Patent Description:
Rotor systems of rotary wing aircraft typically have elastomeric bearings to react to blade root movements. The amount of radial loads (relative to the bearing) determines the size of the bearings. Some rotor systems have addressed this issue by using a flexible beam (a flexbeam) design to share load with the bearings.

Other rotor systems increase the spacing of the bearings to reduce the load magnitude. In particular, a spindle nose or cylindrical extension may be added to a frame structure which mounts the pitch bearing (that is used to react blade bending induced radial loads). The spindle nose is used to increase the spacing between the pitch bearings.

Conventional rotor systems (in particular coaxial rotor systems) are limited by stiffness and stress, which may affect the overall aircraft performance.

Flexbeam configurations as described above may result in a less desirable aerodynamic shape for the inboard portion of the rotor blade. Further, spindle nose configurations as described above may twist the frame structure, thereby decreasing the effective stiffness and creating additional stresses on the frame structure. Additionally, the centrifugal bearing loads the outboard end of the frame structure and induces steady bending stresses in the frame structure and the hub arms. The present disclosure addresses these and other issues.

<CIT> discloses a rotor for use in an aircraft which includes an inner hub, and a plurality of blades arranged around the inner hub, each of the plurality of blades comprising an inner structural member, an outer blade shell surrounding the inner structural member, and a centering block located at a base of the inner structural member proximal to the inner hub.

<CIT> discloses a bushing assembly for receiving a fastener which includes a first bushing portion and a second bushing portion arranged coaxially with the first bushing portion. The second bushing portion defines at least part of an opening for receiving the fastener. <CIT> discloses a wing mounting for a rotary wing aircraft, wherein a flexible blade neck of a helicopter rotor blade is bridged by a torsion rigid sleeve for the blade angle adjustments. <CIT> discloses a bearingless rotor system which includes a flexbeam assembly having a first beam and a second beam arranged in a back-to-back orientation with a pitch shaft channeled therebetween. The invention relates to a rotor system and an aircraft according to the appended claims.

Various embodiments provide for an extension assembly for a rotor system for rotating a plurality of rotor blades about a rotor axis with a central rotor hub that defines the rotor axis. The extension assembly includes a beam assembly and a first bearing assembly. The beam assembly is configured to attach to the central rotor hub and is positioned at least partially within a corresponding one of the plurality of rotor blades. The first bearing assembly is fastened to the beam assembly and to at least one of a leading edge or a trailing edge of the corresponding one of the plurality of rotor blades.

Various other embodiments provide for a rotor system that comprises a plurality of rotor blades, a central rotor hub, and a plurality of extension assemblies. The central rotor hub defines a rotor axis and is configured to rotate the plurality of rotor blades about the rotor axis. The plurality of extension assemblies are configured to attach to the central rotor hub and are positioned at least partially within a corresponding one of the plurality of rotor blades. One or more of the plurality of extension assemblies comprises a first bearing assembly fastened to at least one of a leading edge or a trailing edge of the corresponding one of the plurality of rotor blades. The first bearing assembly is disconnected from a top portion and a bottom portion of the corresponding one of the plurality of rotor blades.

These and other features (including, but not limited to, retaining features and/or viewing features), together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below.

Referring to the figures generally, various embodiments disclosed herein relate to a rotor system that is configured allow a more efficient structural load path compared to previous rotor systems. As described further herein, the particular configuration of the disclosed rotor system eliminates a torsion component in bending reaction path and allows for a line of action to react to centrifugal forces. The area of connection between the rotor blade and the rotor hub (via the extension assembly) is altered to move to a lower stress region of the rotor blade. Furthermore, the rotor system has a lower weight, is more compact, and may be less expensive than conventional rotor systems. The configuration of the present rotor system can be more easily machined while providing a more efficient structural arrangement and load path through the rotor system.

<FIG> illustrate an exemplary vertical takeoff and landing (VTOL) high speed compound or coaxial counter-rotating rigid rotary wing aircraft <NUM> (which may be, for example, a helicopter or a variety of other devices which include at least one rotor blade). The aircraft <NUM> includes an aircraft body or airframe <NUM>, a dual, counter-rotating, coaxial main rotor system <NUM>, a translational thrust system <NUM>, a transmission <NUM>, and at least one engine <NUM> (which may be a gas turbine engine). The overall structure and configuration of the aircraft <NUM> may have a variety of different configurations, including but not limited to the structures disclosed in <CIT>. The airframe <NUM> is a non-rotating frame (relative to the main rotor system <NUM> and the translational thrust system <NUM>) and supports the main rotor system <NUM> and the translational thrust system <NUM>.

The main rotor system <NUM> is driven by the transmission <NUM> and rotates about a central hub or rotor axis <NUM>. The rotor axis <NUM> corresponds to the flapwise axis of the rotor blade <NUM>. According to various embodiments, the main rotor system <NUM> may be a coaxial rotor system that includes an upper rotor assembly <NUM> and a lower rotor assembly <NUM> as dual counter-rotating main rotors in a coaxial configuration. The upper rotor assembly <NUM> is positioned above the lower rotor assembly <NUM>. The upper rotor assembly <NUM> and the lower rotor assembly <NUM> are rotated about the same, single axis (i.e., the rotor axis <NUM>) and may include concentric hub shafts or masts. According to various embodiments, a computer or microcomputer is provided with a processor and a memory and is configured to carry out a control to send a command to cause the rotor assembly <NUM> to control the upper rotor assembly <NUM> and the lower rotor assembly <NUM>, in particular to rotate the upper rotor assembly <NUM> and the lower rotor assembly <NUM> in opposite directions and to control the timing of rotation to cancel out the net torque on the other rotor assembly in real-time, thereby providing a net-zero torque about the airframe <NUM>, increasing the stability of the aircraft <NUM>, and increasing the hovering capabilities of the aircraft <NUM>. However, according to various other embodiments, the main rotor system <NUM> may not be coaxial and may only include one rotor assembly.

