Helicopter Rotor System

Abstract

The coaxial rotor system includes a central mast non-rotatably disposed on and extending from the helicopter. A rotation axis extends along the central mast. An inner mast is disposed along the central mast and is rotatable in a first direction about the rotation axis. A portion of the inner mast extends above an end of the central mast. An outer mast circumscribes the central mast and is rotatable in an opposite second direction about the rotation axis. The central mast extends above an end of the outer mast. An upper rotor blade assembly is rotatable with the inner mast. A lower rotor blade assembly is rotatable with the outer mast. A control system disposed on the central mast between the upper rotor blade assembly and the lower rotor blade assembly is operable to adjust the pitch of the plurality of upper rotor blades and to adjust the pitch of the plurality of lower rotor blades.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 383,933, filed November 16, 2022, and U.S. Provisional Application No. 63 / 362,690, filed April 8, 2022, the entireties of which are incorporated by reference herein.

[0002] The present invention relates generally to the field of rotor systems for helicopters, and more specifically to a control system for a coaxial rotor system for a helicopter. [Background technology]

[0003] It is known to equip helicopters with rotor systems for providing lift and control during helicopter operation. In particular, a coaxial rotor system drives first and second rotor blades in opposite directions so that twisting forces on the helicopter from one set of rotor blades are countered by twisting forces from the other set of rotor blades, thus providing stability and yaw control for the helicopter without the need for a tail rotor as in a single rotor system. Summary of the Invention

[0004] A coaxial rotor system for a helicopter may include a central mast that is non-rotatably arranged on a helicopter equipped with the coaxial rotor system. The central mast extends vertically from the helicopter, for example from the fuselage of the helicopter. A rotation axis of the coaxial rotor system extends along a longitudinal axis of the central mast. The inner mast is arranged along an inner cavity of the central mast and is rotatable in a first direction about the rotation axis relative to the central mast. An upper part of the inner mast extends from an upper end of the central mast. The outer mast is arranged along an outer surface of the central mast and is rotatable in a second direction opposite to the first direction about the rotation axis relative to the central mast. The central mast extends from an upper end of the outer mast. An upper rotor blade assembly includes a plurality of upper rotor blades and is arranged at an upper part of the inner mast. The upper rotor blade assembly is rotatable in a first direction about the rotation axis via rotation of the inner mast. A lower rotor blade assembly includes a plurality of lower rotor blades and is arranged at the outer mast. The lower rotor blade assembly is rotatable in a second direction about the axis of rotation via rotation of the outer mast. The swash plate assembly is disposed along the central mast between the upper rotor blade assembly and the lower rotor blade assembly. The swash plate assembly includes (i) an upper swash plate connected to the upper rotor blade assembly and (ii) a lower swash plate connected to the lower rotor blade assembly. The upper swash plate actuator is operable to adjust a position of the upper swash plate along the central mast and a pitch of the upper swash plate relative to the axis of rotation to adjust the pitch of the plurality of upper rotor blades relative to the axis of rotation. The lower swash plate actuator is operable to adjust a position of the lower swash plate along the central mast and a pitch of the lower swash plate relative to the axis of rotation to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation.

[0005] Thus, the central mast is non-rotatably disposed on the helicopter, the rotatable inner mast extends above the central mast for rotating the upper rotor blade assembly, and the rotatable outer mast extends along the bottom of the central mast for rotating the lower rotor blade assembly. The swash plate assembly is disposed along the non-rotatable central mast and includes an upper swash plate for adjusting the pitch of the upper rotor blades and a lower swash plate for adjusting the pitch of the lower rotor blades. The central mast provides a non-rotatable or fixed mounting location for non-rotating items at a location between the rotor blades, which allows, for example, reduced complexity and weight of mast-mounted components, reduced overall height of the rotor system, reduced swash plate bearing speed, and independent control of the pitch of the upper and lower rotor blades. That is, a control system may be disposed on the central mast between the upper and lower rotor blade assemblies, and the control system operates to independently adjust the pitch of the upper rotor blades and the pitch of the lower rotor blades.

[0006] These and other objects, advantages, objectives and features of the present invention will become apparent from a review of the following specification taken in conjunction with the drawings. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view of a coaxial rotor system for a helicopter in which a control system for adjusting the pitch of the upper and lower rotor blades is disposed between the upper and lower rotor blades along a stationary part of the mast. [Figure 1A] FIG. 2 is a cross-sectional view of the coaxial rotor system of FIG. [Diagram 2] FIG. 2 is an enlarged view of the upper swashplate assembly of the coaxial rotor system of FIG. [Figure 2A] FIG. 3 is a cross-sectional view of the upper swashplate assembly and coaxial rotor system of FIG. [Diagram 3] FIG. 2 is an enlarged view of the lower swashplate assembly of the coaxial rotor system of FIG. [Figure 3A] FIG. 4 is a cross-sectional view of the lower swashplate assembly and coaxial rotor system of FIG. [Figure 4] FIG. 1 is a perspective view of a coaxial rotor system in a default state with the upper and lower rotor blades at flat pitch. [Diagram 5] FIG. 5 is a cross-sectional view of the coaxial rotor system of FIG. [Figure 6] FIG. 5 is a perspective view of the coaxial rotor system in a fully positive packed position with the upper and lower rotor blades pitched upward from the default state of FIG. [Figure 7] FIG. 5 is a perspective view of the coaxial rotor system in a fully negative packed position with the upper and lower rotor blades pitched downward from the default state of FIG. [Figure 8] FIG. 5 is a perspective view of the coaxial rotor system in a forward tilt circulating blade pitch position with the upper and lower swash plate assemblies tilted forward from the default state of FIG. [Figure 9] FIG. 5 is a perspective view of the coaxial rotor system in a leftward tilt circulating blade pitch position in which the upper and lower swash plate assemblies are tilted leftward from the default state of FIG. 4 . [Figure 10] FIG. 5 is a perspective view of the coaxial rotor system in a rearward tilt circulating blade pitch position in which the upper and lower swash plate assemblies are tilted rearward from the default state of FIG. 4 . [Figure 11] FIG. 5 is a perspective view of the coaxial rotor system in a maximum positive differential set position with the upper rotor blades pitched upward and the lower rotor blades pitched downward from the default state of FIG. [Figure 12]FIG. 5 is a perspective view of the coaxial rotor system in a maximum negative differential set position with the upper rotor blades pitched downward and the lower rotor blades pitched upward from the default state of FIG. [Figure 13] FIG. 5 is a perspective view of the coaxial rotor system in a differential rotation position with the upper swash plate assembly tilted rearward and the lower swash plate assembly titled forward from the default state of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A coaxial rotor system for a helicopter includes a first set of rotor blades and a second set of rotor blades that counter-rotate relative to each other along a common axis of rotation so that torque on the helicopter generated from the rotation of one set of rotor blades is canceled by torque generated from the rotation of the other set of rotor blades. The rotation of the rotor blades generates lift for the helicopter, while the pitch of the coaxial rotor blades relative to each other controls the yaw, pitch, and roll of the helicopter.

