Patent Publication Number: US-2018044006-A1

Title: Splice cap nickel abrasion strip caul

Description:
BACKGROUND OF THE INVENTION 
     Exemplary embodiments of the invention relate to a rotary-wing aircraft and, more particularly, to a main rotor blade of a rotary-wing aircraft. 
     Rotary wing aircraft include a plurality of main rotor blades coupled to a central hub. The rotor blades include aerodynamic surfaces that, when rotated, create lift. The configuration of the main rotor blades, particularly the tip section thereof, is selected to enhance rotor blade performance, for example to increase the hover and lift capabilities of the rotary-wing aircraft. Rotor blades are subjected to high stresses and strains resulting from aerodynamic forces developed during operation. 
     The leading edges of helicopter rotor blades are subject to wear, such as fatigue wear for example, due to vibratory loads. In particular there is a recurring problem of erosion of the metal leading edge abrasion strips of the main rotor blades. When such erosion occurs, the affected rotor blades must be removed from the helicopter and sent for repair, resulting in several weeks of downtime for the aircraft. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment of the invention, a caul assembly includes a semi-rigid caul plate formed in a shape complementary to a portion of a component receivable therein and a heater located at an exterior surface of the semi-rigid caul plate. The heater being adapted to apply heat to a localized portion of the component. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the heater includes a plurality of regions and a temperature of each of the plurality of regions is generally identical. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the heater includes a plurality of regions and a temperature of at least one of the plurality of regions is different. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments a plurality of wires associated with the heater is consolidated at a leader tab extending from an edge of the caul assembly. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments comprising a control cabinet configured to control a supply of power to the heater. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments a shape of the caul assembly is complementary to a portion of a rotor blade. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the shape of the caul assembly is complementary to a portion of the rotor blade including an outboard splice cap abrasion strip. 
     According to another embodiment, a method of bonding a splice cap abrasion strip to a rotor blade includes installing the splice cap abrasion strip to a leading edge of the rotor blade and applying localized heat and pressure to the splice cap abrasion strip to bond the splice cap abrasion strip to the rotor blade. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments applying localized heat includes installing a caul assembly including a heater in overlapping arrangement with the splice cap abrasion strip. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments a power supply is operably coupled to the caul assembly. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the localized heat applied by the heater is non-uniform across the caul assembly. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments applying localized pressure includes installing a vacuum bag over a tip section of the rotor blade and the splice cap abrasion strip. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments a vacuum is operably coupled to a port of the vacuum bag. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the splice cap abrasion strip is formed from a nickel material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an example of a rotary wing aircraft; 
         FIG. 2  is a perspective view of an example of a rotor blade of a rotary wing aircraft; 
         FIG. 3  is an exploded perspective view of the component of a portion of the rotor blade of  FIG. 2 ; 
         FIG. 4  is an exploded perspective view of the tip end assembly of a rotor blade according to an embodiment; 
         FIG. 5  is a perspective view of a caul for bonding a portion of the tip end assembly according to an embodiment; 
         FIG. 6  is a perspective view of a rotor blade as the splice cap nickel abrasion strip is mounted to the rotor blade according to an embodiment; and 
         FIG. 7  is a block diagram illustrating a method of using the bonding fixture to bond the outboard splice cap to a rotor blade according to an embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically illustrates a rotary-wing aircraft  10  having a main rotor system  12 . The aircraft  10  includes an airframe  14  having an extending tail  16  which mounts a tail rotor system  18 , such as an anti-torque system for example. The main rotor assembly  12  is driven about an axis of rotation A through a main gearbox (illustrated schematically at T) by one or more engines E. The main rotor system  12  includes a plurality of rotor blade assemblies  20  mounted to a rotor hub assembly H. Although a particular helicopter configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines, such as high speed compound rotary-wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors, and tilt-wing aircraft are also within the scope of the invention. 
     Referring to  FIG. 2 , each rotor blade assembly  20  of the rotor assembly  12  generally includes a root section  22 , an intermediate section  24 , a tip section  26 , and a tip cap  28 . Each rotor blade section  22 ,  24 ,  26 ,  28  may define particular airfoil geometries to tailor the rotor blade aerodynamics to the velocity increase along the rotor blade span. As, illustrated, the rotor blade tip section  26  may include an anhedral form (not shown); however, any angled or non-angled forms such as cathedral, gull, bent, and other non-straight forms are within the scope of the present invention. The anhedral form as defined herein may include a rotor blade tip section  26  which extends at least partially out of a plane defined by the intermediate section  24 . 
     The rotor blade sections  22 - 28  define a span R of the main rotor blade assembly  20  between the axis of rotation A and a distal end  30  of the tip cap  28  such that any radial station may be expressed as a percentage in terms of a blade radius x/R. The rotor blade assembly  20  defines a longitudinal feathering axis P between a leading edge  32  and a trailing edge  34 . 
     Referring now to  FIGS. 3 and 4 , the rotor blade assembly  20  generally includes a main blade assembly  40  and a tip assembly  42 . The main blade assembly  40  includes an upper skin  44 , a main core  46 , a spar  48 , a lower skin  50 , and a leading edge assembly  52 . The main spar  48 , main core  46 , and skins  44 ,  50  are generally referred to as a pocket assembly, the forward portion of which is closed out by the leading edge assembly  52 . The main core  46  may be formed from a single core piece or a plurality of separate core pieces, each of which may be fabricated from a distinct core material to provide particular lift and strength properties. The spar  48  has a generally constant thickness over most of its length. 
