Patent Publication Number: US-2020291783-A1

Title: Blade de-icing

Description:
FOREIGN PRIORITY 
     This application claims priority to European Patent Application No. 19290016.5 filed Mar. 15, 2019, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to blades including for example propeller blades, rotor blades, fan blades wind turbine blades that require de-icing. 
     BACKGROUND 
     It is common in blades that experience low temperatures in use to provide an electrical heater at the leading edge of the blade in order to melt ice that has accumulated on the leading edge. 
     At present, the electrical heater is typically formed as a one-piece component that comprises a metallic heating foil embedded in an elastomeric matrix. The foil and matrix are cured in a vacuum bag to the appropriate  3 D shape that is then bonded to the leading edge of the blade. 
     This design has several potential drawbacks. For example, the  3 D geometry may be difficult to produce, leading to potential high scrappage rates. In addition, it may be difficult accurately to bond the heater on the leading edge due to the softness of the material leading to geometrical discrepancies during bonding. In addition, the whole heater must be removed and replaced when there is a defect on just one side of the blade. The cost of the part is high and the matrix material used may age, necessitating replacement. 
     This disclosure seeks to mitigate at least some of the above potential issues. 
     SUMMARY 
     In accordance with one aspect of this disclosure, there is provided a blade comprises a blade body and a blade de-icer located on the leading edge of the blade body. The blade de-icer comprises a first heater part bonded to an external surface of a face side of the blade body and a separate second heater part bonded to an external surface of a camber side of the blade body. The first and second heater parts may each extend substantially to the leading edge of the blade body. Each heater part comprises an electrical heating element arranged therein sandwiched between an inner layer and an outer layer of the heater part. 
     The first and second heater parts may each have an electrical input terminal and an output terminal at a base end of the respective first and second heater parts. 
     Each of the first and second heater parts may comprise a flange at its base end. The flange may being angled, for example at an angle of about 90°, relative to a longitudinal axis of the heater part whereby the flange may overlie a radially inwardly facing surface of the blade body. 
     The input and output terminals may each comprise a pair of washers, one washer engaging a first side of a terminal portion of the heating element and the other washer engaging an opposed second side of the terminal portion of the heating element. 
     In accordance with a further aspect of the disclosure, there is provided a heater part for attachment to a face side or a camber side of a blade body. The heater part comprises an electric heating element sandwiched between inner and outer layers of the heater part, and a terminal for connection of electrical power to the heating element. The terminal comprises a pair of washers. One washer engages a first side of a terminal portion of the heating element and the other washer engaging an opposed second side of the terminal portion of the heating element. 
     The washers may be received in openings provided in the inner and outer layers of the heater part. 
     In embodiments, the washers may not protrude from the inner and outer layers. Optionally the washers may lie flush with the external surfaces of the inner and outer layers. 
     The blade may comprise a terminal block provided in the blade body for receiving fasteners extending through the washers. 
     The terminal block may comprise one or more fastener receivers having a threaded bore for receiving the fastener. The threaded bore may be provided in a threaded insert mounted in the fastener receiver. 
     The blade may further comprise an erosion resistant layer arranged over the first and second heater parts on the leading edge of the blade body. 
     The blade may be a propeller blade, a propulsor blade, a fan blade, an open rotor blade or a wind turbine blade. 
     The inner and outer layers of the heater part may comprise a fibre reinforced composite material or an elastomeric material with a reinforcing backing. 
     In a further aspect, the disclosure provides a blade heating system comprising a blade in accordance with the disclosure and an electrical power supply connected to the first and second heater parts, the power supply being configured such that one heater part may be energised independently of the other heater part. 
     The blade heating system may further comprise a control configured such that the electrical power supply to each heater part may be controlled independently. 