[0009] For example, a conventional coaxial rotor system includes an upper set and a lower set of rotor blades that are driven about a common axis of rotation and thus mounted on overlapping, counter-rotating masts. In other words, a conventional coaxial rotor system mounts one set of rotor blades to a mast that rotates in a first direction (e.g., clockwise) and the other set of rotor blades to a second mast that rotates in a second direction opposite the first direction (e.g., counter-clockwise), where one mast extends through the other mast. Control of the helicopter's yaw, pitch, and roll is achieved through adjusting the pitch of the sets of rotor blades relative to one another.

[0010] Because conventional coaxial rotor systems mount the upper and lower rotor blades on inverted and overlapping masts, the system for controlling the pitch of the rotor blades relative to one another must typically account for the rotation of the mast along its entire length, and stationary actuators must be located below the rotor blades, and thus conventional systems are limited to adjusting the pitch of the upper and lower rotor blades using complex lever configurations and inverted swash plates, which results in increased size and weight of the rotor system, as well as reduced lifespan of the rotor system. In comparison, the coaxial rotor system of the present disclosure provides a stationary, non-rotating mounting location between the upper and lower rotors such that a control system can be mounted between the upper and lower rotors and, among other advantages, the pitch of the upper and lower rotor blades can be controlled independently of one another.

[0011] For example, a conventional coaxial rotor system may include a lower rotor blade mounted on an outer mast that rotates in a first direction and an upper rotor blade mounted on an inner mast that extends upward through the outer mast and rotates in a second direction opposite the first direction. The actuators for controlling the pitch of the upper and lower rotor blades are hydraulic and located below the lower rotor because there is no non-rotating access to the space between the rotors. Thus, conventional coaxial rotor systems are limited to controlling the pitch of the upper and lower rotor blades relative to one another via a single set of actuators, which means that the pitch of the upper and lower rotor blades must be controlled in tandem.

[0012] Swash plates are typically positioned along a rotating mast to translate stationary actuator movements into adjustments to the pitch of the upper and lower rotor blades. For example, the lower swash plate can adjust the position of the lower rotor blades and the upper swash plate can adjust the position of the upper rotor blades. The lower swash plate can be positioned below the lower rotor blades and can include a stationary portion that receives input from the stationary actuator and a rotatable portion that rotates with the lower rotor blades. A linkage runs from the rotatable portion of the lower swash plate to the lower rotatable portion of the upper swash plate so that adjustments to the lower swash plate can be translated to adjustments to the upper swash plate. The upper swash plate is positioned above the lower rotor blades along the mast and the lower rotatable portion of the upper swash plate rotates with the rotatable portion of the lower swash plate to accommodate a linkage that runs through the lower rotor blades. Since the top of the upper swash plate rotates with and is connected to the upper rotor blades, the adjustment of the upper swash plate through the adjustment of the lower swash plate allows the upper rotor blades to be adjusted. With this typical configuration in existing rotorcraft, the relative speed of the top of the upper swash plate relative to the bottom (which rotates the lower rotor in the opposite direction) is equal to twice the nominal rotor speed. In addition, a differential set lever is typically used to translate the movement between the upper and lower swash plates. Historically, the means to achieve this have been complex and problematic, requiring completely separate mechanical linkages and actuation systems. Having the swash plate actuator and the lower swash plate between the gearbox and the lower rotor increases the height of the lower rotor mast and increases the overall rotor system height (space occupied within the fuselage).

[0013] The life of a swash plate bearing depends on many factors including size, load, and speed. The swash plate must simultaneously transmit axial loads in either direction, side loads, and overturning moments. This requires either a duplex set of two angular contact bearings or cross contact bearings. Because the swash plate bearings in conventional systems must be positioned around the mast and any gimbaling configuration, the bearings tend to be quite large in diameter, and because of this size, speed limitations become a concern. For example, at the bearing diameters typically used, cross contact bearings are not applicable due to the speed limitations of the bearings themselves. Thus, typically, a back-to-back duplex set of two angular contact bearings is used. Further exacerbating this concern in existing systems, the upper swash plate typically rotates at twice the speed of the rotor causing a counter-rotation of the lower swash plate, and therefore the upper swash plate bearing accumulates cycles at twice the speed of the lower swash plate bearing.

[0014] Differential set is the difference in the set blade pitch settings between the upper and lower rotors. Different set settings cause more or less drag of one set of rotors against the other set of rotors, thus inducing a yaw moment in the aircraft. Differential set is traditionally applied via a complex lever arrangement located either above the upper rotor or between the upper and lower rotors with levers passing through holes in the mast. When the arrangement is above the upper rotor, this makes the overall rotor system taller, causing potential storage issues and causing additional drag. When the arrangement includes levers passing through holes in the mast, this causes higher stresses in the mast that must be taken into account by adding more material to the mast in that area, thus increasing the weight. Differential set actuators may traditionally be located below the gearbox, which increases the overall height (space occupied within the fuselage) of the rotor system.

[0015] Phase lag, i.e., the angular difference between the point at which a control input to a rotor blade (e.g., pitch adjustment) occurs and the point of maximum displacement of the blade in response to that control input, is very difficult to predict analytically or even via simulation. Typically, phase lag is closely estimated in practice, tested during ground / flight testing, and adjusted or accounted for by fabricating new mechanical connections between the actuators and the set of rotor blades, such as new swashplate rings and differential set levers, so that the position of maximum blade pitch angle occurs at the correct azimuth blade position. This leads to costly and time-consuming testing procedures and wasted fabrication of parts.

