Rotorcraft rotor comprising a hub made of composite materials obtained from carbon fiber fabric dusted in a thermoplastic resin

Abstract

A rotorcraft rotor comprising a hub made up of a monolithic body of composite material obtained by stacking successive layers of carbon fiber fabric dusted with a thermoplastic resin and compressed while hot. The hub is provided with branches on which respective blades are mounted via hinge systems, each including a strength member bearing radially against a corresponding branch. The strength members are individually received in sockets defined on fabrication so that when the rotor is set into rotation at a predefined operating speed, the radial thrust seat for enabling the strength members to bear against the branches present bearing surfaces that are cylindrical, the radial thrust seats then being of shape complementary to a cylindrical bearing surface of the corresponding strength member.

Claims

1. A rotorcraft rotor having a hub made of composite material obtained by stacking successive layers of mineral fiber fabric that are impregnated with a resin, the hub firstly being mounted coaxially around a rotary shaft extending through a bore in the hub, and secondly including a plurality of branches extending radially from the bore, which branches have respective individual blades mounted thereon, the blades being individually mounted to be movable relative to the hub at least for varying pitch; wherein: the hub is formed essentially by a monolithic body of composite materials obtained by stacking successive layers of carbon fiber fabric dusted with a thermoplastic resin and compressed while hot; the blades are individually mounted to be movable relative to the hub by respective hinge systems, each having a respective assembly strength member for assembling to a respective one of the branches, the strength member bearing radially against the branches while being individually housed at least in part in respective sockets of the monolithic body, extending in its axially-extending direction; and the sockets being deformable under the effect of the rotor being set into rotation, the shape of the sockets is defined on fabrication so as to form a radial thrust seat enabling the strength members to bear against the branches via respective bearing surfaces that become cylindrical under the effect of the rotor being set into rotation at a predefined operating speed, the radial thrust seat having a cylindrical bearing surface extending along a generator line oriented in the axially-extending direction of the hub and being of shape that is complementary to a given cylindrical bearing surface of the strength member.

2. A rotorcraft rotor according to claim 1, wherein the profile of each socket in the diametral plane of the hub is generally oblong in shape, defining a respective circular arc providing the surface portion of the socket that forms the radial thrust seat whereby the strength member bears against the branch; and wherein a first radius of the circular arc as defined by fabrication is greater than a second radius that is imparted to the circular arc under the effect of the rotor being set into rotation at the predefined operating speed, the second radius in the operating situation of the rotor defining the radial thrust seat with a cylindrical bearing surface whereby the strength member bears against the branches.

3. A rotorcraft rotor according to claim 1, wherein the portions of the surfaces of the sockets that form radial thrust seats for enabling the strength members to bear against the branches are free from any tapers for unmolding the monolithic body.

4. A rotorcraft rotor according to claim 1, wherein each strength member has an elastomer/metal laminated body providing multidirectional freedom of movement for the blades on the hub, and the strength members are placed respectively to bear radially against the branches via respective cylindrical bearing surfaces defined by generator lines extending in the axially-extending direction of the hub.

5. A rotorcraft rotor according to claim 1, wherein at least one of the axial end faces of the monolithic body is inclined at least in part relative to the plane of rotation of the hub, and the monolithic body is provided with wedges for compensating the slope that results from the inclination of the at least one axial end face of the monolithic body, the wedges providing axial thrust seats on the hub for enabling the strength members to bear against the branches.

6. A rotorcraft rotor according to claim 5, wherein the wedges are incorporated in the monolithic body by molding.

7. A rotorcraft rotor according to claim 6, wherein the wedges are incorporated more particularly in the monolithic body by overmolding, the wedges being obtained from composite materials incorporating mineral fibers embedded in a thermoplastic resin.

8. A rotorcraft rotor according to claim 1, wherein the blades are also mounted to be movable with lead/lag motion relative to the hub, and the peripheral end faces of each of the branches are provided with respective protector members.

9. A rotorcraft rotor according to claim 8, wherein the protector member may equally well be formed by a wear part and/or by an abutment member limiting the individual lead/lag stroke of a blade.

