Patent Publication Number: US-2023136833-A1

Title: Rotor blade non-counterbored retention assembly via a sliding clamped bushing

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Agreement No. W911W6-19-9-0005, awarded by the Army Contracting Command-Redstone Arsenal. The Government has certain rights in the invention. 
    
    
     FIELD 
     The present application relates generally to rotor blade retention assemblies for a rotary propulsor system. 
     BACKGROUND 
     Rotary propulsor systems include rear-facing rotor blades disposed at the tail of an airframe and generally assist with the generation of forward thrust, although rotary propulsor systems may also generate lift and provide for additional yaw control. The rotor blades may be formed from composite material and have a retention joint including a strap that helps secures the blade to a central hub. 
     SUMMARY 
     In a system such as that described above, the retention joint may include one or several retention pins to secure the retention joint to the strap, which may be a tension-torsion strap. In this configuration, there is an interface between the tension-torsion strap and an inner surface of the rotor blade, which is highly critical to the operation of the rotor blade. The rotor blade may have a counterbored hole which experiences high shear stresses and tight tolerance dimensions are generally needed to maintain a clearance at the interface. 
     Rotor blade configurations of rotary propulsor systems as described above may result in rotor blade failure. Because of the small radius of the counterbored hole in the rotor blade, the counterbored hole creates an area of very high interlaminar shear stress, friction, and bending retention. As a result of the high stresses and loads at this location, the composite rotor blade layers are susceptible to delamination. The high stresses at this location may also lead to failure of the tension-torsion strap. Further, high stresses at the counterbored hole make it difficult to maintain the small gaps and tight tolerance dimensions at the interface. Shims with peelable layers may be used to maintain the tight tolerance dimensions, but the shims may need to be replaced during each installation. A bolt may be used to clamp down the retention joint to maintain the tight tolerance dimensions, but using the bolt to maintain the gap and the tight tolerance dimensions may compress the blade, leading to failure of the retention joint pin. Additionally, multiple retention joint pins may be required to secure the retention joint, which increases the time needed for installing or removing the retention joint. The present disclosure addresses these and other issues. 
     Various embodiments provide for a rotor blade retention assembly without a counterbored hole in the rotor blade. In one embodiment, the rotor blade retention assembly includes a central hub and at least one rotor blade. The rotor blade includes an upper outer surface, a lower outer surface, a blade hole, and a proximal end coupled to the central hub. The rotor blade retention assembly also includes a strap member extending along a portion of the rotor blade such that a distal end receiving portion extends into the blade hole. A retainer assembly is disposed within the blade hole and coupled to the strap member. The retainer assembly includes an upper bushing and a lower bushing slidably disposed within the blade hole The upper bushing includes an upper counterbored portion. Further, the upper bushing and the lower bushing cooperate to form a bushing inner cavity. An outboard blade pin is disposed within the bushing inner cavity and is surrounded by the distal end receiving portion of the strap member. 
     Various embodiments provide for a retainer assembly for use in a rotor blade retention assembly having a retainer cavity. In one embodiment, the retainer assembly includes the upper bushing and the lower bushing slidably disposed within the retainer cavity. The upper bushing includes an upper counterbored portion. The upper bushing and the lower bushing cooperate to form the bushing inner cavity. The retainer assembly also include an outboard blade pin with a blade pin inner cavity and is disposed within the bushing inner cavity. 
