Rotorcraft tail rotor, a rotorcraft fitted with such a tail rotor, and a method of statically and/or dynamically balancing a rotorcraft tail rotor

Abstract

A rotorcraft tail rotor comprising at least two blade elements, each blade element being suitable for pivoting about a collective pitch variation axis Z in order to vary the collective pitch of each blade element of the tail rotor, each blade element including at least one compensation weight comprising a projection emerging substantially perpendicularly to a main inertia axis of the blade element, the main inertia axis being parallel to a longitudinal direction of the blade element. In the invention, the tail rotor is wherein the compensation weight includes a deformable portion that is movable relative to the projection in a plane P that is parallel to the main inertia axis of the blade element.

Claims

1. A rotorcraft tail rotor comprising at least two blade elements, each blade element having a chord and being suitable for pivoting about a collective pitch variation axis Z in order to vary the collective pitch of each blade element of the tail rotor, each blade element including at least one compensation weight comprising a projection extending transverse to the chord of the blade element along a transverse axis Y that is substantially perpendicular to the chord of the blade element, the projection being fixed relative to the blade element; wherein the at least one compensation weight includes a deformable portion that is movable relative to the projection in a plane P that is substantially perpendicular to the transverse axis Y and substantially parallel to the chord of the blade element.

2. The tail rotor according to claim 1, wherein the projection is solid and the deformable portion comprises a flyweight that is movable in rotation at least in part about the transverse axis Y.

3. The tail rotor according to claim 1, wherein the deformable portion comprises a flexible strip.

4. The tail rotor according to claim 3, wherein the flexible strip emerges from the projection in a radial direction relative to the axis of rotation of the rotor.

5. The tail rotor according to claim 3, wherein the flexible strip comprises: a first end secured to the projection by a first joint of the rigid type; and a second end secured to the flyweight by a second joint of the rigid type.

6. The tail rotor according to claim 1, wherein the deformable portion comprises a rigid arm.

7. The tail rotor according to claim 6, wherein the rigid arm comprises: a first end constrained to revolute joint with the projection; and a second end secured to the flyweight by a joint of the rigid type.

8. The tail rotor according to claim 1, wherein the deformable portion has a length lying in the range 0.05 m to 0.09 m.

9. The tail rotor according to claim 1, wherein the flyweight has a weight lying in the range 100 g to 200 g.

10. A rotorcraft including a tail rotor according to claim 1.

11. A method of statically and dynamically balancing a rotorcraft tail rotor comprising at least two blade elements, each blade element having a chord and including at least one compensation weight comprising a projection extending transverse to the chord of the blade element along a transverse axis Y that is substantially perpendicular to the chord of the blade element, the projection being fixed relative to the blade element; wherein the method comprises a step in which the at least one compensation weight is fitted with a deformable portion that is movable relative to the projection in a plane P that is substantially parallel to the chord of the blade element and substantially perpendicular to the transverse axis Y.

12. A rotorcraft tail rotor comprising: at least two blade elements, each of the blade elements having a chord and being pivotable about a collective pitch variation axis Z to vary the collective pitch of each of the blade elements of the tail rotor, each of the blade elements including a compensation weight comprising a projection extending along a transverse axis Y substantially perpendicular to the chord of a respective one of the blade elements, the projection being fixed relative to the blade element; the compensation weight including a deformable portion movable relative to the projection in a plane P that is substantially perpendicular to the transverse axis Y and substantially parallel to the chord of the respective blade element.

13. The tail rotor according to claim 12, wherein the projection is solid and the deformable portion is movable in rotation relative to the projection at least in part about the transverse axis Y.

14. The tail rotor according to claim 12, wherein the deformable portion comprises a flexible strip and a flyweight.

15. The tail rotor according to claim 14, wherein the flexible strip extends from the projection to the flyweight in a radial direction relative to the axis of rotation of the rotor, the flyweight being movable in rotation relative to the projection at least in part about the transverse axis Y.

16. The tail rotor according to claim 14, wherein the flexible strip comprises: a first end secured to the projection by a first rigid joint; and a second end secured to the flyweight by a second rigid joint.

17. The tail rotor according to claim 12, wherein the deformable portion comprises a rigid arm.

18. The tail rotor according to claim 17, wherein the rigid arm comprises: a first end constrained to revolute joint with the projection; and a second end secured to the flyweight by a rigid joint.