     In a further aspect, the disclosure provides a method of constructing a blade in accordance with the disclosure comprising bonding the first heater part to an external surface of a leading edge portion of the camber side of the blade body and bonding the second heater part to an external surface of a leading edge portion of the face side ( 6 ) of the blade body. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some embodiments of the disclosure will now be described by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows a blade in accordance with the disclosure; 
         FIG. 2  shows a sectional view along line II-II of  FIG. 1 ; 
         FIG. 3  shows the heater parts of the blade of  FIG. 1 ; 
         FIG. 4  shows a view of the bottom of the blade of  FIG. 1  in the direction of arrow X in  FIG. 1 ; 
         FIG. 5  is a sectional view along line V-V of  FIG. 4 ; 
         FIG. 6  is a sectional view along line VI-VI of  FIG. 4 ; 
         FIG. 7  illustrates schematically the electrical connections to the heating elements of the heater parts; 
         FIG. 8  is a schematic section through one heater part construction; 
       and 
         FIG. 9  is a schematic section through an alternative heater part construction. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows, schematically, a blade  2  in accordance with the disclosure. In this embodiment, the blade  2  is a propeller blade, although the disclosure is not limited to such and encompasses other types of blade, for example fan blades (for gas turbine engines), rotor blades (including open rotor blades) and wind turbine blades. 
     The blade  2  of  FIG. 1  comprises a blade body  4  having a face side  6  and a camber side  8 , extending between a leading edge  10  and a trailing edge  12  of the blade body  4 . The blade  2  is further provided with a root  14  for attaching the blade  2  to a hub (not shown). 
     The blade body  4  may be of any suitable construction, for example a composite construction comprising a plurality of fibre-reinforced layers arranged around a blade core. Such constructions are well known to the skilled person and need not therefore be described in detail here. 
     The blade  2  further comprises a blade de-icer  20  at the leading edge  10  of the blade body  4 . In this embodiment, the blade de-icer  20  extends over only a portion of the span of the blade  2  from the root  14  towards a tip  22  of the blade  2 . The precise spanwise extent of the blade de-icer  20  will be determined by the particular blade  2  and its expected operating conditions. 
     As can be seen from  FIGS. 1 and 2 , the blade de-icer  20  only extends over a limited chordwise length of the face and camber sides  6 ,  8  of the blade body  4  from the leading edge  10 . Again, the precise chordwise extent of the blade de-icer  20  will be determined by the particular blade  2  and its operating conditions. 
     Also provided on the blade  2  is an anti-erosion layer  24 . This layer  24  extends over the blade de-icer  20  and around the leading edge  10  of the blade from the blade root  14  to the blade tip  22  to protect the blade  2  and the de-icer  20  from damage due to airborne particles such as sand and from other foreign objects. The anti-erosion layer  24  may be of any suitable construction, for example a layer of polyurethane or a thermoplastic material as is known in the art. The anti-erosion layer  24  completely covers the blade de-icer  20  on the face and camber sides  6 ,  8  of the blade body  4  in this embodiment. The anti-erosion layer  24  may act not only to protect the blade de-icer  20  but also diffuse heat over the leading edge  10 . 
     As described so far, in general terms, the blade  2  is conventional. However, as will be described further below, the blade  2  differs from conventional blades  2  by virtue of the construction of the blade de-icer  20 . In conventional blades  2 , the blade de-icer  20  is formed as a single piece heater that is attached to the leading edge  10  of the blade  2 . In a blade in accordance with disclosure, however, the blade de-icer  20  is formed as a heater having a first heater part  26  that is bonded to the external surface of the face side  6  of the blade body  4  and a separate second heater part  28  that is bonded to the external surface of the camber side  8  of the blade body  4 . 
     As can be seen in  FIG. 2 , for example, the first and second heater parts  26 ,  28  are both elongate elements extending from a base end  30  to a tip end  32 . Each heater part  26 ,  28  comprises an electric heating element  34  that is sandwiched between inner and outer layers  36 ,  38  of the heater part  26 ,  28 . The composition of the inner and outer layers  36 ,  38  and indeed the construction of the heating element  34  may vary from embodiment to embodiment, and particular non-limiting examples of constructions will be described in further detail below. 