[0016] Furthermore, the stiffness of the control system is important for the responsiveness of the aircraft to pilot inputs as well as for avoiding instabilities in the linkage. In conventional systems, if the control system is too soft in twisting around the rotor, the control load components tangential to the rotor rotation can cause the control rods to tilt, increasing the tangential loads and further increasing the tilt. This condition is unstable and results in loss of control of the blade pitch. Furthermore, the low control system stiffness is only applied to the upper rotor, causing a different control system stiffness of the upper rotor relative to the lower rotor. This causes unintended differential control inputs that can cause controllability / predictability issues for the aircraft. In other words, in conventional rotor systems, since the control of the pitch of the upper rotor blades depends on the connection to the lower swash plate and the control of the pitch of the lower rotor blades, the stiffness difference between the connection of the upper and lower rotor blades and the upper and lower swash plates can result in unintended differences in the control of the upper and lower rotor blades.

[0017] The coaxial rotor system, described further below, includes a central or center mast non-rotatably disposed on the helicopter, an inner mast extending through an internal cavity of the center mast and above an upper end of the center mast to rotate the upper rotor blade assembly, and an outer mast extending along an outer surface of the center mast to rotate the lower rotor blade assembly. A portion of the non-rotatable center mast is exposed between the upper and lower rotor blade assemblies, and a control system is mounted along the stationary center mast. The control system includes upper and lower actuators for adjusting the pitch of the upper and lower rotor blades, and upper and lower swash plate assemblies for translating the movement of the respective actuators to adjust the pitch of the upper and lower rotor blades. Thus, the coaxial rotor system provides upper and lower rotor blade assemblies that are independently adjustable from one another via upper and lower actuators coupled to the respective upper and lower swash plate assemblies, which pitch, translate, and rotate independently from one another relative to the stationary center mast.

[0018] Referring now to the drawings and the exemplary embodiment illustrated therein, a coaxial rotor system 100 for a helicopter 10 includes a mast assembly 114 extending from a gearbox 112, with an upper rotor blade assembly 176 rotatably disposed on an upper portion of the mast assembly 114 and a lower rotor blade assembly 186 rotatably disposed on a lower portion of the mast assembly 114 ( FIG. 1 ). The pitch of each of the upper rotor blade assembly 176 and the lower rotor blade assembly 186 is independently adjustable relative to one another to control the yaw, pitch, and roll of the helicopter 10. As described below, a central portion of the mast assembly 114 between the upper rotor blade assembly 176 and the lower rotor blade assembly 186 is fixed or stationary or non-rotatable such that a control system 142 for controlling the pitch of the upper rotor blade assembly and the lower rotor blade assembly may be mounted along the central portion of the mast assembly 114 between the upper rotor blade assembly and the lower rotor blade assembly.

[0019] Thus, the coaxial rotor system 100 provides a stationary mounting location along the mast assembly 114 between the upper and lower rotor blades for mounting a control system 142 that is operable to adjust the pitch of the upper and lower rotor blades. Mounting the control system 142 in a stationary location along the mast assembly 114 may enable the use of lighter control system components with longer life spans, independent control of the pitch of the upper and lower rotor blades, the use of electromechanical actuators to adjust the pitch of the upper and lower rotor blades, reduced overall height of the rotor system, and increased stiffness of the control system, among other advantages.

[0020] 1A, the mast assembly 114 includes a center or central mast 116, an inner mast 128, and an outer mast 134. The axis of rotation A of the mast assembly 114 R is the longitudinal axis A of the central mast 116 116, and the central mast 116 may be stationary or fixed, or non-rotatable, such that non-rotatable components may be mounted along the central mast 116. The inner mast 128 controls the rotation of the upper rotor blade assembly 176 and is aligned along a rotation axis A. R The outer mast 134 controls the rotation of the lower rotor blade assembly 186 about a rotation axis A, which is opposite to the first direction. R in a second direction to cause the lower rotor blade assembly 186 to rotate in a second direction. The mast assembly 114 extends from a gearbox 112 of the helicopter 10, which controls the rotation of the inner and outer masts.

[0021] Thus, a central or center mast 116 is rotatably fixed to the gearbox 112 and extends from the helicopter 10 to define the axis of rotation A of the coaxial rotor system 100. R For example, the central mast 116 may be fixedly attached to the helicopter 10 and / or the gearbox 112. The central mast 116 may extend substantially vertically from the helicopter 10, such as when the helicopter is not piloted and positioned on substantially level ground, or positioned above the gearbox 112 and at any suitable angle above the body of the helicopter 10.

[0022] The inner mast 128 is rotatably connected to the gearbox 112 and has a rotation axis A. R and extends from the helicopter 10 along the inside of the central mast 116. For example, the inner mast 128 extends along the inner cavity 118 of the central mast 116, such that when the inner mast 128 rotates, the inner mast 128 rotates within the inner cavity 118 relative to the stationary central mast 116. Thus, the central mast 116 can circumscribe at least a portion of the inner mast 128.

[0023] The outer mast 134 is rotatably connected to the gearbox 112 separately from the inner mast 128 and has a rotation axis A. R and extends from the helicopter 10 along the outside of the central mast 116. For example, the outer mast 134 extends along the outer surface 120 of the central mast 116, such that when the outer mast 134 rotates, the outer mast 134 rotates about the central mast 116 and relative to the stationary central mast 116. The outer mast 134 may circumscribe at least a portion of the central mast 116. The outer mast 134, the central mast 116, and the inner mast 128 may be concentric.

[0024] The inner mast 128 extends along the inner cavity 118 of the central mast 116, with at least an upper portion 130 of the inner mast 128 extending from the upper end 126 of the central mast 116. Thus, a lower portion 132 of the inner mast 128 is rotatably attached to the gearbox 112, and an upper portion 130 of the inner mast 128 extends above the upper end 126 of the central mast 116 and is exposed outside the central mast 116 for receiving an upper rotor blade assembly 176.

[0025] The outer mast 134 extends from the gearbox 112 along the outer surface 120 of the central mast 116 at the lower part 124 of the central mast 116 such that the central mast 116 extends from an upper end 140 of the outer mast 134. The lower part 136 of the outer mast 134 is thus rotatably attached to the gearbox 112, while at least an upper part 138 of the outer mast 134 is exposed to the outside of the helicopter body and optionally surrounds the central mast 116 for receiving a lower rotor blade assembly 186. At least a portion of the stationary central mast 116 is thus exposed between the upper end 140 of the outer mast 134 and the upper end 126 of the central mast 116 and is configured to receive or support a control system 142.