     The leading edge assembly  52  generally includes a main sheath laminate  60  upon which is mounted a wear-resistant material, such as an abrasion resistant system for example. In the non-limiting embodiment illustrated, the abrasion resistant system can be multiple strips, such as a first erosion strip  62  and a second erosion strip  64  to provide abrasion protection. Additional structures, such as weight cups, leading edge counter weights, and trim tab systems for example, may also be provided, in a manner known to a person having ordinary skill in the art. Although not shown, it should be understood that in some embodiments a heater mat may be positioned around a portion of the rotor blade  20 , such as about the leading edge between the spar  48  and the main sheath laminate  60  or between the main sheath  60  and an adjacent erosion strip for example. 
     The tip assembly  42  generally includes a main tip core  66 , a tip end core  68 , a tip leading edge assembly  70 , and a tip cap  72 . The main tip core  66  is substantially aligned with a longitudinal axis of the main core  46  and is positioned directly adjacent the end of the main core  46 . The tip cap  72  is configured to removably couple to the tip end core  68  at the distal end of the rotor blade  20 . 
     With reference now to  FIG. 4 , the tip leading edge assembly  70  is illustrated in more detail. The tip leading edge assembly  70  includes an intermediate splice cap  74  and an outboard splice cap  76  configured to provide abrasion protection. The intermediate splice cap  74  and the outboard splice cap  76  are formed from any suitable material, including but not limited to, titanium, nickel, or a variety of other wear-resistant materials or combinations thereof. The intermediate splice cap  74  and the outboard splice cap  76  are both positioned to overlap the first erosion strip  62  and abut the second erosion strip  64  at a tip interface. As a result of this configuration, it is possible to replace the second erosion strip  64  without affecting or having to remove or replace any portion of the tip assembly  42 . 
     A caul assembly  80 , best shown in  FIG. 5 , is used to bond the outboard splice cap abrasion strip  76  to the leading edge  32  of the rotor blade  20 . The caul assembly  80  includes a semi-rigid caul plate  82 , such as formed from a carbon fiber material for example. As shown, the caul plate  82  is formed in a specific shape generally complementary to the leading edge  32  of the rotor blade  20  at the tip assembly  42 , or at the interface between the leading edge assembly  52  and the tip leading edge assembly  70 . The caul plate  82  is configured to conform the material of the outboard splice cap abrasion strip  76  into a desired structure. The caul plate  82  defines a cavity  84  within which the leading edge  32  of the rotor blade  20  is received such that the caul plate  82  substantially covers the entire surface of the outboard splice cap abrasion strip  76 . 
     A heater blanket  86  is mounted to or integrally formed with an exterior surface of the caul plate  82  such that heat from the heater blanket  86  is transmitted through the caul plate  82  to the splice cap abrasion strip  76  when the caul assembly  80  is installed about the rotor blade  20 . The heater blanket  86  includes one or more heating elements (not shown) configured to generate the heat necessary for the bonding process. In an embodiment, the wiring of the at least one heating element is consolidated and exposed via a leader tab  88  extending outwardly from an end  90  of the caul assembly  80 . A control cabinet controls power output to a single heater or multi-zoned heater. A power supply is configured to couple to the leader tab  88  to control power output to the heater blanket  86 . 
     Depending on the construction of the heating element, the heat output from the heater blanket  86  may be constant, or may vary across at least one of the span and the chord of the rotor blade  20 . The heater blanket  86  may include one or more regions or zones to accommodate variations in thermal cycling and ensure even heating across the outboard splice cap abrasion strip  76  during the adhesive cure. In such embodiments, the temperature across the various regions of the heater blanket  86  may be the same, or may vary. In an embodiment, the thermal cycling of the zones adjacent the ends of the outboard splice cap abrasion strip  76 , such as adjacent the interface with the leading edge assembly  52  and adjacent the tip cap  72  for example, is greater than at a central portion of the heater blanket  86 . 
     A method  100  of bonding the outboard splice cap abrasion strip  76  to the leading edge  32  of a rotor blade  20  is illustrated in more detail in  FIG. 7 . In block  102 , the outboard splice cap abrasion strip  76  is prepped for bonding by applying an adhesive to the surface of the outboard splice cap abrasion strip  76  configured to contact the rotor blade  20  and then locating the outboard splice cap abrasion strip  76  onto the leading edge  32 . In block  104 , the caul assembly  80  is then mounted to the leading edge  32  of the rotor blade  20  in an overlapping relationship with the outboard splice cap abrasion strip  76 . A vacuum bag  92  (see  FIG. 6 ) or another component configured to apply positive pressure to the exterior of the rotor blade  20  is mounted about the tip section  26  of the rotor blade  20  in block  106 . The open end  94  of the vacuum bag  92  is taped to a surface of the rotor blade  20  such that the caul assembly  80  and the outboard splice cap abrasion strip  76  are substantially enclosed within the vacuum bag  92 . In an embodiment, the connections, such as the leader tabs  88  for example, for supplying power to the caul assembly  80  is disposed outside the vacuum bag  92 . Inclusion of the leader tab  88  simplifies the vacuum bagging process and eliminates a leak path generated when not using a consolidated tab. In block  108 , a power supply, for example operated by a controller  96 , is coupled to the heater blanket  86  to energize the one or more heating elements of the heater blanket  86 , and a vacuum is operably coupled to a vacuum port of the vacuum bag  92 . In block  110 , heat and positive pressure are simultaneously applied to the exterior of the rotor blade  20  to bond the outboard splice cap abrasion strip  76  to the rotor blade  20 . 
     The caul assembly illustrated and described herein allows a component, such as an outboard splice cap abrasion strip for example, to be bonded to a rotor blade at room temperature or at an elevated temperature without the need for positioning the rotor blade in a large walk-in oven. As a result, manufacturing and maintenance of the rotor blade may be performed more easily and with an improved process time. 
     While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.