the wing tip device 1003 rotates away from the flight configuration, the structure of the wing tip device 1003 separates from the structure of the fixed wing 1005 along this portion 1039 of the interface cutting line. This is best shown with reference to Figures 9a to 9c when Figures 9a to 9c as the wing tip moves from the flight configuration ( Figure 9a ) to the ground configuration ( Figure 9c ). Figure 8 is a close-up view of the area within the dashed circle in [FIGURE].

[0079] A point P along the interface cutting line 1035 in the curved portion 1039 wt is located on the wing tip device 1003 side and at a position with a radius R1 from the axis of rotation. When the wing tip device is in the flight configuration, the corresponding point P fw on the fixed wing 1005 side of the cutting line 1039 will be located at a position with substantially the same radius (R1) from the axis - see Figure 9a . When the wing tip device 1003 rotates away from the flight configuration by an angle α, the point P wt on the wing tip device 1003 will rotate about the axis - see Figure 9b . This point P wt remains at a position with a radius R1 from the axis 1011 (since it is located on the wing tip device 1003), but due to the increase in the radius of the cutting line 1039 as the cutting line 1039 moves about the axis, the radially outward point P fw α on the wing tip device (which is at the same angular position α about the axis as the new position of P wt ) will be at a greater radius (R2) from the axis due to the characteristics of the curved portion 1039. When the wing tip device 1003 moves away from the flight configuration, the wing tip device 1003 and the fixed wing 1005 will thus necessarily move apart along the interface 1039 (and vice versa, when the wing tip device 1003 moves to the flight configuration, the wing tip device 1003 and the fixed wing 1005 will move towards each other). A similar characteristic continues to occur when the wing tip device 1003 rotates further to an angle θ - seeFigure 9c Since this movement tends to avoid relative sliding movement at interface 1039, this movement is beneficial.

[0080] In the first embodiment, the curved portion 1039 is formed by a spline curve generated by a number of radii such that the curvature generally follows a spiral. In other embodiments (not shown), it will be understood that the curvature may be an exact spiral or may be other shapes showing increasing radii about the axis of rotation.

[0081] It will be understood that the spiral shape of the curved portion 1039 is formed with reference to a view looking from above and along the axis of rotation (i.e., with reference to the projection of the curved portion 1039 onto a plane perpendicular to the axis of rotation 1011). In practice, due to the curved nature of the outer surface of the wing, the shape of the curved portion 1039 may also extend outside of this plane. However, aspects of the present invention recognize that the curvature about the axis of rotation of the wingtip device is particularly important in allowing the fixed wing and the wingtip device to effectively separate, and thus the characteristics of the curved shape are particularly important from this perspective.

[0082] Referring Figures 4 to 9c to the interface cut line in, it mainly relates to the interface cut line 1035 on the upper surface 1031 of the wing. However, corresponding features also exist on the lower surface 1033, and in this regard, reference is now made to Figure 10 . Figure 10 is a view looking from above the axis of rotation 1011, but the portion 1035' of the interface cut line 1035 on the lower surface 1033 is shown in dashed lines.

[0083] The lower portion 1035' of the interface cut line includes a third length 1045 that extends in the lower rear quadrant and is connected via a transition portion 1047 at the trailing edge to the first length 1037 (located in the upper surface rear quadrant). The third length 1045 is curved such that it minimizes the length of the transition portion 1047 but still avoids collisions (e.g., with the upper surface of the wing) when the wingtip device rotates to the ground configuration.

[0084] The interface cut line also includes a curved, generally spiral second portion 1039' located on the lower surface that connects the third length 1045 to the end of the second length 1041 on the lower surface 1033. The second curved portion 1039' also has an increasing radius as the cut line moves from a rear position on the lower surface around the axis 1011 to a front position (in Figure 10is shown in dashed lines, where R1 < R2 < R3 < R4), and where, at the rear position, the second part 1039' engages with the third length 1045, and at the front position, the second part 1039' engages with the second length 1041. Thus, when the wingtip device rotates away from the flight configuration, the fixed wing and the wingtip device also move apart along this interface cut line 1035'.

[0085] Although Figure 10 radii R1 to R4 have been shown in, it will be understood that these radii do not necessarily have the same magnitude / precise characteristics as the radii on the upper surface spiral part 1039.

[0086] Although the invention has been described and illustrated with reference to specific embodiments, those of ordinary skill in the art will understand that the invention is applicable to many different variations not specifically shown herein. For example, in another embodiment of the invention (not shown), the axis of rotation extends vertically out of the plane of the wing, and there is no imaginary main cutting plane that is inclined and oriented such that it passes through the upper and lower surfaces of the wing. Such a wingtip (which rotates within the plane of the wing) may be referred to as a swinging wingtip. In such an arrangement, a curved portion of the interface cut line that is helical or has characteristics similar to those described in the embodiments herein is still beneficial because it can prevent sliding contact at the interface.