     As can be seen from  FIG. 2 , the first heater part  26  and second heater part  28  are located on the leading edge  10  of the blade body  4  and are attached thereto by a layer  40  of adhesive. The adhesive may be of any suitable type, such that the temperature of the heater does not weaken or compromise the bonding of the heater parts  26 ,  28  to the blade body. In certain embodiments, the adhesive may be a thermoplastic adhesive, to facilitate the removal and replacement of a heater part  26 ,  28 . In that event, the melting temperature of the adhesive should be sufficiently above the operating temperature of the heater  2  to avoid problems with weakening or melting of the adhesive bond. 
     In this embodiment, the first and second heater parts  26 ,  28  abut or substantially one another at the leading edge  10 . The layer  40  of adhesive may, as shown extend between the opposed edges of the heater parts  26 ,  28  to fill any gap formed between those opposed edges, thereby avoiding a discontinuity in the leading edge of the blade  2  at the junction of the heater parts  26 ,  28  and also to secure the edges of the heater parts  26 ,  28  to one another. 
     As can be seen in  FIGS. 3 and 6  for example, each heater part  26 ,  28  is formed with a flange  42  at its base end  30 . The flange  42  is angled inwardly relative to a longitudinal axis A of the respective heater part  26 ,  28 . In this example, the flange  42  is arranged at an angle of approximately 80° to 90° relative to the axis A. The particular angle of the flange  42  will be determined by the configuration of the blade  2 , as the flange  42  is intended to engage a radially inwardly facing surface  44  formed at the root end of the blade body  4 . This surface  44  is commonly referred to as a butt face of the blade  2 . 
     As can be seen from  FIG. 6 , the heating element  34  of the heater part  26 ,  28  extends from a main section  46  of the heater part  26 ,  28  that extends along the blade leading edge  10  into the flange  42 . Electrical connections  48  are made to the heater parts  26 ,  28  at the flange  42 , as will be described further below. 
     Each heating element  34  has a terminal portion  50  through which electrical energy is supplied to the heating element  34 . An electrical terminal  52  is formed at the terminal portion  50  of the heater element  34 . As the heater element  34  may be relatively thin (for example 50 microns in thickness) and therefore not that robust, the electrical terminal  52  is formed with a pair of electrically conductive washers  54   a ,  54   b . A first washer  54   a  is attached, for example bonded by an electrically conductive adhesive, to a first side of the heating element  34 . A second washer  54   b  is attached, for example bonded by an electrically conductive adhesive, to a second, opposed side of the heating element  34 . An opening  56  is formed in the terminal portion  50  of the heating element  34  in alignment with the openings in the washers  54   a ,  54   b . The washers  54   a ,  54   b  may reinforce the terminal portion  50  of the heating element  34  making it less susceptible to damage during installation of the heater parts  24 ,  26  on the blade body  4 . They may also resist turning of the terminal portions  50  of the heating element  34  when an electrical connection is made thereto, as will be discussed further below. 
     The washers  54   a ,  54   b  are received within openings  56   a ,  56   b  in the inner and outer layers  36 ,  38  of the heater part  26 ,  28 . The washers  54   a ,  54   b  may be completely received within the thickness of the inner and outer layers  36 ,  38  and may not protrude therefrom. As illustrated, in some embodiments, the washers  54   a ,  54   b  may have substantially the same thickness as the inner/outer layers  36 ,  38  so as to lie substantially flush with the external surfaces thereof. However, in other embodiments, the washers  54   a ,  54   b  may protrude from the inner/outer layers  36 ,  38 . Typically the washers may have a thickness of 0.5 mm. 
     As can be seen from  FIGS. 5 and 6 , electrical leads  60  are attached to the terminal portions  50  of the respective heating elements  34  by fasteners  62 , for example bolts or screws  62 . The electrical leads  60  have suitable blade connectors  64  for receiving the fastener  62 . The fasteners  62  are received in a terminal block  66  provided in the root end of the blade body  4 . Separate terminal blocks  66  may be provided for each fastener  62 , but in the described embodiment and advantageously from the point of ease of construction, a common terminal block  66  to receive multiple, in this case all the fasteners  62 . 
