GB2584133A

GB2584133A - Leading edge moveable devices

Info

Publication number: GB2584133A
Application number: GB1907251.1A
Authority: GB
Inventors: Edwards Henry
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-05-23
Filing date: 2019-05-23
Publication date: 2020-11-25
Anticipated expiration: 2039-05-23
Also published as: GB2584133B; GB201907251D0

Abstract

There is provided an aerofoil structure 10 having an upper aerodynamic surface 101 and a lower aerodynamic surface 102, which meet at a midpoint 12 of the leading edge of the aerofoil structure. The aerofoil structure comprises at least one leading edge moveable device having a spanwise dimension less than or equal to its chordwise dimension and configured to be moveable between an extended position and a retracted position. In the extended position, the moveable device projects forwardly from the lower aerodynamic surface. In the retracted position the moveable device is entirely disposed within he aerofoil structure. The device may extend linearly (figs 4 and 5) from the aerofoil or may rotate with respect to the aerofoil (figs 6 and 7) or it may be inflated/deflated by means of pressurised gas (fig 8). The devices are vortilons and are intended to produce vortices over the aerofoil to reduce a tendency for stalling.

Description

LEADING EDGE MOVEABLE DEVICES

TECHNICAL FIELD

100011 The present invention relates to aerofoil structures comprising at least one leading edge moveable device.

BACKGROUND

[0002] High lift devices on aircraft are intended to improve the lift generation and stall-resistance of the aircraft when operating at low speed and/or high angles of attack. A vortilon is a fixed (that is, non-moveable) high lift device found on certain known aircraft designs. Vortilons function to generate vortices, in a similar manner to a leading-edge engine pylon.

[0003] A vortilon consists of one or more plates attached to the underside of the wing near its leading edge, such that the plane of the device is substantially vertical and aligned with the flight direction. As the speed of the aircraft reduces and it approaches stall, the local flow at the leading edge is diverted outwards. When the outward flowing air encounters a vortilon, a vortex is created. The vortex streams around the top surface of the wing, which energises the boundary layer (that is, the boundary layer becomes more turbulent). A more turbulent boundary layer, in turn, delays the local flow separation and thus prevents a stall.

[00041 Vortilons are also often used to improve low-speed aileron performance.

Furthermore, vortilons can be used as an alternative to wing fences, which also restrict airflow along the span of the wing. Advantageously, vortilons only stream vortices at high angles of attack and produce less drag at higher speeds than wing fences.

[0005] Conventionally, vortilons are only used on relatively small and/or short-range aircraft. This is because the drag penalty caused by a vortilon during the cruise phase of flight is unacceptable for large commercial aircraft flying long range routes. The present invention seeks to address this issue, and proposes a high lift device which provides the aerodynamic effects of a vortilon whilst also being suitable for long range commercial aircraft.

SUMMARY

[0006] A first aspect of the present invention provides an aerofoil structure having an upper aerodynamic surface and a lower aerodynamic surface, which meet at a midpoint of the leading edge of the aerofoil structure. The aerofoil structure comprises at least one leading edge moveable device having a spanwise dimension less than or equal to its chordwise dimension and configured to he moveable between an extended position and a retracted position. In the extended position, the moveable device projects forwardly from the lower aerodynamic surface. In the retracted position, the moveable device is entirely disposed within the aerofoil structure.

[00071 Optionally, the shape of the moveable device is configured such that the moveable device creates a vortex when the moveable device is in the extended position during flight of an aircraft in which the aerofoil structure is comprised.

[0008] Optionally, the moveable device is configured to block spanwise airflow along the lower aerodynamic surface adjacent the midpoint.

[0009] Optionally, a forward-facing surface of the moveable device is flush with the lower aerodynamic surface when the moveable device is in the retracted position.

[0010] Optionally, the moveable device is further configured to be moveable into an over-retracted position in which a forward-facing surface of the moveable device is recessed relative to the lower aerodynamic surface.

