Patent Publication Number: US-11661178-B2

Title: Tail rotor gearbox support assemblies for helicopters

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of co-pending application Ser. No. 16/290,797 filed Mar. 1, 2019. 
    
    
     TECHNICAL FIELD OF THE DISCLOSURE 
     The present disclosure relates, in general, to tail rotor gearbox support assemblies for use on helicopters and, in particular, to tail rotor gearbox support assemblies for shrouded tail rotor assemblies operable to support a tail rotor gearbox within the shroud of the tail rotor assembly using a support column and support crossbars. 
     BACKGROUND 
     Helicopter anti-torque systems counteract the moment exerted on the helicopter fuselage by the main rotor and generally manage yaw during flight. The most common type of helicopter anti-torque system is a tail rotor located on the aft end of the helicopter&#39;s tailboom. One implementation of a tail rotor utilizes a shroud that partially or fully surrounds the tail rotor hub assembly including the rotor blades emanating therefrom. The tail rotor hub assembly and gearbox of a shrouded tail rotor is not typically directly mounted onto or within the fuselage, tailboom or body of the helicopter, but is instead suspended at or near the center of the aperture formed by the shroud to maintain a desired tip gap between the tail rotor blades and shroud. This tip gap, along with other characteristics of the interior of the shroud such as inflow and outflow radii and outflow expansion angle, may be adjusted to enhance the thrust performance of the shrouded tail rotor. Shrouds also serve a number of other important functions for the helicopter, including preventing injury to ground personnel when the helicopter is grounded, protecting the tail rotor from debris or ground obstacles during flight and reducing the footprint and acoustic signature of the tail rotor. 
     Because shrouded tail rotors must maintain a consistent tip gap between the tail rotor blades and the shroud to enhance thrust and prevent collision between these two parts, the means by which the shrouded tail rotor suspends and supports the tail rotor gearbox within the shroud must meet certain stability, reliability and aerodynamic standards. Some existing shrouded tail rotors utilize a tail rotor gearbox housing that encases the tail rotor gearbox and is suspended within the shroud using a stator assembly. Such tail rotor gearbox housings negatively impact the weight and drag of the helicopter. Other existing shrouded tail rotors, in addition to utilizing a tail rotor gearbox housing, employ a stator assembly having several radially emanating spokes that completely encircle the tail rotor gearbox to attach the tail rotor gearbox housing to the shroud. Such stator assemblies fail to transfer torque and thrust loads to stable airframe components in the tailboom in a weight-efficient manner, relying on structural components having less stiffness such as the aft portion of the shroud. The large number of spokes also increase the amount of noise emitted by the shrouded tail rotor. Accordingly, a need has arisen for tail rotor gearbox support assemblies that reduce weight, noise and drag while maintaining the stability, reliability, load transfer and aerodynamic requirements of the tail rotor. 
     SUMMARY 
     In a first aspect, the present disclosure is directed to a tail rotor assembly coupled to a tailboom of a helicopter. The tailboom has a tailboom airframe. The tail rotor assembly includes a tail rotor gearbox having top, bottom and aft sides and a shroud surrounding the tail rotor gearbox. The shroud includes a shroud airframe having top and bottom portions. The tail rotor assembly includes a tail rotor gearbox support assembly configured to support the tail rotor gearbox within the shroud. The tail rotor gearbox support assembly includes a support column coupling the aft side of the tail rotor gearbox between the top and bottom portions of the shroud airframe, an upper support crossbar coupling the top side of the tail rotor gearbox between the support column and the tailboom airframe and a lower support crossbar coupling the bottom side of the tail rotor gearbox between the support column and the tailboom airframe. 
     In some embodiments, the tail rotor gearbox may experience torque and thrust loads during tail rotor operation and the tail rotor gearbox support assembly may transfer the torque and thrust loads to the tailboom. In certain embodiments, the support column may be a substantially vertical support column. In some embodiments, the aft side of the tail rotor gearbox may be coupled to a midpoint of the support column. In certain embodiments, the upper and lower support crossbars may have aft ends coupled to the support column. In some embodiments, the upper and lower support crossbars may be substantially horizontal support crossbars. In certain embodiments, the upper and lower support crossbars may each be perpendicular to the support column. In some embodiments, the support column and the upper and lower support crossbars may be tubular. In certain embodiments, the upper and lower support crossbars and the support column may each have an aerodynamic cross-sectional shape. In some embodiments, the upper and lower support crossbars may be substantially parallel. 
