Propeller blades

A propeller blade comprises a composite blade spar and at least one cover shell section adhesively bonded to the blade spar by a thermoplastic adhesive.

FOREIGN PRIORITY

This application claims priority to European Patent Application No. 18290134.8 filed Nov. 27, 2018, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to propeller blades and to methods of their manufacture and repair.

BACKGROUND

Propeller blades typically comprise a blade spar provided with one or more cover layers, typically of a fiber reinforced thermoset plastic material. The blade spar typically comprises a reinforced composite central structural section and leading and trailing edge inserts typically of a foam material. The covering layers maintain the integrity of the blade spar and provide an aerodynamic profile to the blade surface. The cover layers may also include layers such as a lightning protection layer which may include a metallic mesh structure. It may also include an external erosion resistant layer.

When a propeller blade is damaged, the damaged region of the blade surface has to be removed, the exposed blade surface prepared, for example by abrasive blasting, and new layers of material deposited on the exposed blade substrate. Where there are multiple layers of different materials and constructions, this can be time consuming and expensive.

SUMMARY

From a first aspect, the disclosure provides a propeller blade comprising a composite blade spar and at least one cover shell section adhesively bonded to the blade spar by a thermoplastic adhesive.

The propeller blade may comprise a first cover shell section covering a first side of the blade spar and a second cover shell section covering a second side of the blade spar.

The at least one cover shell section may comprise at least one fiber reinforced layer.

The at least one cover shell section may comprise a plurality of layers.

The layers may comprise, for example, an electrically conductive lightning protection layer.

The electrically conductive lightning protection layer may comprise a metallic mesh.

The layers may comprise an external erosion resistant layer.

The blade spar may comprise a structural spar element and leading and trailing edge cores, and a fiber layer wrapped around the structural spar element and the cores.

The propeller blade may further comprise an erosion resistant sheath and/or an electrical de-icer bonded to the blade with a thermoplastic adhesive.

In any of the above embodiments, the thermoplastic adhesive may be a PPO/PS (polyphenylene oxide/polystyrene), a modified PA (polyamide), PEI (polyether imide), PAEK (polyaryletherketone) or PEKK (polyetherketoneketone) adhesive.

The disclosure also provides a method of manufacturing a propeller blade comprising: adhesively bonding at least one cover shell section to a composite blade spar using a thermoplastic adhesive.

The disclosure also provides a method of repairing a propeller blade comprising a composite blade spar and at least one cover shell section adhesively bonded to the blade spar by a thermoplastic adhesive, the method comprising heating the propeller blade to a temperature above the melting temperature of the thermoplastic adhesive, removing a damaged shell section and adhesively bonding a replacement cover shell section to the blade using a thermoplastic adhesive.

That thermoplastic adhesive may be the same thermoplastic adhesive as attached the original cover shell sections to the blade spar, or a different adhesive.

In any of the above methods, a layer of thermoplastic adhesive may be deposited on opposed surfaces of the blade spar and the at least one cover shell section prior to attachment of the at least one cover shell section to the blade spar.

In any of the above methods, the heating may include passing an electric current through an electrically conductive layer provided in the at least one cover shell section.

The disclosure also extends to a method of heating a propeller blade during manufacture or repair, the method comprising passing an electrical current through an electrically conductive layer formed in a skin of the propeller blade.

Optionally, the electrically conductive layer may comprise a metallic mesh.

The disclosure also provides, broadly, a propeller blade comprising a composite blade spar and at least one component adhesively bonded to the blade spar by a thermoplastic adhesive.

DETAILED DESCRIPTION

With reference toFIGS. 1 and 2, a propeller blade2comprises an airfoil section4and a root section6. The root section6is retained in a hub (not shown) and may allow rotation of the blade2about an axis A of the blade2.

The airfoil section4of the propeller blade2has a leading edge8, a trailing edge10and a tip12. As can be seen fromFIG. 2, the blade2further includes a composite blade spar14which comprises a structural spar16, a leading edge insert18and a trailing edge insert20.

