GB2553847A

GB2553847A - Variable chord length flight control surfaces

Info

Publication number: GB2553847A
Application number: GB1615901.4A
Authority: GB
Inventors: Way Simon
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2016-09-19
Filing date: 2016-09-19
Publication date: 2018-03-21
Also published as: GB201615901D0

Abstract

A flight control surface for an aircraft wing 21 comprises a primary panel 10 mountable to the aircraft wing; and a secondary panel 12, moveably connected to the primary panel such that the secondary panel is moveable between a retracted position, in which a chord length of the flight control surface has a first value and at least one extended position in which the chord length of the flight control surface has a greater value. The secondary panel may be actuated by passing pressurized air through a channel (39, figure 3) or by means of a linear actuator (48, figure 4). There may be a control system operable to place the secondary panel in a high-lift position, a cruise position, or an air braking or lift dumping position.

Description

(54) Title of the Invention: Variable chord length flight control surfaces Abstract Title: Extendable flight control surface (57) A flight control surface for an aircraft wing 21 comprises a primary panel 10 mountable to the aircraft wing; and a secondary panel 12, moveably connected to the primary panel such that the secondary panel is moveable between a retracted position, in which a chord length of the flight control surface has a first value and at least one extended position in which the chord length of the flight control surface has a greater value. The secondary panel may be actuated by passing pressurized air through a channel (39, figure 3) or by means of a linear actuator (48, figure 4). There may be a control system operable to place the secondary panel in a high-lift position, a cruise position, or an air braking or lift dumping position.

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VARIABLE CHORD LENGTH 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. The flight control surfaces of a fixedwing aircraft are typically attached to the airframe on hinges or tracks so they may move and thus deflect the air stream passing over them. This redirection of the air stream generates an unbalanced force to rotate the plane about the associated axis. Flight control surfaces typically used by a commercial aircraft include flaps, slats, spoilers, rudders and elevators.

[0003] Spoilers are used to disrupt airflow over the wing, to increase drag, and thereby reduce lift. This allows a pilot to lose altitude without gaining excessive airspeed. If deployed asymmetrically, spoilers can be used to control an aircraft's roll. Spoilers can also be used as air brakes, and/or as lift-dumpers on landing to press the aircraft into the ground (to avoid a bounce landing). For the purposes of this disclosure, the term “air braking” is used to refer to the deployment of spoilers to increase drag during flight, whereas the term “lift dumping” is used to refer to the deployment of spoilers to destroy lift when the aircraft is moving on the ground (e.g. during landing roll). Some aircraft may have dedicated air brakes in addition to spoilers (e.g. in the form of surfaces which deflect outwardly from the fuselage), which increase drag without affecting lift.

[0004] Spoilers play a key role during an emergency descent manoeuvre, in which the aircraft must descend from cruising altitude to 10,000 feet (approximately 3000 m) or lower, within a maximum time period specified by aircraft certification requirements. The airspeed of the aircraft must be kept below an operational maximum during an emergency descent, so lift must be reduced as much as possible, and additional drag allows a steeper descent rate. How effectively a spoiler can reduce lift depends on the frontal area of the spoiler presented to the air, which in turn depends on the chord length of the spoiler. A longer spoiler presents a greater frontal area to the airflow over a wing than a shorter spoiler, and so can create more drag and thus a greater lift reduction effect. The shortest time in which a given aircraft can perform an emergency descent is therefore limited by the chord length of its spoilers (assuming a fixed or maximum possible deployment angle of the spoilers).

[0005] The length of the spoilers that can be installed on a given aircraft is limited by the distance between the rear spar of the wing and the flap for that aircraft. The sizes of the gap and the overlap between the spoiler trailing edge and the leading edge of the flap are critical parameters for high-lift performance, and it is therefore not generally possible to increase the spoiler length by increasing the overlap between the spoiler and the flap. During flight, the forces experienced by a wing act to pull the spoilers into a deployed position. The force required to hold a spoiler in a retracted position during cruise is, therefore also a factor which limits spoiler length. A larger spoiler will require more force to hold it down against the upper surface of a wing, and therefore a more powerful actuator. There therefore exist challenges in increasing the lift-reduction capabilities of a given aircraft design.

