Articulated rotor systems with blade-to-blade damping

A rotor system includes a yoke, a plurality of blade grip assemblies and a plurality of centrifugal force bearings coupling the blade grip assemblies with the yoke. A plurality of rotor blades are coupled to the blade grip assemblies such that each rotor blade has a coincident hinge and such that each rotor blade has three independent degrees of freedom including blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. A blade-to-blade damping ring includes a plurality of damper anchors each coupled to one of the blade grip assemblies along the respective pitch change axis and a plurality of lead-lag dampers each coupled between adjacent damper anchors. During blade pitch operations, each blade grip assembly is operable to rotate relative to the respective damper anchor, such that the blade-to-blade damping ring is operable to provide pitch independent lead-lag damping.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to rotor systems operable for use on rotorcraft and, in particular, to articulated rotor systems including coincident hinges between the yoke and the rotor blades and having a blade-to-blade damping ring providing pitch independent lead-lag damping.

BACKGROUND

The main rotor of a helicopter typically includes a plurality of rotor blades that are coupled to a rotor hub. This rotor system is mounted on a vertical mast atop the helicopter such that rotation of the rotor system generates vertical lift that supports the weight of the helicopter and lateral thrust that allows the helicopter to engage in forward, backward and sideward flight. Certain main rotors may be articulated rotor systems in which the rotor blades have three degrees of freedom; namely, blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. These articulated rotor systems typically include a lead-lag damper for each rotor blade. In addition, these articulated rotor systems may include a separate hinge for each degree of freedom of each rotor blade requiring, for example, twelve hinges in a rotor system having four rotor blades. One option for reducing the complexity of such articulated rotor systems is to use a centrifugal force bearing that provides a coincident hinge for all three degrees of freedom. It has been found, however, that the damping force of the lead-lag dampers in such coincident hinge articulated rotor systems is affected by the pitch of the rotor blades. Therefore, a need has arisen for an improved articulated rotor system in which the damping force of the lead-lag dampers is not affected by the pitch of the rotor blades.

SUMMARY

In a first aspect, the present disclosure is directed to a rotor system operable for use on a rotorcraft. The rotor system includes a yoke, a plurality of blade grip assemblies and a plurality of centrifugal force bearings each coupling one of the blade grip assemblies with the yoke. A plurality of rotor blades are each coupled to one of the blade grip assemblies such that each rotor blade has a coincident hinge located at the respective centrifugal force bearing and such that each rotor blade has three independent degrees of freedom relative to the yoke including blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. A blade-to-blade damping ring includes a plurality of damper anchors each coupled to one of the blade grip assemblies along the respective pitch change axis and a plurality of lead-lag dampers each coupled between adjacent damper anchors. Each blade grip assembly is operable to rotate relative to the respective damper anchor during blade pitch operations, such that the blade-to-blade damping ring is operable to provide pitch independent lead-lag damping.

In some embodiments, the yoke may include a plurality of pockets and each centrifugal force bearing may include an outboard bearing support, a spherical bearing and an inboard bearing support. In such embodiments, each of the outboard bearing supports may be coupled to one of the pockets. Also, in such embodiments, each of the blade grip assemblies may be coupled to one of the inboard bearing supports such that, for each rotor blade, the respective blade grip assembly and the respective centrifugal force bearing provide a centrifugal force retention load path from the rotor blade to the yoke. In certain embodiments, a plurality of damper anchor supports are each coupled to one of the blade grip assemblies. In such embodiments, each of the damper anchors is rotatably coupled to one of the damper anchor supports such that each blade grip assembly is operable to rotate relative to the respective damper anchor during blade pitch operations. In some embodiments, each damper anchor support may include a pitch horn that is operable to receive input from a pitch control assembly for blade pitch operations.