     In certain embodiments, the tail rotor gearbox support assembly may include a column pin joint assembly coupling the support column to the aft side of the tail rotor gearbox, an upper crossbar pin joint assembly coupling the upper support crossbar to the top side of the tail rotor gearbox and a lower crossbar pin joint assembly coupling the lower support crossbar to the bottom side of the tail rotor gearbox. In some embodiments, the upper crossbar pin joint assembly may include a first support crossbar fitting, a first tail rotor gearbox fitting and a first pin, the lower crossbar pin joint assembly may include a second support crossbar fitting, a second tail rotor gearbox fitting and a second pin and the column pin joint assembly may include a support column fitting, an aft tail rotor gearbox fitting and a third pin. In such embodiments, the first pin may be insertable into the first support crossbar fitting, the upper support crossbar and the first tail rotor gearbox fitting, the second pin may be insertable into the second support crossbar fitting, the lower support crossbar and the second tail rotor gearbox fitting and the third pin may be insertable into the support column fitting, the support column and the aft tail rotor gearbox fitting to secure the tail rotor gearbox. In certain embodiments, each pin may define a respective axis and the tail rotor gearbox may be moveable along at least one of the axes. In some embodiments, the first support crossbar fitting and the first tail rotor gearbox fitting may form a first gap therebetween, the second support crossbar fitting and the second tail rotor gearbox fitting may form a second gap therebetween and the support column fitting and the aft tail rotor gearbox fitting may form a third gap therebetween. In such embodiments, the gaps may accommodate thermal expansion of the tail rotor gearbox. In certain embodiments, the tail rotor assembly may have an axis of rotation and the pins may be radially aligned with the axis of rotation. In some embodiments, the tail rotor gearbox support assembly may include first and second tee connectors coupling aft ends of the upper and lower support crossbars to the support column. 
     In a second aspect, the present disclosure is directed to a helicopter including a fuselage, a tailboom including a tailboom airframe extending from the fuselage and a tail rotor assembly coupled to the tailboom. The tail rotor assembly includes a tail rotor gearbox having top, bottom and aft sides, a shroud including a shroud airframe having top and bottom portions surrounding the tail rotor gearbox and a tail rotor gearbox support assembly configured to support the tail rotor gearbox within the shroud. The tail rotor gearbox support assembly includes a support column coupling the aft side of the tail rotor gearbox between the top and bottom portions of the shroud airframe, an upper support crossbar coupling the top side of the tail rotor gearbox between the support column and the tailboom airframe and a lower support crossbar coupling the bottom side of the tail rotor gearbox between the support column and the tailboom airframe. 
     In some embodiments, the tail rotor assembly may be canted from a vertical plane of the helicopter. In certain embodiments, the support column, the upper support crossbar and the lower support crossbar may each be coupled to the tail rotor gearbox by a respective pin joint assembly including a pin. In some embodiments, the support column, the upper support crossbar and the lower support crossbar may be radially nonaligned with the axis of rotation of the tail rotor assembly and the pins may be radially aligned with the axis of rotation of the tail rotor assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the features and advantages of the present disclosure, reference is now made to the detailed description along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
         FIGS.  1 A- 1 C  are schematic illustrations of a helicopter having a tail rotor gearbox support assembly in accordance with embodiments of the present disclosure; 
         FIGS.  2 A- 2 C  are various views of existing tail rotor assemblies; 
         FIGS.  3 A- 3 C  are various views of a tail rotor assembly in accordance with embodiments of the present disclosure; 
         FIGS.  4 A- 4 C  are various views of a tail rotor gearbox support assembly in accordance with embodiments of the present disclosure; 
         FIGS.  5 A- 5 D  are cross-sectional views of a tail rotor gearbox support assembly in accordance with embodiments of the present disclosure; and 
         FIG.  6    is a side view of a tail rotor gearbox support assembly in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not delimit the scope of the present disclosure. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, and the like described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the devices described herein may be oriented in any desired direction. As used herein, the term “coupled” may include direct or indirect coupling by any means, including by mere contact or by moving and/or non-moving mechanical connections. 
     Referring to  FIGS.  1 A- 1 C  in the drawings, a helicopter is schematically illustrated and generally designated  10 . The primary propulsion assembly of helicopter  10  is a main rotor assembly  12 . Main rotor assembly  12  includes a plurality of rotor blades  14  extending radially outward from a main rotor hub  16 . Main rotor assembly  12  is coupled to a fuselage  18 . Main rotor hub  16  is rotatable relative to fuselage  18 . The pitch of rotor blades  14  can be collectively and/or cyclically manipulated to selectively control direction, thrust and lift of helicopter  10 . A retractable landing gear system may provide ground support for helicopter  10 . 
