Retention bushing for rotor assembly

Abstract

An assembly includes a hub having a spoke, the spoke having a conically shaped interior surface. The assembly further includes a blade, and a blade retention device. The blade retention device has a first end and a second end. The first end of the blade retention device is pinned to the blade. The assembly further includes a retention bushing within the conically shaped interior surface of the spoke, the retention bushing having a conically shaped outer surface. The second end of the blade retention device is pinned to the retention bushing.

Description

RETENTION BUSHING FOR ROTOR ASSEMBLYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 675,523, filed July 25, 2024, which is incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] Embodiments of this disclosure are directed to a rotor assembly, and in particular, to systems and methods for attaching a blade to a hub of a rotor assembly.BACKGROUND OF THE INVENTION

[0003] Rotary aircraft, such as vertical takeoff and landing (VTOL) vehicles, typically generate thrust via blades attached to a rotating hub. The hub and blades rotate about a longitudinal axis aligned with the center of the hub, the blades providing thrust through their interaction with the air. The blades experience an outward force due to their high-speed rotation about the longitudinal axis, also referred to as a centrifugal force.

[0004] To combat the centrifugal force, the blades may be connected to the hub using a device such as a tension-torsion strap (TT strap). TT straps are devices formed to be relatively stiff in tension to prevent movement of the bladed radially away from the hub due to centrifugal force, while being relatively flexible in torsion to allow the blades to change pitch. The TT straps are typically pinned or bolted directly to the rotor hub. Such designs result in increased hub weight, design complexity, and cost. For example, TT strap designs involve machining features that receive connectors directly into the hub. Additionally, such designs can be subject to early wear and are difficult to repair.

[0005] There is a need for systems and devices of a tiltrotor vehicle for attachment of blades to the hub in a manner that allows for easy repair or replacement, as well as a reduction in wear.

[0006] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art, or suggestions of the prior art, by inclusion in this section.SUMMARY OF THE DISCLOSURE

[0007] In one aspect the disclosure relates to a rotor assembly for an aircraft. The rotor assembly may include a hub having a spoke, the spoke having a conically shaped interior surface. The rotor assembly may further include a blade, and a blade retention device having a first end and a second end. The first end of the blade retention device may be pinned to the blade. The rotor assembly may further include a retention bushing within the conically shaped interior surface of the spoke. The retention bushing may have a conically shaped outer surface. The second end of the blade retention device may be pinned to the retention bushing.

[0008] In another aspect, the disclosure relates to an aircraft having a fuselage, a wing connected to the fuselage, a tail connected to the fuselage, and a rotor assembly connected to the wing or to the tail. The rotor assembly may include a hub having a spoke, the spoke defining an angled interior surface. The rotor assembly may further include a blade, a tension-torsion strap having a first end pinned to the blade and a second end, and a retention bushing having an angled exterior surface that contacts the interior surface of the spoke. The second end of the tension-torsion strap may be pinned to the retention bushing.

[0009] In another aspect, the disclosure relates to a bushing for use within a hub of a rotor assembly. The bushing may include a base end, an apex end, a through hole configured to receive a retention pin, an interior opening, and an exterior surface tapering between the base end and the apex end. The taper of the exterior surface may correspond to a taper of an interior surface of the hub of the rotor assembly.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various examples and, together with the description, serve to explain the principles of the disclosed examples and embodiments.

[0011] Aspects of the disclosure may be implemented in connection with embodiments illustrated in the attached drawings. These drawings show different aspects of the present disclosure and, where appropriate, reference numerals illustrating like structures, components, materials, and / or elements in different figures are labeled similarly. It is understood that various combinations of the structures, components, and / or elements, other than those specifically shown, are contemplated and are within the scope of the present disclosure.

[0012] Moreover, there are many embodiments described and illustrated herein. The present disclosure is neither limited to any single aspect or embodiment thereof, nor is it limited to any combinations and / or permutations of such aspects and / or embodiments. Moreover, eachof the aspects of the present disclosure, and / or embodiments thereof, may be employed alone or in combination with one or more of the other aspects of the present disclosure and / or embodiments thereof. For the sake of brevity, certain permutations and combinations are not discussed and / or illustrated separately herein. Notably, an embodiment or implementation described herein as “exemplary” is not to be construed as preferred or advantageous, for example, over other embodiments or implementations; rather, it is intended to reflect or indicate the embodiment s) is / are “example” embodiment(s).

[0013] FIG. 1 illustrates a front perspective view of vertical takeoff and landing vehicle having rotor assemblies, according to aspects of the present disclosure.

[0014] FIG. 2 illustrates an exploded view of a portion of a rotor assembly of FIG. 1.

[0015] FIG. 3 illustrates a sectional view of a portion of a rotor assembly of FIG. 1.