10. A rotorcraft rotor according to claim 8, wherein each of the protector members is fitted with fastener tabs bearing respectively against the axial end faces of the monolithic body, and being fastened to the peripheral end of the corresponding branch by first fastener members extending through respective first passages provided in the monolithic body in its axially-extending direction.

11. A rotorcraft rotor according to claim 1, wherein the monolithic body is of thickness that decreases progressively from an axially-central zone in which at least the bore is provided, towards the outer margin of a peripheral zone of the monolithic body incorporating the branches.

12. A rotorcraft rotor according to claim 1, wherein the monolithic body is symmetrical on either side of a diametral plane that is an axial midplane.

13. A rotorcraft rotor according to claim 1, wherein the branches project towards the periphery of the monolithic body, and the projecting portions of the branches present a radially-extending dimension lying in the range 0.2 to 0.3 times the outside diameter of the monolithic body, and with reference to a given branch, the distance between the peripheral end of a branch and the radial thrust seat whereby a strength member bears against the branch lies in the range 0.1 to 0.15 times the outside diameter of the monolithic body.

14. A rotorcraft rotor according to claim 11, wherein the monolithic body comprises: the axially-central zone of a constant thickness in which there are provided at least the bore and second passages extending along the axially-extending direction of the hub and distributed in a margin around the bore, the second passages receiving second fastener members for fastening the hub to at least one plate of the rotary shaft placed facing either one of the axial end faces of the hub; and the peripheral zone radially extending the axially-central zone while decreasing progressively in thickness towards its periphery from the thickness of the axially-central zone, the peripheral zone including at least part of each of the sockets for receiving respective strength members and third passages oriented along the axially-extending direction of the hub, the third passages receiving third fastener members fastening the strength members to the hub.

15. A rotorcraft rotor according to claim 12, wherein: the thickness of the monolithic body at its periphery lies in the range 30% to 40% approximately of the thickness of the monolithic body in its axially-central zone; and the outside diameter of the monolithic body lies in the range six to ten times approximately the thickness of the monolithic body in the axially-central zone.

16. A rotorcraft rotor according to claim 10, wherein each of the first passages and/or the second passages and/or the third passages may equally well be provided with a respective reinforcing ring.

17. A rotorcraft rotor according to claim 16, wherein the reinforcing rings are incorporated in the monolithic body by sealing.

18. A rotorcraft rotor according to claim 16, wherein the reinforcing rings are incorporated in the monolithic body by overmolding.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) An embodiment of the present invention is described with reference to the figures of the accompanying sheets, in which:

(2) FIG. 1 is a perspective view of a rotorcraft rotor in an embodiment of the present invention;

(3) FIGS. 2 and 3 are views of an embodiment of a monolithic body essential forming a hub of the rotor shown in FIG. 1, shown respectively in perspective and in axial section; and

(4) FIG. 4 comprises two diagrams (a) and (b) showing, in its general plane, a fragment of the monolithic body shown in FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE INVENTION

(5) In FIG. 1, a rotorcraft G is represented diagrammatically. The rotorcraft G has a rotor. This rotorcraft rotor has blades 1 (only one blade is shown in part) that are mounted on a hub 2. In order to be driven in rotation, the hub 2 is mounted on a rotary shaft 3 extending coaxially through a bore 4 of the hub. Such a rotary shaft 3 is constituted in particular by a mast for the main rotor of a rotorcraft, as shown.

(6) The hub 2 has second passages 5 arranged in a margin around the bore 4, in order to receive second fastener members 6 such as screws or bolts for fastening the hub 2 to at least one plate 7 of the rotary shaft 3.

(7) The blades 1 are mounted on the hub 2 so as to be movable, at least so as to vary in pitch, and possibly also so as to vary in lead/lag and in flapping, as in the embodiment shown. For this purpose, each blade 1 is conventionally provided with a blade root 8 for assembly to a respective branch 9 of the hub 2. In a common embodiment, the blades 1 are made to be movable relative to the hub 2 by means of a hinge system 10 interposed between a given blade root 8 and the hub 2.

