GB2572216A - Leading edge flight control surfaces - Google Patents

Abstract

An aircraft leading edge flight control surface comprising an actuation mechanism configured to independently translate and rotate the flight control surface relative to an aircraft aerofoil structure on which the flight control surface is mounted. An aerofoil assembly 2 comprises an aerofoil structure 20 and a leading edge flight control surface 21. The flight control surface includes an actuation mechanism that enables the control surface to be moved between a stowed position 21a to a first intermediate position 21b by a translation movement 201. The mechanism then enables the control surface to move to a second intermediate position 21c by a translation movement 202. The mechanism further enables the control surface to move to a high lift position 21d by means of a rotational movement 203. The control surface can be moved to a spoiling position (21e, fig 3a) by means of an additional translation movement 204. The control surface can also be moved to a braking position (21f, fig 4) from the high lift position 21d by means of a rotation movement (205, fig 4).

Description

LEADING EDGE FLIGHT CONTROL SURFACES

TECHNICAL FIELD [0001] The present invention relates to a flight control surface for a wing, and in particular to a flight control surface for an aircraft wing.

BACKGROUND [0002] Aircraft flight control surfaces allow a pilot to adjust and control an aircraft's flight attitude, direction of flight, and/or air-speed. Some aircraft have flight control surfaces known as Krueger flaps. A Krueger, or leading edge flap, is a high-lift device deployable from the lower aerodynamic surface of an aerofoil, such as an aircraft wing. When stowed, the Krueger trailing edge is disposed at or near the wing leading edge, and a portion of the Krueger device makes up part of the wing lower surface. When deployed the Krueger rotates forwardly from a hinge near the wing leading edge, and the Krueger trailing edge remains adjacent the wing leading edge. A Krueger provides a similar effect to a slat when deployed, whilst also shielding the leading edge of the aerofoil from debris.

SUMMARY [0003] A first aspect of the present invention provides an aircraft leading edge flight control surface comprising an actuation mechanism configured to independently translate and rotate the flight control surface relative to an aircraft aerofoil structure on which the flight control surface is mounted.

[0004] Optionally, the actuation mechanism is configured to move the flight control surface between a stowed position and a high-lift deployed position; and is also configured to one or more of: (i) move the flight control surface between the high-lift deployed position and a spoiling deployed position; and (ii) move the flight control surface between the high-lift deployed position and a braking deployed position.

[0005] Optionally, the actuation mechanism is configured to maintain the rotational orientation, about a spanwise axis, of the flight control surface substantially constant during movement between the high-lift deployed position and the spoiling deployed position.

[0006] Optionally, the actuation mechanism is configured to translate at least a part of the flight control surface aftward, with respect to an intended operational orientation of the aerofoil structure, during movement between the high-lift deployed position and the spoiling deployed position.

[0007] Optionally, the flight control surface is extendible in a chordwise direction, and the actuation mechanism is configured to extend the flight control surface during movement between the high-lift deployed position and the spoiling deployed position, such that a trailing edge part of the flight control surface is translated aftward by a greater amount than a leading edge part of the flight control surface during movement between the high-lift deployed position and the spoiling deployed position.

[0008] Optionally, the actuation mechanism is configured to passively effect the translation of the at least a part of the flight control surface by allowing the at least a part of the flight control surface to move under the influence of an external force.

[0009] Optionally the actuation mechanism is configured to, during movement between the high-lift deployed position and the braking deployed position, rotate the flight control surface about a spanwise axis until a chord of the flight control surface is substantially normal to an intended operational flight direction of the aerofoil structure.

[0010] Optionally, the actuation mechanism is configured to rotate the flight control surface through an angle less than or equal to 90° during a movement between the stowed position and the high-lift deployed position.

[0011] Optionally, during a first part of the movement between the stowed position and the high-lift deployed position the actuation mechanism is configured to translate the flight control surface along a direction substantially normal to a chord of the flight control surface.

[0012] Optionally, during a second part of the movement between the stowed position and the high-lift deployed position which follows the first part, the actuation mechanism is configured to translate the flight control surface forward and upward with respect to an intended operational flight direction of the aerofoil structure, whilst maintaining the rotational orientation about a spanwise axis of the flight control surface substantially constant.

[0013] Optionally, during a third part of the movement between the stowed position and the high-lift deployed position which follows the second part, the actuation mechanism is configured to rotate the flight control surface about a spanwise axis whilst maintaining the translational position of the flight control surface substantially constant.

[0014] Optionally, the flight control surface is a Krueger.

[0015] A second aspect of the present invention provides an aircraft aerofoil structure and a leading edge flight control surface. The leading edge flight control surface is mounted to the aerofoil structure by an actuation mechanism configured to translate the flight control surface relative to the aerofoil structure, and to rotate the flight control surface relative to the aerofoil structure. The actuation mechanism is configured to perform a rotation movement independently of performing a translation movement.

[0016] Optionally, the actuation mechanism is configured to move the flight control surface between a stowed position in which the flight control surface forms part of an aerodynamic surface of the aerofoil structure and a high-lift deployed position in which the flight control surface functions to increase the camber of the aerofoil structure during flight. Optionally, moving the flight control surface between the stowed position and the high-lift deployed position comprises translating and rotating the flight control surface.

[0017] Optionally, the actuation mechanism is further configured to move the flight control surface to a spoiling deployed position in which the flight control surface functions to reduce the lift generated by the aerofoil structure during flight.

[0018] Optionally, the actuation mechanism is further configured to move the flight control surface to a braking deployed position in which the flight control surface functions to increase the drag generated by the aerofoil structure during forward movement of the aerofoil structure.

