Airfoil of an aerodynamic surface and aerodynamic surface

Abstract

The invention relates to an airfoil for a gondola surface, the airfoil comprising: a control surface comprising an upper surface and a lower surface; and actuating means configured to raise or lower the control surface, and wherein at least a portion of one of the upper surface and the lower surface of the control surface is auxetic, has a negative Poisson's ratio, and the other of the upper surface and the lower surface of the control surface comprises a material having a higher Poisson's ratio. The invention also relates to a gondola surface comprising at least one airfoil as described above.

Description

Technical Field

[0001] This invention belongs to the field of movable parts for aircraft, specifically the construction and integration of control surfaces within aerodynamic surfaces. More specifically, this invention relates to an airfoil element of an aerodynamic surface and an aerodynamic surface including at least one such airfoil element. More particularly, this invention relates to the control surfaces themselves and the architecture of actuators that allow the control surfaces to move. Background Technology

[0002] Aircraft typically include two or more aerodynamic surfaces or lifting surfaces (understood as equivalent terms in this document) used to generate lift in flight. These surfaces are usually divided into a leading edge (facing the incoming airflow), a torsion box (providing stiffness to bending and torsional moments), and a trailing edge arranged in a chordal order, with each segment connecting to the next.

[0003] Optionally, the aerodynamic surface may also include one or more control surfaces located at the leading or trailing edge for purposes such as delaying the stall point, allowing in-flight maneuvering, controlling airflow separation, and timely increasing lift. Surrounding all these components, the aerodynamic surface includes upper and lower surfaces forming an airtight enclosure, which is typically continuous except for the mechanical connection between the anti-torsion box and the control surface to allow deflection of the control surface, i.e., raising or lowering it.

[0004] As is well known in aeronautics, aerodynamic surfaces are commonly referred to as wings, but tail structures such as vertical tail surfaces ('VTP') or horizontal tail surfaces ('HTP') can also implement these aerodynamic surfaces. Unlike wings or HTPs, which are geometrically designed to generate lift and typically include asymmetric airfoil elements, VTPs consist of symmetrical geometry with the same camber on both sides of the centerline. This is because VTPs can generate either pull or thrust on both sides, thereby enabling the aircraft to yaw.

[0005] Regarding existing control surfaces in aircraft, they are typically made of rigid fairings, thus reproducing individual, movable airfoil elements that are mechanically deflected by controlled downward movement about a fixed hinge axis along the rear spars of the torsion box due to dedicated actuators. The actuators currently implemented are hydraulic, electric, or hybrid, and are responsible for controlling the deflection of the control surfaces.

[0006] The space between the rear wing spars and the movable individual control surfaces (i.e., where the actuation system components and hinges typically reside) is usually covered by rigid aerodynamic fairings. These fairings are non-deformable, and once the control surfaces are actuated (i.e., deflected), they cause an abrupt change in the external geometry of the aerodynamic surfaces (e.g., the wing), altering the aerodynamic continuity around the transition line between the rigid fairing and the control surfaces. This abrupt transition of the airfoil's external geometry between the rigid fairing and the control surfaces negatively impacts drag and airflow separation at lower airspeeds.

[0007] Modern aircraft are typically equipped with two types of control surfaces. One primary flight control surface includes, for example:

[0008] - Ailerons mounted near the wingtips on the trailing edge of each wing allow for control of the aircraft's roll and rotation.

[0009] - Elevators, typically mounted on the trailing edge of the HTP, allow control of the aircraft's pitch and rotation, as well as

[0010] - The rudder, typically mounted on the trailing edge of the VTP, allows control of the aircraft's yaw rotation.

[0011] The second type of flight control surface includes high-lift devices, such as:

[0012] - Slats, also known as leading-edge slats, are extensions at the front of the wing used to increase lift and are designed to reduce stall speed by altering airflow over the wing.

[0013] -Flaps, mounted on the trailing edge of each wing.

[0014] - Spoilers are used to disrupt airflow over the wings and greatly reduce lift. Spoilers allow glider pilots to lose altitude without gaining excessive airspeed.

[0015] These second type of flight control surfaces tend to reduce the minimum speed at which an aircraft can fly safely and increase the descent angle for landing.

[0016] All these surfaces are extended or deployed for maneuvering during critical phases such as approach or landing, and are controlled by the aircraft's flight management system ('FMS') for safe operation.

[0017] With the emergence of new materials, in order to make the shape of the airfoil closely adapt to the in-situ flight state, it has been proposed to use flexible materials known for their high mechanical properties (e.g., using tensile materials) to manufacture the individual control surfaces.

[0018] A tautological structure is characterized by a negative Poisson's ratio, making it similar to deformation along and across the direction of the applied force. That is, under a longitudinally applied force that tends to cause the material to contract (or extend), the material contracts (and extends accordingly) in the transverse direction.

[0019] As is well known, these elements are capable of providing contraction (or extension) to the airfoil in the lateral direction, while not producing any deformation along the longitudinal direction of the airfoil.

[0020] Depending on the context, these aerodynamic surfaces exhibiting this purposeful and in-situ deformable flexible material are more commonly referred to as 'morphing structures'. These morphing structures provide wings, VTPs, or HTPs with the ability to adapt to specific flight conditions and improve aircraft performance through adjustments to parameters of conventional lifting surfaces such as wingspan, chord, camber, and sweep angle.

[0021] However, all known methods for integrating flexible materials to allow for deformation behavior have been considered ineffective for controlling surfaces, as these methods significantly impact structural stability or reduce lift boost. Accordingly, there is a need for solutions to overcome these drawbacks. Summary of the Invention

[0022] The present invention provides a solution to the above-mentioned problems by proposing an airfoil and an aerodynamic surface according to the aerodynamic surface described below. Advantageous embodiments are further defined below.

[0023] Throughout this document, references will be made to many specific terms that will now be described. Therefore, these terms must be understood as follows.

[0024] Regarding the geometry of the aerodynamic surfaces, the aircraft's wings, horizontal stabilizer ('HTP', horizontal tail surface), and vertical stabilizer ('VTP', vertical tail surface) are all based on airfoil sections.

[0025] Furthermore, regarding the aerodynamic surfaces of the wing or HTP, these aerodynamic surfaces have an upper surface (the so-called 'outer arc surface' or 'suction surface') and a lower surface (the so-called 'inner arc surface' or 'pressure surface'). These surfaces are designed to maintain the aerodynamic shape of the airfoil. Additionally, the term "upper surface" can be defined only as a portion of the entire upper surface, such as the portion corresponding to the control surface, and similarly, the term "lower surface" can be defined only as a portion of the entire lower surface.

[0026] As technicians acknowledge, the construction of the upper / lower surfaces has also been extended to other aerodynamic surfaces of aircraft, such as VTP surfaces.

[0027] The term "airfoil" will be understood as the cross-sectional shape of an aerodynamic or lifting surface, which is determined to generate aerodynamic forces in the event of relative movement through a fluid, the component of which perpendicular to the direction of motion being called lift.

[0028] Then, with regard to "a portion of the aerodynamic surface," "airfoil of the aerodynamic surface" is understood as a structural element of the lifting surface or aerodynamic surface of an aircraft. Accordingly, the sum of the airfoils between two points measured along the spanwise direction on the aerodynamic surface results in a larger portion of the lifting surface or aerodynamic surface. Therefore, the sum of the airfoils spanning the entire wingspan of the aerodynamic surface represents the aerodynamic surface itself, and thus, in another embodiment, this portion of the aerodynamic surface can be the entire aerodynamic surface.

[0029] Therefore, those skilled in the art should understand that the continuous parts mentioned in this article regarding airfoils, such as leading edges, torsion boxes, and spars, are meant to be constructed as portions of these larger parts bounded by the airfoil boundaries, but this does not affect the fact that the sum of these portions may produce a complete part.

[0030] Furthermore, regarding the geometry of aerodynamic surfaces, the term "wingspan" refers to the distance from the tip (e.g., wingtip) of the aerodynamic surface to its root, and then "span" refers to "along the wingspan direction / in the wingspan direction".

[0031] Similarly, the term "chord direction" refers to the direction from the leading edge to the trailing edge, or vice versa, that is, "along the chord direction / in the chord direction".

[0032] The term "leading edge" refers to the leading edge of the lifting surface and therefore the leading edge of the airfoil as the aircraft moves forward.

[0033] The term "trailing edge" refers to the edge opposite to the "leading edge" of the aerodynamic surface and therefore the airfoil. The trailing edge is located at the tail of the torsion box of the lifting surface and therefore the tail of the aircraft as it moves forward.

[0034] "Tail" refers to the rear part of the lifting surface, which has the same meaning as "rear" and contrasts with "front." The front part is closer to the cockpit of the aircraft than either the tail or the rear part.

[0035] Throughout the description, terms related to “flexible” or “flexible material” will be understood as compliant materials, which have the ability to elastically deform when a force is applied and to return to their original shape when the force is removed.

[0036] According to a first aspect of the invention, the present invention provides an airfoil for an aerodynamic surface, the airfoil comprising:

[0037] A control surface, comprising an upper surface and a lower surface; and

[0038] A primary actuator configured to raise or lower the control surface.

[0039] Wherein, at least a first portion of one of the upper and lower surfaces of the control surface is tensile and has a negative Poisson's ratio, and at least a second portion of the other of the upper and lower surfaces of the control surface contains a material with a Poisson's ratio higher than that of the first portion.

[0040] The control surface according to the invention includes an upper surface and a lower surface. These surfaces form the upper surface or skin and the lower surface or skin of the entire airfoil, thus making the surface of the entire airfoil consist of at least two parts, one part corresponding to or surrounding the control surface, and one or more additional parts corresponding to or surrounding the portion of the airfoil other than the control surface.