[0026] As shown in FIGS. 2 and 2A , the upper rotor blade assembly 176 is disposed on or coupled to the upper portion 130 of the inner mast 128 such that the plurality of upper rotor blades 178 rotate about an axis of rotation A via rotation of the inner mast 128. R 1. For example, the upper rotor blade assembly 176 may be fixedly attached to the inner mast 128 via a hub 180 of the upper rotor blade assembly 176 attached to the inner mast 128. In the illustrated embodiment, a plurality of upper rotor blades 178 are attached to the inner mast 128 via an upper rotor blade pitch assembly 182 connected to the hub 180. The upper rotor blade pitch assembly 182 is connected to the control system 142 for adjusting the pitch of the upper rotor blades 178. The upper rotor blade pitch assembly 182 includes a blade pitch horn 184 associated with each respective rotor blade 178 of the upper rotor blade assembly 176, and each blade pitch horn 184 is independently connected to the control system 142 for independent control of the corresponding upper rotor blade 178, as described below.

[0027] As shown in FIGS. 3 and 3A , the lower rotor blade assembly 186 is disposed on or coupled to the upper portion 138 of the outer mast 134 such that the plurality of lower rotor blades 188 rotate about an axis of rotation A via rotation of the outer mast 134. R1 in a second direction about the hub 190 of the lower rotor blade assembly 186. For example, the lower rotor blade assembly 186 may be fixedly mounted to the outer mast 134 via a respective hub 190 of the lower rotor blade assembly 186 mounted to the outer mast 134. A plurality of lower rotor blades 188 are mounted to the outer mast 134 via a lower rotor blade pitch assembly 192 connected to a control system 142 for adjusting the pitch of the lower rotor blades 188. The lower rotor blade pitch assembly 192 includes a blade pitch horn 194 associated with each respective rotor blade 188 of the lower rotor blade assembly 186, with each blade pitch horn 194 independently connected to the control system 142 for independent control of the corresponding lower rotor blade 188, as described below.

[0028] Thus, each rotor blade assembly includes a plurality of rotor blades mounted or coupled to or mounted at a respective inner or outer rotatable mast, with the pitch of each respective rotor blade being adjustable via adjustment of a respective blade pitch horn. Each rotor blade assembly may be mounted to a respective rotatable mast via a respective hub fixedly attached to the mast, with the plurality of rotor blades extending radially from the hub. The rotor system may have any number of rotor blades, for example, two or more rotor blades, such as three or four, or five or more rotor blades.

[0029] The control system 142 is disposed along or coupled to the stationary central mast 116 between the upper rotor blade assembly 176 and the lower rotor blade assembly 186, and includes an upper swash plate assembly 148 mechanically connected to the upper rotor blade assembly 176 and a lower swash plate assembly 162 mechanically connected to the lower rotor blade assembly 186. The control system 142 controls the upper swash plate assembly 148 and the lower swash plate assembly 162 relative to the central mast 116, e.g., along a longitudinal axis A of the central mast 116. 116 Adjust the position and pitch of each swash plate assembly to the rotation axis A. R That is, by adjusting the upper swash plate assembly 148 relative to the central mast 116, the pitch of the upper rotor blades 178 is adjusted relative to the axis of rotation A. R 1, and by adjusting the lower swash plate assembly 162 relative to the central mast 116, the pitch of the plurality of lower rotor blades 188 is adjusted relative to the axis of rotation A. R As discussed further below, the control system 142 includes one or more actuators for adjusting the position and pitch of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the central mast 116.

[0030] One or more upper swash plate actuators 144 control the position of the upper swash plate assembly 148 along the central mast 116 and the longitudinal axis A of the central mast 116. 116 4. Adjust the pitch of the upper swash plate assembly 148 relative to the axis of rotation A. R Similarly, one or more lower swash plate actuators 146 are operable to adjust the pitch of the plurality of upper rotor blades 178 relative to the longitudinal axis A of the central mast 116.116 Adjust the pitch of the lower swash plate assembly 162 relative to the axis of rotation A R The rotor blades 188 are operable to adjust the pitch of the plurality of lower rotor blades 188 relative to the

[0031] In the illustrated embodiment, the upper swash plate actuator 144 and the lower swash plate actuator 146 are attached or coupled to or disposed at the central mast 116 between the upper rotor blade assembly 176 and the lower rotor blade assembly 186 (e.g., between the top of the central mast and the top of the outer mast). The swash plate actuators are mounted to a stationary mounting platform 196 disposed along the outer surface 120 of the central mast 116 and between the upper and lower swash plate assemblies. The mounting platform 196 may be integrally formed with the central mast 116 or, as shown in the figures, the mounting platform 196 may be attached to the central mast 116, for example, at the overlapping junction of the upper portion 122 of the central mast and the lower portion 124 fixedly attached to the helicopter 10. Optionally, the swashplate actuators may be individually mounted to the central mast 116, for example on individual mounting platforms or brackets integral with or extending from the central mast 116.

[0032] In the illustrated embodiment, the swash plate actuators include three upper swash plate actuators and three lower swash plate actuators. The upper swash plate actuators 144 and the lower swash plate actuators 146 are independently operable to independently control the pitch of the upper and lower rotor blades. In other words, the upper swash plate actuator 144 is operable to adjust the plane of the upper swash plate relative to the mast assembly to adjust the pitch of the upper rotor blades 178, and the lower swash plate actuator 146 is operable to adjust the plane of the lower swash plate relative to the mast assembly to adjust the pitch of the lower rotor blades 188, with operation of one set of actuators not affecting the operation of the other actuator and therefore not affecting the pitch of the other set of rotor blades. Furthermore, operation of one individual actuator does not affect operation of another individual actuator. For example, operation of one individual upper swash plate actuator does not affect operation of either another individual upper swash plate actuator or the lower swash plate actuator.

