Abstract:
A pin wrap having a unitary construction that includes a first elongated arm extending from an inboard end to an outboard end; a second elongated arm extending from the inboard end to the outboard end; and a curved end having an internal surface and a directly opposing external surface. The curved end integrally connects the first elongated arm to the second elongated arm at the outboard end. Also, the curved end is arcuate having a plurality of radii of curvatures. A blade and a helicopter with a blade can include the pin wrap.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to propellers and to a structurally efficient pin wrap configuration for a propeller blade. 
       DESCRIPTION OF RELATED ART 
       [0002]    Traditional composite pin wraps used in rotor blades are spar-type members made from, typically, uniform orthotropic composite materials such as, e.g., graphite or fiberglass. These traditional pin wraps consist of a composite beam of a given height. The pin wrap includes a curved loop at an outboard end having a single radius of curvature that wraps around a circular clamp or fitting at the outboard end. However, traditional composite pin wrap can have structural deficiencies in their design. One deficiency comes from contact with the circular clamp or fitting. The circular clamp or fitting places a large stress concentration at a tangency where the flat portion of the wrap meets a circle of the composite beam. This non-uniform stress at the tangency point results in a pin wrap that is oversized the wrap area of the composite pin wrap. Another deficiency comes from use of orthotropic materials in the composite pin wrap, which causes a non-uniform pressure distribution across a height of the composite pin wrap that is in contact with the circular clamp or fitting at the outboard end. The non-uniform pressure distribution causes localized stress concentrations at the top and bottom edges of the composite pin wrap. A need therefore exists for a structurally efficient composite pin wrap that addresses the deficiencies of traditional pin wraps. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    According to one embodiment of the invention, a pin wrap having a unitary construction includes a first elongated arm extending from an inboard end to an outboard end; a second elongated arm extending from the inboard end to the outboard end; and a curved end having an internal surface and a directly opposing external surface. The curved end integrally connects the first elongated arm to the second elongated arm at the outboard end. Also, the curved end is arcuate having a plurality of radii of curvatures. 
         [0004]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a plurality of radii of curvatures that include a first radius of curvature for a first section of the interior surface and a second radius of curvature for a second section of the interior surface. 
         [0005]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a first radius of curvature that is dissimilar from the second radius of curvature. 
         [0006]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an internal surface that has a convex shape along a height of the curved end, the height being perpendicular relative to a plane defined by the plurality of radii. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a convex shape that is configured to redistribute stress uniformly along the height of the curved end. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an external surface that has a concave shape along a height of the curved end, the height being perpendicular relative to a plane defined by the plurality of radii. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a curved end that is configured to receive a connecting element along the internal surface. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a plurality of radii of the curved end are configured to create a uniform pressure distribution along the internal surface. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments could include first and second elongated arms that are tapered from the inboard end to the outboard end. 
         [0012]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a pin wrap that is made from an orthotropic composite material. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an inboard end with a plurality of bolt holes for attachment to a structure. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a rotor blade having a body that contains the pin wrap. 
         [0015]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a rotor blade that is configured to be coupled to a rotor hub. 
         [0016]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a helicopter that contains the pin wrap. 
         [0017]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a plurality of rotor blades coupled to a rotor hub; where the pin wrap is contained within each of the rotor blades and being configured to connect each of the rotor blades to the rotor hub. 
         [0018]    The technical function achieved by one or more embodiments and/or alternatives described above includes distributing stress along a pin wrap when tension is applied to the pin wrap. With the plurality of multiple radii, stress concentration along an edge of tangency is minimized as stress in the pin wrap is distributed along the entire perimeter of curved end which creates a uniform pressure distribution at curved end and a structurally efficient pin wrap. Also, in an embodiment of a pin wrap with an orthotropic composite material, by pre-curving the pin wrap with convex and concave surfaces, loads or stress can be redistributed along entire height of curved end when tension is applied. 