[0041] According to the invention, the control surface may be located at the trailing edge of the airfoil and / or toward the trailing edge, at the leading edge of the airfoil and / or toward the leading edge, and / or at a portion of the airfoil between the leading and trailing edges. The airfoil may include more than one control surface.

[0042] In one embodiment, the control surface is positioned toward the leading edge of the airfoil, and the entire upper and lower surfaces of the airfoil comprise at least two portions: one corresponding to or surrounding the leading edge and the torsion box (if present), and another corresponding to or surrounding the control surface. Furthermore, in another embodiment, there may be another portion of the upper surface or skin and the lower surface or skin corresponding to another control surface positioned toward and / or at the leading edge (such as a slat).

[0043] According to the invention, at least a first portion of one of the upper and lower surfaces of the control surface is tensile and has a negative Poisson's ratio; that is, this first portion has a tensile structure and / or contains tensile material, thus allowing tensile behavior of this portion of the upper or lower surface. For example, applying a unidirectional tension in one of the directions contained on the surface increases the dimension in that direction and also increases the dimension in the vertical direction contained on the surface. On the other hand, applying a unidirectional compressive force in one of the directions contained on the surface decreases the dimension in that direction and also decreases the dimension in the vertical direction contained on the surface. In both cases, when the force application ceases, the first portion returns to its original shape. During normal use of the aircraft, the first portion and the force applied to it are thus adapted to produce elastic deformation of the first portion rather than plastic deformation.

[0044] The Poisson's ratio of a tensile material can be as low as or close to -1 (negative one). In this case, the magnitude of the decrease or increase in the lateral dimension is the same as the direction in which the load is applied.

[0045] In the airfoil according to the invention, at least a second portion of the other of the upper and lower surfaces of the control surface comprises a material with a Poisson's ratio higher than that of the first portion, thus providing deformation of the overall airfoil segment. This deformation is a result of the different Poisson's ratios of the first and second portions, which generates different magnitudes of lateral reaction forces in the first and second portions of the airfoil, thereby causing unequal length variations in the upper and lower surfaces of the control surface and deformation of the overall airfoil segment.

[0046] In some embodiments, the second portion may be made of a conventional material having a positive Poisson's ratio (also referred to below as a non-tensile material). Compared to the first portion, the second portion made of a conventional material exhibits opposite properties: applying uniaxial tension in one of the directions contained on the surface increases the dimension in that direction and also decreases the dimension in the vertical direction contained on the surface. Conversely, applying uniaxial compressive force in one of the directions contained on the surface decreases the dimension in that direction and also increases the dimension in the vertical direction contained on the surface. Examples of conventional materials may include composite laminates, metals such as aluminum alloys, honeycomb sandwich structure designs, truss structure designs, etc.

[0047] In other embodiments, the second portion may have a negative Poisson's ratio that is higher than that of the first portion, i.e., the negative Poisson's ratio of the second portion has a smaller absolute value (including zero) than that of the first portion, thus exhibiting weaker stretching behavior.

[0048] In some embodiments, the other of the upper and lower surfaces of the control surface is made of a material with a Poisson's ratio higher than that of the first portion. That is, the entire surface is made of the conventional material or a material exhibiting weaker tensile behavior.

[0049] The combination of the first portion on either the upper or lower surface and the second portion on the opposite surface of the control surface also facilitates the unfolding of the control surface while reducing secondary stresses on the control surface.

[0050] Advantageously, the combination of tensile materials and conventional materials / tensile materials with a higher Poisson's ratio on the two opposite surfaces of the control surface allows the control surface to be actuated in both the spanwise and chordwise directions.

[0051] Advantageously, and unlike conventional materials, in use, the tensile material reduces the risk of buckling in the shell or panel forming the aerodynamic surface, allowing the aerodynamic surface to assume its primary function of lift boosting without the adverse consequences of excessive stiffness loss observed when using conventional materials under compressive loads. Therefore, the unique structural properties of the first part, as previously explained, that allow it to deform, compared to how conventional materials deform under external loads, produce more flexible shell elements that better adapt to and follow the curvature of the aerodynamic surface under external loads.

[0052] In other words, the first part allows a single compressive force or a single traction force applied to the trailing edge to be converted into a combination of compressive and traction stresses on the surface, thus making the surface less sensitive to buckling and thus making the force distribution more efficient and balanced.

[0053] Furthermore, the combination of a first portion of the elastotropic material on one surface and a second portion on the opposite surface enables differentiated chordal displacement that can facilitate shape changes of the aerodynamic surface (e.g., to increase its curvature), wherein the second portion is made of a conventional material / elastotropic material with a higher Poisson's ratio.

[0054] Regarding the control surface, the main actuator is configured to raise or lower the control surface and provide the ability to adapt to takeoff, flight, and landing states based on the forces and strains applied to the airfoil.

[0055] In one embodiment, the upper and lower surfaces of the control surface are continuous with the remaining upper or lower surface of the airfoil. In another embodiment, the portion containing the tensile material forms a continuous upper or lower surface with the remaining upper or lower surface, preferably made of a conventional material having a positive Poisson's ratio.

[0056] Advantageously, the continuity between the tensile and non-tensile materials on the upper and / or lower surfaces provides a continuous outer and / or inner curved surface from the leading edge to the trailing edge. This allows for skin continuity of the aerodynamic surfaces, thereby avoiding and controlling any steps and gaps that may exist on conventional airfoils, as is associated with the interface between the control surfaces and the rigid fairing, which have a significant impact on drag.

[0057] Therefore, by eliminating the previous gaps and steps, the wetting area of ​​the airfoil is increased and the actuation of the control surface is improved. Furthermore, this avoids side effects and allows for delayed airflow separation.

[0058] In one embodiment, the airfoil includes a torsion box comprising an upper skin, a lower skin, a rear spar, and a front spar. That is, in this embodiment, the airfoil includes a leading edge, a torsion box, a control surface, and a trailing edge. Specifically, the torsion box includes a front spar and a rear spar. The leading edge may be at least fixed to the front spar positioned in front of the torsion box. Therefore, the torsion box is positioned between the leading edge and the trailing edge.

[0059] In one embodiment, the control surface is positioned at the tail of the rear spar, and a first portion extends at most into the rear spar, such that the first portion bridges:

[0060] - The upper skin of the anti-torsion box and the upper surface of the control surface; or

[0061] - The lower skin of the anti-torsion box and the lower surface of the control surface;

[0062] This provides aerodynamic continuity.

[0063] In one embodiment, the control surface is positioned at the front of the front wing spar, and the first portion extends at most into the front wing spar, such that the first portion bridges:

[0064] - The upper skin of the anti-torsion box and the upper surface of the control surface; or

[0065] - The lower skin of the anti-torsion box and the lower surface of the control surface;

[0066] This provides aerodynamic continuity.

[0067] The airfoil may include more than one control surface according to the invention, such as a first control surface located at the tail of the rear spar and a second control surface located at the front of the front spar.

[0068] In one embodiment where the control surface is positioned at the tail of the rear spar, the rear spar is positioned at approximately 50% of the chord length of the airfoil, wherein 0% of the chord length corresponds to the leading edge and 100% of the chord length corresponds to the trailing edge. In one embodiment, the first portion extends at least 50% to 75% of the chord length.

[0069] Unlike existing technologies where the hinge line for controlling surface deployment is positioned at 75% of the chord length, thus rendering the front of the rigid fairing immovable, embodiments of the present invention cover an area with a first portion (i.e., with a tensile material), thereby increasing the lift capability of the airfoil. In other words, instead of a rigid fairing covering 25% of the chord length to accommodate actuators, this is replaced by a first portion, providing a continuous and gradual deployment of the control surface, thus avoiding any abrupt contours.

[0070] In one embodiment, the first portion extends from 50% to 100% of the chord length. Advantageously, in this embodiment, the upper or lower surface of the airfoil is tensile along 50% of the entire chord and provides a more efficient force distribution and control over the surface curvature (if desired).

[0071] In one embodiment, the first part includes a flexible mesh structure covered by a flexible skin.

[0072] If a material has a negative Poisson's ratio, it is considered to be tensile. The first part of an embodiment of the invention can have a concave hexagonal geometry, that is, a hexagonal design with negative angles. Specifically, the concave hexagonal geometry exhibits four identical angles less than 90 degrees and two identical angles greater than 90 degrees between consecutive lateral edges. By adjusting these angles, the tensile behavior of this geometry can be tuned as needed.

[0073] In one embodiment, the flexible mesh structure is formed of rigid segments that are connected together by flexible joints or connectors at the intersections of the rigid segments (i.e., allowing rotation). Thus, the interconnected rigid segments can rotate relative to each other about the joints, thereby producing a tensile state that behaves like an adiabatic material.

[0074] In one embodiment, the first portion is assembled with the non-tensile portion. Furthermore, the assembly can be achieved using mechanical means such as rivets, or by binding or co-curing.

[0075] For example, any of these surfaces can be formed by a rigid grid with a conventional hexagonal design (e.g., as a conventional honeycomb), which modifies its pattern to a concave hexagonal design of a certain length to create a first section with tensile behavior. Thus, advantageously, a flexible skin can cover the boundary between the first section and the non-tensile section, thereby producing a progressive and continuous profile.

[0076] The resulting flexible mesh structure is covered with a flexible skin material such as flexible resin or rubber-like skin, and assembled together by mechanical bonding such as adhesives, or by bonding or by co-curing.

[0077] Advantageously, the combination of the grid structure and its flexible skin allows the tensile material to deform and cover the voids, which ensures that the air is compressed to form an optimal aerodynamic skin surface.

[0078] An additional advantage of this embodiment, which combines rigid meshes with conventional and tensile patterns, is that the fabrication of these patterns can be directly incorporated into the additive manufacturing process. Ultimately, the fabrication of the flexible skin covering the patterns can also be incorporated into the additive manufacturing process. These previously mentioned additive manufacturing processes can include the generation of tensile and non-tensile portions of controlled surfaces or the entire pneumatic surface. Advantageously, these portions and even the entire pneumatic surface can be fabricated in a single step, thus reducing the cost and time required to assemble different components.

