US-A-3651661, US-A-3970495, DE-A-4414384 and GB-A-2187819 each discloses a rotary power transmission shaft comprising a tube which is a one-piece moulded fibre reinforced plastic structure made up of a plurality of bonded layers. In forming the tube, the layers which each comprise thermo-setting resin reinforced by the fibres, are laid up one upon another on a former, whereafter the resultant laminate is subjected to heat and pressure in a mould to cure the resin and mould the resultant shaft.

It has proved difficult to produce such shafts to the standard of quality, integrity and reliability required for use to activate flaps in aircraft wings.

An object of this invention is to provide a rotary power transmission shaft which can be made to the required standards.

According to one aspect of this invention there is provided a method of forming a rotary power transmission shaft as claimed in claim 1.

According to another aspect of this invention there is provided a rotary power transmission shaft according to claim 9.

The shafts disclosed in US-A-3651661, US-A-3970495 and GB-A-2187819

comprise tubes with integrant flanges at either end. The requirement for forming flanges integrally at either end of the tube places an additional demand on the standards of quality integrity and reliability of the required shafts.

It had been considered necessary to provide a metallic annular end plate at either end of the fibre reinforced resin tube, to form each end plate with an integral annular spigot portion, which conveniently was hexagonal in form, and to fit the end plate to the respective end of the tube by having its spigot portion spigotted into the tube at the respective end of the tube. This had been thought necessary in order to achieve the standards of quality, integrity and reliability of the shafts required for use to activate flaps in aircraft wings. There was, however, a cost penalty, especially if the end plates with their integral hexagonal spigot portions were formed of titanium.

The present invention renders it unnecessary to provide such metallic annular end plates with integral hexagonal spigot portions even though it may be preferable for the radial flanges that are formed by extending the helical windings of the continuous tape of woven fibre into those flanges to be reinforced by simple annular end plates.

According to a feature of said one aspect of this invention there is provided a method including the additional steps claimed in claim 2.

Preferred features of a method which embodies this invention as claimed in claims 3 to 8.

Preferred features of a rotary shaft according to said other aspect of this invention are claimed in claims 10 to 20.

Two forms of rotary power transmission shaft in which this invention is embodied and methods of their manufacture will be described now by way of example with reference to the accompanying drawings, of which:- Figure 1 is a half sectioned elevation of one form of the shaft, the upper half of the shaft being shown sectioned in a radial plane; Figure 2 is a view on arrow A in Figure 1 of an end plate of the shaft shown in Figure 1; Figures 3 to 5 illustrate steps in a process for manufacture of the shaft that is shown in Figure 1; Figures 6A and 6B are elevations of a pair of mould clamp plates which form an annular mould when fixed together, each being seen along the axis of the annular mould they form when fitted together; Figure 7 is a view on arrow B of Figure 6A; Figure 8 is a view on arrow C of Figure 6B; Figure 9 is a transverse section of a mould including the mould clamp plates shown in Figures 6A, 6B, 7 and 8 fitted around the end of the flanged tubular intermediate product shown in Figure 5 during manufacture of the shaft shown in Figure 1; Figure 10 is an exploded view illustrating assembly of one end of another form of the shaft;

Figure 11 is a view along the axis of one of the stacks of annular layers shown in Figure 10; and Figure 12 is a view on arrow D in Figure 10.

Figure 1 shows a rotary power transmission shaft comprising an annular end plate 10 at either end. Each end plate 10 is formed of metal such as titanium. An annular rib 11 is formed co-axially with the central aperture 12 of each end plate 10. The radially inner face of each rib 11 is cylindrical and has a diameter which is a little larger than the diameter of the central aperture 12 of the respective end plate 10. The cylindrical surface of each rib 11 forms an annular shoulder with the material of the respective end plate 10 that extends radially inwards from it to the central aperture 12 of that end plate 10. The radially outer surface of each rib 11 is arcuate in the radial plane of the section shown in Figure 1 so that each rib 11 tapers to form a sharp annular ridge, the height of the ridge being similar to the axial thickness of the remainder of the respective end plate 10.

A tubular mandrel 13 of a carbon fibre reinforced plastics material is spigotted at either end into the annular shoulder formed by the rib 11 of a respective one of the end plates 10, whereby that end is located relative to the respective end plate 10.

The tubular mandrel 13 lines the inner surface of a tube 14 which has an integrant annular flange 15, 16 at either end, each flange 15, 16 following the arcuate surface of the rib 11 and the adjacent radially extending surface of the respective end plate 10 to which it is bonded.

Figure 2 shows that each end plate 10 has four holes 17 formed through

it parallel to the axis of the central aperture 12 at equi-angularly spaced locations on a common pitch-circle diameter. The mouth of each hole 17 formed in the side of the respective end plate 10 opposite from the rib 11 is formed in a respective mesa 18 in the face of the annular end plate 10.