[00111 Optionally, the moveable device comprises an actuation mechanism configured to drive movement of the moveable device between the extended position and the retracted position.

[0012] Optionally, the actuation mechanism is configured to drive translational and/or rotational movement of the moveable device.

[0013] Optionally, the upper aerodynamic surface and the lower aerodynamic surface are formed by an outer skin of the aerofoil structure, and the outer skin comprises an opening through which the moveable device projects, at least in the extended position of the moveable device.

[0014] Optionally, the aerofoil structure is configured such that the moveable device is controllably moveable between the extended position and the retracted position.

[0015] Optionally, the moveable device is configured to receive control signals from an aircraft in which the aerofoil structure is comprised, and is controllably moveable in response to received control signals.

[0016] Optionally, the aerofoil structurc is an aircraft wing. Optionally, the aircraft wing is a swept wing.

[0017] A second aspect of the present invention provides an aircraft comprising an aerofoil structure according to the first aspect.

[0018] Optionally, the aircraft further comprises a control system in communication with the leading edge moveable device. The control system is configured to: send a first control signal to the moveable device, the first control signal being configured to cause the moveable device to move to the extended position; and send a second control signal to the moveable device, the second control signal being configured to cause the moveable device to move to the retracted position.

[0019] Optionally, the control system is further configured to: send a third control signal configured to cause the moveable device to move to an intermediate position between the extended position and the retracted position; and/or send a fourth control signal configured to cause the moveable device to move to an over-retracted position in which a forward-facing surface of the moveable device is recessed relative to the lower aerodynamic surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the invention will now he described, by way of example only, with reference to the accompanying drawings, in which: [0021] Figure la is a schematic plan view of an aircraft wing comprising an example aerofoil structure according to the invention in which the leading edge moveable devices arc in the extended position; [0022] Figure l b is a schematic plan view of the aircraft wing of Figure lain which the leading edge moveable devices arc in the retracted position; [0023] Figure lc is a cross section through the aircraft wing of Figures la and lb; [0024] Figure 2a is a schematic perspective view of a leading edge part of the aerofoil structure of Figures la-c with the leading edge moveable devices in the extended position; [0025] Figure 2b is a schematic perspective view of the leading edge part of the aerofoil structure of Figures la-c with the leading edge moveable devices in the retracted position; [0026] Figure 3 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention; [0027] Figure 4 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention having a first example actuation mechanism; [0028] Figure 5 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention having a second example actuation mechanism; [0029] Figure 6 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention having a third example actuation mechanism; [0030] Figure 7 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention having a fourth example actuation mechanism; [0031] Figure 8 is a schematic cross-section through a leading edge part of a further example aerofoil structure according to the invention having a fifth example actuation mechanism; and [0032] Figure 9 is a schematic front view of an example aircraft comprising an aerofoil structure according to the invention.

DETAILED DESCRIPTION

[0033] Each example described below comprises an aerofoil structure having an upper aerodynamic surface and a lower aerodynamic surface, which meet at a leading edge of the aerofoil structure. In each example the aerofoil structure comprises at least one leading edge moveable device having a spanwise dimension less than or equal to its chordwise dimension and configured to he moveable between an extended position and a retracted position. In the extended position, the moveable device projects forwardly from the lower aerodynamic surface and in the retracted position the moveable device is entirely disposed within the aerofoil structure.

[0034] Example aerofoil structures according to the invention have the advantage that the high-lift effects associated with vortilons are created when the moveable device is in the extended position, but the moveable device incurs little or no drag penalty when it is in the retracted position. Since the moveable device can be moved between the extended position and the retracted position, the extended position can be used when lift enhancement is required (such as during the take-off and landing phases) and the retracted position can be used when lift enhancement is not required (such as during the cruise phase). The example aerofoil structures according to the invention are therefore suitable for use on long range commercial aircraft.

