GB2148819A

GB2148819A - Helicopter countertorque rotor assembly

Info

Publication number: GB2148819A
Application number: GB08426452A
Authority: GB
Inventors: Emilio Pariani
Original assignee: Costruzioni Aeronautiche Giovanni Augusta SpA
Current assignee: Agusta SpA
Priority date: 1983-10-26
Filing date: 1984-10-19
Publication date: 1985-06-05
Also published as: GB8426452D0; FR2554079A1; JPS60166596A; DE3437811A1; IT8368109A0; IT1161531B

Abstract

Helicopter countertorque rotor assembly (1) on which a hollow drive shaft (2) projecting from a drive box (3) houses a pitch-change control shaft (23) mounted in axially-sliding manner inside the drive shaft (2) and angularly integral with the same by means of external calipers (34); one end of the control shaft (23) projecting from the drive box (3) and being connected in rotary manner to a pitch-change servocontrol (53) by means of thrust bearings (41) outside the drive shaft (2) and drive box (3). <IMAGE>

Description

SPECIFICATION Helicopter countertorque rotor assembly The present invention relates to a helicopter countertorque rotor.

On helicopter countertorque rotors, a hollow drive shaft is known to be employed, the said shaft being supported in rotary manner at one end by a casing housing drive components for transmitting rotation to the said drive shaft. The latter is fitted on its free end with a hub, usually provided with two or more variable-pitch, radial blades. On known types of countertorque rotors, blade pitch is controlled by a shaft extending inside and projecting from the free end of the said tubular drive shaft, so as to support a plate the outer rim of which is connected to each blade by a pitchchange connecting rod.

At the end opposite the one connected to the said plate, the said control shaft is connected to the output of a servocontrol designed to impart axial displacement on the control shaft, the said displacement being transmitted to the blades by means of the said connecting rods for determining the required pitch variation.

On known types of countertorque rotors, the said control shaft is usually divided into two parts, the first connected to the said servocontrol and angularly fixed, and the second turning together with the drive shaft. The said two parts are usually connected to each other by a coupling comprising a thrust bearing designed to render the said two parts axially integral, while at the same time allowing them to turn in relation to each other round their own axes.

The aforementioned known types of countertorque rotors involve a number of drawbacks, mainly due to a more or less long section of the control shaft being mounted angularly fixed in relation to the casing supporting the drive shaft, and on account of the location of the said thrust bearing.

To be more precise, the said angularly-fixed section of the control shaft is usually supported inside the drive shaft by bearings the working life of which is relatively short on account of the strain they are subjected to, both circumferential, caused by the relative rotation of the said control shaft section in relation to the drive shaft, and axial, caused by axial displacement of the control shaft in relation to the drive shaft. As for the thrust bearing, this is normally located inside the said casing or drive shaft, in such an inaccessible position as to make immediate inspection impossible and routine maintenance or replacement extremely troublesome.

The aim of the present invention is to provide a helicopter countertorque rotor involving none of the aformentioned drawbacks.

With this aim in view, the present invention relates to a helicopter countertorque rotor assembly comprising a drive box, a tubular drive shaft projecting from and turning in relation to the said box, a rotor fitted on the free end of the said drive shaft, a pitch-change control shaft partially housed inside the said drive shaft, a servocontrol for imparting pitch-change axial displacement on the said control shaft, in relation to the said drive shaft, bearing type connecting means between the said control shaft and said servocontrol, and connecting means for angularly connecting the said two shafts together, characterised by the fact that the said control shaft extends along the entire length of the said drive shaft and is supported in axially-sliding and angularly-fixed manner by the said drive shaft with the aid of locating bushes, a first end of the said control shaft projecting from the said drive shaft and said drive box and being connected with the said bearing type connecting means.

The invention will now be described with reference to the attached drawing showing an axial section of one non-limiting arrangement.

Number 1 on the attached drawing indicates a helicopter countertorque rotor assembly comprising a tubular drive shaft 2 projecting from a drive box or casing 3 and being fitted on its free end with the hub 4 of a countertorque rotor indicated as a whole by 5.

Shaft 2 and hub 4 are angularly connected by means of a splined coupling 6, whereas hub 4 is locked axially against tapered shoulder and locating ring 7 on shaft 2 by means of ring nut 8 fitted on to a threaded end of shaft 2 and acting on hub 4 with collar 9 inbetween, the latter also being angularly connected to shaft 2 by means of splined coupling 6.

Casing 3 consists of two essentially-cup-shaped integral bodies, 10 and 11, arranged with their concave sides facing each other on opposite sides of a bevel gear 12 integral with a portion of shaft 2 inside casing 3 and acting as a drive for shaft 2 itself.

Body 10 comprises a removable end cover 13 coaxial with shaft 2 and having a centre hole 14.