Figure 1 shows a tubular bush 1 9 which extends through the upper hole 17 and though a co-axial hole in the juxtaposed flange 15, the tubular bush 19 serving as a tubular rivet by which the flange 15 is riveted to the juxtaposed end plate 10. Similar tubular bushes 19 are provided in each of the holes 17 of the end plates 10 so that both flanges 15 and 16 are riveted to the respective end plate 10 by four such tubular bushes 19.

To form the rotary power transmission shaft described above with reference to Figures 1 and 2, the mandrel 1 3 is formed from carbon fibre reinforced plastics material by moulding and is cut to length. When so formed, it is supported between centres in a CNC tape winding machine. Each centre comprises two coaxially-spaced right cylindrical spigot portions 21 and 22 with a larger diameter body portion between them as is shown in Figure 3.

The spigot portion 21 is for fitting into a chuck or collet of the winding machine and has an outside diameter which is substantially the outside diameter of the mandrel 1 3. The larger diameter body portion comprises a medial right cylindrical portion 23 between a pan of frusto-conical portions 24 and 25 which each taper away from it to the respective spigot portion 21,22, whereas the diameter of the smaller end of the frusto-conical portion 24 is the same as the outside diameter of the spigot portion 21 and as the diameter of the smaller end of the frusto-conical portion 25 the latter is greater than that of the spigot portion 22 which is a push fit into the mandrel 13, there being a step formed between the spigot portion 22 and the smaller end of the frusto-conical portion 25. The spigot portion 22 is

spigotted into the mandrel 13 so that the respective end of the mandrel 13 abuts the step between the spigot portion 22 and the smaller end of the frusto-conical portion 25.

The mandrel 13 is then rotated with the centres by the machine whilst carbon fibre tape impregnated with thermo-setting resin is helically wound, firstly on the spigot portion 21 of the centre at one end of the mandrel, over the larger diameter body portion of that centre, as shown in Figure 3, then along the whole length of the mandrel 13, onto the larger diameter body portion of the centre at the other end of the mandrel 13 and finally onto the spigot portion 21 of that other centre where it is turned around and helically wound back over the larger diameter body portion of that other centre and back along the whole length of the mandrel 13 to the centre at the first mentioned end of the mandrel 13. The spiral path of the tape is substantially at 45" to the axis of the mandrel 13. This is repeated for the required number of layers of pre-impregnated tape of carbon fibre material that are to be laid to form the tube 14, each alternate layer being wound in the opposite direction to its juxtaposed layers. The tape is arranged with continuous lengths of carbon fibre running along its length substantially parallel to its edges. Also the edges of the tape abut one another as the tape is helically wound.

The mandrel 13, with centres at its end and the helically wound tape thereon is then removed from the tape winding machine. The end portions of the helically wound tape that extends from the spigot portion 21 over the frusto-conical portion 24 and up to the centre of the medial portion 23 are cut away, that is to the cut away at the plane Ill-Ill shown in Figure 3, and removed. The centres are then withdrawn from the mandrel 13 so as to leave the mandrel 13 with helically wound tape projecting therefrom at

either end by an amount which is sufficient to form the integrant flanges 15 and 16 at either end as is shown in Figure 4. The flared ends of helically wound tape that project from the mandrel 13 at either end are then deformed into substantially radial flanges as shown in Figure 5. The centres with the larger diameter body portions having spaced frusto-conical portions 24 and 25 which taper away from one another are used so that the helically wound tape follows the required geodetic path into these flanges.

Adhesive is applied to the face of each end plate 10 from which the respective rib 11 projects. Each of the end plates 10 is then presented to the respective end of the mandrel 13 so that the latter is spigotted into the annular shoulder formed by the rib 11 of the respective end plate 10 and the respective radial flange of helically wound tape is brought into face to face contact with respective face of the respective end plate 10, including the annular arcuate surface of the rib 11, that is coated with the adhesive, as is shown in Figure 5.

A mould is then assembled at either end of the mandrel 13 around the respective end plate 10 at that end.

Figures 6A, 6B, 7 and 8 show a pair of mould clamp plates 31 and 32 which are to be screwed together to form one of the moulds. The other mould is formed by screwing together a similar pair of such mould clamp plates 31 and 32.

Each mould clamp plate 31, 32 is generally semi-circular and has a stepped semi-cylindrical recess 33, 34 formed concentrically with its semi-circular edge. The smaller diameter end of each semi-cylindrical recess 33, 34 is formed by a semi-circular wall 35, 36 which projects axially from the

remainder of each mould clamp plate 31, 32. The radially inner surface of each semi-circular wall 35, 36 is cylindrical and the radially outer surface tapers to the open end of the smaller diameter portion of the respective recess 33, 34. The mould clamp plate 31 has a pair of rectangular slots 37 and 38 formed symmetrically, one on either side of the mouth of the smaller diameter portion of the respective recess 33. The longer sides of the slots 37 and 38 are substantially parallel to the axis. The mould clamp plate 32 has a pair of rectangular spigots 39 and 41, one on either side of the mouth of the smaller diameter portion of the respective recess 34. Each spigot 39, 41 is a sliding fit in the respective slot 37, 38 and thereby locates the mould clamp plates 31 and 32, one relative to the other so that the semi- cylindrical recesses 33 and 34 together form an open ended stepped cylindrical mould cavity and the two semi-circular walls 35 and 36 together form an annular wall having an axially extending externally tapered surface.