(8) In the example shown in FIGS. 1 and 4, such a hinge system 10 is of the type making use of a laminated elastomer/metal body 11 comprising metal laminations and layers of elastomer, and commonly referred to as a spherical thrust bearing. The laminated elastomer/metal body 11 is incorporated in a strength member 12 whereby the hinge system 10 is mounted between a given blade root 8 and the hub 2.

(9) The hub 2 has sockets 13 respectively housing the strength members 12. A given strength member 12 uses bolts to connect a blade root 8 to the hub 2, while bearing axially against the axial end faces of the hub 2.

(10) As shown in FIG. 4, the strength member 12 may for example be of the type comprising at least one said elastomer/metal laminated body 11 interposed between two strength member elements 12, 12. The elastomer/metal laminated body 11 is compressed between the strength member elements 12, 12, an outer strength element member 12 bearing radially against the corresponding branch 9. Consequently, by bearing radially against the hub 2 via its outer strength member element 12, the elastomer/metal laminated body 11 deforms so as to allow the blade root 8 to move relative to the hub 2.

(11) It should be observed at this point that the concept axial, and consequently the concepts diametral and/or radial are to be considered relative of the axis of rotation A of the hub 2. In this context, it should be understood that the thickness of the hub 2 is to be considered along axially-extending direction.

(12) The hub 2 is essentially constituted by a monolithic body 14 made by molding a stack of layers of carbon fiber fabric dusted with a thermoplastic resin, said fabric layers being stacked inside a mold and then compressed while hot and at high pressure.

(13) In FIGS. 1, 2, and 3, the monolithic body 14 has an axially-central zone 15 containing the bore 4 and said second passages 5. Said axially-central zone 15 is extended diametrically by a peripheral zone including the branches 9, at least in part.

(14) As can be seen more particularly in FIG. 3, the monolithic body 14 is symmetrical about a diametral plane P constituting an axial midplane. The axially-central zone 15 of the monolithic body 14 is of constant thickness E1, thereby enhancing thrust engagement of the hub against the plate(s) of the rotary shaft.

(15) The peripheral zone of the monolithic body is of thickness E2 that decreases progressively going towards its periphery from the axially-central zone 15. The thickness E2 of the monolithic body 14, when considered at its periphery, is about 30% to 40% its thickness E1 considered in its axially-central zone 15. As can be seen more particularly in FIG. 3, the outside diameter D of the monolithic body 14 is about eight times its thickness E1 as considered in the axially-central zone 15.

(16) Furthermore, in FIGS. 1 to 4, the sockets 13 provide radial thrust seats 16 with cylindrical bearing surfaces for the strength members 12 to bear against the branches 9, in particular via the elastomer/metal laminated bodies 11 with which they are fitted.

(17) As shown in FIG. 1, the radially-extending dimension d1 of the projecting portions 26 of the branches 9 towards the periphery of the monolithic body 14 lies in the range approximately 0.2 to 0.3 times the outside diameter D of the monolithic body 14, with a separation distance d2 between the peripheral ends of the branches 9 and the radial thrust seats 16 where the strength members 12 bear against the branches 9 lying in the range approximately 0.1 to 0.15 times the outside diameter D of the monolithic body 14, for any given branch 9.

(18) As shown in FIG. 2, the sockets 13 are generally oblong in shape, each defining respective circular arcs AC providing the surface portions of the sockets 13 that form said radial thrust seats 16 via which the strength members 12 bear against the branches 9.

(19) Nevertheless, as shown in FIG. 4, the sockets 13 tend to deform under the effect of centrifugal force when the rotor is set into rotation. More particularly, in diagram (a), the monolithic body 14 is shown when the hub is stationary, whereas in diagram (b) the monolithic body 14 is shown in the situation in which the hub is rotating. As a result of the sockets 13 deforming, the initial radius defined on fabrication for said circular arcs, and as shown in the diagram (a), tends to become smaller so as to match the radius of the surfaces of the strength members 12 that bear radially against the branches 9, as can be seen in diagram (b).