As described further herein, the main rotor system <NUM> includes a plurality of main rotor blades <NUM> (e.g., a rotor blade spar), a plurality of extension assemblies <NUM> (as shown in <FIG> and corresponding to each of the rotor blades <NUM>), and at least one central rotor hub <NUM>. In particular, each of the upper rotor assembly <NUM> and the lower rotor assembly <NUM> includes a set of rotor blades <NUM>, a set of corresponding extension assemblies <NUM>, as well as a central rotor hub <NUM> (as described further herein) to which each of the extension assemblies <NUM> is attached. The rotor system <NUM> is configured to rotate the rotor hub <NUM> (and thus also the rotor blades <NUM> and the extension assemblies <NUM>) about the rotor axis <NUM>.

The translational thrust system <NUM> provides translational thrust generally parallel to an aircraft longitudinal axis <NUM> (that extends along the length of the aircraft <NUM>). The translational thrust system <NUM> may be selected from one of a plurality of propeller systems including, but not limited to a pusher propeller, a tractor propeller, a nacelle mounted propeller, etc. In the example of <FIG>, the translational thrust system <NUM> includes an auxiliary propulsor <NUM>. In an embodiment, the auxiliary propulsor <NUM> is a pusher propeller system with a propeller rotational axis oriented substantially horizontal and parallel to the aircraft longitudinal axis <NUM> to provide thrust for high speed flight. The translational thrust system <NUM> may be driven through a main gearbox <NUM> which also drives the main rotor system <NUM>.

The transmission <NUM> includes the main gearbox <NUM> driven by the one or more engines <NUM>. The main gearbox <NUM> and the engines <NUM> may be mounted on the airframe <NUM> of the aircraft <NUM>. Thus, the main gearbox <NUM> and engines <NUM> form part of the overall assembly including airframe <NUM>. In the case of a rotary wing aircraft, the main gearbox <NUM> may be interposed between the one or more engines <NUM>, the main rotor system <NUM>, and the translational thrust system <NUM>. In one embodiment, the main gearbox <NUM> is a split torque gearbox which carries torque from the engines <NUM> through a multitude of drivetrain paths.

Although a particular rotary wing aircraft configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines with rotor systems are within the scope of the present disclosure. It is to be appreciated that while the description herein relates to a rotary wing aircraft with a dual coaxial counter-rotating rotor system, the disclosure herein may be as readily applied to other rotor systems, such as turboprops, tilt-rotors, and tilt-wing aircraft, or a conventional single rotor system.

The rotor system <NUM> (in particular each of the rotor assemblies <NUM>, <NUM>) may include any number of rotor blades <NUM>, such as three or four rotor blades <NUM>, that rotate with the rotor hub <NUM> and the corresponding extension assembly <NUM>, about the rotor axis <NUM>. Each of the rotor blades <NUM> is directly mounted to a respective extension assembly <NUM>. The rotor blades <NUM> are circumferentially spaced apart from each other about the respective rotor hub <NUM>. Although the extension assemblies <NUM> and the rotor hub <NUM> are shown herein with the main rotor blades <NUM>, according to various other embodiments, the extension assemblies <NUM> and the rotor hub <NUM> may be used with other types of rotor blades.

As shown in <FIG>, each of the rotor blades <NUM> includes a rotor blade body <NUM> and a rotor blade neck <NUM>. The blade neck <NUM> is radially closer to the rotor hub <NUM> than the blade body <NUM>, and the blade body <NUM> extends radially outward from the blade neck <NUM> (and radially outward from the extension assembly <NUM>) and provides the main lifting surface for the rotor blade <NUM>. The blade body <NUM> terminates at the outboard end or tip of the rotor blade <NUM>. Optionally, the blade neck <NUM> and the blade body <NUM> may be two separate components that are attachable (and removable and reattachable) to each other. Alternatively, the blade neck <NUM> and the blade body <NUM> may be constructed as a single, integral, unitary piece or component that cannot be separated without destruction. The blade body <NUM> may be a radially-outer aerodynamic portion of the rotor blade <NUM>, and the blade neck <NUM> may be a radially-inner portion of the rotor blade <NUM> that provides an area to at least partially house or contain and to attach to the various bearing assemblies <NUM>, <NUM>, <NUM> (as described further herein).

As shown in <FIG>, each of the rotor blades <NUM> has an outer wall <NUM> with an outer aerodynamic surface that extends along (and is a part of) both the blade body <NUM> and the blade neck <NUM>. At least a portion of the outer wall <NUM> of the rotor blade <NUM> (in particular along at least a portion of the blade neck <NUM>) defines an inner portion or area <NUM> such that the outer wall <NUM> forms a housing that houses at least a portion of the extension assembly <NUM>.