[0035] Figures la and lb are plan views of an example aircraft wing 1. The wing 1 is a swept. wing designed for use on a commercial airliner. The wing 1 comprises an aerofoil structure 10 and an engine 11 mounted on the aerofoil structure 10. The wing 1 may also comprise various fixed or moveable trailing edge devices and/or leading edge devices (not. shown), as is conventional for commercial airliners. The wing 1 has a cantilevered structure with a length extending in a spanwisc direction from a root to a tip, the root being configured for attachment to an aircraft fuselage.

[0036] Figure lc is a cross-section through the aerofoil structure 10, along the line A-A as shown in Figure la. From Figure lc it can be seen that the aerofoil structure 10 has an upper aerodynamic surface 10 and a lower aerodynamic surface 11. The upper and lower aerodynamic surfaces 10, 11 are formed by an outer skin of the aerofoil structure 10, which may be continuous between the upper and lower aerodynamic surfaces 10, 11. That is, the use of the terms upper and lower aerodynamic surfaces should not be taken to mean that a physical discontinuity is present between the upper and lower aerodynamic surfaces. The upper aerodynamic surface 10 and the lower aerodynamic surface 11 meet at a midpoint 12 of the leading edge of the aerofoil structure. It will be appreciated that the midpoint 12 is actually a line which extends along the full spanwise length of the aerofoil structure 10. The leading edge midpoint 12 may be located at the stagnation point of the aerofoil structure 10.

[0037] The example aerofoil structure 10 comprises a plurality of leading edge moveable devices 13. In the particular illustrated example, there are four such moveable devices 13. However; in other examples the number of leading edge moveable devices may be fewer or greater than four. In some examples an aerofoil structure 10 may comprise just a single leading edge moveable device 13.

[0038] Each of the moveable devices 13 has a spanwise dimension that is less than or equal to its chordwise dimension. The chordwise dimension of a moveable device 13 is considered to be the length, in the chordwisc direction, of the part of the moveable device 13 which projects out of the aerofoil structure 10 when the moveable device 13 is in the extended position. Any parts of the moveable device 13 which remain within the aerofoil structure 10 when the movcahle device is in the extended position are not considered to contribute to the chordwisc dimension of the movcahle device 13. The chordwisc dimension of each movcahle device 13 is selected based on factors specific to the particular implementation, such as the configuration of the aerodynamic structure 10, and the magnitude of the aerodynamic effect it is desired for the moveable device 13 to create.

[0039] Each moveable device 13 is configured to he moveable between an extended position and a retracted position. hi Figure la all of the moveable devices 13 arc in the extended position and in Figure lb all of the moveable devices 13 are in the retracted position. It is also possible for some of the moveable devices 13 to he in the extended position whilst some other of the moveable devices 13 are in the retracted position. In some examples it is also possible for some or all of the moveable devices 13 to be in one or more intermediate positions between the retracted position and the extended position. This enables the chordwise dimension of the moveable devices 13, and therefore the magnitude of the aerodynamic effect they create, to he tailored.

[0040] When a given moveable device 13 is in the extended position, that moveable device 13 projects forwardly from the lower aerodynamic surface 102. That is, at least part of the moveable device 13 is disposed below the midpoint 12 of the aerofoil structure 10 when the moveable device 13 is in the extended position. In some examples all of the moveable device 13 is disposed below the midpoint 12 when the moveable device 13 is in the extended position.

[0041] The shape of each moveable device 13 is configured such that the moveable device 13 creates a vortex when the moveable device 13 is in the extended position during flight of the aircraft in which the aerofoil structure 10 is comprised. In particular, each moveable device 13 is configured to block spanwisc airflow along the lower aerodynamic surface 102 adjacent the midpoint 12, and it is this blocking which creates the vortex. Each moveable device 13 therefore functions in substantially the same manner as a conventional vortilon when in the extended position. Configurations of the aerofoil structure 10 in which one or more of the moveable devices 13 are in the extended position are therefore suitable for use in flight phases where lift enhancement is required (such as take-off and landing).