(20) In this context, a first radius R1 of said circular arc AC is defined on fabrication to be greater than a second radius R2 of said circular arc AC as identified under conditions of the rotor rotating at its nominal operating speed. Said first radius R1 for the circular arc AC is identified, in particular by testing, so that by deformation the sockets 13 give said circular arc AC the second radius R2 that is at least substantially equal to the radius of the cylindrical surfaces of the elastomer/metal laminated bodies 11 bearing against the branches 9 via the strength members 12.

(21) Furthermore, and as can be seen more particularly in FIGS. 1 and 2, in order to optimize the thrust surfaces whereby the strength members 12 bear against the branches 9, both radially and axially, it is proposed to ensure that the portions of the surfaces of the sockets 13 that define said respective radial thrust seats 16 whereby the strength members 12 bear against the branches 9 are to be free of any taper.

(22) As can be seen more particularly in FIG. 3, the end faces of the monolithic body 14 are preferably inclined, as mentioned above, so as to reduce the thickness of the branches 9 at the periphery of the hub.

(23) In this context, and as shown in FIGS. 1 to 4, the axial end faces of the monolithic body 14 are provided with wedges 17 for compensating their slope in order to strengthen the axial seat whereby each strength member 12 bears against the hub 2. Such wedges 17 are obtained from composite materials incorporating thermoplastic resin that enables the wedges 17 to be incorporated in the monolithic body 14, in particular during an overmolding operation.

(24) In FIGS. 1 to 3, the monolithic body 14 includes third passages 18 arranged axially through the monolithic body 14 and passing through the wedges 17. Third fastener members 19, such as bolts, extend through the third passages 18 in order to fasten the strength members 12 to the monolithic body 14, via said outer strength member elements 12 connecting the blade roots 8 to the hub 2.

(25) The blades are also mounted to be movable in lead/lag relative of the hub.

(26) In this context, the peripheral end faces of the branches 9 have protector members 20, as may be constituted by wear parts and/or by abutment members for limiting the lead/lag stroke of each blade.

(27) By way of example, such protector members 20 may comprise fastener tabs 21 bearing respectively against the axial end faces of the monolithic body 14.

(28) The protector members 20 are fastened to the monolithic body 14 by first fastener members 22, e.g. such as bolts, extending through first passages 23 formed through the branches 9 at the margins of their peripheries in the radially extending direction of the hub.

(29) Auxiliary wedges 24 may potentially be interposed between the fastener tabs 21 and the axial end faces of the monolithic body 14 in order to compensate for the slopes of the axial end faces of the branches 9.

(30) Such auxiliary wedges 24 are potentially incorporated in the monolithic body 14 during molding, and more particularly during overmolding, by incorporating a thermoplastic resin in the same manner as for the wedges 17 against which the strength members 12 bear axially against the monolithic body 14.

(31) Also by way of example, the auxiliary wedges 24 could each be made of a flexible mass, e.g. made of elastomer, that is compressed to a greater or lesser extent by the first fastener members 22 when installing the protector members 20 on the branches 9. Such flexible masses could possibly be incorporated in the monolithic body 14 and/or the protector member 20.

(32) The various passages 5, 18, and 23 are formed by leaving voids in the monolithic body 14 while it is being molded and by housing reinforcing rings inside said voids, such as reinforcing rings similar to the reinforcing rings 27 that can be seen in the diagrams (a) and (b) of FIG. 4 that are housed inside the third passages 18. The operations of machining the monolithic body 14 can then potentially be limited to machining said voids prior to installing reinforcing rings such as 27 inside the voids by sealing.

(33) In an advantageous variant, the reinforcing rings such as 27 may be incorporated in the hub by overmolding and the operations of machining the monolithic body 14 may then possibly be limited to machining the inside recesses of said reinforcing rings such as 27.

(34) In FIG. 2, there can also be seen a keying member 25 to enable an operator to install the hub 2 on the rotor in a predefined orientation for its axial end faces that face the fastener plate(s) 7 of the rotary shaft 3.