ROTOR BLADE WITH A SYSTEM FOR SEPARATE RETENTION AND ABSORPTION OF FORCES AND ROTOR WITH SUCH BLADES

Description

[0001] The present invention relates to the field of aircraft rotors, and in particular to the forward propellers of an aircraft.

[0002] The present invention relates to a rotor blade with a dissociated force retention and reabsorption system and to a rotor equipped with such blades.

[0003] A rotor can be a main rotor of a rotary-wing aircraft, providing lift and even propulsion. A rotor can also be an auxiliary rotor of a rotary-wing aircraft, counteracting the yaw moment exerted by a main rotor on the aircraft's fuselage and also helping to control the aircraft's yaw movements. A rotor can also be a propeller, also referred to simply as a propeller, equipping a fixed-wing or rotary-wing aircraft. Propellers can be located, for example, on either side of the aircraft's fuselage, or possibly on a fixed wing. When the aircraft has only one propeller, this propeller can be mounted on the aircraft's fuselage.

[0004] Such a rotor traditionally comprises a rotating hub and several blades mounted in the hub, the number and dimensions of the blades being in particular dependent on the forward force to be generated.

[0005] The blade pitch can be varied, at least collectively—that is, identically for all blades—to modify the blade angle of attack and achieve the required aerodynamic performance of the rotor. This pitch variation is achieved, for example, by a single-degree-of-freedom rotational joint, such as a pivot joint, between the blade root of each blade and the rotor hub.

[0006] According to a widespread prior art for a propeller, such a single-degree-of-freedom rotational linkage comprises one or more ball bearings arranged between the hub and the blade root to guide the blade's rotation about a pitch axis. The blade root also includes a translational stop relative to the hub to restrain the blade from centrifugal force during propeller rotation.

[0007] The blade may include a profiled portion and a blade root fitted with a cylindrical sleeve, the profiled portion being attached to the cylindrical sleeve by various means.

[0008] The profiled portion of the blade can, for example, be attached to the cylindrical sleeve by removable fasteners, such as screws, as described in US documents 2765859 and US 6305905. The profiled portion can then be removed or replaced fairly easily. However, these removable fasteners bear most, if not all, of the tensile, bending, and torsional stresses on the blade.

[0009] A removable fastening means between a profiled portion of blade and a cylindrical sleeve can also be a removable shaft as described in US document 5017092.

[0010] A profiled portion can, for example, be fixed to the cylindrical sleeve by a non-removable retention system, particularly when the profiled portion of the blade is made of composite materials.

[0011] A non-removable retention system may include, for example, a shape or a series of undercut shapes between the cylindrical sleeve and the profiled portion as described in documents US 2013 / 0129507 and US 6666651. Each undercut shape constitutes a mechanical means of retaining the profiled portion of the blade on the cylindrical sleeve.

[0012] The cylindrical sleeve can also be made of metal, even stainless steel, and may have a single undercut shape. The profiled portion of the blade can be bonded to the cylindrical sleeve in addition to the undercut shape. In this case, the cylindrical sleeve may be referred to as a "tulip" to describe its distinctive shape.

[0013] According to US documents 2002 / 0008177 and EP 2862799, a non-removable retention system may include a composite structure of the profiled portion of the blade wrapping around a ring to form a mechanical stop with the cylindrical sleeve and with the aid of a cylindrical part disposed inside the cylindrical sleeve and the profiled portion to prevent deformation of this ring.

[0014] Document FR 3021030 concerns a blade comprising a profiled portion extending along a longitudinal direction and a sleeve. The sleeve has a passage restriction in a direction perpendicular to the longitudinal direction. The base of the profiled portion is fixed to the hub or the sleeve by means of a socket perpendicular to the longitudinal axis and has an overall dimension strictly greater than the width of the passage restriction, such that in the event of failure of the fixing of said base to the socket, the base abuts against the passage restriction, thus retaining the profiled portion within the sleeve.

[0015] Documents FR 2970943 and US 9085986 describe a blade comprising a fitting for attaching to a hub and an attachment zone surrounding a sleeve connected to the fitting. The blade also includes a torsional force transmission element formed by two half-shells jointly enclosing the attachment zone. Each half-shell has a first part positioned inside the fitting and a second part cooperating with a torsion box.