In certain embodiments, each damper anchor is coupled to the yoke to prevent relative rotation therebetween. For example, each damper anchor may include a fitting and an anti-rotation rod. Each fitting may include a shaft that extends through the respective damper anchor support and a pair of oppositely disposed clevises extending in an in-plane direction. Each anti-rotation rod may couple the respective fitting and the yoke to prevent relative rotation therebetween. In such embodiments, each lead-lag damper may be coupled to devises of adjacent fittings using, for example, a spherical bearing coupling. In some embodiments, each lead-lag damper has an in-plane spring rate that is independent of blade pitch. In certain embodiments, each lead-lag damper may include an elastomer spring having an in-plane spring rate operable to provide lead-lag damping to the respective rotor blades. In other embodiments, each lead-lag damper may include a mechanical spring having an in-plane spring rate operable to provide lead-lag damping to the respective rotor blade. In further embodiments, each lead-lag damper may include a fluid spring having an in-plane spring rate operable to provide lead-lag damping to the respective rotor blade.

In a second aspect, the present disclosure is directed to a rotorcraft that includes a fuselage, a power system disposed within the fuselage, a mast coupled to the power system and a yoke coupled to the mast and operable to rotate therewith. A plurality of centrifugal force bearings each couples a blade grip assembly with the yoke. A plurality of rotor blades are each coupled to one of the blade grip assemblies such that each rotor blade has a coincident hinge located at the respective centrifugal force bearing and such that each rotor blade has three independent degrees of freedom relative to the yoke including blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. A blade-to-blade damping ring includes a plurality of damper anchors each coupled to one of the blade grip assemblies along the respective pitch change axis and a plurality of lead-lag dampers each coupled between adjacent damper anchors. Each blade grip assembly is operable to rotate relative to the respective damper anchor during blade pitch operations, such that the blade-to-blade damping ring is operable to provide pitch independent lead-lag damping.

DETAILED DESCRIPTION

While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not delimit the scope of the present disclosure. In the interest of clarity, not all features of an actual implementation may be described in the present disclosure. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, and the like described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. As used herein, the term “coupled” may include direct or indirect coupling by any means, including moving and nonmoving mechanical connections.

Referring now toFIGS. 1A-1Bin the drawings, a rotorcraft depicted as helicopter10is schematically illustrated. Helicopter10includes a body depicted as fuselage12and tailboom14. Helicopter10includes a rotor system depicted as main rotor16that is supported atop helicopter10by a mast18. Main rotor16includes six rotor blades20coupled to a rotor hub22including a blade-to-blade damping ring24operable to provide pitch independent lead-lag damping. The pitch of rotor blades20can be collectively and cyclically manipulated by a pitch control assembly26including, for example, a rise and fall swashplate. Helicopter10includes an anti-torque system depicted as tail rotor28. Torque and rotational energy is provided to main rotor16through mast18from a power system depicted as engines30a,30band a main gearbox32. Main gearbox32includes gear systems such as a gear reducing transmission designed to enable optimum engine speed and optimal rotor speed during flight operations. In the illustrated embodiment, engines30a,30bare depicted as power turbine engines. The angular velocity or revolutions per minute (RPM) of main rotor16, the pitch of rotor blades20and the like are determined using a flight control system34, with or without pilot input, to selectively control the direction, thrust and lift of helicopter10during flight. Helicopter10has a landing gear system36to provide ground support for the aircraft.

Even though the rotor system of the present disclosure has been depicted and described as having a particular number of rotor blades, it should be understood by those having ordinary skill in the art that, a rotor system of the present disclosure could have alternate numbers of rotor blades both greater than or less than six. Also, even through the rotor system of the present disclosure has been depicted and described as be being the main rotor of a helicopter, it should be understood by those having ordinary skill in the art that the teachings of certain embodiments relating to the rotor systems described herein may apply to other rotor systems, including, but not limited to, helicopter tail rotors, proprotors for tiltrotor aircraft, rotor systems for quad and multi rotor aircraft and the like. In addition, it should be understood by those having ordinary skill in the art that the teachings of certain embodiments relating to the rotor systems of the present disclosure described herein may apply to both manned and unmanned aircraft.