SUMMARY [0006] A first aspect of the present invention provides a flight control surface for a wing. The flight control surface comprises a primary panel mountable to an aircraft wing; and a secondary panel, positioned adjacent to an external surface of the primary panel at least in a retracted position of the secondary panel. The secondary panel is moveably connected to the primary panel such that the secondary panel is moveable between the retracted position in which a chord length of the flight control surface has a first value and at least one extended position in which the chord length of the flight control surface has a second value, the second value being greater than the first value.

[0007] Optionally, the chord length of the flight control surface when the secondary panel is in the retracted position is equal to a chord length of the primary panel.

[0008] Optionally, a leading edge of the primary panel is pivotally mountable to an aircraft wing such that the flight control surface is pivotable between a stowed position in which the flight control surface forms part of an aerodynamic surface of a wing on which the flight control surface is mounted, and at least one deployed position in which the flight control surface is angled with respect to the aerodynamic surface of the wing.

[0009] Optionally, the secondary panel is configured to be contained within an aerodynamic profile of the aircraft wing when the secondary panel is in the retracted position and the flight control surface is in the stowed position.

[0010] Optionally, the secondary panel is configured to be pneumatically extended by directing air from a relatively high pressure region adjacent the flight control surface to exert a pushing force on the secondary panel.

[0011] Optionally, the secondary panel is configured to be pneumatically retracted by directing air from a relatively low pressure region adjacent the flight control surface to exert a suction force on the secondary panel.

[0012] Optionally, the flight control surface further comprises an actuator connected to the primary panel and the secondary panel, and connectable to the aircraft wing. The actuator may, for example, be configured to drive pivoting movement of the primary panel and linear movement of the secondary panel.

[0013] Optionally, the flight control surface further comprises a first actuator connected to the primary panel and configured to drive pivoting movement of the primary panel, and a second actuator connected to the secondary panel and configured to drive linear movement of the secondary panel.

[0014] Optionally, the secondary panel is mounted on tracks attached to a surface of the primary panel.

[0015] Optionally, the primary panel is mountable to an upper surface of an aircraft wing and the secondary panel is positioned adjacent a lower surface of the primary panel in the retracted position of the secondary panel.

[0016] Optionally, a chord of the secondary panel is substantially parallel to a chord of the primary panel in all possible positions of the secondary panel.

[0017] Optionally, the flight control surface further comprises a biasing mechanism to bias the secondary panel into the retracted position.

[0018] Optionally, the primary panel comprises a non-extendable flight control surface.

[0019] Optionally, the primary panel comprises a spoiler.

[0020] A second aspect of the present invention provides an aircraft comprising a wing having a flight control surface according to the first aspect; and a control unit for controlling movement of the secondary panel between the retracted position and the extended position.

[0021] Optionally, the control unit is configured to: cause the secondary panel to be in the extended position when the flight control surface is positioned for air braking or lift dumping; and cause the secondary panel to be in the retracted position when the flight control surface is positioned for cruise.

[0022] Optionally the control unit is configured to cause the secondary panel to be in a selected position when the flight control surface is positioned for high-lift, wherein the selected position is one of: the retracted position, the extended position, and a partially extended position intermediate the retracted position and the extended position, and wherein the selected position is selected to create a predetermined gap and/or a predetermined overlap between a trailing edge of the flight control surface and a leading edge of a further flight control surface of the aircraft wing, for example in order to maximise trailing edge flap performance.

BRIEF DESCRIPTION OF THE DRAWINGS [0023] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0024] Figure la is a schematic side view of a flight control surface according to an embodiment, with a secondary panel in a retracted position;

[0025] Figure lb is a schematic side view of the flight control surface of Figure 1, with the secondary panel in an extended position;

[0026] Figure 2a is a partial schematic side view of a wing having a flight control surface according to an embodiment, in a cruise configuration;

[0027] Figure 2b is a partial schematic side view of the wing of Figure 2a, in a high-lift configuration;

[0028] Figure 2c is a partial schematic side view of the wing of Figure 2a, in a liftdumping configuration;

[0029] Figure 2d is a partial schematic side view of the wing of Figure 2a, in a highspeed air braking configuration;

[0030] Figure 3 is a partial schematic side view of a wing having a flight control surface according to an embodiment;

[0031] Figure 4 is a partial schematic side view of a wing having a flight control surface according to an embodiment; and [0032] Figure 5 is a schematic top view of an aircraft having a flight control surface according to an embodiment.