[0016] Document EP 0296014 describes a composite material blade for a shrouded helicopter tail rotor. The blade has a root loop attached to the blade spar surrounding a mounting sleeve attached to the hub.

[0017] This connection between the blade and the rotor hub is subjected to both tensile stress generated by the centrifugal force due to the blade's rotation around the rotor hub's axis, and bending and torsional stresses resulting from the aerodynamic and inertial loads on the blade. The tensile stress acts approximately parallel to the blade's longitudinal direction.

[0018] Bending forces may include forces not parallel to the longitudinal direction of the blade and resulting from bending stresses on the blade about its longitudinal direction due to aerodynamic and inertial loads. Torsional forces may include forces and / or one or more moments located in a plane substantially perpendicular to the longitudinal direction of the blade and resulting from torsional stresses on the blade about its longitudinal direction due to aerodynamic and inertial loads.

[0019] This bonding connection is thus subjected to multiaxial stresses of various kinds. Consequently, this bonding connection does not allow for the optimal distribution of these tensile, bending, and torsional forces within the blade components, as the fibers constituting the composite materials of the blade and possibly the blade root can hardly be oriented in such a way as to simultaneously withstand all the normal and shear stresses combined with high static and fatigue loads.

[0020] The prior art of the invention also includes documents US 2021 / 0062661 and US 2013 / 0336796.

[0021] The present invention then relates to a rotor blade with a system for retaining and resuming dissociated forces and a rotor equipped with such blades making it possible to overcome the limitations mentioned above by optimizing the resuming of combined tensile, flexural and torsional forces in the components of the blade.

[0022] The present invention therefore relates to a blade for a rotor. This blade is defined in claim 1.

[0023] The blade according to the invention is remarkable in that: the blade includes a hollow torsion box attached to the profiled portion and having a bearing area in contact with the inner wall of the cylindrical sleeve, the anchoring device is positioned inside the cylindrical sleeve and surrounds at least partially the stop, the blade body is positioned inside the cylindrical sleeve.

[0024] The blade is designed to be fitted to a rotor comprising at least two blades and a rotating hub. Each blade is connected to the hub by a single-degree-of-freedom rotational joint, such as a pivot joint, to allow variation of the blade's pitch around a pitch axis substantially parallel to the blade's longitudinal axis. More precisely, the single-degree-of-freedom rotational joint is positioned between the hub and the blade's cylindrical sleeve. During rotor rotation around the hub's axis of rotation, the blade's longitudinal axis essentially coincides with a radial direction of the rotating rotor.

[0025] This rotor can be a main rotor or an auxiliary rotor of a rotary-wing aircraft. A rotor can also be a propeller used on a fixed-wing or rotary-wing aircraft.

[0026] During rotor rotation, the stop ensures that the blade is held in place, via the anchoring device, in a direction parallel to the longitudinal axis AXL, from the cylindrical sleeve towards the profiled portion. The profiled portion of the blade is thus held in contact with the rotor hub. As the rotor, and therefore the blade, rotates around the hub's axis of rotation, centrifugal force tends to displace the blade radially out of the hub. The anchoring device and the stop thus allow the tensile forces generated by the centrifugal force during the rotation of the hub, and therefore the blades, around this axis of rotation of the hub.

[0027] The torsion box is positioned at least partly inside the cylindrical sleeve and, together with the cylindrical sleeve, thanks to the support area of ​​the torsion box which is in contact with the internal wall of the cylindrical sleeve, allows the transfer of the bending forces suffered by the blade as a consequence of the forces suffered by the blade during the rotation of the rotor.

[0028] The torsion box is hollow and at least partially encloses the blade body and the anchoring device. The torsion box may also optionally enclose part of a blade spar.

[0029] The blade body is positioned at least partially in the torsion box and is in contact with the torsion box and the anchoring device so as to limit deformations of the torsion box and the anchoring device.

[0030] The thrust bearing, the anchoring device, the blade body, the cylindrical sleeve, and the torsion box thus constitute a system for retaining and absorbing forces independently of the blade. This system of retaining and absorbing forces advantageously allows the forces generated and experienced by the blade to be absorbed independently by the blade components, and in particular by the system of retaining and absorbing forces.

