Rotor system shear bearing

A shear bearing for a rotor system has a four bar linkage and a grip configured to retain a flexural yoke and the grip is connected between a first set of opposing links of the four bar linkage. A rotor system has a flexural yoke and a shear bearing configured to perform at least one of transmitting forces to the yoke and receiving forces from the yoke, wherein the yoke is free of cavities for receiving the shear bearing. A rotational system has a flexural yoke and a damper disposed on a surface of the yoke.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Rotor systems, such as, but not limited to, rotor systems for helicopters, may comprise a flexural yoke that supports rotor blades. In some cases, the transmission of torsional forces (pitching loads) or (feathering loads) generally about a spanwise axis of the rotor blade may be accomplished by coupling a vertical shear bearing between the flexural yoke and the pitch links connected to a rotating control system. With a vertical shear being offset from the spanwise (pitching axis) either to the leading or training edge, vertical shear may flap the rotor blade about a flapping axis if not reacted out through a vertical shear bearing. In some cases, locating the vertical shear bearing in a kinematically suitable position may require providing an aperture in the flexural yoke and disposing at least a portion of the shear bearing in the aperture to accommodate vertical shear and/or in-plane shears from chord loads.

SUMMARY

In some embodiments of the disclosure, a rotor system is disclosed as comprising a flexural yoke and a shear bearing configured to perform at least one of transmitting forces to the yoke and receiving forces from the yoke, wherein the yoke is free of cavities for receiving the shear bearing.

In other embodiments of the disclosure, a shear bearing for a rotor system is disclosed as comprising a four bar linkage and a grip configured to retain a flexural yoke, the grip being connected between a first set of opposing links of the four bar linkage.

In yet other embodiments of the disclosure, a rotational system is disclosed as comprising a flexural yoke and a damper disposed on a surface of the yoke.

DETAILED DESCRIPTION

In some cases, it may be desirable to couple a rotor blade, such as, but not limited to, a helicopter rotor blade, to a flexural yoke without providing an aperture and/or cavity in the flexural yoke to accommodate a vertical shear bearing. In some embodiments of the disclosure, systems and methods are disclosed that comprise providing a flexural yoke that is free of apertures and/or cavities configured to receive any portion of a vertical shear bearing. In some embodiments, a vertical shear bearing is provided that may be attached to an exterior of a flexural yoke and/or a component substantially rigidly attached to a flexural yoke. In some embodiments, the vertical shear bearing may comprise a four bar linkage configured to transmit torsional forces about a spanwise axis of a rotor blade between the flexural yoke and one or more of a pitch horn and a rotor blade. In some embodiments, unlike the yoke 121 of FIG. 2 of U.S. Pat. No. 8,231,346 B2 issued to Stamps et al. on Jul. 31, 2012, the vertical shear bearing of this disclosure may be connected to a yoke generally at outer sides of yoke arms instead of being disposed and/or connected to a yoke at an aperture of the yoke. In some cases, the above-described external connection between a vertical shear bearing of this disclosure and a yoke of this disclosure may allow load bearing fibers of a composite yoke to extend between opposing yoke arms via a shorter path, a straighter path, and/or a path that does not deviate to accommodate an aperture for a vertical shear bearing.

Referring now toFIGS. 1-3, an oblique top view of a rotor system100, a close-up oblique top view of a portion of the rotor system100, and a substantially orthogonal side view of a portion of the rotor system100are shown, respectively. Rotor system100generally comprises a mast102that may rotate about a mast axis of rotation104. The rotor system100may further comprise a flexural yoke106comprising a plurality of arms108. The flexural yoke106may comprise composite laminate materials and/or metal. In this embodiment, each yoke106comprises two arms108that are each generally configured for connection to a rotor blade and/or airfoil. In this embodiment, two yokes106are vertically stacked and angularly offset relative to each other to create the four-arm configuration shown. In some embodiments, the arms108may be substantially enveloped by associated cuffs110. In some embodiments, each arm108may be associated with a spanwise axis112. In some cases, the spanwise axis112may be referred to as a pitch axis and/or a feathering axis about which the arms108, cuffs110, and/or rotor blades may rotate and/or twist in response to environmental, operational, and/or control perturbations. In some embodiments, a pitch change about this spanwise axis112of the cuffs110and/or rotor blades may be adjusted by vertically translating a pitch link114that is pivotally linked to a pitch horn116attached to the cuff110.

