GB2059897A

GB2059897A - Helicopter rotor blade-to-hub connections

Info

Publication number: GB2059897A
Application number: GB8031193A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1979-10-02
Filing date: 1980-09-26
Publication date: 1981-04-29
Also published as: FR2466394A2

Abstract

A rotor for a rotary wing aircraft has rotor blades 6 which are hingelessly supported in the rotor head and carried in blade pitch angle bearing assemblies 13 mounted between the legs 2.1 of a fork associated with the rotor head. A connection 8 is provided which takes up blade forces in the longitudinal direction of the blade but which enables the blade pitch to be changed. The blade root extends via an intermediate part 6.1 to the blade angle bearing 13 situated at the root of the blade mounting. An outer annulus 13.1 of the bearing is the central part of a component which is connected to respective sides of the flat legs 2.1 through a bonded elastomeric layer 13.2, 13.3, which yields and absorbs loadings in the plane of the rotor. <IMAGE>

Description

SPECIFICATION A rotor of a rotary wing aircraft This invention relates to a rotor for a rotary wing aircraft wherein the rotor blades are mounted for rotation about a longitudinal axis in blade pitch angle bearings in a central head part having mounting parts for each blade extending radially outward, the central head part comprising an integral structure of a fibrous composite material in which the blade mounting parts have a bifurcated structure with each arm thereof flat and at right angles to the axis of the rotor.

In a rotor blade structure as aforesaid an intermediate part of the shank constitutes a blade root extension which is secured to form a hingeless blade to head connection. With hingeless rotor blades, if the movements of the blade in the drag direction are inadequately damped unstable oscillations may occur, and an object of this invention is to provide a suitable damping system active in the drag direction of the blade without adding appreciably to the complexity.

According to this invention there is provided a rotor for a rotary wing aircraft wherein the rotor blades are mounted on the rotor head in a manner affording adjustment of the angle of pitch through blade pitch angle bearings, blade shank mountings extending radially outwards and being associated with a central head part comprising an integral structure of fibrous composite material in which each blade mounting comprises a fork with the arms thereof flat and at right angles to the axis of the rotor, each blade mounting and the associated rotor blade or shank having a connection which can be subjected to forces in a longitudinal direction of the blade and which provides for blade pitch angle changes, the blade shank extending to the blade pitch angle bearing located on the root of the blade shank by an intermediate shank part which bridges the connection which can be subjected to force, characterised by an outer annulus part of the blade pitch angle bearing forming a central component of an assembly adapted for connection with the blade mounting fork arms through a material of high damping factor which is resilient to movement in the plane of the rotor, the connection being provided between each arm of a fork and the central component.

By means of a damping system integrated with the blade pitch angle bearing the intermediate shank part supported in the blade angle bearing forms a blade root extension, and during blade flexure acts as a lever having a pivot axis parallel to the rotation axis of the rotor located at the connection which can be subjected to force. Movement of the lever in relation to the blade mounting or the legs of the mounting fork leads to deformation of the material having high damping factor provided between the legs of the fork and a part integral with the annulus of the bearing.The magnitude of the deformation or damping force of the connection, which is preferably provided by means of an elastomeric material, is mainly governed by its distance from the pivot axis of the lever, so that if the intermediate part of the shank is of a suitable length a high degree of damping is obtainable with a relatively moderate damping force.

Further features of the invention are described in conjunction with the accompanying drawings showing an embodiment by way of example, and wherein: Figure 1 shows a vertical longitudinal section through a rotor arm and rotor head part at the rotor blade root, and Figure 2 is a section, to a larger scale, taken on line ll-ll of Fig. 1.

For the suspension of the rotor blades in the bifurcated blade mounting 2, the so called rotor arm, of a rotor head, the blade root shank 6 is extended by an intermediate part 6.1 which extends beyond an elastomeric bearing 8 to a radial elastomeric bearing 1 3.

The intermediate part 6.1 can, as shown, be detachably connected to a yoke piece 11 which is supported in the bearing 1 3 by a pin 11.1 to form an integral part of the blade shank 6, or this may equally well be a socket arrangement which is detachable from the shank. The intermediate piece 6.1 is not of itself important in so far as the construction is concerned, but simply enables a damping system coupled to the bearing 1 3 by the outer bearing annulus 13.1 to make use of the principle of force transmission through a leverage law arrangement.In this intermediate part 6.1 forms a lever arm of which the pivot is at the axis 7.1 (parallel to the rotation of the rotor) of the bearing 8 and relatively high forces for shear loading applied to layers 1 3.2 and 13.3 are obtained when the blade root 6 is subjected to flexure about pivot axis 7.1.

