Patent Description:
The present invention falls within the scope of technical fields that exploit fluids to generate fluid-dynamic forces suitable for different purposes, such as in the aeronautical field (fixed-wing or rotary-wing aircraft), in the automotive field (e.g. wings, ailerons, aerodynamic appendages of vehicles), in power generation plants (e.g. wind power plants but also turbines of power plants).

In this field, the possibility of modifying the twist law of the wing is of considerable interest because of the resulting advantages in terms of efficiency and forces generated. For example, with reference to rotary wings or blades, the possibility of modifying the twist law of the blade of a helicopter is of considerable interest for flight regimes (hover and vertical climb) normally penalized in the design phase, as characterized by conflicting requirements with respect to other phases (cruise) more extended in the helicopter envelope. In addition to the aforementioned hover and vertical climb regimes, blade twist can also play an important role during slow cruise. The alteration of the twist angle of the wing or blade along its span represents a very effective type of "morphing" as it is extremely distributed but, at the same time, difficult to implement due to the small space available, the magnitude of centrifugal forces and the high flexibility of the blade structure. Conventional implementation solutions, not compact and characterized by several components whose relative movement could be altered if not completely inhibited by centrifugal actions, are difficult to implement and pose significant maintenance problems.

Known type solutions adopt shape memory rotary actuators to cause the wing or blade to twist.

For instance, document <CIT> discloses a rotary actuator employed in a helicopter blade. The rotary actuator comprises a torsion tube formed from a shape memory alloy (SMA), a super elastic NiTinol return spring associated with the torsion tube and configured to return the torsion tube to an initial position, and an element for heating the torsion tube and activating it to cause a rotation of an object connected to the torsion tube or to generate a torque on such an object. The torsion tube and spring are connected at their ends and the torsion tube is pre-twisted relative to the spring to ensure its martensitic state. Activation of the heating element causes transition of the torsion tube to an austenitic state in which it is brought into the previous non-twisted configuration. Removal of the heat allows the torsion tube to return to the martensitic state when the return spring twists the torsion tube again. Document <CIT> discloses a rotary actuator similar to that illustrated in document <CIT>.

Document <CIT> discloses propeller blades actuated via a shape memory alloy. The propeller blade includes a blade body, a plate coupled to the blade body, a torque transfer element, and a shape memory alloy (SMA) actuator. The torque transfer element has a distal end attached to the plate, such that the torque transfer element applies to the plate at least a portion of the torque applied to a proximal end of said torque transfer element. A distal end of the shape memory alloy (SMA) actuator is attached to the torque transfer element while a proximal end of the SMA actuator is attached to the blade body. The SMA actuator is configured to apply torque to the proximal end of the torque transfer element in response to the application of heat to the SMA actuator. Since the portion of the blade body adjacent to the plate rotates but the blade root does not, the rotation causes a twist deformation of the blade body.

Document <CIT> discloses a wing-twist aircraft having a wing, an actuation system, a sensor and a controller. The wing has a wingspan that extends to a wing tip. The wing includes a spar aligned in a spanwise direction, wherein ribs are operatively coupled to the spar. The actuation system is configured to rotate the spar, which, in turn, torsionally rotates the ribs coupled to the spar, thereby twisting the wing. The sensor is configured to measure a characteristic of the wing, while the controller is configured to command the actuation system to rotate the spar based on input from the sensor.

Document <CIT> discloses a rotational actuator assembly which employs a first torsion actuator having a shape memory alloy tube with a first trained twist direction and a second torsion actuator having a shape memory alloy tube with an opposite trained twist direction collinear with the first torsion actuator with abutting proximal ends. A central fitting joins the proximal ends. A control system for temperature control of the first torsion actuator and second torsion actuator about an average temperature provides combined antagonistic rotation of the central fitting.

The Applicant has observed that the known solutions described above are definitely invasive because they imply the design of structures clearly different from the classical wings/blades structures (i.e. those that do not provide for the possibility to actively vary the twist along the span) in order to achieve the desired effect (i.e. the active variation of the twist along the span). This implies the need to redesign the entire structure in order to integrate the devices that enable the desired effect, such as the torsional actuators shown above.

