GB2122156A

GB2122156A - A counter-torque rotor for helicopters

Info

Publication number: GB2122156A
Application number: GB08315196A
Authority: GB
Inventors: Emilio Pariani
Original assignee: Costruzioni Aeronautiche Giovanni Augusta SpA
Current assignee: Agusta SpA
Priority date: 1982-06-18
Filing date: 1983-06-02
Publication date: 1984-01-11
Also published as: FR2528794B1; GB8315196D0; IT8267778A0; FR2528794A1; GB2122156B; IT1156055B; JPS5963299A; DE3320081A1; JPH0356960B2

Abstract

A counter-torque rotor (1) for helicopters, in which a central hub (2) has two opposite arms constituted by plates (12) the end of each of which is engaged within an associated fork element (3) for attachment to an associated blade; the coupling between each said plate (12) and the associated fork element (3) being formed by means of an elastomeric bearing (32) and a ball joint (17). <IMAGE>

Description

SPECIFICATION A counter-torque rotor for helicopters The present invention relates to a countertorque rotor for helicopters.

In general, counter-torque rotors in use until now have comprised a tubular hub centrally keyed onto a transverse drive axis and closed at the opposite ends by plugs of elastomeric material.

Each of these latter serves as a pivotal connection for a tie rod which projects from the associated end of the hub and is pivotally connected to an associated blade. This latter has a tubular attachmentfoot keyed onto an associated tubular end of the hub with the interposition of a bush of elastomeric material.

In the above described rotors the hub has been chosen to be of tubular form for the purpose of conferring rigidity to the whole structure; however, it has been established that precisely because of its rigidity the structure of the said known counter-torque rotors broke down following continuous pitch variations. This occurred because the critical frequency of these rotors varied with the pitch variation, with the continuous danger that at some time forced vibrations would be initiated, which in a very short time would lead to the blades breaking off.

The object of the present invention is that of providing a counter-torque rotor which will be free from the disadvantages described above and, further, will have a simpler and more economical structure than the said known rotors.

The said object is achieved by the present invention in that it relates to a counter-torque rotor for helicopters comprising a hub for attachment to a drive shaft, the hub being provided with two arms extending transversely of the axis of the said drive shaft and on opposite sides of a central portion of the said hub, and each said arm engaging an associated fork element for attachment to an associated blade, characterised by the fact that each said arm is constituted by an elongate plate the major axis of which is substantially coincident with an axis of pitch variation of the associated said blade, and lying substantially perpendicular to the said drive shaft; each said fork element being of tubular form, being keyed on the associated said plate, and being coupled at an intermediate point thereof by means of a ball joint, and at a free end thereof by means of a cylindrical pivot preferably constituted by a cylindrical elastomeric bearing, the axis of which is substantially coincident with the said axis of pitch variation of the associated said blade.

Further characteristics and advantages of the present invention will become apparent from the following description with reference to the attached drawings, which illustrate a non limitative embodiment thereof, in which: Figure lisa plan view, with parts in section and parts removed for clarity, of a counter-torque rotor formed according to the principles of the present invention; and Figure 2 is a section taken on the line Il-Il of Figure 1.

In Figure 1 there is illustrated a counter-torque rotor for helicopters, generally indicated 1 and comprising a central hub 2 supporting two fork elements 3, connected thereto, which fork elements can be each connected to an associated blade not illustrated.

The hub 2 includes a central portion constituted by a tubular body 4 closed at its opposite ends by two plugs 5 and having a radial hole 6. Within the tubular body 4 there is mounted a coupling shaft 7 provided centrally with a splined transverse hole 8 connectable to a splined end of a drive shaft 9 fixed to the shaft 7 by means of a nut 10.

The opposite ends (not illustrated) of the shaft 7 are threaded and extend slidably through respective axial holes (not illustrated) formed in the plugs 5, from which they project to be engaged by respective nuts 11, by acting on which it is possible transversely to displace the axis of the drive shaft 9 along the axis of the shaft 7.

The hub 2 further includes two arms 12 constituted by respective plates having in plan a substantially rectangular elongate form and a diametral attitude with respect to the tubular body 4. The said plates 12 are slightly tapered towards their free ends and are disposed with their major axes parallel to one another and oblique with respect to the axis of the tubular body 4 and each substantially coincident with the axis of pitch variation of the associated blade (not illustrated).

Each plate 12 has, in its central portion, a through hole 1 3 the axis of which is substantially parallel to the axis of the drive shaft 9. Within each hole 13 is fixably embedded a ring 14 internally limited by a partly spherical surface defining a seat 15 for a knee joint 16 of a ball joint 17 which connects the said plate 12 to the associated fork element 3. This latter has at its end facing the cylindrical body 4 two axial projections 1 8 parallel to one another and facing one another, which are disposed on opposite sides of the associated plate 12 and have respective through holes 1 9 coaxial with one another.