19. The tail rotor according to claim 12, wherein the deformable portion has a length of 0.05 m to 0.09 m.

20. The tail rotor according to claim 12, wherein the flyweight has a weight of 100 g to 200 g.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the context of the following description of embodiments given by way of illustration and with reference to the accompanying figures, in which:

(2) FIG. 1 is a perspective view of a blade element in a first variant of compensation weights of the invention;

(3) FIG. 2 is a cross-section view in a first plane yOz perpendicular to a deformation plane P of the deformable portion and showing compensation weights in a second variant of the invention; and

(4) FIG. 3 shows a cross-section view in a second plane xOy perpendicular to the deformation plane P of the deformable portion and showing a compensation weight of the second variant of the invention.

(5) Elements present in more than one of the figures may be given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(6) It should be observed that three mutually orthogonal directions X, Y, and Z are shown in FIGS. 1, 2, and 3.

(7) As shown in FIG. 1, the direction of the axis Z is referred to as longitudinal insofar as it corresponds to the direction in which the longest dimension of a blade element 1 lies. Thus, the term length is used below relative to a longitudinal dimension of the blade element 1 of the rotor in said longitudinal direction of the axis Z. In addition, as a result of the shape of said rotor, a first main inertia axis 5 of said blade element 1 is parallel to the longitudinal direction of the axis Z.

(8) The two other directions along the axes X and Y are said to be transverse. The axes X and Z serve in particular to describe a plane P in which a deformable portion of a compensation weight is free to move.

(9) As shown, each blade element 1 comprises two compensation weights 2, each comprising a respective projection 4 extending from the plane P that is substantially perpendicular to the main inertia axis 5.

(10) In this variant of FIG. 1, a deformable portion 6 of the compensation weight 2 comprises a flexible strip 7 having a first end 9 that is secured to the projection 4 and a second end 10 that is secured to a flyweight 8. Such a flyweight 8 can then make a rotary movement in the plane P. In other words, the flyweight 8 is secured in revolute joint of axis Y relative to the projection 4 of the blade element 1.

(11) The flyweights make it possible to produce static and dynamic torque in the same direction around the pitch axis. Thus, it is advantageous to fit the deformable portions of the compensation weights with angular abutments that are useful in particular when stopped in order to avoid interference with the rudder bar being operated while starting or stopping stages of the rotorcraft.

(12) As shown in FIG. 2, and in another variant of the invention, the deformable portion 16 may present another shape and, for example, it may comprise a rigid arm 17 having its first end 19 pivotally connected to a projection 14 of the compensation weight 12 so as to pivot about the axis Y. Such a revolute joint may in particular be provided by means of a bearing such as a ball-bearing or a bronze bushing in order to limit friction.

(13) As shown, these projections 14 emerge substantially perpendicularly to a main inertia axis 15. In addition, a pin may be screw-fastened in the projections 14 to form the axis of the revolute joint between the rigid arm 17 and each projection 14.

(14) The second end 20 of the rigid arm 17 is secured to a flyweight 18. As shown diagrammatically in FIG. 2, such a flyweight 18 can form a single-piece unit together with the rigid arm 17.

(15) However, in other variants (not shown), it may also be envisaged to enable the flyweight 18 to be replaced independently of the rigid arm 17. Under such circumstances, reversible securing means, such as screws or bolts are used to form the rigid-type joint between the flyweight 18 and the rigid arm 17.

(16) As shown in FIG. 3, only one of the projections 14 of the blade element 11 needs to be fitted with a deformable portion 16. In the invention, it is possible to adapt the number, the shape, the weight, the length, and the position of the deformable portions of a blade element so as to make it possible to attenuate vibration at various frequencies and in particular at frequencies corresponding to those of the speed of rotation of the tail rotor.

(17) By way of example, by using a length of rigid arm that is substantially equal to the length of the spacing corresponding to the distance between the axis of the revolute joint of the arm and the axis of the revolute joint of the blade element, certain kinds of vibration can be attenuated. As a result, the forces in the pitch rod of each blade element are significantly reduced with, for example, a reduction of about 30%.

(18) In addition, with suitable deformable portions and under steady conditions it is possible to obtain efficiency that is twice that obtained using conventional Chinese weights. Consequently, it is possible to reduce the overall weight of the rotor and the induced dynamic forces.

(19) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described, it should readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.