GB2148820A

GB2148820A - Helicopter rotor blades

Info

Publication number: GB2148820A
Application number: GB08426453A
Authority: GB
Inventors: Fiorenzo Mussi; 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: DE3437942C2; GB2148820B; IT8368111A0; GB8426453D0; DE3437942A1; FR2554077A1; IT1161533B; FR2554077B1; JPS60166592A

Abstract

Helicopter rotor blade (1) on which the longitudinal member (2) consists of a single piece of composite synthetic material, made by joining a front nose (10), a top (15) and bottom (16) back, each defined by a number of adjacent axial straps (17), and a rear axial cover element (18) having an essentially C-shaped section and consisting of composite synthetic material prehardened by means of the precompacting or precuring process. The member (2) includes an inner skin (5) and an outer skin (7) enclosing nose (10), top and bottom (15, 16) and rear elements (18). A honeycomb rear fixing (23) is secured to the member (2) by a skin (24). <IMAGE>

Description

SPECIFICATION Helicopter blade The present invention relates to a helicopter blade.

Helicopter blades generally comprise a front loadbearing structure, usually consisting of a longitudinal member having a root area at one end with through holes for connecting the blade to a hub, and rear fairing defining the trailing edge of the blade and usually having a honeycomb inner structure.

On known helicopter blades of advanced design, such as the one described in USA Patent n.

4.095.322, the longitudinal member is made in two connectable parts extending along the entire length of the member itself. The first of the said two parts is made by stretching reinforced resin straps over a removable core so as to form a tubular structure which is then hot-cured in a mold for setting its shape. The second of the said parts is made using the same process as the first and is made integral with the said rear fairing before being connected to the respective first part. The said second part presents an essentially C-shaped structure designed to house a rear portion of the said tubular structure on the first part. Though extremely reliable, known blades of the aforementioned type involve a number of drawbacks.Firstly, having to match the two parts on the aforementioned longitudinal member requires extreme accuracy in terms of shape and, consequently, involves a relatively painstaking manufacturing process.

Secondly, manufacturing the said two parts on the longitudinal member separately requires the use of a large number of molds and complicated, highcost assembly procedures. Lastly, as the said two parts on the longitudinal member require accurate matching, it is essentially impossible without altering the said molds, to alter the physical characteristics of the said two parts for adjusting the elastic response of the blade as required in each individual case.

The aim of the present invention is to provide a helicopter blade involving none of the aforementioned drawbacks. With this aim in view, the present invention relates to a helicopter blade comprising a tubular front longitudinal member, rear fairing and an outer covering connecting the said longitudinal member and the said rear fairing together, characterised by the fact that the said longitudinal member is made in one piece from synthetic composite material comprising a tubular body, in turn, comprising an axial front nose, a top and bottom back, each comprising a number of adjacent axial straps, and an axial rear cover element, the said cover element having an essentially Cshaped section with its concave side facing the said nose, extending part-way along the said top and bottom backs contacting the relative said straps, and being made of synthetic materal preferably prehardened using the precompacting or precuring process.

A non-limiting arrangement of the present invention will now be described with reference to the attached drawings in which: Figure 1 shows a view in perspective of a helicopter blade according to the present invention; Figure 2 shows a larger-scale cross section of the Figure 1 blade.

Number 1 in Figure 1 indicates a helicopter blade comprising a longitudinal member 2 extending axially along the whole length of blade 1 and defining, at one end, a root portion 3 with holes 4 for connecting blade 1 to a hub (not shown).

As shown in Figure 2, longitudinal member 2 presents a tubular structure and comprises an inner tubular countertwist body 5, consisting of a strip of cross-woven-fibre cloth 6 of synthetic composite material wound into a tube, and a tubular outer covering 7 consisting of a number of crosswoven-fibre cloth strips 8 (three in number in the example shown) made of synthetic composite material and also wound into respective tubes by overlapping the side edges of the respective strip 8 along a rear edge of longitudinal member 2.

Inner body 5 and outer covering 7 combine to enclose a middle tubular body 9 made of synthetic composite material and comprising a front nose 10 extending axially along a front edge of body 9 and comprising an essentially triangular-section front portion 11 and an essentially C-section rear portion 12 with its concave side facing rearwards. Portions 11 and 12 combine to define a cylindrical recess 13 extending at least part-way along the length of body 9 and engaged by a cylindrical balancing insert 14 usually made of lead.