DETAILED DESCRIPTION [0033] The following disclosure relates to flight control surfaces for wings, e.g. aircraft wings, which have a variable chord length. Such flight control surfaces can enable a greater degree of lift-reduction and drag generation to be achievable for a given type of aircraft. Alternatively or additionally, such flight control surfaces can enable the lift dumping and/or air braking capability of a given aircraft to be increased without requiring any other changes to the wings of that aircraft. In some examples, flight control surfaces according to embodiments of the invention enable smaller and/or less powerful actuators to be used to drive pivoting movement of the flight control surfaces, for a given level of lift reduction achievable by those flight control surfaces.

[0034] Figures la and lb show a flight control surface 1 for a wing (not shown). The flight control surface 1 may, for example, be any flight control surface of aircraft, such as a spoiler, flap, aileron, rudder, etc. The flight control surface 1 comprises a primary panel 10, which is mountable to an aircraft wing, and a secondary panel 12. The secondary panel 12 is positioned adjacent to an external surface of the primary panel 10 at least in a retracted position of the secondary panel 12. Figure la shows the secondary panel 12 in such a retracted position. The secondary panel 12 is moveably connected to the primary panel 10 such that the secondary panel 12 is moveable between the retracted position in which a chord length of the flight control surface has a first value xi and at least one extended position in which the chord length of the flight control surface has a second value X2. The second value X2 is greater than the first value xi. Figure lb shows the secondary panel 12 in an extended position.

[0035] The chord length of the flight control surface is the distance between an axis about which the flight control surface is arranged to pivot, when mounted on a wing, and a trailing edge 16 of the flight control surface. In the particular illustrated example the axis is located at the centre of a hinge 14 for connecting the primary panel 10 to a wing. In some examples, such as the particular example shown in Figures la and lb, the chord length of the flight control surface, when the secondary panel 12 is in the retracted position, is equal to a chord length of the primary panel 10. This advantageously means that the flight control surface 1 can be installed in the same space on a wing as a conventional fixed chord spoiler having a chord length equal to the chord length of the primary panel 10.

[0036] In some examples (such as the particular example shown in Figures la and lb) a leading edge of the primary panel 10 is pivotally mountable to an aircraft wing, e.g. by means of the hinge 14, such that the flight control surface 1 is pivotable between a stowed position and at least one deployed position. In the stowed position the flight control surface 1 forms part of an aerodynamic surface of a wing on which the flight control surface is mounted. More particularly, an upper (with respect to an intended inuse orientation) surface of the flight control surface 1 may form part of an upper aerodynamic surface of a wing on which the flight control surface 1 is mounted. In the at least one deployed position, the flight control surface is angled with respect to the aerodynamic surface of the wing. The flight control surface 1 may be pivotable between a plurality of deployed positions, each of which is angled by a different amount with respect to the aerodynamic surface of the wing.

[0037] Pivoting of the flight control surface 1, when mounted on an aircraft, may be actuated in any suitable manner known in the art. For example, if the flight control surface 1 comprises a spoiler, a conventional spoiler actuation system may be used to support and pivot the primary panel 10 of the flight control surface 1. In some examples an actuation system may be configured to create a space between the primary panel 10 and the actuation mechanism, to permit the secondary panel 12 to retract into the created space. A point of attachment of an actuation system to a wing (e.g. the rear spar of a wing) may be selected to enable the secondary panel 12 to be fully contained within an aerodynamic profile of the wing when the secondary panel 12 is in the retracted position.

[0038] In some examples the primary panel 10 has a similar construction to a conventional (i.e. fixed chord length) aircraft spoiler. The primary panel 10 may comprise a non-extendable flight control surface. Indeed, in some examples the primary panel 10 is a conventional aircraft spoiler, to which a secondary panel 12 has been attached. Advantageously, such examples permit the invention to be implemented on an existing aircraft (in other words, retrofitted). In some examples the primary panel 10 is shorter than a minimum length of a non-extendable flight control surface for use in an equivalent application. Advantageously, such examples can reduce the force required to hold the flight control surface 1 in a non-deployed position, meaning that a lesspowerful actuation system can be provided to drive pivoting movement of the flight control surface 1.