     A tailboom  22  is coupled to fuselage  18  and extends from fuselage  18  in the aft direction. An anti-torque system  24  includes a tail rotor assembly  26  coupled to an aft end of tailboom  22 . Anti-torque system  24  controls the yaw of helicopter  10  by counteracting the torque exerted on fuselage  18  by main rotor assembly  12 . As best seen in  FIG.  1 B , tail rotor assembly  26  is canted relative to a vertical plane  28  of helicopter  10 . Tail rotor assembly  26  is canted by an angle  30  of about 15 to 20 degrees. Cant angle  30  may be any angle, however, in a range between 0 and 45 degrees. In some embodiments, cant angle  30  may be 0 degrees and tail rotor assembly  26  may be aligned with vertical plane  28  of helicopter  10 . Tail rotor assembly  26  includes a vertical fin  32  that is substantially parallel with vertical plane  28  of helicopter  10 . In other embodiments, vertical fin  32  may be substantially parallel to or aligned with tail rotor assembly  26  such that vertical fin  32  is also canted at cant angle  30  from vertical plane  28  of helicopter  10 . 
     Tail rotor assembly  26  includes a tail rotor hub  34  having tail rotor blades  36  emanating radially therefrom. While tail rotor hub  34  is illustrated as including seven tail rotor blades  36 , tail rotor hub  34  may have any number of tail rotor blades. Tail rotor blades  36  may be uniformly or nonuniformly radially spaced from one another. For example, tail rotor blades  36  may be nonuniformly spaced to reduce the noise generated when tail rotor blades  36  pass adjacent stationary or nonrotating components of tail rotor assembly  26 . Tail rotor hub  34  receives rotational energy from a drivetrain  38  that includes an engine  40  or other power source, a main transmission or gearbox  42 , a tail rotor driveshaft  44  and a tail rotor gearbox  46 . Engine  40 , main transmission  42 , tail rotor driveshaft  44  and tail rotor gearbox  46  are interconnected such that rotational energy generated by engine  40  is delivered to tail rotor hub  34  to produce thrust. The magnitude of anti-torque thrust generated by tail rotor assembly  26  may be adjusted in a variety of ways. For example, tail rotor blades  36  may be variable pitch tail rotor blades whose pitch is collectively changeable by a pitch mechanism. In another example, tail rotor blades  36  may be fixed pitch tail rotor blades and tail rotor gearbox  46  or another portion of drivetrain  38  may be clutchable and/or have a variable rotational speed. 
     Tail rotor assembly  26  includes a shroud, or duct,  48  that surrounds tail rotor hub  34  and tail rotor gearbox  46 . Shroud  48  may serve a variety of functions. For example, shroud  48  may protect ground personnel from coming into contact with rotating tail rotor blades  36  and may block debris from hitting tail rotor blades  36  during flight. Shroud  48  may also be used to enhance the anti-torque thrust generated by tail rotor assembly  26  by utilizing a duct effect as is known by those of ordinary skill in the art. Indeed, the term “shroud” encompasses any type of duct, whether or not a duct effect is produced. All or a portion of shroud  48  may also provide structural support for other components of tail rotor assembly  26  such as tail rotor gearbox  46 . For example, the forward portion of shroud  48  may be structurally tied to tailboom  22  so as to provide a stable structural base from which to support tail rotor gearbox  46  while the aft portion of shroud  48  may be nonstructurally supportive and lighter to conserve weight. 
     Tail rotor assembly  26  includes a tail rotor gearbox support assembly  50  to support tail rotor gearbox  46  within shroud  48 . Tail rotor gearbox support assembly  50  substantially centers tail rotor gearbox  46  within the aperture formed by shroud  48  to maintain a substantially constant and/or predetermined tip gap between tail rotor blades  36  and shroud  48 . Tail rotor gearbox support assembly  50  includes a support column  52  coupled to the aft side of tail rotor gearbox  46 . Support column  52  is substantially vertical and has a top end fixedly coupled to the top portion of shroud  48  and a bottom end fixedly coupled to the bottom portion of shroud  48 . Tail rotor gearbox support assembly  50  also includes upper and lower support crossbars  54 ,  56  coupled to the top and bottom sides of tail rotor gearbox  46 , respectively. The forward ends of upper and lower support crossbars  54 ,  56  are fixedly coupled to the forward portion of shroud  48  and the aft ends of upper and lower support crossbars  54 ,  56  are fixedly coupled to support column  52 . Support column  52 , upper and lower support crossbars  54 ,  56 , tail rotor driveshaft  44  and tail rotor gearbox  46  may all lie within a common plane. During operation, tail rotor gearbox  46  experiences torque loads  58  and thrust loads  60 . Thrust loads  60  can cause tail rotor hub  34  to deflect out of shroud  48 . Tail rotor gearbox support assembly  50  prevents tail rotor hub  34  and tail rotor gearbox  46  from deflecting out of shroud  48  and reacts to torque and thrust loads  58 ,  60 . In particular, tail rotor gearbox support assembly  50  reacts to torque and thrust loads  58 ,  60  by transferring or redirecting torque and thrust loads  58 ,  60  to a stable and supported structure of helicopter  10  such as tailboom  22 . For example, upper and lower support crossbars  54 ,  56  may be driven to a line of action that directs torque and thrust loads  58 ,  60  to tailboom  22 . Tail rotor gearbox support assembly  50  reacts loads due, at least in part, to the mass of tail rotor gearbox  46  and tail rotor assembly  26 . Support column  52  may also react to bending loads of tail rotor assembly  26 . 