In general, rotor systems for rotorcraft should be designed to achieve blade flap or out-of-plane frequencies and lead-lag or in-plane frequencies that are sufficiently distant from the excitation frequencies generated by the rotor systems corresponding to 1/rev (1 per revolution), 2/rev, 3/rev, etc. As an example, if a rotor system has an operating speed of 360 RPM, the corresponding 1/rev excitation frequency is 6 Hertz (360/60=6 Hz). Similarly, the corresponding 2/rev excitation frequency is 12 Hz and the corresponding 3/rev excitation frequency is 18 Hz. It should be understood by those having ordinary skill in the art that a change in the operating speed of a rotor system will result in a proportional change in the excitation frequencies generated by the rotor system. Preferably, rotor blades20are formed from a high-strength and lightweight material. For example, the structural components of rotor blades20may be formed from carbon-based materials such as graphite-based materials, graphene-based materials or other carbon allotropes including carbon nanostructure-based materials such as materials including single-walled and multi-walled carbon nanotubes. Rotor blades20are preferably designed to a desired in-plane stiffness such that when operated within the rotor systems of the present disclosure, the first-in-plane lead-lag frequency of rotor blades20is decoupled from the per revolution excitations frequencies and the out-of-plane flapping frequency.

Referring next toFIGS. 2A-2B and 3A-3Cin the drawings, an articulated rotor system with pitch independent blade-to-blade damping is depicted and generally designated100. In the illustrated embodiment, rotor system100includes a yoke102having six rotor blades104coupled thereto. As best seen inFIG. 3A-3B, yoke102includes six pockets102a. A mast106couples rotor system100to the power system of the rotorcraft including an engine and transmission that provide torque and rotational energy to rotor system100to enable rotation about a rotational axis108. In the illustrated embodiment, each rotor blade104includes a root section110that is coupled to a respective blade grip assembly112using connecting members114such as pins, bolts or other suitable means. As best seen inFIG. 3B, each blade grip assembly112includes an upper grip plate112aand a lower grip plate112b. A damper anchor support118is coupled between each upper and lower grip plate112a,112busing connecting members120such as pins, bolts or other suitable means. In the illustrated embodiment, each damper anchor support118includes a pitch horn118aand a central opening118b.

Each blade grip assembly112is coupled to yoke102by a centrifugal force bearing122. As illustrated, each centrifugal force bearing122is a twin spherical bearing having an outboard bearing support122aand an inboard bearing support122b. Each inboard bearing support122bis coupled between an upper and a lower grip plate112a,112busing connecting members116such as pins, bolts or other suitable means. The inboard spherical surface of each twin spherical bearing corresponds to a spherical surface of inboard bearing support122band the outboard spherical surface of each twin spherical bearing corresponds to a spherical surface of outboard bearing support122a. The connections between the twin spherical bearing and the bearing supports are permanent and may be made by vulcanizing the elastomeric material of each twin spherical bearing directly on these surfaces or by bonded, adhered or otherwise secured the elastomeric material in a non-removable manner to these surfaces. Centrifugal force bearings122may include a plurality of rigid shims disposed between layers of the elastomeric material. The durometer and thickness of the materials as well as the stiffness, softness and/or spring rate of centrifugal force bearings122may be tailored to achieve the desired operational modes based upon the loads and motions expected in the particular application. In operation, each centrifugal force bearing122is operable to provide a centrifugal force retention load path from a rotor blade104to yoke102via a blade grip assembly112.

Each centrifugal force bearing122provides a coincident hinge with a center point126for the pitch change degree of freedom, the flapping degree of freedom and the lead-lag degree of freedom of the respective rotor blade104relative to yoke102. As best seen inFIG. 3C, pitch change axis128, flapping axis130and lead-lag axis132all pass through coincident hinge point126. As such, centrifugal force bearings122allow each rotor blade104to move independent of the other rotor blades104and independent of yoke102with a pitch change degree of freedom, a flapping degree of freedom and a lead-lag degree of freedom about coincident hinge point126.

