Patent Publication Number: US-9429025-B2

Title: Erosion resistant helicopter blade

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 61/398,304, filed Jun. 22, 2010, the entire contents of which are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Agreement No. W911W6-08-2-0006 for Rotor Durability Army Technology Objective (ATO). The Government has certain rights in the invention. 
    
    
     BACKGROUND 
     Existing rotor blades for helicopters include fiberglass and carbon fiber composite skins and titanium and nickel leading edge shields. The titanium and nickel leading edge shields are designed to combat erosion. The titanium shield oxidizes as it is impacted by sand and rocks, and causes a halo around the rotor path, which is highly visible at nighttime. This is detrimental because the aircraft is highly visible and the halo can be a distraction to pilots trying to land an aircraft under the assistance of night vision equipment. There is a need in the art to provide erosion protection to rotor blades to improve the life of the blades and to eliminate effects of shield oxidation. 
     SUMMARY 
     An exemplary embodiment is a rotor blade including a main portion having a main portion leading edge shield; a main portion impact-resistant layer formed on a nose of the leading edge shield; a main portion erosion-resistant layer formed on a top and bottom of the main portion, rearward of the main portion impact-resistant layer; a main portion foil formed on the top and the bottom of the main portion rearward of the main portion erosion-resistant layer; a tip cap having a tip cap leading edge shield; a tip cap impact-resistant layer formed on a surface of the tip cap leading edge shield; and a tip cap foil formed on the top and the bottom of the tip cap rearward of the tip cap erosion-resistant layer. 
     Another exemplary embodiment is a method of manufacturing a rotor blade including obtaining a main portion having a main portion leading edge shield; applying a main portion erosion-resistant layer on a top and bottom of the leading edge shield; applying a main portion impact-resistant layer on a nose of the leading edge shield, forward of the main portion erosion resistant layer; applying a main portion foil on the top and the bottom of the main portion rearward of the main portion erosion-resistant layer; obtaining a tip cap having a tip cap leading edge shield; applying a tip cap impact-resistant layer on a surface of the tip cap leading edge shield; and applying a tip cap foil on the top and the bottom of the tip cap rearward of the tip cap erosion-resistant layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above described and other features, aspects, and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a rotary wing aircraft for use with the present invention; 
         FIG. 2  is a top view of a main rotor blade in exemplary embodiments; 
         FIGS. 3-5  depict formation of a tip cap; 
         FIGS. 6-8  depict formation of a main rotor blade; 
         FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 2 ; 
         FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 2 ; 
         FIG. 11  is a cross-sectional view taken along line  9 - 9  of  FIG. 2  in an alternate embodiment; and 
         FIG. 12  is a cross-sectional view taken along line  10 - 10  of  FIG. 2  in an alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       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. 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 1 -E 3 . The main rotor system  12  includes a multiple of rotor blade assemblies  20  mounted to a rotor hub 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, will also benefit from the present invention. 
       FIG. 2  is a top view of a main rotor blade  30  in exemplary embodiments. The rotor blade  30  includes a main portion  32  and a tip cap  34 . As embodiments relate to modifications to the leading edge and upper and lower surfaces of the main portion  32  and tip cap  34 , description of the entire structure of the rotor blade  30  is not provided herein.  FIG. 3  is a top view of the tip cap  34  prior to applying erosion resistant materials. Tip cap  34  includes a tip cap body  36  formed from, for example, a composite material as is known in the art, and a tip cap leading edge shield  38  formed from a nickel material as is known in the art. Tip cap leading edge shield  38  extends rearward from the nose of the tip cap body  36  to serve as a tip cap erosion-resistant layer that provides protection high-velocity impacts at the tip cap leading edge. 
       FIG. 4  illustrates application of an impact-resistant layer  40  to the nose of the tip cap leading edge shield  38 . In exemplary embodiments, the tip cap impact-resistant layer  40  is an HVOF high-velocity sprayed, tungsten carbide coating. Impact-resistant layer  40  provides protection against high angle, high velocity impacts to the leading edge of the tip cap  34 . 
