Aircraft blade and methods of forming and repairing an aircraft blade

Abstract

A method of making an aircraft blade is provided. The method comprises the steps of: assembling two or more fibre-reinforced thermoplastic composite parts into a blade assembly; and welding the fibre-reinforced thermoplastic composite parts together utilising an additional thermoplastic located at least at locations where the parts will abut when assembled. The additional thermoplastic has a melting or softening temperature lower than a melting temperature of each of the fibre-reinforced thermoplastic composite parts being assembled. The step of welding comprises heating the blade assembly to a temperature above the melting/softening temperature of the additional thermoplastic and below the melting temperature of each of the fibre-reinforced thermoplastic composite parts so as to melt/soften the additional thermoplastic and thereby weld the fibre-reinforced thermoplastic composite parts together to form the aircraft blade.

Claims

1. A method of making an aircraft blade, the method comprising the steps of: assembling a plurality of fibre-reinforced thermoplastic composite parts into a blade assembly, wherein the plurality of fibre-reinforced thermoplastic composite parts include a core, at least two planar inserts, two shells, and a stringer or I-beam having a first end and a second end; and welding the fibre-reinforced thermoplastic composite parts together utilising an additional thermoplastic located at least at locations where the parts will abut when assembled; wherein the step of welding comprises heating at least a portion of the blade assembly where the parts abut to a temperature which softens or melts the additional thermoplastic but is below the temperatures at which the thermoplastic of each of the composite parts melts, so as to weld the fibre-reinforced thermoplastic composite parts together by means of the softened or melted additional thermoplastic to form the aircraft blade, and wherein, in the blade assembly, the two shells form a blade of the aircraft blade, the at least two planar inserts are attached to the core, and the stringer or I-beam connects to a first of the at least two planar inserts at said first end and to a second of the at least two of the planar inserts at said second end.

2. The method according to claim 1, wherein the step of welding comprises one or more of friction heating, laser heating, microwave heating, and ultrasonic heating to locally heat portions of the blade assembly.

3. The method according to claim 1, wherein each of the plurality of fibre-reinforced thermoplastic composite parts comprise the same thermoplastic; or wherein the plurality of of the fibre-reinforced thermoplastic composite parts comprise different thermoplastics.

4. The method according to claim 1, wherein the fibre-reinforced thermoplastic composite parts comprise PEEK and/or PEKK; and wherein the additional thermoplastic is PEI or PAEK.

5. The method according to claim 1, wherein the fibre-reinforced thermoplastic composite parts are at least partially coated with the additional thermoplastic during manufacture of the composite parts; or wherein the additional thermoplastic is applied to the manufactured fibre-reinforced thermoplastic composite parts during assembly.

6. The method according to claim 1, wherein, prior to the step of assembling, the method further comprises forming the plurality of fibre-reinforced thermoplastic composite parts by thermoforming or thermostamping; and/or after the heating step, a step of overmoulding the blade.

7. The method according to claim 1, wherein fibres of the fibre-reinforced thermoplastic composites are carbon fibres, glass fibres, aramid fibres, or a mixture thereof.

Description

DESCRIPTION OF THE FIGURES

(1) Certain embodiments of the present disclosure will now be described in greater detail by way of example only and with reference to the accompanying drawings in which:

(2) A plurality of parts to be assembled into a blade for an aircraft are shown, in particular Figure 1a illustrates inserts, Figure 1b illustrates shells, Figure 1c illustrates a core and Figure 1d illustrates an I-beam; and

(3) FIG. 2 shows a view of the assembled blade.

DETAILED DESCRIPTION

(4) FIGS. 1a to 1d show a plurality of separate pre-formed parts used to construct an aircraft blade 10. In FIG. 1b there are shown two shells 12, 14 that, in the finished blade 10, form the airfoil surface of the blade. In FIG. 1c there is illustrated a core 18 that is provided with a connector 20 (e.g. a tulip) that allows for connection of the core 18 to a rotor hub or disc (not shown). As illustrated in FIG. 1a, one or more inserts 16a-d are provided. In the finished blade 10, these connect the core 18 to the blade 10. Each insert 16a-d has a central aperture 17 that is sized so as to fit snugly around the core 18 at the correct position along the core for that insert 16a-d. Of course, other shapes of inserts may be used. The one or more inserts 16a-d are used to connect the shells 12, 14 to the core 18 to form the blade 10. A stringer or an I-beam 22 may optionally be provided as illustrated in FIG. 1d.

(5) FIG. 2 shows the finished blade 10 with the internal parts (e.g. core 18, inserts 16a-c) visible through the shells 12, 14. The stringer or I-beam 22 may be included to connect two adjacent inserts, e.g. 16b and 16c, such that in the finished blade 10 these two inserts 16b, 16c are connected together by each of: the core 18, the I-beam 22, and the shells 12, 14. The stringer or I-beam 22 may thus provide reinforcement along at least a longitudinal axis of the blade 10.