The Applicant also noted that the known solutions described above are bulky and difficult to integrate into pre-existing structures and are not usually able to cooperate with such pre-existing structures in absorbing external loads.

The Applicant therefore set itself the objective of proposing a non-invasive solution, in the sense of not requiring for its integration a distortion of the classic construction of the blade/wing.

The Applicant also set itself the objective of proposing a compact and preferably monolithic solution.

The Applicant also set itself the objective of proposing a solution that can be integrated into pre-existing structures.

The Applicant also set itself the objective of proposing a solution capable of collaborating with said pre-existing structures in taking the external loads (aerodynamic, centrifugal, inertial forces).

The Applicant also set itself the objective of proposing a solution allowing accurate adjustment of the wing/blade geometry.

In particular, the Applicant set itself the objective to propose a solution that would allow the wing/blade geometry to be reconstructed from strain measurements and to use that geometry to increase the adjustment accuracy.

The invention consists of an integrated system, capable of altering the twist angle of a wing element and reconstructing the deformed configuration produced by the combined action of the torsion system and external actions (aerodynamic, centrifugal, inertial), distinguishing the various components (torsion, bending).

The invention relates to a structural module for fixed or rotary wing according to claims <NUM> to <NUM>.

The invention also relates to a fixed or rotary wing according to claims <NUM> and <NUM> The leading edge structure or front structural element is capable of taking both loads arising from the actuation system incorporated within (torsion bar and actuation devices) and external loads (aerodynamic, inertial, centrifugal).

The Applicant has verified that, due to the torsional preload with which the torsion bar is mounted on the leading edge structure and due to the elastic deformability of the leading edge structure, the structural module arranges itself in a configuration/point of elastic equilibrium (corresponding to the predefined twist of the leading edge structure), in which the torsional force exerted by the torsion bar and the elastic torsional force of the leading edge structure balance each other. When the actuating devices change the torsional stiffness and/or angular geometry of the torsion bar, the structural module arranges in a different configuration/point of elastic balance corresponding to a different twist of the leading edge structure. The Applicant has also verified that the torsional preload and elasticity of the leading edge structure ensures that it will return to its initial configuration.

The plurality of preload positions allow the level of preload and pre-twist to be modulated, depending on the application.

The Applicant has first verified that the invention allows the geometry and in particular the twist of a wing along its span to be verified and controlled/set with accuracy and speed.

In particular, the Applicant has verified that the invention is capable of altering the twist angle of a blade element and reconstructing the deformed configuration produced by the combined action of the torsion system and external actions (aerodynamic, centrifugal, inertial), distinguishing the various components (torsion, bending).

The Applicant has verified that the structure of the module(s) according to the invention is simple, compact, durable and reliable.

The Applicant has also verified that the structure of the module(s) according to the invention is unobtrusive, compact, monolithic, can be integrated into the pre-existing structure and is capable of cooperating with it in absorbing external loads.

In particular, the Applicant has verified that the integration of the structural modules according to the invention for about <NUM>% of the span of a blade of a reference helicopter, produces a benefit in terms of power saving in hover condition, quantifiable in <NUM>%, net of the power required by the activation of the device. A further power saving is also expected in the slow cruise regime, up to practically <NUM>/<NUM> of the maximum flight speed. This second benefit is quantifiable in an average power reduction over the entire slow cruise range of more than <NUM>%.

Further features and advantages will become clear from the detailed description of a preferred, but not exclusive, embodiment of a structural module for a fixed or rotary wing in accordance with the present invention.

Such description will be set forth below by reference to the set of drawings, provided simply as a non-limiting example, in which:.

Referring to the attached <FIG>, a structural module for a fixed or rotary wing in accordance with the present invention is identified by reference numeral <NUM>.