Cover 13 is connected integral with a tubular portion 15 of body 10, the said portion supporting in rotary manner one end of shaft 2 with two bearings 16 inbetween. The inner ring of the latter is locked axially against a shoulder ring on shaft 2 by means of ring nut 17 on the threaded end of shaft 2 itself. The outer rings of bearings 16 cooperate with the inner surface of portion 15 and are supported axially, on the side facing cover 13, by ring nut 18 cooperating with an internal thread on portion 15 and supporting a radial seal 19.

Body 11 presents an end wall 20 with a centre hole 21 through which extends a centre portion of shaft 2, the latter being supported in rotary manner inside hole 21 by means of a support 22 preferably consisting of a roller bearing.

Through drive shaft 2 extends a pitch-change control shaft 23 consisting of three segments, 24, 25 and 26, top-connected by couplings 27 and 28.

Segment 26 is supported in sliding manner inside shaft 2 by locating bush 29, on a level with ring nut 8, projects from the free end of shaft 2 and is fitted with plate 30 blended on to the end of shaft 2 by deformable cover bellows 31. Plate 30 presents two diametrically-opposed ears 32 (only one of which is shown) connected to two matching ears 33 (only one of which is shown) on collar 9 by means of respective calipers 34 designed to keep shaft 23 angularly fixed in relation to shaft 2. Plate 30 is also provided with a further two diametrically-opposed ears 35 (only one of which is shown) each connected to a pitch-control connecting rod 36 designed to convert axial slide on shaft 23 in relation to shaft 2 into corresponding pitch variations on a respective blade (not shown) of rotor 5.

Middle segment 25 on shaft 23 is supported in axially-sliding manner by shaft 2 with the aid of a locating bush 37 on a level with support 22, whereas segment 24 engages, in axially-sliding manner, locating bush 38 inside shaft 2 on a level with ring nut 18.

Segment 24 projects from casing 3 through hole 14 and presents on the end a cylindrical tailpiece 39 followed by a threaded section 40. Tail piece 39 is engaged inside the inner ring of two thrust bearings 41 fixed axially on to tailpiece 39 by nut 42 screwed on to threaded section 40. Tail piece 39 supports, in rotary manner by means of bearings 41, a bushing 43 blended on to cover 13 by cover bellows 44 and located between the arms of fork 45 constituting one arm of rocker arm 46. Bushing 43 presents two diametrically-opposed, radial holes (not shown) each aligned with a corresponding hole (not shown) through a corresponding arm of fork 45. Each pair of the said corresponding holes (not shown) is engaged by a respective pin 47 extending from a pad 48 connected to the relative arm on fork 45 by screw 49.

Rocker arm 46 is hinged centrally on to the end of an articulated link 50, in turn hinged, at the other end, on to appendex 51 integral with body 10 of casing 3.

The end of rocker arm 46, opposite the one connected to bushing 43, is hinged to the end of an output rod 52 on on pitch-change servocontrol 53.

The foregoing description clearly illustrates how, thanks to bearings 41, the whole of shaft 23 is angularly integral with shaft 2 with which it turns so as to exert relatively little strain on bushings 29, 37 and 38, the sole function of which is to guide axial slide of shaft 23 along shaft 2.

Furthermore, locating bearings 41 outside casing 3 simplifies inspection of the coupling connecting shaft 23 to the kinematic chain connected to servocontrol 53, such inspection being performed by simply unscrewing nut 42 and removing bellows 44 for slipping bush 43 and bearings 41 off tailpiece 39.

Claims

1. Helicopter countertorque rotor assembly comprising a drive box, a tubular drive shaft projecting from and turning in relation to the said box, a rotor fitted on the free end of the said drive shaft, a pitch-change control shaft partially housed inside the said drive shaft, a servocontrol for imparting pitch-change axial displacement on the said control shaft, in relation to the said drive shaft, bearing type connecting means between the said control shaft and said servocontrol, and connecting means for angularly connecting the said two shafts together, characterised by the fact that the said control shaft extends along the entire length of the said drive shaft and is supported in axially-sliding and angularly-fixed manner by the said drive shaft with the aid of locating bushes, a first end of the said control shaft projecting from the said drive shaft and said drive box and being connected with the said bearing type connecting means.

2. Assembly according to Claim 1, charising at least one caliper integral, on one side, with the said drive shaft and, on the other, with the said control shaft.

3. Assembly according to Claim 1 or 2, characterised by the fact that the said bearing type connecting means comprise at least one thrust bearing, fitted onto the said first end of the said control shaft, and a bushing supported in rotary manner by the said bearing and connected to an output on the said servocontrol.

4. Helicopter countertorque rotor assembly constructed and arranged for use and operation substantially as described herin with reference to the accompanying drawing.