[0079] In addition, the portion of the skin covering the rigid mesh can also be rigid (rather than flexible material) to increase the strength of the parts where flexible skin is not needed.

[0080] In another embodiment, the first portion and / or the non-tensile portion are each made of a continuous material without joints, which allows for continuous and faster manufacturing steps. The continuous material without joints can be a composite material with geometrical changes or including voids in its structure.

[0081] Similarly, in this embodiment with continuous material without joints, such as in the case of a combination of mesh and flexible skin, additive manufacturing processes are also suitable for reducing the uptime costs of assembly processes.

[0082] In one embodiment, the first portion includes at least one of the following:

[0083] - A continuous fiber laminate formed by embedding a reinforced plastic in a resin material to create a tetraskel structure.

[0084] - A cavity-containing foam material with macroscopic continuity and microscopic porosity.

[0085] - Graphene materials with vacancy defects, or

[0086] - Crystalline materials with a negative uniform Poisson's ratio.

[0087] In one embodiment, the tensile behavior of the first portion is obtained by orienting a continuous fiber laminate embedded in a resin material to form a reinforced plastic having a quadrilateral structure.

[0088] In another embodiment, the tensile behavior of the first part is obtained by using a cavity-filled foam material with macroscopic continuity and microscopic voids.

[0089] In another embodiment, the stretching behavior is achieved at the microscale by implementing a graphene material with vacancy defects in regions previously identified as requiring stretching.

[0090] In another embodiment, the first part may be made of a material that naturally exhibits tensile behavior, such as α-cristobalite, rock, or mineral that has negative Poisson properties at the micro or nanoscale.

[0091] In one embodiment, the main actuation device includes at least one first actuator configured to apply a force to the control surface substantially along the spanwise direction, causing the first portion to deform substantially along the chordwise direction.

[0092] In one embodiment in which the airfoil includes a torsion box with a rear spar, wherein the first portion extends at most to the rear spar, the main actuator includes a first swivel rod that is fixed to the rear spar at a first end by means of a swivel joint and fixed at a second end opposite the first end to the inner surface of the control surface adjacent to the surface including the first portion by means of a swivel joint.

[0093] In one embodiment, the first slewing rod is fixed to the slewing via a slewing joint positioned near the joint between the rear slewing and the surface opposite to the surface including the first portion.

[0094] According to this embodiment, the first rotating rod and the first portion form a triangular shape, such that when the first portion deforms, the second end of the first rotating rod is constrained to move about a circumference, the center of which is located on the first end of the first rotating rod, and the subsequent rigid movable surface (i.e., the control surface is a pneumatic structure not formed of a tensile material) describes the desired rotational movement. Due to the triangular shape, the main actuator can utilize a minimum number of rotating rods to ensure the desired deformation of the movable control surface and support the vertical load generated by aerodynamic forces.

[0095] Compared to conventional movable control surfaces such as tail fins or wings, this embodiment offers significant advantages due to the requirement of only one swivel rod, as previously stated, unlike prior art control surfaces that require two swivel rods to create a triangular articulated joint structure. Furthermore, the dedicated retractable actuators of the prior art are eliminated. Additionally, the rotation point of the movable control surface is positioned forward (i.e., relative to the leading edge of the airfoil) compared to conventional systems. Specifically, the rigid structure bridging the torsion box and the first portion (i.e., the expanded portion) of the rigid movable surface of the control surface are positioned further forward than the actuation point of a conventional dedicated retractable linear actuator fixed to the inner surface of the rigid movable part for deflecting the control surface. Advantageously, a larger surface (i.e., wetting area) with improved aerodynamic continuity deforms (i.e., deflects) compared to conventional control surfaces with rigid fairings, thus making the control surface more effective.

[0096] In one embodiment where the airfoil includes a torsion box with a front spar, wherein a first portion extends at most to the front spar, the main actuator includes a first swivel rod that is fixed to the front spar at a first end by means of a swivel joint and fixed at a second end opposite the first end to an inner surface of the control surface adjacent to the surface including the first portion by means of a swivel joint.

[0097] In one embodiment, the first slewing rod is fixed to a slewing joint via a pivot joint positioned near the joint between the front slewing and the surface opposite to the surface including the first portion.

[0098] In one embodiment, the main actuation device may include more than one rotary rod to improve control over the deployment of the surface. In this way, stiffness is enhanced and control over the deployment can be increased.

[0099] In one embodiment, the main actuator includes a second swivel rod that is fixed at a first end to a rear or front spar by means of a swivel joint adjacent to a swivel joint of the first swivel rod, and at a second end opposite to the first end to an inner surface of the control surface adjacent to the surface opposite to the surface including the first portion by means of a swivel joint.

[0100] In one embodiment, the at least one first actuator is embedded within the first portion and arranged substantially along a chordal direction.

[0101] In one embodiment, the at least one first actuator is embedded within the first portion and arranged substantially along the spanwise direction.

[0102] In one embodiment, the main actuator includes at least one second actuator embedded within the second portion and arranged substantially in a chordal direction.

[0103] In one embodiment, the main actuator includes at least one second actuator embedded within the second portion and arranged substantially along the spanwise direction.

[0104] In one embodiment, the at least one embedded first and / or second actuator is one of the following: a piezoelectric actuator, a shape-memory material (such as a metal alloy or polymer) activated by electrical energy, a thermal actuator, or a magnetic actuator.

[0105] Advantageously, the actuators embedded in the lower and / or upper surfaces (i.e., the first and / or second portions) of the control surface cause the extension of one surface and the compression or lesser extension of the opposite surface to occur simultaneously. Furthermore, the embedding of one or more actuators results in a continuous distribution of force and strain along the aerodynamic surface, and thus provides a uniform and precise deformation shape that improves the efficiency of the control surface and the actuation performance.

[0106] In one embodiment, the main actuation device includes an electric actuator that, when a positive or negative voltage is applied through the electric actuator, causes the control surface to extend or contract, which means movement of the control surface.

[0107] Electric actuators can be piezoelectric actuators arranged continuously or in a distributed pitch or shape memory materials (such as metal alloys or polymers) activated by electrical energy.

[0108] In one embodiment, the at least one first actuator is one of the following: a pneumatic, hydraulic, electric, or hybrid telescopic rod fixedly attached at a first end to a rear or front spar and fixedly attached at a second end opposite to the first end to an inner surface of a control surface corresponding to the surface including the first portion.

[0109] In one embodiment, the at least one first actuator is one of the following: a pneumatic, hydraulic, electric, or hybrid telescopic swivel rod, which is fixed at a first end to a rear or front spar by means of a swivel joint, and at an opposite end to an inner surface of a control surface corresponding to the surface including the first portion by means of a swivel joint.

[0110] In one embodiment, any of the above-defined rods is retractable and includes a dedicated actuator configured to control its extension.

[0111] In one embodiment, the main actuation device includes a plate, preferably a rib, arranged in a chordal direction and securely attached to the first and second portions, the plate being adapted to be actuated by a force in the spanwise direction that tends to displace the plate, thereby transferring compressive or traction loads to the first and second portions.

[0112] In one embodiment, the control surface further includes a control adjustment tab and an auxiliary actuator configured to raise or lower the control adjustment tab at its trailing edge.

[0113] In aeronautics, a trim tab is configured to rotate in the opposite direction to the rest of the movable control surface, generating a counter-load. The resulting torque compensates for the torque of the rest of the elevator, thereby reducing the drag of deploying the entire movable part. Consequently, this trim tab also reduces the role of the main actuator in deploying the entire control surface.

[0114] Because the adjusting plate is positioned far from the anti-torsion box, the adjusting plate typically includes a large horizontal arm extending over a high distance, and therefore, even for much lower loads, the magnitude of the torque produced is usually comparable to that of the main actuator.

[0115] In one embodiment, the auxiliary actuation device includes an actuator and a horizontal arm mechanism.

[0116] In an alternative embodiment, the upper or lower surface of the adjustment piece is tensile and provides the same characteristics mentioned above with respect to the first part.

[0117] Advantageously, unlike complex mechanisms that require further space allocation between the rear spar and the movable control surface extending to the trim plate, the upper or lower surface of the trim plate is tensile, allowing for remote actuation or simpler actuators, as explained above, without the need for long arms or additional dedicated actuators.

[0118] Advantageously, having a tensile material on one surface of the control adjustment piece allows for better control of the unfolded profile across the entire control surface, for example, from 50% to 100% of the chord length, while reducing resistance.

[0119] In one embodiment, the stretching surface of the adjustment piece is positioned on the same side (upper or lower surface) as the first portion and arranged as a continuation of the first portion. Furthermore, the adjustment piece is designed to produce additional deformation of the movable control surface in the same direction, thereby increasing the curvature of the entire movable control surface and increasing the aerodynamic forces that the movable control surface can generate.

[0120] In one embodiment, the stretching surface of the adjustment piece is positioned on the side opposite to the surface containing the first portion (upper or lower surface). Furthermore, the adjustment piece is designed to produce additional deformation of the movable control surface in the opposite direction, thereby reducing the curvature of the movable control surface as a whole and providing a load-reducing effect.

[0121] In one particular embodiment, the control surface includes a plurality of honeycomb expandable elements housed between an upper surface and a lower surface, and the main actuator is configured to selectively expand or contract the honeycomb expandable elements such that when the honeycomb expandable elements expand, at least one of the honeycomb expandable elements extends from within the internal volume of the control surface, thereby applying a spanwise force that causes deformation of the first and / or second portions in the chord direction.

[0122] Conversely, when the pressure applied to the expandable cellular element decreases, the expandable cellular element contracts along the span of the airfoil. This contraction triggers a chordal contraction of the first section and causes the control surface to deflect in the opposite direction.