[0039] The secondary panel 12 may have a similar construction to the primary panel

10. For example, the secondary panel 12 may have a similar construction to a conventional aircraft spoiler. A cross-sectional thickness of the secondary panel 12 may be less than or equal to a cross-sectional thickness of the primary panel 10. A crosssectional thickness of the secondary panel 12 may vary along the length, in the chordwise direction, of the secondary panel 12. For example, the cross-sectional thickness of the secondary panel 12 may decrease (e.g. taper) towards the trailing edge 16 of the secondary panel 12.

[0040] In some examples the secondary panel is configured to be contained within an aerodynamic profile of the aircraft wing when the secondary panel is in the retracted position and the flight control surface is in the stowed position. This can be achieved, for example, by the secondary panel 12 having a length less than a chord length of the primary panel 10, and/or by a cross-section of the secondary panel 12 being sufficiently thin (in a direction perpendicular to the chord) to permit the secondary panel 12 to be received within a space (e.g. a cavity or recessed portion) in a surface of a wing on which the flight control surface 1 is mounted. Such a space may be defined, for example, partly by a trailing edge profile of the wing and partly by a leading edge profile of a flap mounted on the wing, at least when the flap is in a fully retracted position.

[0041] The flight control surface 1 may further comprise a linkage 18, connecting the secondary panel 12 to the primary panel 10. In some examples the linkage 18 may support and/or retain the secondary panel 12 adjacent to the primary panel 10. In some examples the linkage 18 may drive movement of the secondary panel 12 between the retracted and extended positions. In some examples the linkage 18 may both support/retain the secondary panel 12 and drive movement of the secondary panel 12. The linkage 18 comprises a first part which is fixedly attached to the primary panel 10, and a second part which is fixedly attached to the secondary panel 12. The second part is moveable with respect to the first part. The second part may be driveable to move with respect to the first part.

[0042] In some examples the linkage 18 comprises a linear actuator, which can be, for example, hydraulically, pneumatically or electromechanically driven. Such a linear actuator may be of any suitable type known in the art. For example, such a linear actuator may be of the same type as, or maybe a similar type to, a linear actuator for driving pivoting movement of a conventional fixed-chord spoiler. In some examples the linkage 18 comprises one or more rails (tracks) attached to one of the primary part 10 and the secondary part 12, and one or more rail followers attached to the other of the primary part 10 and the secondary part 12. The rail followers are arranged to engage with the rails to support, retain and/or guide movement of the secondary panel 12. The rails and rail followers may be of any suitable type known in the art. In the particular example shown in Figures la and lb, the linkage 18 comprises a hydraulic linear actuator, a first end of which is fixedly attached to a lower surface of the primary panel 10, and a second end of which is fixedly attached to a leading edge part of the secondary panel 12.

[0043] An example of how the flight control surface 1 can be operated when mounted on a wing will now be explained with reference to Figures 2a-d. Figures 2a-d show three different configurations of a wing (only a trailing-edge portion is shown) comprising an aerofoil section 21, the flight control surface 1 and a flap 23. Each of the flap 23 and the flight control surface 1 is mounted to the aerofoil section 21 by any suitable means known in the art. The configurations of Figures 2a, 2b, 2c and 2d correspond to a cruise configuration, a high-lift configuration, a high-lift air braking or lift dumping configuration, and a high-speed air braking configuration respectively.

[0044] In the cruise configuration, shown in Figure 2a, the slat the flap 23 is fully retracted and the flight control surface 1 is positioned such that its upper surface is substantially parallel to an upper surface of the aerofoil section 21 and an upper surface of the flap 23. The flight control surface 1 seals a gap between the upper surface of the flap 23 and the trailing edge of the aerofoil section 21. A continuous upper wing surface is thereby formed by the flap 23, the flight control surface 1, and the aerofoil section

21. In the illustrated example, the primary panel 10 of the flight control surface 1 seals a gap between the upper surface of the flap 23 and the trailing edge of the aerofoil section 21. The secondary panel 12 is fully retracted, and in the illustrated example is received within a cavity formed by the trailing edge of the aerofoil section 21 and the leading edge of the flap 23 such that the secondary panel 12 is contained within an aerodynamic profile of the wing.