[0087] In the foregoing description, where the overall or element mentioned has known, obvious, or foreseeable equivalents, then these equivalents are incorporated herein as if specifically set forth. The true scope of the invention should be determined with reference to the claims, which should be interpreted as covering any such equivalents. The reader will also understand that the overall or features described as preferred, advantageous, convenient, etc. of the invention are optional and do not limit the scope of the independent claims. Additionally, it should be understood that these optional overall or features that may be beneficial in some embodiments of the invention may not be required and may therefore be absent in other embodiments.

Claims

1. An aircraft, comprising a wing having a fixed wing and a wingtip device, the wingtip device being movably mounted at an outer end portion of the fixed wing, and the wingtip device being capable of moving between: (a) a flight configuration for use during flight; and (b) a ground configuration for use during ground-based operations, in which the wingtip device moves away from the flight configuration such that the wingspan of the wing of the aircraft is reduced. Among them, The wingtip device is capable of rotating between the flight configuration and the ground configuration about a rotation axis such that the wingtip device rotates upwardly and rearwardly when moving from the flight configuration to the ground configuration, and the rotation axis is inclined with respect to a plane defined by the spanwise direction and the chordwise direction of the fixed wing. And wherein, when the wingtip device is in the flight configuration, the outer end portion of the fixed wing abuts against the inner end portion of the wingtip device along an interface cut line that separates the outer surface of the fixed wing from the outer surface of the wingtip device. The interface cut line includes a curved portion, wherein the radius of the curved portion is the distance between the rotation axis and the curved portion, and the radius of the curved portion continuously increases in a direction toward the leading edge of the wingtip device along the curved portion, such that when the wingtip device moves from the flight configuration toward the ground configuration, adjacent portions of the fixed wing and the wingtip device on both sides of the interface cut line are separated.

2. The aircraft according to claim 1, wherein, The wing includes an upper surface extending from the leading edge to the trailing edge above the wing, and the wing includes a lower surface extending from the leading edge to the trailing edge below the wing, and wherein the curved portion is located on the upper surface of the wing.

3. The aircraft according to claim 1 or 2, wherein, The interface cut line further includes a first length and a second length, the first length extending from the curved portion toward the trailing edge of the fixed wing, and the second length extending from the curved portion toward the leading edge of the fixed wing.

4. The aircraft according to claim 3, wherein, The second length is formed by a cut passing through the outer surface, the cut extending in a plane containing or parallel to the rotation axis.

5. The aircraft according to any one of claims 1, 2 and 4, wherein, The wing of the aircraft is a first aircraft wing attached to the fuselage of the aircraft, and the aircraft further includes a second aircraft wing located on the opposite side of the fuselage with respect to the first aircraft wing.

6. The aircraft according to any one of claims 1, 2, and 4, wherein, The interface cut line further includes: a leading edge portion that passes through the leading edge on the upper surface and reaches the lower surface, the leading edge portion of the interface cut line being formed by a cut extending in a plane containing the rotation axis. an upper surface portion that is located on the upper surface and behind the rotation axis, and the upper surface portion is offset inwardly from the plane containing the rotation axis; and the interface cut line includes a lower surface portion that is located on the lower surface and behind the rotation axis, and the lower surface portion is offset outwardly from the plane containing the rotation axis.

7. The aircraft according to claim 6, wherein, The leading edge portion and the upper surface portion are connected by the curved portion, and the other end portion of the leading edge portion is connected to the lower surface portion by another curved portion, which is also of a generally spiral shape centered on the axis of rotation. The radius of the other curved portion continuously increases as the interface cut line moves around the axis of rotation, such that when the wingtip device moves from the flight configuration towards the ground configuration, adjacent portions of the fixed wing and the wingtip device on both sides of the interface cut line separate.

8. A method for designing an interface between an outer end portion of a fixed wing for an aircraft and an inner end portion of a wingtip device, wherein the wingtip device is movable between: (i) a flight configuration for use during flight; and (ii) a ground configuration for use during ground-based operations, in which the wingtip device moves away from the flight configuration such that the wingspan of the aircraft's wing is reduced, Among them, the wingtip device being rotatable about an axis of rotation between the flight configuration and the ground configuration such that the wingtip device rotates upwardly and rearwardly as it moves from the flight configuration to the ground configuration, the axis of rotation being inclined with respect to a plane defined by the wingspan direction and the chordwise direction of the fixed wing, wherein the method comprises the steps of: defining an interface cut line separating the outer surface of the fixed wing from the outer surface of the wingtip device by defining a curved portion, wherein the radius of the curved portion is the distance between the axis of rotation and the curved portion, and the radius of the curved portion continuously increases along the curved portion in a direction towards the leading edge of the wingtip device, such that when the wingtip device moves from the flight configuration towards the ground configuration, adjacent portions of the fixed wing and the wingtip device on both sides of the interface cut line separate.

9. The method according to claim 8, wherein, The wingtip device is manufactured according to the design.

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