[0123] The expandable cellular element can occupy a portion of the internal volume of the control surface. Preferably, the expandable cellular element is disposed between the lower and upper surfaces. In one particular embodiment, the expandable cellular element is provided over the entire internal volume of the control surface.

[0124] The expandable honeycomb element can be formed from woven or braided high-strength fibers that are covered or impregnated on an elastic material or a resin or similar material such as rubber.

[0125] In one embodiment, the expandable cellular element can be implemented as a cellular skin with a patterned shape that does not tend to become cylindrical under pressure, but rather tends to adopt a desired profile volume upon expansion. In one embodiment, this is achieved by means of so-called open-knit or 3D knitting, in which some of the fibers connect one side of the cellular skin to the other. These fibers are able to withstand loads from pressure along their direction when under tension, thus maintaining maximum distance between the relative skins of the cellular structure and ensuring that the expandable element does not exert pressure on the upper and lower surfaces.

[0126] In this embodiment, the main actuator is preferably a pneumatic actuator having one or more needle-expandable elements.

[0127] In a second aspect of the invention, the present invention also provides an aerodynamic surface comprising at least one airfoil element as described in any one of the embodiments of the first aspect of the invention.

[0128] In one embodiment, the aerodynamic surface includes a plurality of airfoils according to a first aspect of the invention.

[0129] In one embodiment, the pneumatic surface has a control surface comprising an upper or lower surface with a continuous first strip having a negative Poisson's ratio, the continuous first strip extending in the spanning direction, preferably substantially from the root to the tip.

[0130] In other words, the first portion of each airfoil forming the aerodynamic surface is positioned next to the first portion of the adjacent airfoil, such that this group of first portions forms a continuous stretched first strip along the spanwise direction. Preferably, all first portions extend from the same percentage of the chord length.

[0131] Because of the tunable first section, the control surface can be gradually deployed as needed, thus forming waves, steps, etc., across the wingspan.

[0132] Preferably, the surface opposite to the surface comprising the first strip comprises a continuous second strip containing a material with a Poisson's ratio higher than that of the first strip.

[0133] In one embodiment, the pneumatic surface has a control surface comprising an upper or lower surface with a continuous strip comprising alternating portions of material having a negative Poisson's ratio and a higher Poisson's ratio along the spanwise direction.

[0134] The alternation of tensile materials and conventional materials / tensile materials with a higher Poisson's ratio results in multiple strips alternating along the spanwise and tangential directions. Advantageously, this allows for the individual deployment of certain control surfaces to achieve effective flight control.

[0135] For example, as explained in the background, some control surfaces are designed for flight attitude control, while others are intended for lift boost. Therefore, for safety reasons, these control surfaces will be used at different stages of flight, allowing for individual control of them.

[0136] Furthermore, the combination of the elastotropic portion and the conventional portion / elastotropic material with a higher Poisson's ratio helps to compensate for the spanwise deformation caused by the stretching and compression of the skin along the chord direction, and thus reduces the secondary stress at the interface between the elastotropic portion and the conventional portion / elastotropic material with a higher Poisson's ratio.

[0137] In one embodiment, the aerodynamic surface includes an actuating device arranged in the spanwise direction and configured to apply a force in the spanwise direction to at least one strip containing a material having a negative Poisson's ratio, thereby deforming the strip in the chordwise direction.

[0138] Actuators can be distributed across the wingspan and act only locally on a portion of the aerodynamic surface (i.e., a few airfoils), or act globally on the deployment of the entire control surface, or be actuated from the fuselage.

[0139] In other words, the fact that the first part is pulled or pushed along the spanwise direction at one end of the first part (e.g., on the fuselage side) due to the ability of the taut part to deform 'inward' or 'outward' in a plane causes chordal deformation of the first part, which can cause the unfolding of the control surface if the chordal deformation is compensated by another surface made of a conventional material or a taut material with a higher Poisson's ratio.

[0140] Advantageously, this allows a single actuating device configured to apply force in the spanwise direction to at least one strip containing a material with a negative Poisson's ratio throughout the entire control surface of the aerodynamic surface. Furthermore, this particular embodiment, where the control surface can be actuated by means of an actuating device located within the aircraft fuselage and configured to apply force in the spanwise direction to the strip, allows for centralized control of two aerodynamic surfaces (such as two HTP elevators or movable control surfaces of the wing on each side) arranged on opposite sides of the aircraft's vertical plane (i.e., from a single actuating device located within the aircraft fuselage), rather than implementing separate dedicated and distributed actuation systems on each side as in the prior art.

[0141] In one embodiment, the main actuation device of the airfoil includes a plate, preferably a rib, arranged chordally and securely attached to the first and second portions, the plate being adapted to be actuated by a spanwise force that tends to displace the plate, thus transmitting compressive or traction loads to the first and second portions, and the actuation device of the aerodynamic surface includes a rod connected to the plate. The actuation device of the aerodynamic surface further includes at least one of the following: a pneumatic, hydraulic, electric, or hybrid actuator configured to drive the rod in the spanwise direction such that the rod is configured to apply a spanwise force to the plate that tends to displace the plate, thus transmitting compressive or traction loads to the first and second strips.

[0142] In a third aspect of the invention, the present invention provides an aircraft comprising at least one aerodynamic surface as described in any one of the embodiments of the second aspect of the invention.

[0143] In one particular embodiment, the actuator configured to apply force in the spanwise direction is adapted to be operated by a pneumatic, hydraulic, electric, or hybrid actuator located within the aircraft fuselage.

[0144] All features described in this specification (including the claims, description and drawings) can be combined in any combination except for combinations of these mutually exclusive features. Attached Figure Description

[0145] These and other features and advantages of the invention will become clearer from the following detailed description of preferred embodiments provided with reference to the accompanying drawings, which are provided as illustrative rather than limiting examples only.

[0146] Figures 1a to 1c These figures illustrate schematic representations of conventional airfoils according to existing technology.

[0147] Figures 2a to 2b These figures illustrate schematic representations of conventional airfoils according to existing technology.

[0148] Figure 3 This diagram illustrates an ideal airfoil.

[0149] Figures 4a to 4e These figures illustrate schematic representations of airfoil elements according to embodiments of the invention, and representations of deformations occurring at the upper and lower surfaces of the airfoil elements.

[0150] Figures 5a to 5g These figures illustrate schematic representations of tensile and non-tensile materials.

[0151] Figures 6a to 6e These figures illustrate schematic representations of airfoil components according to embodiments of the present invention.

[0152] Figures 7a to 7e These figures illustrate embodiments of the aerodynamic surface according to the present invention.

[0153] Figures 8a to 8e These figures illustrate schematic and partial representations of an airfoil according to an embodiment of the invention, wherein the actuating device is embedded within a control surface.

[0154] Figure 9 This figure illustrates an embodiment of the pneumatic surface according to the invention, wherein the actuating device is implemented in the form of a rod along the spanwise direction.

[0155] Figure 10a , Figure 10b These figures illustrate embodiments of the aerodynamic surface according to the present invention.

[0156] Figure 11 This figure illustrates an embodiment of the pneumatic surface according to the invention, wherein the actuating device is implemented in the spanwise direction in the shape of a double rod.

[0157] Figure 12 This figure illustrates an embodiment of the pneumatic surface according to the invention, wherein the actuating device is implemented in the form of a cable driven by a rotating device along the spanwise direction.

[0158] Figures 13a to 13c These figures illustrate embodiments of the aerodynamic surface according to the invention and partial representations of the airfoil including control adjustment tabs according to the invention. Detailed Implementation

[0159] As those skilled in the art will understand, aspects of the present invention can be implemented as an airfoil (1), an aerodynamic surface (10), or an aircraft.

[0160] Figure 1a Depict an airfoil (20) including a leading edge (21), a torsion box (22) having a front spar (22.1) and a rear spar (22.2), and a control surface (23) adjacent to the trailing edge (23.1) of the airfoil (20).

[0161] Specifically, it can be seen that the leading edge (21) is located at 0% of the chord, the front spar (22.1) is located at approximately 15%, and the torsion box (22) extends to approximately 50% of the chord length, where the rear spar (22.2) is located. Rearward, the control surface (23) extends between approximately 75% and 100% of the chord length, where 100% of the chord length corresponds to the trailing edge (23.1).

[0162] As can be observed, the space between the rear spar (22.2) and the beginning of the control surface (23) (e.g., about 50% to 75% of the chord length) accommodates the actuators (24) configured to raise and lower the control surface (23). Typically, this space is covered by a rigid aerodynamic fairing (24.3), where the free edge (e.g., at about 75% of the chord length) allows the control surface to rotate up and down about the hinge axis (see...). Figure 1b and Figure 1c ).

[0163] The control surface (23) replicates a movable rigid structure. Therefore, there is usually a step between the free edge of the rigid aerodynamic fairing (24.3) that houses the actuator (24) and the movable control surface (23) itself.

[0164] according to Figure 1b and Figure 1c The movable control surface (23) is actuated upward or downward by an actuating device (24) (downward movement is shown only), which includes a rotary rod (24.1) actuated by a hydraulic, electric or hybrid dedicated actuator (24.2).

[0165] like Figure 1b As can be seen, the control surface (23) is attached to the first attachment point (24.4) via a hinge axis, which is fixed to the anti-torsion box by means of two swivel rods (24.1). In some cases, the hinge axis may be fixed to the anti-torsion box by means of a fitting instead of the two swivel rods (24.1).