[0045] Typically, a conventional fixed-chord spoiler will overlap the leading edge of the flap by some amount in the cruise configuration. However; in principle in the cruise configuration a spoiler need only be long enough to close the gap between the upper trailing edge of the aerofoil section and the leading edge of the flap. As discussed above, an actuation force is required to hold a spoiler in the non-deployed position required by the cruise configuration, which increases with the size of the spoiler. Therefore, in some examples the length of the primary panel 10 is substantially equal to the length of the gap between the upper trailing edge of the aerofoil section 21 and the leading edge of the flap 23 (i.e. there is little or no overlap between the trailing edge of the flight control surface 1 and the flap 23). Advantageously, the actuation force required to maintain the flight control surface in the non-deployed position is thereby minimised.

[0046] In the high-lift configuration shown in Figure 2b (which may be used, e.g., during take-off), the flap 23 is partially deployed and the upper surface of the flight control surface 1 is substantially parallel to the upper surface of the aerofoil section 21. A gap has opened up, due to the rearward movement of the flap from its fully retracted position, between the trailing edge of the flight control surface 1 and the leading edge of the flap 23. Creating the gap forces high-pressure air from below the wing to flow through the gap and over the upper surface of the flap 23, which helps the airflow remain attached to the flap, increasing lift compared to a flap without such a gap. The amount of air flow through the gap affects how much lift is generated, and depends on the size of the gap.

[0047] With a conventional fixed-chord spoiler, the size of the gap can be altered by varying the angular position of the spoiler. However; with the flight control surface 1, it is possible to vary both angular position and chord length (i.e. by extending the secondary panel 12). Increasing the chord length of the flight control surface 1 in the high-lift configuration has the effect of increasing the amount by which the trailing edge of the flight control surface 1 overlaps the leading edge of the flap 23. A greater overlap may advantageously improve the alignment of the airflow through the gap, ensuring it remains attached to the flap 23. In Figure 2b, therefore, the secondary panel 12 is partially extended to create such an increased overlap. In the high-lift configuration both the angle of the flight control surface 1 and the degree of extension of the secondary panel 12 may be independently variable between a plurality of values, and/or may be continuously variable over a range of values. A fine degree of control over desired the airflow through the gap may thereby be achieved.

[0048] In the air braking/lift dumping configuration, shown in Figure 2c, the flap 23 is fully extended rearwardly and downwards from the trailing edge of the aerofoil section 21, to create a gap (slot) between the flap 23 and the trailing edge of the aerofoil section 21 through which air can flow. The flight control surface 1 is rotated clockwise by approximately 60° relative to its cruise position. This has the effect of spoiling airflow over the top surface of the wing, to significantly reduce lift, increase drag and to slow the forward motion of an aircraft on which the wing is mounted. The size of the lift reduction effect depends on the chord length of the flight control surface 1, as discussed above. Figure 2c shows the secondary panel 12 in the fully extended position, for maximum lift reduction. In some examples the degree of extension of the secondary panel 12 may be variable between a plurality of values, and/or may be continuously variable over a range of values. In such examples the degree of extension of the secondary panel 12 may be selected to achieve a desired amount of lift reduction, according to the particular operational scenario.

[0049] As mentioned above, spoilers can also be deployed asymmetrically (e.g. on one wing but not the other, or varying degrees of deployment between the wings), to control the roll of an aircraft. As such, it will be appreciated that the flight control surface 1 need not always be in the positions shown by Figures 2a-c. For example, during a roll manoeuvre executed during cruise, the flight control surface 1 may be at least partially deployed (i.e. pivoted clockwise relative to the non-deployed position shown in Fig. 2a).

[0050] It will further be appreciated that typically, a plurality of flight control surfaces 1 are provided along the spanwise length of a wing, and that each flight control surface 1 of the plurality may be independently deployable. For example, in the air braking/lift dumping configuration shown in Figure 2c, some of a plurality of flight control surfaces 1 may remain in a non-deployed position, and/or some of a plurality of flight control surfaces 1 may be deployed by a greater amount than others of the plurality of flight control surfaces 1. Such a scenario may arise, for example, when roll control is required simultaneously with increasing or reducing lift.

[0051] Various alternative options are possible for actuating movement of the secondary panel between the retracted position and the at least one extended position. Two such options will now be described with reference to Figures 3 and 4.

