Rotor for a hover-capable aircraft and related method of control

A method of controlling a rotor (3′″, 3″″) for a hover-capable aircraft (1);

• said rotor (3″′, 3″″), comprising:
• a hub (7) rotatable about a first axis (A);
• and
• at least two blades (6) hinged to said hub (7);
• each said blade (6) comprising a main portion (10) hinged to said hub (7) and a tip portion (11′″, 11″″), which is arranged radially outermost with respect to said first axis (A) with respect to the corresponding main portion (10);
• said method comprising the steps of:
• i) connecting said tip portion (11″′, 11″″) in movable way with respect to said main portion (10);
• ii) moving said tip portion (11″′, 11″″) with respect to said main portion (10) between:
• a first angular position, in which it defines a first dihedral or anhedral angle (α) with respect to the corresponding said main portion (10);
• and
• a second angular position, in which it defines a second dihedral or anhedral angle (α) or a null angle, different from said first dihedral or anhedral angle (α), with respect to the corresponding said main portion (10);
• said method being characterized by comprising the steps of selectively:
• iii) allowing the rotation of said tip portion (11″′, 11″″) with respect to said main portion (10) in a first angular direction and up to said first angular position, by means of the resultant moments (Mr) generated by inertia forces and aerodynamic forces on said tip portion (11′″, 11″″);
• and
• iv) preventing said tip portion (11″′, 11″″) from rotating in a second angular direction, opposite to said first direction, with respect to said main portion (10).

A rotor (3, 3′, 3″) for a hover-capable aircraft (1), comprising:

• a hub (7) rotatable about a first axis (A);
• and
• at least two blades (6) hinged to said hub (7);
• each said blade (6) comprising a main portion (10) hinged to said hub (7) and a tip portion (11, 11″), which is arranged radially outermost from said first axis (A) with respect to the corresponding main portion (10);
• said tip portion (11, 11″) of each said blade (6) being movable with respect to the corresponding said main portion (10) of that blade (6) between:
• a first position, in which it defines a dihedral or anhedral angle (α) with respect to the corresponding said main portion (10);
• and
• a second position, in which it defines a positive or negative sweep angle (β) with respect to the corresponding said main portion (10);
• characterized in that each said blade (6) comprises at least two actuating rods (21), which are operatively connected to the respective said tip portion (11, 11″) to cause its transition with respect to the corresponding main portion (10);
• each said actuating rod (21) being rotatable about said second axis (C) and being curved, at least in part, with respect to said second axis (C);
• said tip portion (11, 11″) comprising at least one rib (28) lying on a plane transversal to said second axis (C) and defining a pair of apertures (27), which are engaged in a freely rotatable manner about said second axis (C) by said respective actuating rods (21);
• said ribs (28) maintaining, in use, the respective sections undeformed on planes transversal to said actuating rods (21) during the transition between said first and second positions;
• the sections of said tip portion (11, 11″) interposed between said ribs shear deforming, in use, transversely to said tip portion (11, 11″) during the transition between said first and second positions.

A method of controlling a rotor (3, 3, 3″) for a hover-capable aircraft (1), said rotor (3, 3, 3″) comprising:

• a hub (7) rotatable about a first axis (A);
• and
• at least two blades (6) hinged to said hub (7);
• each said blade (6) comprising a main portion (10) hinged to said hub (7) and a tip portion (11, 11″), which is arranged radially outermost with respect to said first axis (A) with respect to the corresponding main portion (10);
• said method comprising the steps of:
• i) arranging said tip portions of said blades (6) in respective first positions in which they define respective dihedral or anhedral angles (α) with respect to the associated main portions (10), when said aircraft (1) is in hovering conditions;
• ii) arranging said tip portions (11, 11″) of said blades (6) in respective second positions in which they define positive or negative sweep angles (β) with respect to the associated main portions (10), when said aircraft (1) is in forward flight conditions;
• characterized by comprising the steps of:
• iii) housing at least one pair of actuating rods (21) in a rotationally free manner inside respective through apertures (27) in the ribs (28) of said tip portion (11, 11″);
• iv) rotating said actuating rods (21) about a second axis (C) transversal to said first axis (A) to move the associated tip portions (11, 11″) between the corresponding first and second positions;
• v) maintaining the sections of said ribs (28) undeformed in respective planes transversal to said actuating rods (21) during the transition between said first and second positions;
• vi) shear deforming the sections of said tip portions (11) interposed between said ribs (28);
• said actuating rods (21) comprising respective first sections (25) and second sections (26) inclined with respect to the corresponding first sections (25);
• said second sections (26) being housed inside said apertures (27) in a rotationally free manner with respect to said ribs (28);
• and
• said ribs (28) lying on respective planes transversal to said second axis (C).