         [0019]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    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 like elements are numbered alike in the several FIGURES: 
           [0021]      FIG. 1  is a general perspective view of a rotary wing aircraft according to an embodiment of the invention; 
           [0022]      FIG. 2A  is a perspective view of a pin wrap according to an embodiment of the invention; 
           [0023]      FIG. 2B  is a partial perspective view of an exemplary pin wrap according to an embodiment of the invention; 
           [0024]      FIG. 3  is a partial plan view of the pin wrap of  FIGS. 2A-2B  showing a detail of an outboard end according to an embodiment of the invention; 
           [0025]      FIG. 4  is a partial side perspective view of the pin wrap of  FIGS. 2A-2B  but showing a detail of the outboard end according to an embodiment of the invention; and 
           [0026]      FIG. 5  is a schematic cross-section view of the pin wrap of  FIG. 4  according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring to the drawings,  FIG. 1  illustrates an example of a vertical takeoff and landing (VTOL) high speed compound or coaxial contra-rotating rotary wing aircraft  10 . In an embodiment, rotary wing aircraft  10  can include an orthotropic pin wrap  30  in a plurality of rotor blades  20  or propeller blades  26  for connecting to a rotor hub of rotor system  14  according to embodiments. Aircraft  10  has an airframe  12  which supports a dual, contra-rotating main rotor system  14  and a translational thrust system  16 . Main rotor system  14  rotates about a rotor axis of rotation R and is driven for rotation by one or more engines  18 . Main rotor system  14  includes a plurality of rotor blades  20  mounted to a contra-rotating rotor system  22 ,  24  for lift, anti-torque and thrust. Also, a translational thrust system  16  can provide supplemental or auxiliary thrust for aircraft  10  through a plurality of propeller blades  26 . Although a particular configuration of rotary wing aircraft  10  is illustrated and described in the disclosed non-limiting embodiments, other configurations, and/or machines with rotor systems are within the scope of the present invention. While the invention is described with reference to rotary-wing aircraft, where weight and strength advantages of composites over other technologies is exemplary, the concepts and ideas expressed herein can also benefit and be equally applicable to other structures such as, for example, other portions of an aircraft (such as a yoke), in wind turbines, and other systems with rotary elements. As such, embodiments of the disclosed invention are not restricted to application in aircraft, but are applicable wherever an efficient pin wrap is desired. 
         [0028]    Referring to  FIG. 2 , a pin wrap  30  is shown in perspective view. In an embodiment, pin wrap  30  is generally a U-shaped flexible member that is made from an orthotropic composite material such as fiberglass or graphite; but, in other embodiments, pin wrap  30  may be made from a metal or metal alloy. Pin wrap  30  is generally oriented along a vertical plane and extends for a finite length L from an inboard end  32  to an outboard end  34 . Pin wrap  30  includes substantially identical first elongated arm  38  and second elongated arm  42  connected by a curved end  39  at the outboard end  34 . First arm  38  has a first end  36  at inboard end  32  and traverses for a finite length L where it gradually tapers to a smaller height at outboard end  34 . At outboard end  34 , first arm  38  terminates into curved end  39  and continues as second arm  42  towards inboard end  32 . Second arm  42  traverses a finite length L from curved end  39  where it gradually tapers to a larger height at second end  40 . The height of pin wrap  30  varies according to the taper; however, the thickness of pin wrap  30  remains generally constant. First and second ends  36  and  40  include openings for bolts that attach to, in an embodiment, a rotor hub connecting member (not shown). While not required in all aspects, the curved end  39  could be encased in a clamp or fitting (not shown) for connecting to other elements of the rotor blade  20  or wrapped around a pin  41  as is depicted in  FIG. 2B . 