[0016] FIG. 4 illustrates a top perspective view of a portion of a rotor assembly of FIG.1.

[0017] FIG. 5 illustrates a top perspective view of a portion of a rotor assembly, according to a further embodiment of the present disclosure.

[0018] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term “exemplary” is used in the sense of “example,” rather than “ideal.” In addition, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish an element or a structure from another. Moreover, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of one or more of the referenced items.

[0019] Notably, for simplicity and clarity of illustration, certain aspects of the figures depict the general structure and / or manner of construction of the various embodiments. Descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring other features. Elements in the figures are not necessarily drawn to scale; the dimensions of some features may be exaggerated relative to other elements to improve understanding of the example embodiments. For example, one of ordinary skill in the art appreciates that the side views are not drawn to scale and should not be viewed as representing proportional relationships between different components. The side views are provided to help illustrate the various components of the depicted assembly, and to show their relative positioning to one another.DETAILED DESCRIPTION

[0020] Reference will now be made in detail to examples of the present disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the discussion that follows, relative terms such as “about,” “substantially,” “approximately,” etc. are used to indicate a possible variation of a numerical range in a stated numeric value, as will be designated below

[0021] The present disclosure generally provides for systems, methods, and devices of a vertical takeoff and landing (VTOL) aircraft at various speeds, modes, and phases of flights to control position, orientation, direction, and / or speed of the VTOL aircraft. Although the present disclosure makes reference to a VTOL aircraft, those of ordinary skill in the art will readily recognize that reference to an aircraft is exemplary, and that the concepts of the present disclosure may be used in conjunction with any suitable or comparable aircraft, e.g., airplanes, helicopters, aerostats, flight simulators, space crafts, commercial airplanes, electrical vertical takeoff and landing aircraft (eVTOL aircraft), or any other type of rotor-propelled aircraft. Still further, aspects of the present disclosure may be used in conjunction with any vehicle or rotor assembly, including, but not limited to, vehicles designed for operation on land, on water, in the air, in space, or any combination thereof, as well as turbines, such as wind turbines. The above list is not, in any matter, supposed to signify a limited list of what the term “aircraft” defines in terms of structure.

[0022] FIG. 1 is a front perspective view of a vertical takeoff vehicle takeoff and landing vehicle (hereinafter vehicle 100) having at least one rotor assembly 107. Vehicle 100 includes a fuselage 101 and one or more wings 103. The fuselage may further be connected to a tail 105. At least one rotor assembly 107 may be connected on each of the wings 103 and / or the tail 105. Rotor assembly 107 may include a central hub 131 with at least one blade 111 extending radially outward therefrom. The rotor assembly 107 may transition between a vertical orientation (FIG. 1) and a horizontal orientation (not shown). In the vertical orientation, the rotor assemblies 107 allow the vehicle 100 to hover and translate vertically for takeoff and landing. In the horizontal orientation, the rotor assemblies 107 allow the vehicle 100 to propel itself forward with increased efficiency.

[0023] In the example shown in FIG. 1, some of the rotor assemblies 107 are in a tractor configuration in which the blades 111 are in front of the engine (not shown) relative to the airflow, and other rotor assemblies 107 are in a pusher configuration in which the blades 111are behind the engine relative to the airflow. In the tractor configuration, the rotor assemblies 107 pull the vehicle 100 through the air, while in the pusher configuration, the rotor assemblies 107 push the vehicle 100 through the air. In some examples, all of the rotor assemblies 107 may be in the tractor configuration. In other examples, all of the rotor assemblies 107 may be in the pusher configuration.

[0024] In the example shown in FIG. 1, the vehicle 100 shows each of the rotor assemblies 107 in the vertical orientation. In other examples, the rotor assemblies 107 may all be in the horizontal orientation. In some examples, the rotor assemblies 107 may be in different positions, such that at least some of the rotor assemblies 107 may be in the vertical orientation, some of the rotor assemblies 107 may be in the horizontal orientation, and some of the rotor assemblies 107 may be between the vertical and horizontal orientation. In some examples, some of the rotor assemblies 107 may transition between the vertical and horizontal orientations, while other rotor assemblies 107 may be fixed in either the vertical or horizontal orientation (fixed rotor assemblies 107 not shown in FIG. 1).

[0025] In the example shown in FIG. 1, the vehicle 100 has ten rotor assemblies 107. In other examples, the vehicle 100 may have more or less rotor assemblies 107. For example, the vehicle 100 may have two, four, six, eight, or twelve rotor assemblies 107. In the example shown in FIG. 1, the vehicle 100 has rotor assemblies 107 mounted to both the wings 103 and the tail 105. In other examples, the rotor assemblies 107 may be mounted to just the wings 103 or the tail 105. In further examples, the vehicle 100 may have rotor assemblies 107 that are additionally or alternatively attached to the fuselage 101.

