Rotorcraft rotor head, which is rigid in drag and articulated in pitch and flapping

A rotorcraft rotor head having a rotor axis and a rotor plane, comprising:

• an even number of blades arranged in pairs of blades, said blades having a foot portion;
• a hub body on which said blades are mounted in diametrically opposed pairs;
• and
• rotating means for rotating said blades;
• each of said pair of blades including, between said foot portion of said blades, a connection which is elastic in torsion and in flapping bending, said connection being without any link with said hub body;
• wherein said rotating means includes hollow sleeves each having two ends, and a single laminated spherical stop having a rigid internal reinforcement and a rigid external reinforcement;
• said single laminated spherical stop including an alternate stacking of rigid spherical caps and of strips made of an elastic material between said rigid internal reinforcement and said rigid external reinforcement, wherein said single laminated spherical stop is in a shape of a portion of a sphere and has an internal end connected to one of said two ends of a respective one of said hollow sleeves, the other one of said two ends of said respective one of said hollow sleeves being directly coupled to said foot portion of a connected one of said pair of blades;
• said respective one of said hollow sleeves including an introduction lever for controlling a pitch of a connected one of said pair of blades, and being coupled on an end thereof to said hub body by said external reinforcement to a periphery of said hub body on which said single laminated spherical stop bears;
• wherein diametrically opposed ones of said hollow sleeves are connected to each other by two identical tie rods arranged in parallel to said rotor plane and are spaced apart on either side of a longitudinal axis which is common to each of said diametrically opposed pairs of blades, each end of each of said tie rods including a bore with an axis substantially parallel to said rotor axis;
• a bolt passing through each said bore of each of said tie rods for fixing a respective one of each of said sleeves thereto;
• wherein each group of two tie rods is disposed in a plane, the planes of each respective said group of two tie rods are arranged parallel to each other with an offset along said rotor axis of sufficient magnitude to allow the free deflection of the respective ones of said tie rods during their bending and torsion in order to follow flapping and change of pitch of said blades, said offset being obtained by a corresponding offset of a position parallel to said rotor axis of a respective said single laminated spherical stop corresponding to each said group of two tie rods on said hub body;
• wherein a material composing each of said tie rods, as well as dimensions of each of said tie rods, are selected so that said tie rods are flexible in bending in a plane perpendicular to said rotor plane as well as in torsion along a longitudinal axis thereof;
• wherein relative rigidity and traction of each said group of two tie rods, linking two diametrically opposed sleeves are in a pre-established ratio, wherein said pre-established ratio is such that centrifugal force originating from each of said blades during rotation is balanced out in proportion to rigidities of a diametrically opposite one of said blades to thereby load the corresponding said two tie rods in traction;
• each of said tie rods is a bundle of stacked thin metallic strips;
• wherein ones of said stacked thin metallic strips which are situated on the outside of the bundle have a smaller width than that of internal strips so as to distribute therebetween the shear stresses due to torsions thereof;
• and
• wherein said stacked thin metallic strips are covered with an antifriction plastic coating in order to avoid contact corrosion.

A rotorcraft rotor head having a rotor axis and a rotor plane, comprising:

• an even number of blades arranged in pairs of blades, said blades having a foot portion;
• a hub body on which said blades are mounted in diametrically opposed pairs;
• and
• rotating means for rotating said blades;
• each of said pair of blades including, between said foot portion of said blades, a connection which is elastic in torsion and in flapping bending, said connection being without any link with said hub body;
• wherein said rotating means includes hollow sleeves each having two ends, and a single laminated spherical stop having a rigid internal reinforcement and a rigid external reinforcement;
• said single laminated spherical stop including an alternate stacking of rigid spherical caps and of strips made of an elastic material between said rigid internal reinforcement and said rigid external reinforcement, wherein said single laminated spherical stop is in a shape of a portion of a sphere and has an internal end connected to one of said two ends of a respective one of said hollow sleeves, the other one of said two ends of said respective one of said hollow sleeves being directly coupled to said foot portion of a connected one of said pair of blades;
• said respective one of said hollow sleeves including an introduction lever for controlling a pitch of a connected one of said pair of blades, and being coupled on an end thereof to said hub body by said external reinforcement to a periphery of said hub body on which said single laminated spherical stop bears;
• wherein diametrically opposed ones of said hollow sleeves are connected to each other by two identical tie rods arranged in parallel to said rotor plane and are spaced apart on either side of a longitudinal axis which is common to each of said diametrically opposed pairs of blades, each end of each of said tie rods including a bore with an axis substantially parallel to said rotor axis;
• a bolt passing through each said bore of each of said tie rods for fixing a respective one of each of said sleeves thereto;
• wherein each group of two tie rods is disposed in a plane, the planes of each respective said group of two tie rods are arranged parallel to each other with an offset along said rotor axis of sufficient magnitude to allow the free deflection of the respective ones of said tie rods during their bending and torsion in order to follow flapping and change of pitch of said blades, said offset being obtained by a corresponding offset of a position parallel to said rotor axis of a respective said single laminated spherical stop corresponding to each said group of two tie rods on said hub body;
• wherein a material composing each of said tie rods, as well as dimensions of each of said tie rods, are selected so that said tie rods are flexible in bending in a plane perpendicular to said rotor plane as well as in torsion along a longitudinal axis thereof;
• wherein relative rigidity and traction of each said group of two tie rods, linking two diametrically opposed sleeves are in a pre-established ratio, wherein said pre-established ratio is such, that centrifugal force originating from each of said blades during rotation is balanced out in proportion to rigidities of a diametrically opposite one of said blades to thereby load the corresponding said two tie rods in traction;
• wherein each said bolt respectively fastening each tie rod to each sleeve is arranged on the outside of the laminated spherical stop with respect to the rotor axis, in such a way that the length of the two tie rods is significantly greater than the distance between two diametrically opposed laminated spherical stops;
• wherein the ends of two neighboring tie rods which are linked to the same sleeve are integral with each other;
• wherein the ends of two neighboring tie rods linked to the same sleeve comprise a laminated structure in order to be integral with each other;
• and
• wherein the laminated structure comprises a shell made of synthetic fiber fabrics, sheathed in a synthetic resin and having a filling, said laminated structure being heat polymerized under pressure in a shaped mold;
• wherein each of the sleeves caps the two ends of the corresponding tie rods which themselves are integral with the laminated structure, and the fastening members of which are fixed into said sleeves by the two bolts which pass through bores made in the two bushes.

A rotorcraft rotor head having a rotor axis and a rotor plane, comprising:

