Abstract:
A propeller blade assembly includes a spar extending along a propeller blade axis and an outer sleeve surrounding the spar portion at a root end of the rotor blade assembly. The spar is adhesively bonded to the outer sleeve at an interface portion. A spar maximum diameter along the interface portion is larger than an outer sleeve minimum diameter along the interface portion. A method of assembling a propeller blade includes installing an outer sleeve over a spar at a root end of the spar, the spar a not fully cured composite component, and urging the spar into compressive conformance with the outer sleeve at an interface portion of the propeller blade assembly. A spar maximum diameter along the interface portion is larger than an outer sleeve minimum diameter along the interface portion. The spar is cured thereby adhesively bonding the spar to the outer sleeve at the interface portion.

Description:
BACKGROUND 
     The subject matter disclosed herein generally relates to propellers for fixed wing aircraft, rotary wing aircraft and the like. More specifically, the present disclosure relates to lightweight propeller blade construction. 
     Modern propeller blades typically incorporate composite materials to reduce weight and enhance performance. However, the inboard portion of the blade, called the retention member  104 , is typically made of steel. Shown in  FIG. 11  is an example of a present composite propeller blade  100 . The blade  100  includes an outer portion or spar  102  formed of lightweight composite materials. A retention member  104  is formed from a metal, such as steel, aluminum, or titanium, and includes features to interact with bearings  106  at a propeller hub  108 . The bearings  106  react the blade centrifugal and bending loads, while allowing the blade  100  to change pitch. The steel retention member  104  is rather long to accommodate a bond joint  110  with the spar  102 , at which the retention member  104  extends inside of the spar  102 , and is secured to the spar  102 . Due to the features described above, the weight of the steel retention member  104  can be about ⅓ the total blade weight. 
     BRIEF SUMMARY 
     In one embodiment, a propeller blade assembly includes a spar extending along a propeller blade axis and an outer sleeve surrounding the spar portion at a root end of the rotor blade assembly. The spar is adhesively bonded to the outer sleeve at an interface portion and a spar maximum diameter along the interface portion is larger than an outer sleeve minimum diameter along the interface portion. 
     Additionally or alternatively, in this or other embodiments an inner ring is located in a spar cavity and a wedge is positioned inside of the inner ring. Installation of the wedge urges the inner ring into contact with the spar, thus urging the spar into conformal compressive contact with the outer sleeve at the interface portion. 
     Additionally or alternatively, in this or other embodiments the inner ring is segmented. 
     Additionally or alternatively, in this or other embodiments the wedge is an inboard wedge and an outboard wedge, relative to the propeller blade axis. The inboard wedge is secured to the outboard wedge via one or more bolts. 
     Additionally or alternatively, in this or other embodiments an outer surface of the outer sleeve is configured to interface with one or more bearing rows. 
     Additionally or alternatively, in this or other embodiments the interface portion is defined by a convex surface of the spar and a complimentary concave surface of the outer sleeve. 
     Additionally or alternatively, in this or other embodiments the interface portion is defined by a concave surface of the spar and a complimentary convex surface of the outer sleeve. 
     Additionally or alternatively, in this or other embodiments the spar is formed from a composite material and the outer sleeve is formed from a metal material. 
     In another embodiment, a method of assembling a propeller blade includes installing an outer sleeve over a spar at a root end of the spar, the spar a not fully cured composite component, and urging the spar into compressive conformance with the outer sleeve at an interface portion of the propeller blade assembly. A spar maximum diameter along the interface portion is larger than an outer sleeve minimum diameter along the interface portion. The spar is cured thereby adhesively bonding the spar to the outer sleeve at the interface portion. 
     Additionally or alternatively, in this or other embodiments urging the spar into compressive conformance with the outer sleeve at the interface portion includes installing an inner ring in a spar cavity and installing a wedge assembly inside of the inner ring. Installation of the wedge assembly urges the inner ring into contact with the spar, thus urging the spar into conformal compressive contact with the outer sleeve at the interface portion. 
     Additionally or alternatively, in this or other embodiments installation of the wedge results in expansion of the inner ring into contact with the spar. 
     Additionally or alternatively, in this or other embodiments the wedge is an inboard wedge and an outboard wedge, relative to the propeller blade axis. The inboard wedge is tightened to the outboard wedge via one or more bolts and the tightening of the inboard wedge to the outboard wedge urges the inner ring into contact with the spar. 
     Additionally or alternatively, in this or other embodiments the interface portion of the spar is preformed prior to installing the outer sleeve over the spar. 
     Additionally or alternatively, in this or other embodiments the interface portion is defined by a convex surface of the spar and a complimentary concave surface of the outer sleeve. 
     Additionally or alternatively, in this or other embodiments the interface portion is defined by a concave surface of the spar and a complimentary convex surface of the outer sleeve. 