[0033] Further, the individual upper and lower swash plate actuators are independently operable to adjust the pitch of the respective rotor blades. For example, each of the actuators of an upper or lower set of actuators may be collectively actuated to vertically translate a respective swash plate assembly along the central mast 116, thus collectively adjusting the pitch of a respective set of rotor blades. In other words, the rotor blades are aligned along the longitudinal axis A of the central mast 116. 116 The individual actuators may also be actuated independently (or to different degrees relative to each other) to tilt the central mast 116 along the longitudinal axis A 116The swashplate assembly can be tilted or pitched relative to the longitudinal axis A of the central mast 116 to cause the blades to pitch up and down in a sinusoidal manner as the rotor rotates. 116 is periodically pitched via tilting of the swash plate assembly relative to the

[0034] Each of the upper and lower swashplate actuators may include any suitable actuator (e.g., electromechanical or hydraulic actuator) operable to vertically translate a rod or piston or linkage connected to the respective upper or lower swashplate assembly to affect the position and tilt of the swashplate assembly. As shown in FIG. 1A, wiring 198 for powering and controlling the actuators may be routed from the helicopter 10, through the gearbox 112, and along the stationary central mast 116 to the actuator platform 196 for connection to the individual actuators. In this manner, the wiring 198 may be routed along the central mast 116 to the control system 142 without damaging or colliding with the rotating components and systems of the coaxial rotor system.

[0035] The upper swash plate assembly 148 is disposed along above the swash plate actuator 144 and below the upper rotor blade assembly 176 and is attached or coupled to the central mast 116. The upper swash plate assembly 148 includes a non-rotatable ring 150 disposed along the central mast 116 and mechanically connected to the upper swash plate actuator 144 to adjust the position and pitch of the upper swash plate assembly 148 when the upper swash plate actuator 144 is actuated. The non-rotating ring 150 may be mechanically connected to the stationary central mast 116 via a stationary scissor linkage 156 to prevent rotation of the non-rotating ring 150.

[0036] A rotating ring 152 of the upper swash plate assembly 148 is rotatably disposed along the central mast 116 and is mechanically connected to an upper rotor blade assembly 176 for adjusting the pitch of upper rotor blades 178 when the position and pitch of the upper swash plate assembly 148 is adjusted. The rotating ring 152 may be mechanically connected to the upper rotor blade assembly 176, e.g., an upper rotor hub 180, by a rotating scissor linkage 158 to drive and synchronize the rotation of the swash plate with the rotation of the upper rotor blade assembly 176.

[0037] The upper swash plate assembly 148 (see FIGS. 2 and 2A ) includes cross-contact bearings 154 that provide a mounting interface between the non-rotating ring 150 and the rotatable ring 152 and hold the non-rotating ring 150 and the rotatable ring 152 in the same translational and tilted position relative to the central mast 116 while allowing the rotatable ring 152 to rotate about the non-rotating ring 150 and the central mast 116. For example, the upper swash plate cross-contact bearing 154 includes a ball bearing ring having a plurality of ball bearings disposed along a bearing race or ring or disposed between an inner race / ring and an outer race / ring, with the cross-contact bearing 154 disposed between the non-rotating ring 150 and the rotatable ring 152. The cross-contact bearing 154 ensures alignment of the rotatable ring 152 relative to the non-rotating ring 150 while allowing the rotatable ring 152 to rotate about the non-rotating ring 150. That is, the cross-contact bearing 154 allows the rotatable ring 152 to rotate about the non-rotatable ring 150 while maintaining consistent alignment and tilt between the two rings. The cross-contact bearing 154 does not allow the rotatable ring 152 and non-rotatable ring 150 to tilt or translate relative to one another. The upper swashplate cross-contact bearing 154 rotates at the same speed as the upper rotor blade assembly 176.

[0038] A gimbal ball 155 (FIG. 2A) is disposed between the upper swash plate assembly 148 and the central mast 116 such that the upper swash plate assembly 148 can pitch and translate vertically relative to the central mast 116 while the rotatable ring 152 remains rotatable (via cross-contact bearings 154) relative to the non-rotating ring 150 throughout the range of motion of the upper swash plate assembly 148. Thus, the gimbal ball 155 allows the non-rotating ring 150 and the rotatable ring 152 to simultaneously slide or translate up and down along the central mast 116 in response to movement of the gimbal ball 155 along the central mast 116, and to tilt relative to the central mast 116 about the gimbal ball 155, without the gimbal ball 155 preventing or limiting rotation about the central mast 116. That is, the rotating ring 152 is locked to the non-rotating ring 150 against vertical and tilted positions via cross-contact bearings 154, and the rotating ring 152 and non-rotating ring 150 translate along the central mast 116 with and in coordinated relation to the gimbal ball 155, and tilt or pivot relative to the central mast 116 with and around the gimbal ball 155.

[0039] Upper swash plate assembly 148 is mechanically connected to upper rotor blade assembly 176 via upper rotor pitch link 160, which is a fixed length link that extends from upper swash plate rotating ring 152 to upper rotor blade pitch assembly 182. That is, upper rotor pitch link 160 extends between upper swash plate rotating ring 152 and upper rotor blade assembly 176. Each pitch link 160 mechanically connects to a respective upper blade pitch horn 184 to control the pitch of each individual upper rotor blade 178.

[0040] The lower swash plate assembly 162 is disposed along below the swash plate actuator and above the lower rotor blade assembly 186, and is attached or coupled to the central mast 116. The lower swash plate assembly 162 is non-rotatably disposed along the central mast 116 and includes a non-rotating ring 164 mechanically connected to the lower swash plate actuator 146 for adjusting the position and pitch of the lower swash plate assembly 162 when the lower swash plate actuator 146 is actuated. The non-rotating ring 164 may be mechanically connected to the stationary central mast 116 with a stationary scissor linkage 170 to prevent rotation of the non-rotating ring 164.

[0041] A rotating ring 166 of the lower swash plate assembly 162 is rotatably disposed along the central mast 116 and is mechanically connected to the lower rotor blade assembly 186 for adjusting the pitch of the lower rotor blades 188 when the position and pitch of the lower swash plate assembly 162 is adjusted. The rotating ring 166 may be mechanically connected to a lower rotor hub 190 with a rotating scissor linkage 172 for driving and synchronizing the rotation of the swash plate with the rotation of the lower rotor blade assembly 186.