As described further herein and shown in <FIG>, the blade neck <NUM> of the rotor blade <NUM> is configured to directly attach to a corresponding one of the extension assemblies <NUM>. In particular, at least a portion of the extension assembly <NUM> extends into, is positioned within, and is housed within a portion of the inner area <NUM> of the rotor blade <NUM> that is along the blade neck <NUM>. At least a portion of the rotor blade <NUM> extends radially outwardly from the extension assembly <NUM>.

As shown in <FIG>, the rotor blade <NUM> includes a leading edge <NUM> and a trailing edge <NUM> that each extend along both the blade body <NUM> and the blade neck <NUM>. The leading edge <NUM> is the upstream edge of the rotor blade <NUM>, and the trailing edge <NUM> is the downstream edge of the rotor blade <NUM> in the rotational direction of travel of the rotor blade <NUM> about the rotor axis <NUM>. The leading edge <NUM> and the trailing edge <NUM> each extend along the radial length of the rotor blade <NUM> and are opposite each other.

The rotor blade <NUM> further includes a top side or portion <NUM> and a bottom side or portion <NUM> that each extend along both the blade body <NUM> and the blade neck <NUM>. The top portion <NUM> faces axially upward, away from the airframe <NUM>. The bottom portion <NUM> faces axially downward, toward the airframe <NUM>. The top portion <NUM> and the bottom portion <NUM> each extend along the radial length of the rotor blade <NUM>, are opposite each other, and extend between the leading edge <NUM> and the trailing edge <NUM>. Similarly, the leading edge <NUM> and the trailing edge <NUM> each extend between the top portion <NUM> and the bottom portion <NUM>.

As shown in <FIG>, the rotor blade <NUM> defines a plurality of blade attachment holes <NUM> (e.g., through-holes) that each extend through the outer wall <NUM> of the rotor blade <NUM> and provide areas to individually attach to the bearing assemblies <NUM>, <NUM>, <NUM>, as described further herein. The blade attachment holes <NUM> are positioned along the leading edge <NUM> and the trailing edge <NUM> of the rotor blade <NUM> (along the blade neck <NUM>) (rather than the top portion <NUM> and the bottom portion <NUM> of the rotor blade <NUM>). According to one embodiment, the rotor blade <NUM> includes two blade attachment holes <NUM> for each of the three bearing assemblies <NUM>, <NUM>, <NUM> (i.e., a total of six blade attachment holes <NUM> on the rotor blade <NUM>), where a first blade attachment hole <NUM> for one of the three bearing assemblies <NUM>, <NUM>, <NUM> is positioned along the leading edge <NUM> and a second blade attachment hole <NUM> for the one of the three bearing assemblies <NUM>, <NUM>, <NUM> is positioned along the trailing edge <NUM>, directly opposite the first blade attachment hole <NUM>. Each of the three bearing assemblies <NUM>, <NUM>, <NUM> is attached to the rotor blade <NUM> at the top opposite blade attachment holes <NUM>. Accordingly, each rotor blade <NUM> is attached to the corresponding extension assembly <NUM> at six different attachment locations (i.e., at the six blade attachment holes <NUM>), all of which are along the leading edge <NUM> or the trailing edge <NUM> of the rotor blade <NUM>.

The longitudinal, pitch, or feathering axis <NUM> of the rotor blade <NUM> refers to the axis about which the pitch angle of the rotor blade <NUM> is varied and the direction of centrifugal force of the rotor blade <NUM>. In particular, the rotor blade <NUM> pitches, rotates, feathers, or twists about its feathering axis <NUM> about at least one bearing assembly <NUM>, <NUM>, <NUM> (as described further herein) to change the pitch angle, which changes the lift and drag. For example, by increasing the pitch angle, the rotor blade <NUM> provides more lift. Conversely, by decreasing the pitch angle, the rotor blade <NUM> provides less lift. As shown in <FIG>, the feathering axis <NUM> extends substantially perpendicular to the rotor axis <NUM>. As shown in <FIG>, the feathering axis <NUM> and the rotor axis <NUM> extend substantially perpendicular to an edgewise axis <NUM>.

The central rotor hub <NUM> (e.g., a hub body) is configured to rotate about and define the rotor axis <NUM> (thereby rotating the rotor blades <NUM> and the extension assemblies <NUM> about the rotor axis <NUM>), and the rotor blades <NUM> and the extension assemblies <NUM> are mounted to the rotor hub <NUM>. As shown in <FIG>, the rotor hub <NUM> includes a hub mast <NUM> and a plurality of hub attachment portions <NUM>. The rotor hub <NUM> may be constructed as a single, integral, unitary piece or component that cannot be separated without destruction. According to various other embodiments, the rotor hub <NUM> may be constructed out of metal (such as titanium).

The rotor hub shaft or mast <NUM> extends upwardly along and around the rotor axis <NUM> and is rotated about the rotor axis <NUM> relative to the airframe <NUM> to rotate the rest of the rotor hub <NUM> (and thus the rotor blades <NUM>) about the rotor axis <NUM>. As shown in <FIG>, the hub mast <NUM> includes an outer wall that defines a hollow inner area, within which a portion of the inboard pitch bearing assembly <NUM> can extend, as described further herein.