[0026] FIG. 2 illustrates an exploded view of a portion of rotor assembly 107 of FIG. 1. FIG. 3 illustrates a sectional view of a portion of a rotor assembly of FIG. 1. Referring to FIGS. 2-3, blade I l l is attached to a hub 131 by a blade retention strap, such as TT strap 113 or a strap pack, pinned to a centrifugal force retention bushing (hereinafter “CFRB 115”) within a spoke 133 of the hub 131. The CFRB 115 may have an angled outer surface 145 (e.g., a tapered surface, conically-shaped surface, etc.) that mates with a similarly shaped angled interior surface 134 of the spoke 133, such that the outer surface 145 of the CFRB 115 contacts the angled interior surface 134 of the spoke 133. The cooperating shapes of the outer surface 145 of the CFRB 115 and the angled interior surface 134 of the spoke 133 prevent the CFRB 115 from moving in an outboard direction when the hub 131 rotates.

[0027] Rotor assembly 107 may further include the TT strap 113, the CFRB 115, an outboard journal bearing 127, and an inboard journal bearing 129 which may be used to rotatably connect blade 111 to the hub 131. The rotor assembly 107 may define a longitudinalor vertical Z axis that is aligned with the center of rotation of the hub 131 and blades 111, and a radial or pitch Y axis that is perpendicular to the Z axis.

[0028] The outer surface 145 of the CFRB 115 may be angled relative to the Y axis, such that the CFRB 115 has an outboard apex end 122 and an inboard base end 124, the apex end 122 having a smaller width or diameter than the base end 124. A rectangular boss 117 (FIG. 2) may extend or protrude from the base end 124, such that a longitudinal axis running though a top end 155 and a bottom end 157 of the boss 117 is parallel to the Z axis of the hub 131. The CFRB 115 may further include a fastener opening 120 (e.g., a through hole) aligned about a center of the CFRB 115 (or in a direction perpendicular to the Y axis). The CFRB 115 may also include an interior opening 116 in communication with the fastener opening 120 via a hollow interior 128 of the CFRB 115.

[0029] The CFRB 115 may be metallic, composite, or another suitable material. In some examples, the CFRB 115 may include an anti -fretting coating that prevents fretting due to contact between the CFRB 115 and the angled interior spoke surface 134. Fretting may be wear caused by the rubbing of surfaces, such as the outer surface 145 of the CFRB 115 and the interior spoke surface 134, due to vibrations or small movements. The anti -fretting coating may provide a protective layer between the CFRB 115 and the interior spoke surface 134 that prevents surface to surface contact. In some examples, the coating may be applied to the entire CFRB 115. In other examples, the coating may be applied to certain portions of the CFRB 115, such as the angled outer surface 145, to the boss 117, or another portion of the CFRB 115.

[0030] In the example embodiment shown in FIGS. 2-3, the CFRB 115 may have a generally conic shape with a longitudinal axis aligned with the Y axis and a cross section that is axially symmetric about the Y axis. In other embodiments, the CFRB 115 may be spherical or hemispherical. In the case of a hemispherical CFRB 115, the CFRB 115 may be aligned such that a radius of the CFRB 115 extending perpendicular to the base end 124 is aligned with the Y axis. In the example of a spherical CFRB 115, the CFRB 115 may be aligned such that a diameter of the CFRB 115 lies along the Y axis. In some embodiments the CFRB 115 may have a tapering shape with a non-axially symmetric cross section. For example, the CFRB 115 may have an elliptical cross section while maintaining a generally conic shape. In other examples the CFRB 115 may be a polygonal conic solid that has a polygonal cross section. The polygonal conic solid may be formed by a number of sides connected at the base end 124 that all meet at the apex end 122 such that the longitudinal axis of the CFRB 115 aligns with the Y axis. For example, the CFRB 115 may be a four sided pyramid, with a square cross section and a longitudinal axis aligned with the Y axis. Such non-axially symmetric shapesmay prevent rotation of the CFRB 115 and eliminate the need for the boss 117 (described in more detail below).

[0031] In the example embodiment shown in FIGS. 2-3, the CFRB 115 may have a rectangular boss 117 at the base end 124 with a longitudinal axis aligned with the Z axis and extending across the diameter of the base end 124 that prevents rotation of the CFRB 115 via its interaction with the slot 137 of a spinner mount 135 (explained further below). In some examples, the boss 117 may be aligned perpendicularly to both Y axis and the Z axis, or may be aligned at another angle relative to the Z axis. In other examples, the CFRB 115 may have more than one boss 117. The one or more protrusions may be rectangular, cylindrical, spherical, or another geometric shape. In further examples, one or more bosses 117 or protrusions may be located on the outer surface 145 of the CFRB 115 that aligns with an opening or slot on the interior spoke surface 134 (not shown).