     It should be appreciated that helicopter  10  is merely illustrative of a variety of aircraft that can implement the embodiments disclosed herein. Indeed, tail rotor gearbox support assembly  50  may be implemented on any rotorcraft. Other aircraft implementations can include hybrid aircraft, tiltwing aircraft, tiltrotor aircraft, quad tiltrotor aircraft, unmanned aircraft, gyrocopters, propeller-driven airplanes, compound helicopters, drones and the like. As such, those skilled in the art will recognize that tail rotor gearbox support assembly  50  can be integrated into a variety of aircraft configurations. It should be appreciated that even though aircraft are particularly well-suited to implement the embodiments of the present disclosure, non-aircraft vehicles and devices can also implement the embodiments. 
     Referring to  FIGS.  2 A- 2 C  in the drawings, various existing shrouded tail rotor assemblies are schematically illustrated. In  FIG.  2 A , shrouded tail rotor assembly  100  includes a tail rotor gearbox housing  102  in which a tail rotor gearbox (not shown) is encased. Spokes  104  radially emanate from tail rotor gearbox housing  102  to connect tail rotor gearbox housing  102  to shroud  106 . Spokes  104  distribute the loads experienced by the tail rotor gearbox to the entire circumference of shroud  106 , thereby requiring aft portion  106   a  of shroud  106  to be heavy enough to support such loads. Shrouded tail rotor assembly  100  thus fails to effectively transfer tail rotor gearbox loads to tailboom  108  to reduce the weight penalty of aft portion  106   a  of shroud  106 . The tail rotor gearbox also requires tail rotor gearbox housing  102 , further adding to the weight of shrouded tail rotor assembly  100 . In  FIG.  2 B , shrouded tail rotor assembly  110  includes tail rotor gearbox  112  encased by tail rotor gearbox housing  114 . Tail rotor gearbox housing  114  is mounted to vertical post  116 . Tail rotor gearbox housing  114  is also mounted to shroud  118  by a tail rotor driveshaft casing  120 , which encases an aft portion of tail rotor driveshaft  122 . Because shrouded tail rotor assembly  110  relies upon a single horizontal tube that encases driveshaft  122  (tail rotor driveshaft casing  120 ), shrouded tail rotor assembly  110  is susceptible to catastrophic failure should tail rotor driveshaft casing  120  fail and either dislodge tail rotor gearbox  112  or cause tail rotor driveshaft  122  to malfunction. Shrouded tail rotor assembly  110  also requires that tail rotor gearbox  112  be encased by tail rotor gearbox housing  114 , adding additional weight to shrouded tail rotor assembly  110 . 
     In  FIG.  2 C , a shrouded tail rotor assembly  126  includes tail rotor gearbox  128  encased by tail rotor gearbox housing  130 . Diagonal beams  132 , which are parallel to one another, couple tail rotor gearbox housing  130  to shroud  134 . Tail rotor gearbox housing  130  is also coupled to shroud  134  by horizontal tail rotor driveshaft casing  136  through which tail rotor driveshaft  138  extends. Like shrouded tail rotor assemblies  100  and  110  in  FIGS.  2 A- 2 B , shrouded tail rotor assembly  126  requires a tail rotor gearbox housing  130  to support tail rotor gearbox  128  within shroud  134 . Indeed, none of shrouded tail rotor assemblies  100 ,  110  or  126  allow for direct connections to the tail rotor gearbox, opting instead for the heavier alternative of requiring a tail rotor gearbox housing. The positioning of diagonal beams  132  and tail rotor driveshaft casing  136  also fail to effectively transfer loads to tailboom  140 . A lighter and more effective system for supporting a tail rotor gearbox within a shrouded tail rotor assembly is needed to rectify the deficiencies of existing shrouded tail rotor assemblies. 