[0042] The lower swash plate assembly 162 (see FIGS. 3 and 3A ) includes cross-contact bearings 168 that provide a mounting interface between the non-rotating ring 164 and the rotatable ring 166 and hold the non-rotating ring 164 and the rotatable ring 166 in the same translational and tilted position relative to the central mast 116 while allowing the rotatable ring 166 to rotate about the non-rotating ring 164 and the central mast 116. For example, the lower swash plate cross-contact bearing 168 includes a ball bearing ring having a plurality of ball bearings disposed along a bearing race or ring or disposed between an inner race / ring and an outer race / ring, with the cross-contact bearing 168 disposed between the non-rotating ring 164 and the rotatable ring 166. The cross-contact bearing 168 ensures alignment of the rotatable ring 166 relative to the non-rotating ring 164 while allowing the rotatable ring 166 to rotate about the non-rotating ring 164. That is, the cross-contact bearing 168 allows the rotatable ring 166 to rotate about the non-rotatable ring 164 while maintaining consistent alignment and tilt between the two rings. The cross-contact bearing 168 does not allow the rotatable ring 166 and the non-rotatable ring 164 to tilt or translate relative to each other. The lower swashplate cross-contact bearing 168 rotates at the same speed as the lower rotor blade assembly 186.

[0043] A gimbal ball 169 (FIG. 3A) is disposed between the lower swash plate assembly 162 and the central mast 116 such that the lower swash plate assembly 162 can pitch and translate vertically relative to the central mast 116 while the rotatable ring 166 remains rotatable relative to the non-rotating ring 164 (via cross-contact bearings 168) throughout the range of motion of the lower swash plate assembly 162. Thus, the gimbal ball 169 allows the non-rotating ring 164 and the rotatable ring 166 to simultaneously slide or translate up and down along the central mast 116 in response to movement of the gimbal ball 169 along the central mast 116, and to tilt relative to the central mast 116 about the gimbal ball 169, without the gimbal ball 169 preventing or limiting rotation about the central mast 116. Similar to the upper swash plate assembly 148, the non-rotating ring 164 and the rotatable ring 166 of the lower swash plate assembly 162 are locked in vertical and tilt positions relative to the central mast 116 via cross-contact bearings 168 and the rotatable ring 166, with the non-rotating ring 164 translating along the central mast 116 together with and in conjunction with the gimbal ball 169 and tilting relative to the central mast 116 together with and in conjunction with the gimbal ball 169 around the gimbal ball 169.

[0044] 2A and 3A, the gimbal balls 155, 169 of the upper and lower swash plate assemblies each include a respective partial spherical portion or element at the central mast that allows the respective rotating and non-rotating rings to tilt and slide relative to the central mast and about the partial spherical element. In other words, the gimbal balls 155, 169 allow the respective swash plates to simultaneously slide up and down along the central mast 116 and tilt relative to the central mast 116. When the control system 142 operates to adjust the position of the respective upper and lower swash plates along the mast assembly 114, the respective non-rotating rings (and therefore the respective rotating rings) translate together along the central mast 116 and in conjunction with the respective gimbal balls. When the control system 142 operates to adjust the pitch of the respective upper and lower swash plates relative to the mast assembly 114, the respective non-rotating rings (and therefore the respective rotating rings) tilt or pivot about their respective gimbal balls and relative to the central mast 116. Although shown and described as being coupled to the central mast via a gimbal ball arrangement, the swash plates can optionally be coupled to the central mast 116 via other suitable gimbal structures, such as universal joint-type gimbals with slip joints, such that the swash plate assemblies can each translate and tilt relative to the central mast.

[0045] Lower swash plate assembly 162 is mechanically connected to lower rotor blade assembly 186 via lower rotor pitch link 174, which is a fixed length link that extends from lower swash plate rotating ring 166 to lower rotor blade pitch assembly 192. That is, lower rotor pitch link 174 extends between lower swash plate rotating ring 166 and lower rotor blade assembly 186. Each pitch link 174 mechanically connects to a respective lower blade pitch horn 194 to control the pitch of each individual lower rotor blade 188.

[0046] The anti-rotating rings of both the upper and lower swash plate assemblies include a respective hub portion that circumscribes the central mast and a number of fingers or protrusions that extend radially from the hub, where each protrusion mechanically connects to a respective upper or lower actuator. The hubs of the respective anti-rotating rings are disposed at respective gimbal balls such that they cannot rotate about the gimbal balls, but are longitudinally (vertically) movable and tiltable relative to the mast assembly through the action of the gimbal balls and the connected actuators. The gimbal balls allow the anti-rotating rings and the rotating rings to be longitudinally movable and tiltable. For example, the anti-rotating rings are disposed at respective gimbal balls such that when the anti-rotating rings are translated along the mast assembly 114, the gimbal balls and the anti-rotating rings translate together and translate in unison along the mast assembly 114. When the anti-rotating rings tilt relative to the mast assembly 114, the anti-rotating rings tilt about their respective gimbal balls. Thus, upper non-rotating ring 150 includes a hub 150a with protrusions 150b extending therefrom, and lower non-rotating ring 164 includes a hub 164a with protrusions 164b extending therefrom. Each protrusion may be attached to a respective actuator via a respective bearing disposed on the protrusion such that the swashplate assembly can pitch and tilt relative to vertical movement of the actuators.

[0047] Thus, when each upper or lower actuator acts in conjunction with its respective protrusion of the non-rotating ring, the respective swashplate assembly translates (e.g., vertically translates) along the longitudinal axis of the central mast, and when the upper or lower actuators act to different degrees relative to each other along the longitudinal axis of the central mast (i.e., one actuator extends a greater distance than one or more other upper or lower actuators), the plane of the swashplate assembly may tilt relative to the longitudinal axis of the central mast. A static pincer may connect between the central mast and the hub of the non-rotating ring to provide torsional support to the swashplate assembly against any rotational forces felt by the respective rotor blade assemblies. Optionally, the static pincer may connect between the central mast and any suitable structure of the non-rotating ring, such as one of the protrusions.

[0048] Similar to the non-rotating rings, the rotating rings of both the upper and lower swash plate assemblies include a hub portion circumscribing the central mast and a number of projections extending radially from the hub, where each projection mechanically connects to a respective pitch link that is mechanically connected to a respective upper or lower rotor blade assembly. The hub of each rotating ring is disposed in and rotatable about a respective cross contact bearing. The rotating rings are longitudinally movable and tiltable relative to the mast assembly via longitudinal movement of the non-rotating ring along the mast assembly with the respective gimbal balls and tilting of the non-rotating ring about the respective gimbal balls. In other words, the upper rotating ring 152 includes a hub 152a with projections 152b extending from the hub 152a, and the lower rotating ring 166 includes a hub 166a with projections 166b extending from the hub 166a. Thus, when the swash plate assembly is translated along the longitudinal axis of the central mast, or when the plane of the swash plate assembly is tilted about the longitudinal axis of the central mast, that motion can be imparted to the blade pitch assemblies via fixed length pitch links that connect to the prongs of the rotating ring via respective bearings disposed in the prongs. Rotating scissors can connect between the hubs of the rotating ring (or additional prongs) and the hubs of the respective rotor blade assemblies to couple the rotation of the rotor blade assemblies to the rotation of the rotating ring.