[0032] In the example embodiment shown in FIGS. 2-3, the axis of the fastener opening 120 may perpendicular to both the Y axis and the Z axis, such that the pin 123 is inserted into or out of the page from the perspective of FIG. 3. In other embodiments, the axis of the fastener opening 120 may be aligned with the Z axis such that the pin 123 is inserted along the Z axis. In yet further embodiments, the axis of the fastener opening 120 may be at angle to the Y axis and the Z axis.

[0033] The hollow interior 128 of the CFRB 115 may extend from the interior opening 116 at the apex end 122 towards the base end 124. In the example shown in FIGS. 2-3, the hollow interior 128 extends a partial length of the CFRB 115, stopping short of the base end 124. In other embodiments, the hollow interior 128 may extend to or past the base end 124, such that the hollow interior 128 interrupts the boss 117. The interior opening 116 and hollow interior 128 may generally be sized to accommodate the TT strap 113. For example, the interior opening 116 and the hollow interior 128 may be generally rectangular to generally match the shape of the inboard end of the TT strap 113. In the example shown in FIGS. 2-3, the generally rectangular interior opening 116 and hollow interior 128 may be aligned such that the longest dimension of the cross section of the interior opening 116 is parallel to the Z axis. In other embodiments, the generally rectangular interior opening 116 and hollow interior 128 may be aligned such that the longest dimension of the interior opening 116 and the hollow interior 128 are perpendicular to the Y axis and the Z axis. In further embodiments, the generally rectangular interior opening 116 and hollow interior 128 may be aligned such that the longest dimension of the interior opening 116 and hollow interior 128 are at an angle relative to the Z axis. In other embodiments, the interior opening 116 and hollow interior 128 may have adifferent shape that corresponds to the shape of the blade retention strap, such as the TT strap 113.

[0034] With reference to FIG. 3, the hub 131 may include a hollow cylindrical central portion 136, as well as at least one spoke 133 that extends radially outward from the hub 131. The number of spokes may be the same as the number of blades 111 to be attached to the hub 131. For example, if two, three, or four blades 111 are to be attached to the hub 131, then the hub 131 may include two, three, or four spokes 133, respectively. The spoke 133 may have an exterior spoke surface 132, a flat (e.g., cylindrical or non-tapered) interior spoke surface 147, and an angled interior spoke surface 134 (e.g., an angled surface, a chamfered surface, a conical surface, etc.).

[0035] At least of portion of the exterior spoke surface 132 may be flat. In the example shown in FIG. 3, the exterior spoke surface 132 has an inboard, or radially inner, flat portion (e.g., a portion that contacts journal bearing 129). The exterior spoke surface 132 may also include an outboard, or radially outer, flat portion (e.g., a portion that contacts journal bearing 127). This flat portion may extend to the distal-most end of the spoke 133, defining an opening into which the TT strap 113 is received. An angled or tapered portion of the exterior spoke surface 132 may extend from the inboard flat portion to the outboard flat portion.

[0036] In the example shown in FIGS. 2-3, the spoke 133 has both a flat interior spoke surface 147 and an angled interior spoke surface 134. The flat interior spoke surface 147 may be located at an outboard end of the spoke 133, and the angled interior spoke surface 134 may be located at the inboard end of the spoke 133. In other examples, the spoke 133 may only have an angled interior spoke surface 134 that extends the entire length of the hub 131.

[0037] The angled interior spoke surface 134 may be angled similar to the outer surface 145 of the CFRB 115, such that both the angled interior spoke surface 134 and the outer surface 145 of the CFRB 115 have the same taper (explained further below) or approximately the same taper. The CFRB 115 may be received within a recess defined by the angled interior spoke surface 134, such that the angled interior spoke surface 134 and the CFRB 115 form a mating connection, with the exterior surface of the CFRB 115 contacting the interior spoke surface 134.

[0038] In the example embodiment shown in FIGS. 2-3, the angled interior spoke surface 134 may be a chamfered surface in the shape of a cone (e.g., a conical surface or conically shaped), with a longitudinal axis that is aligned with the Y axis and a cross section that is axially symmetric about the Y axis. In other embodiments, the angled interior spoke surface 134 may be hemispherical to match the shape of the CFRB 115. As described abovewith respect to the CFRB 115, in the case of a hemispherical interior spoke surface 134, the angled interior spoke surface 134 may be aligned such that a radius defining the angled interior spoke surface 134 extends perpendicular to the base end 124 is aligned with the Y axis.