     Referring to  FIGS.  3 A- 3 C  in the drawings, a tail rotor assembly for a helicopter is schematically illustrated and generally designated  200 . Tail rotor assembly  200  includes tail rotor hub  202  with tail rotor blades  204  emanating radially therefrom. Tail rotor hub  202  receives rotational energy from a drivetrain of the helicopter including tail rotor driveshaft  206  and tail rotor gearbox  208 . Tail rotor gearbox  208  is supported centrally within shroud  210  by tail rotor gearbox support assembly  212 . Tail rotor gearbox support assembly  212  includes support column  214  coupled to the aft side of tail rotor gearbox  208 . Support column  214  is substantially vertical, although in other embodiments support column  214  may be nonvertically or diagonally oriented. The aft side of tail rotor gearbox  208  is coupled to support column  214  at or near midpoint  214   a  of support column  214 . Tail rotor gearbox support assembly  212  also includes upper and lower support crossbars  216 ,  218  coupled to the top and bottom sides of tail rotor gearbox  208 , respectively. The aft ends of upper and lower support crossbars  216 ,  218  are coupled to support column  214  by tee connectors  220 ,  222 , respectively. Upper and lower support crossbars  216 ,  218  are substantially horizontal and parallel to one another, although in other embodiments upper and lower support crossbars  216 ,  218  may be nonhorizontal and/or nonparallel to one another. Also, while upper and lower support crossbars  216 ,  218  are illustrated as being parallel to tail rotor driveshaft  206 , either or both of upper and lower support crossbars  216 ,  218  may form a nonparallel relationship with tail rotor driveshaft  206 . 
     Tail rotor blade sweep over the nonradial, horizontally-oriented upper and lower support crossbars  216 ,  218  and the nonradial, vertically-oriented support column  214  is relatively gradual as compared to radially-oriented support struts or spokes that cause instantaneous blade sweep and shallow induced pressure (loading) gradients on tail rotor blades  204 . Thus, the nonradial orientations of support column  214  and upper and lower support crossbars  216 ,  218  reduce induced blade loading noise. Support column  214  and upper and lower support crossbars  216 ,  218  may each have an aerodynamic cross-sectional shape to further reduce the noise and drag of tail rotor assembly  200 . In particular, support column  214  and upper and lower support crossbars  216 ,  218  may be aerodynamically shaped relative to the airflow produced by tail rotor hub  202  toward tail rotor gearbox support assembly  212 . The aerodynamic cross-sectional shape of support column  214  and upper and lower support crossbars  216 ,  218  may be an airfoil, circular, elliptical, polygonal, irregular or any other aerodynamic shape. For example, the sides of support column  214  and upper and lower support crossbars  216 ,  218  that face tail rotor hub  202  may have a rounded shape. Unlike the existing shrouded tail rotor assemblies illustrated in  FIGS.  2 A- 2 C , tail rotor gearbox support assembly  212  does not require tail rotor driveshaft  206  or tail rotor gearbox  208  to be housed or encased. Because tail rotor driveshaft  206  and/or tail rotor gearbox  208  may be exposed when implementing tail rotor gearbox support assembly  212 , the weight of tail rotor assembly  200  is reduced. 
     Referring to  FIGS.  4 A- 4 C  in the drawings, tail rotor assembly  200  is schematically illustrated in the side views of  FIGS.  4 A- 4 B  and the cross-sectional view of  FIG.  4 C  with shroud skin  224  and the tail rotor hub hidden from view to more clearly illustrate tail rotor gearbox support assembly  212 . Tailboom  226  is supported by a tailboom airframe  228  that includes frames, ribs, longerons  230 , stringers, bulkheads, struts  232  interconnecting longerons  230  and/or other elements that provide structural support to absorb the torque and thrust loads of tail rotor assembly  200  via tail rotor gearbox support assembly  212 . The structurally supportive elements of tailboom airframe  228  including longerons  230  and struts  232  may be solid or hollow and have any cross-sectional shape based on operational needs. Each support of tail rotor gearbox support assembly  212  including support column  214  and upper and lower support crossbars  216 ,  218  is directly or indirectly coupled or tied into a structural element of tailboom airframe  228  such as longerons  230  and/or struts  232  to maximize the stability of tail rotor gearbox  208  when reacting to torque and thrust loads. Portions of a shroud airframe  234  may be used to structurally couple tail rotor gearbox support assembly  212  to tailboom airframe  228 . Forward portion  234   a  of shroud airframe  234  is coupled to tailboom airframe  228 . Forward portion  234   a  of shroud airframe  234  includes a forward support boot  236  structurally interposed between the forward ends of upper and lower support crossbars  216 ,  218  and one or more of longerons  230  of tailboom airframe  228 . A forward support strap  238  couples the forward end of lower support crossbar  218  to one or more of struts  232  of tailboom airframe  228 . While upper and lower support crossbars  216 ,  218  are illustrated as being indirectly coupled to tailboom airframe  228  via intervening shroud airframe elements including forward support boot  236  and forward support strap  238 , in other embodiments the forward ends of upper and lower support crossbars  216 ,  218  may be directly coupled to one or more structural elements of tailboom airframe  228  such as longerons  230  or struts  232 . Upper and lower support crossbars  216 ,  218  may also be coupled to a forward portion  240   a  of shroud airframe ring  240 , which is itself coupled to tailboom airframe  228 . The top end of support column  214  is coupled to top portion  240   b  of shroud airframe ring  240  and the bottom end of support column  214  is coupled to the bottom portion  240   c  of shroud airframe ring  240 . Thus, tail rotor gearbox support assembly  212  is structurally tied into the forward, top and bottom portions of shroud airframe  234 , itself supported by tailboom airframe  228  to enhance the stability and load reactions of tail rotor gearbox support assembly  212 . Because tail rotor gearbox support assembly  212  does not couple to aft portion  240   d  of shroud airframe ring  240 , aft portion  240   d  may be lighter or smaller to reduce the weight of tail rotor assembly  200 . 