As is known in the art, the structural spar16may comprise a fiber reinforced composite material which provides the structural strength to the blade2. Various structural spar constructions are known in the art so they do not need to be described further here. In a typical arrangement, however, the structural spar may comprise a foam core around which a number of layers (typically 10 to 30 layers) of fiber, for example carbon or glass fiber are deposited, for example braided, impregnated with a resin and cured.

The leading and trailing edge inserts18,20provide a basic aerodynamic profile to the blade2. For weight reasons the inserts18,20may be made from a foam material. The leading edge and trailing edge inserts18,20are positioned adjacent the leading edge and trailing edge of the structural spar16respectively and the spar16and the inserts18,20are surrounded by a fiber layer22, for example, a Kevlar® (Poly-paraphenylene terephthalamide) or fiber glass layer. In alternative embodiments the fiber layer could be in the form of a glass fiber or carbon fiber layer. The fiber layer22may be pre-impregnated with a resin or have resin applied to it prior to curing of the blade spar14. The fiber layer22assists in holding the structural spar16and the inserts18,20together. The fiber layer22may comprise just a single layer or multiple layers, for example two layers.

In a conventional blade, the exterior surface of the blade2is formed by the fiber layer22. The surface may then need to be finished, and further material, for example an erosion resistant paint, may be deposited on the surface layer.

This is time consuming both in terms of manufacture but also in terms of repair of the blade should it be damaged by, for example, foreign object impact. In those circumstances, the damaged section of the blade will have to be removed, the exposed substrate prepared for repair, new layers of fiber material deposited in the damaged region, impregnated with resin and cured, and then any surface treatments such as painting be carried out on the newly deposited material. Not only is this process time consuming but it requires the appropriate storage of many materials, some of which have particular Environmental Health and Safety considerations.

The blade2of the present disclosure in its described embodiments seeks to mitigate these problems by means of its basic construction.

With continuing reference toFIGS. 1 and 2and with reference toFIGS. 3 and 4, in a blade2in accordance with the disclosure, rather than having an external structure which is formed by depositing, for example braiding, multiple layers of fiber around the blade spar14, impregnating the layers with resin and curing or consolidating the layers, at least one pre-manufactured cover shell30a,30bis bonded to the spar14by means of a layer32of thermoplastic adhesive. The use of a thermoplastic adhesive is important as it will allow removal of the shell30a,30bshould the blade2need to be repaired at a later stage. This will facilitate both the initial manufacture of the blade2and its subsequent repair.

As illustrated inFIG. 4, the blade may be provided with two cover shells30a,30b. The first cover shell30amay cover all or substantially all of the face surface34of the blade spar14and, after mounting, form the face surface36of the blade2. Similarly the second cover shell30bmay cover all or substantially all of the camber surface38of the blade spar14and, after mounting, form the face surface40of the blade2. The first and second cover shell portions30a,30bwill meet at the leading edge8and the trailing edge10of the blade2and thereby form the entire external surface of the blade2. Of course in other embodiments, more or less than two cover shell portions30a,30bmay be provided and they may not necessarily cover the entire blade surface. Also, the cover shell portions30a,30bmay meet at locations other than the leading and trailing edges8,10of the blade2.

As discussed above, the shell sections30a,30bare pre-manufactured. Moreover, they may be manufactured for attachment to a specific blade spar14. Thus a manufacturer or repairer may hold a stock of differently sized and shaped shells30for use in manufacturing and repairing different blades2.

Each cover shell section30amay comprise a plurality of layers42a,42b,42c, (collectively referred to as layers42) as illustrated schematically inFIG. 3. The particular number of layers42and their structure and composition will be determined by the particular blade2being manufactured.

In some embodiments, the layers42a. . . may include one or more layers of fiber reinforced material, for example thermoset or thermoplastic impregnated fiber layers. The layers42may be of a woven construction, for example. In various embodiments, the cover shell section30may comprise one, two or three layers42a,42b,42c. The layer(s) may be of Kevlar®, glass fiber or carbon fiber for example.

In various embodiments, the layers42may also include an embedded lightning protection layer42b. This would typically be in the form of an electrically conductive element, for example a metallic mesh, metallic braid or metallic tape, e.g. copper tape, provided along a length of the blade2. The layers42may also include an erosion resistant outer layer42cat least in an area of the cover shell30a,30bforming an area of the blade expected to experience high erosion, such as in a leading edge region. An anti-collision paint may also be applied onto regions of the cover shells30a,30bto improve visibility of the blade and thereby avoid people inadvertently walking into the blade when it is rotating.