As shown in <FIG>, each of the rotor hub attachment sites or portions <NUM> corresponds to one of the extension assemblies <NUM> and the corresponding one of the rotor blades <NUM>. The hub attachment portions <NUM> provide an area along the rotor hub <NUM> for each of the extension assemblies <NUM> to attach or mount to. As shown in <FIG>, each of the hub attachment portions <NUM> extends radially outwardly from an outer surface and perimeter of the hub mast <NUM> and are positioned about an outer circumference of the hub mast <NUM> (circumferentially spaced apart from each other about the hub mast <NUM>). Each of the hub attachment portions <NUM> may include an upper attachment portion <NUM> and a lower attachment portion <NUM>, which correspond and attach to a top beam <NUM> and a bottom beam <NUM>, respectively, of an extension frame <NUM> of the extension assembly <NUM> (as described and shown further herein). The upper attachment portion <NUM> and the lower attachment portion <NUM> are at least partially radially and transversely aligned with each other and are configured to statically attach to a portion (i.e., the extension frame <NUM>) of a corresponding one of the extension assemblies <NUM>.

Each of the lower attachment portion <NUM> and the upper attachment portion <NUM> includes at least one hub arm projection or extension <NUM> that extends radially outward from an outer surface of the hub mast <NUM>. According to one embodiment, each of the lower attachment portion <NUM> and the upper attachment portion <NUM> includes a set of extensions <NUM> (e.g., two or more extensions <NUM>) that are positioned together and radially and transversely aligned with each other. As shown in <FIG> and described further herein, the two extensions <NUM> of each of the lower attachment portion <NUM> and the upper attachment portion <NUM> are positioned and extend radially along the top surface and the bottom surface along the radial ends of the bottom beam <NUM> and the top beam <NUM>, respectively.

As shown in <FIG>, each of the extensions <NUM> defines at least one (preferably two) through-hole <NUM> that is configured to receive a fastener (e.g., a bolt or screw) to statically or rigidly attach to the extension frame <NUM> by, for example, a bolted connection. According to one embodiment, the two through-holes <NUM> are transversely spaced apart from each other along the length of the extension <NUM>. The through-holes <NUM> of one of the extensions <NUM> in a set (of the lower or upper attachment portion <NUM>, <NUM>) are radially and transversely aligned with corresponding through-holes <NUM> of the other of the extensions in a set and with through-holes <NUM> of the extension frame <NUM> such that the fastener can extend through each of the extensions <NUM> within a set of the extensions <NUM> and through the bottom or top beam <NUM>, <NUM> of the extension frame <NUM>.

As shown in <FIG>, each of the hub attachment portions <NUM> defines a hub through-hole <NUM> that extends radially through the hub mast <NUM>. The hub through-hole <NUM> is positioned axially between and is radially aligned with the lower attachment portion <NUM> and the upper attachment portion <NUM>. The hub through-hole <NUM> provides an area for an end portion of the inboard pitch bearing assembly <NUM> (as described further herein) to extend into and through the outer wall of the hub mast <NUM> (and into an inner area of the hub mast <NUM>, as shown in <FIG>).

Each of the extension assemblies <NUM> is configured to attach a respective one of the rotor blades <NUM> to the rotor hub <NUM>. Since the rotor system <NUM> (in particular each of the rotor assemblies <NUM>, <NUM>) include any number of rotor blades <NUM>, the rotor system <NUM> includes the same number of extension assemblies <NUM> and rotor blades <NUM>, such that each rotor blade <NUM> has a corresponding extension assembly <NUM>. The extension assembly <NUM> (and thus also the corresponding rotor blade <NUM>) rotates with the rotor hub <NUM> about the rotor axis <NUM>.

As described further herein, each of the extension assemblies <NUM> includes a beam assembly (referring to herein as an extension frame <NUM>) and a plurality of bearing assemblies <NUM>, <NUM>, <NUM> that are each attached or fastened to and disposed in or on the extension frame <NUM>. The portions other than the extension frame <NUM> are not shown in three of the four extension assemblies <NUM> in <FIG>, and none of the extension frames <NUM> are shown in <FIG> solely for ease of review. It is understood that these portions not shown are nevertheless included.

Each of the extension assemblies <NUM> is directly mounted, fastened, or attached to a corresponding one of the rotor blades <NUM> and to the rotor hub <NUM> (specifically to a corresponding one of the hub attachment portions <NUM> of the rotor hub <NUM>). Accordingly, each of the extension assemblies <NUM> attach one of the rotor blades <NUM> to the rotor hub <NUM> such that the rotor blade <NUM> is not otherwise attached or mounted to (i.e., are detached, separated, or disconnected from) the rotor hub <NUM>. According to one embodiment, the rotor blades <NUM> may be only indirectly attached to the rotor hub <NUM> via the respective one of the extension assemblies <NUM> (e.g., each of the extension assemblies <NUM> provides a connection between the corresponding rotor blade <NUM> and the rotor hub <NUM>), allowing the rotor blades <NUM> to move (e.g., pivot or flap) relative to the rotor hub <NUM>. Accordingly, the rotor blades <NUM> may not be directly mounted, fastened, or attached to the rotor hub <NUM>. The extension assemblies <NUM> are circumferentially spaced apart from each other about the rotor hub <NUM> (and radially and tangentially aligned with a corresponding one of the rotor blades <NUM> and a corresponding one of the hub attachment portions <NUM>). Each extension assembly <NUM> extends extend radially outwardly from the rotor hub <NUM>.