The wing, not illustrated as a whole, may comprise a single structural module <NUM> or a plurality of structural modules <NUM> arranged sequentially along a wingspan and mutually connected, as will be described below. The wing further comprises a covering arranged around and connected to the structural module(s) to define a surface of the wing.

The structural module <NUM> consists of an integrated system, able to alter the twist angle of a wing element and to reconstruct the deformed configuration produced by the combined action of the torsion system and external actions (aerodynamic, centrifugal, inertial), distinguishing the various components (torsion, bending). The structural module <NUM> comprises a leading edge structure <NUM> (<FIG>) meaning a structure located toward the leading edge of the wing to which it belongs.

The leading edge structure <NUM> comprises a first connecting member <NUM>, a second connecting member <NUM>, a first spar section <NUM> (forwardly positioned towards the leading edge) and a second spar section <NUM> (rearwardly positioned with respect to the leading edge). Each of said first spar section <NUM> and said second spar section <NUM> has the outline of a flat bar. Each of said first spar section <NUM> and second spar section <NUM> is interposed between said first connecting member <NUM> and said second connecting member <NUM> and is integral with said first connecting member <NUM> and said second connecting member <NUM> to form a monolithic structure made of metallic material, for example made from solid or by casting.

As best seen in <FIG> and <FIG>, the first connecting member <NUM> has a front part with a shape corresponding to a portion of the airfoil located at the leading edge of the wing, a rear part provided with rear attachments <NUM>, an inner side and an outer side. The attachments <NUM> are defined, for example, by perforated plates.

From the inner side, the first spar section <NUM> and the second spar section <NUM> are developed. The inner side also has a first seat <NUM> which is located between the first spar section <NUM> and the second spar section <NUM>. The first seat <NUM> has a substantially square outline.

On the outer side, a first recess <NUM> located near the front part, a second recess <NUM> further back and a second seat <NUM> located between the first recess <NUM> and the second recess <NUM> are made. The first recess <NUM> has a substantially triangular section, similar to the outline of the front part. The second recess <NUM> has a substantially rectangular outline section. The second seat <NUM> and the first seat <NUM> define a through hole.

At a corner bounded by the inner side of the first connecting member <NUM> and a front surface of the first spar section <NUM> a front attachment <NUM> is positioned for anchoring a possible balancing mass <NUM>, visible in <FIG>.

Holes <NUM> opening in the first recess <NUM> and the second recess <NUM> are made in the first connecting member <NUM>. An additional hole <NUM> is made in the first connecting member <NUM> for anchoring any external balancing mass, not shown.

The balancing masses are intended to maintain the position of the center of gravity in the first quarter of the airfoil chord.

The second connecting member <NUM> also has a front part with a shape corresponding to a portion of the airfoil located at the leading edge of the wing, a rear part provided with rear attachments <NUM>, an inner side and an outer side (<FIG>). The attachments <NUM> are defined, for example, by perforated plates.

From the inner side, the first spar section <NUM> and the second spar section <NUM> are developed.

From the external side, a first projection <NUM> and a second projection <NUM> are developed, counter-shaped respectively to the first recess <NUM> and to the second recess <NUM>, that is to say, the first recess <NUM> presents an outline that reproduces in negative the outline of the first projection <NUM> and the second recess <NUM> presents an outline that reproduces in negative the outline of the second projection <NUM>.

The first recess <NUM> and the second recess <NUM> on one side and the first projection <NUM> and the second projection <NUM> on the other side allow connection of the structural module <NUM> with adjacent structures. For example, if the wing comprises multiple structural modules <NUM>, the first recess <NUM> and the second recess <NUM> house the first projection <NUM> and the second projection <NUM> of a structural module <NUM> adjacent to the first connecting member <NUM> while the first projection <NUM> and the second projection <NUM> are housed in the first recess <NUM> and the second recess <NUM>, respectively, of a different structural module <NUM> adjacent to the second connecting member <NUM>.

