Rotorcraft rotors having twistable blades

Abstract

The invention relates to a rotorcraft rotor (10) comprising a hub (25, 26, 28), a first blade (13) having a first twistable structure (21) secured to the hub by a first bolt (32) and a first ring (34) or washer (35), a second blade having a second twistable structure secured to the hub by a second bolt and a second ring or washer; the rotor includes stop means for preventing each ring or washer from turning relative to the hub or relative to the corresponding twistable structure.

Description

The present invention relates to an improvement to rotorcraft rotors having twistable blades.

FIELD OF THE INVENTION

The technical field of the invention is that of manufacturing helicopters.

The invention applies in particular to a helicopter rotor having a plurality of blades secured to the hub of the rotor, each blade having an internal portion (or root) sometimes referred to as a twistable bundle or arm that is elongate along the longitudinal axis of the blade and that presents great capacity for elastic deformation in twisting about said axis, thereby enabling the pitch of the blade to be adjusted in spite of said twistable root being rigidly secured to the hub.

BACKGROUND OF THE INVENTION

Such a rotor is described in particular in French patent FR 2 685 675 and U.S. patient U.S. Pat. No. 5,330,322.

The invention applies more particularly to a rotor of that type in which the twistable structure is secured to the hub by clamping the twistable structure between two parts of the hub, using a bolt associated with a washer or ring for transmitting a clamping force.

It has been found that under certain circumstances, during tightening of the nut and/or the bolt, the washer or ring can be caused to turn due to friction against the nut, and that this turning can lead to harmful deformation of the portion of the twistable structure through which the bolt extends, this deformation being more accentuated when the twistable structure is thin.

OBJECTS AND SUMMARY OF THE INVENTION

The invention seeks to solve that problem.

Another object of the invention is to provide such rotorcraft rotors that are improved and/or that remedy, at least in part, the shortcomings or drawbacks of known rotorcraft rotors.

The invention provides for fitting such a rotor with stop means to prevent the ring or washer from turning relative to the hub part or relative to the twistable structure.

Thus, in an aspect of the invention, a rotorcraft rotor is provided comprising a hub, a first blade having a first twistable structure secured to the hub by a first bolt and a first ring or washer, and a second blade having a second twistable structure secured to the hub by a second bolt and a second ring or washer; the rotor further comprising stop means for preventing each ring or washer from turning relative to the hub or relative to the corresponding twistable structure.

In preferred embodiments of the invention:

the stop means comprise an abutment secured to the hub and forming part of the connection means serving to secure the second twistable structure of the second blade to the hub; in particular, said abutment is essentially constituted by the second bolt;

the second washer fitted to the second bolt is rigidly secured to the first washer fitted to the first bolt;

said first and second blades are adjacent;

said first and second washers are formed by a thin plate pierced by two orifices that are spaced apart by a distance corresponding to the distance between the axes of the first and second bolts;

each twistable structure is secured to the hub by a bolt, by a ring for transmitting clamping force to the twistable structure, and by a washer bearing against the ring, each twistable structure comprising a plurality of metal strips in a stack; and

the rotor includes at least one third blade having a third twistable structure secured to the hub by a third bolt and a third ring or washer, the angles formed by each adjacent pair of blades being unequal.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, characteristics, and advantages of the invention appear from the following description which refers to the accompanying drawings that show preferred embodiments of the invention without any limiting character.

FIG. 1 is a cutaway face view of a helicopter antitorque rotor of the invention.

FIG. 2 is a fragmentary section on II-II of the rotor shown in FIG. 1.

MORE DETAILED DESCRIPTION

The rotor 10 shown in FIGS. 1 and 2 comprises a shaft 11 extending along an axis 12 of rotation. The shaft is hollow and receives a control mechanism (not shown) for varying the pitch of the rotor blades.

The rotor has blades, such as the blade referenced 13, with respective longitudinal axes 14 to 17 extending radially relative to the axis 12 in a plane that is orthogonal to the axis 12.

The angles in this plane, such as angles 18 and 19 in FIG. 1, between the respective longitudinal axes of two consecutive blades have values that are not equal.

Each of the blades, and in particular the blades 13, is secured to the rotor hub by means of a bearing 20 that allows the blade to pivot about its longitudinal axis 14, thus allowing the pitch of the blade to be changed by a control rod 24, and by a twistable structure 21 having an outer portion 22 rigidly connected to the hub, as described below.