(6) The shells 12, 14, inserts 16a-d, the core 18, and any stringers or I-beams 22 are each be made from a fibre-reinforced thermoplastic composite. The thermoplastic used for each fibre-reinforced thermoplastic composite part may be a first thermoplastic having a first melting temperature. For example, the first thermoplastic may be PEEK or PEKK.

(7) Alternatively, different thermoplastics may be used for the different parts 12, 14, 16a-d, 18, 22. For example, the shells 12, 14 may be made using one thermoplastic (e.g. PEEK) while one or more of the inserts 16a-d is made from another thermoplastic (e.g. PEKK) etc. Importantly, the one or several thermoplastics used for the parts must each have a higher melting temperature than the melting temperature or the softening temperature (for an amorphous thermoplastic) of an “additional thermoplastic” (in the language of the claims) used to join the parts together, as discussed in more detail below. For simplicity, the different parts 12, 14, 16a-d, 18, 22 will be referred to as being made from a first thermoplastic and the additional thermoplastic is the “second thermoplastic”; however, it is to be understood that the different parts may nonetheless each comprise a different thermoplastic (i.e. different “first thermoplastics”).

(8) The parts may be formed by any suitable process, e.g. thermoforming, thermostamping, pultruding, lay-up processes etc. In thermostamping, the composite is first heated by infrared and placed between the moulds of a press. The moulds have the same temperature during the process, below the melting point of the composite. The composite part is formed between the moulds and it cools down at the same time. In thermoforming, the composite is placed in the mould, either having been pre-heated by e.g. infrared, or, the mould itself is heated to the forming temperature. The heat to the mould is then turned off, and the temperature of the mould decreases from the forming temperature (above the melting/softening point) to a temperature below the melting/softening point. The composite part can then be removed.

(9) In this described embodiment, after forming the composite parts, a second (“additional”) thermoplastic is applied to various of the parts at various locations 30a-d where the parts will be joined to one another in the finished blade 10. The second thermoplastic is to perform the function of “gluing together” the disparate parts into a finished blade 10. Therefore, the second thermoplastic is selected to have a second melting temperature, or a softening temperature (for the case of an amorphous thermoplastic that does not have a defined “melting point”), that is lower than a first melting temperature of the first thermoplastic. Consequently, when the disparate parts are heated to a temperature between the first and second melting temperatures (or between the softening temperature and the first melting temperature), the second thermoplastic melts (or exhibits sufficiently liquid-like behavior) while the first thermoplastic stays solid. The process of joining the parts together is explained in greater detail below.

(10) As one non-limiting example shown in FIG. 1b, the second thermoplastic may be applied to one or more regions 30a of the shells 12, 14. The second thermoplastic may be applied to one or more regions 30c of the inserts 16a-d (FIG. 1a). The second thermoplastic may be applied to one or more regions 30b of the core 18 (FIG. 1c). The second thermoplastic may be applied to one or more regions 30d of the I-beam 22 (FIG. 1d).

(11) On the inserts 16a-d, the second thermoplastic may be applied to either, both or neither of the outer circumference of the insert (where it abuts the shells 12, 14, in the finished blade) or the circumference 17a of the central aperture 17 where the insert abuts the core 18 in the finished blade 10.

(12) In some embodiments, the second thermoplastic is only applied to one side of a join, i.e. it is applied to one out of two parts that are to be joined together at a given join. As one non-limiting example, the second thermoplastic may be applied to one of the shells 12 at a region 30a, and not applied to the outside of the specific insert 16 that will join to that region of the shell 12. Alternatively, and sometimes more preferably, the second thermoplastic may be applied to both parts that are to be joined together at a given join before joining the parts together.

(13) In a further embodiment described later, the additional (second) thermoplastic is coated on the outside of the part during manufacture of the part.

(14) To form the finished blade 10, the plurality of separate fibre-reinforced parts 12, 14, 16, 18, 20, 22 may have the second thermoplastic applied to the selected regions as described above and then be placed together in a heated press.

(15) The blade assembly is heated to a temperature above the melting temperature/softening temperature, as appropriate, of the additional (second) thermoplastic and below the melting temperature(s) of each of the composite parts, i.e. below the lowest melting temperature among the thermoplastic(s) used for the plurality of parts. Such heating may be achieved for example by ultrasonic heating, laser heating, heating wire, infrared radiation, microwave radiation, and/or friction heating. This melts/softens the additional thermoplastic and thereby welds the composite parts together to form the aircraft blade.

(16) If the heat is directed to the particular regions where the parts are to be welded, this may have the advantage of only affecting a single joint at a time, which may make replacement of a single part, e.g. a damaged part, simpler without requiring deconstruction of other (undamaged) parts of the blade 10.

(17) The assembling step may comprise laying the composite parts in a press which holds the parts in the assembled configuration. The press may then be heated in order to melt/soften the additional thermoplastic and weld the parts together. The heat is then removed from the press and it cools down to below the melting/softening temperature of the additional thermoplastic. The assembled blade is then removed from the press.