The first projection <NUM> and the second projection <NUM> are provided with holes <NUM> (<FIG> and <FIG>) configured to receive locking pins or screws, not shown, inserted into holes <NUM> of the first connecting member <NUM>, to lock the first projection <NUM> and the second projection <NUM> into the respective first recess <NUM> and second recess <NUM> of the adjacent structural module <NUM>.

The second connecting member <NUM> has a circular through-seat <NUM> (<FIG>) that opens on both the inner and outer sides and is positioned between the first projection <NUM> and the second projection <NUM> and between the first spar section <NUM> and the second spar section <NUM>. Radial through holes <NUM> are drilled in the second connecting member <NUM> and open into the circular through-seat <NUM>.

A front attachment <NUM> (<FIG> and <FIG>) for anchoring any additional balancing mass <NUM>, visible in <FIG>, is positioned at a corner bounded by the inner side of the second connecting member <NUM> and the front surface of the first spar section <NUM>.

The second spar section <NUM> has first passages <NUM> for wiring, such as for power cables and/or sensors, and second passages <NUM> for engaging compressed air from a compressed air source, the function of which will be explained later.

The structural module <NUM> comprises a torsional actuator <NUM> which is mounted on the leading edge structure <NUM> and comprises a torsion bar <NUM>, actuating devices <NUM> operatively coupled to the torsion bar <NUM>, and a preload crown <NUM> coupled to the torsion bar <NUM>. The torsion bar <NUM> may be solid or tubular.

The torsion bar <NUM> of the illustrated embodiment example comprises a central portion <NUM> located between a first end <NUM> (or first interface zone) and a second end <NUM> (or second interface zone).

The central portion <NUM> is made of a Shape Memory Alloy (SMA) such as NiTinol (Nickel Titanium Naval Ordinance Laboratory). The central portion <NUM> has, for example, a circular cross-section.

Each of the first end <NUM> and second end <NUM>, on the other hand, has a non-circular cross-section, for example substantially square. The first end <NUM> is counter-shaped to the first seat <NUM> so as to fit axially into said first seat <NUM> formed in the first connecting member <NUM> and, once inserted, not to be able to rotate with respect to said first connecting member <NUM>.

The preload crown <NUM> (<FIG>) has a cylindrical outer surface and an axial bore <NUM> having a non-circular cross-section and configured to accommodate the second end <NUM> of the torsion bar <NUM>. The axial bore <NUM> is counter-shaped to the second end <NUM> of the torsion bar <NUM> and accommodates said second end <NUM> so that the preload crown <NUM> cannot rotate relative to the torsion bar <NUM>. The second end <NUM> of the torsion bar <NUM> and the axial bore <NUM> are, in particular, shaped to be able to axially mount the preload crown <NUM> on the second end <NUM> according to a plurality of keying angles.

An edge of said preload crown <NUM> that, when the preload crown <NUM> is properly mounted on the torsion bar <NUM>, faces away from the central portion <NUM>, has a shaped profile (or interface) configured to engage with a tool capable of applying a torque to the preload crown <NUM> and to the torsion bar <NUM>. In <FIG>, said shaped profile has teeth <NUM> and recesses. In the illustrated non-limiting example, there are four teeth <NUM> and recesses.

The preload crown <NUM> also has a plurality of radial holes <NUM> formed in the cylindrical outer surface and opening into the axial bore <NUM>.

The actuating devices <NUM> are defined by a heating element comprising an electrical resistance spirally wound around the central portion <NUM> of the torsion bar <NUM>. The electrical resistance is connected to a source of electrical energy, not illustrated in the Figures, and is intended to heat by Joule effect and to heat by conduction the central portion <NUM> of the torsion bar <NUM> with which it lies in contact. An axial spacing of the coils of the electrical resistance is intended to obtain a uniform distribution of temperature over the central portion <NUM>. The cross-sectional area of the bead of which the coils are formed is shaped to maximize contact with the shape memory alloy bar and, therefore, the heat transmitted to it.

In other embodiments, not shown, the shape memory alloy may be activated by any type of heating, such as direct electrical heating by Joule effect or by hot gas.