The said layers 1 3.2 and 1 3.3 consist of an elastomeric material having a high damping capacity, such as silicon, polyurethane or a rubber composition. For this purpose the outer annulus 13.1 of the bearing 13 forms a central and integral part of an assembly which is integrated with the two flat legs 2. 1 of the blade mounting 2. The central part includes, on both sides, two metal plate structures 1 3.4 each bonded at the sides (for example by vulcanization) with an elastomeric layer 1 3.2 further bonded to a metal outer plate 13.5 connected with respective legs 2.1. Additionally a connection is provided between the plates 13.5 and the two legs 2.1, by means of two bolts 13.6, each of which extends between the legs.The bolts pass through the outer plates 1 3.5 without clearance, but have a clearance fit through plates 13.4 at 13.7.

This clearance is governed by the maximum required deflection of elastomeric layers 13.2.

It is thus possible for the intermediate part 16.1 of the blade shank 6 or the outer annulus 1 3.1 of the bearing 1 3 to move in relation to the blade mounting 2 in the leadlag swing direction of the blade and over a distance corresponding to the clearance 1 3.7 between the bolts 1 3.6 and the plates 1 3.4 of the outer annulus 1 3.1, with this movement being accompanied by shear deformation of the elastomeric layers 13.2. The blade movements about the pivot axis 7.1 are thus damped.In order to increase the damping effect it is a preferable feature (see Fig. 2) for the plates 1 3.4 to be divided in a region extending beyond the bolts 13.6, so that two further elastomeric layers 13.3, with a metal intermediate plate 13.9, fit into the division 13.8. Each bolt 1 3.6 also passes without clearance through the intermediate plates 13.9, whilst the slits 1 3.8 have at the bases a gap 1 3.10 of which the width corresponds to the maximum deflection of the elastomeric layers 13.3. A bonded connection is provided between the elastomeric layers 1 3.3 and respective plates 13.9, and between the respective plates 13.4. A pivoting movement of the intermediate part 6.1 in the plane of the rotor blades will cause also a shear deformation of the elastomeric layers 13.3, and thus damping of the blade pivoting movement.

The invention thus provides, by using a number of elastomeric connections which take effect together between the outer annulus 1 3.1 or plates 1 3.4 integral therewith, and the respective legs 2.1 of the blade mounting 2 with the use of the bolts 13.6, an effective damping system for blade pivoting movements, in addition to fulfilling the requirement that the elastomeric bearing 1 3 should be removable and replaceable without difficulty.

If necessary, further elastomeric connections can be provided on a similar principle between the outer annulus 13.1 of the bearing and the legs 2.1.

Claims

1. A rotor for a rotary wing aircraft wherein blade shank mountings extend radially outwards from a central head part, each blade mounting and the associated rotor blade or shank having a connection which can be subjected to force in a longitudinal direction of the blade and which provides for blade pitch angle changes, the blade shank extending to a bearing located at the root of the blade shank and forming an intermediate shank part which bridges the connection which can be subjected to force, and the bearing forming a central component of an assembly connected with the blade mounting through a material of high damping factor which is resilient to movement in the plane of the rotor.

2. A rotor for a rotary wing aircraft wherein the rotor blades are mounted on the rotor head in a manner affording adjustment of the angle of pitch through blade pitch angle bearings, blade shank mountings extending radially outwards and being associated with a central head part comprising an integral structure of a fibrous composite material in which each blade mounting comprises a fork with the arms thereof flat and at right angles to the axis of the rotor, each blade mounting and the associated rotor blade or shank having a connection which can be subjected to forces in a longitudinal direction of the blade and which provides for blade pitch angle changes, the blade shank extending to the blade pitch angle bearing located on the root of the blade shank by an intermediate shank part which bridges the connection which can be subjected to force, characterised by an outer annulus part of the blade pitch angle bearing forming a central component of an assembly adapted for connection with the blade mounting fork arms, through a material of high damping factor which is resilient to movement in the plane of the rotor, the connection being provided between each arm of a fork and the central component.

3. A rotor in accordance with Claim 1 or 2, wherein the material having a high damping factor is deformable and comprises an elastomeric material.

4. A rotor in accordance with Claims 2 or 3, wherein plates are integral with the annulus part of the bearing on both sides of the blade mounting and include a bonded eiastomeric material connected with a further plate forming the connection with respective arms.

5. A rotor in accordance with Claim 4, wherein connection between the further plates and the fork arms is provided by bolts which extend between the arms and which pass through said plates without clearance, and through the plates of the annulus with clearance determined by the maximum required deformation of the elastomeric material.

6. A rotor in accordance with Claim 4 or 5, wherein each plate integral with the annulus part of the bearing is divided in a region extending beyond the bolts, each division housing an intermediate plate with elastomeric material bonded thereto, the bolts passing through the plates without clearance, clearance being provided between the closed end of the division and the plate end, the clearance being determined according to the maximum required deformation of the elastomeric material.

7. A rotor head structure for a rotary wing aircraft constructed and arranged to function substantially as herein described with reference to the accompanying drawings.