(18) It may also be desirable to repair a FRC blade 10. A blade 10 constructed according to the above method may be repaired by removing one or more damaged parts 12, 14, 16a-d, 18 etc. and replacing the damaged part with an undamaged one and re-forming the blade. Having the second thermoplastic with a lower melting/softening temperature than the first thermoplastic allows the blade 10 as a whole to be deconstructed into individual FRC parts, or for individual parts of the blade 10 to be removed without affecting other parts.

(19) In one embodiment, a method of repairing a blade includes heating specific regions of a given (damaged) part of the blade 10, so as to melt/soften the second thermoplastic that joins that part of the blade onto the rest of the blade 10. For example, to repair a damaged shell 12, the method includes heating the shell 12 at specific regions 30a so as to melt/soften the second thermoplastic that joins the shell 12 to other parts of the blade 10.

(20) This may be done without melting/softening the second thermoplastic where it joins the insert(s) 16a-d to the core 18, and without melting/softening the second thermoplastic where it joins the inserts to the other shell 14. Thus, the first shell 12 may be removed from the blade 10 and replaced with a new shell 12 part. Again, local heating may be applied to regions 30a of the new shell 12 part so as to melt/soften the second thermoplastic and join the new shell 14 part to the remainder of the blade 10.

(21) Alternatively, the whole blade 10, including the damaged part, may be heated to melt/soften all regions of the second thermoplastic and thus separate all constituent parts 12, 14, 16, 18, 20, 22 of the blade 10. The or each damaged part may then be replaced with a new (undamaged) part and the whole blade 10 may then be reconstructed by welding, in the manner described above for the initial construction of the blade. Enough second thermoplastic may still be present on the blade assembly where the replacement part is to be attached that the assembly is simply heated in order to weld the replacement part by means of this existing second thermoplastic. Or, where required, the second thermoplastic may be re-applied to regions 30a-d to be re-joined.

(22) The finished blade 10 shown in FIG. 2 is also illustrative of a blade 10 that has been repaired by the above method. It will be appreciated that the above described method of making the blade is only one way of making the finished blade 10, and that alternative methods may be used to construct a blade according to the scope of the disclosure, such as a blade that comprises a plurality of fibre-reinforced thermoplastic composite parts, wherein the plurality includes: two fibre-reinforced thermoplastic composite shells 12, 14, forming an airfoil surface of the aircraft blade; one or more fibre-reinforced thermoplastic composite inserts 16a-d joined to the two shells 12, 14; a core 18 joined to the one or more fibre-reinforced thermoplastic composite inserts 16a-d; wherein each of the plurality of fibre-reinforced thermoplastic composite parts comprises a first thermoplastic having a first melting temperature that is above the melting/softening temperature of a second thermoplastic such, wherein the second thermoplastic joins the plurality of fibre-reinforced thermoplastic composite parts into the aircraft blade.

(23) A blade 10 having the structure described above may be readily repaired by melting/softening the second thermoplastic (either locally or globally) to replace any damaged parts. This may be easier to perform on such a blade 10 than on another blade X entirely constructed of a single fibre-reinforced thermoplastic composite (i.e. with no second thermoplastic having a lower melting/softening temperature).

(24) It is notoriously difficult to repair FRC parts by comparison with, say, metal parts. In some FRC the matrix is irreversibly solidified during construction (e.g. many polymerisation reactions are irreversible), and addition of material during repairs may not bond properly to the already-polymerized portions of the part.

(25) In such a blade X, a damaged portion cannot be repaired by the above method, and damage to one portion may lead to scrapping the entire blade X. Thus, a blade 10 according to the above description may be advantageous over the prior art blade X in terms of reducing wastage, improved construction and repair speeds, as well using a simpler and lower cost construction techniques.

(26) In some examples, the second (additional) thermoplastic may be applied during manufacture of the parts as an outermost layer (a coating) to each of the different parts 12, 14, 16a-d, 18, 22 after the parts have been made from their own (e.g. first) thermoplastic. During construction of a blade, or repair of a blade, having the second thermoplastic already covering the parts eliminates the need to apply the second thermoplastic to specific locations for the welding. That is, the second thermoplastic is already present at all locations where two parts may abut one another.

(27) Alternatively, the second (additional) thermoplastic may be applied as an outermost layer to each of the different parts 12, 14, 16a-d, 18, 22 only on surfaces that will face other parts. For example, the additional thermoplastic may be applied to an entire face of a shell 12 that will face inwards towards the core 18 when the blade 10 is assembled, while the opposite outwardly facing face is not coated with the additional thermoplastic (as no part of this face is ever welded to another part).

(28) As one non-limiting example, the process of forming separate FRC parts and joining them together may comprise the steps:

(29) 1) Thermoform a first part comprising PEEK with carbon fibres at a temperature of 400° C. with PEI on the surface of the part;

(30) 2) Thermoform a second part comprising PEEK with carbon fibres in the same way, with the PEI on the surface;

(31) 3) Place the parts together and heat the PEI and PEEK parts, using an ultrasonic welder, to a temperature of 335° C. for 10 seconds. This softens the PEI to such an extent that it welds the PEEK parts together; and

(32) 4) Allow the parts to cool to room temperature having been welded together.