[0049] When the respective swash plate actuators connected to the respective non-rotating rings of the upper and lower swash plates are operated to adjust the position and pitch of the respective swash plate assembly, the actuators act on the stationary non-rotating rings of the swash plate assemblies. Each rotating ring is positionally fixed relative to its corresponding non-rotating ring such that adjusting the position and pitch of the non-rotating ring adjusts the position and pitch of the rotating ring accordingly. In other words, the position and pitch of the rotating ring relative to the central mast corresponds to the position and pitch of the non-rotating ring as the rotating ring rotates about the central mast. The rotating rings are connected to the corresponding upper and lower rotor blade assemblies and translate the position and pitch of the swash plate assembly to pitch the respective upper and lower rotor blades. Thus, the actuators are aligned along the longitudinal axis A of the central mast 116. 116 to affect the collective pitch of the respective rotor blades and the longitudinal axis A of the central mast 116. 116 The plane of the non-rotating ring is tilted relative to the rotor blades to affect the periodic pitch of each rotor blade. Because the upper and lower swash plates are independently controlled, a more direct and stiffer load path is achieved between the actuators and each rotor blade assembly.

[0050] Optionally, a fairing may be disposed around the control system 142 and the central mast 116 to provide an aerodynamic housing that houses or covers at least the actuators of the control system 142. Conventionally, the fairing on the rotating mast between the rotors of a coaxial rotor system must be made cylindrical and able to rotate with the rotors, and if it is made in a more aerodynamic shape (wings), it must be counter-rotated through a complex counter-clocking system that is heavy and difficult to design. The central mast 116 of the present coaxial rotor system provides a stationary mounting location so that a cost-effective and lighter fairing can be easily attached to the stationary central mast, eliminating the need for any counter-clocking system.

[0051] It has been found desirable to have the same control stiffness for both the upper and lower rotors. Thus, as shown in Figures 4 and 5, the coaxial rotor system 100 provides identical control system paths for both rotors, resulting in the same system stiffness for the upper and lower rotors without undesirable weight gain or loss of control stiffness for either rotor. That is, the control system 142 is non-rotatably disposed along the mast assembly 114 at the non-rotating central mast 116 and between the upper rotor blade assembly 176 and the lower rotor blade assembly 186, so that the control system 142 can have substantially similar mechanical linkages with the respective upper and lower rotor blade assemblies to adjust the pitch of the upper and lower rotor blades. In other words, the connection between the control system 142 and the upper rotor blade assembly 176 can substantially mirror the connection between the control system 142 and the lower rotor blade assembly 186.

[0052] For example, the control system 142 includes an upper swash plate actuator 144 and a lower swash plate actuator 146 that are non-rotatably mounted along or coupled to the central mast 116 via a mounting platform 196. The mounting platform 196 is mounted to a central region of the mast assembly 114 between the upper rotor blade assembly 176 and the lower rotor blade assembly 186, with the respective actuators extending above and below the mounting platform 196 to couple to the respective upper swash plate assembly 148 and lower swash plate assembly 162. The mounting platform 196 may be substantially equidistant from the upper swash plate assembly 148 and lower swash plate assembly 162. The upper swash plate actuator 144 mechanically connects to a non-rotating ring 150 of the upper swash plate assembly 148, and the lower swash plate actuator 146 mechanically connects to a non-rotating ring 164 of the lower swash plate assembly 162. In a default state (i.e., with the upper and lower rotor blades at flat pitch, such as shown in FIG. 4 ), the upper and lower non-rotating rings may be positioned equidistantly relative to the mounting platform 196 along the mast assembly 114. Thus, the non-rotating portions of the control system 142, including the mounting platform 196, the upper swash plate actuator 144, the lower swash plate actuator 146, the upper swash plate non-rotating ring 150, and the lower swash plate non-rotating ring 164, may be substantially mirrored or similar between the mounting platform 196 and the upper and lower rotor blade assemblies 176, 186. Wiring 198 for the electromechanical actuators may be routed through the gearbox 112, along the non-rotatable central mast 116, and to the mounting platform 196, and thus does not affect or interfere with the positioning of the non-rotating or rotating components of the control system 142.

[0053] Additionally, the rotating or rotatable portions of the control system 142, including the upper swash plate rotating ring 152, the lower swash plate rotating ring 166, the upper swash plate rotating scissor linkage 158, the lower swash plate rotating scissor linkage 172, the upper rotor pitch link 160, and the lower rotor pitch link 174, may also be substantially mirrored or similar between the upper swash plate non-rotating ring 150 and the upper rotor blade assembly 176, and between the lower swash plate non-rotating ring 164 and the lower rotor blade assembly 186. As discussed further below, this allows the control system 142 to adjust the pitch of the upper rotor blades 178 and the pitch of the lower rotor blades 188 together and in conjunction (e.g., FIGS. 6-10), in opposite directions and with equal magnitudes (e.g., FIGS. 11 and 12), or to adjust the pitch of the upper rotor blades 178 and the pitch of the lower rotor blades 188 separately and independently of one another (e.g., FIG. 13).

[0054] As shown in Figure 4, the control system 142 is operated to position the upper rotor blades 178 and the lower rotor blades 188 in a flat pitch, or default state. To adjust the rotor blades from the default state shown in Figure 4 to the fully positive collective position shown in Figure 6, both the upper swash plate assembly 148 and the lower swash plate assembly 162 are moved in the same direction (e.g., downward along the mast assembly 114 in Figure 6) to pitch the upper rotor blades 178 and the lower rotor blades 188 upward. Thus, the upper swash plate actuators 144 can be collectively retracted to move the upper swash plate assembly 148 downward toward the mounting platform 196, and the lower swash plate actuators 146 can be collectively extended to move the lower swash plate assembly 162 downward from the mounting platform 196. In Figure 6, the downward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to Figure 4. As shown, the swash plate assemblies move uniformly downward along the mast assembly 114 to collectively pitch the rotor blades upward.