Each twistable structure comprises a plurality of metal strips stacked along an axis substantially parallel to the axis 12; each strip is elongate in shape along the longitudinal axis of the blade, and extends substantially in a plane perpendicular to the stacking axis.

The rotor hub has a main part 25 carrying the bearings 20, and secured to the shaft 11 by means of a flange 26 provided with fluting 27 for transmitting drive.

The hub also includes a second flange 28 facing the flange 26; each of these two flanges is pierced by orifices 29, 30 in an angular distribution around the axis 12 common to the flanges and to the shaft, which angular distribution is identical to that of the blades around said axis 12.

In order to secure the structure 21 to the hub, a fastener 31 is used that comprises a bolt 32 and a nut 33, the shank of the bolt extending through four orifices in alignment pierced respectively through the part 25, the flange 26, the inner end 23 of the structure 21, and the flange 28, as can be seen in FIG. 2 in particular.

An annular bushing (or ring) 34 and a washer 35 are engaged around the bolt; the washer 35 serves to transmit the clamping force of the fastener from the nut 33 to the bushing 34. The bushing 34 serves to transmit the clamping force from the washer 35 to the structure 21, 23 in order to rigidly secure the structure 21, 23 to the flange 26 of the hub.

The ring 34 is mounted to slide along the axis 42 of the bolt, in the orifice 30 pierced through the flange 28; this flange is secured to the flange 26 by bolts 51 and a nut 50 screwed on the end of the shaft 11.

The function of the ring 34 is to take up the mounting clearance between the flanges 26 and 28, but without inducing interfering forces in the flange 28.

By preventing the washer 35 from turning, the washer 35 is prevented from turning the ring 34 about the axis 42 while the nut 33 is being tightened.

As shown in FIG. 1 in particular, the washer is formed by a thin plate or strip 52 that is elongate along a circular arc 36, having longitudinal edges extending along other circular arcs 37 and 38; these arcs 36 to 38 share a common center on the axis 12; the washer 35 presents two rounded end portions 39 and 40 presenting respective arcs interconnecting the arcs 37 and 38; the overall shape of the washer is roughly that of a kidney bean.

The washer 35 is pierced by two identical orifices 41 of respective axes 42 and 43 that are parallel to the axis 12 and that intersect the axes 14 and 15 respectively of two adjacent blades of the rotor.

In a variant that is not shown, the plate 52 acting as the multiple washer can be pierced by as many orifices 41 for passing screws 32 as there are blades on the rotor.

Claims

1. A rotorcraft rotor (10) comprising a hub (25, 26, 28), a first blade (13) having a first twistable structure (21) secured to the hub by a first bolt (32) and a first ring (34), a second blade having a second twistable structure secured to the hub by a second bolt and a second ring, each twistable structure comprising a plurality of stacked metal strips, said first and second blades being adjacent, wherein: the first twistable structure is secured to the hub by the first bolt, by a washer (35) serving to transmit clamping force to the first ring, the washer bearing against the first ring, and by the first ring transmitting clamping force to the first twistable structure; the second twistable structure is secured to the hub by the second bolt, by said washer (35) serving to transmit clamping force to the second ring, the washer bearing against the second ring, and by the second ring transmitting clamping force to the second twistable structure; and said washer being formed by a thin plate pierced by two orifices spaced apart by a distance corresponding to the spacing between the axes of the first and second bolts; whereby the shank of a blade-fastener forms an abutment preventing the washer from turning relative to the hub or relative to the corresponding twistable structure.

2. A rotor according to claim 1, including at least one third blade having a third twistable structure secured to the hub by a third bolt and a third ring or washer, and in which the angles (18, 19) formed by each adjacent pair of blades are unequal.

3. A rotor according to claim 1, in which each of the blades is secured to the hub of the rotor via a bearing (20) allowing the blade to pivot about its own longitudinal axis (14), thus enabling the pitch of the blade to be modified, and by a twistable structure (21) having an inner portion (23) rigidly secured to the hub, which rotor comprises: a shaft (11) extending along an axis (12); a main hub part (25) carrying the bearings (20) and secured to the shaft (11) via a first flange (26) having fluting (27) for transmitting drive; and a second flange (28) extending in register with the first flange (26); each of the two flanges being pierced by orifices (29, 30) in an angular distribution about the axis (12) common to the flanges and to the shaft, which angular distribution is identical to that of the blades about said axis (12), each bolt (32) having a shank extending through four aligned orifices formed respectively in the part (25), in the flanges (26, 28), and in the inner end (23) of the structure (21), a ring (34) and a washer (35) being engaged about each bolt.