Body 9 also comprises a top and bottom back, 15 and 16, each consisting of a number of adjacent axial straps 17 (four in number in the example shown) consisting of synthetic composite material.

Finally, body 9 comprises an essentially C-section rear axial cover element 18 with its concave side facing front nose 10 and consisting of synthetic composite material prehardened by means of the precompacting or precuring process. Rear element 18 comprises a core 19, constituting an essentially flat rear wall on body 9, and two wings 20 defining part of top and bottom backs 15 and 16 respectively and arranged laterally contacting respective straps 17.

By curing bodies 5 and 9 and outer covering 7 in a mold, longitudinal member 2 is formed into a tubular, one-piece structure covered along its front edge with an ice-proof covering 21 usually made of glass fibre with built-in electric resisters (not shown).

As shown in Figure 2, blade 1 also comprises rear fairing 22, preferably consisting of a body 23 with a honeycomb inner structure, and being essentially triangular in shape on the outside. Fairing 22 is arranged with its front side contacting the portion of covering 7 extending along the outer surface of core 19 on rear element 18, and is joined to longitudinal member 2 by means of outer cloth covering 24. The latter, consisting of synthetic composite material, is wrapped round the whole of rear fairing 22 as well as a rear portion of longitudinal member 2 the front part of which is covered with an outer abrasionproof metal cover ing 25 usually made of steel or titanium.

By curing cloth 24 in a mold, longitudinal member 2 and fairing 22 are joined indestructibly together, the join being further strengthened by a strip 26 of synthetic composite cloth, extending over the point of contact between longitudinal member 2 and fairing 22, underneath cloth 24.

From the foregoing description, it clearly follows that only a first mold (not shown) for making longitudinal member 2 and a second mold for fitting it on to fairing 22 are required for making blade 1, the most outstanding structural characteristic of which consists in rear element 18 closing off body 9 on longitudinal member 2. Element 18, made of prehardened synthetic material, not only provides for fast, extremely efficient compacting of the material constituting straps 17 when forming longitudinal member 2, but also enables the characteristics of blade 1 to be varied very easily, without affecting in any way the curing processes employed or the manner in which the component parts on blade 1 are assembled.This is made possible by element 18 being a ready-made inner element, the geometry, size and physical characteristics of which may be varied as required, within certain limits, without necessarily affecting the parts on blade 1 surrounding it. Consequently, the weight of element 18 may be varied for achieving a corresponding shift in the centre of gravity of blade 1. Furthermore, the fibre arrangement on element 18 may be varied, for example, for varying the location of the shearing centre on each section of blade 1; or the thickness of element 18 may be varied for varying the centre location of each section on blade 1.

In other words, providing blade 1 with a readymade inner element, such as element 18, essentially independent of surrounding parts in terms of size and physical characteristics, enables the elastic response of blade 1 as a whole to be modified by means of appropriate modification of the said ready-made element prior to assembly of blade 1 and without affecting either the other parts on blade 1 or the assembly procedures involved.

Claims

1. Helicopter blade comprising a tubular front longitudinal member, rear fairing and an outer covering connecting the said longitudinal member and the said rear fairing together, characterised by the fact that the said longitudinal member is made in one piece from synthetic composite material comprising a tubular body, in turn, comprising an axial front nose, a top and bottom back, each comprising a number of adjacent axial straps, and an axial rear cover element, the said cover element having an essentially C-shaped section with its concave side facing the said nose, extending part way along the said top and bottom backs contacting the relative said straps, and being made of prehardened synthetic material.

2. Blade according to Claim 1, characterised by the fact that the material for the said cover element is prehardened by means of the precompacting process.

3. Blade according to Claim 1, characterised by the fact that the material for the said cover element is prehardened by means of the precuring process.

4. Blade according to any one of the foregoing Claims, characterised by the fact that the said longitudinal member also comprises an inner tubular countertwist body extending in contact and integral with an inner surface of the said nose, of the said top and bottom backs and of the said cover element.

5. Blade according to any one of the foregoing Claims, characterised by the fact that the said longitudinal member comprises an outer covering consisting of a number of overlapping cloth strips of synthetic material; the said rear fairing comprising a body having a honeycomb inner structure and the front end of which is arranged directly contacting the rear end of the said longitudinal member.

6. Helicopter blade essentially as described and illustrated with reference to the attached drawings.