[0039] In some embodiments the angled interior spoke surface 134 may have a tapering shape with a non-axially symmetric cross section that is similar to the CFRB 115. For example, the angled interior spoke surface 134 may have an elliptical cross section while maintaining a generally conical shape. In other examples the angled interior spoke surface 134 may be a polygonal conic solid that has a polygonal cross section that is similar to the CFRB 115. For example, the angled interior spoke surface 134 may be a four sided pyramid with a square cross section and a longitudinal axis aligned with the Y axis. Such non-axially symmetric shapes may prevent rotation of the CFRB 115 within the angled interior spoke surface 134 and eliminate the need for the boss 117.

[0040] In the example shown in FIGS. 2-3, wherein the CFRB 115 and the angled interior spoke surface 134 have a similar tapered or conical shape, the taper of the CFRB 115 and the interior spoke surface 134 may be measured from an axis A (also referred to as “A axis”) that is parallel to the Y axis. The taper of the CFRB forms angle X, angle X being measured from the A axis to the outer surface 145 of the CFRB 115. The taper of the interior spoke surface 134 may be approximately equal to the taper of the CFRB 115, the taper of the interior spoke surface 134 being equal to or approximately equal to angle X, as measured from the A axis to the interior spoke surface 134. In the example shown in FIGS. 2-3, angle X, the taper of the outer surface 145 of the CFRB 115 and the interior spoke surface 134, may be about 8 degrees. In other examples, angle X may be about 7 degrees to about 9 degrees, about 6 degrees to about 10 degrees, or about 5 degrees to about 11 degrees. In some examples, tapers of about 8 degrees, or more than about 8 degrees allows for the contact forces between the interior spoke surface 134 and the CFRB 115 to be spread along a greater area (as explained further below), while allowing the CFRB 115 to be easily removable.

[0041] In the examples shown in FIGS. 2-3, the CFRB 115 and the angled interior spoke surface 134 may have a continuous taper. For example, the CFRB 115 may have a continuous taper from the base end 124 to the apex end 122, such that the diameter at the base end 124 is larger than the diameter of the apex end 122. In other examples the CFRB 115 and the angled interior spoke surface 134 may have discontinuous tapers, such that the different sections of the CFRB 115 and the angled interior spoke surface 134 have different tapers. For example, the taper at the apex end 122 of the CFRB 115 may be smaller than the taper near the base end 124. In other examples, the taper at the apex end 122 may be larger than the taper nearthe base end 124. In some examples, the outer surface 145 of the CFRB 115 may include regions where no taper is present. For example, the CFRB 115 may have a first section with a first taper near the apex end 122, a second section with a second taper near the base end 124, and third section between the first and second sections where there is no taper. In such examples, the angled interior spoke surface 134 may have a similar surface taper pattern (e.g., a first section with a first taper near the outboard end, a second section with a second taper near the inboard end, and third section between the first and second sections where there is no taper). Although the taper of the CFRB 115 and the angled interior spoke surface 134 shown FIGS. 2- 3 is linear, in other examples, outer surface 145 may include a curved (e.g., non-linear) portion.

[0042] In the examples shown in FIGS. 2-3, the CFRB 115 is about the same length as the angled interior spoke surface 134, and the CFRB 115 occupies about the volume formed within the angled interior spoke surface 134. In other examples, the angled interior spoke surface 134 may have a length that is more or less than the length of the CFRB 115, such that it has smaller or larger diameters than the CFRB 115 at the outboard or inboard ends of the angled interior spoke surface 134, respectively.

[0043] Referring again generally to FIGS. 2-3, the outboard journal bearing 127 may be rigidly attached to a flat section of the exterior spoke surface 132 near the outboard end of the spoke 133, and the inboard journal bearing 129 may be rigidly attached to a flat section of the exterior spoke surface 132 near the inboard end of the spoke 133. The outboard journal bearing 127 and the inboard journal bearing 129 may react to in-plane and out-of-plane bending forces, and may have a running interface or surface. The outboard journal bearing 127 and the inboard journal bearing 129 may have surfaces with low friction coefficients so as to allow the blade 111 rotate over their surfaces. The outboard journal bearing 127 and inboard journal bearing 129 may be made from metallic or composite substrates with low friction coatings. The outboard journal bearing 127 and inboard journal bearing 129 may be include a surface or a surface coating made from polytetrafluoroethylene (PTFE), a high-strength material (e.g., resin, stainless steel, bronze alloy, fiberglass) embedded with solid lubricants (e.g., solid PTFE), a polyester resin-based material included with PTFE particles, or another suitable substance.