The cover shell30a,30bmay also comprise de-icing features and/or a leading edge protection feature such as a metallic sheath.

The cover shells30a,30bare therefore pre-manufactured such that, upon attachment to the blade spar14, no substantive additional processing may be necessary on the external surface of the blade2.

The assembly of the blade2will now be described.

As a first step, the blade spar14, with its surrounding fiber layer22may be prepared in a conventional manner, by forming the structural spar16, attaching the leading edge and trailing edge inserts18,20thereto and positioning and curing the surrounding fiber layer22.

Appropriate cover shells30a,30bare then attached to the blade spar14. As discussed above, the shells30a,30bare pre-manufactured for attachment to the particular shape and size of blade spar14being used.

To attach the cover shells30a,30bto the blade spar14, a layer32of thermoplastic adhesive is then provided between the blade spar14and the cover shells30a,30b. The adhesive may be provided on just one of the components, for example either of the cover shells30a,30bor the blade spar14, but a better bond may be provided by applying adhesive to both the cover shells30a,30band the blade spar14. The adhesive may be pre-applied to the cover shells30a,30b(and indeed the blade spar14) as part of its manufacturing process, or it may be applied at the time of bonding.

The cover shells30a,30bare then positioned on the blade spar14. Pressure may be applied to the cover shells30a,30bto ensure good contact between the cover shells30a,30band the blade spar14. For example, the process may be carried out in a vacuum bag which will press the cover shells30a,30binto firm contact with the blade spar14.

The assembly is then heated in order to melt the thermoplastic adhesive for bonding. The temperature required to effect this will depend on the particular adhesive used. For example, some adhesives may melt at or below 180° C. The adhesive should be chosen such that the temperature needed to melt the adhesive should not be so high as to damage the materials of either the blade spar14, for example the foam inserts18,20thereof, or the cover shell30a,30b. Suitable adhesives may include, for example PPO/PS (polyphenylene oxide/polystyrene), a modified PA (polyamide), PEI (polyether imide), PAEK (polyaryletherketone) or PEKK (polyetherketoneketone). The particular adhesive used will depend on the particular blade construction and materials.

The cover shells30a,30bwill normally be attached one at a time to facilitate handling of the blade.

The heating may be effected in any suitable manner. For example, the assembly may be placed in a temperature controlled atmosphere such as an oven and heated therein. In an alternative arrangement, heat may be applied to the relevant area by means of a heating blanket applied to the blade2. In a yet further arrangement, an infra-red heater may be used. A yet further heating mechanism will be described further below.

After an appropriate heating period, the assembly may be left to cool to allow the bond between the blade spar14and the cover shells30a,30bto form.

The external surface of the blade2formed by the cover shells30a,30bwill not need substantial finishing, apart perhaps from removal of excess adhesive which may have exuded from between the cover shells30a,30b.

Thus, the blade2as described above is simple to manufacture and allows pre-manufacture of a range of standard cover shells30a,30bwhich can then be applied to a chosen blade spar14to produce a blade2. Minimal assembly and finishing of the blade2is required. Moreover, as a thermoplastic adhesive is being used, if a problem is noted with the cover shell after assembly, it may simply be removed by re-heating the adhesive and a replacement cover shell30a,30bapplied. This avoids the potential scrapping of an entire blade2as might happen with conventional constructions.

This ability to remove the cover shells30a,30balso facilitates repair of a damaged blade2.

If a blade2becomes damaged in use, then one or more of the cover shells30a,30bwhich have been damaged can be removed by heating the blade2to a temperature which softens or melts the adhesive layer32allowing the cover sheet30a,30bto be removed.

The underlying surface of the blade spar14may then be prepared to receive a new cover shell30a,30b, for example by cleaning to remove extraneous matter and to provide a suitable bonding surface. Anew layer of thermoplastic adhesive may then be deposited on the blade spar14in order to receive a new cover shell30a,30b. The new cover shell30a,30bmay already be provided with a layer of adhesive, as described above. The new cover shell30a,30bis then positioned on the blade spar14and attached as during the manufacturing process. The repaired blade2may then be finished as necessary, as in the manufacturing process.