[0166] More specifically, regarding the operation of the conventional airfoil architecture shown, it can be seen that the movable control surface (23) is also attached to a second attachment point (24.5) by means of an additional slewing rod with an actuator (24.2), the second attachment point (24.5) being separated from the first attachment point (24.4) by a vertical offset. The slewing rod with the actuator (24.2) is also attached to an anti-torsion box. Figure 1c In the diagram, the force applied by the actuator (24.2) is schematically depicted by a solid arrow, which illustrates an operational example where the actuator extends axially to push the second attachment point (24.5) away from the anti-torsion box. The subsequent downward rotation of the movable control surface (23)... Figure 1bThe movable control surface (23) is shown changing from an undeflected position (indicated by a dashed line) to a deflected position (indicated by a solid line). Therefore, the actuator (24.2) can extend and retract in a controlled manner, thereby generating a force in the chordal direction that tends to push the second attachment point (24.5) away from / pull it closer to the anti-torsion box, resulting in rotation of the movable control surface (23) about the hinge axis of the first attachment point (24.4) due to the vertical offset between the two attachment points (24.4, 24.5) of the movable control surface (23). The hinge axis is perpendicular to the cross-sectional plane of the airfoil.

[0167] Figure 1c The booster aerodynamic lift is also depicted by a dashed arrow near the trailing edge. These booster aerodynamic lifts generate combined bending moments and shear loads that are transmitted to those attachment points (24.4, 24.5). In addition, a solid arrow located at the slewing rod (24.1) depicts the reaction force generated on the conventional actuator (24) represented on the control surface (23) to counteract these aerodynamic forces.

[0168] Since the rigid fairing (24.3) is non-deformable, the deflection of the movable control surface (23) is restricted, resulting in abrupt profile transitions (and undesirable parasitic drag even when not deployed).

[0169] Figures 1a to 1c This represents a simple airfoil architecture with a single rotational control surface, which is typically used in conventional tail fins such as horizontal and vertical tail surfaces. In this case, the movement of the control surface (23) involves only rotation and no translation.

[0170] Figure 2a This represents a more complex airfoil (25) for a large passenger aircraft wing. It can be seen that movable control surfaces can be mounted on both the leading edge (referred to as a slat (25.1)) and the trailing edge (referred to as a flap (25.3)). Furthermore, it can be seen that the movable control surfaces (25.1, 25.4) can be composed of several movable surfaces to increase the movable deflection of the airfoil, as shown for the slat in the closed position (25.1) and deployed position (25.2), or as shown for the flap in the closed position (25.3) and deployed position (25.4). In the case of the wing, both the flaps and slats can describe not only rotation about a single axis but also translational movement.

[0171] As schematically shown, in these cases, the rigid fairing (25.5) cannot cover the gaps and steps created by the movement of the control surfaces, thus increasing drag and significantly affecting the efficiency of the aerodynamic surfaces.

[0172] Figure 2bExamples of other movable control surfaces (25.2, 25.4) located on the trailing and leading edges of the airfoil (25) are shown. In all cases, it can be seen that undesirable steps and gaps, as well as abrupt profile transitions, are present due to the non-deformable movable control surfaces and the rigid aerodynamic fairing.

[0173] Figure 3 A schematic representation of an ideal concept for an airfoil, including control surfaces, is depicted, wherein the outer surface of the airfoil (26) can be deformed in a progressively controlled and elastic manner until the optimal shape required for each flight state is achieved. The leading edge (26.1) and trailing edge (26.2) are capable of changing their curvature and camber, as well as their chord length.

[0174] Undeformed shapes are represented by solid lines on the leading edge (26.1) and trailing edge (26.2). Deformed shapes (26.3 and 26.4, respectively) that change only the curvature of the leading edge (26.1) and trailing edge (26.2) are represented by dashed lines. Additional alternative deformed shapes (26.5 and 26.6, respectively) that change both the curvature and chord length of the leading edge (26.1) and trailing edge (26.2) are represented by dashed lines.

[0175] Figure 3 The airfoil (26) shows deformable surfaces, also known as deformable surfaces, which are capable of deforming in a continuous manner without steps and gaps between the fixed part and the movable part and without abrupt contour transitions, thus providing significant aerodynamic performance improvements.

[0176] Figures 4a to 4c An airfoil (1) or a portion thereof is depicted as an aerodynamic surface according to an embodiment of the present invention. The airfoil (1) includes: a control surface (2) including an upper surface (2.2) and a lower surface (2.3); and a main actuator (3) configured to deflect the control surface (2) upward or downward.

[0177] According to the invention, the first portion (4) of one of the upper surface (2.2) and the lower surface (2.3) of the control surface (2) is tensile and has a negative Poisson's ratio, and the second portion (5) of the other of the upper surface (2.2) and the lower surface (2.3) of the control surface (2) has a higher Poisson's ratio.

[0178] exist Figures 4a to 4cIn one embodiment, the airfoil (1) includes a torsion box (6) comprising an upper skin (6.1), a lower skin (6.3), and a rear spar (6.2), with a control surface (2) positioned at the tail of the rear spar (6.2). A first portion (4) extends at most into the rear spar (6.2) such that the first portion (4) bridges the upper skin (6.1) of the torsion box (6) and the upper surface (2.2) of the control surface (2), or the lower skin (6.3) of the torsion box (6) and the lower surface (2.3) of the control surface (2), thereby providing aerodynamic continuity.

[0179] As can be observed, in this embodiment, the first part (4) is positioned at at most a predetermined position (e.g., about 75% of the chord length) at the tail of the rear spar (6.2) (e.g., at about 50% of the chord length of the airfoil (1)), thereby bridging the upper skin (6.1) of the anti-torsion box (6) and the upper surface (2.2) of the control surface (2), so that there is no gap and aerodynamic continuity is provided.

[0180] Therefore, in Figures 4a to 4c In this embodiment, the first portion (4) is part of the upper surface (2.2), and the second portion (5) is part of the lower surface (2.3) of the control surface (2). The first portion (4) provides a higher deflection angle to the entire control surface (2). Furthermore, the first portion (4) of the upper surface (2.2) is continuous with the remaining upper surface of the airfoil (1).

[0181] Figure 4b and Figure 4c Depicting according to Figure 4a Detailed views of the airfoil (1) in the embodiment. These two figures illustrate how the airfoil (1) deflects the control surface (2) (downwards in the specific operational example shown) and provides contact with the control surface. Figure 1b and Figure 1c The existing technology shown demonstrates a greater deflection capability compared to other technologies. For example, by... Figure 4c The dashed arrows in the diagram schematically depict how a larger wetted surface area results in a greater lift boost.

[0182] In this embodiment, the main actuator (3) includes: a first actuator (3.4) configured to apply force to the control surface (2) substantially in a chordal direction; and a first swivel rod (3.1) fixed at a first end to the rear spar (6.2) by means of a swivel joint, and fixed at a second end to the inner surface of the control surface (2) adjacent to the upper surface (2.2) by means of a swivel joint. The main actuator (3) further includes: a second swivel rod (3.2) fixed at a first end to the rear spar (6.2) by means of a swivel joint adjacent to the swivel joint of the first swivel rod (3.1), and fixed at a second end to the inner surface of the control surface (2) adjacent to the lower surface (2.3) by means of a swivel joint. The main actuator (3) also includes an actuator (3.4) in the shape of a telescopic rotary rod (3.4), which is fixed to the rear wing spar (6.2) at a first end by means of a swivel joint and at a second end by means of a swivel joint to the inner surface of the control surface (2) adjacent to the upper surface (2.2).

[0183] In the illustrated embodiment, the first end of the first slewing rod (3.1) and the first end of the second slewing rod (3.2) are fixed to the rear spar (6.2) at the same attachment point. Furthermore, the second end of the first slewing rod (3.1) and the second end of the telescopic slewing rod (3.4) are fixed to the inner surface of the control surface (2) at the same attachment point.

[0184] In particular, the stretch portion (4) of the upper surface (2.2), preferably located between approximately 50% and 75% of the chord length, is stretched by the actuation of the main actuator (3), which applies a series of forces transmitted by a telescopic slewing rod (3.3) and a slewing rod (3.2) that are rotatably fixed at one end to the rear wing beam (6.2) and fixed at the opposite end to the corresponding opposite inner surface of the control surface (2) by means of a corresponding slewing joint.

[0185] The second part (5) can have a positive Poisson's ratio (and thus be a "conventional" material) or a negative Poisson's ratio higher than that of the first part (4) (and thus have tensile properties that result in smaller deformation in the transverse plane relative to the direction of force application compared to the first part). Figures 5a to 5e In one embodiment, the second part (5) is made of conventional materials.

[0186] Upon deployment, the first portion (4) of the upper surface (2.2) is stretched in the chordal direction, while the second portion (5) of the lower surface (2.3) is compressed in the chordal direction. Due to the different behaviors of the first portion (4) and the second portion (5), the deformation of the control surface and thus the entire airfoil is achieved. Furthermore, since the upper and lower surfaces are continuous, the deployed airfoil achieves better aerodynamic behavior without abrupt profile transitions or gaps. Figure 4b and Figure 4c In the middle, a dash indicates the position where there is no deflection.

[0187] Figure 4d and Figure 4e The spanwise deformation of the first part (4) of the upper surface (2.2) and the corresponding deformation of the second part (5) of the lower surface (2.3) are depicted. It can be observed that, due to the difference in Poisson's ratio between the first part (4) and the second part (5), the upper surface (2.2) is under stretching in the chord direction (as shown in the figure). Figure 4d (as shown) and the lower surface (2.3) is under contraction (as shown) Figure 4e As shown (as indicated by the full arrow), both the upper and lower surfaces undergo stretching in the direction indicated by the dashed arrow.

[0188] This similar spanwise deformation on the upper surface (2.2) and lower surface (2.3) provides a reduction in the transverse bending of the control surface in the spanwise direction. Transverse bending deforms the control surface in the spanwise direction and reduces the efficiency and strength of the control surface. This disadvantage is overcome or at least reduced by the present invention.

[0189] Through Figures 5a to 5g It describes the representation of conventional materials with a positive Poisson's ratio and tensile materials to illustrate their properties.