As shown in <FIG>, at least a portion of each of the extension assemblies <NUM> is positioned within and extends into the inner area <NUM> of a corresponding one of the blade necks <NUM> of the rotor blade <NUM>. A radially-inward end portion of the extension assembly <NUM> extends beyond a radially inward end of the rotor blade <NUM> (in particular of the blade neck <NUM>) to attach to the rotor hub <NUM>. Optionally an end portion of the inboard pitch bearing assembly <NUM> of the extension assembly <NUM> may extend through the hub through-hole <NUM> and into the rotor hub <NUM> (as shown in <FIG>).

The hub arm extension or extension frame <NUM> of the extension assembly <NUM> is configured to be mounted, attached, bolted, or fastened to a respective one of the hub attachment portions <NUM> of the rotor hub <NUM> (in a static, rigid, or fixed manner) such that the bearing assemblies <NUM>, <NUM>, <NUM> are attached to the rotor hub <NUM> via the extension frame <NUM>. The extension frame <NUM> provides an area for each of the bearing assemblies <NUM>, <NUM>, <NUM> to individually mount, attach, or fasten to.

The extension frame <NUM> provides a central mounting area for the bearing assemblies <NUM>, <NUM>, <NUM> to attach to with a clevis-type attachment to the rotor hub <NUM>. Comparatively, typical rotor systems include two laterally-displaced hub arms that the bearings are positioned between. The particular orientation, configuration, shape, and structure of the extension frame <NUM>, as described further herein, provides a more efficient structural arrangement and decreases the overall weight and cost of the rotor system <NUM> (compared to conventional rotor systems). Furthermore, due to the shape of the extension frame <NUM>, the extension frame <NUM> may optionally be a composite beam, which decreases the weight of the overall weight of the rotor system <NUM> (compared to using metal for the extension frame). However, according to various other embodiments, the extension frame <NUM> may be constructed out of metal (such as titanium).

The extension frame <NUM> is a separate component from (and is separately formed from and attachable to) the rotor hub <NUM>. Comparatively, conventional rotor systems include a single, integral rotor hub that the bearings are directly attached to (rather than via such an extension frame <NUM> that is a separate component from the rotor hub), which creates manufacturing limitations as an integral structure, requires a large amount of material to machine, and is more difficult to machine. The configuration of the extension frame <NUM> and the rotor hub <NUM> allows the extension frame <NUM> and the rotor hub <NUM> together to avoid expensive forging with limited locations capable of machining the hub configuration. For example, the rotor hub <NUM> has a more compact body, allowing the rotor hub <NUM> to be more easily machined with less material.

As shown in <FIG>, the extension frame <NUM> includes a bottom beam <NUM>, at least one central beam <NUM> (preferably a plurality of central beams <NUM>), and a top beam <NUM>. The extension frame <NUM> may be constructed as a single, integral, unitary piece or component that cannot be separated without destruction. The bottom beam <NUM>, the central beam <NUM>, and the top beam <NUM> may form an I-beam cross-sectional or end shape (as shown in <FIG>), where the transverse widths of the bottom beam <NUM> and the top beam <NUM> are larger than the transverse width of the central beam <NUM> (and the central beam <NUM> is approximately centered along the transverse widths of the bottom beam <NUM> and the top beam <NUM>). Accordingly, the extension frame <NUM> is configured and oriented in a completely different manner from conventional flexbeams about the feathering axis.

The bottom beam <NUM> and the top beam <NUM> extend radially and transversely parallel to each other and are axially spaced apart from each other (by the central beam(s) <NUM>), in an axial or vertical direction that is substantially parallel to the rotor axis <NUM> (as shown in <FIG>). As shown in <FIG>, the bottom beam <NUM> and the top beam <NUM> may be radially and transversely aligned with each other. As shown in <FIG>, the bottom beam <NUM> is positioned axially directly below the bearing assemblies <NUM>, <NUM>, <NUM> and the top beam <NUM>, and the top beam <NUM> is positioned axially directly above the bearing assemblies <NUM>, <NUM>, <NUM> and the bottom beam <NUM>. Furthermore, at least a portion of the bearing assemblies <NUM>, <NUM>, <NUM> are radially aligned with the bottom beam <NUM> and the top beam <NUM>. Accordingly, at least a portion of the bearing assemblies <NUM>, <NUM>, <NUM> are positioned axially between the bottom beam <NUM> and the top beam <NUM>. By orienting the bottom beam <NUM> and the top beam <NUM> relative to each other in such a manner (i.e., axially above and below each other), the extension frame <NUM> is oriented to more efficiently handle the largest loads (which are in the vertical (axial) direction, which extends along, is parallel to, and corresponds to the rotor axis <NUM>), compared to if the bottom beam and the top beam were positioned next to each other in a tangential direction perpendicular to the vertical direction (which extends along the rotor axis <NUM>).

The bottom beam <NUM> and the top beam <NUM> are each configured to directly (separately and individually) mount, fasten, or attach to the rotor hub <NUM> (in a static or rigid manner) and extend radially outwardly from the rotor hub <NUM> along their length. Accordingly, as shown in <FIG>, a radially-inward end portion of each of the bottom beam <NUM> and the top beam <NUM> define at least one (preferably two) through-hole <NUM> that is configured to receive the fastener (e.g., a bolt or screw) to statically or rigidly attach to the respective hub attachment portion <NUM> (in particular, to the lower attachment portion <NUM> and the upper attachment portion <NUM>, respectively) of the rotor hub <NUM>. According to one embodiment, the two through-holes <NUM> are transversely spaced apart from each other along the width of the end portion of the bottom beam <NUM> and the top beam <NUM>.

