Abstract:
A blade shank assembly for an aircraft propeller blade includes a blade shank; a split blade retention race encircling the blade shank, the split blade retention race including two splits, wherein the split blade retention race comprises: inner chamfers located between the blade shank and the split blade retention race at each of the two splits; and outer chamfers located adjacent to a race surface of the split blade retention race at each of the two splits; and a plurality of ball bearings located on the race surface of the split blade retention race.

Description:
FIELD OF INVENTION 
       [0001]    The subject matter disclosed herein relates generally to the field of a split blade retention race for an aircraft propeller blade. 
       DESCRIPTION OF RELATED ART 
       [0002]    A propeller for use in an aircraft includes a central rotating hub having a plurality of blade receiving sockets disposed about the hub. The propeller blades each have a shank located at the base of each propeller blade, and each shank is disposed in a respective blade receiving socket. The blade receiving sockets and the blade shanks are provided with opposed, separated ball bearing race surfaces, and a plurality of ball bearings are held between the blade receiving socket and the blade shank on the race surfaces, allowing adjustment of the pitch of the blade. The ball bearing race on the blade shank may be a separate component, referred to as a blade retention race, that encircles the blade shank. Currently, the blades are shipped with a one piece blade race. 
         [0003]    Due to the movement and loading of the ball bearings on the race surface, and resulting damage that occurs to the race, one piece races may be replaced by split races at overhaul. Such a multisection blade retention race may be referred to as a split blade retention race. Once the one-piece race is replaced by split races, the movement and loading of the ball bearings on the edges of the split races has a tendency to damage the blade shank beyond repair. 
       BRIEF SUMMARY 
       [0004]    According to one aspect of the invention, a blade shank assembly for an aircraft propeller blade includes a blade shank; a split blade retention race encircling the blade shank, the split blade retention race including two splits, wherein the split blade retention race comprises: inner chamfers located between the blade shank and the split blade retention race at each of the two splits; and outer chamfers located adjacent to a race surface of the split blade retention race at each of the two splits; and a plurality of ball bearings located on the race surface of the split blade retention race. 
         [0005]    According to another aspect of the invention, a split blade retention race for a blade shank assembly for an aircraft propeller blade includes a race surface, the race surface configured to hold a plurality of ball bearings; a split surface, the split surface being configured to be located inside of split separating a first section of the split blade retention race from a second section of the split blade retention race; an inner surface, the inner surface being configured to be located adjacent to a blade shank in the blade shank assembly; an inner chamfer, wherein the inner chamfer is angled back along an interface between the split surface to the inner surface; and an outer chamfer, wherein the outer chamfer is angled back along an interface between the split surface and the race surface. 
         [0006]    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 
         [0007]    Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
           [0008]      FIG. 1  illustrates an embodiment of a blade shank assembly for an aircraft propeller blade including a split blade retention race. 
           [0009]      FIG. 2  illustrates a top view of an embodiment of a split blade retention race. 
           [0010]      FIG. 3  illustrates a side view of an embodiment of a blade shank with a split blade retention race at a split. 
           [0011]      FIG. 4  illustrates a side view of an embodiment of a split blade retention race. 
           [0012]      FIG. 5  illustrates a side view of an embodiment of a split blade retention race on a blade shank. 
           [0013]      FIG. 6  illustrates a detailed view of an embodiment of inner and outer chamfers and associated inner and outer radii. 
           [0014]      FIG. 7  illustrates a detailed view of a compressive deflection of a ball on a race surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of a split blade retention race with inner and outer chamfers are provided, with exemplary embodiments being discussed below in detail. Current split blade races may have a limited lifespan due to the load from the ball bearings that are held in the race loading the split blade retention race and the geometry of the race at the split. Inclusion of chamfers (defined as a straight beveled edge connecting two surfaces) at the split on both the inner surface of the split blade retention race (adjacent to the blade shank) and the outer surface of the split blade retention race (adjacent to the race surface that holds the ball bearings) prevents the ball bearings from loading the unsupported portion at the edge of the split blade retention race at the split. A radius connecting the chamfer to the adjacent surface provides a smooth race transition for the ball bearings over the split to prevent damage to the blade shank. This extends the life of the split blade retention race, and reduces the number of propeller blades that need to be scrapped due to damage to the blade shank. As noted above, the chamfers further include associated radii, which are curved surfaces that blend the chamfers to adjacent surfaces on the split blade retention race. The radii provide a smooth transition between the chamfers and the adjacent surfaces. 
         [0016]      FIG. 1  shows an embodiment of a blade shank assembly  100  for insertion into a blade receiving socket (not shown) of an aircraft propeller. The blade shank assembly  100  includes blade shank  101 , ball bearings  102 , and split blade retention races  103 . Splits  104  are located between sections of split blade retention race  103 . The edges of split blade race  103  at the splits  104  each include a chamfer on the internal side, adjacent to the shank  101 , and on the external side, adjacent to the race surface of the split blade retention races  103  on which ball bearings  102  are located. The proportions of the internal and external chamfers ensure that the race is not loaded over the unsupported portion at the edges of the inner split blade retention races  103 . The internal and external radii provide a smooth transition by ball bearings  102  between the chamfers and the adjacent race surfaces on the split blade retention race  103  in order to prevent damage to the blade shank  101  as the ball bearings  102  pass over the splits  104 . This helps to reduce damage to the split blade retention race  103  and the blade shank  101  from the ball bearings as they pass over the splits  104 . The width of the splits  104  are a resultant of the manufacturing process. The split blade retention race  103  is manufactured as a complete ring and then cut in half to form splits  104 . Manufacturing the split blade retention race  103  as a complete ring before splitting ensures that the race curvatures of both halves of the split blade retention race  103  are identical. 