[0190] on the one hand, Figure 5a A 'conventional material' (5) with a positive Poisson's ratio is depicted, such as a hexagonal mesh structure (5.1) forming a honeycomb design. In this case, applying a uniaxial tension (T) in one of the two in-plane directions of the unit geometry results in an increase in the dimension in that direction and a decrease in the dimension in the other perpendicular direction contained in that plane. On the other hand, applying a uniaxial compressive force (not shown in this figure) in one of the directions contained in that plane results in a decrease in the dimension in that direction and an increase in the dimension in the other perpendicular direction contained in that plane. This is also the behavior of conventional materials (5), such as conventional materials used in aircraft structures, such as aluminum, titanium, steel, other metallic materials, and fiber-reinforced polymers with high-strength fibers (such as carbon fiber, glass fiber, etc.).

[0191] There exist material or structural geometries that exhibit the opposite behavior, known as expansibility, and have a negative Poisson's ratio. Figures 5b to 5dA tensile material (4) is described, which is a tensile material formed by a concave hexagonal structure (4.1) that exhibits tensile behavior in two in-plane directions of the unit geometry. In this case, when a uniaxial tension (T) is applied in one of the two in-plane directions of the unit geometry, the result is an increase in size in that direction as well as an increase in size in another perpendicular direction contained in that plane.

[0192] On the other hand, applying a unidirectional compressive force (not shown in the figure) in one of the directions contained in the plane results in a reduction in the dimension in that direction as well as a reduction in the dimension in another vertical direction contained in the plane.

[0193] However, there are other known two-dimensional geometries that exhibit scalar behavior and are formed, for example, by a cell arrangement structure comprising multiple adjacent cells.

[0194] In fact, negative Poisson's ratio regions can be achieved by adding voids or vacancies to conventional materials. These voids or vacancies create a mesh-like structure that deforms with a negative Poisson's ratio.

[0195] Figure 5c A tensile mesh structure (4.1) is presented, which can be covered by a flexible skin (4.2) such as flexible resin or rubber, which can be connected by mechanical links such as adhesives or by binding. The flexible skin (4.2) allows the tensile material (4.1) to deform, cover voids, and ensure air tightness in order to provide a pneumatic skin surface.

[0196] In addition, if the mesh structure (4.1) material is also formed of a polymer material, which can be reinforced with continuous or discontinuous fibers of high-strength materials such as carbon fiber, glass fiber or other fibers, the flexible skin (4.2) material can be directly co-cured with the mesh structure material.

[0197] Figure 5d and Figure 5e A detailed schematic diagram of the mesh structure (4.1) is shown. Figure 5d As can be seen, the mesh structure (4.1) comprises multiple mesh segments (4.1.1) connected together by means of multiple flexible joints or rotary joints (4.1.2) to form hinges. In particular, the mesh structure (4.1) is formed by rotation axes at the ends of the mesh segments (4.1.1), which are perpendicular to the in-plane surface of the unit, thereby allowing the mesh segments (4.1.1) to rotate about the rotation axis but not about the in-plane axis, so that the mesh segments (4.1.1) cannot be excessively deformed by aerodynamic pressure in a direction perpendicular to the in-plane direction of the unit.

[0198] Figure 5f and Figure 5gAn alternative embodiment of the flexible joint (4.1.2) is shown, wherein the hinge axis and the rotation axis are replaced by the reduction of inertia of the rigid segment (4.1.1) at its interface (4.1.3) (i.e. at the point where at least two rigid segments (4.1.1) in the grid structure (4.1) converge). Figure 5g The rigid segment (4.1.1) is shown at the interface ( Figure 5g (b) and at different points that do not correspond to the interface ( Figure 5g (a) is the cross section.

[0199] like Figure 5f and Figure 5g As can be seen above, the cross-section of the rigid segment (4.1.1) tapers longitudinally toward the interface (4.1.3) where the rigid segments (4.1.1) converge. This reduction in structural size results in a significantly reduced moment of inertia at the interface (4.1.3), particularly about the axis (X) perpendicular to the plane of the unit geometry, compared to the other transverse axis of the rigid segment. Thus, the rigid segment (4.1.1) can deform in a very flexible and elastic manner when rotating about this first axis (X) with reduced inertia, allowing the rigid element (4.1.1) to rotate and deform about this first axis (X) rather than about the other direction within the plane of the unit geometry.

[0200] Furthermore, in this case, the inertia of the other axis is higher, and the rigid segment (4.1.1) cannot bend around the axis at its interface, so that the fairing does not cause excessive deformation due to aerodynamic pressure in the plane perpendicular to the unit.

[0201] This embodiment offers the following advantages: the joints of the mesh structure (4.1) are removed, and the mesh structure (4.1) forms a continuous deformable mesh that can be manufactured in one go, without the assembly complexity of all these rotary joints.

[0202] The tectonic mesh structure (4.1) is also suitable for fabrication using metallic or polymeric materials via additive manufacturing, particularly for achieving continuous deformable meshes. If the tectonic mesh structure (4.1) is made of a polymeric material, the added polymer can include continuous or discontinuous embedded fibers of carbon fibers, glass fibers, aramid fibers, or other high-strength materials. These fibers are deposited at the same time as the polymeric material, which increases the strength of the resulting tectonic mesh structure (4.1).

[0203] Flexible skin (4.2) is also suitable for use in additive manufacturing of elastomer materials deposited in the same additive manufacturing process, which has the advantage of reducing manufacturing and assembly time and complexity.

[0204] Advantageously, the grid structure (4.1) formed by periodic concave hexagonal units can be combined with conventional honeycomb hexagonal units (5.1) to present unique materials with higher or lower Poisson's ratios in different parts.

[0205] By modifying the angles of the hexagonal geometry, the Poisson's ratio can be constrained to exhibit different behaviors across the grid as needed, and the size of the Poisson's ratio can also be controlled as needed to obtain optimal behavior.

[0206] exist Figures 4a to 4e In one embodiment, the first part (4) is made of a tensile material having a concave hexagonal structure (4.1), and the second part (5) is made of a conventional material (5) having a hexagonal honeycomb structure (5.1).

[0207] Figure 6a and Figure 6d An airfoil (1) of an aerodynamic surface (10) according to an embodiment of the present invention is depicted. In this embodiment, the first portion is part of the upper surface (2.2) of the control surface (2), and the second portion (5) is made of conventional material and is part of the lower surface (2.3) of the control surface (2). In this embodiment, the first portion (4) includes a flexible mesh structure (4.1) and a flexible skin (4.2), such as Figure 5c The diagram is schematically depicted. In this embodiment, the main actuation device includes a plurality of distributed actuators (3.4) embedded in the upper surface (2.2) of the control surface (2) in the chord direction, and particularly embedded in a flexible skin (4.2) covering the mesh structure (4.1) of the first portion (4) of the control surface (2). The main actuation device further includes a first swivel rod (3.1) and a second swivel rod (3.2), which are fixed at a first end to the rear spar (6.2) by means of a swivel joint and at a second end to the inner surface of the control surface (2) by means of a swivel joint. Figure 6d As can be seen, the first rotating rod (3.1) is fixed to the inner surface of the control surface (2) at an attachment point adjacent to the upper surface (2.2), while the second rotating rod (3.2) is fixed to the inner surface of the control surface (2) at an attachment point adjacent to the lower surface (2.3). The actuator (3.4) is configured to actuate the control surface (2) by applying different forces responsible for stretching or compressing the first portion (4) and, consequently, compressing or stretching the second portion (5) of the conventional material on the opposite lower surface (2.3) of the control surface (2).

[0208] Specifically, the embedded actuator (3.4) may be one of the following: an electric actuator, a piezoelectric actuator, a shape memory material or polymer activated by electrical energy, having a continuous or distributed pitch that allows for improved control of the deflection angle of the control surface (2).

[0209] like Figure 6d The expression indicates that, with Figures 4a to 4e Compared to the embodiments described above, an additional advantage of this embodiment is that the telescopic slewing rod (such as...) Figure 4c The conventional dedicated actuator (3.4) in the form shown is suppressed, so only two rotating rods (3.1, 3.2) are included in the actuator, thus reducing their complexity. In addition, the actuation load is more distributed and uniform, thus reducing the concentration of load and stress and increasing strength.

[0210] In the embodiment of FIG6, the mesh structure (4.1) of the first part (4) is formed by periodic concave hexagonal units and is alternately arranged with parts formed by conventional honeycomb hexagonal units, such that the upper surface (2.2) has a higher or lower Poisson's ratio in different parts. Figure 6b and Figure 6c The diagram schematically illustrates the conventional portion and the first portion, as well as the deformation of the portions under tension, where the full arrow represents tensile tension and the strip arrow represents the obtained deformation.

[0211] Figure 6e Showing something similar to Figure 6d Detailed views of an embodiment of the airfoil (1) depicted. In this embodiment, the second swivel rod (3.2) is removed, resulting in only a first swivel rod (3.1) along a diagonal, further reducing the complexity of the main actuator. According to this embodiment, the first swivel rod (3.1) is fixed to the rear spar (6.2) via a rotational joint positioned near the joint between the rear spar (6.2) and the lower surface. When the first portion deforms, the second end of the first swivel rod (3.1) is constrained to move within a circle of radius R, the center of which is located on the first end of the first swivel rod (3.1), and the rear rigid movable surface (i.e., the aerodynamic structure of the control surface not formed of tensile material) describes the desired rotational movement. Due to the triangular shape defined by the first portion and the first swivel rod (3.1), the main actuator can ensure the desired deformation of the movable control surface and support the vertical load generated by aerodynamic forces using a minimum number of swivel rods. Figure 6d and Figure 6e In the middle, a dash indicates the position where there is no deflection.

[0212] Figure 7a A description of an embodiment of the present invention includes... Figure 7b A top view of the aerodynamic surfaces (10) of the multiple airfoil elements (1) presented above.