[0031] As a result, each element of the blade can be optimized in terms of dimensions, mass and mechanical strength, without compromising the operation and mechanical resistance to stress and fatigue of the rotor as a whole.

[0032] Furthermore, the profiled portion of the blade is completely removable from the cylindrical sleeve thanks to the use of a removable connection, for example comprising at least one screw and a nut, between the stop and the cylindrical sleeve while maintaining a high level of assembly security, this removable connection being mainly stressed in shear.

[0033] The blade according to the invention may further comprise one or more of the following features, taken alone or in combination.

[0034] According to the invention, the anchoring device is U-shaped. This U-shape allows the anchoring device to surround the stop, preventing it from escaping when the blade is subjected to a centrifugal force due to rotor rotation. The anchoring device can thus form a blade wrap.

[0035] According to the invention, the blade body is positioned at least between the two arms of the U-shaped anchoring device so as to prevent these two arms from coming together during the stresses experienced by the anchoring device.

[0036] In another example, the anchoring device may consist of unidirectional fibers. These fibers are arranged parallel to each other, for example, along a U-shaped form of the anchoring device. These fibers may also be arranged parallel to each other, essentially parallel to the longitudinal axis. These fibers may, for example, be carbon fibers and / or glass fibers impregnated with resin.

[0037] In another example, the stop may comprise a cylindrical part and at least one device for attaching this cylindrical part to the cylindrical sleeve. This cylindrical part may be arranged perpendicular to the longitudinal axis AXL. The cylindrical part thus cooperates with the anchoring device to form an effective and reliable stop for the anchoring device, and consequently for the profiled portion of the blade, in a direction parallel to the longitudinal axis AXL, namely in a radial direction of the rotor during its rotation.

[0038] In another example, the stop may include a hollow sleeve integral with the anchoring device, a cylindrical part, and at least one device for attaching the cylindrical part to the cylindrical sleeve. The hollow sleeve and the cylindrical part are arranged perpendicular to the longitudinal axis AXL. The anchoring device then at least partially surrounds the hollow sleeve, and the cylindrical part is positioned within the sleeve to connect the anchoring device to the cylindrical sleeve.

[0039] According to these last two examples, at least one fastening device allows the cylindrical part to be fixed onto the cylindrical sleeve.

[0040] Furthermore, according to these last two examples, the components of the stop can be metallic.

[0041] In another example, the inner wall of the cylindrical sleeve may be cylindrical with a circular base, and the bearing area of ​​the torsion box may at least partially include a cylindrical shape with a circular base that cooperates with said inner wall to form a joint with one degree of freedom in rotation about the longitudinal axis AXL and one degree of freedom in translation about the longitudinal axis AXL, such as a sliding pivot joint. The bearing area of ​​the torsion box may, for example, have a single circumferential span covering 360° around the longitudinal axis AXL or several spans distributed radially around the longitudinal axis AXL. Similarly, the bearing area may have several spans distributed longitudinally along the longitudinal axis AXL or a single span long enough to allow for a "long centering" type joint with the inner wall of the cylindrical sleeve.

[0042] Regardless of the number of spans, the bearing area may include, for example, a part made of metal or a polymer derivative, with or without surface treatment, in order to reduce wear at the contact point between the inner wall of the cylindrical sleeve and the bearing area of ​​the torsion box.

[0043] In another example, the torsion box, the anchoring device, and / or the blade body are integral to the airfoil portion. The torsion box, the anchoring device, and / or the blade body can thus be directly continuous with the airfoil portion, for example, by being part of the composite structure of this airfoil portion of the blade. The torsion box, the anchoring device, and / or the blade body can also be attached to the airfoil portion, for example, to its composite structure.

[0044] In another example, the torsion box, the anchoring device, and / or the blade body are integral with at least one blade spar. According to the invention, the anchoring device is an integral part of this at least one spar, namely, it is in direct continuity with this at least one spar.