     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 plan view of an embodiment of a propeller assembly; 
         FIG. 2  is a cross-sectional view of an embodiment of a propeller blade assembly and attachment to a propeller hub; 
         FIG. 3  illustrates a portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 4  illustrates another portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 5  illustrates yet another portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 6  illustrates a cross-sectional view of another embodiment of a propeller blade assembly and attachment to a propeller hub; and 
         FIG. 7  illustrates a portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 8  illustrates another portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 9  illustrates yet another portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 10  illustrates still another portion of an exemplary assembly method of an embodiment of a propeller blade assembly; 
         FIG. 11  is a cross-sectional view of a prior propeller blade assembly. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a propeller assembly  10  of, for example, an aircraft such as a fixed wing aircraft or a rotary wing aircraft. Although a configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines with propeller or rotor systems are within the scope of the present invention. Further, one skilled in the art will readily appreciate that the present disclosure may be utilized in other, non-aircraft applications. The propeller assembly  10  includes a plurality of propeller blades  12  secured at a propeller hub  14 . Each propeller blade  12  has a root end  70  closest to the propeller hub  14  and a tip end  72  furthest from the propeller hub  14 . The propeller hub  14  rotates about a propeller hub axis  68 . The propeller blades  12  are retained at the propeller hub  14  by one or more sets or rows of bearings  26  (see  FIG. 2 ) that are configured to react propeller blade  12  centrifugal and bending loads, while allowing the propeller blade  12  to change pitch about a propeller blade axis  16 . 
     Referring now to  FIG. 2 , an exemplary embodiment of the propeller blade  12  is illustrated. The propeller blade  12  includes a radially outboard portion, or spar  18 , formed from a composite material, such as graphite or carbon fiber or the like. It is to be noted that, as utilized in the present application, the terms “inboard” and “outboard” denote position relative to, or relative distance from, the propeller hub axis  68 , while the terms “inner” and “outer” denote position relative to, or relative distance from the propeller blade axis  16 . The spar  18  is insertable into, and is secured to, a radially inboard retention member, or outer sleeve  20 . The outer sleeve  20  is formed from a steel or other metallic material, and in some embodiments includes a trunion pin  46 . The outer sleeve  20  is secured to the spar  18  at a sleeve inner surface  22 , while a sleeve outer surface  24  is configured to interact with the bearings  26 . The bearings  26  are arranged in bearing rows and support the propeller blade  12  at the propeller hub  14 . While a single row of bearings  26  is shown in  FIG. 2 , it is to be appreciated that the present disclosure may be readily applied to propeller blades retained by two or more rows of bearings. 
     The sleeve inner surface  22  includes a concave sleeve portion  28  at which a convex spar portion  30  of the spar  18  is located and retained via adhesive. To urge the convex spar portion  30  into contact with the concave sleeve portion  28 , the propeller blade  12  includes a segmented inner ring  32  installed inside of the spar  18 , which is urged outwardly into contact with the spar  18  by an outboard wedge  34  and an inboard wedge  36 . The segmented inner ring  32  is formed by a plurality of inner ring segments extending partially around the propeller blade axis  16 . When the outboard wedge  34  and inboard wedge  36  are installed, the segmented inner ring  32  is expanded, thus urging the convex spar portion  30  into contact with the concave sleeve portion  28 . 
     The spar  18  transmits the blade loads to the outer sleeve  20  along the adhesive interfaces defined as areas A and B in  FIG. 2 , of the concave sleeve portion  28 . The spar  18  is also mechanically locked to the outer sleeve  20  along the concave sleeve portion  28  due to the fact that a spar maximum diameter  38  is larger than an outer sleeve minimum diameter  40 . 
     One challenge for lightweight propeller blades is that the bending moment (BM) capacity of the retention is often reduced due to the lower centrifugal load (CL). The bearings  26  can be sized to withstand high bending moments, but the interface between the spar  18  and outer sleeve  20  may become unloaded due to insufficient centrifugal loading. The blade CL is transmitted through the adhesive interface between the spar  18  and outer sleeve  20  at area A. The through-thickness adhesive stresses are compressive. This is desirable because adhesive compressive strength is considerably higher than tensile. The BM reduces the compressive stresses at area A. The propeller blade  12  improves the BM capacity because the shape of interface between the spar  18  and the outer sleeve  20  prevents the load at area A from going into tension. In particular, this is accomplished by providing a secondary load path at area B when the BM is very high. In this case, the adhesive interface at area B is subjected to compressive stresses. 
     A method for assembly of the propeller blade assembly  12  is illustrated in  FIGS. 3-5 . Referring to  FIG. 3 , the outer sleeve  20  is installed over an uncured or partially cured composite spar  18  from an inboard end  42  of the composite spar  18 . Installing from the inboard end  42  is desirable, as opposed to installing the outer sleeve  20  from an outboard end  44  of the spar  18  as this method does not limit the spar  18  geometry outboard of the outer sleeve  20 . An outer surface  48  of the uncured spar  18  may be substantially straight when the outer sleeve  20  is installed thereon, as shown in  FIG. 3 . In other embodiments, the convex spar portion  30  may be formed prior to installation of the outer sleeve  20  utilizing, for example, a wash out mandrel, foam or other material of the selected shape onto which the spar material is braided at the inboard end  42 . The wash out mandrel or foam is then removed and the spar  18  may be collapsed so that the outer sleeve  20  will fit over the spar  18 . Pre-forming the convex spar portion  30  in this manner helps ensure that the spar  18  has the desired braiding coverage necessary at the convex spar portion  30 , as opposed to braiding the inboard end  42  in a straight configuration, and then merely expanding it to form the convex spar portion  30 . 