     Support column  214  is illustrated as a single and integral tube, although in other embodiments support column  214  may be formed from two or more coaxial beams or tubes having upper and lower portions. Support column  214  may also be straight, as illustrated, or alternatively may form a convex or concave curve. Angle  242  between upper support crossbar  216  and support column  214  and angle  244  between lower support crossbar  218  and support column  214  are right angles such that upper and lower support crossbars  216 ,  218  are perpendicular to support column  214 . While angle  242  is illustrated as congruent to angle  244 , in other embodiments angles  242 ,  244  may be noncongruent. In yet other embodiments, either or both of angle  242  or angle  244  may be an acute, obtuse or reflex angle. As best seen in  FIG.  4 C , which is a cross-sectional view taken along line  4 C- 4 C in  FIG.  1 B , support column  214  and upper and lower support crossbars  216 ,  218  are tubular and therefore have hollow cores. In other embodiments, support column  214  and upper and lower support crossbars  216 ,  218  may be solid or semi-solid. For example, support column  214  and upper and lower support crossbars  216 ,  218  may have foam or honeycomb cores. Support column  214  and upper and lower support crossbars  216 ,  218  may be formed from any material capable of effectively reacting to the loads of tail rotor gearbox  208  including carbon or composite materials such as carbon fiber. Upper and lower support crossbars  216 ,  218  are coupled to tail rotor gearbox  208  by upper and lower crossbar pin joint assemblies  246 ,  248 , respectively. Support column  214  is coupled to tail rotor gearbox  208  by column pin joint assembly  250 . 
     Referring to  FIGS.  5 A- 5 D  in the drawings, pin joint assemblies  246 ,  248 ,  250  as well as other portions of tail rotor gearbox support assembly  212  are schematically illustrated. Upper crossbar pin joint assembly  246  couples upper support crossbar  216  to top side  208   a  of tail rotor gearbox  208 . As best seen in  FIG.  5 B , upper crossbar pin joint assembly  246  includes a support crossbar fitting  252  around upper support crossbar  216 . Support crossbar fitting  252  forms an aperture  252   a . Upper crossbar pin joint assembly  246  also includes a tail rotor gearbox fitting  254  coupled on top side  208   a  of tail rotor gearbox  208 . Tail rotor gearbox fitting  254  may be coupled to top side  208   a  of tail rotor gearbox  208  in any manner such as by utilizing a pin-and-receiver interference joint  256 , fasteners, adhesive or other coupling technique. Upper crossbar pin joint assembly  246  also includes a pin, bolt or other fastener  258  that is insertable through support crossbar fitting  252  at aperture  252   a  and upper support crossbar  216  and received by receiver slot  254   a  of tail rotor gearbox fitting  254 . Bushings  260  are positioned along aperture  252   a  of support crossbar fitting  252  and receiver slot  254   a  of tail rotor gearbox fitting  254  to secure pin  258  in its engaged position. A gap  262  is formed between support crossbar fitting  252  and tail rotor gearbox fitting  254  when pin  258  is engaged, although in other embodiments gap  262  may be eliminated. In embodiments in which gap  262  is reduced or eliminated, gap  262  may be shimmed using one or more shims (not shown) or a shoulder (not shown) may be used on pin  258  that bears up against the top of tail rotor gearbox fitting  254 . In yet other embodiments in which gap  262  is reduced or eliminated, a jam nut or other part (not shown) threaded onto or disposed adjacent to pin  258  may be added between support crossbar fitting  252  and tail rotor gearbox fitting  254 . 