[0045] In another example, the blade body may have at least one flat surface, and the cylindrical sleeve may have at least one flat face cooperating with that flat surface. This at least one flat face of the cylindrical sleeve is thus in contact with this at least one flat surface of the blade body, effectively ensuring the transfer of torsional forces generated by the aerodynamic forces experienced by the blade during rotor rotation, particularly in response to variations in blade pitch. These torsional forces are transmitted from the airfoil portion of the blade by the torsion box, advantageously preventing all these torsional forces from being transmitted to a blade spar and / or the blade body.

[0046] At least one flat face of the cylindrical sleeve and at least one flat surface of the blade body are preferably arranged parallel to the longitudinal axis AXL.

[0047] The cylindrical sleeve may, for example, have two flat faces and a yoke, this yoke having two supports, each with a flat face. The blade body then has two flat surfaces positioned respectively in planar bearing against a flat face of the yoke.

[0048] Furthermore, the yoke allows the stop to be fixed to the cylindrical sleeve. The blade body can then frame the anchoring device between the two flat faces, and therefore between the two yoke supports. The expression "the blade body can then frame the anchoring device between the two flat faces" means that the blade body comprises two plates, each with a flat surface, located on either side of the anchoring device, with the blade body and anchoring device assembly positioned between the two yoke supports.

[0049] In the absence of a flat support between the blade body and the cylindrical sleeve, the torsional forces generated by the aerodynamic forces acting on the blade during rotor rotation can be absorbed by the thrust bearing connected to the cylindrical sleeve. In this case, these torsional forces are transmitted from the airfoil portion of the blade to the thrust bearing via the torsion box and the anchoring device, and possibly also via a blade spar and / or the blade body.

[0050] In another example, the torsion box can have fibers oriented at angles between ±10° and ±80° with respect to the longitudinal axis AXL. This fiber orientation allows the torsion box to have a high shear modulus. The fibers of the torsion box are oriented, for example, at ±45° with respect to the longitudinal axis AXL. The torsion box can be manufactured by winding these fibers or by draping fabrics made from these fibers.

[0051] These fibers can, for example, include carbon, glass, and / or Kevlar fibers impregnated with resin.

[0052] The cylindrical sleeve, for example, is made of metal and may include raceways to accommodate ball bearings. The cylindrical sleeve may also be made of composite materials, such as carbon fibers and / or glass fibers impregnated with resin, and include raceways adapted, for example with metal inserts, to accommodate ball bearings.

[0053] The present invention also relates to a rotor comprising a hub and at least two blades. This rotor may be, for example, a lift rotor, an auxiliary anti-torque rotor, or a forward propeller. The blades are as previously described, with the longitudinal axis AXL of the cylindrical sleeve coinciding with a blade pitch axis. Furthermore, the rotor includes a single-degree-of-freedom rotational joint, such as a pivot joint, between the hub and each cylindrical sleeve around the longitudinal axis AXL to allow for blade pitch variations. During rotor rotation about the hub's axis of rotation, the blade's longitudinal axis also substantially coincides with a radial direction of the rotating rotor.

[0054] Furthermore, the rotor includes at least one rotational guide device connecting each cylindrical sleeve and the hub, respectively, in order to achieve a one-degree-of-freedom rotational connection between the hub and each cylindrical sleeve around the longitudinal axis AXL. This rotational guide device includes, for example, one or more angular contact ball bearings, needle bearings, or roller bearings.

[0055] Each guide device may include, for example, an inner ring, an outer ring, and rolling elements such as balls, needles, or rollers. The inner ring is then integral with a cylindrical sleeve, and the outer ring is integral with the hub. The cylindrical sleeve may include, for example, a first stop device for the rotation of the guide device and its inner ring in particular, along the longitudinal axis AXL, and the hub may include a second stop device for the rotation of the guide device and its outer ring in particular, along the longitudinal axis AXL, in order to restrain the entire blade from the centrifugal force during rotor rotation.

[0056] The rotor according to the invention advantageously allows the assembly and disassembly of the blade to be facilitated compared to existing solutions where mechanical stopping is only achieved, for example, by balls of the guide device.

[0057] Each cylindrical sleeve may include a pitch lever to adjust the blade pitch. The pitch lever is offset on the cylindrical sleeve relative to the longitudinal axis AXL.