[0052] Figure 3 shows an example flight control surface 3 which is configured such that extension of the flight control surface 3 (i.e. increase of a chord length of the flight control surface 3) is pneumatically actuated by the pressure differences which occur in the environment of a wing during flight. The flight control surface 3 comprises a primary panel 30 and a secondary panel 32, connected by a linkage 38, which may have any or all of the features of the primary panel 10, the secondary panel 12, and the linkage 18 of the flight control surface 1 described above. The flight control surface 3 is pivotally connected to an upper part of a trailing edge of an aerofoil section 31 of a wing by a hinge 34. Pivoting movement of the flight control surface 3 may be driven in any suitable manner known in the art.

[0053] When the flight control surface 3 is at least partially deployed (e.g. in the position shown in Figure 3), the resulting kink in the upper wing surface (i.e. at the join between the upper surface of the aerofoil section 31 and the upper surface of the primary panel 30) creates a relatively high pressure (i.e. above static air pressure) first region 32 adjacent an upper surface of the aerofoil section 31 and an upper surface of the flight control surface 3 (i.e. the region within the dashed line in Figure 3). A second region 34 adjacent a lower surface of the flight control surface 3 (i.e. the region within the dotted line in Figure 3) is at a relatively low pressure (i.e. below static air pressure). This pressure difference is exploited to drive movement of the secondary panel 32, in the following manner.

[0054] The linkage 38 comprises a pneumatic linear actuator arranged to drive movement of the secondary panel 32 from a retracted position to an extended position. A conduit 37 connects the linear actuator to a first opening 39 located in an upper surface of the wing, which is in fluid communication with the first (high pressure) region 32. In some examples the conduit 37 connects a pneumatic chamber of the linear actuator to the opening 39. In the illustrated example, the first opening 39 is located in an upper surface of the aerofoil section 31, near the spoiler hinge. However; the first opening may alternatively be located in any location which permits it to be in fluid communication with the first region 32.

[0055] The first opening 39 is selectively openable by means of a first valve (not visible). The first valve may be configured to be closed in a default condition of the first valve, such that air is not able to enter the conduit 37. During flight, when the first valve is opened, air from the high pressure first region 32 will be driven (by the pressure differential) to enter the conduit through the first opening 37, and will increase the air pressure in a pneumatic chamber of the linear actuator, driving extension of the linear actuator.

[0056] In some examples the flight control surface 3 includes a biasing mechanism (not shown) (e.g. a spring) to bias the secondary panel 32 into the retracted position. In such examples the secondary panel 32 returns to the retracted position under the influence of the biasing mechanism when the first valve is closed.

[0057] In other examples, including the illustrated example, the flight control surface comprises second opening 33, provided in a wall of the linear actuator, to provide an air flow path between a pneumatic chamber of the linear actuator and the second (low pressure) region 34. The second opening is also selectively openable by means of a second valve (not visible). The second valve may be configured to be closed in a default condition of the second valve, such that air is not able to pass through the second opening 33. During flight, when the second valve is opened, air may be sucked out of the pneumatic chamber, under the influence of a pressure differential between the pneumatic chamber and the second region 34. The air pressure in the pneumatic chamber will consequently decrease, driving retraction of the linear actuator.

[0058] Thus, during flight, movement of the secondary panel 32 between a retracted position and at least one extended position can be effected by selectively opening and closing the first valve (and, if present, the second valve). Advantageously, this arrangement means that an actuator for driving movement of the secondary panel does not need to be connected to a power supply.

[0059] Figure 4 shows an example flight control surface 4 which is configured such that both pivoting of the flight control surface 4 and extension (i.e. increase in chord length) of the flight control surface 4 are commonly driven. The flight control surface 4 comprises a primary panel 40 and a secondary panel 32, connected by a linkage 38, which may have any or all of the features of the primary panel 10, the secondary panel 12, and the linkage 18 of the flight control surface 1 described above. The flight control surface 4 is pivotally connected to an upper part of a trailing edge of an aerofoil section 41 of a wing by a hinge 44.

[0060] The primary panel 40 comprises an arm 40b, which extends from the location of the hinge 44 at an angle to the main part 40a of the primary panel 40. A distal end of the arm 40b is pivotally connected to a first end of a linear actuator 47. A second, opposite end of the linear actuator is fixedly connected to a rear spar 49 of the aerofoil section 41. Extension and retraction of the linear actuator 47 thereby causes pivoting movement of the flight control surface 4 about the hinge 44. Extension and retraction of the linear actuator 47 also causes movement of the secondary panel 42 between a retracted position and at least one extended position, as follows.