The rotor system100may further comprise a shear bearing120that may generally comprise a four bar linkage connected to each of an arm108and an associated cuff110. In some embodiments, the shear bearing120may comprise an upper link122, a lower link124, two forward links126, and two rear links128. A plurality of bearings130may be utilized in concert with pins132for joining the components of the four bar linkage. In some embodiments, the bearings130may comprise elastomeric components configured to return the system to a neutral pitch. In some embodiments, the upper link122and the lower link124may be pinned to the pitch horn116and the pitch horn116may be attached to and/or substantially carry the cuff110. The shear bearing120may further comprise a grip134connected between the forward links126and the rear links128utilizing bearings130and pins132. The grip134may generally extend around the arm108and may be sufficiently rigid to snugly retain damper pads136between the grip134and the arm108on both an upper side of the arm108and a lower side of the arm108. The above-described mechanical linkages of the shear bearing120may be configured to primarily transmit rotational forces about the spanwise axis112between the arms108of the flexural yoke106and the pitch horn116. In alternative embodiments, the shear bearing120may additionally and/or alternatively be connected directly to the cuff110and/or pitch link114.

In operation, the rotor system100may rotate the flexure yoke106and the related components about the mast axis of rotation104. In some cases, a rotational force about the spanwise axis112that may tend to change a pitch of the rotor blade and/or cause feathering of the rotor blade may be imparted to at least one of the rotor blade associated with an arm108, the cuff110associated with the arm108, and/or the pitch horn116associated with the arm108. The rotational force applied to the rotor blade and/or the cuff110may be a result of air loads generated in flight or other environmental condition while the rotational force applied to the pitch horn116may be the result of a control input to the rotor system100via the pitch link114. Regardless the source of the pitching and/or feathering movement and/or related forces, the shear bearing120may be configured to transfer and/or partially absorb the movement and/or energy related to the forces. Particularly, the shear bearing120may be configured to receive rotational inputs about the spanwise axis112, alter a position of the four bar linkage of the shear bearing120, and resultantly transmit rotational movement and/or forces to the arm108via the grip134and associated damper pads136. The kinematic behavior of the four bar linkage of the shear bearing120may be described as converting rotational inputs from the pitch horn116into relative translational movements of the upper and lower links122,124relative to the grip134.

Referring now toFIG. 4, a schematic cut-away view of the shear bearing120is as viewed from a relatively inboard location and looking generally radially outward along the spanwise axis112. As a function of the grip134being pinned between the forward and rear links126,128of the four bar linkage, the above-described relative translational movements are effectively converted from the translational movements to a rotational movement of the arm108about a center of rotation140of the shear bearing120. In some embodiments, the center of rotation140may be positioned substantially coincident with the spanwise axis112. In some cases, the center of rotation140may also be a point about which the four bar linkage of the shear bearing120cocks or otherwise is racked out of plane as a function of one or more of the bearings130accommodating spherical and/or orbiting movement between interconnected links of the four bar linkage. In some cases, one or more of the bearings130may be configured as a spherical bearing while other bearings130are configured to substantially limit movement to rotation about the pins132. In some cases, an elasticity and/or spring rating of the bearings130may be relatively high as compared to other components of the shear bearing. More specifically, the bearings130may be selected to have spring rates that do not substantially interfere with an effectiveness of the damper pads136and/or any other primary damping component. In some cases, providing the damper pads136directly on the arm108may provide a more consistent damping functionality that is substantially independent of any flapping and/or pitching of the arm108. In some cases, the utilization of the damper pads136in the manner described above may negate a need for a separate fluid damper in the rotor system100.

Further,FIG. 4shows that the shear bearing120may require no centrally located aperture, cavity, and/or recess in the flexural yoke106for the purpose of accommodating a shear bearing within the aperture, cavity, and/or recess because the accommodation of vertical shear in the rotor system100is achieved by applying forces to the outside and/or continuous upper and/or lower surfaces of the flexural yoke106. Particularly, the systems and methods disclosed may prevent the need for a through hole or aperture in a yoke such as hole202ofFIG. 2that may otherwise be provided to accommodate a typical shear bearing that may comprise a center of rotation located substantially similarly as the center of rotation140. As such, the rotor system100may comprise a flexural yoke comprising only holes for accommodating passage of a mast therethrough and/or for accepting bolts and/or other fasteners associated with securing the flexural yoke106to the mast102. In some cases, providing a flexural yoke106that comprises a composite layup of materials may significantly strengthen the yoke106in tension along a load bearing continuous fiber that extends between opposing yoke arms108, decrease an overall mass, decrease an overall radial footprint, and/or otherwise improve a performance characteristic of the flexural yoke106.

While the shear bearing120and associated components and configurations are described above in the context of a rotor system100for a helicopter, the shear bearing120and the rotor system100may be applied to any other suitable rotor related application. In some case, a fixed wing aircraft in which a pitch of a propeller may be adjusted (e.g. constant speed propeller systems) may utilize a rotor system100. Similarly, any other craft or device that may selectively control a pitch and/or feathering of a rotor blade may benefit from utilization of the shear bearing120and/or rotor system100.