As shown in <FIG>, the radially-inward end portions of the bottom beam <NUM> and the top beam <NUM> are configured to be positioned axially between each of the two extensions <NUM> of the lower attachment portion <NUM> and the upper attachment portion <NUM>, respectively, of one of the hub attachment portions <NUM>. The through-holes <NUM> of each of the bottom beam <NUM> and the top beam <NUM> are configured to axially align with the through-holes <NUM> of the lower attachment portion <NUM> and the upper attachment portion <NUM>, respectively, such that each of the sets of through-holes <NUM>, <NUM> are configured to receive a fastener (and the fastener can extend through all of the aligned through-holes <NUM>, <NUM>) to statically attach the extension frame <NUM> to the rotor hub <NUM> via, for example, a bolted connection with the through-holes <NUM>, <NUM>. With this arrangement, the top beam <NUM> and the bottom beam <NUM> are configured to fasten or attach to the upper attachment portion <NUM> and the lower attachment portion <NUM>, respectively.

As shown in <FIG>, the central beam <NUM> of the extension frame <NUM> extends axially (i.e., substantially vertically) between and connects the top beam <NUM> and the bottom beam <NUM>. The extension frame <NUM> may include a plurality of central beams <NUM> (for example, two central beams <NUM>) that are radially spaced apart from each other along the radial lengths of the top beam <NUM> and the bottom beam <NUM>, thereby by creating radial gaps (between a central beam <NUM> and the rotor hub <NUM> and/or between two central beams <NUM>) within which at least a portion of the bearing assemblies <NUM>, <NUM>, <NUM> can be positioned. The central beams <NUM> are radially and transversely aligned with the bearing assemblies <NUM>, <NUM>, <NUM> (along the lengths of the bottom beam <NUM> and the top beam <NUM>). As described further herein, the central beams <NUM> each provide areas for the bearing assemblies <NUM>, <NUM>, <NUM> to directly and statically attach, fasten, or mount to.

The extension assembly <NUM> includes at least one bearing assembly to stabilize the motion of the rotor blades <NUM>. According to one embodiment, each of the extension assemblies <NUM> includes three elastomeric bearing blocks or assemblies <NUM>, <NUM>, <NUM> (i.e., an inboard pitch bearing assembly <NUM>, a centrifugal bearing assembly <NUM>, and an outboard pitch bearing assembly <NUM>). Each of the three bearing assemblies <NUM>, <NUM>, <NUM> may be referred to as a first bearing assembly, a second bearing assembly, and a third bearing assembly. Each of the bearing assemblies <NUM>, <NUM>, <NUM> is statically and individually fastened or mounted to the extension frame <NUM> and to at least one of the leading edge <NUM> and/or the trailing edge <NUM> of the rotor blade <NUM> in a manner which permits a pitching motion of the rotor blade <NUM>. As shown in <FIG>, the bearing assemblies <NUM>, <NUM>, <NUM> may be at least partially positioned, housed, or contained within the inner area <NUM> of and directly attached to the outer wall <NUM> of the blade neck <NUM> of the rotor blade <NUM>.

As shown in <FIG>, the inboard pitch bearing assembly <NUM> and the outboard pitch bearing assembly <NUM> each support the rotor blade <NUM> by resisting deflection in the flapwise direction (i.e., in a direction along the rotor axis <NUM>) and the edgewise direction (e.g., by reacting against the flapwise and edgewise motion of the rotor blade <NUM>), while permitting rotation of the rotor blade <NUM> about the feathering axis <NUM>. The flapwise motion extends along a direction corresponding to the rotor axis <NUM>, and the edgewise motion extends along a direction corresponding to the edgewise axis <NUM>, as shown in <FIG>. The inboard pitch bearing assembly <NUM> and the outboard pitch bearing assembly <NUM> each react to radial loads and allow the rotor blade <NUM> to react axially and to pitch about the feathering axis <NUM>. As shown in <FIG>, the centrifugal bearing assembly <NUM> supports the rotor blade <NUM> by resisting deflection along the feathering axis <NUM> and reacts to the centrifugal forces, while permitting rotation about the feathering axis <NUM>. The centrifugal bearing assembly prevents radial motion of the rotor blade <NUM> relative to the rotor axis <NUM> of the rotor hub <NUM>.

As shown in <FIG>, each of the bearing assemblies <NUM>, <NUM>, <NUM> are axially and transversely aligned with each other and radially spaced apart from each other along the feathering axis <NUM> of the rotor blade <NUM>. In particular, the inboard pitch bearing assembly <NUM> is positioned radially inward from the centrifugal bearing assembly <NUM> and the outboard bearing assembly <NUM>. The centrifugal bearing assembly <NUM> is positioned radially in between the inboard pitch bearing assembly <NUM> and the outboard bearing assembly <NUM>. The outboard bearing assembly <NUM> is positioned radially outward from the centrifugal bearing assembly <NUM> and the inboard pitch bearing assembly <NUM>.