[0044] The blade 111 may include a pitch horn 125 at its inboard or root end and a blade fastener opening 126 outboard with respect to the pitch horn 125. The length of the blade 111 may be generally aligned with the radial or pitch Y axis about which the blade may rotate to change pitch. The blade 111 may have a hollow section at its inboard end formed by an interior surface 110 having a varying geometry. The blade 111 may be fitted to the hub 131such that the spoke 133 extends into the opening formed by the interior surface 110 of the blade 111, and the outer surfaces of the outboard journal bearing 127 and the inboard journal bearing 129 contact the interior surface 110 of the blade 111. The interior surface 110 of the blade 111 may have a running face (not shown) that moves or slides relative to the running interface of the outboard journal bearing 127 and the inboard journal bearing 129. The running face of the blade may be an integrally formed metallic or composite ring, or the running face may be the inner surface of the blade 111 itself. The running interface of the outboard journal bearing 127 and the inboard journal bearing 129 may allow the blade 111 to change pitch while being connected to the hub 131. The pitch horn 125 may be connected to a pitch link 139. The pitch link 139 may be connected to the control system of the vehicle 100 and be used to pitch the blade 111.

[0045] In the example shown in FIGS. 2-4, the spoke 133 extends into the blade 111. In other examples, the blade 111 may extend into the spoke 133, and the outboard journal bearing 127 and the inboard journal bearing 129 may be placed on the outer diameter of the blade 111.

[0046] The TT strap 113 may have an elongate shape with a first outboard end 112 and a second inboard end 114. The outboard end 112 may have an outboard fastener opening 118, and the inboard end 114 may have an inboard fastener opening 119. The inboard end 114 of the TT strap 113 may be received by the interior opening 116 and the hollow interior 128 of the CFRB 115 such that the inboard fastener opening 119 of the TT strap 113 aligns with the fastener opening 120 of the CFRB 115 (FIG. 2). An inboard strap pin 123 may be placed through both the fastener opening 120 and the inboard fastener opening 119 of the TT strap 113 to connect the TT strap 113 to the CFRB 115. The outboard end 112 of the TT strap 113 may be placed within the blade 111 such that a longitudinal axis of the TT strap 113 aligns with the pitch Y axis of the blade 111, and the outboard fastener opening 118 of the TT strap 113 aligns with the fastener opening 126 of the blade 111. An outboard strap pin 121 may be placed through the fastener opening 126 and the outboard fastener opening 118 to connect the TT strap 113 to the blade 111. The connection of the TT strap 113 to the blade 111 and the hub 131 may cause a tension force within the TT strap 113 that pulls the blade 111 towards the hub 131, and also pulls the CFRB 115 towards the outboard end of the blade 111. The tension force of the CFRB 115 may cause the exterior surface of the CFRB 115 to contact the conically shaped interior spoke surface 134.

[0047] FIG. 4 illustrates a top perspective view of a portion of a rotor assembly of FIG.1. As seen in FIG. 4, the spinner mount 135 may be rigidly mounted to an axial end of the hub131. The spinner mount 135 may include a neck 138 that extends into the hollow cylindrical central portion 136 of the hub 131. The neck 138 may include at least one slot 137 (FIG. 3) that extends parallel to the axial direction of the hub 131 (e.g., parallel to the Z axis). The slot 137 may have an open bottom end 149, a closed top end 151, and two sidewalls 153. The slot 137 may receive at least of the portion of the rectangular boss 117 of the CFRB 115, which may aid in preventing rotation of the CFRB 115 within the spoke 133, and may also aid in retaining the CFRB 115 within the spoke 133.

[0048] The spinner mount 135 may include a slot 137 for each blade 111 to be attached to the hub 131. In some embodiments, the spinner mount 135 may include multiple slots per blade 111, such that the spinner mount 135 may receive multiple bossesl 17 for a given blade 111. In the example shown in FIG. 4, the slots 137 are shown as rectangular with the longest dimension aligned with the Z axis. In other examples, the longest dimension of the slot 137 may be perpendicular to the Z axis and the Y axis, or at an angle relative to the Z axis. In some examples, the slots may have a shape other than rectangular, such that the slots 137 correspond to the shape of the boss. In certain examples, the slot 137 may be omitted when the shape of the CFRB 115 is such that rotation within the spoke 133 is prevented.

[0049] Referring now generally to FIGS. 2-4, during operation, the hub 131 and blade 111 may rotate about the longitudinal Z axis of the hub 131. As the hub 131 and blade 111 rotate, the outward force generated by the rotation of the hub 131 (e.g., centrifugal force) may act upon the blade I l l as well as the CFRB 115 in a direction radially away from the hub 131. Outward motion of the CFRB 115 may be prevented by the interior surface 134 of the spoke 133 pressing against the exterior surface of the CFRB 115. In particular, the shape of the CFRB 115 and the shape of the interior surface 134 of the spoke 133 may help to distribute the forces along the contact surface between the two, limiting wear. Wear, such as fretting, may be further limited by the addition of an anti -fretting coating to the CFRB 115.

