Abstract:
An erosion strip to protect a leading edge surface is provided including an outer layer comprising a wear-resistant material. An elastomer is affixed to an interior surface of the outer layer. An adhesive layer is shaped to adhere the leading edge surface to the elastomer such that the elastomer and adhesive layers are between the outer layer and the leading edge surface. The elastomer is configured to at least partially isolate strain at the outer layer from strain at the adhesive layer and the leading edge surface.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Exemplary embodiments of the invention relate to a rotary-wing aircraft and, more particularly, to a main rotor blade of a rotary-wing aircraft. 
         [0002]    Rotary wing aircrafts 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. 
         [0003]    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 
       [0004]    According to one embodiment of the invention, an erosion strip to protect a leading edge surface is provided including an outer layer comprising a wear-resistant material. An elastomer is affixed to an interior surface of the outer layer. An adhesive layer is shaped to adhere the leading edge surface to the elastomer such that the elastomer and adhesive layers are between the outer layer and the leading edge surface. The elastomer is configured to at least partially isolate strain at the outer layer from strain between the adhesive layer and the leading edge surface. 
         [0005]    In addition to one or more of the features described above, or as an alternative, in further embodiments the outer layer is formed from a nickel material. 
         [0006]    In addition to one or more of the features described above, or as an alternative, in further embodiments the elastomer is bonded to the interior surface of the outer layer with an epoxy. 
         [0007]    In addition to one or more of the features described above, or as an alternative, in further embodiments the elastomer is vulcanized to the interior surface of the outer layer. 
         [0008]    In addition to one or more of the features described above, or as an alternative, in further embodiments the elastomer extends over all of the interior surface of the outer layer. 
         [0009]    In addition to one or more of the features described above, or as an alternative, in further embodiments the outer layer is formed from a ceramic material. 
         [0010]    According to another embodiment of the invention, a main rotor blade assembly is provided including a spar having a leading edge assembly. The leading edge assembly includes a main sheath laminate and a first erosion strip. The first erosion strip includes a wear-resistant outer layer, a layer of elastomer attached to and extending over at least a portion of an interior surface of the outer layer, and an adhesive which adheres the elastomer to the main sheath laminate. The elastomer is configured to at least partially isolate the strain at the outer layer from strain generated between the adhesive and the main sheath laminate. 
         [0011]    In addition to one or more of the features described above, or as an alternative, in further embodiments the elastomer is vulcanized to the interior surface of the outer layer. 
         [0012]    In addition to one or more of the features described above, or as an alternative, in further embodiments the elastomer is bonded to the interior surface of the outer layer with an epoxy. 
         [0013]    In addition to one or more of the features described above, or as an alternative, in further embodiments an adhesive is arranged over an exposed surface of the elastomer. The adhesive is configured to couple the erosion strip to an adjacent component of the leading edge assembly. 
         [0014]    In addition to one or more of the features described above, or as an alternative, in further embodiments the adhesive bonds the first erosion strip directly to a portion of the main sheath laminate. 
         [0015]    In addition to one or more of the features described above, or as an alternative, in further embodiments the leading edge assembly includes a second erosion strip mounted upon the main sheath laminate. The second erosion strip is formed from a wear-resistant material, wherein the adhesive is configured to bond the first erosion strip to the second erosion strip. 
         [0016]    A method of installing an erosion strip of a main rotor blade is provided including preparing a surface of an adjacent component configured to receive the erosion strip. The erosion strip includes an outer layer of a wear resistant material an elastomer affixed to a portion of the outer layer. The elastomer is configured to at least partially isolate the outer layer from strain generated in the erosion strip. An adhesive configured to couple the erosion strip to the adjacent component is prepared and the erosion strip is affixed to the adjacent component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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: 
           [0018]      FIG. 1  is a perspective view of an exemplary rotary wing aircraft; 
           [0019]      FIG. 2A  is a perspective view of a main rotor blade according to an embodiment of the invention; 
           [0020]      FIG. 2B  is an expanded perspective view of a tip section of the rotor blade of  FIG. 2A ; 
           [0021]      FIG. 2C  is an expanded rear oblique perspective view of a tip section of the rotor blade of  FIG. 2A ; 
           [0022]      FIG. 2D  is an expanded front oblique perspective view of a tip section of the rotor blade of  FIG. 2A ; 
           [0023]      FIG. 2E  is an expanded top view of a top section of the rotor blade of  FIG. 2A ; 
           [0024]      FIG. 2F  is an expanded front view of a tip section of the rotor blade of  FIG. 2A ; 
           [0025]      FIG. 3A  is a perspective, exploded view of a main rotor blade according to an embodiment of the invention; 
           [0026]      FIG. 3B  is a top view of a main rotor blade according to an embodiment of the invention; 
           [0027]      FIG. 4  is a perspective view of an erosion strip according to an embodiment of the invention; and 
           [0028]      FIG. 5  is a flow chart of a method of attaching an the erosion strip to a main rotor blade assembly according to an embodiment of the invention. 
       
    
    
       [0029]    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 
       [0030]      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 aircrafts with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors, and tilt-wing aircrafts are also within the scope of the invention. 
         [0031]    Referring to  FIG. 2A , 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  27  ( FIGS. 2B-2F ); however, any angled or non-angles forms such as cathedral, gull, bent, and other non-straight forms are within the scope of the present invention. The anhedral form  27  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   
         [0032]    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 . The distance between the leading edge  32  and the trailing edge  34  defines a main element chord length Cm. 