As shown in <FIG>, each of the bearing assemblies <NUM>, <NUM>, <NUM> includes a first bearing portion <NUM>, <NUM>, <NUM>, a second bearing portion <NUM>, <NUM>, <NUM>, and an elastomeric bearing <NUM>, <NUM>, <NUM>, respectively. As shown in <FIG>, the first bearing portions <NUM>, <NUM>, <NUM> are statically attached or fastened to various portions (such as different portions of the central beams <NUM>) of the extension frame <NUM>. As shown in <FIG> in view of <FIG>, the second bearing portions <NUM>, <NUM>, <NUM> are statically attached or fastened to the leading edge <NUM> and the trailing edge <NUM> of the rotor blade <NUM>. As shown in <FIG>, the bearings <NUM>, <NUM>, <NUM> are positioned between and rotatably attach the first bearing portions <NUM>, <NUM>, <NUM> and the second bearing portions <NUM>, <NUM>, <NUM> (respectively). Accordingly, the first bearing portions <NUM>, <NUM>, <NUM> and the second bearing portions <NUM>, <NUM>, <NUM> are rotatably or twistably attached together via the bearings <NUM>, <NUM>, <NUM>, which allows the rotor blade <NUM> to move relative to the extension frame <NUM> (and thus relative to the rotor hub <NUM>).

As shown in <FIG>, each of the bearing assemblies <NUM>, <NUM>, <NUM> is attached or fastened to the extension frame <NUM> and to the blade attachment holes <NUM> at the leading edge <NUM> and the trailing edge <NUM> of the rotor blade <NUM> (which are lower stress regions of the rotor blade <NUM> compared to the top portion <NUM> and the bottom portion <NUM> of the rotor blade <NUM>). While not required in all aspects, the blade attachment holes <NUM> are at the leading edge <NUM> and the trailing edge <NUM> of the blade neck <NUM> in various embodiments. Each of the bearing assemblies <NUM>, <NUM>, <NUM> are not configured to be fastened or attached to (i.e., are detached, separated, or disconnected from) the top portion <NUM> or the bottom portion <NUM> of the rotor blade <NUM>. Accordingly, the centrifugal load is reacted along the principal axis of the extension frame <NUM> without inducing internal moments within the extension frame <NUM>. Comparatively, in conventional rotor systems, the centrifugal load is offset from the legs of the structure supporting the centrifugal bearing, which induces local bending in those legs.

With this configuration within the main rotor system <NUM>, the outboard pitch bearing assembly <NUM> (which may connect to the rotor blade <NUM> using a recess in a bulkhead) no longer introduces twisting moments on its supporting structure and instead transmits bending moments into the extension frame <NUM> that can efficiently react these moments. Comparatively, in conventional rotor systems, the bearings are attached to the rotor blade through the top portion and/or the bottom portion of the rotor blade. Since the bending moments for coaxial rotor of a high-speed compound aircraft (e.g., an X2 rotor) are greatest in the flapwise direction (i.e., in a direction along the rotor axis <NUM>), this configuration of conventional rotor systems results in connections between the rotor blade and the bearings being in the most highly stressed portions of the rotor blade.

Moving or rotating the connections between the bearing assemblies <NUM>, <NUM>, <NUM> and the rotor blade <NUM> (from being attached to the top and bottom of the rotor blade in conventional rotor system to being attached to the leading edge <NUM> and the trailing edge <NUM> of the rotor blade <NUM> in the present rotor system) allows for a more efficient structural load path between the bearing assemblies <NUM>, <NUM>, <NUM> and the rotor blade <NUM> and increases the flapwise stiffness of the rotor blade <NUM> (thus increasing the overall strength of the rotor blade <NUM>). In particular, this configuration eliminates the torsion component in a bending reaction path, allows for a line of action reaction to each of the bearing assemblies <NUM>, <NUM>, <NUM>, avoids bending (in particular with the centrifugal bearing assembly <NUM>), and moves the connection of the rotor blade <NUM> to the rotor hub <NUM> (via the extension assembly <NUM>) to a lower stress region of the rotor blade <NUM>. Furthermore, this configuration allows the rotor blade <NUM> to need less buildup or added support in the inboard region of the rotor blade <NUM> because the locations of attachment to the bearing assemblies <NUM>, <NUM>, <NUM> (in particular, the locations of the blade attachment holes <NUM>) are in more benign and less stressed locations along the rotor blade <NUM>, and therefore have a smaller associated stress concentration factor. Accordingly, as the rotor blade <NUM> bends, the areas around the locations of the blade attachment holes <NUM> are less likely to fail due to lower stresses.

Each of the bearing assemblies <NUM>, <NUM>, <NUM> is individually attached or fastened to one of the rotor blades <NUM> and to a corresponding extension frame <NUM>. To attach to the rotor blade <NUM>, each of the second bearing portions <NUM>, <NUM>, <NUM> of the bearing assemblies <NUM>, <NUM>, <NUM> is statically or rigidly fastened, mounted, or attached to the rotor blade <NUM> via a fastener (e.g., a bolt or screw). Accordingly, as shown in <FIG>, each of the second bearing portions <NUM>, <NUM>, <NUM> defines at least one bearing attachment hole <NUM>, <NUM>, <NUM>, respectively, that is configured to receive a fastener to extend through the bearing attachment hole <NUM>, <NUM>, <NUM> and the corresponding blade attachment hole <NUM>. The bearing attachment holes <NUM>, <NUM>, <NUM> provide an area for each of the bearing assemblies <NUM>, <NUM>, <NUM> to be individually attached to the rotor blade <NUM> by statically attaching, mounting, or fastening the second bearing portion <NUM>, <NUM>, <NUM> to a portion of the rotor blade <NUM>.