         [0029]      FIG. 3  shows a partial plan view of a detail of outboard end  34  for pin wrap  30  according to an embodiment of the invention. In an embodiment, outboard end  34  incorporates multiple radii of curvatures around connecting pin  41  ( FIG. 2B ). Arm  38  has a generally linear portion  44  that terminates into curved end  39  at outboard end  34 . Curved end  39  has generally arcuate or curved portions  46  and  50 , each with a radius of curvature. In an embodiment, first curved portion  46  has a first radius of curvature  48  while second curved portion  50  has a second radius of curvature  52 . In embodiments, first radius of curvature  48  can be dissimilar to second radius of curvature  52  or same as second radius of curvature  52 . Further, curved end  39  terminates into a generally linear portion  54  of second arm  42  as it loops around connecting pin  41 . While a double radius of curvature is discussed in an embodiment in  FIG. 3 , additional radii of curvature at curved end  39 , e.g., three, four or other multiple radii, could also be contemplated so as to provide other optimal shapes of pin wrap  30  in other applications. 
         [0030]    Conventional pin wraps are typically made with a uniform geometry at a curved portion with a single radius of curvature  49  (shown in phantom in  FIG. 3 ) around a circular clamp or fitting. With these conventional pin wraps, stress concentration is at an edge of tangency where the curved portion wraps around a clamp or fitting when tension is applied. This non-uniform stress concentration results in a pin wrap that is oversized in other areas of the curved portion for a given stress value. In the present pin wrap  30 , stress concentration along edge of tangency  56  is minimized as the multiple radii of curvatures such as, for example, a double radius of curvature  48  and  52  can contact more surface area of connecting clamp or fitting (not shown). Stress in pin wrap  30  is distributed along the entire perimeter of the inside surface of curved portions  46  and  50 , which creates a uniform pressure at curved end  39 . As the stress is distributed, the overall structure of pin wrap  30  can also be made smaller than what would be required for a conventional pin wrap with a circular outboard end having a single radius of curvature or a bolted connection. A technical effect is a structurally efficient pin wrap  30  that optimizes the geometry of pin wrap  30 . 
         [0031]      FIG. 4  shows curved end  39  in a partial elevation view and  FIG. 5  shows a cross-section view of curved end  39 . In an embodiment, curved end  39  includes a first radius of curvature R 1  for interior surface  64  (See  FIG. 5 ) along a height H of curved end  39  extending into interior cavity  61  and exterior surface  66  has a second radius of curvature R 2  (see  FIG. 5 ) along the height of curved end  39  extending into interior cavity  61 . In embodiments, first radius of curvature R 1  is substantially the same as second radius of curvature R 2  or could be dissimilar. A cross-section view of a conventional pin wrap with a uniform geometry at a curved portion (shown as a phantom rectangle in  FIG. 5 ) is also depicted and shows a generally orthogonal interior surface  65  and a generally orthogonal exterior surface  65 . In the present invention, curved end  39  has a top edge  60  and bottom edge  62 , which define a height H. Inner surface  64  of curved end  39  is convex along height H and outer surface  66  of curved end  39  is concave along height H. 
         [0032]    With a conventional pin wrap made from an orthotropic composite material, as the outboard end wraps around a circular clamp or fitting and tension is applied to the circular clamp or fitting, the pin wrap curves radially outwards from an interior cavity of pin wrap. As a result, top and bottom corners are in contact with the surface of the connecting fitting (along top and bottom edges of the pin wrap). These top and bottom corners see a higher stress concentration than other areas of the curved end  39  causing higher loads or stress at these areas at an expense of other areas of the pin wrap  30 . In the present invention, by pre-curving the pin wrap  30  radially towards interior cavity  61 , loads or stress can be redistributed along entire height H of curved end  39  when tension is applied to connecting clamp or fitting (not shown) or connecting pin  41  ( FIG. 2B ). 
         [0033]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. For instance, aspects of the invention are not limited to propeller blades for aircraft, and can be used in other portions of an aircraft (such as a yoke), in wind turbines and other systems with rotary elements. Many modifications, variations, alterations, substitutions or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the 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.