[0058] Thanks to the rotor according to the invention, the forces found at the base of each blade are advantageously taken up independently by the elements of the retention and force transfer system separated from each blade, namely the stop, the anchoring device, the blade body, the cylindrical sleeve and the torsion box.

[0059] Furthermore, the components of the independent load-bearing and retention system for each blade are primarily made of composite materials and are subjected to optimal operating conditions based on the fiber orientations of their constituent elements, which are determined by the forces borne by each component. Consequently, the dimensions and mass of each of these components of the independent load-bearing and retention system for each blade can be optimized, as can their mechanical strength.

[0060] Furthermore, the risks of failure due to corrosion are also reduced, or even eliminated, by limiting the use of metal parts.

[0061] The rotor according to the invention thus offers a new architecture for the connection between each blade and the hub, as well as for the assembly and disassembly of a blade. Furthermore, the rotor according to the invention can also improve the lifespan of the blades.

[0062] The invention and its advantages will become apparent in more detail in the following description, with illustrative examples given by reference to the attached figures which represent: there figure 1 , a view of a rotor equipped with blades for an aircraft, the figure 2 , a view of the blade root of a rotor blade, the figure 3 , an exploded view of the blade root, the figure 4 , a longitudinal cross-sectional view of the blade root, the figure 5 , a longitudinal cross-sectional view of the blade root of a blade from another rotor, the figure 6 , a first cross-sectional view of the blade root according to the figure 5 , and the figure 7 , a second cross-sectional view of the blade root according to the figure 5 .

[0063] Elements present in several separate figures are assigned a single reference.

[0064] A rotor 10 for an aircraft is shown on the figure 1 This rotor 10 comprises a hub 11, at least two blades 1, and a rotation axis AXROT of the hub 11. The example of a rotor 10 shown in the figure 1 comprises six blades 1, although a different number of blades 1 may be used without affecting the implementation of the invention. The example of rotor 10 shown in the figure 1 is a propeller of an aircraft intended to provide at least part of the forward propulsion of the aircraft, which may be fixed-wing and / or rotary-wing. The rotor 11 may also be a lift rotor or an auxiliary anti-torque rotor of a rotary-wing aircraft.

[0065] Each blade 1 comprises a blade root 15, a profiled portion 3, and a free end 32, the profiled portion 3 being formed by a succession of aerodynamic profiles. The longitudinal axis AXL of a blade 1 extends in a root direction from the blade root 15, fixed to the hub 11, towards the free end 32 of the blade 1.

[0066] During the rotation of the rotor 10 around the axis of rotation AXROT, the blades 1 are driven in rotation by the hub 11 around this axis of rotation AXROT so that each blade 1, and more particularly the profiled portion 3 of each blade 1, generates an aerodynamic force. During such a rotation of the rotor 10, the longitudinal axis AXL of each blade 1 essentially coincides with a radial direction of the rotating rotor 10 and hub 11. This radial direction extends perpendicularly to the axis of rotation AXROT of the hub 11 around this axis of rotation AXROT.

[0067] There figure 2 represents in detail the blade root 15 and the junction with the profiled portion 3. The blade root 15 includes a stop 7, an anchoring device 5, a blade body 4, a cylindrical sleeve 2 and a torsion box 6.

[0068] The torsion box 6, the anchoring device 5 and the blade body 4 are integral with the profiled portion 3. The torsion box 6, the anchoring device 5 and the blade body 4 can thus be continuous with the structure of the profiled portion 3, for example by being integral with at least one spar of the blade 1. The torsion box 6, the anchoring device 5 and the blade body 4 can also be fixed to the structure of the profiled portion 3.

[0069] The cylindrical sleeve 2 is hollow and extends around the longitudinal axis AXL. The cylindrical sleeve 2 has an internal wall 25.

[0070] The torsion box 6 is hollow and extends around the longitudinal axis AXL. The torsion box 6 is positioned between the axis of rotation of the hub AXROT and the profiled portion 3. The torsion box 6 is positioned at least partially within the cylindrical sleeve 2.

[0071] The anchoring device 5 and the blade body 4 are positioned at least partially in the torsion box 6. The anchoring device 5 and the blade body 4 are also positioned at least partially in the cylindrical sleeve 2.