[0213] The aerodynamic surface (10) includes a control surface (8), which comprises an upper surface and a lower surface. The upper surface of the control surface (8) comprises a continuous first strip (7) made of a tensile material, located between approximately 50% and 75% of the chord length. The aerodynamic surface (10) includes an actuator (not shown) configured to apply force to the continuous strip (7) in the spanwise direction. The lower surface of the control surface (8) comprises a second strip containing a material with a Poisson's ratio higher than that of the first strip (7).

[0214] In this embodiment, the first portion (4) of each airfoil (1) forming the aerodynamic surface (10) is arranged next to the first portion of the adjacent airfoil, such that the set of first portions (4) forms a continuous stretched first strip (7) in the spanwise direction. Similarly, the second portion (5) of each airfoil (1) is arranged next to the second portion of the adjacent airfoil, such that the set of second portions (5) forms a continuous second strip in the spanwise direction.

[0215] The main actuator (3) of the airfoil (1) is driven by a force applied in the spanwise direction by an actuator of the aerodynamic surface (10), such that both the first portion (4) on the upper surface (2.2) and the second portion (5) of conventional material on the opposite lower surface (2.3) are configured to deform in the chordwise direction. Solid arrows indicate the force applied in the spanwise direction, and dashed arrows indicate the deflection of the first portion (4) in the chordwise direction.

[0216] Figure 7e Depicting according to Figure 7a and Figure 7b A detailed view of the airfoil (1) of the embodiment presented above. It can be seen that... Figure 7c and Figure 7d The opposite deformation of the upper surface (2.2) and lower surface (2.3) in the chord direction, schematically shown above, produces the desired deflection of the movable control surface (2) of the airfoil (1). Figure 7e In the middle, the undeflected position of the control surface (2) is indicated by a dash.

[0217] Figures 8a to 8e Depicting Figures 7a to 7e An embodiment of an aerodynamic surface (10) and an airfoil (1) wherein the actuating device of the aerodynamic surface (10) comprises a plurality of actuators (9.1) arranged in the spanwise direction and configured to apply force in the spanwise direction to a continuous first strip (7) made of a tensile material, such that the first strip (7) deforms substantially in the chordwise direction. In particular, these actuators (9.1) are embedded in the strip (7) provided on the upper surface and also embedded in a second strip made of a conventional material on the opposite lower surface, distributed in the spanwise direction.

[0218] Specifically, the embedded distributed actuator (9.1) simultaneously generates traction or compressive forces in the spanwise direction on both the upper surface (2.2) and the lower surface (2.3) of the control surface (2) of the airfoil (1), resulting in subsequent opposite chordal deformation due to the tensile properties of the material of the first portion (4) of the upper surface (2.2). In the case of compression, the forces applied to both the upper surface (2.2) and the lower surface (2.3) in the spanwise direction are indicated by solid arrows, and the resulting differential lateral deformation is indicated by dashed arrows. Figure 8e In the middle, the undeflected position of the control surface (2) is indicated by a dash.

[0219] Specifically, the embedded actuator (9.1) is a piezoelectric actuator that generates extension or contraction on both surfaces by increasing or decreasing the voltage on the upper surface (2.2) and lower surface (2.3) of the control surface (2).

[0220] Figure 9 An embodiment of an aerodynamic surface (10) according to the invention is depicted. The aerodynamic surface (10) includes a control surface (8) comprising an upper surface and a lower surface. The upper surface of the control surface (8) comprises a continuous first strip (7) made of a tensile material. The lower surface of the control surface (8) comprises a second strip comprising a conventional material. The first strip (7) and the second strip are respectively formed by a first portion (4) and a second portion (5) of an airfoil (1) arranged adjacent to each other in the spanwise direction within the aerodynamic surface (10).

[0221] The aerodynamic surface (10) includes an actuating device arranged along the spanwise direction and configured to apply force in the spanwise direction to a continuous first strip (7) made of tensile material. In this embodiment, the actuating device includes a rod (9.3) for transmitting traction or compression to both the upper surface (2.2) and the opposite lower surface (2.3) in the spanwise direction.

[0222] Specifically, the rod (9.3) arranged along the spanwise direction is adapted to be operated by actuators such as pneumatic, hydraulic, electric, or hybrid actuators located in the fuselage (12) of the aircraft. The rod (9.3) is positioned along the wingspan from root to tip at the tail of the anti-torsion box (6) to apply a force in the spanwise direction to a continuous first strip (7), which causes the first strip (7) to deform substantially in the chordwise direction and thus activate (i.e., deflect) the control surface (8).

[0223] For the transmission of the axial load applied by the rod (9.3) to the remaining elements of the aerodynamic surface, primarily to the first strip (7) of the tensile material, the rod (9.3) is connected to the outer rib (9.5) or fitting (i.e., the structural element of the aerodynamic surface (10) located near the tip, connecting to the upper and lower surfaces). The inner rib or fitting (not shown) of the aerodynamic surface (10) located near the fuselage (12) is attached to the upper and lower surfaces and fixedly secured to a fixed structure such as the fuselage (12) or anti-torsion box (6) to react against the traction or compressive load transmitted by the outer rib or fitting (9.5). The inner rib or fitting may be attached to the fixed structure by means of a rod or other attachment device. Therefore, when the actuator (not shown) applies a spanwise load to the rod (9.3) in the outer direction (i.e., from root to tip) of the pneumatic surface (10), the rod (9.3) pushes the outer rib (9.5) or fitting in the outer direction, thus causing traction on the upper and lower surfaces. The traction transmitted to the first strip (7) in the spanwise direction by the outer rib (9.5) pushed by the rod (9.3) produces the subsequent stretching of the first strip (7) in the tangential direction and the contraction of the second strip. This different deformation on the upper and lower surfaces produces the desired downward deflection of the movable control surface (8).

[0224] Conversely, when the actuator (not shown) applies a spanwise load to the rod (9.3) in the inward direction (not shown), the reaction load transmitted to the outer rib (9.5) and fixed to the upper and lower surfaces of the inner rib causes the first strip (7) made of tensile material to experience compressive stress in the spanwise direction, which in turn leads to compression of the first strip (7) in the tangential direction and subsequent extension of the second strip made of conventional material. This different deformation on the upper and lower surfaces in this case produces the desired upward deflection of the movable control surface.

[0225] Figure 10a and Figure 10b Two embodiments of an aerodynamic surface (10) according to a second aspect of the invention are shown, each embodiment comprising a plurality of airfoils (1) according to a first aspect of the invention.

[0226] Figure 10a A continuous first strip (7) of tensile material is depicted on the upper surface of the control surface of the aerodynamic surface (10), extending from the root to the tip of the aerodynamic surface. The aerodynamic surface (10) has conventional non-tensile material on its remaining portion.

[0227] In one embodiment, the lower surface opposite to the control surface of the pneumatic surface (10) (not shown in this figure) contains a non-expanding material or an expandable material with a higher Poisson's ratio.

[0228] Figure 10a The illustrated embodiment offers the advantage of manufacturing a single skin spanning the entire wingspan in a single step without having to connect and assemble the taut and non-taut sections along the spanwise direction. This can be achieved, for example, by using known automated manufacturing techniques on composite materials such as prepreg fibers, by automated tape-laying processes, or by additive manufacturing techniques.

[0229] Figure 10b Another embodiment of a continuous strip is shown, comprising alternating material portions (4) with negative Poisson's ratios and material portions (5) with higher Poisson's ratios along the spanwise direction. Specifically, the alternation occurs along the entire span from the root to the tip of the aerodynamic surface (10). The remaining upper and lower surfaces of the control surface of the aerodynamic surface (10), as well as the remaining aerodynamic surface (10), comprise conventional non-tensile material.

[0230] Figure 11 The aerodynamic surface (10) comprises a continuous first strip (7) having alternating portions of a material (4) with a negative Poisson's ratio and a material (5) with a higher Poisson's ratio along the spanwise direction on the upper surface of the control surface (8). The lower surface (not shown) of the control surface (8) of the aerodynamic surface (10) also includes a second strip having alternating portions of a material with a negative Poisson's ratio and a material with a higher Poisson's ratio. However, the positions of the different portions alternate relative to the position of the first strip (7) on the upper surface, such that in the spanwise direction, there is an extension of the portion with a higher Poisson's ratio and a contraction of the portion with a lower Poisson's ratio, and thus all portions of the lower surface experience contraction in the chordwise direction.

[0231] Figure 11 An embodiment of an integrated actuator arranged along the spanwise direction on an aerodynamic surface (10) is shown, the actuator being configured to apply force to a continuous strip in the spanwise direction.

[0232] Figure 11 A double rod (9.3, 9.3') is depicted, arranged along the spanwise direction and adapted to be operated by aerodynamic, hydraulic, electric, or hybrid actuators located within the aircraft fuselage (12). Advantageously, the continuous structure, actuated from the fuselage (12) and without movable joints or axes, facilitates maintenance and assembly. This embodiment, for example, has particular applications in multi-spar aerodynamic surfaces.

[0233] It was observed that the actuating device includes multiple ribs (9.6, 9.6') distributed along the chord direction and rods (9.3, 9.3') distributed along the spanwise direction.

[0234] Specifically, the ribs (9.6, 9.6') are correspondingly positioned between the stretched portions (4) and the conventional non-stretched portions (5) of the upper and lower surfaces and are capable of transmitting the movement of the rods (9.3, 9.3') to the ribs (9.6, 9.6'). The rods (9.3, 9.3') are in mechanical contact with the ribs (9.6, 9.6'). When the first rod (9.3) is configured to extend the first set of ribs (9.6), the second rod (9.3') is configured to contract the second set of ribs (9.6'), or vice versa.

[0235] The two rods (9.3, 9.3') apply opposing forces to each set of ribs (3.6, 3.6'), causing the upper surface (2.2) to exhibit longitudinal extension of the taut portion (4) and longitudinal contraction of the non-taut portion (5). Therefore, due to the different Poisson's ratios, all parts of the upper surface undergo extension in the chord direction.