[0019] Optionally, the actuation mechanism is configured such that, in the stowed position, a leading edge of the flight control surface is forward of a trailing edge of the flight control surface, with respect to an intended operational flight direction of the aerofoil structure.

[0020] Optionally, in the stowed position the flight control surface forms part of a lower aerodynamic surface of the aerofoil structure, with respect to an intended operational orientation of the aerofoil structure.

[0021] Optionally, in the high-lift deployed position the flight control surface is disposed in front of a leading edge of the aerofoil structure at a first angle to a chord of the aerofoil structure. Optionally, in the spoiling deployed position the flight control surface is translated rearwardly and upwardly with respect to the high-lift deployed position. Optionally, in the braking deployed position the flight control surface is disposed in front of a leading edge of the aerofoil structure at a second angle to a chord of the aerofoil structure; wherein the second angle is larger than the first angle.

[0022] Optionally, the flight control surface is a flight control surface according to the first aspect.

[0023] A third aspect of the present invention provides an aircraft comprising an aerofoil structure; a flight control surface according to the first aspect mounted on the aerofoil structure; and a control unit for controlling the actuation mechanism of the flight control surface.

BRIEF DESCRIPTION OF THE DRAWINGS [0024] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0025] Figure 1 is a set of schematic side views of a prior art flight control surface, at various stages of a movement between a stowed position and a high-lift deployed position;

[0026] Figure 2 is a schematic side view of an example flight control according to the invention, showing a movement path of the example flight control surface between a stowed position and a high-lift deployed position;

[0027] Figure 3 a is a schematic side view of the example flight control surface of Figure 2, showing a movement path of the example flight control surface between a high-lift deployed position and a spoiling deployed position;

[0028] Figure 3b is a set of schematic side views of an alternative example flight control surface, in retracted and extended states of the alternative example flight control surface;

[0029] Figure 4 is a schematic side view of the example flight control surface of Figure 2, showing a movement path of the example flight control surface between a high-lift deployed position and a braking deployed position;

[0030] Figures 5a-f are schematic views showing an example actuation mechanism for the example flight control surface of Figure 2 in various different positions;

[0031] Figures 6a and 6b are schematic side views of two further example flight control surfaces according to the invention; and [0032] Figure 7 is a schematic side view of an example aircraft having an example flight control surface according to the invention.

DETAILED DESCRIPTION [0033] The following disclosure relates to leading edge flight control surfaces for aircraft aerofoil structures, e.g. wings. Figure 1 shows a prior art aircraft leading edge flight control surface, in the form of a Krueger 11. An aircraft aerofoil leading edge assembly 1 (only a leading edge part of the assembly 1 is shown) comprises the Krueger 11 and an aerofoil structure 10 (only a leading edge part of the structure 10 is shown). The aerofoil structure 10 may comprise, for example, a fixed leading edge structure. The Krueger 11 is mounted to the aerofoil structure 10 by an actuation mechanism, which is illustrated schematically as a linkage 12. Movement of the linkage 12 is driven by a source of motive power such as an electric motor, or a hydraulic system (not shown).

[0034] In operation, the Krueger 11 is moveable by the actuation mechanism between a stowed position (shown in part (i) of Figure 1) and a high-lift deployed position (shown in part (iv)). In the stowed position a portion of the Krueger 11 makes up part of a lower aerodynamic surface of the aerofoil structure 10. In the high-lift deployed position the Krueger 11 is disposed in front of the leading edge of the aerofoil structure 10, with a gap or slot being present between the trailing edge of the Krueger 11 and the leading edge of the aerofoil structure 10. In the high-lift deployed position the Krueger 11 functions to increase the camber, and thereby to increase the coefficient of lift, of the aerofoil assembly 1. A Krueger may generally be deployed whenever increased lift is desired, such as during the take-off, climb, approach and landing phases of an aircraft flight cycle.

[0035] Parts (ii) and (iii) of Figure 1 show intermediate positions of the Krueger 11 during a movement between the stowed position and the high-lift deployed position. It can be seen that the leading edge of the Krueger (with respect to its deployed orientation) faces aft when it is in the stowed position, and that it rotates by nearly 180° during a movement from the stowed position to the high-lift deployed position. Simultaneously with this rotation, the Krueger is translated forwards and upwards, with respect to its stowed position. Known actuation mechanisms integrate the translation and rotation components of the deployment movement, such that it is not possible to vary the rotation of a Krueger whilst maintaining its translational position, and vice versa.

[0036] Figure 2 shows a further example aircraft aerofoil assembly 2, which comprises an aerofoil structure 20 and an example leading edge flight control surface 21 according to the invention. In the illustrated example the flight control surface 21 is a Krueger. The flight control surface 21 comprises an actuation mechanism (not shown) which connects it to the aerofoil structure 20. The actuation mechanism is configured to independently translate and rotate the flight control surface 21 relative to the aerofoil structure 20. This means that, in contrast to the prior art Krueger 11, the flight control surface 21 can be rotated whilst maintaining a constant translational position, or translated whilst maintaining a constant rotational position. The actuation mechanism is configured to move the flight control surface 21 between a stowed position 21a in which the flight control surface 21 forms part of an aerodynamic surface (in the particular example, a lower aerodynamic surface) of the aerofoil structure 20 and a highlift deployed position 21d in which the flight control surface 21 functions to increase the camber of the aerofoil structure 20 during flight. In particular, the actuation mechanism is configured to move the flight control surface 21 between the stowed position 21a and the high-lift deployed position 21d by translating and rotating the flight control surface 21.