[0072] Furthermore, to allow the blade 1 to rotate about a pitch axis substantially coinciding with its longitudinal axis AXL, at least one rotational guide 13 is arranged between the cylindrical sleeve 2 and the hub 11, and more specifically a bore of the hub 11, to form a one-degree-of-freedom rotational joint, such as a pivot joint, between the hub 11 and the cylindrical sleeve 2. For example, two guide devices 13, such as ball bearings, are positioned around the cylindrical sleeve 2. A guide device 13 may, for example, comprise an inner ring, an outer ring, and rolling elements, namely balls in the example shown. According to another example, one or more angular contact ball bearings may be positioned around the cylindrical sleeve 2.

[0073] The cylindrical sleeve 2 may also include a first stop device 27 forming a stop parallel to the longitudinal axis AXL for an inner ring of a guide device 13. A first stop device 27 is for example a shoulder integrated into the cylindrical sleeve 2.

[0074] The hub bore 11 may also include a second stop device forming a stop parallel to the longitudinal axis AXL for an outer ring of a guide device 13. This second stop device may include a shoulder integrated into the hub bore 11 and / or be formed by one or more added parts.

[0075] The cylindrical sleeve 2 may also include a pitch lever 22, eccentric with respect to the longitudinal axis AXL, to control the pitch variation of the blade 1.

[0076] The anchoring device 5 is therefore positioned inside the cylindrical sleeve 2 and surrounds at least partially the stop 7 fixed to the cylindrical sleeve 2 so that the assembly formed by the stop 7 and the anchoring device 5 provides a longitudinal stop of the blade 1, in a direction parallel to the longitudinal axis AXL, and from the blade root 15 towards the free end 32 of the blade 1. This longitudinal stop thus opposes a displacement of the blade 1 under the effect of the centrifugal force applied to the blade 1 during the rotation of the rotor 10 around the axis of rotation AXROT.

[0077] An example of the connection between the stop 7 and the anchoring device 5 is shown on the figure 3 in exploded view. The anchoring device 5 surrounds the stop 7 over 180 degrees (180°) to achieve longitudinal restraint. The stop 7 comprises a cylindrical part 72 arranged perpendicular to the longitudinal axis AXL, and the anchoring device 5 has a U-shaped end 51 to ensure complementary shapes with the cylindrical part 72 and, consequently, good absorption of the forces generated by the centrifugal force applied to the blade 1 during the rotation of the rotor 10. The anchoring device 5 also includes two arms 52, 53 connecting the U-shaped end 51 to the profiled portion 3. The blade body 4 is positioned between the arms 52, 53 and bears against each arm 52, 53 to limit deformation of the arms 52, 53.

[0078] The cylindrical part 72 of the stop 7 is, for example, fixed between two supports of a yoke 26 of the cylindrical sleeve 2, each support of the yoke 26 having an opening 29. The stop 7 may include at least one removable fastening device 73, such as a screw 73, for fixing the cylindrical part 72 to each support of the yoke 26, the cylindrical part 72 having a tapped hole at each end. A washer 74 may be inserted between a support and a fastening device 73.

[0079] The stop 7 may also include, according to the example shown on the figure 4 a hollow cylindrical sleeve 71, a cylindrical part 72, and at least one removable fastening device 73. The sleeve 71 and the cylindrical part 72 are arranged perpendicular to the longitudinal axis AXL. The sleeve 71 is integral with the anchoring device 5, which has a U-shaped end 51 to ensure complementary shapes with the sleeve 71 for resisting the forces generated by the centrifugal force applied to the blade 1 during the rotation of the rotor 10. The anchoring device 5 also includes two arms 52, 53 connecting the U-shaped end 51 to the profiled portion 3.

[0080] The cylindrical part 72 is positioned in the sleeve 71 and is fixed between two supports of the yoke 26 of the cylindrical sleeve 2, each support of the yoke 26 having an opening 29. The stop 7 then has two removable fastening devices, such as two nuts 73 for example, to fix the cylindrical part 72 to each support of the yoke 26, the cylindrical part 72 having a threaded rod at each end. A washer 74 can be inserted between a support and a fastening device 73.