     Lower crossbar pin joint assembly  248  couples lower support crossbar  218  to bottom side  208   b  of tail rotor gearbox  208 . As best seen in  FIG.  5 C , lower crossbar pin joint assembly  248  includes support crossbar fitting  264  around lower support crossbar  218 . Support crossbar fitting  264  forms an aperture  264   a . Lower crossbar pin joint assembly  248  also includes tail rotor gearbox fitting  266  coupled on bottom side  208   b  of tail rotor gearbox  208 . Tail rotor gearbox fitting  266  may be coupled to bottom side  208   b  of tail rotor gearbox  208  in any manner such as by utilizing pin-and-receiver interference joint  268 , fasteners, adhesive or other coupling technique. Lower crossbar pin joint assembly  248  also includes pin, bolt or other fastener  270  that is insertable through support crossbar fitting  264  at aperture  264   a  and lower support crossbar  218  and received by receiver slot  266   a  of tail rotor gearbox fitting  266 . Bushings  272  are positioned along aperture  264   a  of support crossbar fitting  264  and receiver slot  266   a  of tail rotor gearbox fitting  266  to secure pin  270  in its engaged position. Gap  274  is formed between support crossbar fitting  264  and tail rotor gearbox fitting  266  when pin  270  is engaged, although in other embodiments gap  274  may be eliminated. In embodiments in which gap  274  is reduced or eliminated, gap  274  may be shimmed using one or more shims (not shown) or a shoulder (not shown) may be used on pin  270  that bears up against the bottom of tail rotor gearbox fitting  266 . In yet other embodiments in which gap  274  is reduced or eliminated, a jam nut or other part (not shown) threaded onto or disposed adjacent to pin  270  may be added between support crossbar fitting  264  and tail rotor gearbox fitting  266 . 
     Column pin joint assembly  250  couples support column  214  to aft side  208   c  of tail rotor gearbox  208 . As best seen in  FIG.  5 D , column pin joint assembly  250  includes support column fitting  276  around support column  214 . Support column fitting  276  forms an aperture  276   a . Column pin joint assembly  250  also includes tail rotor gearbox fitting  278  coupled on aft side  208   c  of tail rotor gearbox  208 . Tail rotor gearbox fitting  278  may be coupled to aft side  208   c  of tail rotor gearbox  208  in any manner such as by utilizing pin-and-receiver interference joint  280 , fasteners, adhesive or other coupling technique. Column pin joint assembly  250  also includes pin, bolt or other fastener  282  that is insertable through support column fitting  276  at aperture  276   a  and support column  214  and received by receiver slot  278   a  of tail rotor gearbox fitting  278 . Bushings  284  are positioned along aperture  276   a  of support column fitting  276  and receiver slot  278   a  of tail rotor gearbox fitting  278  to secure pin  282  in its engaged position. Gap  286  is formed between support column fitting  276  and tail rotor gearbox fitting  278  when pin  282  is engaged, although in other embodiments gap  286  may be eliminated. In embodiments in which gap  286  is reduced or eliminated, gap  286  may be shimmed using one or more shims (not shown) or a shoulder (not shown) may be used on pin  282  that bears up against the aft side of tail rotor gearbox fitting  278 . In yet other embodiments in which gap  286  is reduced or eliminated, a jam nut or other part (not shown) threaded onto or disposed adjacent to pin  282  may be added between support column fitting  276  and tail rotor gearbox fitting  278 . 
     Support crossbar fittings  252 ,  264  and support column fitting  276  may partially or fully surround, or glove, upper support crossbar  216 , lower support crossbar  218  and/or support column  214 , respectively. In the illustrated embodiment, support crossbar fittings  252 ,  264  fully surround upper and lower support crossbars  216 ,  218 , respectively, and support column fitting  276  partially surrounds support column  214 . Support crossbar fittings  252 ,  264  and support column fitting  276  may be formed from any material capable of securing upper and lower support crossbars  216 ,  218  and support column  214 , respectively, including composite materials and metallic materials such as machined aluminum. Pins  258 ,  270 ,  282  are unthreaded relative to tail rotor gearbox fittings  254 ,  266 ,  278  and no rotation of upper or lower support crossbars  216 ,  218  or support column  214  is permitted about pins  258 ,  270 ,  282 , respectively. In other embodiments, all or a portion of pins  258 ,  270 ,  282  may be threaded into tail rotor gearbox fittings  254 ,  266 ,  278 , respectively. Pins  258 ,  270 ,  282  may also be threaded or unthreaded, in any combination, relative to fittings  252 ,  264 ,  276  depending on the embodiment. In one example, one of pins  258 ,  270 ,  282  may be a threaded bolt that locks tail rotor gearbox  208  into a hard-mounted position with little or no freedom of movement relative to tail rotor gearbox support assembly  212 . One or all of pin joint assemblies  246 ,  248 ,  250  may utilize a threaded bolt to lock out the position of tail rotor gearbox  208  in this manner. For example, each pin  258 ,  270 ,  282  may be hard-mounted into tail rotor gearbox fittings  254 ,  266 ,  278  (such as by using threads or another coupling technique) to restrain the movement of tail rotor gearbox  208  along the axes defined by pins  258 ,  270 ,  282 . In the illustrated embodiment, tail rotor gearbox  208  is free-floating due to the freedom of movement provided by gaps  262 ,  274 ,  286 . Gaps  262 ,  274 ,  286  accommodate thermal expansion of tail rotor gearbox  208  to keep tail rotor gearbox  208  aligned without rigid bonding. Gaps  262 ,  274 ,  286  also reduce the thermal load or pressure on tail rotor gearbox support assembly  212  when tail rotor gearbox  208  thermally expands. Tail rotor gearbox support assembly  212  continues to effectively transfer torque and thrust loads from tail rotor gearbox  208  should one of pins  258 ,  270 ,  282  fail, thereby providing a more fail-safe design for increased safety. Pins  258 ,  270 ,  282  may also be removed from pin joint assemblies  246 ,  248 ,  250  to allow for the removal of tail rotor gearbox  208  for convenient maintenance. 