The torsional actuator <NUM> is mounted on the leading edge structure <NUM> and is preloaded using, for example but not necessarily, the device <NUM> shown in <FIG>. Said device <NUM> for preloading the torsional actuator <NUM> on the leading edge structure <NUM> is a monolithic metal piece comprising a first auxiliary projection <NUM> and a second auxiliary projection <NUM> shaped respectively as the first projection <NUM> and the second projection <NUM> of the structural module <NUM> and a pair of external protrusions <NUM> configured to straddle the first connecting member <NUM>. The first auxiliary projection <NUM> and the second auxiliary projection <NUM> are disposed between the two external protrusions <NUM>.

On the side of the device <NUM> opposite the first auxiliary projection <NUM>, the second auxiliary projection <NUM>, and the external protrusions <NUM> is a portion <NUM> configured to be clamped in a clamp or bolted to a flange, not shown.

The torsional actuator <NUM> is mounted on the leading edge structure <NUM> by inserting the first end <NUM> of the torsion bar <NUM> into the first seat <NUM> so as to accommodate the preload crown <NUM> keyed to the second end <NUM> in the circular through-seat <NUM>. The torsion bar <NUM> is located between the first spar section <NUM> and the second spar section <NUM> and is substantially parallel to the first spar section <NUM> and the second spar section <NUM>.

The assembly thus formed is mounted on the device <NUM> for preloading the torsional actuator by arranging the first connecting member <NUM> between the external protrusions <NUM> and inserting the first auxiliary projection <NUM> and the second auxiliary projection <NUM> into the first recess <NUM> and the second recess <NUM>, respectively. The assembly is then locked onto the device <NUM> by means of screws or pins inserted into holes <NUM> formed through the first auxiliary projection <NUM> and the second auxiliary projection <NUM> and/or into holes <NUM> formed through the external protrusions <NUM> (<FIG>).

The device <NUM> for preloading the torsional actuator is then clamped, for example, on a clamp via the portion <NUM>.

While the assembly is thus clamped, a suitable tool, not shown, is engaged with the teeth <NUM> of the shaped profile of the preload crown <NUM> and a torque is applied to the preload crown <NUM> and thus also to the torsion bar <NUM>. The preload crown <NUM> rotates within the circular through-seat <NUM> and the torsion bar <NUM> is elastically twisted about its own longitudinal axis, for example with reference to <FIG> in a clockwise direction until the radial holes <NUM> are brought into correspondence with the radial through holes <NUM> of the second connecting member <NUM>. Pins are now inserted into the radial holes <NUM> and the radial through holes <NUM> to lock the torsion bar <NUM> in the elastically twisted configuration, i.e., with a given torsional preload.

The preload obtained is a function of the angle at which the preload crown <NUM> is mounted on the second end <NUM>.

The radial holes <NUM>, the radial through holes <NUM>, and the pins constitute locking devices interposed between the second end <NUM> of the torsion bar <NUM> and the circular through-seat <NUM> for locking the second end <NUM> in the preload position. Such locking devices are configured to lock the second end <NUM> in a plurality of preload positions, each corresponding to a preload torsion of the torsion bar <NUM>. In other words, it is possible to torque the bar <NUM> by more or less by aligning different holes <NUM> and <NUM>. Due to the torsional preload with which the torsion bar <NUM> is mounted on the leading edge structure <NUM> and due to the elastic deformability of the leading edge structure <NUM>, the structural module <NUM> arranges in a configuration/point of elastic equilibrium (corresponding to a predefined twist of the leading edge structure <NUM>), in which the torsional force exerted by the torsion bar <NUM> and the torsional elastic force of the leading edge structure <NUM> are balanced.

In the example of <FIG>, since the torsion bar <NUM> is preloaded in a clockwise direction, it tends to twist the leading edge structure <NUM> in a counterclockwise direction, so in the equilibrium configuration, the leading edge structure <NUM> will be twisted with a predefined counterclockwise twist to dive from the first member <NUM> toward the second member <NUM>.