     Referring to  FIG. 4 , the outboard wedge  34  is then inserted into a spar cavity  50 , followed by the segmented inner ring  32 . The inner ring  32  segments may be connected by, for example, pins or other connecting means to make handling and installation easier, while still allowing for expansion of the inner ring  32  and the spar  18 . Next, an expanding tool, schematically shown as  52 , is utilized to expand the segmented inner ring  32  forcing the uncured spar  18  to take the shape of the concave sleeve portion  28  and also puts the adhesive in areas A and B into compression. The expansion tool  52  is removed, and referring now to  FIG. 5 , the inboard wedge  36  is inserted into the spar cavity  50 . Bolts  54  or other means are used to draw the outboard wedge  34  and inboard wedge  36  together, which expands the segmented inner ring  32  further, which in turn compresses the spar  18  and adhesive into contact with the outer ring  30  at the concave sleeve portion  28 /convex spar portion  30  interface. The propeller blade  12  is then injected with resin and cured to achieve the selected shape. The segmented inner ring  32 , the outboard wedge  34  and the inboard wedge  36  prevent collapse of the spar  18  when the CL and BM are applied to the propeller blade  12 . 
     Referring again to  FIG. 2 , additional components such as a blade balance tube  56  aiding in achieving propeller assembly  10  balance and a bore plug  58  to prevent ingress of oil or other material into the spar cavity  50 , may be installed at an inboard end  80  of the propeller blade  12 . 
     Referring now to  FIG. 6 , another exemplary embodiment of a propeller blade  12  is illustrated. In this embodiment, the sleeve inner surface  22  includes an convex sleeve portion  60  at which an concave spar portion  62  of the spar  18  is located and retained via adhesive. To urge the concave spar portion  62  into contact with the convex sleeve portion  60 , the propeller blade  12  includes an outboard inner ring  64  and an inboard inner ring  66  installed inside of the spar  18 , which are each urged outwardly into contact with the spar  18  by the outboard wedge  34  and the inboard wedge  36 . The outboard inner ring  64  and the inboard inner ring  66  may be unitary or alternatively may be formed by a plurality of inner ring segments extending partially around the propeller blade axis  16 . When the outboard wedge  34  and inboard wedge  36  are installed, the outboard inner ring  64  and the inboard inner ring  66  are expanded, thus urging the concave spar portion  62  into contact with the convex sleeve portion  60 . 
     As with the embodiment of  FIG. 2 , the spar  18  transmits the blade loads to the outer sleeve  20  along the adhesive interfaces defined as areas A and B in  FIG. 6 , of the convex sleeve portion  60 . The spar  18  is also mechanically locked to the outer sleeve  20  along the convex sleeve portion  60  due to the fact that the spar maximum diameter  38  is larger than the outer sleeve minimum diameter  40 . The propeller blade  12  improves the BM capacity because the shape of interface between the spar  18  and the outer sleeve  20  prevents the load at area A from going into tension. In particular, this is accomplished by providing a secondary load path at area B when the BM is very high. In this case, the adhesive interface at area B is subjected to compressive stresses. 
     Another exemplary method for assembly of the propeller blade assembly  12  is illustrated in  FIGS. 7-10 . Referring to  FIG. 7 , the outboard wedge  34  is inserted into the spar cavity  50  followed by the outboard inner ring  64 . A clamp or other tool is then used to compress the inboard end  42  of the uncured spar  18 . Referring to  FIG. 8 , the outer sleeve  20  is then installed over the uncured spar  18  from the inboard end  42 . The expansion tool  52  is then utilized to expand the uncured spar  18  to form the concave spar portion  62  which conforms with the convex sleeve portion  60 . This expansion also puts the adhesive at areas A and B into compression. 
     Referring now to  FIG. 9 , the expansion tool  52  is removed and the inboard inner ring  66  is installed in the spar cavity  50 , followed by the inboard wedge  36 . Referring to  FIG. 10 , bolts  54  or other means are used to draw the outboard wedge  34  and inboard wedge  36  together, which expands the outboard inner ring  64  and inboard inner ring  66 , which in turn compresses the spar  18  and adhesive into contact with the outer sleeve  20  at the convex sleeve portion  60 /concave spar portion  62  interface. The propeller blade  12  is then injected with resin and cured to achieve the selected shape. The outboard inner ring  64  and inboard inner ring  66 , the outboard wedge  34  and the inboard wedge  36  prevent collapse of the spar  18  when the CL and BM are applied to the propeller blade  12 . 
     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.