[0042] When a given moveable device 13 is in the retracted position, that moveable device is entirely disposed within the aerofoil structure 10. In other words, no part of the moveable device protrudes outside of the aerodynamic profile of the aerofoil structure 10. As can be seen from Figure lb, the leading edge of the aerofoil structure 10 is a straight line with substantially no discontinuities when all of the moveable devices 13 arc in the retracted position. This means that the aerofoil structure 10 does not incur any drag penalty from comprising the moveable devices 13, when all of the moveable devices 13 are in the retracted position. This configuration of the aerofoil structure 10 is therefore suitable for use during the cruise phase of a flight.

[00431 The moveable devices 13 are each configured to receive control signals from the aircraft in which the aerofoil structure 10 is comprised. Each moveable device is controllably moveable in response to received control signals. hi some examples, each moveable device comprises an actuation mechanism to drive movement of that moveable device between the extended and retracted positions, and in such examples the actuation mechanism of each moveable device may he configured to receive and respond to the control signals.

[0044] Figures 2a and 2h show a section of the leading edge part of the aerofoil structure in more detail. In Figure 2a the moveable devices 13 are in the extended position and are creating vortices V which stream over the upper aerodynamic surface 101. hi Figure 2b the moveable devices 13 are in the retracted position, and no such vortices are created. It can be seen from Figures 2a and 2h that each moveable device is approximately box-shaped and has a forward-facing surface 131, an upper surface 132, a lower surface 133, and two side surfaces 134 (only one side surface of each moveable device 13 is visible). The forward-facing surface 131 of each moveable device 13 is configured to match the shape of the leading edge pro file of the aerodynamic structure 10. The forward-facing surface of each moveable device 13 is flush with the lower aerodynamic surface 102 (and, if applicable, the upper aerodynamic surface 101) of the aerofoil structure 10 when that moveable device 13 is in the retracted position. These features mean that a substantially smooth and continuous aerodynamic surface is formed by the forward-facing surfaces of the moveable devices 13 and the aerodynamic surfaces 101, 102 or the aerofoil structure 10 when the moveable devices 13 are in the retracted position. Although the illustrated side surfaces 134, upper surface 132 and lower surface 133 arc substantially flat, in other examples one or more of these surfaces could have a more complex surface shape, to tailor the aerodynamic effects created by the moveable device when in the extended position.

[0045] Figure 3 is a cross-section through the leading edge part of a second example aerofoil structure 30 according to the invention. The second example aerofoil structure 30 comprises an upper aerodynamic surface 301, a lower aerodynamic surface 302, and at least one moveable device 33, each of which has substantially the same features as the corresponding structure of the first example aerofoil structure 10. However; the at least one moveable device 33 is additionally configured to be moveable into an over-retracted position. Figure 3 shows the at least one moveable device 33 in the over-retracted position. In the over-retracted position, a forward-facing surface 331 of the at least one moveable device 33 is recessed relative to the lower aerodynamic surface 302. In the illustrated example, the at least one moveable device 33 is disposed entirely below the midpoint of the aerofoil structure, and this arrangement is likely to be advantageous for the majority of aircraft applications. However; examples (such as the example of Figures la-c and 2a-b) in which a moveable device 33 is disposed partly above the midpoint 32 of the aerofoil structure 30 may also be configured such that the moveable device 33 is moveable into an over-retracted position. In such examples the forward-facing surface of the moveable device is also recessed relative to the upper aerodynamic surface in the over-retracted position.

[0046] In both of the above-described examples, each moveable device comprises an actuation mechanism configured to drive movement of that moveable device between the extended position and the retracted position (and, in the case of the aerofoil structure 30, the over-retracted position). These actuation mechanisms can he of any suitable design known in the art. Figures 4-8 illustrate a selection of different actuation mechanisms suitable for driving the movement of leading edge moveable devices according to the invention.