Prior to locking the second end <NUM> in the preload position permanently, it is also possible to rotate the preload crown and release it a plurality of times, to maximize the percentage of martensitic phase in the torsion bar <NUM>, which is an indication of the exploitability of the alloy for the purpose of subsequent actuation.

The structural module <NUM> further comprises a first appendage <NUM> that is connected to the first connecting member <NUM> through a first interface <NUM> connected to respective rear attachments <NUM> of the first connecting member <NUM> and extends toward a trailing edge of the wing. A second appendage <NUM> is connected to the second connecting member <NUM> through a second interface <NUM> connected to respective rear attachments <NUM> of the second connecting member <NUM> and extends toward a trailing edge of the wing (<FIG>). As can be seen by observing <FIG>, the first connecting member <NUM> and the first appendage <NUM> together define a respective first rib of the structural module <NUM>, and the second connecting member <NUM> and the second appendage <NUM> together define a respective second rib of the structural module <NUM>.

Both the first and second appendages <NUM>, <NUM> have a substantially lattice structure with stiffening elements. Their geometry is such that they do not cause an undue backward displacement of the center of gravity of the assembly of <FIG>. Housing holes <NUM> are also provided for connection of any additional subsystems and sensors. The first appendage <NUM> and second appendage <NUM> are connected to the coating, not shown, by screws or rivets housed in respective holes <NUM> cut in said first appendage <NUM> and second appendage <NUM>.

The first appendage <NUM> has, when properly mounted on the respective first connecting member <NUM>, an inner side facing the second appendage <NUM> of the same structural module <NUM> and an outer opposite side. Similarly, the second appendage <NUM> has, when properly mounted on the respective second connecting member <NUM>, an inner side facing the first appendage <NUM> of the same structural module <NUM> and an outer opposite side.

The outer side of the first appendage <NUM> has a shaped hole <NUM> located at a tail end of the first appendage <NUM> while the outer side of the second appendage <NUM> has an extrudate <NUM> located at a tail end of the second appendage <NUM>. The shaped hole <NUM> is configured to possibly house the extrudate <NUM> of the second appendage <NUM> of an adjacent structural module <NUM> (<FIG>, <FIG>).

The inner side of the first appendage <NUM> has a first shaped hole <NUM> and the inner side of the second appendage <NUM> has a second shaped hole <NUM> (<FIG> and <FIG>). A plate-shaped elongate element <NUM> (<FIG>) connects one end of the first appendage <NUM> with one end of the second appendage <NUM> and is disposed at the trailing edge of the wing. A first end <NUM> of the elongate element <NUM> is inserted into the first shaped hole <NUM>, is herein secured/locked by screws while a second end <NUM> of the elongate element <NUM>, is inserted into the second shaped hole <NUM> of the second appendage <NUM> and can slide into said second shaped hole <NUM> with a certain clearance and without exiting therefrom.

The first appendage <NUM> and second appendage <NUM> are intended to transmit the load to the covering and the strain to the elongated member <NUM>.

Strain sensors are operatively coupled to the elongate member <NUM>. In the illustrated non-limiting example, three strain gauges S1, S2, S3 are applied to the elongate member <NUM> as schematically shown in <FIG> and are configured to detect strains in the elongate member <NUM> and, indirectly, in the structural module <NUM>. Other types of strain sensors may be used, such as fiber optic sensors.

The three strain gauges comprise: a first strain gauge S1 sensitive to axial strain arranged at the first end of the elongate member <NUM> and oriented along the longitudinal development of said elongate member; a second strain gauge S2 sensitive to shear strain arranged at an intermediate zone of the elongate member <NUM> and inclined at <NUM>° with respect to the longitudinal development of the elongate member <NUM>; a third strain gauge S3 sensitive to axial strain arranged near the second strain gauge S2 and oriented along the longitudinal development of said elongate member.