The two mould clamp plates 31 and 32 are then screwed together around the tape wound mandrel 13 and around the end plate 10 at the respective end of the mandrel 13 as well as being screwed to a back plate 42 which is presented to the face of the end plate 10 opposite to the radial flange of tape, to complete the mould as is shown in Figure 10. Elastic bagging material which may be a non-porous PTFE, is applied around the two moulds and the length of tape wound mandrel that extends between them.

The resultant assembly is placed within an autoclave. The pressure within the autoclave is increased so as to exert pressure on the elastic bagging.

The temperature within the autoclave is raised to cure both the resin with which the tape was pre-impregnated and the adhesive that was applied to the faces of the end plates 10 that are contiguous with the flanges 15 and 16.

The resultant tubular structure with the end plates 10 bonded thereto is then removed from the autoclave and the edges finished. The holes 17 in the end plates 10 are extended through the aligned portions of the flanges 15 and 16 and the tubular bushes 19 are fitted to mechanically rivet the flanges 15 and 16 and the respective end plates 10 together.

It is theoretically possible to use carbon fibre filaments instead of pre- impregnated tape and to apply resin after the filaments have been placed around the mandrel, but it would be difficult to achieve the required standards of quality, integrity and reliability if one did.

An annular composite structure can be used at either end of the mandrel 13 instead of the metal end plates 10 to make up the integrant flanges at either end of the rotary power transmission shaft. Figure 10 illustrates elements which comprise such an annular composite structure.

Once the flared ends of helically wound tape at either end of the mandrel 13 have been deformed into substantially radial flanges, as shown in Figure 5, a suitable number of stacks 43 of contiguous annular layers 44 of thin sheet material which comprises carbon fibre impregnated with uncured resin are assembled substantially coaxially with each other and with the mandrel 13 at either end of the mandrel 13. The inside and outside diameters of each of the annular layers 44 are respectively substantially the same as the inside diameter of the mandrel 13 and of the outside diameter of the radial flanges. Each layer 44 has carbon fibres which extend parallel to each other and to a diameter of the respective layer, as is shown at 44A in Figure 10. The carbon fibres 44A of each layer 44 of a stack 43 are oriented at 45" to the carbon fibres 44A of each of the juxtaposed layers 44 so that the carbon fibres 44A of each alternate layer 44 of a stack 43 are

oriented at 90C to each other. Each annular layer 44 was formed by stamping from stock material in sheet form which conveniently is 0.005 inches (0.13 mm) thick. The number of stacks 43 and number of layers 44 in each stack is a matter of design choice governed by the thickness required for the resultant end flange of the shaft. The radially inner edges of each of the layers 44 may be deformed so as to flare axially to a small extent, those flared deformations being arranged to extend into the bore of the mandrel 13 to provide a tidy finish and improved material density to either end of the bore of the resultant shaft.

The radial flanges formed at either end of the mandrel 13 by the flared ends of helically wound tape taper radially outwardly because the material of the tape has a substantially constant volume. To compensate for the consequent relative thinness of the radially outer portions of the flanges, an additional stack 45 of contiguous annular layers 46 of resin impregnated carbon fibre material is assembled coaxially with and in juxtaposition with the stacks 43, either between the stacks 43 and the respective radial flange or at the other of the stacks 43. The inside diameter of each annular layer 46 is somewhat greater than that of each of the layers 44.

A mould is then assembled around the assembly of the stacks 43 and 45 and the radial flanges formed by the helically wound tape at either end of the mandrel 13, and moulding of the integrant flanges is carried out in substantially the same way as has been described above with reference to Figure 6 to 9.

If required, additional reinforcing material in a form similar to that tape material from which the annular layers that comprise the stacks were formed could be provided if required in order to further thicken the resultant

integrant flanges. Such additional material could be provided simultaneously with the final steps of winding the helical tape that forms the radial flanges.

The use of the pre-moulded and cured length of fibre reinforced plastics material in tubular form as a former upon which the remainder of the tube is formed by helically winding the layers of fibre reinforced thermo-setting resin material in tape form enabies small diameter tubes with a high aspect ratio (that is to say the ratio of tube diameter to wall thickness), to be made to the required quality especially where such tubes are formed with integrant flanges at each end which are required to be produced to the same standards of quality, integrity and reliability.

The dimensions of small diameter tubes for which the invention is especially suitable range from tubes with an outside diameter of about 23 mm and a bore of about 17 mm to tubes with an outside diameter of about 30 mm and a bore of about 23 mm. The preferred embodiment has an outside diameter of 26 mm and a bore of 20 mm.