[0047] Figure 4 shows the leading edge part of an example aerofoil structure 40 according to the invention, comprising a sliding rail actuation mechanism 45a, 45b configured to drive movement of a moveable device 43 between a retracted position (as shown in part (i) of Figure 4) and an extended position (as shown in part (i i)). The aerofoil structure 40 and the moveable device 43 have substantially the same features as the example aerofoil structure 10 and moveable device 13 described above. The actuation mechanism 45a, 45b is configured to drive translational movement of the moveable device 43, as indicated by the block arrow.

[0048] The actuation mechanism comprises two rails 45a, 45b, which are connected such that they can slide axially relative to each other. A first one 45a of the rails is fixedly attached to the moveable device 43. The other one 45b of the rails is fixedly attached to a fixed load-bearing component of the aerofoil structure 40 (such as a rib or a spar). Although two rails are shown in Figure 4. other examples are possible in which the actuation mechanism comprises three or more slidingly connected rails. Sliding movement of the first rail 45a relative to the other rail 45b may be driven by any suitable arrangement known in the art, such as a rack and pinion connected to an electric motor.

[0049] Figure 5 shows the leading edge part of an example aerofoil structure 50 according to the invention, comprising a scissor actuation mechanism 55 configured to drive movement of a moveable device 53 between a retracted position (as shown in part (i) of Figure 5) and an extended position (as shown in part (ii)). The aerofoil structure 50 and the moveable device 53 have substantially the same features as the example aerofoil structure 10 and moveable device 13 described above. The actuation mechanism 55 is configured to drive translational movement of the moveable device 53, as indicated by the block arrow.

[0050] The actuation mechanism comprises a plurality of linked arms arranged as a scissor mechanism. The foremost ends of the foremost pair of arms arc slidingly connected to the moveable device 53, and the rearmost ends of the rearmost pair of arms are slidingly connected to a fixed load-bearing component of the aerofoil structure 50 (such as a rib or a spar). Although two pairs of arms are shown in Figure 5, other examples are possible in which the actuation mechanism comprises more or fewer pairs of arms. Extension and retraction of the scissor mechanism may be driven by any suitable arrangement known in the art.

Hydraulic, pneumatic or electric power supplied by an aircraft system may be used to drive the extension/retraction.

[0051] Figure 6 shows the leading edge part of an example aerofoil structure 60 according to the invention, comprising a pivoting actuation mechanism 65 configured to drive movement of a moveable device 63 between a retracted position (as shown in part (i) of Figure 6) and an extended position (as shown in part (ii)). The aerofoil structure 60 and the moveable device 63 have substantially the same features as the example aerofoil structure 10 and moveable device 13 described above. The actuation mechanism 65 is configured to drive rotational movement of the moveable device 63, as indicated by the block arrow.

[0052] The actuation mechanism comprises a hinge 65 arranged parallel to the leading edge of the aerofoil structure 60. The hinge 65 pivotally connects a corner of the moveable device 63 to a fixed load-bearing component of the aerofoil structure 60 (such as a rib). In the illustrated example, clockwise rotation of the moveable device 63 moves it from the retracted position to the extended position, and anti-clockwise rotation of the moveable device 63 moves it from the extended position to the retracted position. Rotational movement of the moveable device 63 may be driven by any suitable arrangement known in the art, such as a drive shaft connected to an electric motor.

[0053] Figure 7 shows the leading edge part of an example aerofoil structure 70 according to the invention, comprising an alternative pivoting actuation mechanism 75 configured to drive movement of a moveable device 73 between a retracted position (as shown in part (i) of Figure 7) and an extended position (as shown in part (ii)). The aerofoil structure 70, moveable device 73, and actuation mechanism 75 have substantially the same features as the example aerofoil structure 60, moveable device 63, and actuation mechanism 65 of Figure 6, except that the hinge 75 is not located at a corner of the moveable device 73. Instead, the hinge 75 comprises a pin which passes through the structure of the moveable device 73, near to a corner of the moveable device 73. Depending, for example, on the space available within the leading edge part of an aerofoil structure, one or other of the alternative example rotational actuation mechanisms 65, 75 may he more suitable for a given application.