[0037] The movement path followed by the flight control surface 21 during a movement between the stowed position 21a and the high-lift deployed position 21d is shown in Figure 2. It can be seen that this movement path differs significantly from the movement path followed by the prior art Krueger 11. A key difference is that, in the stowed position 21a, a leading edge of the flight control surface 21 is forward of a trailing edge of the flight control surface 21, with respect to an intended direction of travel of the aerofoil assembly 2. Consequently, the flight control surface 21 is rotated through an angle of less than or equal to 90° during a movement between the stowed position 21a and the high-lift deployed position 21d. In the high-lift deployed position 21d the flight control surface 21 is disposed in front of the leading edge of the aerofoil structure 20 at a first angle a to a chord of the aerofoil structure 20. The first angle a is an acute angle. During a movement between the stowed position 21a and the high-lift deployed position 21d the flight control surface passes through the intermediate positions 21b and 21c.

[0038] During a first part of the movement between the stowed position 21a and the high-lift position 21d the actuation mechanism is configured to translate the flight control surface directly away from the lower surface of the aerofoil structure 20, along a direction substantially normal to a chord of the flight control surface 21. This first part of the movement, which may be known as the “breakout”, is indicated by the arrow 201.

[0039] It is desirable for the breakout movement to be along a direction substantially normal to the chord of the flight control surface 21 (and thus substantially normal to the lower surface of the aerofoil structure 20 immediately adjacent the flight control surface 21) because it minimizes friction between a seal provided between the flight control surface 21 and the lower surface of the aerofoil structure 20 during the breakout movement. There will be no rubbing of such a seal in a direction tangential to the surface of the flight control surface 21, meaning that the seal break out force is lower, and wear of the seal and risk of tearing the seal are reduced. The quality of the aerodynamic sealing when the flight control surface 21 is stowed can also be improved, which improves the aerodynamic performance of the aerofoil structure 20 when the Krueger is stowed.

[0040] During a second part of the movement between the stowed position 21a and the high-lift deployed position 21d which follows the first part, the actuation mechanism is configured to translate the flight control surface 21 forward and upward with respect to an intended operational flight direction of the aerofoil structure 20. The rotational orientation about a spanwise axis of the flight control surface 21 is maintained substantially constant during the second part of the movement. This second part of the movement is indicated by the arrow 202 on Figure 2, and moves the flight control surface from the intermediate position 21b to the intermediate position 21c. The flight control surface 21 may follow a substantially straight linear path during the second part 202 of the movement.

[0041] The translational position of the intermediate position 21c is equal to the translational position of the high-lift deployed position 21d - that is, no further translation of the flight control surface 21 is required to move it from the intermediate position 21c to the high-lift deployed position 21d. During the second part of the movement between the stowed position 21a and the high-lift deployed position 21d the flight control surface 21 may be translated along a direction parallel to a chord of the flight control surface 21. Advantageously, translating the flight control surface along a direction parallel to its chord creates significantly less aerodynamic disturbance than a conventional rotational Krueger deployment movement.

[0042] During a third part of the movement between the stowed position 21a and the high-lift deployed position 21d which follows the second part, the actuation mechanism is configured to rotate the flight control surface 21 about a spanwise axis whilst maintaining the translational position of the flight control surface 21 substantially constant. The third part of the movement moves the flight control surface 21 from the intermediate position 21c to the high-lift deployed position 21d. During the third part of the movement, the actuation mechanism rotates the flight control surface through an angle less than or equal to 90°. The actuation mechanism may rotate the flight control surface until the angle between a chord of the flight control surface 21 and a chord of the aerofoil structure 20 is equal to a. In many cases, the actuation mechanism may rotate the flight control surface 21 through an angle significantly less than 90°. In some examples the actuation mechanism is configured to rotate the flight control surface 21 through an angle less than 50°.

[0043] In some examples the rotational position of the flight control surface 21 in the high-lift deployed position 21d may be selected to create a particular effect. For example, the rotational position of the flight control surface 21 may be selected in dependence on a current angle of attack of the aerofoil structure 20. The rotational position of the flight control surface 21 may be selected to optimize the extent to which the leading edge of the aerofoil structure 20 is shielded from debris. This may be achieved, for example, by angling the flight control surface 21 such that the wake created by the flight control surface 21 encompasses as much of the leading edge as possible, or encompasses a selected part of the leading edge. For example, the upper surface of the leading edge is most critical for achieving laminar flow and so it may be advantageous to angle the flight control surface 21 such that it deflects debris away from the upper surface of the leading edge. The rotational and/or the translational position of the flight control surface 21 in the high-lift position 21d may be selected to create a gap of a particular size between the trailing edge of the flight control surface and the leading edge of the aerofoil structure 20. Tailoring this gap can improve high lift performance of the aerofoil structure 20.

[0044] The movement path between the stowed position 21a and the high-lift deployed position 21d is advantageous compared to the prior art Krueger deployment movement illustrated by Figure 1 for the reasons described above. However; the actuation mechanism of the flight control surface 21 also makes it possible to position the flight control surface 21 in one or more additional deployed positions, which enable further advantageous effects to be produced. In particular, the actuation mechanism is able to move the flight control surface 21 into a spoiling deployed position in which the flight control surface functions to reduce the lift generated by the aerofoil structure 20 during flight, and/or is able to move the flight control surface 21 into a braking deployed position in which the flight control surface 21 functions to increase the drag generated by the aerofoil structure 20 during forward movement of the aerofoil structure 20.

[0045] The actuation mechanism may, for example, be configured to move the flight control surface 21 between the high-lift deployed position 21d and the spoiling deployed position 21e. The actuation mechanism may be configured to maintain the rotational orientation, about a spanwise axis, of the flight control surface 21 substantially constant during movement between the high-lift deployed position 21d and the spoiling deployed position. The actuation mechanism may be configured to translate at least a part of the flight control surface 21 aftward, with respect to an intended operational orientation of the aerofoil structure 20, during movement between the high-lift deployed position 21d and the spoiling deployed position.