     Various other embodiments provide for a method for installing a retainer assembly of a rotor blade retention assembly. The method includes inserting the distal end receiving portion into the blade hole, inserting, after inserting the distal end receiving portion into the blade hole, the upper bushing and the lower bushing into the blade hole, and inserting, after inserting the upper bushing and the lower bushing into the blade hole, the outboard blade pin into the bushing inner cavity and through the distal end receiving portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying Figures, wherein like reference numerals refer to like elements unless otherwise indicated, in which: 
         FIG.  1    is perspective view of a rotary wing aircraft in accordance with an exemplary embodiment as seen in U.S. Patent Pub. No. US 2020/0385107 A1, which is incorporated by reference herein in its entirety for the technical and background information therein; 
         FIG.  2    is perspective view of a central hub of the retention assembly without a plurality of rotor blades in at least one exemplary embodiment; 
         FIG.  3    is a top view of the central hub of the retention assembly show in  FIG.  1    with a plurality of rotor blades installed in at least one exemplary embodiment; 
         FIG.  4    is a perspective exploded view of Detail A show in  FIG.  2    in at least one exemplary embodiment; 
         FIG.  5    is a cross-sectional exploded view of Detail A show in  FIG.  2    taken along plane A-A, in at least one exemplary embodiment; 
         FIG.  6    is a cross-sectional view of Detail A shown in  FIG.  2    taken along plane A-A, in at least one exemplary embodiment; 
         FIG.  7    is a detailed view of Detail B shown in  FIG.  5   , in at least one exemplary embodiment; 
         FIG.  8    is a cross-sectional view of Detail A shown in  FIG.  2    taken along plane B-B, in at least one exemplary embodiment; and 
         FIG.  9    is a flowchart illustrating the process for installing a retainer assembly of the rotor blade retention assembly in at least one exemplary embodiment. 
     
    
    
     It will be recognized that the Figures are the schematic representations for purposes of illustration. The Figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the Figures will not be used to limit the scope of the meaning of the claims. 
     DETAILED DESCRIPTION 
     Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and for providing a rotor blade retention assembly for a rotary propulsor system. The various concepts introduced above and discussed in greater detail below may be implemented in any of a number of ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes. 
     I. Overview 
     Referring to the figures generally, various embodiments disclosed herein relate to a rotor blade retention assembly for a rotary propulsor system. As explained in more detail herein, the retention assembly facilitates transfer of a load while reducing the high shear stresses and loads normally experienced by other rotor blade retention assemblies. Other configurations of rotor blade retention assemblies experience high shear stresses and loads at critical locations, which can lead to failure of the rotor blade retention assembly. 
     Implementations described herein are related to a rotor blade retention assembly with a central hub, a rotor blade including an upper outer surface, a lower outer surface, a blade hole, and a proximal end coupled to the central hub, a strap member (e.g., tension-torsion strap, etc.) extending along a portion of the rotor blade such that a distal end receiving portion (e.g., spool, etc.) extends into the blade hole, and a retainer assembly disposed within the blade hole and coupled to the strap member. The retainer assembly facilitates transfer of a load from the rotor blade to the central hub. The retainer assembly includes an upper bushing and a lower bushing slidably disposed within the blade. The inclusion of sliding bushings and the absence of a counterbored hole contributes to lower shear stresses and loads on the rotor blade, reducing the likelihood of delamination. 
     Further, because the upper bushing and lower bushing can slide within the blade hole, the upper bushing and the lower bushing are able to repeatably clamp and support the distal end receiving portion of the strap member. Therefore, the sliding upper and lower bushings eliminate the need to maintain a small gap and allow for a larger range of component tolerances. This also eliminates the need to use shims with peelable layers to maintain the tight tolerance dimensions at the internal interface between the strap member and the rotor blade. In place of the counterbored hole in the rotor blade, the upper bushing includes a counterbored portion. Because the counterbored portion is in the upper bushing rather than the rotor blade, fastening the retainer assembly does not compress the rotor blade, thereby reducing the potential for rotor blade failure. The retainer assembly also includes a single outboard blade pin disposed within the distal end receiving portion of the strap member. The outboard blade pin includes a blade pin inner cavity, which cooperates with a first fastener and a second fastener to secure the retainer assembly. The single outboard blade pin also reduces the time needed for installation and removal processes. 
