Flexbeam unit for a bearingless or a hinge- and bearingless multi-blade rotor of a rotary wing aircraft

1. A flexbeam unit for a multi-blade rotor of a rotary wing aircraft, the flexbeam unit comprising a plurality of flexbeam elements defining a predetermined number of torsion elements that are connectable with associated rotor blades of the multi-blade rotor, at least one of the predetermined number of torsion elements comprising at least one flexbeam element having an associated longitudinal direction, the at least one flexbeam element comprising a plurality of inner layers of a first fiber reinforced material that are embedded between at least two outer layers of a second fiber reinforced material, the at least two outer layers being composed of main plies comprising unidirectional fibers and the plurality of inner layers defining a cross section profile center in the associated longitudinal direction of the at least one flexbeam element, the cross section profile center being at least substantially composed of interconnected bias plies comprising fibers that are oriented transversely relative to the unidirectional fibers, wherein at least one of the plurality of inner layers comprises at least two curved bias plies that are embedded between at least two substantially plane bias plies and connected with the plane bias plies, the curved bias plies defining associated cavities and having curved sections, wherein the curved bias plies comprise straight sections extending from the curved sections, and wherein the at least one of the plurality of the inner layers comprises at least four main plies that are arranged in the form of axial extensions of the straight sections of the curved bias plies between the plane bias plies.

2. The flexbeam unit according to claim 1 , wherein the first and second fiber reinforced materials comprise glass fiber reinforced material and/or carbon fiber reinforced material.

3. The flexbeam unit according to claim 1 , wherein the first and second fiber reinforced materials are identical.

4. The flexbeam unit according to claim 1 , wherein the cross section profile center defines a torsion weak and shear force resistant area of the at least one flexbeam element.

5. The flexbeam unit according to claim 1 , wherein the interconnected bias plies comprise fibers that are oriented in an angle of about ±45° relative to the unidirectional fibers of the main plies.

6. The flexbeam unit according to claim 5 , wherein the unidirectional fibers are at least substantially arranged along the associated longitudinal direction of the at least one flexbeam element.

7. The flexbeam unit according to claim 1 , wherein two first main plies of the at least four main plies are associated with the straight sections of a first curved bias ply of the curved bias plies, the two first main plies being separated by a first slot and confining the associated cavity defined by the first curved bias ply.

8. The flexbeam unit according to claim 7 , wherein the first slot has a thickness comprised in a range from 0.1 mm to 10 mm.

9. The flexbeam unit according to claim 7 , wherein two second main plies of the at least four main plies are associated with the straight sections of a second curved bias ply of the curved bias plies, the two second main plies being separated by a second slot and confining the associated cavity defined by the second curved bias ply, wherein the first and second slots are in parallel offset with a predetermined offset distance.

10. The flexbeam unit according to claim 1 , wherein the at least two curved bias plies define with the at least two substantially plane bias plies layer cavities that are filled with associated fill material.

11. The flexbeam unit according to claim 10 , wherein the fill material comprises unidirectional fibers, short fibers, oriented fibers, resin and/or foam.

12. The flexbeam unit according to claim 1 , wherein the curved bias plies define a U-shaped, bulb-shaped, clip collar-like shaped or circle sector shaped cross section, wherein the straight section of the clip collar-like shaped cross section extends from the curved section along a slot.

13. The flexbeam unit according to claim 1 , wherein the curved sections are interconnected.

14. The flexbeam unit according to claim 1 , wherein the curved sections are spaced from one another.

15. The flexbeam unit according to claim 1 , wherein the at least two curved bias plies are embedded between at least two intermediate, substantially plane bias plies, each of the at least two intermediate bias plies being connected with one of the at least two substantially plane bias plies, wherein the at least two curved bias plies and the at least two intermediate bias plies are embedded between the at least two substantially plane bias plies such that the at least two curved bias plies are connected with the at least two substantially plane bias plies by means of the at least two intermediate bias plies.

16. A flexbeam unit for a multi-blade rotor of a rotary wing aircraft, the flexbeam unit comprising a plurality of flexbeam elements defining a predetermined number of torsion elements that are connectable with associated rotor blades of the multi-blade rotor, at least one of the predetermined number of torsion elements comprising at least one flexbeam element having an associated longitudinal direction, the at least one flexbeam element comprising a plurality of inner layers of a first fiber reinforced material that are embedded between at least two outer layers of a second fiber reinforced material, the at least two outer layers being composed of main plies comprising unidirectional fibers and the plurality of inner layers defining a cross section profile center in the associated longitudinal direction of the at least one flexbeam element, the cross section profile center being at least substantially composed of interconnected bias plies comprising fibers that are oriented transversely relative to the unidirectional fibers, wherein at least one of the plurality of inner layers comprises at least two curved bias plies that are embedded between at least two substantially plane bias plies and connected with the plane bias plies, the curved bias plies defining associated cavities and having curved sections;

wherein the interconnected bias plies comprise fibers that are oriented at an angle relative to the unidirectional fibers of the main plies, and

wherein the at least two curved bias plies are embedded between at least two intermediate, substantially plane bias plies, each of the at least two intermediate bias plies being connected with one of the at least two substantially plane bias plies, and wherein the at least two curved bias plies and the at least two intermediate bias plies are embedded between the at least two substantially plane bias plies such that the at least two curved bias plies are connected with the at least two substantially plane bias plies by means of the at least two intermediate bias plies.

17. The flexbeam unit according to claim 16 , wherein the unidirectional fibers are at least substantially arranged along the associated longitudinal direction of the at least one flexbeam element.

18. The flexbeam unit according to claim 16 , wherein the at least two intermediate bias plies comprise smaller dimensions than the at least two substantially plane bias plies.

19. A flexbeam unit for a multi-blade rotor of a rotary wing aircraft, the flexbeam unit comprising a plurality of flexbeam elements defining a predetermined number of torsion elements that are connectable with associated rotor blades of the multi-blade rotor, at least one of the predetermined number of torsion elements comprising at least one flexbeam element having an associated longitudinal direction, the at least one flexbeam element comprising a plurality of inner layers of a first fiber reinforced material that are embedded between at least two outer layers of a second fiber reinforced material, the at least two outer layers being composed of main plies comprising unidirectional fibers and the plurality of inner layers defining a cross section profile center in the associated longitudinal direction of the at least one flexbeam element, the cross section profile center being at least substantially composed of interconnected bias plies comprising fibers that are oriented transversely relative to the unidirectional fibers, wherein at least one of the plurality of inner layers comprises at least two curved bias plies that are embedded between at least two substantially plane bias plies and connected with the plane bias plies, the curved bias plies defining associated cavities and having curved sections;

wherein the curved bias plies comprise straight sections extending from the curved sections; and

wherein the at least one of the plurality of inner layers comprises at least four main plies that are arranged in the form of axial extensions of the straight sections of the curved bias plies between the plane bias plies.