[0061] The secondary panel 42 is moveably mounted on a lower surface of the primary panel 40 by means of rails and rail followers (not visible), which may have any of the features of the rails and rail followers described above in relation to the flight control surface 1. The secondary panel 42 is also connected to the linear actuator 47 by means of a linkage 43. In the illustrated example the linkage 43 comprises a rigid arm pivotally mounted at one end to the secondary panel 42 and at the other end to an arm of the linear actuator 47. The linkage 43 transmits the linear movement of the actuator arm to the secondary panel 42, which thereby drives movement of the secondary panel 42 between the retracted position and the at least one extended position. It will be appreciated that any other form of linkage suitable for transmitting linear movement of the linear actuator 47 to the secondary panel 42 could equally be used.

[0062] In examples, such as the example of Figure 4, in which a common actuator drives both pivoting of a flight control surface 4 and extension of that flight control surface, pivoting and extension movements are not independently controllable. Such examples may advantageously achieve the benefits of greater lift-reduction capability and/or easier spoiler hold-down during cruise, using a simplified mechanism as compared to other examples in which two or more actuators are provided.

[0063] Figure 5 shows a schematic top view of an example of a vehicle according to an embodiment. In the example of Figure 5 the vehicle is an aircraft 5, which comprises a fuselage 51, a pair of wings 52, and a pair of tailplanes 53. Each wing 52 is provided with flight control surfaces in the form of flaps 54, slats 55, ailerons 56, outboard spoilers 57, and inboard spoilers 58. Each of the outboard spoilers 57 and/or each of the inboard spoilers 58 comprises a variable-chord flight control surface, and may have any or all of the features of the flight control surfaces 1, 3, 4 described above. The aircraft 5 may also comprise further spoilers to those specifically shown in Figure 5, for example on the lower surfaces of the wings, and/or on winglets of the aircraft 5. Such spoilers may comprise variable-chord flight surfaces having any or all of the features of the flight control surfaces 1, 3, 4 described above.

[0064] The aircraft 5 further comprises at least one control unit (not shown) for controlling movement of the secondary panels of each of the spoilers 57, 58 between a retracted position and at least one extended position. In some examples the control unit is configured to control the position of the secondary panel of each spoiler 57, 58 independently. In some examples the control unit may be configured to also control pivoting movement of each of the spoilers 57, 58 between a non-deployed position and at least one deployed position. In some examples the control unit is configured to independently control pivoting movement of each spoiler 57, 58 independently. The control unit may be comprised in an avionics system of the aircraft 5.

[0065] In some examples, the control unit may be configured to control a particular one of the spoilers 57, 58 as follows. The control unit may be configured to cause a secondary panel of the particular spoiler 57, 58 to be in the extended position when the particular spoiler 57, 58 is positioned for air braking or lift dumping. The control unit may be configured to cause the particular spoiler to adopt an air braking/lift dumping configuration (e.g. the configuration shown in Figure 2c) by causing the secondary panel to move to an extended position and causing the primary panel to pivot to a deployed position. The control unit may be configured to a cause the secondary panel to be in the retracted position when the particular spoiler is positioned for cruise. The control unit may be configured to cause the particular spoiler to adopt a cruise configuration (e.g. the configuration shown in Figure 2a) by causing the secondary panel to move to a retracted position and causing the primary panel to pivot to a nondeployed position.

[0066] The control unit may further be configured to cause the secondary panel to be in a selected position when the particular spoiler is positioned for high-lift. The selected position may be one of the retracted position, the extended position, and a partially extended position intermediate the retracted position and the extended position. The selected position may be selected to create a predetermined gap and/or a predetermined overlap between a trailing edge of the flight control surface and a leading edge of a further flight control surface of the aircraft wing (e.g. a trailing edge flap).

[0067] In some examples the control unit is configured to automatically set one or more of the secondary panel position of a given flight control surface and the angular position of a given flight control surface based on (e.g. as a function of) one or more measured variables relating to the flight of the aircraft 5. Such measured variables can include, for example, airspeed, Mach number, angle of attack “S” level, etc. The control unit may be configured to set parameters of the flight control surfaces so as to meet one or more predetermined criteria, such as a minimum efficiency level, a maximum load on a flight control surface, a desired roll amount, etc. The control unit may be configured to set parameters of the flight control surfaces to alleviate load resulting from a particular manoeuvre, or to alleviate gust load.