The bearing attachment holes <NUM>, <NUM>, <NUM> are oriented to face either the leading edge <NUM> or the trailing edge <NUM> of the rotor blade <NUM> (rather than the top portion <NUM> or the bottom portion <NUM> of the rotor blade <NUM>) and are thereby each positioned to radially align with one of the blade attachment holes <NUM>. Each of the second bearing portions <NUM>, <NUM>, <NUM> may include two bearing attachment holes <NUM>, <NUM>, <NUM>, where a first bearing attachment hole <NUM>, <NUM>, <NUM> faces directly toward the leading edge <NUM> of the rotor blade <NUM> and a second bearing attachment hole <NUM>, <NUM>, <NUM> faces directly toward the trailing edge <NUM>, directly opposite the first bearing attachment hole <NUM>, <NUM>, <NUM>. Accordingly, a portion (i.e., the second bearing portions <NUM>, <NUM>, <NUM>) of each of the bearing assemblies <NUM>, <NUM>, <NUM> may attach and be fastened to both the leading edge <NUM> and the trailing edge <NUM> of the rotor blade <NUM> (along opposite sides of the bearing assembly <NUM>, <NUM>, <NUM>).

Each of the bearing assemblies <NUM>, <NUM>, <NUM>, is attached, mounted, or fastened to the rotor blade <NUM> with at least one fastener (e.g., a bolt or screw) that extends through one of the blade attachment holes <NUM> of the rotor blade <NUM> and through a corresponding one of the bearing attachment holes <NUM>, <NUM>, <NUM> (thereby creating, for example, a bolted attachment or connection). Due to this configuration, the bearing assemblies <NUM>, <NUM>, <NUM> (or any associated attachments between the bearing assemblies <NUM>, <NUM>, <NUM> and the rotor blade <NUM>) are not attached to and do not extend through the top portion <NUM> or the bottom portion <NUM> of the rotor blade <NUM>.

To attach to the extension frame <NUM>, each of the first bearing portions <NUM>, <NUM>, <NUM> of the bearing assemblies <NUM>, <NUM>, <NUM> is fastened, mounted, or attached to the extension frame <NUM> via at least one fastener that forms, for example, a bolted, clevis-style joint. Accordingly, as shown in <FIG>, each of the first bearing portions <NUM>, <NUM>, <NUM> includes at least one bearing attachment plate <NUM>, <NUM>, <NUM>, respectively, that provides an area for each of the bearing assemblies <NUM>, <NUM>, <NUM> to be individually attached to the extension frame <NUM> by statically attaching, mounting, or fastening the first bearing portion <NUM>, <NUM>, <NUM> to a portion of the extension frame <NUM>. Each of the first bearing portions <NUM>, <NUM>, <NUM> may include two bearing attachment plates <NUM>, <NUM>, <NUM> that extend parallel to each other (along the radial direction) and are spaced apart from each other (along the transverse direction).

Each set of two bearing attachment plates <NUM>, <NUM>, <NUM> is positioned along and attached to opposite sides of one of the central beams <NUM> of the extension frame <NUM>. As shown in <FIG> and <FIG>, each of the bearing attachment plates <NUM>, <NUM>, <NUM> defines at least one hole (such as a through-hole) that is configured to receive a fastener (e.g., a bolt or screw) that extends into both the bearing attachment plates <NUM>, <NUM>, <NUM> and at least a portion of the central beam <NUM> to statically or rigidly attach or fasten the first bearing portions <NUM>, <NUM>, <NUM> of the bearing assemblies <NUM>, <NUM>, <NUM> to the extension frame <NUM>. Accordingly, a portion (i.e., the first bearing portions <NUM>, <NUM>, <NUM>) of each of the bearing assemblies <NUM>, <NUM>, <NUM> is configured to be attached and fastened to and extend along opposite sides of one of the central beams <NUM>. Optionally, more than one bearing assembly <NUM>, <NUM>, <NUM> may be attached to the same central beam <NUM> (e.g., along opposite radial ends of the central beam <NUM>).

Although each of the various aspects, features, components, and configurations are not separately described for each embodiment, each of the various embodiments disclosed herein may have any of the aspects, features, components, and configurations of the other embodiments, except where noted otherwise and insofar as falls within the scope of the appended claims.

As utilized herein, the terms "approximately," "substantially," and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. The terms "approximately" and "substantially" as used herein refers to ±<NUM>% of the referenced measurement, position, or dimension. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described are considered to be within the scope of the presently claimed invention, as far as they fall within the scope of the appended claims.

The terms "coupled," "attached," and the like as used herein mean the joining of two members directly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable).

References herein to the positions of elements (e.g., "top," "bottom," "above," "below," etc.) are merely used to describe the orientation of various elements in the FIGURES.

Claim 1:
A rotor system comprising:
a plurality of rotor blades (<NUM>);
an extension assembly (<NUM>) for rotating the plurality of rotor blades (<NUM>) about a rotor axis (<NUM>) with a central rotor hub (<NUM>) that defines the rotor axis, the extension assembly comprising:
a beam assembly configured to attach to the central rotor hub (<NUM>) and positioned at least partially within a corresponding one of the plurality of rotor blades (<NUM>); and
a first bearing assembly (<NUM>, <NUM>, <NUM>) fastened to the beam assembly and to at least one of a leading edge or a trailing edge of the corresponding one of the plurality of rotor blades (<NUM>).