[0054] Figure 8 shows the leading edge part of an example aerofoil structure 80 according to the invention, comprising a pneumatic actuation mechanism 85 configured to drive movement of a moveable device 83 between a retracted position (as shown in part (i) of Figure 8) and an extended position (as shown in part (ii)). The aerofoil structure 80 has substantially the same features as the example aerofoil structure 10. However, in this example the moveable device 83 comprises a sealed chamber formed within the leading edge part of the aerofoil structure 80. A wall 831 of the chamber forms part of the aerodynamic surface of the aerofoil structure 80. The wall 831 is flexible and elastic. The wall 831 has a suitable stiffness such that it is able to maintain the aerodynamic profile shape of the aerodynamic structure 80 when the moveable device 83 is in the retracted position, but is able to stretch into the extended position shown in part (ii) of Figure 8.

[0055] The pneumatic actuation mechanism 85 comprises a source of variable pressure (such as a pump) which is in fluid communication with the sealed chamber of the moveable device 83. In the retracted position, the pressure supplied by the variable pressure source is relatively low (but is sufficient to maintain a desired shape of the wall 831 during flight). To extend the moveable device 83, the variable pressure source supplies an increased pressure, such that the pressure inside the chamber increases. This causes the flexible wall 831 to bulge outwards. The pressure is increased until the moveable device 83 has achieved the extended position.

[0056] Each of the example actuation mechanisms described above may additionally be configured to move the associated moveable device into an over-retracted position in which the surface of the moveable device which forms part of the aerodynamic surface of the aerofoil structure is recessed relative to the surrounding surface of the aerofoil structure. In the example of Figure 8, an over retracted position could be achieved by causing the variable pressure source 85 to supply a lower pressure to the sealed chamber than the pressure required to maintain the wall 831 in the retracted position.

[0057] Each of the example actuation mechanisms described above may be configured to receive control signals from an aircraft in which the associated aerofoil structure is comprised. The example actuation mechanisms may be configured to drive movement from the retracted position to the extended position (and/or any intermediate position, and/or an over-retracted position) in response to receiving a first type of control signal, and to drive movement from the extended position to the retracted position in response to receiving a second type of control signal. The control signals may be configured, for example, to activate an electric motor, pump, or any other source of motive power configured to drive the actuation mechanisms.

[0058] Figure 9 shows an example aircraft 9. The aircraft 9 comprises a pair of wings 90a, 90b, each of which is an aerofoil structure according to the invention and therefore comprises one or more leading edge moveable devices according to the invention. Each wing 90a, 90b may have the features of any of the example aerofoil structures described above. Each wing 90a, 90b is a swept wing. The aircraft 9 also comprises a pair of horizontal stabilizers (or tailplanes) 96a, 96h, and a vertical stabilizer 97. Any or all of the horizontal stabilizers 96a, 966 and vertical stabilizer 97 may comprise an aerofoil structure according to the invention.

[00591 The aircraft 9 further comprises a control system 98 for controlling movement of the leading edge moveable devices comprised in the wings 90a, 90b. In the illustrated example the control system 98 is located in the avionics bay of the aircraft 9. The control system 98 is in communication with each of the leading edge moveable devices and is configured to, in respect of each leading edge moveable device: Send a first control signal to the moveable device, the first control signal being configured to cause the moveable device to move to the extended position; and send a second control signal to the moveable device, the second control signal being configured to cause the moveable device to move to the retracted position. The control system may, in some examples, additionally be configured to send a third control signal to the moveable device, the third control signal being configured to cause the moveable device to move to a position intermediate between the retracted position and the extended position. In some examples the control system may additionally be configured to send a fourth control signal to the moveable device, the fourth control signal being configured to cause the moveable device to move to an over-retracted position in which a forward-facing surface of the moveable device is recessed relative to the lower aerodynamic surface.