A rotor (3′, 3″) for a hover-capable aircraft (1), comprising:

• a hub (7) rotatable about a first axis (A);
• and
• at least two blade (6) hinged to said hub (7);
• each said blades (6) comprising a main portion (10) hinged to said hub (7) and a tip portion (11), which is arranged radially outermost from said first axis (A) with respect to the corresponding main portion (10);
• said tip portion (11, 11″) of each said blade (6) being movable with respect to the corresponding said main portion (10) of that blade (6) between:
• a first position, in which it defines a dihedral or anhedral angle (α) with respect to the corresponding said main portion (10);
• and
• a second position, in which it defines a positive or negative sweep angle (β) with respect to the corresponding said main portion (10);
• said main portion (10) of each said blade (6) extending along a second axis (C) transversal to said first axis (A);
• said tip portion (11, 11″) being movable on a plane transversal to said second axis (C) between said first and second positions;
• each said blade (6) comprising at least two actuating rods (21′), which are operatively connected to the respective said tip portion (11, 11″) to cause its transition with respect to the corresponding main portion (10);
• each said actuating rod (21′) being rotatable about said second axis (C) and being curved, at least in part, with respect to said second axis (C);
• characterized in that it comprises at least two selectively operable freewheels (51′) operatively connected to said actuating rod (21′);
• said freewheels (51′) enabling the rotation of said actuating rods (21′) in respective mutually opposite directions, following the aerodynamic action acting on the respective said blade (6).

A method of controlling a rotor (3′, 3″) for a hover-capable aircraft (1), said rotor (3′, 3″) comprising:

• a hub (7) rotatable about a first axis (A);
• and
• at least two blades (6) hinged to said hub (7);
• each said blade (6) comprising a main portion (10) hinged to said hub (7) and a tip portion (11, 11″), which is arranged radially outermost with respect to said first axis (A) with respect to the corresponding main portion (10);
• said main portion (10) of each said blade (6) extending along a second axis (C) transversal to said first axis (A);
• said method comprising the steps of:
• i) arranging said tip portions (11, 11″) of said blades (6) in respective first positions in which they define respective dihedral or anhedral angles (a) with respect to the associated main portions (10), when said aircraft (1) is in hovering conditions;
• ii) arranging said tip portions (11, 11″) of said blades (6) in respective second positions in which they define positive or negative sweep angles (β) with respect to the associated main portions (10), when said aircraft (1) is in forward flight conditions;
• iii) housing at least one pair of actuating rods (21) in a rotationally free manner inside respective through apertures (27) in the ribs (28) of said tip portion (11, 11″);
• and
• iv) rotating said actuating rods (21′) about said second axis (C) transversal to said first axis (A) to move the associated tip portions (11, 11″) between the corresponding first and second positions;
• said method being characterized by comprising the steps of:
• v) operating said actuating rods (21′) by means of the aerodynamic action acting on said tip portions (21) during the rotation of said rotor (3′), at least when said hover-capable aircraft (1) is in forward flight at speeds above a threshold value;
• vi) enabling the rotation of said actuating rods (21′) in respective opposite directions by means of at least two selectively operable freewheels (51′) operatively connected to at least one said rod (21′), and following the aerodynamic action acting on the respective said blade (6).