[0050] As the blade 111 is attached to the CFRB 115 via the TT strap 113, the blade 111 may be prevented from moving due to the interaction of the CFRB 115 with the interior surface 134 of the spoke 133 and the stiffness of the TT strap 113 in tension. The TT strap 113 may be stiff in tension, such that the TT strap 113 undergoes little, if any, elongation when the rotor assembly 107 is in operation. The stiff tension of the TT strap 113 helps to keep the blades 111 attached to the hub 131 by preventing radial movement. Although stiff in tension, the TT strap 113 may have low torsional stiffness, such that the TT strap 113 may twist about the Y axis. The twisting motion of the TT strap 113 allows the blades 111 to pitch about the Y axisthrough interaction of the pitch horn 125 with the pitch link 139 or another portion of the control system of the vehicle 100.

[0051] To assemble the rotor assembly 107, and attach the blade 111 to the hub 131, the CFRB 115 is first inserted into spoke 133, such that the angled outer surface 145 of the CFRB 115 contacts the angled interior surface 134 of the spoke 133 (FIG. 3). The TT strap 113 may then be inserted into the interior opening 116 of the CFRB 115 through the spoke 133 such that the inboard end 114 of the TT strap 113 is within the hollow interior 128 of the CFRB 115. The fastener opening 119 and fastener opening 120 may then be aligned. With the fastener opening 119 and fastener opening 120 aligned in this manner, the inboard strap pin 123 may be inserted into and through the aligned inboard fastener opening 119 and fastener opening 120, thereby connecting the TT strap 113 and the CFRB 115 together (FIG. 3).

[0052] The blade 111 may be placed over the spoke 133 such that interior surface 110 of the blade 111 contacts both the outboard journal bearing 127 and the inboard journal bearing 129, the outboard journal bearing 127 and the inboard journal bearing 129 being fixedly secured to the spoke 133 (FIG. 3). With blade 111 in position on the spoke 133, the outboard fastener opening 118 of the TT strap 113 and fastener opening 126 of the blade 111 may be aligned. The outboard strap pin 121 may then be inserted through the aligned outboard fastener opening 118 and fastener opening 126, connecting the blade 111 to the TT strap 113, as well as to the CFRB 115 (FIG. 3).

[0053] The connection of the blade 111 to the TT strap 113 may cause tension in the TT strap 113, which may pull the CFRB 115 into the angled interior spoke surface 134 while also pulling the blade 111 towards the hub 131. The spinner mount 135 may then be placed within the hollow cylindrical central portion 136 of the hub 131, such that the slot 137 receives the boss 117 of the CFRB 115 (FIG. 4). The slot 137 may contact the sides of the boss 117 preventing the rotation of the CFRB 115 within the spoke 133.

[0054] In some examples, the TT strap 113 may first be attached to the CFRB 115 before the CFRB 115 is inserted into the spoke 133. In other examples, the blade 111 may be placed onto the spoke 133 before the CFRB 115 is inserted into the spoke 133. In such examples, the TT strap 113 may first be attached to either the blade 111 or the CFRB 115 before the CFRB 115 is inserted into the spoke.

[0055] The CFRB 115 may be removed from the rotor assembly 107 to facilitate replacement or repair of the rotor assembly 107. The CFRB 115 may be removed from the hub 131 by removing the pin 123 from the fastener opening 120 and from the inboard fastener opening 119 (unpinning the CFRB 115), and by removing the spinner mount 135 from the hub131. In some examples, the blade 111 may also be unpinned from the TT strap 113. With the CFRB 115 unpinned from the TT strap 113, the CFRB 115 may be removed from the spoke 133 through the hollow cylindrical central portion 136 of the hub 131. Once removed the CFRB 115 may be repaired, or another CFRB 115 may be substituted. The rotor assemblies 107 may then be reassembled using the steps described above. This process may allow for quick repair or replacement of the CFRB 115.

[0056] The design of the CFRB 115 also allows for adjustment of the fastener opening 120 from a horizontal a position where the fastener opening 120 is perpendicular to the Z axis, to a vertical position where the axis of the fastener opening 120 is parallel to the Z axis, or to another position in between the horizontal position and the vertical position. To adjust the position of the fastener opening 120, the CFRB 115 may be removed as described above from the rotor assembly 107 and replaced with a new CFRB 115 having a fastener opening 120 in the desired position. In some examples, a new blade 111 may be attached to the hub 131 that has a fastener opening 126 aligned with the new axis of the fastener opening 120.