     The terminal block  66  comprises a base part  68  that is arranged in a recess  70  in the root end of the blade body  4 . The base part  68  may be of an electrically insulating material such as a plastics material. The base part  68  may be fitted into the recess  70  during the manufacture of the blade body  4 , or fitted therein after the manufacture of the blade body  4 . 
     The base part  68  has a plurality of (in this embodiment four) recesses  72 , each recess  72  receiving a fastener receiver  74 . The fastener receiver  74  may be a push fit within the recess  72  or be adhesively secured therein. The fastener receiver  74  comprises a body  76 , for example a moulded plastics body  76 , which comprises a threaded insert  78 . The threaded insert receives the threaded end  80  of the respective fastener  62 . In some embodiments, the body  76  may be provided with a threaded portion rather than with a threaded insert  78 . 
     The fastener receivers  74  will be visible on the radially inner surface  44  of the blade body  4  and will align with the washers  54   a ,  54   b  attached to the heater elements  34  when the heater parts  26 ,  28  are mounted to the blade body  4  to receive the fasteners  62 . 
     The illustrated arrangement provides a robust mounting for the electrical connections to the heater parts  26 ,  28  and to the blade body  4 . When the fastener is screwed into the receiver  74 , the connectors  64  will clamp against the washers  54   a , rather than the heater element  34  itself, reducing the likelihood of damage to the heating element by crushing or tearing through turning. 
     While the fastener  62  in this embodiment has been illustrated as being a screw fastener  62  received in a threaded insert  78 , other forms of fastener  62  may be used. For example the fastener  62  may comprise a stud received in the threaded insert  78 , and the electrical connectors  64  be fastened in position by a nut threaded onto the stud. In a yet further arrangement, a stud may be moulded into the fastener receiver  74  or into the base part  68  directly to receive a nut. 
     Turning now to the control of the blade de-icer  20 ,  FIG. 7  illustrates schematically, a blade heating system. The heating system comprises a power supply  80   a ,  80   b  attached to the terminal portions  50  of the respective heating elements  34  of the first and second heater parts  26 ,  28 . Although shown separately, the power supplies  80   a ,  80   b  may be a common power supply  80   c . A separate control  82   a ,  82   b  is also provided for each heater part  26 ,  28 . 
     The advantage of providing a separate power supply  80   a ,  80   b  (or a power supply  80   c  supplying the heater parts in parallel rather than in series) is that should the heater element  34  of one of the heater parts  26 ,  28  be damaged, power can still be supplied to the other heater part  26 ,  28  thereby providing at least some heating to the leading edge of the blade  2 . In some embodiments, should power be disconnected to just one heater part  26 ,  28 , in order to avoid possible out of balance problems in a rotor comprising multiple blades, power may be disconnected to a blade on the opposite side of the rotor. 
     In addition, the advantage of providing a separate control  82   a ,  82   b  for each heater part  26 ,  28  is that each heater part  26 ,  28  may be controlled independently of the other. This allows the heating regime applied to either side of the blade  2  to be tailored to specific needs. For example, the power supply to the respective heater parts  26 ,  28  may be controlled so as to optimise the heating time on each side of the blade  2  so as to minimise energy requirements. 
     Returning now to the construction of the heater parts  26 ,  28 , the lay-up of the heater parts  26 ,  28  has been described in broad terms above, with a heating element  34  being sandwiched between inner and outer layers  36 ,  38 . Some exemplary heater part lay-ups will now be described with reference to  FIGS. 8 and 9 . 