         [0017]      FIG. 2  shows a top view of the split blade retention race  103  of  FIG. 1 . The ball bearings  102  move on the race surface of split blade race  103 , and pass over splits  104 . Splits  104  are located between the sections of split blade retention race  103 . The split blade retention race  103  includes inner chamfers  201 , at the edge of the each of the splits  104  on the inner surface of the split blade retention race  103  that is placed adjacent to blade shank  101 . The split blade retention race  103  also includes outer chamfers  202 , located at the edge of the splits  104  on the race surface of the split blade retention race  103  adjacent to the ball bearings  102 . The outer chamfers  202  prevent loading from the ball bearings  102  from being transferred to the unsupported section of the split blade retention race  103 . Therefore, a ball bearing that is located on a portion of the radius or chamfer where the distance below the race surface equals the compressive deflection of the ball on the race is fully unloaded. The split configuration of the split blade retention race  103  is such that only one ball bearing of ball bearings  102  is unloaded at any given time; the rest of the ball bearings  102  share the load. This helps to minimize the amount of load carried by each ball. 
         [0018]      FIG. 3  shows a side view of a blade shank  101  and a split blade retention race  103  at a split  104 . Race surface  301  is the surface on which the ball bearings  102  are held. Split surface  302  of split blade retention race  103  is located inside a split  104  directly facing a corresponding split surface on another section of the split blade retention race  103  on the other side of the split  104 . Inner chamfer  201  is angled back from split surface  302  to an inner surface of split blade retention race that is adjacent to the blade shank  101 . A curved inner radius (discussed in further detail with respect to  FIG. 6 ) is associated with inner chamfer  201  to provide a smooth blend between the inner chamfer  201  and the surface of the split blade retention race  103  that is adjacent to blade shank  101 . Outer chamfer  202  is angled back from split surface  302  to race surface  301  such that there is a dip in the race that holds the ball bearings adjacent to the split  104 . A curved outer radius  303  (discussed in further detail with respect to  FIG. 6 ) is associated with outer chamfer  202  to provide a smooth blend between the outer chamfer  202  and the adjacent race surface  301 . The inner and outer radii ensure that there are no sharp edges between the chamfers  201 / 202  and adjacent surfaces, as sharp edges tend to cause damage to both the blade shank  101  and race  103 . 
         [0019]      FIG. 4  shows a side view of a split blade retention race  103  at a split  104 . The inner chamfers  201 , outer chamfers  202 , and race surface  301  are also shown. Load lines  401   a - b , located at the edges of the outer radii associated with outer chamfers  202 , show the points at which a ball bearing of ball bearings  102  is fully loaded on the race surface  301  of the split blade retention race  103 . Between load lines  401   a  and  401   b,  the inner chamfers  201 , outer chamfers  202 , and radii ensure that a ball bearing unloads and becomes fully unloaded over the inner unsupported section of the race. The chamfers  201 / 202  are sized such that only one ball bearing of ball bearings  102  is unloaded at a time, and the outer chamfers  202  are larger than the inner chamfers  201 . 
         [0020]      FIG. 5  shows a side view of a blade shank  101  with a split blade retention race  103  at a split  104 . Inner chamfers  201  and outer chamfers  202  are located on split blade retention race  103  at the edges of the split  104 . Load lines  401   a - b , located at the edges of the outer radii associated with outer chamfers  202 , show the point at which a ball bearing is fully loaded on the race surface  301  of the split blade retention race  103 . As a ball passes between load lines  401   a  and  401   b,  the ball bearing becomes unloaded on either split blade retention race  103  due to the presence of outer chamfers  202  and associated outer radii, preventing loading of the unsupported section of the split blade retention race  103 . Inner chamfers  201  and associated radii are located on the side of the split blade retention race  103  that is adjacent to the blade shank  101 . 
         [0021]      FIG. 6  illustrates a detailed view of an embodiment of inner and outer chamfers and associated inner and outer radii. Split blade retention race  103 , with race surface  301  and ball bearings  102  located on race surface  301 , is shown; the split blade retention race  103  is located on blade shank  101 . Detailed view  600   a  shows an inner chamfer  201  and associated inner radius  601  Inner chamfer  201  is a straight surface, and inner radius  601  is a curved surface joining the inner chamfer  201  to the surface of split blade retention race  103  that is adjacent to blade shank  101 . The curve of radius  601  prevents damage to the blade shank  101 . Detailed view  600   b  shows an outer chamfer  202  and associated outer radius  303 . Outer chamfer  202  is a straight surface, and outer radius  303  is a curved surface joining the outer chamfer  202  to the race surface  301 , ensuring a smooth transition for the ball bearings  102  as the ball bearings  102  pass over the outer chamfers  202  and outer radii  303 . Load lines  401   a - b  are located on the outer edges of the outer radii  303 . Line  603  illustrates the center load line  603  of a ball bearing  102 . When the center load line  603  of a ball bearing  102  is between load lines  401   a - b , the ball bearing starts to unload then becomes fully unloaded when the depth below the race surface  301  equals the compressive deflection of the ball bearing  102 . This is shown in further detail with respect to  FIG. 7 . The compressive deflection  701  of a ball  102  is shown with respect to cross-section  702  along line A-A′. In detailed view  703  of  FIG. 7 , when depth below the race surface  301  (on radius or chamfer), indicated by lines  704 , equals the compressive deflection  702  of the ball bearing  102 , ball bearing  102  is fully unloaded. 
         [0022]    The technical effects and benefits of exemplary embodiments include reduction of blade shank damage due to blade race split configuration as well as reduction in wear in the split race edges. 
         [0023]    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. 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 various embodiment 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.