• an even number of blades arranged in pairs of blades, said blades having a foot portion;
• a hub body on which said blades are mounted in diametrically opposed pairs;
• and
• rotating means for rotating said blades;
• each of said pair of blades including, between said foot portion of said blades, a connection which is elastic in torsion and in flapping bending, said connection being without any link with said hub body;
• wherein said rotating means includes hollow sleeves each having two ends, and a single laminated spherical stop having a rigid internal reinforcement and a rigid external reinforcement;
• said single laminated spherical stop including an alternate stacking of rigid spherical caps and of strips made of an elastic material between said rigid internal reinforcement and said rigid external reinforcement, wherein said single laminated spherical stop is in a shape of a portion of a sphere and has an internal end connected to one of said two ends of a respective one of said hollow sleeves, the other one of said two ends of said respective one of said hollow sleeves being directly coupled to said foot portion of a connected one of said pair of blades;
• said respective one of said hollow sleeves including an introduction lever for controlling a pitch of a connected one of said pair of blades, and being coupled on an end thereof to said hub body by said external reinforcement to a periphery of said hub body on which said single laminated spherical stop bears;
• wherein diametrically opposed ones of said hollow sleeves are connected to each other by two identical tie rods arranged in parallel to said rotor plane and are spaced apart on either side of a longitudinal axis which is common to each of said diametrically opposed pairs of blades, each end of each of said tie rods including a bore with an axis substantially parallel to said rotor axis;
• a bolt passing through each said bore of each of said tie rods for fixing a respective one of each of said sleeves thereto;
• wherein each group of two tie rods is disposed in a plane, the planes of each respective said group of two tie rods are arranged parallel to each other with an offset along said rotor axis of sufficient magnitude to allow the free deflection of the respective ones of said tie rods during their bending and torsion in order to follow flapping and change of pitch of said blades, said offset being obtained by a corresponding offset of a position parallel to said rotor axis of a respective said single laminated spherical stop corresponding to each said group of two tie rods on said hub body;
• wherein a material composing each of said tie rods, as well as dimensions of each of said tie rods, are selected so that said tie rods are flexible in bending in a plane perpendicular to said rotor plane as well as in torsion along a longitudinal axis thereof;
• wherein relative rigidity and traction of each said group of two tie rods, linking two diametrically opposed sleeves are in a pre-established ratio, wherein said pre-established ratio is such that centrifugal force originating from each of said blades during rotation is balanced out in proportion to rigidities of a diametrically opposite one of said blades to thereby load the corresponding said two tie rods in traction;
• wherein an integral fixing of the internal reinforcement of the laminated spherical stop to the internal end of the sleeve includes two through bolts having axes thereof which are parallel to each other and parallel to the rotor axis;
• wherein the internal reinforcement of each laminated spherical stop is mounted in a linking brace which is integral with the corresponding sleeve by the two fixing bolts, said linking brace having bores, and wherein said two fixing bolts pass through said bores in said linking brace;
• and
• wherein the internal reinforcement of each laminated spherical stop comprises an axial cylindrical housing which receives a corresponding cylindrical tenon made on the linking brace, the axis of the axial cylindrical housing and of the tenon being substantially parallel to the longitudinal axis of the sleeve and of the corresponding blade.

A rotorcraft rotor head having a rotor axis and a rotor plane comprising:

• an even number of blades arranged in pairs of blades, said blades having a foot portion;
• a hub body on which said blades are mounted in diametrically opposed pairs;
• and
• rotating means for rotating said blades;
• each of said pair of blades including, between said foot portion of said blades, a connection which is elastic in torsion and in flapping bending, said connection being without any link with said hub body;
• wherein said rotating means includes hollow sleeves each having two ends, and a single laminated spherical stop having a rigid internal reinforcement and a rigid external reinforcement;
• said single laminated spherical stop including an alternate stacking of rigid spherical caps and of strips made of an elastic material between said rigid internal reinforcement and said rigid external reinforcement, wherein said single laminated spherical stop is in a shape of a portion of a sphere and has an internal end connected to one of said two ends of a respective one of said hollow sleeves, the other one of said two ends of said respective one of said hollow sleeves being directly coupled to said foot portion of a connected one of said pair of blades;
• said respective one of said hollow sleeves including an introduction lever for controlling a pitch of a connected one of said pair of blades, and being coupled on an end thereof to said hub body by said external reinforcement to a periphery of said hub body on which said single laminated spherical stop bears;
• wherein diametrically opposed ones of said hollow sleeves are connected to each other by two identical tie rods arranged in parallel to said rotor plane and are spaced apart on either side of a longitudinal axis which is common to each of said diametrically opposed pairs of blades, each end of each of said tie rods including a bore with an axis substantially parallel to said rotor axis;
• a bolt passing through each said bore of each of said tie rods for fixing a respective one of each of said sleeves thereto;
• wherein each group of two tie rods is disposed in a plane, the planes of each respective said group of two tie rods are arranged parallel to each other with an offset along said rotor axis of sufficient magnitude to allow the free deflection of the respective ones of said tie rods during their bending and torsion in order to follow flapping and change of pitch of said blades, said offset being obtained by a corresponding offset of a position parallel to said rotor axis of a respective said single laminated spherical stop corresponding to each said group of two tie rods on said hub body;
• wherein a material composing each of said tie rods, as well as dimensions of each of said tie rods, are selected so that said tie rods are flexible in bending in a plane perpendicular to said rotor plane as well as in torsion along a longitudinal axis thereof;
• wherein relative rigidity and traction of each said group of two tie rods, linking two diametrically opposed sleeves are in a pre-established ratio, wherein said pre-established ratio is such that centrifugal force originating from each of said blades during rotation is balanced out in proportion to rigidities of a diametrically opposite one of said blades to thereby load the corresponding said two tie rods in traction;
• and
• wherein the hub body is a hollow cylinder arranged at the end of rotor shaft and in which are housed the tie rods linking the diametrically opposed sleeves as well as the laminated spherical stops, and the hollow cylinder including radial openings for the passage of the sleeves, said hub body including two parts:
• one internal part and one external part, the internal part being connected to the rotor shaft by a flared zone in the shape of a conical frustum, and the external part being in the shape of a cover which is integral with the internal part, by means of bolts which are arranged in bores made on portions of flanges situated on a perimeter of the internal part and of the cover in the shape of a crown, by means of bolts arranged in bores drilled in said external reinforcements of the laminated spherical stops, and in bores made in alignment with flange elements situated on the perimeter of the internal part and of the cover, near to a central zone of recesses of the sleeves, the bolts thus integrally fixing the external reinforcements of the laminated spherical stops on the periphery of the hub body.