     II. Overview of Example Rotor Blade Retention Assembly 
       FIG.  1    is perspective view of a rotary wing aircraft in accordance with an exemplary embodiment.  FIGS.  2 - 9    depict an exemplary rotor blade retention assembly  100  (e.g., rotary retention system, propulsion retention system, etc.) or portions thereof. 
       FIG.  1    depicts an exemplary embodiment of a rotary wing, vertical takeoff and landing (VTOL) aircraft  10 . Aircraft  10  includes an airframe or fuselage  12  having a plurality of surfaces (not separately labeled) with an extending tail  14 . A coaxial main rotor assembly  18  is located at the fuselage  12  and rotates about a main rotor axis. In an exemplary embodiment, the fuselage  12  includes a cockpit  20  having two seats for flight crew (e.g., pilot and co-pilot) and six seats for passengers (not shown). The coaxial main rotor assembly  18  is driven by a power source, for example, one or more engines  24 , via a gearbox  26 . The coaxial main rotor assembly  18  includes an upper rotor assembly  28  that may be driven in a first direction (e.g., counter-clockwise) about the main rotor axis, and a lower rotor assembly  32  that may be driven in a second direction (e.g., clockwise) about the main rotor axis opposite to the first direction (i.e., counter rotating rotors). 
     In accordance with an exemplary embodiment, the upper rotor assembly  28  includes a first plurality of rotor blades  34  supported by a first or upper rotor hub  36 . The lower rotor assembly  32  includes a second plurality of rotor blades  38  supported by a second or lower rotor hub  39 . In some embodiments, the aircraft  10  may include a translational thrust system  40  having a propeller  42  located at the extending tail  14  to provide translational thrust (forward or rearward) for aircraft  10 . Propeller  42  includes a plurality of blades  43 . 
     The propeller  42  or translational thrust system  40  is connected to and driven by the engine  24  via the gearbox  26 . The translational thrust system  40  may be mounted to the rear of the fuselage  12  with a translational thrust axis oriented substantially horizontal and parallel to the aircraft longitudinal axis to provide thrust for high-speed flight. The term “parallel” should be understood to include a translational thrust axis that is coincident with the longitudinal axis. The translational thrust axis corresponds to the axis of rotation of propeller  42 . While shown in the context of a pusher-prop configuration, it is understood that the propeller  42  could also be a more conventional puller prop or could be variably facing so as to provide yaw control in addition to or instead of translational thrust. It should be further understood that any such system or other translational thrust systems may alternatively or additionally be utilized. Alternative translational thrust systems may include different propulsion forms, such as a jet engine. 
     In accordance with an aspect of an exemplary embodiment, the propeller blades  43  of the translational thrust system  40  may include a variable pitch. More specifically, the pitch of the propeller blades  43  may be altered to change the direction of thrust (e.g., forward or rearward). In accordance with another aspect of an exemplary embodiment, the extended tail  14  includes a tail section  50  including starboard horizontal stabilizers  51  and port horizontal stabilizers  52 . The tail section  50  also includes a vertical stabilizer  53  that extends downward from the extending tail  14 . The starboard horizontal stabilizer  51  includes a starboard active elevator  54  and a starboard active rudder  56 . Similarly, the port horizontal stabilizer  52  includes a port active elevator  58  and a port active rudder  60 . The starboard active elevator  54 , the port active elevator  58 , the starboard active rudder  56 , and the port active rudder  60  act as controllable surfaces, e.g., surfaces that alter a flight path/characteristics of aircraft  10 . 