     As best seen in  FIG.  5 A , support column  214  and upper and lower support crossbars  216 ,  218  are radially nonaligned with axis of rotation  288  along mast  290  of the tail rotor assembly, as support column  214  and upper and lower support crossbars  216 ,  218  extend along respective axes that do not intersect axis of rotation  288 . Conversely, pins  258 ,  270 ,  282  are radially aligned with axis of rotation  288  since pins  258 ,  270 ,  282  extend along axes  292  radially emanating from and intersecting axis of rotation  288 . Orienting pins  258 ,  270 ,  282  toward axis of rotation  288  also accommodates the thermal growth of tail rotor gearbox  208 , which thermally expands radially outward along axes  292 . Orienting pins  258 ,  270 ,  282  along radial axes  292  also reduces or prevents movement of tail rotor gearbox  208  when tail rotor gearbox  208  thermally expands, thereby maintaining the position of axis of rotation  288  during thermal expansion. Tail rotor gearbox  208  may be moveable along one or more of axes  292  defined by pins  258 ,  270 ,  282  depending on which, if any, of pins  258 ,  270 ,  282  is unconstrained or unthreaded relative to tail rotor gearbox fittings  254 ,  266 ,  278 . 
     Tee connectors  220 ,  222  couple the aft ends of upper and lower support crossbars  216 ,  218  to support column  214 , respectively. Support column  214 , upper support crossbar  216  and/or lower support crossbar  218  may be coupled to tee connectors  220 ,  222  using an interference fit, fasteners, adhesive or any other coupling technique. While tee connectors  220 ,  222  are illustrated as fully surrounding or gloving support column  214 , in other embodiments tee connectors  220 ,  222  may partially surround support column  214 . Also, while tee connectors  220 ,  222  are illustrated as contacting the outer surfaces of upper and lower support crossbars  216 ,  218 , in other embodiments tee connectors  220 ,  222  may be inserted into the aft ends of upper and lower support crossbars  216 ,  218 . Tee connectors  220 ,  222  may be formed from any material capable of securing upper and lower support crossbars  216 ,  218  and support column  214  including composite materials and metallic materials such as machined aluminum. 
     Referring to  FIG.  6    in the drawings, a tail rotor assembly is schematically illustrated and generally designated  300 . Tail rotor assembly  300  includes tail rotor gearbox support assembly  302  to support tail rotor gearbox  304  within shroud  306 . Support column  308  is in a nonvertical and diagonal position. Additionally, upper and lower support crossbars  310 ,  312  are nonhorizontal and nonparallel to one another. Upper support crossbar  310  is parallel to tail rotor driveshaft  314 . Lower support crossbar  312 , however, is nonparallel to tail rotor driveshaft  314 , forming angle  316 . Angle  316  may be any acute angle. In other embodiments, both upper and lower support crossbars  310 ,  312  may be nonparallel to tail rotor driveshaft  314 . Upper support crossbar  310  may form an acute angle  318  with support column  308  and lower support crossbar  312  may form a right or obtuse angle  320  with support column  308 . Angles  318  and  320  are noncongruent. Angles  318  and  320  may be acute, right or obtuse angles depending on the configuration of tail rotor gearbox support assembly  302 . Tail rotor gearbox support assembly  302  illustrates that support column  308  and upper and lower support crossbars  310 ,  312  can have numerous orientations relative to one another as suitable for the particular aircraft on which tail rotor gearbox support assembly  302  is implemented. 
     The foregoing description of embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the present disclosure. Such modifications and combinations of the illustrative embodiments as well as other embodiments will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.