Abstract:
A method of repairing a damaged portion of a rotor blade includes filling the damaged portion with a filler material. A pre-cured patch assembly is applied over the damaged portion, the patch assembly including one or more laminate packs positionable at at least one of an upper rotor blade surface and a lower rotor blade surface and one or more overwrap plies positionable over the upper rotor blade surface and the lower blade surface. A repair structure for a damaged portion of a rotor blade includes a volume of fill material disposed at the damaged portion.

Description:
FEDERAL RESEARCH STATEMENT 
     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 OF THE INVENTION 
     The subject matter disclosed herein relates to rotor blades. More specifically, the subject disclosure relates to repair of composite structure rotor blades. 
     Rotor blades, for example, main rotors of helicopters, are often formed from composite materials including graphite, fiberglass, or other such materials. While having certain advantages over rotor blades formed from other materials, when a composite rotor blade is damaged repairs can be costly and time consuming. Of particular concern are trailing edge areas of the rotor blades, where severe limitations are placed on what conditions are repairable, so that even blades with damage such as scratches, or delaminations between plies can result in the blade requiring extensive repair procedures to be performed, such as stripping and rebuilding of the blade. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a method of repairing a damaged portion of a rotor blade includes filling the damaged portion with a filler material. A patch assembly is applied over the damaged portion, the patch assembly including a precured laminate pack positionable at least one of an upper rotor blade surface and a lower rotor blade surface and one or more precured overwrap plies positionable over the upper rotor blade surface and the lower blade surface. 
     According to another aspect of the invention, a repair structure for a damaged portion of a rotor blade includes a volume of fill material disposed at the damaged portion. One or more precured laminate packs are located over the fill material at least one of an upper rotor blade surface and a lower rotor blade surface. One or more precured overwrap plies are affixed over the precured laminate pack over the upper rotor blade surface and the lower blade surface. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       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 schematic view of an embodiment of a helicopter; 
         FIG. 2  is a plan view of an embodiment of a rotor blade for a helicopter; 
         FIG. 3  is a perspective view of a trailing edge portion of a rotor blade; and 
         FIG. 4  is an exploded view of an embodiment of a repair structure for a rotor blade. 
     
    
    
     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 
     Shown in  FIG. 1  is a schematic of a rotary wing aircraft, in this embodiment, a helicopter  10 . The helicopter  10  includes a main rotor assembly  12 , and an airframe  14  having an extending tail  16  at which is mounted an anti-torque rotor  18 . Although the aircraft illustrated is a helicopter  10 , it is to be appreciated that other machines, such as turbo props, tilt-rotor aircraft, or wind turbines may also benefit from the system of the present disclosure. Further, while the description herein is of the system applied to the main rotor assembly  12  if a helicopter  10 , it may also be applied to the anti-torque rotor  18 . The main rotor assembly  12  includes a plurality of blade assemblies  20  located about a rotor shaft  22  via a swashplate  24 . 
     Referring now to  FIG. 2 , each blade assembly  20  includes a rotor blade  26  with a leading edge  32  and a trailing edge  28 . The trailing edge  28  is formed of a plurality of material plies  30  (best shown in  FIG. 3 ), in some embodiments, a graphite material, which are bonded together. While the structure and method described below is directed toward repair of the trailing edge  28 , it is to be appreciated that the repair may be utilized at other portions of the rotor blade  26 , for example, the leading edge  32  or a blade tip  34 . 
     Referring to  FIG. 3 , during operation of the helicopter  10 , the blade assembly  20  may become damaged, as indicated by damaged area  36 . The damaged area  36  is removed from the trailing edge  28  leaving a specified repair shape  38 , determined by limit loads of the blade assembly  20 . In some embodiments, as shown, the repair shape  38  is an arc or a segmented arc (having a flat portion interposed between two arc segments), and in some embodiments the repair shape has a width that is about 10 times the depth. 
     Referring now to  FIG. 4 , the repair shape  38  is filled with a filler material  40 , which may be a mixture of adhesive and fiberglass powder, fiberglass whisker or other suitable material. Once the filler material  40  is applied, it is cured in position and sanded to a desired finish. In an alternative embodiment, a precured filler material  40  is bonded into the damaged area  36  with an adhesive. For example, a foaming adhesive or fiberglass material cut to a selected shape may be used. Further, in some embodiments, the damaged area is not removed  36  to leave a repair shape or prepared damage area  38 , and the filler material  40  is applied directly to the damaged area  36 . 
     A patch assembly  52  is then installed over the repair prepared damage area  38 . The patch assembly  52  includes one or more patch laminate packs  42 . The patch laminate packs  42  are configured to substantially conform to an upper blade surface  44  and/or a lower blade surface  46 , covering the damaged area  38  and filler material  40 . Each patch laminate pack  42  includes a plurality of plies  48 , which are assembled and in some embodiments precured separately. In some embodiments, the patch laminate pack  42  is four plies  48  of material that may be the same material, or alternatively may be of at least two different materials. In some embodiments, the patch laminate pack  42  is formed of plies  48  of two materials, stacked in an alternating fashion, for example, alternating layers of woven fiber glass/epoxy prepreg fabric and carbon fiber tape. Additionally, other composite materials, for example, Kevlar, may be utilized. In one embodiment, the patch laminate pack is formed of four plies  48 . 
     The patch laminate packs  42  are then integrated with an overwrap ply  50 . The overwrap ply  50  is substantially U-shaped in cross-section and is configured to overwrap the patch laminate packs  42  and the trailing edge  28 . The overwrap ply  50  is an assembly of one or more plies of woven fiber glass/epoxy prepreg, Kevlar, carbon fiber tape, or other composite material. Once the patch laminate packs  42  and the overwrap ply  50  are cured into the patch assembly  52 , the patch assembly  52  is secured to the rotor blade assembly  20  such that the patch assembly  52  covers the repair area  42  at the upper blade surface  44  and/or the lower blade surface  46 , wrapping over the trailing edge  28 . The resulting rotor blade assembly  20  including the repair components is cured at room temperature under vacuum or mechanical pressure for, in some embodiments, 24 hours. Alternatively, the assembly  20  may be cured under heat to shorten the cure time. In some embodiments, in addition to an overwrap ply  50 , the patch assembly  52  includes an underwrap ply located between the patch laminate packs  52  and the rotor blade assembly  20 . 
     While in the embodiments described above, the patch assembly  52  is installed to the rotor blade assembly  20  as a unitary piece, in other embodiments it may be installed to the rotor blade assembly  20  as multiple components. For example the patch laminate packs  52  may be installed to the upper blade surface  44  and lower blade surface  56 . Next, the overwrap ply  50  may be installed. 
     The repair described herein allows for repairs to significant portions of the rotor blade assembly  20 , particularly the trailing edge  28 , while being configured to mimic the stiffness of the original rotor blade assembly  20 , i.e. so that any variations in blade strength and dynamic properties are acceptable with respect to operability and structural integrity of the original rotor blade assembly  20 . 
     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.