[0068] Although only the outboard spoilers 57 of the aircraft 5 have been explicitly described as comprising variable chord-length flight control surfaces, any of the other flight control surfaces comprised in the aircraft 5 may alternatively or additionally comprise variable chord-length flight control surfaces, and may therefore have any or all of the features of the flight control surfaces 1, 3, 4 described above.

[0069] The above embodiments are to be understood as illustrative examples of the invention. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS:

1. A flight control surface for a wing, the flight control surface comprising: a primary panel mountable to an aircraft wing; and a secondary panel, positioned adjacent to an external surface of the primary panel at least in a retracted position of the secondary panel;

wherein the secondary panel is moveably connected to the primary panel such that the secondary panel is moveable between the retracted position in which a chord length of the flight control surface has a first value and at least one extended position in which the chord length of the flight control surface has a second value, the second value being greater than the first value.

2. A flight control surface according to claim 1, wherein the chord length of the flight control surface when the secondary panel is in the retracted position is equal to a chord length of the primary panel.

3. A flight control surface according to claim 1 or claim 2, wherein a leading edge of the primary panel is pivotally mountable to an aircraft wing such that the flight control surface is pivotable between a stowed position in which the flight control surface forms part of an aerodynamic surface of a wing on which the flight control surface is mounted, and at least one deployed position in which the flight control surface is angled with respect to the aerodynamic surface of the wing.

4. A flight control surface according to claim 3, wherein the secondary panel is configured to be contained within an aerodynamic profile of the aircraft wing when the secondary panel is in the retracted position and the flight control surface is in the stowed position.

5. A flight control surface according to any of claims 1 to 4, wherein the secondary panel is configured to be pneumatically extended by directing air from a relatively high pressure region adjacent the flight control surface to exert a pushing force on the secondary panel.

6. A flight control surface according to any of claims 1 to 5, wherein the secondary panel is configured to be pneumatically retracted by directing air from a relatively low pressure region adjacent the flight control surface to exert a suction force on the secondary panel.

7. A flight control surface according to claim 3 or claim 4, further comprising an actuator connected to the primary panel and the secondary panel, and connectable to the aircraft wing, wherein the actuator is configured to drive pivoting movement of the primary panel and linear movement of the secondary panel.

8. A flight control surface according to claim 3 or claim 4, further comprising a first actuator connected to the primary panel and configured to drive pivoting movement of the primary panel, and a second actuator connected to the secondary panel and configured to drive linear movement of the secondary panel.

9. A flight control surface according to any preceding claim, wherein the secondary panel is mounted on tracks attached to a surface of the primary panel.

10. A flight control surface according to any preceding claim, wherein the primary panel is mountable to an upper surface of an aircraft wing and the secondary panel is positioned adjacent a lower surface of the primary panel in the retracted position of the secondary panel.

11. A flight control surface according to any preceding claim, wherein a chord of the secondary panel is substantially parallel to a chord of the primary panel in all possible positions of the secondary panel.

12. A flight control surface according to any preceding claim, further comprising a biasing mechanism to bias the secondary panel into the retracted position.

13. A flight control surface according to any preceding claim, wherein the primary panel comprises a non-extendable flight control surface.

14. A flight control surface according to claim 13, wherein the primary panel comprises a spoiler.

15. An aircraft comprising:

a wing having a flight control surface according to any of claims 1 to 14; and a control unit for controlling movement of the secondary panel between the retracted position and the extended position.

16. An aircraft according to claim 15, wherein the control unit is configured to: cause the secondary panel to be in the extended position when the flight control surface is positioned for air braking or lift dumping; and cause the secondary panel to be in the retracted position when the flight control surface is positioned for cruise.

17. An aircraft according to claim 15 or 16, wherein the control unit is configured to cause the secondary panel to be in a selected position when the flight control surface is positioned for high-lift, wherein the selected position is one of: the retracted position, the extended position, and a partially extended position intermediate the retracted position and the extended position, and wherein the selected position is selected to create a predetermined gap and/or a predetermined overlap between a trailing edge of the flight control surface and a leading edge of a further flight control surface of the aircraft wing.

Intellectual

Property

Office

Application No: GB1615901.4 Examiner: Mr Michael Shaw