         [0033]    Referring now to  FIG. 3A , 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 spar  48  has a generally constant thickness over most of its length. In one embodiment, the root end of the spar  48  has a substantially increased size, thickness, and/or strength to allow for the attachment of the blade  20  to a rotor hub, such as rotor hub H for example, without the need for a separate composite or metallic cuff and other associated attachment hardware. The main core  46  may be formed from a plurality of separate core pieces, each of which may be fabricated from a distinct core material to provide particular lift and strength properties. 
         [0034]    The leading edge assembly  52  generally includes a main sheath laminate  60  upon which is mounted a wear-resistant material as an abrasion resistant system. As shown in  FIG. 3A , the abrasion resistant system can be multiple strips, such as the shown first erosion strip  62  and second erosion strip  64  to provide abrasion protection. Alternatively, as shown in  FIG. 3B , the sheath laminate  60  may include a single erosion strip  64  as the abrasion resistant system to provide the abrasion protection. Additional structures, such as weight cups  61 , leading edge counter weights  63 , and trim tab systems  65  for example, may also be provided, in a manner known to a person having ordinary skill in the art. The tip assembly  42  generally includes a main tip core  66 , a tip end pocket core  68 , a tip leading edge assembly  70 , and a tip cap  28 . The main tip core  66  is substantially aligned with a longitudinal axis of the main core  46  and is positioned directly adjacent the third piece  58  of the main core  46 . 
         [0035]    Referring now to  FIG. 4 , an example of the erosion strip  64  is illustrated in more detail. The erosion strip  64  includes an outer layer  80  having a contour generally complementary to the outer mold line of the blade. The outer layer  80  may be formed from an abrasion and wear resistant material, including, but not limited to nickel, ceramic, titanium, or stainless steel for example. In one embodiment, the thickness of the outer layer  80  is between about 0.005 and 0.035 inches. While not required in all aspects, the outer layer  80  can be manufactured from AM355. It should be understood that a variety of wear-resistant materials may alternatively or additionally be provided for the leading edge assembly  52 . 
         [0036]    Extending over at least a portion of an interior surface  82  of the outer layer  80  is an elastomer  84 , such as rubber for example. The selected elastomer  84  is sufficient to endure the vibratory strain thereon. By way of example, the elastomer  84  may be of a thickness at or between about 0.020 and 0.080 inches. However, other thicknesses are within the scope of the invention. A ratio of the thickness of the elastomer  84  to the outer layer  80  may be between about 1:1.75 to about 16:1. In addition, inclusion of the elastomer  84  is compatible with a portion of an adjacent ice removal system (not shown), such as a heater thereof for example. In one embodiment, the elastomer  84  extends over the entire interior surface  82  of the outer layer  80 . A first surface  86  of the elastomer  84  may be bonded to the adjacent interior surface  82  of the outer layer  80  with an epoxy or other adhesive for example. In another embodiment, the elastomer  84  is vulcanized to the interior surface  82  of the outer layer  80 . An adhesive  88  adheres the elastomer  84  to the leading edge of the blade, such as at the main sheath laminate  60  of  FIG. 3A  or the leading edge main sheath laminate  60  of  FIG. 3B . In this way, the elastomer  84  reduces the effect of a strain mismatch between the leading edge of the blade and the outer layer  80  which, without the elastomer  84 , could lead to a disbonding at the adhesive layer  88 . 
         [0037]    A method  100  for installing the erosion strip  64  of the main blade assembly  40  is illustrated in  FIG. 5 . As shown in block  102 , an outer surface of a component configured to receive the erosion strip  64 , such as the first erosion strip  62  or the main sheath laminate  60  for example, is generally prepared such as by cleaning the surface  69  ( FIG. 3A ) for example. In embodiments where the erosion strip  64  is being replaced, preparation of the outer surface  69  includes removing any material from a previous erosion strip or any material used to attach the erosion strip thereto. In block  104 , an adhesive  88  configured to chemically couple the erosion strip  64  to the outer surface of the component is then prepared. In one embodiment, the adhesive  88  is a paste or film that is applied either to the exterior surface of either the first erosion strip  62  or the main sheath laminate  60  or to an interior surface of the elastomer  84  of the erosion strip  64 . Alternatively, the adhesive  88  may be prepared by removing a protective lining or other material to expose the adhesive material. Once the adhesive  88  is prepared, the erosion strip  64  is aligned with and connected to either the main sheath laminate  60  or the first erosion strip  62 , as shown in block  106 , by arranging the adhesive  88  in contact with the prepared outer surface  69 . 
         [0038]    The layer of elastomer  84  positioned between the outer surface  69  and the outer layer  80  of the erosion strip  64  is able to withstand a high strain generated by the vibratory forces of the main rotor blade  20 . As a result, inclusion of the elastomer  84  prevents cracking or disbonding of the hard outer layer  80  from the composite leading edge material, thereby improving the durability and life of the erosion strip  64 . 
         [0039]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention 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 invention. By way of example, while shown with an integrated cuff as the root section  22 , it is understood that aspects of the invention can be used with other types of root sections, such as root end cuff that is attached to the main rotor spar through a multiple fastener configuration, each fastener of which must be torqued to a required standard. Further, while shown in the context of a rotary wing aircraft, it is understood that aspects could be used with blades used on fixed wing aircraft, wind turbines, maritime propellers or other blades where edges need abrasive protection. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.