[0046] Figure 3 a illustrates an example movement of the flight control surface 21 between the high-lift deployed position 21d and a spoiling deployed position 21e. During the movement between the high-lift deployed position 21d and the spoiling deployed position 21e, the actuation mechanism translates the entire flight control surface 21 aftwards (rearwards), with respect to an intended operational orientation of the aerofoil structure 20. This movement is represented by the arrow 204 on Figure 3a. The direction of translation is parallel to a chord of the flight control surface 21. As a result of the orientation of the flight control surface 21 in the high-lift deployed position 21d, the direction of the translation is upwards as well as aftwards with respect to the high-lift deployed position 21d. The flight control surface 21 does not undergo any rotation during the movement 204, thus the angle between a chord of the flight control surface 21 and a chord of the aerofoil structure 20 is the same in the spoiling deployed position 21e as in the high-lift deployed position 21d (that is, a). The actuation mechanism is configured to translate the flight control surface 21 by a sufficient amount that the trailing edge of the flight control surface 21 protrudes into the airflow over the aerofoil structure 20, to spoil that airflow.

[0047] The spoiling deployed position 21e shown in Figure 3a is a fully-deployed spoiling position, meaning that further aftwards and upwards translational movement of the flight control surface 21 is not possible. In some examples the actuation mechanism may be configured to maintain the flight control surface 21 in one or more intermediate translational positions, each of which is disposed on the movement path 204 between the high-lift deployed position 21d and the fully-deployed spoiling deployed position 21e. The amount by which the trailing edge of the flight control surface 21 protrudes into the airflow, and thus the magnitude of the spoiling effect created, may be less in the intermediate translational positions than in the fully-deployed spoiling deployed position 21e. The amount of spoiling may therefore be controlled by selecting an appropriate intermediate position between the high-lift deployed position 21d and the fully-deployed spoiling deployed position 21e (such selection may be effected, for example, via a controller communicatively connected to the actuation mechanism).

[0048] In some examples the translational movement of the flight control surface 21 from the high-lift deployed position 21d to the spoiling deployed position 21e is achieved by the actuation mechanism in the same manner as, or in a similar manner to, the second part 202 of the movement of the flight control surface 21 between the stowed position 21a and the high-lift deployed position 21d (that is, the movement between the intermediate position 21b and the intermediate position 21c). For example, a sliding rail system may be used to effect both movements, as described below in relation to Figures 5a-f. In such examples the translational movement of the flight control surface 21 is actively driven. However; other examples are possible in which the actuation mechanism is configured to passively effect the translation of the flight control surface 21 by allowing the flight control surface 21 to move under the influence of an external force.

[0049] In some examples, the dynamic pressure of the oncoming airflow during flight moves the flight control surface 21 from the high-lift deployed position 21d to the spoiling deployed position 21e. In such examples the actuation mechanism comprises a controllably releasable locking feature (such as a latch) to maintain the flight control surface 21 in the high-lift deployed position 21e. Releasing this locking feature during flight permits the flight control surface 21 to translate towards the spoiling deployed position 21e under the influence of the oncoming airflow. The locking feature may be configured such that it can be controllably engaged at various intermediate translational positions of the flight control surface 21 between the high-lift deployed position 21d and the fully-deployed spoiling position 21e, to enable the amount of spoiling to be controlled, as described above.

[0050] Figure 3b illustrates an example movement of an alternative example flight control surface 311 for the aerofoil structure 20 between a high-lift deployed position 3 Id and a spoiling deployed position 31e. The alternative flight control surface 311 is extendible in a chordwise direction and comprises an actuation mechanism (not shown) that is configured to extend the flight control surface 311 during movement between the high-lift deployed position 3 Id and the spoiling deployed position 31e. The extension movement is represented by the arrow 301 on Figure 3b(ii). A trailing edge part of the flight control surface 311 is thereby translated aftward by a greater amount than a leading edge part of the flight control surface 311 during movement between the highlift deployed position 3 Id and the spoiling deployed position 31e. In some examples the leading edge part of the flight control surface 31 may maintain a constant translational position during the movement between the high-lift deployed position 3 Id and the spoiling deployed position 31e.

[0051] Extension of the flight control surface 311 may be achieved in any suitable manner. In the illustrated example, the flight control surface 311 comprises a main aerofoil part 311a, and a moveable panel 311b which is substantially completely received within the aerofoil part 311a in a non-extended configuration of the flight control surface 311, and which is configured to move aftwards along a chordwise direction of the flight control surface 311 until most of the chordwise length of the panel 311b protrudes from a slot provided in the trailing edge of the aerofoil part 311a. For example, the panel 311b may slide on tracks or rails provided within the aerofoil part 311a. Extension of the panel 311b may be actively driven, for example by hydraulic pistons, or by a motor driven rack-and-pinion system. Alternatively, extension of the panel 311b may be passively driven, for example by the pressure created by oncoming air during flight. In examples in which extension of the panel 31 lb is passively driven, the panel 311b and/or the aerofoil part 311a may comprise one or more features to facilitate the exertion of a motive force on the panel 31 lb by oncoming airflow.

[0052] The actuation mechanism may be configured to maintain the panel 31 lb in one or more intermediate positions between the non-extended (fully retracted) position and the fully extended position. The degree of extension of the panel 311b may thereby be selectively controllable, providing a mechanism to selectively control the amount of spoiling provided by the flight control surface 311.