[0060] The control system may be configured to generate control signals in response to a manual input, e.g. by a pilot. Alternatively or additionally, the control system may be configured to generate control signals in response to an input received from a further aircraft system, such as an autopilot system. Tn some examples the control system may he configured to determine whether the flight conditions meet certain predefined criteria, and to generate a particular control signal when a given set of predefined criteria is met. For example, the control system may he configured to determine when the aircraft has entered a cruise phase and to generate the second control signal in response to that determination.

[0061] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

[0062] Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.

[0063] Where the term "or" has been used in the preceding description, this term should be understood to mean "and/or", except where explicitly stated otherwise.

Claims

CLAIMS: 1. An aerofoil structure having an upper aerodynamic surface and a lower aerodynamic surface, which meet at a midpoint of the leading edge of the aerofoil structure, the aerofoil structure comprising at least one leading edge moveable device having a spanwise dimension less than or equal to its chordwise dimension and configured to be moveable between an extended position and a retracted position; wherein: in the extended position, the moveable device projects forwardly from the lower aerodynamic surface; and in the retracted position, the moveable device is entirely disposed within the aerofoil structure.
2. An aerofoil structure according to claim 1, wherein the shape of the moveable device is configured such that the moveable device creates a vortex when the moveable device is in the extended position during flight of an aircraft in which the aerofoil structure is comprised.
3. An aerofoil structure according to claim 2, wherein the moveable device is configured to block spanwise airflow along the lower aerodynamic surface adjacent. the midpoint..
4. An aerofoil structure according to any preceding claim, wherein a forward-facing surface of the moveable device is flush with the lower aerodynamic surface when the moveable device is in the retracted position.
5. An aerofoil structure according to any preceding claim, wherein the moveable device is further configured to be moveable into an over-retracted position in which a forward-facing surface of the moveable device is recessed relative to the lower aerodynamic surface.
6. An aerofoil structure according to any preceding claim, wherein the moveable device comprises an actuation mechanism configured to drive movement of the moveable device between the extended position and the retracted position.
7. An aerofoil structure according to claim 6, wherein the actuation mechanism is configured to drive translational and/or rotational movement of the moveable device.
8. An aerofoil structure according to any preceding claim, wherein the upper aerodynamic surface and the lower aerodynamic surface arc formed by an outer skin of the aerofoil structure, and wherein the outer skin comprises an opening through which the moveable device projects, at least in the extended position of the moveable device.
9. An aerofoil structure according to any preceding claim, configured such that the moveable device is controllably moveable between the extended position and the retracted position.
10. An aerofoil structure according to claim 9, wherein the moveable device is configured to receive control signals from an aircraft in which the aerofoil structure is comprised, and is controllably moveable in response to received control signals.
11. An aerofoil structure according to any preceding claim, wherein the aerofoil structure is an aircraft. wing.
12. An aerofoil structure according to claim 11, wherein the aircraft wing is a swept wing.
13. An aircraft comprising an aerofoil structure according to any of claims 1 to 12.
14. An aircraft according to claim 13, further comprising a control system in communication with the leading edge moveable device, wherein the control system is configured to: send a first control signal to the moveable device, the first control signal being configured to cause the moveable device to move to the extended position; and send a second control signal to the moveable device, the second control signal being configured to cause the moveable device to move to the retracted position.
15. An aircraft according to claim 14, wherein the control system is further configured to: send a third control signal configured to cause the moveable device to move to an intermediate position between the extended position and the retracted position; and/or send a fourth control signal configured to cause the moveable device to move to an over-retracted position in which a forward-facing surface of the moveable device is recessed relative to the lower aerodynamic surface.