[0081] The blade body 4 and the anchoring device 5 are positioned inside the cylindrical sleeve 2 and the torsion box 6 as shown in the figure 4 The torsion box 6 has a bearing area 9 in contact with the inner wall 25 of the cylindrical sleeve 2.

[0082] This support zone 9, which is in contact with the internal wall 25 of the cylindrical sleeve 2, advantageously allows the transfer of bending forces suffered by the blade 1 as a consequence of the aerodynamic forces suffered by the blade 1 during the rotation of the rotor 10.

[0083] According to the example shown on the figure 4 , the bearing area 9 of the torsion box 6 has a single cylindrical span around the longitudinal axis AXL and covering along the longitudinal axis AXL a length greater than the diameter of the internal wall 25 in order to form a "long centering" type connection between the cylindrical sleeve 2 and the torsion box 6.

[0084] According to another example shown on the figure 5 , the support area 9 of the torsion box 6 has two cylindrical bearing surfaces positioned along the longitudinal axis AXL.

[0085] Furthermore, the blade body 4 can be supported against the stop 7, and in particular against the bushing 71 in the example shown, along the longitudinal axis AXL.

[0086] There figure 6 represents a cross-sectional view of the example of the figure 5 perpendicular to the longitudinal axis AXL at the level of a span of the bearing area 9. The inner wall 25 of the cylindrical sleeve 2 may be cylindrical with a circular base and the bearing area 9 may at least partially have a cylindrical shape with a circular base, as shown in the figure 6 , in order to form a link with one degree of freedom in rotation around the longitudinal axis AXL and with one degree of freedom in translation along the longitudinal axis AXL, such as a sliding pivot type link, between the cylindrical sleeve 2 and the torsion box 6.

[0087] The anchoring device 5 and the blade body 4 are positioned at least partially within the torsion box 6, according to the example of the figure 6 , and in contact with an internal surface of the torsion box 6.

[0088] There figure 7 represents a cross-sectional view of the example of the figure 5perpendicular to the longitudinal axis AXL and passing through an axis of the stop 7, in particular an axis of the bushing 71 and the cylindrical part 72. According to this example, the blade body 4 has at least one flat 41 and specifically two flats 41 diametrically opposed with respect to the longitudinal axis AXL. Each support of the yoke 26 then has at least one flat face 61 cooperating respectively with a flat 41, and specifically two flat faces 61. These two flat faces 61 are thus in contact respectively with the two flats 41 so as to participate in resisting the torsional force generated by the aerodynamic forces experienced by the blade 1 during the rotation of the rotor 11.

[0089] Other complementary shapes can be used for the blade body 4 and the cylindrical sleeve 2 to help resist this torsional force. For example, the blade body 4 and an internal cylindrical sleeve 2 can be parallelepiped-shaped or ovoid.

[0090] The stop 7, the anchoring device 5, the blade body 4, the cylindrical sleeve 2 and the torsion box 6 thus allow the different forces generated and experienced by the blade 1 to be independently absorbed during the rotation of the rotor 11. The stop 7, the anchoring device 5, the blade body 4, the cylindrical sleeve 2 and the torsion box 6 can thus form a system for retaining and absorbing forces independent of the blade 1.

[0091] The stop 7, the anchoring device 5, the blade body 4, the cylindrical sleeve 2 and the torsion box 6 can thus be advantageously optimized in terms of their dimensions, their masses as well as their mechanical strength, without compromising the operation and the mechanical strength to stress and fatigue of the rotor 11 as a whole.

[0092] In the absence of such complementary shapes between the blade body 4 and the cylindrical sleeve 2, the torsional forces generated by the aerodynamic forces experienced by the blade 1 during the rotation of the rotor can be taken up by the stop 7 in connection with the cylindrical sleeve 2.

[0093] Naturally, the present invention is subject to many variations in its implementation.