       FIG. 5  illustrates application of tip cap metal foils  42  to the tip cap body  36 , rearward of the nickel strip  38 . In exemplary embodiments, the metal foils  42  are stainless steel foils bonded to the composite tip cap body  36 . The metal foils  42  are applied to the upper and lower composite skins on the tip cap body  36  to provide protection from lower angle, glancing impacts. 
       FIG. 6  illustrates the tip cap  34  secured to the main portion  32  of main rotor  30 .  FIG. 6  also depicts application of a main portion impact-resistant layer  52 . Impact-resistant layer  52  is applied to the nose of an existing metal (e.g. titanium) leading edge shield  50  of the main portion  32  of rotor blade  30 . In exemplary embodiments, the main portion impact-resistant layer  52  is an HVOF high-velocity sprayed, tungsten carbide coating. Impact resistant layer  52  provides protection against high angle impacts to leading edge shield  50  of the main portion  32 . 
       FIG. 7  illustrates application of a main portion erosion-resistant layer  54  to the top and bottom of leading edge shield  50  of the main portion  32  of main rotor  30 . The erosion-resistant layer  54  overlaps an edge of impact-resistant coating  52 , but does not encompass the entire impact-resistant layer  52 . In exemplary embodiments, the main portion erosion-resistant layer  54  is a cold-spray niobium metal. Erosion-resistant layer  54  provides protection from the lower angle impacts. Both impact-resistant layer  52  and erosion-resistant layer  54  are applied minimally, to minimize weight. Impact-resistant layer  52  and erosion-resistant layer  54  are only applied onto the leading edge titanium shield  50  for two reasons. First, the severity of the application processes facilitates applying the coatings to a metal substrate. Second, covering the leading edge titanium shield  50  eliminates the sparking halo effect. 
       FIG. 8  illustrates application of main portion metal foils  56  to the main portion  32 , rearward of the erosion-resistant layer  54 . In exemplary embodiments, the metal foils  56  are stainless steel foils bonded to the composite main portion  32 . The metal foils  56  are applied to the upper and lower composite skins on the main portion  32  to provide protection from lower angle, glancing impacts. 
     A tail rotor blade (not shown), may be formed in the same manner as the main portion  32  of rotor blade  30 . As noted above, this entails an impact-resistant layer on the nose of the leading edge, an erosion-resistant layer on the top and bottom, rearward of the impact-resistant coating and metal foils on the upper and lower composite skins. 
       FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 2 .  FIG. 9  shows the main portion  32  of main rotor blade  30 . Evident in  FIG. 9  is the impact-resistant layer  52  formed on the nose of metal leading edge shield  50 , top and bottom erosion-resistant layers  54  formed rearward to the impact-resistant layer  52 , and top and bottom metal foils  56  formed rearward of the erosion-resistant layer  54 . Bottom metal foil  56  extends further back from the leading edge than the top metal foil  56 . 
       FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 2 .  FIG. 10  shows the tip cap  34 . Evident in  FIG. 10  are the impact-resistant layer  40  formed on the nose of tip cap leading edge shield  38  and top and bottom metal foils  42  formed rearward of the tip cap leading edge shield  38 . Bottom metal foil  42  extends further back from the leading edge than the top metal foil  42 . 
       FIG. 11  is a cross-sectional view taken along line  9 - 9  of  FIG. 2  in an alternate embodiment. This embodiment is similar to that in  FIG. 9 , except that top and bottom erosion-resistant layers  54  are formed prior to formation of the impact-resistant layer  52 . As such, the erosion-resistant layers  54  underlap the impact-resistant layer  52 . As discussed above, top and bottom metal foils  56  are formed rearward of the erosion-resistant layer  54 . Bottom metal foil  56  extends further back from the leading edge than the top metal foil  56 . 
       FIG. 12  is a cross-sectional view taken along line  10 - 10  of  FIG. 2  in an alternate embodiment. This embodiment is similar to that in  FIG. 10 , except that the impact resistant layer  40  covers entire leading edge strip  38 , rather than just the nose. Further, tip cap metal foils  42  extend same length on upper and lower side of the tip cap body  36 . 
     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. 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.