       FIG.  2    depicts a perspective view of the rotor blade retention assembly  100  included in the translational thrust system  40  and to which the propeller blades  43  of  FIG.  1    are attached. The rotor blade retention assembly  100  includes a hub system  102  (e.g. hub body, rotor hub, etc.) coupled (e.g., mounted, attached, fixed, welded, fastened, riveted, bonded, pinned, etc.) to the rotary wing aircraft  10  (e.g., an airframe, an aircraft, a rotorcraft, etc.), as seen in  FIG.  1   . The hub system  102  includes a rotor mast  104  and a central hub  106  coupled to the rotor mast  104 . The rotor mast  104  extends upwardly along and around a rotor axis R and is rotated about the rotor axis R relative to another structure to rotate the central hub  106  about the rotor axis R. The hub system  102  includes a plurality of projections  108  extending radially outward from the central hub  106  and orthogonal to the rotor axis R. 
       FIG.  3    depicts a top view of the central hub  106  of the rotor blade retention assembly  100  show in  FIG.  2   . Each rotor blade retention assembly  100  includes a rotor blade  110  (e.g., blade spar, etc.), as shown as the propeller blade  43  in  FIG.  1   . The rotor blade  110  may be made of a layered composite structure and is coupled to the central hub  106 . The rotor blade  110  extends radially outward from the central hub  106  and is orthogonal to the rotor axis R. The rotor blade  110  rotates about the rotor axis R along with the central hub  106  to produce a propulsion or lift force to move another structure. 
       FIGS.  4 - 6    depict various views of Detail A shown in  FIG.  3   . For example,  FIG.  4    depicts a perspective view of Detail A,  FIG.  5    depicts a perspective, cross-sectional exploded view of Detail A taken along plane A-A, and  FIG.  6    depicts a cross-sectional view of Detail A taken along plane A-A. As depicted in  FIGS.  4 - 6   , in some embodiments, the rotor blade  110  includes a blade body  112 , a blade hole  114  in the blade body  112 , a blade shaft  116  at a proximal end of the blade body  112 , and a blade inner cavity  118  that extends radially outward along an interior of the blade shaft  116  and the blade body  112 , as seen in  FIG.  4   , for example. The blade shaft  116  is configured to directly attach (e.g. couple, mount, etc.) to and extend radially outwardly from the central hub  106 . The blade body  112  directly attaches to and extends radially outwardly from the blade shaft  116 . The blade shaft  116  may optionally extend into the blade inner cavity  118 . Optionally, the blade shaft  116  and the blade body  112  may be two separate components that are attachable (e.g., removable, reattachable, etc.) to each other. Alternatively, the blade shaft  116  and the blade body  112  may be constructed as a single unitary piece or component that cannot be separated without destruction. 
     At the blade shaft  116 , the blade inner cavity  118  has a diameter of a distance D 1 . As the blade inner cavity  118  extends radially outward along the along the interior of the rotor blade  110 , the diameter tapers such that the diameter reduces to a distance D 2 . The rotor blade  110  may be further defined by an upper outer surface  120  and a lower outer surface  122  separated by the blade inner cavity  118 . In some embodiments, the rotor blade  110  also includes a blade seal  124  (e.g., seal, band, etc.). The blade seal  124  is disposed between the blade shaft  116  and the central hub  106  such as to create a seal between the blade inner cavity  118  and the environment. Each rotor blade  110  also includes a mounting bracket  126  mounted to the central hub  106  that indirectly attaches the blade shaft  116  to the central hub  106 . 
     Referring to  FIG.  6   , which shows a cross-sectional view of the rotor blade retention assembly  100 , in some embodiments, in each rotor blade retention assembly  100 , the projection  108  of the central hub  106  extends at least partially into the blade inner cavity  118  of the blade shaft  116 . The projection  108  extends into the blade inner cavity  118  where the diameter of the blade inner cavity  118  is at a distance Dl. The projection  108  includes a first bearing  128  (e.g., titanium races, etc.). The first bearing  128  is coupled to the central hub  106  and cooperates with the rotor blade  110  and the central hub  106  to change the pitch angle, which changes the lift and drag. For example, by increasing the pitch angle, the rotor blade  110  provides more lift. Conversely, by decreasing the pitch angle, the rotor blade  110  provides less lift. In some embodiments, the projection  108  includes a second bearing  130  (e.g., titanium races, etc.). The second bearing  130  also cooperates with the first bearing  128 , the rotor blade  110 , and the central hub  106  to adjust the pitch angle. The projection  108  also includes at least one inboard blade pin  132 . The inboard blade pin  132  is disposed between the first bearing  128  and the second bearing  130 , and is fixedly attached to rotate with the rotor blade  110 . 