As illustrated in Figure 2, each knee joint 16 has a diametral through hole 20 through which extends a tubular pin 21 a flanged end of which engages one of the holes 1 9 and another end of which engages the other of the holes 1 9. The tubular pin 21 is coupled externaliy to two tubular spacers 22 each of which engages at one end with the lateral surface of the knee joint 1 6 and at the other with one of the holes 1 9.The assembly comprising the ball 1 6 and the two spacers 22 between the projections 1 8 is secured by means of a screw 23 the head of which is disposed in contact with the flanged end of the tubular pin 21 and the threaded free end of which is coupled to a nut 24 cooperating with the other end of the pin 21 and with one of the spacers 22 with the interposition of a washer 25.

Each fork element 3 is of substantially tubular form and has an axial cavity 26 engaged by an end section of the associated plate 12 and closed outwardly by a bottom wall 27. From this latter extend outwardly two plates 28 which face one another and which have holes 29 for receiving fixing pins (not illustrated) of an associated blade (not illustrated).

To the outer surface of the wall 27 is fixed, by means of screws 30, an attachment flange 31 of a cylindrical elastomer bearing 32 the axis of which is substantially coincident with the pitch change axis of the associated blade. Each bearing 32 comprises an outer cover 33 extending through an axial through hole 34 of the wall 27, and an inner sleeve 35 coaxial with the casing 33 and coupled to it by means of an axially pierced cylindrical plug 36 made of elastomeric material. Within the inner sleeve 35 is slidably mounted a pin 37 an outer end 38 of which is threaded and projects through the flange 31 for connection to a clamping nut 39, and an inner end of which carries a U-shape bracket 40 connected thereto, which embraces the free end of the associated plate 12 and is fixed to it by means of two bolts 41.

Outwardly from each fork element 3 extends a substantially transverse arm 42 provided at its free end with a fork 43 disposed facing an associated nut 11 and having two holes 44 for mounting a pin (not illustrated), the axis of which is substantially perpendicular to that of the shaft 7 for the connection of a pitch control link (not illustrated).

From the preceding description it will be immediately apparent how the structure of the rotor 1 described, being free from attachment tie rods for the blades and support bushes for the terminal fork elements, is decisively simpler than that of the above described known rotors.

Further, the tubular structure of the fork elements 3 permits all the connection elements between the hub 2 and the blades to be protected against the action of impacting bodies.

In the rotor 1, the distribution of forces is also more uniform in comparison with that of the previously described known rotors. In fact, in the rotor 1, the moments due to a pitch change are practically not transmitted to the hub 2 in that they are absorbed both by the elastomeric bearings 32 and by the ball joints 1 7.

Consequently the plates 12 are stressed, in use, almost exclusively by driving tensions due to the bending moments which are transmitted through the elastomeric bearings 32, and to the centrifugal forces which are transmitted through the ball joints 17.

Finally, and importantly, the hub 2 having arms constituted by plates 12, has less rigidity than that of the known tubular hubs previously described and varies with the variation in the plane of flexure. In other words, the hub 2 behaves as an anisotropic body so that the risk of the initiation of vibrations upon pitch variation of the blades is reduced substantially to zero.

Claims

1. A counter-torque rotor for helicopters, comprising a hub for attachment to a drive shaft, the hub being provided with two arms extending transversely of the axis of the said drive shaft on opposite sides of a central portion of the said hub, and each said arm engaging an associated fork element for attachment to an associated blade, characterised by the fact that each said arm is constituted by an elongate plate the major axis of which is substantially coincident with an axis of pitch variation of the associated said blade and lies substantially perpendicular to the said drive shaft each said fork element being of tubular form, being keyed onto the associated said plate, and being coupled at an intermediate point thereof by means of a ball joint, and at a free end thereof by means of a cylindrical pivot the axis of which is substantially coincident with the said axis of pitch variation of the associated said blade.

2. A rotor according to Claim 1, characterised by the fact that the said cylindrical pivot is constituted by a cylindrical elastomeric bearing.

3. A rotor according to Claim 1 or Claim 2, characterised by the fact that each said fork element has an axial cavity engaged by the associated said plate; the said elastomeric bearing being mounted through a bottom wall of the said cavity and being interposed between the said bottom wall and a pin extending axially from the free end of the associated said plate.

4. A rotor according to Claim 3, characterised by the fact that each said pin is connected to the end of the associated said plate by means of a U-shape bracket.

5. A rotor according to any of the preceding Claims, characterised by the fact that the said ball joint comprises a ball rotatably mounted within a spherical seat formed through the associated said plate; the said ball being traversed diametrally by a support pin extending between two axial projections of the associated said fork element and connected thereto.

6. A counter-torque rotor for helicopters substantially as described and with reference to the attached drawings.