[0053] In examples in which the leading edge part of the flight control surface 31 maintains a constant translational position during the movement between the high-lift deployed position 3 Id and the spoiling deployed position 31e, the movement of the panel 311b from its fully retracted position (shown in Figure 3b(i)) to its fully extended position (shown in Figure 3b(ii)) comprises the entire movement of the flight control surface 311 from the high-lift deployed position 3Id to the (fully-deployed) spoiling deployed position 3 le. In other examples, the movement of the panel 311b from its fully retracted position (shown in Figure 3b(i)) to its fully extended position (shown in Figure 3b(ii)) comprises part of the movement of the flight control surface 311 from the highlift deployed position 3 Id to the (fully-deployed) spoiling deployed position 31e. In such examples the entire flight control surface 311 may translate aftwards parallel to its chord to provide a remaining part of the movement of the flight control surface 311 from the high-lift deployed position 3 Id to the (fully-deployed) spoiling deployed position 31e. The translation may be actuated in the same manner as for the example flight control surface 21 described above, and may be actively or passively driven.

[0054] The actuation mechanisms of each example flight control surface 21,31 are also configured to translate the flight control surface (or part thereof) 21, 31 in the opposite direction to the arrows 205, 301, so that the flight control surface 21, 31 moves from the spoiling deployed position 21e, 31e, to the high-lift deployed position 21d, 3 Id. This may be performed as part of a larger movement back to the stowed position 21a (which may be the reverse of the deployment movement illustrated by Figure 2), or it may be performed as a movement in its own right.

[0055] In the spoiling deployed position, an example flight control surface according to the invention is deployed above the aerofoil structure 20, close to the leading edge of the aerofoil structure 20. As such, the flight control surface is close to the suction peak of the aerofoil structure 20, where most of the lift is generated. Consequently, the leading edge flight control surface can be much more effective at spoiling the airflow over the aerofoil structure than a conventional trailing edge spoiler. Depending on the particular design of the aerofoil structure 20, it is expected that it would be unnecessary to provide trailing edge spoilers in addition to leading edge flight control surfaces according to the invention. Omitting the trailing edge spoilers could significantly decrease the weight and complexity of a wing comprising the aerofoil structure 20.

[0056] Figure 4 illustrates an example movement of the flight control surface 21 between the high-lift deployed position 21d and a braking deployed position 21 f. During the movement between the high-lift deployed position 2Id and the braking deployed position 2If, the actuation mechanism rotates the entire flight control surface 21 about a spanwise axis such that the trailing edge of the flight control surface 21 moves forwards (with respect to an intended operational orientation of the aerofoil structure 20) and the leading edge of the flight control surface 21 moves aftwards. This movement is represented by the arrow 205 on Figure 4. The actuation mechanism is configured to rotate the flight control surface 21 until a chord of the flight control surface 21 is substantially normal to an intended operational flight direction of the aerofoil structure (which may be substantially parallel to a chord of the aerofoil structure 20). In the braking deployed position the flight control surface 21 is disposed in front of the leading edge of the aerofoil structure 20 at an angle β to a chord of the aerofoil structure. The angle β is larger than the angle a.

[0057] In some examples the rotational position of the flight control surface 21 in the braking deployed position 21 f (that is, the size of the angle β) may be selected to create a particular effect. For example, the rotational position of the flight control surface 21 may be selected in dependence on a current angle of attack of the aerofoil structure 20. In some examples, a movement of the flight control surface 21 from the high-lift deployed position 21d to the braking deployed position 21f may additionally involve translating the flight control surface 21 along a direction substantially parallel to a chord of the aerofoil structure 20, for example to decrease or increase the size of the gap between the leading edge of the aerofoil structure 20 and the flight control surface 21. It may be desirable in some situations to eliminate this gap, so that the flight control surface 21 is in contact with the leading edge of the aerofoil structure 20. The rotational and/or the translational position of the flight control surface 21 in the braking deployed position 2If may be selected to maximize the extent to which the flight control surface disrupts airflow over the aerofoil structure 20. The rotational and/or the translational position of the flight control surface 21 in the braking deployed position 21f may be dynamically controlled to vary the effect created by the flight control surface 21. The amount of braking and/or lift dumping caused by the flight control surface 21 can thereby be tailored to meet the requirements of a given operational situation.

[0058] The actuation mechanism is also configured to rotate the flight control surface 21 in the opposite direction to the arrow 205, so that the flight control surface 21 moves from the braking deployed position 21 f to the high-lift deployed position 2Id. This may be performed as part of a larger movement back to the stowed position 21a (which may be the reverse of the deployment movement illustrated by Figure 2), or it may be a movement in its own right. For example, if a landing is aborted it may be desired to move the flight control surface from the braking deployed position 21 f to the high-lift deployed position 21d.

[0059] In the braking deployed position, an example flight control surface according to the invention is in front of the leading edge of the aerofoil structure 20, angled substantially perpendicularly to a chord of the aerofoil structure 20 (and thus substantially perpendicularly to the oncoming airflow). In this position it blocks the oncoming airflow and creates a dirty wake behind the flight control surface, which substantially prevents the aerofoil structure 20 from generating lift, and also significantly increases the drag generated by the aerofoil structure 20. The lift reduction helps keep the aircraft on the ground, whilst the drag increase assists with decelerating an aircraft on which the aerofoil structure 20 is installed immediately after landing. It is therefore expected that a flight control surface according to the invention would be moved to the braking deployed position just before or during a landing. A further advantageous effect created by the example flight control surfaces when in the braking deployed position is that the leading edge of the aerofoil structure is substantially entirely shielded from insects and other debris in the airflow.

[0060] Various mechanisms are envisaged as suitable for actuating the movements described in relation to Figures 2-4. Figures 5a-f show one such example actuation mechanism, which is suitable for use as the actuation mechanism of the flight control surface 21. Each of Figures 5a-f, includes a bottom view (i) of the aerofoil structure 20 on which the actuation mechanism is installed (relative to an intended operational orientation of the aerofoil structure 20) and a cross-section (ii) through the aerofoil structure 20.