     Referring to  FIGS.  6  and  7   , which show a cross-sectional view of the rotor blade retention assembly  100  and a detailed view of Detail B, respectively, in some embodiments, the rotor blade retention assembly  100  includes a strap member  134 . The strap member  134  cooperates with the inboard blade pin  132  to transfer a centrifugal force from the rotor blade  110  to the central hub  106 . For example, in some embodiments, the strap member  134  includes a proximal end receiving portion  136  and a distal end receiving portion  138 . The proximal end receiving portion  136  is configured to receive the inboard blade pin  132  such that the proximal end receiving portion  136  surrounds the inboard blade pin  132 . The strap member  134  extends radially away from the central hub  106  in the blade inner cavity  118  such that the distal end receiving portion  138  extends into a region of the blade inner cavity  118  in which the diameter is a distance D 2 . 
     Referring to  FIG.  5 - 7   , in some embodiments, the rotor blade retention assembly  100  includes a retainer assembly  140 .  FIG.  5    depicts an exploded view of the retainer assembly  140 .  FIG.  6    depicts a cross-sectional view of the retainer assembly  140 , as seen in Detail B.  FIG.  7    is a detailed view of the retainer assembly  140 . The retainer assembly  140  is disposed within the blade hole  114  and has a cylindrical shape. The distal end receiving portion  138  extends into the blade hole  114  and is configured to receive the retainer assembly  140 . The distal end receiving portion surrounds  138  a portion of the retainer assembly  140  such as to define an inner mating component surface  142 . The inner mating component surface  142  cooperates with the retainer assembly  140  to reduce or eliminate a gap between the retainer assembly  140  and the inner mating component surface  142 , further described below. 
     Referring to  FIGS.  6 - 8   , in some embodiments, the retainer assembly  140  includes a protective layer  144  (e.g. bushing, liner, etc.).  FIGS.  6  and  7    depict the protective layer  144  along with other components of the retainer assembly  140 , whereas  FIG.  8   , a cross-sectional view of Detail A taken along plane B-B, depicts the protective layer  144  without the other components of the retainer assembly  140 . The protective layer  144  defines an exterior layer of the retainer assembly  140  such as to line an inner wall  146  of the blade hole  114 . A first portion of the protective layer  144  extends from the distal end receiving portion  138  to the upper outer surface  120  while a second portion of the protective layer  144  extends from the distal end receiving portion  138  to the lower outer surface  122 . The protective layer  144  is made of a durable material (e.g. fiberglass, etc.) and protects the blade hole  114 . The retainer assembly  140  includes an upper bushing  148 . The upper bushing  148  is radially inward from the protective layer  144  such that the first portion of the protective layer  144  is disposed between the inner wall  146  and the upper bushing  148 . The upper bushing  148  is slidably disposed within the blade hole  114 . The upper bushing  148  extends from the inner mating component surface  142  to the upper outer surface  120  of the rotor blade  110 . The retainer assembly  140  also includes a lower bushing  150 . The lower bushing  150  is radially inward from the protective layer  144  such that the second portion of the protective layer  144  is disposed between the inner wall  146  and the lower bushing  150 . The lower bushing  150  is slidably disposed within the blade hole  114 . The lower bushing  150  extends from the inner mating component surface  142  to the lower outer surface  122  of the rotor blade  110 . Because the upper bushing  148  and the lower bushing  150  are slidably disposed within the blade hole  114 , the upper bushing  148  and the lower bushing  150  are able to clamp the inner mating component surface  142  to allow for a larger range of component tolerances. Additionally, the sliding action of the upper bushing  148  and the lower bushing  150  enables repeatable clamp up on the inner mating component surface  142  without overstressing the retainer assembly  140  and the rotor blade  110 . 