A rotorcraft rotor head having a rotor axis and a rotor plane, comprising:

• an even number of blades arranged in groups of two blades which are diametrically opposed to each other;
• a hub body on which said blades are mounted in diametrically opposed pairs, said hub body having a periphery;
• a connection system respectively linking each of said diametrically opposed pairs of blades, wherein said connection system is without any link with said hub body, wherein:
• each blade has a root and is articulated in flapping and in pitch on said hub body by a sleeve which is disposed between said root of said blade and said hub body, a laminated spherical stop is carried by said sleeve, and said sleeve bears against said periphery of said hub body by said laminated spherical stop, and said sleeve further comprising an introduction member for controlling pitch of said blade;
• each said system for connecting two diametrically opposed blades includes two tie rods linking said two diametrically opposed sleeves of said two diametrically opposed blades, said two tie rods being parallel to said rotor plane on either side of a longitudinal axis which is common to said two diametrically opposed blades, said two tie rods being parallel and spaced apart in a direction along said common longitudinal axis;
• a member fastening said two tie rods to each sleeve, said member being disposed on an opposite side of each said laminated spherical stop from said rotor axis and such that a length of each of said two tie rods is significantly greater than a distance between centers of diametrically opposed ones of said laminated spherical stops;
• each of said sleeves respectively caps an end of each corresponding one of said tie rods;
• two bolts connecting said end of each corresponding one of said tie rods into a corresponding said sleeve;
• each of said laminated spherical stops comprises a central part, which can be deformed in torsion, and having an internal reinforcement and an external reinforcement, said internal reinforcement being integral with an internal end of corresponding said sleeve, and said external reinforcement being linked to said periphery of said hub body;
• said tie rods are relatively rigid in tension along their respective longitudinal axes and are flexible in bending in a plane perpendicular to said plane of said rotor as well as in torsion along their respective longitudinal axes;
• a relative rigidity in tension of said two tie rods, and a relative rigidity in compression of said two laminated spherical stops installed between the corresponding said sleeves and said hub body, are in a predetermined ratio such that centrifugal force arising due to rotation of each rotating blade is balanced out in proportion to said relative rigidity in tension and said relative rigidity in compression in part by the diametrically opposite blade, thus loading said two tie rods in traction, and is balanced out in a remaining part by said hub body via the corresponding one of said laminated spherical stops, which is loaded in compression;
• each group of two tie rods lying in a respective plane, wherein said respective planes of each group of two tie rods are parallel to each other with a slight offset along said rotor axis of sufficient amount to allow free defection of said tie rods during bending and torsion thereof in order to follow flapping and change of pitch of said blades, said offset being in a direction along said rotor axis.