     With reference to  FIG. 8 , in one embodiment, a heater part  126  comprises an elastomeric inner layer  136  for example of nitrile rubber, polychloroprene or the like. The heater part  126  further comprises an outer layer  138  which is itself made up from an elastomeric layer  140  for example of nitrile rubber, polychloroprene or the like and a reinforcement layer  142 , for example of a fabric such as fiberglass. A heating element  134  is sandwiched between the inner and outer layers  136 ,  138 . The heating element  134  may be a metallic or other conductive element such as a foil, for example of stainless steel or copper, carbon or other conductive wires, or an electrically conductive paint. The various layers may be laid up and bonded together using a technique as discussed above, for example using impregnation of fibres with resin, autoclaving and so on. 
     In another embodiment, illustrated in  FIG. 9 , a heating part  226  comprises an inner layer  236  and an outer layer  238 . The inner and outer layer  236 ,  238  are in this embodiment made up from multiple layers, for example two layers  240 , of a composite material, such as a fiberglass or aramid material. The material and the number of plies of material making up the inner and outer layers  236 ,  238  may be the same or different and may be chosen to suit the particular installation. The materials of the A heating element  234  is sandwiched between the inner and outer layers  236 ,  238 . The heating element  234  may have a similar construction to that in the previous embodiment. The various layers may be laid up and bonded together using a technique as discussed above. 
     Having described the structure of the blade  2  above, an exemplary method of manufacture will now be described. 
     A blade body  4 , including the terminal block  66 , the first heater part  26  and the second heater part  28  are manufactured separately. The blade body  4  may be made by any suitable method, as would be known to the skilled person. 
     The first and second heater parts  26 ,  28  may be manufactured using a mould and counter-mould technique or a mould and vacuum bag technique. In the former technique, component layers of the heater parts  26 ,  28  are built up in a mould and a counter-mould then placed over the deposited layers to shape the layers to the appropriate shape. Depending on the materials used, the mould may be heated to cure the layers. In the latter technique, component layers of the heater parts  26 ,  28  are built up in a mould and a vacuum bag then placed over the mould and deposited layers and a vacuum drawn to force the layers into the mould and take up the shape of the mould. The assembly may be placed in an autoclave for example to cure the deposited layers. 
     Whichever technique is used, making the de-icer  20  in two separate parts  26 ,  28 , for attachment to opposed faces of a blade body  4 , facilitates the construction as the parts  26 ,  28  do not need to have such a complicated geometry as the previously one-piece heaters. They may therefore be more accurately produced and potentially lead to less scrap being generated during the manufacturing process. The process is therefore more repeatable that with previous constructions, and even if a part should have to be scrapped for whatever reason, it will be a lesser value part than previously. 
     The first and second heater parts  26 ,  28  are then adhesively bonded to the external surface of the blade body  4  at the leading edge thereof, on the face and camber sides  6 ,  8  thereof respectively. The blade body  4  and the heater parts  26 ,  28  may be prepared for bonding by any suitable technique, for example cleaning and surface preparation. 
     A suitable adhesive may then be applied to either or both of the blade body  4  and the heater parts  26 ,  28 . Depending on the adhesive used, the adhesive could be pre-applied to either the blade body  4  or the heater parts  26 ,  28 . Suitable adhesives include epoxy adhesives and polyurethane adhesives. In some embodiments, as discussed above, a thermoplastic adhesive may be used as this may facilitate removal of the heater parts  26 ,  28  should they need repair or replacement. The heater parts  26 ,  28  may be suitably clamped to the blade body  4  to assist in forming a successful bond and depending on the adhesive used, the assembly may be heated to cure the bond. 
     After attachment of the heater parts  26 ,  28 , the anti-erosion layer  24  may be applied over the heater parts  26 ,  28 . The anti-erosion layer  24  may be adhesively secured to the blade  2 . In some embodiments, the anti-erosion layer  24  may be a sheet, which is self-adhesive. In other embodiments, an adhesive may be applied between the anti-erosion layer  24  and the blade  2 , for example on opposed surfaces of both. 
     The described technique of providing a leading edge blade de-icer is advantageous for the various reasons given above. In addition, by providing two separate heater parts  26 ,  28 , should one part become damaged that part can be removed and replaced, avoiding the need to replace the whole heater, which is clearly advantageous in terms of repair time and costs.