     In some embodiments, the upper bushing  148  and the lower bushing  150 , collectively, form a bushing inner cavity  152 , as seen, for example, in  FIG.  5   . The upper bushing  148  includes an upper counterbored portion  154 . Unlike in other retainer assemblies, the upper counterbored portion  154  is in the upper bushing  148  rather than the blade body  112 . Because the upper counterbored portion  154  is in the upper bushing  148 , the blade body  112  does not experience high shear stresses at the blade hole  114 . Similarly, the lower bushing  150  may include a lower counterbored portion  156 . 
     Referring to  FIGS.  4 - 7    depicting various views of the retainer assembly  140  in the rotor blade retention assembly  100 , in some embodiments, the retainer assembly  140  includes an outboard blade pin  158 . The outboard blade pin  158  is radially inward from the upper bushing  148  and the lower bushing  150  and is disposed within the bushing inner cavity  152 . The outboard blade pin  158  includes a blade pin body portion  160 . The outboard blade pin  158  is disposed within the distal end receiving portion  138  of the strap member  134  such that the distal end receiving portion  138  surrounds the blade pin body portion  160 . The outboard blade pin  158  includes a blade pin inner cavity  162 . The blade pin inner cavity  162  extends along the entire length of the outboard blade pin  158 . In some embodiments, the portion of the blade pin inner cavity  162  that extends through the blade pin body portion  160  and has a diameter with a distance D 3 . The outboard blade pin  158  also includes a top portion  164 . The top portion  164  is radially inward from the upper bushing  148 . The portion of the blade pin inner cavity  162  that extends through the top portion  164  has a diameter with a distance D 4 , which is greater than the distance D 3 . In some embodiments, the outboard blade pin  158  includes a base portion  166 . The base portion  166  is at an end opposite of the top portion  164  and extends into the lower counterbored portion  156  of the lower bushing  150  such that the base portion  166  is below a portion of the lower bushing  150 . 
     In some embodiments, the retainer assembly  140  includes a first fastener  168 . The first fastener  168  cooperates with the upper bushing  148  to clamp the inner mating component surface  142  and reduce the gap at the inner mating component surface  142 . The first fastener  168  includes a cap portion  170 . The cap portion  170  is disposed within the upper counterbored portion  154  such that the first fastener  168  remains below the upper outer surface  120  of the rotor blade  110 . Because the cap portion  170  is disposed within the upper counterbored portion  154 , the cap portion  170  is disposed above a portion of the upper bushing  148  and the outboard blade pin  158 . The first fastener  168  also includes a lower portion  172 . The lower portion  172  extends below the cap portion  170  such that the lower portion  172  is disposed within the blade pin inner cavity  162 . Specifically, the lower portion  172  is disposed within the portion of the blade pin inner cavity  162  that extends through the top portion  164  of the outboard blade pin  158 , but is not disposed within the portion of the blade pin inner cavity  162  that extends through the blade pin body portion  160 . Because the lower portion  172  of the first fastener  168  is disposed within the blade pin inner cavity  162 , the top portion  164  of the outboard blade pin  158  is disposed between the lower portion  172  and the upper bushing  148 . The first fastener  168  further includes a fastener cavity  174 . The fastener cavity  174  extends down through the cap portion  170  and the lower portion  172  such that the fastener cavity  174  and the blade pin inner cavity  162  are aligned with one another. 