[0061] The example actuation mechanism comprises first, second, third and fourth arm members 52, 53, 54, 55 and a pair of pistons 51. In the illustrated example the first, second, third and fourth arm members 52, 53, 54, 55 are substantially equal in length, although this need not necessarily be the case. The flight control surface 21 is fixedly connected to the first arm member 52, such that a translation or rotation of the first arm member 52 causes an equivalent translation or rotation of the flight control surface 21. The first arm member 52 is slidingly connected to the second arm member 53 such that the first arm member 52 may translate relative to the second arm member 53 along a direction parallel to the long axis of the second arm member 53, but is substantially prevented from rotating or translating along any other direction relative to the second arm member 53. For example, a rail system may be used to provide such a sliding connection. The actuation mechanism is connected to one or more sources of motive power for driving movement of the pistons 51 and first, second, third and fourth arm members 52, 53, 54, 55. The source(s) of motive power may comprise, for example, a hydraulic circuit, a servo motor, geared rotary actuator, or the like. The actuation mechanism is also communicatively connected to a control system, which provides control commands to cause the actuation mechanism to move the flight control surface 21 into a desired position.

[0062] An end of the second arm member 53 is pivotally connected to a forward end of the third arm member 54 by a pivot pin 56. The connection permits the second arm member 53 to rotate but not translate relative to the third arm member 54. Rotation of the second arm member 53 causes equivalent rotation of the first arm member 52, and thus equivalent rotation of the flight control surface 21. The pivotal connection between the second and third arm members 53, 54 may comprise a limiting mechanism to limit the range of possible relative angular positions of the second and third arm members

53, 54. For example, such a limiting mechanism may prevent the internal angle between the second and third arm members 53, 54 from exceeding 90°. A hinge or any other suitable pivotal connecting mechanism may be used to connect the second and third arm members 53, 54.

[0063] The third arm member 54 is slidingly connected to the fourth arm member 55 such that the third arm member 54 may translate relative to the fourth arm member 55 along a direction parallel to the long axis of the fourth arm member 55, but is substantially prevented from rotating or translating along any other direction relative to the fourth arm member 55. For example, a rail system may be used to provide such a sliding connection.

[0064] The fourth arm member 55 is connected to the lower end of each piston 51. The pistons 51 are configured to extend and retract along a direction parallel to the long axes of the pistons 51. The extension/retraction of the pistons 51 causes translation of the fourth arm member 55, and also of the first, second and third arm members 52, 53, 54. The actuation mechanism may be configured such that extension and/or retraction of the pistons 51 is only permitted when the first, second, third and fourth arm members 52, 53, 54, 55 are in a particular configuration (for example the fully retracted configuration shown in Figures 5a and 5b).

[0065] The operation of the actuation mechanism to move the flight control surface 21 between the stowed position, the high-lift deployed position, the spoiling deployed position and the braking deployed position will now be described. Although the below descriptions relate to moving the flight control surface 21 into the various deployed positions, it should be appreciated that the actuation mechanism may also be operated in reverse to move the flight control surface 21 out of the various deployed positions.

[0066] Figure 5a shows the flight control surface 21 in the stowed position 21a. The pistons 51 are in a maximally retracted state, and the four arm members 52, 53, 54, 55 are positioned such that they lie adjacent each other, substantially within the crosssectional footprint of the flight control device 21. In other words, the second, third and fourth arm members 53, 54, 55 are adjacent to and aligned with the first arm member 52. The flight control surface 21 is within the cross-section of the aerofoil structure 20, and a lower surface of the flight control surface 21 forms part of the outer surface of the aerofoil structure 20. The outer surface of the aerofoil structure 20 comprises an opening having a size and shape equal to or slightly larger than the size and shape of the flight control surface 21, so that the flight control surface 21 may be received within the opening when in the stowed position.

[0067] Figure 5b shows the flight control surface 21 in the first intermediate deployed position 21b, in which it is translated downwardly but not rotated relative to the stowed position 21a. The actuation mechanism moves the flight control surface from the stowed position to the first intermediate deployed position 21b by extending the pistons 51.

[0068] Figure 5c shows the flight control surface 21 in the second intermediate deployed position 21c, in which it is translated forwardly but not rotated relative to the first intermediate deployed position 21b. The actuation mechanism moves the flight control surface from the first intermediate deployed position to the second intermediate deployed position 21c by sliding the third arm member 54 forwardly relative to the fourth arm member 55. The sliding movement of the third arm member 54 may be driven by any suitable source of motive power, such as a hydraulic circuit, servo motor, geared rotary actuator, or the like. The first and second arm members 52, 53 move together with the third arm member 54 but are maintained stationary relative to the third arm member 54.

[0069] Figure 5d shows the flight control surface 21 in the high-lift deployed position 21d. The actuation mechanism moves the flight control surface 21 to the high-lift deployed position 21d from the second intermediate deployed position 21c by rotating the second arm member 53 relative to the third arm member 54 about the pivot pin 56. The rotation may be driven by any suitable source of motive power, such as a hydraulic circuit, servo motor, geared rotary actuator, or the like. The first arm member 52 moves together with the second arm member 53, but is maintained stationary relative to the second arm member 53.

[0070] Figure 5e shows the flight control surface 21 in the spoiling deployed position 21e. The actuation mechanism moves the flight control surface 21 to the spoiling deployed position 21e from the high-lift deployed position 21d by sliding the first arm member 52 rearwardly and upwardly relative to the second arm member 53. The sliding movement of the first arm member 52 may be driven by any suitable source of motive power, such as a hydraulic circuit, servo motor, geared rotary actuator, or the like. In some examples the sliding movement of the first arm member 52 may be passively driven by the oncoming airflow, as explained above. The actuation mechanism is configured to be able to maintain the first arm member 52 in a plurality of translational positions relative to the second arm member 53, in order to vary the degree of spoiling provided by the flight control surface 21.