[0236] The stretching of a portion of the first strip (7) on the upper surface and the contraction of a portion of the second strip on the lower surface in the chord direction produce the desired downward deflection of the movable control surface (8). Therefore, when the first bar (9.3) pulls a set of ribs (9.6) inward and the second bar (9.3') pushes another set of ribs (9.6') outward, the movable control surface (8) produces the opposite upward deflection.

[0237] This allows for compensating forces, and therefore does not produce overall deformation along the wingspan.

[0238] Figure 12 An embodiment is depicted in which the double rods (9.3, 9.3') have been replaced by a cable or chain. Advantageously, the cable is in a closed loop configuration, wherein the two segments (9.3, 9.3') of the cable can be actuated by an actuator (9.4) in the form of a rotating device and pulley, located at the tip of the cable near the pneumatic surface (10).

[0239] Figure 13a Furthermore, it indicates that according to Figure 10b The aerodynamic surface (10) includes a rod (9.3) positioned near the trailing edge of the movable control surface (8) (that is, close to 100% of the chord length of the airfoil (1)). The rod (9.3) is configured to actuate the trim tabs (100) of the control surface (2) from the fuselage (12) by means of a plurality of distributed auxiliary actuators (9.7).

[0240] like Figure 13b and Figure 13cIt can be observed that the adjusting piece (100) can be rigid or may include a stretched portion on one of its surfaces (100.2, 100.3). Therefore, the combined actuation of the adjusting piece and the entire control surface (8) can be achieved by rotating the auxiliary actuating device (9.7). Figure 13c (See in) the fixed connection with the rod, or benefit from the reverse deformation of the first part (4) containing the tensile material relative to the conventional part / part (5) with a higher Poisson's ratio, and properly unfolded by the load transmitted from the first part (4) of the control surface (2).

[0241] The actuation of the adjustment piece (100) provides the ability to more pronounced deflection of the control surface (2). The deflection angle of the adjustment piece (100) may be in the same direction or in the opposite direction to the deflection angle of the first portion (4) of the control surface (2).

[0242] In embodiments where the adjustment piece (100) includes a stretching portion at one of its surfaces (100.2, 100.3), actuation of the control surface (2) causes the adjustment piece (100) to unfold.

[0243] Figure 13b A cross-sectional view of the airfoil (1) with two superimposed states is shown: when neither the control surface (2) nor the adjustment piece (100) is deployed (the control surface (2) is shown as a discontinuous line), and when both are deployed (the control surface (2) is shown as a solid line). The adjustment piece (100) is shown as a thick line in both states.

[0244] Throughout this description, the first part (4) has been described as being contained in the upper surface (2.2), while the second part (5), with a Poisson's ratio higher than that of the first part (4), has been described as being contained in the lower surface (2.3) and as being embodied in a conventional material, i.e., a material with a positive Poisson's ratio. Alternatively, the upper surface (2.2) may be a surface containing an elastomeric material with a higher negative Poisson's ratio (i.e., the second part (5)), and the lower surface (2.3) may be a surface containing an elastomeric material with a lower negative Poisson's ratio (i.e., the first part (4)). In this particular case, the spanwise extension in both surfaces (2.2, 2.3) will produce the chordal extension in both surfaces (2.2, 2.3), but the upper surface (2.2) will have a higher chordal extension compared to the lower surface (2.3). Thus, the movable control surface (2) will undergo downward bending and rearward extension, which will simultaneously increase the chord of the aerodynamic surface (10) and its curvature. This results in the aerodynamic efficiency of the airfoil (1), which will provide the additional benefit of more lift.

[0245] Therefore, the higher the difference in Poisson's ratio between the upper surface (2.2) and the lower surface (2.3) (i.e., between the first part (4) and the second part (5)), the greater the curvature produced. Conversely, the lower the difference in Poisson's ratio between the upper surface (2.2) and the lower surface (2.3), the greater the chord extension produced.

[0246] The invention has been described with respect to the airfoil (1) from the rear spars (6.2) to the rear edge, and provides alternatives to conventional trailing edge control surfaces (8) such as elevators, rudders, or flaps. However, the invention is also applicable to the airfoil (1) from the front spars (6.4) to the front edge, and provides alternatives to conventional leading edge movable control surfaces such as slats.

Claims

1. An airfoil (1) of an aerodynamic surface (10), said airfoil (1) comprising: Control surface (2), the control surface includes an upper surface (2.2) and a lower surface (2.3); as well as A main actuator (3) is configured to raise or lower the control surface (2); The control surface (2) is characterized in that at least a first portion (4) of one of the upper surface (2.2) and the lower surface (2.3) is tensile and has a negative Poisson's ratio, and at least a second portion (5) of the other of the upper surface (2.2) and the lower surface (2.3) comprises a material with a Poisson's ratio higher than that of the first portion (4).

2. The airfoil (1) according to claim 1, wherein, The airfoil (1) further includes a torsion box (6) comprising an upper skin (6.1), a lower skin (6.3), a rear spar (6.2), and a front spar (6.4), wherein the control surface (2) is positioned at the tail of the rear spar (6.2), wherein the first portion (4) extends at most to the rear spar (6.2), such that the first portion (4) bridges: - The upper skin (6.1) of the anti-torsion box (6) and the upper surface (2.2) of the control surface (2); or - The lower skin (6.3) of the anti-torsion box (6) and the lower surface (2.3) of the control surface (2). This provides aerodynamic continuity.

3. The airfoil (1) according to claim 1, wherein, The airfoil (1) further includes a torsion box (6) comprising an upper skin (6.1), a lower skin (6.3), a rear spar (6.2), and a front spar (6.4), wherein the control surface (2) is positioned at the front of the front spar (6.4), wherein the first portion (4) extends at most to the front spar (6.4) such that the first portion (4) bridges: - The upper skin (6.1) of the anti-torsion box (6) and the upper surface (2.2) of the control surface (2); or - The lower skin (6.3) of the anti-torsion box (6) and the lower surface (2.3) of the control surface (2). This provides aerodynamic continuity.

4. The airfoil (1) according to any one of claims 1 to 3, wherein, The first part (4) includes a flexible mesh structure (4.1) covered by a flexible skin (4.2).

5. The airfoil (1) according to claim 4, wherein, The flexible mesh structure (4.1) includes a plurality of rigid segments (4.1.1), the plurality of rigid segments being located by means of a plurality of rigid segments (4.1.1). Multiple flexible joints or rotatable joints (4.1.2) at the intersection of 4.1.1) are connected together.

6. The airfoil (1) according to any one of claims 1 to 3, wherein, The main actuation device (3) includes at least one first actuator (3.4) configured to apply force to the control surface (2) along the spanwise direction.

7. The airfoil (1) according to claim 2 or 3, wherein, The main actuator (3) includes a first slewing rod (3.1), which is fixed at a first end to the rear spar (6.2) or the front spar (6.4) by means of a slewing joint, and at a second end to the inner surface of the control surface (2) adjacent to the surface including the first portion (4) by means of a slewing joint.

8. The airfoil (1) according to claim 7, wherein, The main actuator (3) includes a second slewing rod (3.2), which is fixed at a first end to the rear spar (6.2) or the front spar (6.4) by means of a slewing joint adjacent to the slewing joint of the first slewing rod (3.1), and at a second end to the inner surface of the control surface (2) adjacent to the surface opposite to the surface including the first portion (4) by means of a slewing joint.

9. The airfoil (1) according to claim 6, wherein, The at least one first actuator (3.4) is embedded within the first part (4) and arranged in a chordal direction.

10. The airfoil (1) according to claim 9, wherein, The main actuator (3) includes at least one second actuator embedded within the second part (5) and arranged along the chord direction.

11. The airfoil (1) according to any one of claims 1 to 3, wherein, The main actuating device (3) includes a plate (9.5) arranged in the chord direction and firmly attached to the first part (4) and the second part (5), the plate (9.5) being adapted to be actuated by a force in the spanwise direction that tends to displace the plate (9.5), the plate (9.5) thus transmitting compressive or traction loads to the first part (4) and the second part (5).

12. The airfoil (1) according to any one of claims 1 to 3, wherein, The airfoil has a trailing edge, and the control surface (2) further includes a control adjustment piece (100) and an auxiliary actuator (9.7) configured to raise or lower the control adjustment piece (100) at the trailing edge.

13. The airfoil (1) according to any one of claims 1 to 3, wherein, The control surface (2) includes a plurality of honeycomb expandable elements housed between the upper surface (2.2) and the lower surface (2.3), wherein the main actuator (3) is configured to expand or contract the honeycomb expandable elements such that when the honeycomb expandable elements expand, at least one of the honeycomb expandable elements applies a spanwise force, thereby causing deformation of the first portion (4) and / or the second portion in the chord direction.

14. The airfoil (1) according to claim 5, wherein, The flexible mesh structure (4.1) forms a concave hexagonal structure.

15. The airfoil (1) according to claim 11, wherein, The plate is ribbed.

16. An aerodynamic surface (10) comprising at least one airfoil (1) according to any one of claims 1 to 15.

17. The pneumatic surface (10) according to claim 16, wherein the pneumatic surface (10) has a control surface, the control surface comprising: - An upper or lower surface of a continuous first strip (7) extending in the spanning direction and having a negative Poisson's ratio, wherein the surface opposite to the upper or lower surface includes a continuous second strip containing a material with a Poisson's ratio higher than that of the first strip (7); or - An upper or lower surface with a continuous strip comprising alternating portions of material having a negative Poisson's ratio and a higher Poisson's ratio along the spanning direction.

18. The pneumatic surface (10) according to claim 17, the pneumatic surface comprising an actuator arranged in the spanwise direction and configured to apply a force in the spanwise direction to at least one strip comprising a material having a negative Poisson's ratio, such that the strip thereby deforms in the chordwise direction.

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