As best seen inFIG. 2A, rotor system100includes a blade-to-blade damping ring134that provides pitch independent lead-lag damping for rotor blades104. Blade-to-blade damping ring134includes a damper anchor136coupled to each of the blade grip assemblies112along the respective pitch change axis128, as best seen inFIGS. 3B-3C. Each damper anchor136includes a fitting138having a hollow shaft138athat extends through central opening118bof the respective damper anchor support118. In the illustrated embodiment, spanwise movement of fitting138is prevented by an outboard flange138band an inboard nut140. Preferably, a bearing system142such as a rotary bearing142aand/or an inboard thrust bearing142bprovides low friction contact between fitting138and damper anchor support118. The outboard end of each fitting138includes oppositely disposed devises138c,138dthat extend in the in-plane direction of rotor system100, as best seen inFIG. 3A. Each damper anchor136also includes an anti-rotation rod144that couples each fitting138to yoke102to prevent relative rotation therebetween. In the illustrated embodiment, each anti-rotation rod144is depicted as a hex rod extending between a bearing cap146, which is coupled to an outboard surface of yoke102, and the inner cavity138eof a fitting138. A spring138fmay be disposed within inner cavity138eto support anti-rotation rod144. The hex rods prevent relative rotation between each fitting138and yoke102but may allow certain movement in the in-plane (lead-lag) and/or out-of-plane (flapping) directions.

Blade-to-blade damping ring134also includes a lead-lag damper148extending between each pair of adjacent damper anchors136. In the illustrated embodiment, each lead-lag damper148is coupled between a clevis138cof a first damper anchor136and a clevis138dof a second damper anchor136, as best seen inFIG. 2A. As best seen inFIG. 3C, the couplings between lead-lag dampers148and damper anchors136include spherical bearings150to allow certain degrees of freedom therebetween such as during blade flapping to minimize blade flap and lead-lag coupling. Each lead-lag damper148has an in-plane spring rate operable to apply a damping force to the lead-lag degree of freedom of the rotor blades104to reduce the in-plane oscillation of the rotor blades104. The stiffness, softness and/or in-plane spring rate of lead-lag dampers148may be tailored to achieve the desired operational modes based upon the loads and motions expected in the particular application. In one example, lead-lag dampers148may be elastomeric dampers with an in-plane spring rate operable to provide lead-lag damping to the rotor blades104responsive to shearing of elastomeric layers. In another example, lead-lag dampers148may have mechanical springs with an in-plane spring rate operable to provide lead-lag damping to the rotor blades104. In a further example, lead-lag dampers148may be fluid springs having an in-plane spring rate operable to provide lead-lag damping to the rotor blades104. In a yet another example, lead-lag dampers148may be mechanical springs in combination with fluid springs having an in-plane spring rate operable to provide lead-lag damping to the rotor blades104.

As discussed herein, each damper anchor support118includes a pitch horn118athat is coupled to a pitch link152of a pitch control assembly154depicted as a rise and fall swash plate operable to collectively and/or cyclically control the pitch of rotor blades104, as best seen inFIG. 2B. Each rotor blade104is operable to independently rotate about its pitch change axis128relative to other rotor blades104and yoke102, changing pitch responsive to changes in position of the respective pitch link152. During pitch change operations, blade grip assemblies112rotate relative to damper anchors136which are inline with pitch change axes128and are rotationally fixed relative to yoke102such that devises138c,138dremain extended in the in-plane direction of rotor system100. As such, rotation of blade grip assemblies112responsive to pitch change operations does not affect the in-plane spring rate of lead-lag dampers148. During flight operations, rotor blades104may tend to oscillate forward to a lead position and backwards to a lag position as rotor system100rotates as a result of conservation of momentum and acceleration/deceleration caused by the Coriolis effect. Lead-lag dampers148have an in-plain spring rate operable to apply a damping force to prevent excess back and forth movement of rotor blades104. As discussed herein, the lead-lag damping force is unaffected by and/or independent of the flapping degree of freedom of rotor blades104. In addition, as discussed herein, the lead-lag damping force is unaffected by and/or independent of the pitch change degree of freedom of rotor blades104.

The foregoing description of embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the present disclosure. Such modifications and combinations of the illustrative embodiments as well as other embodiments will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.