     In some embodiments, the retainer assembly  140  includes a second fastener  176  (e.g., tension second fastener, etc.). The second fastener  176  is a threaded fastener disposed within the blade pin inner cavity  162  and extends from the lower outer surface  122  of the rotor blade  110  up into the fastener cavity  174  such that the second fastener  176  remains fixed in the lower portion  172  of the first fastener  168 . As described above, the cap portion  170  is disposed above a portion of the upper bushing  148  and the outboard blade pin  158 . Consequently, as the second fastener  176  is inserted into the blade pin inner cavity  162  and up into the fastener cavity  174 , the second fastener  176  engages with the first fastener  168  such that the cap portion  170  compresses the upper bushing  148 . Therefore, the upper bushing  148  clamps the inner mating component surface  142  and reduces the gap between the upper bushing  148  and the inner mating component surface  142 . Because the gap is reduced in this way, shims with peelable layers are not needed to maintain the tight tolerance dimensions at the inner mating component surface  142 . 
     In some embodiments, the rotor blade  110  further includes an upper blade drain hole  178  and a lower blade drain hole  180 . The upper blade drain hole  178  and the lower blade drain hole  180  are located radially outward from the retainer assembly  140 . The upper blade drain hole  178  extends from the blade inner cavity  118  to the upper outer surface  120 . The lower blade drain hole  180  extends from the blade inner cavity  118  to the lower outer surface  122 . Both the upper blade drain hole  178  and the lower blade drain hole  180  are configured to facilitate the removal of a liquid (e.g., water, condensation, etc.) from the blade inner cavity  118 . 
     While not shown, it is understood that a cover can be installed over the blade hole  114  to cover the cap portion  170  and outboard blade pin  158  in order to continue an aerodynamic shape of the upper outer surface  120  and the lower outer surface  122 . 
     III. Example Method of Installing the Retainer Assembly 
       FIG.  9    illustrates an installation process  900  (e.g., method, etc.) for installing the retainer assembly  140  of a rotor blade retention assembly  100 . 
     The installation process  900  begins (step  902 ) by inserting the distal end receiving portion  138  of the strap member  134  into the blade hole  114 . The installation process  900  continues (step  904 ) by inserting the upper bushing  148  and the lower bushing  150  into the blade hole  114 . As a result, the distal end receiving portion  138  is disposed between and supported by the upper bushing  148  and the lower bushing  150 . 
     The installation process  900  continues (step  906 ) by inserting the outboard blade pin  158  into the bushing inner cavity  152  and through the distal end receiving portion  138 . As a result, the distal end receiving portion  138  surrounds the blade pin body portion  160  of the outboard blade pin  158  and the base portion  166  is disposed within the lower counterbored portion  156 . 
     The installation process  900  continues (step  908 ) by inserting the first fastener  168  into the upper counterbored portion  154 . As a result, the lower portion  172  of the first fastener  168  is disposed within the blade pin inner cavity  162 , and the top portion  164  of the outboard blade pin  158  is disposed between the lower portion  172  and the upper bushing  148 . Further, the cap portion  170  is disposed above the upper bushing  148 . 
     The installation process  900  continues (step  910 ) by inserting the second fastener  176  into the blade pin inner cavity  162  and the first fastener  168  such as to compress the upper bushing  148  and reduce a gap between the upper bushing  148  and the distal end receiving portion  138 . 
     IV. Configuration of Example Embodiments 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     As utilized herein, the terms “substantially,” “generally,” “approximately,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the appended claims. 
     The term “coupled” and the like, as used herein, mean the joining of two components directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two components or the two components and any additional intermediate components being integrally formed as a single unitary body with one another, with the two components, or with the two components and any additional intermediate components being attached to one another. 
     It is important to note that the construction and arrangement of the various systems shown in the various example implementations is illustrative only and not restrictive in character. All changes and modifications that come within the spirit and/or scope of the described implementations are desired to be protected. It should be understood that some features may not be necessary, and implementations lacking the various features may be contemplated as within the scope of the disclosure, the scope being defined by the claims that follow. When the language “a portion” is used, the item can include a portion and/or the entire item unless specifically stated to the contrary.