Claims

1. Blade (1) for a rotor (10), said blade (1) comprising: - a hollow cylindrical sleeve (2) extending about a longitudinal axis (AXL) and provided with an internal wall (25), - an abutment (7) fixed to said cylindrical sleeve (2), - a profiled portion (3), - an anchoring device (5) integral with said profiled portion (3), and - a blade body (4) secured to said profiled portion (3), - at least one spar, a hollow torque box (6) secured to said profiled portion (3) and enveloping at least partially the blade body (4), the torque box (6) comprising a bearing zone (9) in contact with said internal wall (25) of said cylindrical sleeve (2), - where said anchoring device (5) is positioned inside said cylindrical sleeve (2) and surrounds at least partially said abutment (7), and - said blade body (4) is positioned inside said cylindrical sleeve (2), the anchoring device (5) having a U-shape in continuity of this at least one spar of the blade (1), the blade body (4) being positioned at least between two branches of the anchoring device (5) forming the U.

2. Blade (1) according to claim 1, wherein said cylindrical sleeve (2) and the blade body (4) have complementary shapes.

3. Blade (1) according to any one of claims 1 to 2, wherein said anchoring device (5) comprises one-directional fibres.

4. Blade (1) according to any one of claims 1 to 3, wherein said anchoring device (5) and said blade body (4) are secured to at least one spar of said blade (1).

5. Blade (1) according to any one of claims 1 to 4, wherein said abutment (7) comprises a cylindrical part (72) arranged perpendicularly to said longitudinal axis (AXL) and connecting said anchoring device (5) to said cylindrical sleeve (2) and at least one fixing device (73) of said cylindrical part (72) on said cylindrical sleeve (2).

6. Blade (1) according to any one of claims 1 to 4, wherein said abutment (7) comprises a hollow socket (71) are secured to said anchoring device (5) and a cylindrical part (72) arranged perpendicularly to said longitudinal axis (AXL), as well as at least one fixing device (73) of said cylindrical part (72) on said cylindrical sleeve (2), said anchoring device (5) surrounding at least partially said socket (71), said cylindrical part (72) being positioned in said socket (71) in order to connect said anchoring device (5) to said cylindrical sleeve (2).

7. Blade (1) according to any one of claims 1 to 6, wherein said internal wall (25) of said cylindrical sleeve (2) is cylindrical with a circular-base, and said bearing zone (9) of said torque box (6) may comprise at least partially a cylindrical-shape with a circular-base, engaging with said internal wall (25) to form a connection with a degree of freedom in rotation about the longitudinal axis (AXL) and with a degree of freedom in translation about the longitudinal axis (AXL).

8. Blade (1) according to any one of claims 1 to 7, wherein said torque box (23) comprises fibres oriented with angles of between ±10° and ±80° with respect to said longitudinal axis (AXL).

9. Blade (1) according to any one of claims 1 to 8, wherein said blade body (4) comprises at least one flat spot (41) and said cylindrical sleeve (2) comprises at least one flat face (61) engaging with said flat spot (41).

10. Blade (1) according to claim 9, wherein said cylindrical sleeve (2) comprises two flat faces (61) and a yoke (26), said yoke (26) comprising two supports, each provided with a flat face (61), said blade body (4) framing said anchoring device (5) between said two flat faces (61).

11. Blade (1) according to any one of claims 1 to 10, wherein said blade body (4) bears against said abutment (7) about said longitudinal axis (AXL).

12. Rotor (10) comprising: - a hub (11), and - at least two blades (1), wherein said at least two blades (1) are according to any one of claims 1 to 11, said longitudinal axis (AXL) of said cylindrical sleeve (2) coinciding with a pitch axis of said blade (1), said rotor (10) comprising a connection with a degree of freedom in rotation between said hub (11) and each cylindrical sleeve (2) about said longitudinal axis (AXL).

13. Rotor (10) according to claim 12, wherein said rotor (11) comprises at least one rotating guiding device (13) connecting respectively each cylindrical sleeve (2) and said hub (11).

14. Rotor (10) according to claim 13, wherein said at least one guiding device (13) comprises an inner ring (51), an outer ring (52) and rolling elements (53), said inner ring (51) being secured to said cylindrical sleeve (2) and said outer ring (52) being secured to said hub (11), said cylindrical sleeve (2) comprising a first abutment device (27) and said hub (11) comprising a second abutment device about said longitudinal axis (AXL).

15. Rotor (10) according to any one of claims 12 to 14, wherein each cylindrical sleeve (2) comprises a piloting pitch lever (22) of said blade (1).