The process described in the above embodiment not only simplifies the repair process but also allows premanufactured and tested/inspected components to be assembled which may reduce the need for extensive inspection and testing of the repaired blade. The cover shells30a,30bmay be non-destructively tested prior to application by any suitable technique such as ultrasound, X-ray or tap-testing. It also avoids the need to stock and store multiple components. In addition, the repair process can be carried out relatively quickly as there is no need to cure layers of repair material as in existing procedures.

The embodiment described above is merely exemplary and the skilled person will recognise that modifications may be made thereto without departing from the scope of the disclosure.

In the embodiment above, the cover shells30a,30bmay, during their manufacture, be provided with protective features at their leading edges. For example, they may be provided with a de-icer comprising one or more heating elements and a protective sheath, for example of a metallic material such as nickel. In an alternative embodiment, illustrated inFIG. 5, these features are provided as separate components.

Thus with reference toFIG. 5, in this embodiment the blade102comprises a blade spar114having cover shells130a,130band a separate (rather than an integrated) de-icer150and leading edge protective sheath152. The de-icer150may comprise just a de-icer element or comprise additional layers of fibers.

In this embodiment the de-icer150is received in recesses154formed in the respective edges156of the cover shells130a,130b. In certain embodiments, the cover shells130a,130bdo not overlie the de-icer150so that one of the components can be removed without removing the other. The sheath152also may not overlie the cover shells130a,130bor the de-icer150so that one of the components can be removed without removing the other.

The de-icer150and the sheath152are also adhesively attached to the blade2by means of a thermoplastic adhesive. This may be the same adhesive as attaches the cover shells130a,130bto the blade2or a different adhesive. By choosing an appropriate adhesive, it may be possible to remove just the de-icer150or the leading edge sheath152by heating that component without removing the cover shells130a,130b.

In the exemplary method described above, it was mentioned that the heating necessary to melt the thermoplastic adhesive during manufacture or repair may be provided by placing the blade2in an appropriate heated environment, by applying a heating blanket or using an infrared heater. It was also mentioned that certain cover shells30a,30bmay incorporate lightning protection in the form of an electrically conductive layer such as a metallic mesh layer42b. It has been recognised that in such embodiments, it may be possible to provide at least some of the heating required for the melting of the adhesive by passing an electric current through that layer42b.

FIG. 6illustrates, schematically, a possible heating arrangement using this concept. As shown, the mesh layer42bof a cover shell30ais connected to a power source200through appropriate electrical connections202,204. A switch206and controller208may also be provided to control the heating effect provided by the mesh layer42b. The heat produced by the mesh layer42bis close to the adhesive layer32and therefore provides heat in a targeted and efficient manner which may reduce overheating of other components of the blade2.

It will also be appreciated that this heating technique may be used more widely than in the arrangement described above.

Conventional propeller blade constructions include a multi-layer cured fiber reinforced skin which may also incorporate a lightning protection layer. By passing an electric current through the lightning protection layer, it may be possible to heat the skin. The heat generated could be used during initial manufacture or repair of the blade in order to assist in curing of the layers of the blade skin. This may reduce or completely remove the need for external heating to effect curing. Moreover, it may be possible with an appropriate layout of lightning protection layer to heat just selected regions of the blade, thereby reducing energy requirements.

In addition, the heating may be used to assist in blade finishing processes such as in assisting the drying of paint applied to the external surface of a blade. This may accelerate the process, which particularly in the case of repair is advantageous.

From the above it will be seen that the disclosure provides, in its various embodiments, an advantageous blade construction and manufacturing and/or repair method which streamlines manufacturing and/or repair.

It will also be appreciated that modifications may be made to the above embodiments without departing from the scope of the disclosure.

For example, while the embodiments primarily describe the attachment of one or more composite cover shell sections30a,30bto a blade spar14, it will be understood that the disclosure extends to the attachment of other components to a blade spar14using a thermoplastic adhesive. For example the attachment of a de-icer150or sheath152to a blade leading edge8is also described and encompassed by the disclosure. Other components may be attached to the blade spar surface in a similar manner.