[0071] Figure 5f shows the flight control surface 21 in the braking deployed position 2If. The actuation mechanism moves the flight control surface 21 to the braking deployed position 21 f from the high-lift deployed position 21d by rotating the first arm member 52 clockwise (i.e. so that the internal angle between the second arm member 53 and the third arm member 54 increases) about the pivot pin 56 until the upper (relative to the stowed position) surface of the flight control surface 21 is substantially perpendicular to the oncoming airflow. The actuation mechanism then slides the third arm member 54 rearwardly relative to the fourth arm member 55, to decrease the size of the gap between the leading edge of the aerofoil structure 20 and the flight control surface 21. The rotation and sliding movements occur by the same mechanisms described above in relation to the movement into the high-lift deployed position 21d.

[0072] Although the embodiments described utilise an entirely different movement path and actuation mechanism to the conventional Krueger mechanism illustrated in Figure 1, and various benefits are conferred by the novel movement path, simplified examples are also possible in which a conventional Krueger movement path and actuation mechanism are used for at least some of the movements of an example flight control surface according to the invention. Figures 6a and 6b illustrate two such simplified examples.

[0073] Figure 6a shows an example aircraft aerofoil assembly 6a. The assembly 6a comprises a conventional actuation mechanism for moving a flight control surface 610 from a stowed position (which is the same as the stowed position shown in Figure 1 (i)) to a high-lift deployed position 6 Id (which is the same as the high-lift deployed position shown in Figure l(iv)). The actuation mechanism, and the movement between the stowed position and the high-lift deployed position 6Id may be effected in the same manner as described above in relation to the prior art aerofoil assembly 1. However; the flight control surface 610 further comprises an additional actuation mechanism for moving the flight control surface 610 from the high-lift deployed position 6Id to a spoiling deployed position 61e. The additional actuation mechanism may be, for example, a rail system of the type described above in relation to Figure 5e. The movement between the high-lift deployed position 6Id and the spoiling deployed position 61e has the same features as the equivalent movement of the example flight control surface 21. In particular, it involves translation of the flight control surface 610 whilst maintaining a constant rotational position of the flight control surface 610.

[0074] Figure 6b shows a further example aircraft aerofoil assembly 6b. The assembly 6b is the same as the assembly 6a, except that the flight control surface 620 is an extendible flight control surface of the type shown in Figure 3b. The flight control surface 620 comprises a main aerofoil part 611a, and a moveable panel 611b, which have the same features as the corresponding components of the example flight control surface 311 described above. The flight control surface 620 comprises, in addition to a conventional actuation mechanism for moving the flight control 620 between the stowed position and the high-lift deployed position 6If, a further actuation mechanism for extending the flight control surface 620. The further actuation mechanism may have the same features as the actuation mechanism for extending the flight control surface 311. The movement of the flight control surface 620 between the high-lift deployed position 61d and the spoiling deployed position 61e has the same features as the equivalent movement of the example flight control surface 31. In particular, it involves translation of a part of the flight control surface 620 whilst maintaining a constant rotational position of the flight control surface 620.

[0075] Figure 7 shows a schematic side view of an example aircraft 7 according to an embodiment. The aircraft 7 comprises a pair of wings 71 (only one is visible), a vertical stabilizer 73, and a pair of tailplanes 72 (only one is visible). At least one leading edge flight control surface 74 according to the invention is mounted on each wing 71. The (or each) flight control surface 74 has any or all of the features of the example flight control surfaces 21, 31, 610, 620 described above. The flight control surface 74 is in a stowed position in Figure 7. The other aerodynamic structures of the aircraft 7 (e.g. the vertical stabilizer 73, tailplanes 72, etc.) may also comprise one or more flight control surfaces according to the invention.

[0076] The aircraft 7 further comprises at least one control unit 75 for controlling movement of the (or each) flight control surface 74 between the stowed position and at least one deployed position. In the illustrated example the control unit 75 is housed in an avionics bay of the aircraft 7. The control unit 75 may be configured to cause the flight control surface 4 to move from a stowed position to a high-lift deployed position in a first set of circumstances, such as receipt of a first command that has been input by a pilot, or a determination that a first criterion has been met. The control unit 75 may be configured to cause the flight control surface 74 to move from the high-lift deployed position to a spoiling deployed position in a second set of circumstances, such as receipt of a second command that has been input by a pilot, or a determination that a second criterion has been met. The control unit 75 may further be configured to cause the flight control surface 74 to be in a selected one of several possible high-lift deployed positions. The selected position may be selected to create a particular amount of spoiling of the airflow over the wing 71. The control unit 75 may be configured to cause the flight control surface 74 to move from the high-lift deployed position to a braking deployed position in a third set of circumstances, such as receipt of a third command that has been input by a pilot, or a determination that a third criterion has been met. The first, second and third criteria may, for example, correspond to different flight phases or situations.

[0077] In some examples the control unit 75 is configured to automatically select a deployed position and move the flight control surface 74 to the selected deployed position based on (e.g. as a function of) one or more measured variables relating to the flight of the aircraft 7. Such measured variables can include, for example, airspeed, Mach number, angle of attack “S” level, etc. The control unit 75 may be configured to select a position of the flight control surface 74 so as to generate a desired effect, such as to generate a particular amount of lift, or to spoil the air flow over the wing 71 by a particular amount.

