Abstract:
A hub for mounting propeller blades has a plurality of mount locations for receiving propeller blades at a radially outer location. The hub has a piloting diameter centered on a center axis. The hub has a plurality of openings to receive a drive member for transmitting rotation/torque from an adapter. There are reliefs cut into the piloting diameter at locations circumferentially aligned with the openings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/724,314, filed Nov. 9, 2012. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application relates to a hub for mounting propeller blades where a piloting diameter is formed on an inner diameter, and has reliefs cut at locations circumferentially aligned with openings. 
         [0003]    Propeller blades are often mounted within a hub connected to an adapter through a plurality of connecting members which may be press-fit. The adapter is connected to a source of drive, such as a driveshaft. 
         [0004]    The press-fit connecting members can cause deformation at locations circumferentially aligned with the openings. 
       SUMMARY 
       [0005]    A hub has a plurality of mount locations for receiving propeller blades at a radially outer location. The hub has a piloting diameter centered on a center axis. The hub has a plurality of openings to receive a connection member for transmitting rotation/torque from an adapter. There are reliefs cut into the piloting diameter at locations circumferentially aligned with the openings. A system is also disclosed. 
         [0006]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a prior art arrangement. 
           [0008]      FIG. 2  shows a detail of the prior art. 
           [0009]      FIG. 3  shows an issue raised in the prior art. 
           [0010]      FIG. 4  shows an inventive hub. 
           [0011]      FIG. 5  shows a detail of one embodiment. 
           [0012]      FIG. 6  shows another feature of the  FIG. 5  embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A hub  34  is shown in  FIG. 1  illustrating a press-fit dowel pin  32  installed in the hub  34  which is used to transmit torque/rotation from a driveshaft  22  to propeller blades. Alternatively, a dowel bolt or other connection member may be used. An inner piloting diameter  100  of hub  34  sits on an outer piloting diameter  102  of an adapter  26 . The adapter is secured, such as by splines  24 , to driveshaft  22 . 
         [0014]    As shown in  FIG. 2 , the hub  34  includes a plurality of press-fit dowel pins  32  in the openings  36  spaced circumferentially about a center line X which transmit the rotation of the driveshaft  22  to the hub  34  and propeller blades  140 . Mount locations  38  receive propeller blades  140 . The piloting diameter  100  may be locally deformed, such as shown at  142 , at locations circumferentially aligned with the openings  36  as a result of the press fit between the dowel pins  32  and the hub  34 . 
         [0015]      FIG. 3  shows a portion of the piloting diameter  100  across an angle A. Hoop stresses across this portion range from very high stresses centered on the opening  36 , and decrease moving circumferentially away from the center of opening  36 . These hoop stresses are the result of the press fit of the dowel pin  32  in the opening  36  and results in the deformation mentioned above. 
         [0016]    The piloting diameters  100  and  102  are utilized to center the adapter  26  and hub  34 . With the deformation  142  from the press-fit dowel pins/dowel bolts, lobes are created which become contact point(s) between the piloting diameter  100 , and the piloting diameter  102 . The parts rub under load, and fretting can occur, which can cause a reduction in fatigue strength. This has sometimes resulted in fatigue cracks. 
         [0017]      FIG. 4  shows a relief  40  cut into the piloting diameter  201  of an inventive hub  134 . As shown, the relief  40  is circumferentially positioned across a circumferential extent of the opening  136  which will receive the press-fit dowel pin or dowel bolt. The relief  40  can be seen to have a transition radius between points  42  and  43  at each circumferential extent. 
         [0018]    As shown in  FIG. 5 , the relief  40  extends across an entire axial length of the hub flange  134 . 
         [0019]      FIG. 6  shows a detail of the relief  40 . A nominal pilot diameter  201  is formed at a radius R 1 . In one embodiment, R 1  was 3.876 inch (9.845 centimeter). 
         [0020]    At a point  42 , a transition blend begins and extends to an end  43  leading into a nominal portion  400  of the relief  40 . The same transition blend is found at the opposed circumferential end of nominal portion  400 . The transition portion between points  42  and  43  is formed by a convex and concave radius R 2 . This radius should be as large as possible to minimize contact edge affects and stress raisers. In one embodiment, R 2  was 0.5 inch (1.27 centimeter). 
         [0021]    The nominal portion  400  is shown to be formed at a radius R 3 . In one embodiment, R 3  was 3.887 inch (9.873 centimeter). The values of R 1  and R 3  are defined such that contact between the piloting diameters do not occur in this region once the dowel pins  32 , or dowel bolts (or other connection members), are pressed in the hub  34  while maintaining hoop stress values, due to the press fit, that are acceptable for the material used. These values may also be determined based on the ratio required to remove existing fretting from parts that have not been originally produced with the reliefs. Again, hoop stress values must be considered when determining this ratio. In embodiments, a ratio of R 3  to R 1  was between 1.0014 and 1.0043. A ratio of R 3  to R 2  was between 7.6871 and 7.8626. 
         [0022]    As can be seen, the entire relief  40  including the transition portion  42 - 43  and the nominal portion  400  is formed across an angle B. In one embodiment, angle B was 50.18 degrees. In embodiments, angle B may be between 48.18 and 52.18 degrees. The transition portions extend across an angle C. In one embodiment, angle C was 7.25 degrees. In embodiments, angles B and C may result from required angles needed to remove existing fretting while maintaining significant circumferential pilot diameter to keep the mating parts centered. Angle B, in any case, should be such that the end of the transition  42  is located such that the hoop stress from the press fit is negligible. In embodiments, angle C may be between 5.25 and 9.25 degrees. 
         [0023]    In these embodiments, the circumferential extent of the opening  136  is at an Angle D. Angle D is between 11.45 and 11.48 degrees. A ratio of angle B to angle D is between 4.197 and 4.557 in embodiments of this disclosure. All of the angles are measured from a center line X. 
         [0024]    With the relief, the problems raised by the hub  34  deformation mentioned above, due to the press-fit of the dowel pin  32  or, alternatively, dowel bolt, are reduced. 
         [0025]    A method of repairing a propeller system includes the steps of removing connecting members  32  from openings  36  in a  34  hub and an adapter  26 , and placing a replacement hub  34  on the adapter  26  with the replacement hub having reliefs  40  cut into a piloting diameter  201  at locations circumferentially aligned with the openings. 
         [0026]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.