The aforementioned first shaped hole <NUM> and second shaped hole <NUM> and also the first and second ends <NUM>, <NUM> of the elongate element <NUM> have shaped recesses to facilitate the passage of cables of the strain gauges S1, S2, S3 integrated on the elongate element <NUM>.

The strain gauges S1, S2, S3 are operatively connected to an electronic control unit that is configured and/or programmed to receive strain signals from the strain gauges S1, S2, S3 and to calculate the twist of the structural module <NUM> as a function of the received strain signals. The electronic control unit, not shown, is part of, for example, the control systems of the apparatus on which the wing is mounted, such as a fixed-wing or rotary-wing aircraft (e.g., helicopter), a vehicle, a vessel, or a power-generating apparatus (e.g., wind blade).

The same electronic control unit is also configured/programmed to control/command the torsional actuator <NUM>. In particular, the electronic control unit is configured/programmed to power the heating element, i.e., the electrical resistance spirally wound around the central portion <NUM> of the torsion bar <NUM> so as to heat said central portion <NUM>. Since the heating element is integrated with a thermal sensor connected to the control unit, said control unit is therefore able to control and maintain the temperature at a desired and/or predefined value. Said predefined temperature value is a function of the type of shape memory material adopted for the torsion bar <NUM>. For example, for the torsion bar <NUM> described herein, it is between <NUM> and <NUM>, depending on the level of activation to be achieved. In fact, it is possible to set intermediate temperatures, to which intermediate twist transfers correspond.

At room temperature, the configuration/point of elastic preload equilibrium (between the leading edge structure <NUM> and preloaded torsion bar <NUM>) is illustrated in the Strain - Stress diagram in <FIG> with the Roman numeral "I" (equilibrium point at first temperature T1).

In that diagram, the line C represents the leading edge structure <NUM>.

Lines A, B, (A-B), (B-A), (A-B)' and (B-A)' represent the, inherently known, behavior of the shape memory torsion bar <NUM> during loading and unloading and at different temperatures.

Line A represents the austenitic behavior of the shape memory alloy torsion bar <NUM>, line B represents the martensitic behavior of the torsion bar <NUM>.

Line (A-B) is the austenite to martensite transition of the shape memory alloy torsion bar <NUM> in a loading phase, line (B-A) is the martensite to austenite transition of the shape memory alloy torsion bar <NUM> in an unloading phase, both performed at a first temperature "T1" of said bar <NUM>, specifically at the ambient temperature at which the torsion bar <NUM> is mounted with preload on the leading edge structure <NUM>.

Line (A-B)' is the change from austenite to martensite of shape memory alloy torsion bar <NUM> in a loading step, line (B-A)' is the change from martensite to austenite of the shape memory alloy torsion bar <NUM> in an unloading step, both performed at a second temperature "T2" of said bar <NUM> greater than the first temperature "T1".

When the torsion bar <NUM> is preloaded at room temperature "T1" it follows the line (A-B) and then B. Once clamped on the leading edge structure <NUM>, as shown above, the leading edge structure <NUM> and the shape memory bar <NUM> move to the equilibrium point "I".

Heating operated by the heating element upon command of the electronic control unit results in a transformation of the stress-strain curve of the shape memory alloy part/portion of the torsion bar <NUM> that shifts upward and follows the lines (A-B)' and (B-A)' in <FIG>. Heating causes a change in the torsional stiffness of the torsion bar <NUM> and in its angular geometry. As a result, the torsional elastic configuration/equilibrium point of the leading edge structure <NUM> associated with torsion bar <NUM> changes and, in <FIG>, this new equilibrium point is denoted by the Roman numeral "II" (equilibrium point at the second temperature T2).

The structural module <NUM> is arranged in a different configuration/point of elastic equilibrium corresponding to a different twist of the leading edge structure. In particular, in the example illustrated herein, the increase in stiffness of the torsion bar <NUM> and the change in its angular geometry result in a decrease in the twist of the leading edge structure <NUM>, i.e., the preload of the present example is at diving and when the SMA is activated the end angle is even more at diving. In variant embodiments, the increase in stiffness and the change in geometry may correspond to an increase in the twist of the leading edge structure compared to the default twist.