[0057] FIG. 5 illustrates a top perspective view of a portion of a rotor assembly according to a further embodiment, and according to aspects of the present disclosure. In the rotor assembly 107 of FIG. 5, a twist ring 141 may be located within the hub 131. The twist ring 141 may pass through a key way within the boss 117, between the top end 155 and the bottom end 157 of the boss 117. A bolt 143 may pass through the boss 117 and the twist ring 141, rigidly connecting the boss 117 and the twist ring 141. In this embodiment, any torsion of the boss 117 would be reacted into the twist ring 141.

[0058] The twist ring 141 may pass through at least one boss 117 for each blade 111. For example, as shown in FIG. 4, the rotor assemblies 107 may have four blades 111 each having a boss 117. In other examples, the rotor assemblies 107 may have a different number of blades 111 and bosses 117, and the twist ring 141 may pass through all or some of the bosses 117. In other examples, the twist ring 141 may be bolted to the top end 155 or the bottom end 157 of the bosses 117, instead of passing through the boss 117. In further examples, the base end 124 of the CFRB 115 may extend into the hollow cylindrical central portion 136, and the twist ring 141 may pass through a keyway in the base end 124 of the CFRB 115.

[0059] From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present disclosure which come within the province of those persons having ordinary skill in the art to which the aforementioned disclosure pertains. However, it is intended that all such variations notdeparting from the spirit of the disclosure be considered as within the scope thereof as limited by the appended claims.

Claims

CLAIMS1. A rotor assembly for an aircraft, the rotor assembly comprising: a hub having a spoke, the spoke having a conically shaped interior surface; a blade; a blade retention device having a first end and a second end, the first end of the blade retention device being pinned to the blade; and a retention bushing within the conically shaped interior surface of the spoke, the retention bushing having a conically shaped outer surface, the second end of the blade retention device being pinned to the retention bushing.

2. The rotor assembly of claim 1, wherein the conically shaped outer surface of the retention bushing contacts the conically shaped interior surface of the spoke.

3. The rotor assembly of claim 1, wherein the retention bushing has a base end an apex end, a boss of the retention bushing being located on the base end.

4. The rotor assembly of claim 1, wherein a taper between a first end and a second end of the retention bushing is at least 8 degrees.

5. The rotor assembly of claim 1, wherein the rotor assembly further comprises: a boss formed at a base end of the retention bushing; and a spinner mount having a slot, the boss of the retention bushing being received within the slot of the spinner mount.

6. The rotor assembly of claim 1, wherein the rotor assembly further comprises a first journal bearing and a second journal bearing attached to an exterior surface of the spoke.

7. The rotor assembly of claim 1, wherein the second end of the blade retention device is an end of a strap that is retained within an opening of the retention bushing.

8. An aircraft having: a fuselage, a wing connected to the fuselage,a tail connected to the fuselage, and a rotor assembly connected to the wing or to the tail, the rotor assembly comprising: a hub having a spoke, the spoke defining an angled interior surface; a blade; a tension-torsion strap having a first end pinned to the blade and a second end; and a retention bushing having an angled exterior surface that contacts the interior surface of the spoke, the second end of the tension-torsion strap being pinned to the retention bushing.

9. The aircraft of claim 8, wherein the retention bushing is conically shaped, and the interior surface of the spoke is conically shaped.

10. The aircraft of claim 8, wherein the retention bushing further includes an interior opening, and the second end of the tension-torsion strap is received within the interior opening.

11. The aircraft of claim 8, wherein a pin is inserted through a fastener opening of the retention bushing and the tension-torsion strap.

12. The aircraft of claim 8, wherein the rotor assembly further comprises a twist ring within the hub, and a boss at an end of the retention bushing, the twist ring passing through the boss.

13. The aircraft of claim 8, further including a spinner mount having a slot, and wherein the retention bushing includes a boss that is received by the slot.

14. The aircraft of claim 8, wherein in the retention bushing has an anti-fretting coating.

15. A bushing for use within a hub of a rotor assembly, the bushing comprising: a base end; an apex end; a through hole configured to receive a retention pin; an interior opening; andan exterior surface tapering between the base end and the apex end, the taper of the exterior surface corresponding to a taper of an interior surface of the hub of the rotor assembly.

16. The bushing of claim 15, further comprising a boss protruding from the base end.

17. The bushing of claim 15, wherein the bushing further comprises an opening at the apex end, a shape of the opening corresponding to a shape of a portion of an end of a blade retention device.

18. The bushing of claim 15, wherein the through hole extends through the bushing in a direction perpendicular to the direction of the taper between the base end and the apex end.

19. The bushing of claim 15, wherein the taper of the exterior surface of the bushing is at least 8 degrees.

20. The bushing of claim 15, wherein the exterior surface of the bushing has an antifretting coating.

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