[0078] In examples in which a wing 71 comprises more than one leading edge flight control surface 74 according to the invention, the control unit 75 may be configured to control the movement of each flight control surface 74 independently. The control unit 75 may be comprised in an avionics system of the aircraft 7.

[0079] 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.

[0080] 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 (20)

CLAIMS:

1. An aircraft leading edge flight control surface comprising an actuation mechanism configured to independently translate and rotate the flight control surface relative to an aircraft aerofoil structure on which the flight control surface is mounted.

2. A flight control surface according to claim 1, wherein the actuation mechanism is configured to move the flight control surface between a stowed position and a highlift deployed position; and is also configured to one or more of:

(i) move the flight control surface between the high-lift deployed position and a spoiling deployed position;

(ii) move the flight control surface between the high-lift deployed position and a braking deployed position.

3. A flight control surface according to claim 2, wherein the actuation mechanism is configured to maintain the rotational orientation, about a spanwise axis, of the flight control surface substantially constant during movement between the high-lift deployed position and the spoiling deployed position.

4. A flight control surface according to claim 2 or claim 3, wherein the actuation mechanism is configured to translate at least a part of the flight control surface aftward, with respect to an intended operational orientation of the aerofoil structure, during movement between the high-lift deployed position and the spoiling deployed position.

5. A flight control surface according to claim 4, wherein the flight control surface is extendible in a chordwise direction, and wherein the actuation mechanism is configured to extend the flight control surface during movement between the high-lift deployed position and the spoiling deployed position, such that a trailing edge part of the flight control surface is translated aftward by a greater amount than a leading edge part of the flight control surface during movement between the high-lift deployed position and the spoiling deployed position.

6. A flight control surface according to claim 4 or claim 5, wherein the actuation mechanism is configured to passively effect the translation of the at least a part of the flight control surface by allowing the at least a part of the flight control surface to move under the influence of an external force.

7. A flight control surface according to any of claims 2 to 6, wherein the actuation mechanism is configured to, during movement between the high-lift deployed position and the braking deployed position, rotate the flight control surface about a spanwise axis until a chord of the flight control surface is substantially normal to an intended operational flight direction of the aerofoil structure.

8. A flight control surface according to any of claims 2 to 7, wherein the actuation mechanism is configured to rotate the flight control surface through an angle less than or equal to 90° during a movement between the stowed position and the high-lift deployed position.

9. A flight control surface according to any of claims 2 to 8, wherein during a first part of the movement between the stowed position and the high-lift deployed position the actuation mechanism is configured to translate the flight control surface along a direction substantially normal to a chord of the flight control surface.

10. A flight control surface according to claim 9, wherein during a second part of the movement between the stowed position and the high-lift deployed position which follows the first part, the actuation mechanism is configured to translate the flight control surface forward and upward with respect to an intended operational flight direction of the aerofoil structure, whilst maintaining the rotational orientation about a spanwise axis of the flight control surface substantially constant.

11. A flight control surface according to claim 10, wherein during a third part of the movement between the stowed position and the high-lift deployed position which follows the second part, the actuation mechanism is configured to rotate the flight control surface about a spanwise axis whilst maintaining the translational position of the flight control surface substantially constant.

12. A flight control surface according to any preceding claim, wherein the flight control surface is a Krueger.

13. An aircraft aerofoil structure and a leading edge flight control surface, wherein the leading edge flight control surface is mounted to the aerofoil structure by an actuation mechanism configured to translate the flight control surface relative to the aerofoil structure, and to rotate the flight control surface relative to the aerofoil structure, wherein the actuation mechanism is configured to perform a rotation movement independently of performing a translation movement.

14. An aerofoil structure and flight control surface according to claim 13, wherein the actuation mechanism is configured to move the flight control surface between a stowed position in which the flight control surface forms part of an aerodynamic surface of the aerofoil structure and a high-lift deployed position in which the flight control surface functions to increase the camber of the aerofoil structure during flight, wherein moving the flight control surface between the stowed position and the high-lift deployed position comprises translating and rotating the flight control surface.

15. An aerofoil structure and flight control surface according to claim 14 wherein the actuation mechanism is further configured to (i) move the flight control surface to a spoiling deployed position in which the flight control surface functions to reduce the lift generated by the aerofoil structure during flight; and/or to (ii) move the flight control surface to a braking deployed position in which the flight control surface functions to increase the drag generated by the aerofoil structure during forward movement of the aerofoil structure.

16. An aerofoil structure and flight control surface according to claim 14 or claim 15, wherein the actuation mechanism is configured such that, in the stowed position, a leading edge of the flight control surface is forward of a trailing edge of the flight control surface, with respect to an intended operational flight direction of the aerofoil structure.

17. An aerofoil structure and flight control surface according to any of claims 14 to

16, wherein in the stowed position the flight control surface forms part of a lower aerodynamic surface of the aerofoil structure, with respect to an intended operational orientation of the aerofoil structure.

18. An aerofoil structure and flight control surface according to any of claims 14 to

17, wherein:

in the high-lift deployed position the flight control surface is disposed in front of a leading edge of the aerofoil structure at a first angle to a chord of the aerofoil structure;

in the spoiling deployed position the flight control surface is translated rearwardly and upwardly with respect to the high-lift deployed position; and in the braking deployed position the flight control surface is disposed in front of a leading edge of the aerofoil structure at a second angle to a chord of the aerofoil structure; wherein the second angle is larger than the first angle.

19. An aerofoil structure and flight control surface according to claim 13, wherein the flight control surface is a flight control surface according to any of claims 1 to 12.

20. An aircraft comprising:

an aerofoil structure:

a flight control surface according to any of claims 1 to 12 mounted on the aerofoil structure; and a control unit for controlling the actuation mechanism of the flight control surface.