<FIG> also illustrates an equilibrium point "III" at the maximum allowable recovery.

When, again at the command of the electronic control unit, the power supply to the heating element ceases and the torsion bar <NUM> cools down, i.e., in the absence of thermal stress, the torsional preload of the torsion bar <NUM> and the elasticity of the leading edge structure <NUM> ensure return to the initial configuration (i.e., to the equilibrium point "I"). The return may be facilitated/accelerated by cooling the torsion bar <NUM>, for example by compressed air from the compressed air source part of the apparatus on which the wing is mounted.

Prior to mating the torsion bar <NUM> to the leading edge structure <NUM>, relaxation cycles of the torsion bar <NUM> can be performed, consisting of heating to an appropriately higher temperature than the austenite finish temperature and subsequent cooling. Such thermal cycles work to stabilize the performance of the shape memory alloy. As previously described, the electronic control unit integrates a system capable of reconstructing the shape of the structural module <NUM> from the signals of the strain gauges S1, S2, S3.

To this end, the operation of the shape reconstruction system involves a calibration operation to be performed only once in the operational life of the structural module <NUM>. This process comprises the following operations:.

Instead, the process of reconstructing the shape under a generic stress and separating the torsional and flexural contributions involves the following steps:.

In use, the electronic control unit adjusts the twist of the wing by acting on the actuation devices <NUM> according to a received command and/or at least one predefined twist profile contained in a memory of the same electronic control unit and according to the deformation signals coming from the deformation sensors. In other words, the electronic control unit knows at any time the current geometry of the structural module <NUM> and of the wing to which the structural module <NUM> belongs and is able to vary/correct said geometry when receiving appropriate commands so as to make said wing assume a target geometry.

Claim 1:
Structural module for fixed or rotary wing, comprising:
a leading edge structure (<NUM>) comprising a first connecting member (<NUM>), a second connecting member (<NUM>) and at least one spar section (<NUM>, <NUM>) interposed between the first connecting member (<NUM>) and the second connecting member (<NUM>) and integral with said first connecting member (<NUM>) and second connecting member (<NUM>); wherein each of said first connecting member (<NUM>) and second connecting member (<NUM>) is configured to engage with a respective adjacent structure;
a torsional actuator (<NUM>) mounted on the leading edge structure (<NUM>) and comprising a torsion bar (<NUM>) and actuating devices (<NUM>) operatively coupled to the torsion bar (<NUM>);
wherein the torsion bar (<NUM>) has a first end (<NUM>) connected to the first connecting member (<NUM>) and a second end (<NUM>) opposite the first end and connected to the second connecting member (<NUM>);
wherein the torsion bar (<NUM>) is mounted or mountable on the leading edge structure (<NUM>) with a preload torsion, so as to give the structural module (<NUM>) a respective predefined twist wherein, with respect to a rest condition of the leading edge structure (<NUM>), the first connecting member (<NUM>) is rotated with respect to the second connecting member (<NUM>);
wherein the actuating devices (<NUM>) are configured to vary a torsional stiffness of the torsion bar (<NUM>) and/or an angular geometry of the torsion bar (<NUM>), so as to vary the twist of the structural module (<NUM>) with respect to the predefined twist;
wherein the first connecting member (<NUM>) has a first seat (<NUM>) configured to accommodate the first end (<NUM>) of the torsion bar (<NUM>) while preventing rotation thereof, and the second connecting member (<NUM>) has a circular through-seat (<NUM>) configured to accommodate the second end (<NUM>) of the torsion bar (<NUM>) and allow rotation of the second end (<NUM>) relative to the first end (<NUM>) to impart to the torsion bar (<NUM>) said preload torsion; locking devices being interposed between the second end (<NUM>) and the circular through-seat (<NUM>) to lock said second end (<NUM>) in a plurality of preload positions each corresponding to a preload torsion of the torsion bar (<NUM>).