[0055] When adjusting the rotor blades from the default state shown in FIG. 4 to the fully negative collective position shown in FIG. 7, both the upper swash plate assembly 148 and the lower swash plate assembly 162 move in the same direction (e.g., upward along the mast assembly 114 in FIG. 7) to pitch the upper rotor blades 178 and the lower rotor blades 188 downward. Thus, the upper swash plate actuators 144 can be collectively extended to move the upper swash plate assembly 148 upwardly away from the mounting platform 196, and the lower swash plate actuators 146 can be collectively retracted to move the lower swash plate assembly 162 upwardly towards the mounting platform 196. In FIG. 7, the upward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to FIG. 4. As shown, the swash plate assembly moves uniformly upward along the mast assembly 114 to collectively pitch the rotor blades downward.

[0056] As shown in FIG. 8, to adjust the rotor blades from the default state shown in FIG. 4 to a forward-tilted cyclical blade pitch, the upper rotor blade 178 and the lower rotor blade 188 are pitched downward when rotated and positioned on the first or aft-facing side of the mast assembly 114 (right side in FIG. 8), and the upper rotor blade 178 and the lower rotor blade 188 are pitched upward when rotated and positioned on the second or forward-facing side of the mast assembly 114 (left side in FIG. 8). Thus, the pitch of the upper and lower rotor blades varies sinusoidally and periodically as the blades move about the azimuth angle. That is, the upper and lower rotor blades are rotated and positioned on the axis of rotation A. RAs the rotor blades rotate about their respective axes, the pitch of each rotor blade changes from being pitched downward when rotated and positioned on the aft-facing side of the mast assembly 114 to being pitched upward when rotated and positioned on the forward-facing side of the mast assembly 114.

[0057] The upper swash plate assembly 148 and the lower swash plate assembly 162 are pitched in the same direction (e.g., downward along the forward-facing side of the mast assembly 114 in FIG. 8 and upward along the rearward-facing side of the mast assembly) to tilt the respective swash plate assemblies forward and pitch the upper rotor blades 178 and lower rotor blades 188 accordingly. Thus, the upper swash plate actuator 144 affecting the forward-facing side of the upper swash plate assembly 148 can be retracted to move the forward-facing side of the upper swash plate assembly 148 downward toward the mounting platform 196, and the upper swash plate actuator 144 affecting the rearward-facing side of the upper swash plate assembly 148 can be extended to move the rearward-facing side of the upper swash plate assembly 148 upward from the mounting platform 196. The lower swash plate actuator 146 affecting the forward facing side of the lower swash plate assembly 162 can be extended to move the forward facing side of the lower swash plate assembly 162 downwardly away from the mounting platform 196, and the lower swash plate actuator 146 affecting the aft facing side of the lower swash plate assembly 162 can be retracted to move the aft facing side of the lower swash plate assembly 162 upwardly towards the mounting platform 196. In FIG. 8 , the downward and upward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to FIG. 4 . As shown in the figure, the swash plate assemblies are uniformly tilted forward relative to the mast assembly (i.e., moved downward in a forward facing lateral direction along the mast assembly 114 and upward in aft facing lateral direction along the mast assembly) to allow for cyclical blade pitch.

[0058] As shown in FIG. 9 , to adjust the rotor blades from the default state shown in FIG. 4 to a left-tilted cyclical blade pitch, the upper rotor blade 178 and the lower rotor blade 188 are pitched downward when rotated and positioned on the third or left-facing side of the mast assembly 114 (where the left-facing side is shown in FIG. 9 ), and the upper rotor blade 178 and the lower rotor blade 188 are pitched upward when rotated and positioned on the fourth or right-facing side of the mast assembly 114 (where the right-facing side is not shown in FIG. 9 ). Thus, the pitch of the upper and lower rotor blades varies sinusoidally and periodically as the blades move about the azimuth angle. That is, the upper and lower rotor blades are rotated and positioned on the axis of rotation A. R , the pitch of each rotor blade changes from being pitched downward when rotated and positioned on the left-facing side of the mast assembly 114 to being pitched upward when rotated and positioned on the right-facing side of the mast assembly 114.

[0059] The upper swash plate assembly 148 and the lower swash plate assembly 162 are pitched in the same direction (e.g., downward along the left-facing side of the mast assembly 114 in FIG. 9 and upward along the right-facing side of the mast assembly) to tilt the respective swash plate assemblies leftward and pitch the upper and lower rotor blades 178, 188 accordingly. Thus, the upper swash plate actuator 144 affecting the left-facing side of the upper swash plate assembly 148 can be retracted to move the left-facing side of the upper swash plate assembly 148 downward toward the mounting platform 196, and the upper swash plate actuator 144 affecting the right-facing side of the upper swash plate assembly 148 can be extended to move the right-facing side of the upper swash plate assembly 148 upward from the mounting platform 196. The lower swash plate actuator 146 affecting the left facing side of the lower swash plate assembly 162 can be extended to move the left facing side of the lower swash plate assembly 162 downwardly away from the mounting platform 196, and the lower swash plate actuator 146 affecting the right facing side of the lower swash plate assembly 162 can be retracted to move the right facing side of the lower swash plate assembly 162 upwardly towards the mounting platform 196. As shown in the figures, the swash plate assembly is uniformly tilted leftward relative to the mast assembly (i.e., moved downwardly in a leftward direction along the mast assembly 114 and moved upwardly in a rightward direction along the mast assembly) to allow for circular blade pitch.

[0060] As shown in FIG. 10, to adjust the rotor blades from the default state shown in FIG. 4 to a cyclical blade pitch that is tilted backward or aft, the upper rotor blade 178 and the lower rotor blade 188 are pitched upward when rotated and positioned on the first or aft facing side of the mast assembly 114 (right side in FIG. 10), and the upper rotor blade 178 and the lower rotor blade 188 are pitched downward when rotated and positioned on the second or forward facing side of the mast assembly 114 (left side in FIG. 10). Thus, the pitch of the upper and lower rotor blades varies sinusoidally and periodically as the blades move about the azimuth angle. That is, the upper and lower rotor blades rotate in a cyclical manner that is tilted backward or aft from the default state shown in FIG. R , the pitch of each rotor blade changes from being pitched upward when rotated and positioned on the aft-facing side of the mast assembly 114 to being pitched downward when rotated and positioned on the forward-facing side of the mast assembly 114.

[0061] The upper swash plate assembly 148 and the lower swash plate assembly 162 are pitched in the same direction (e.g., in FIG. 10 , upward along the forward-facing side of the mast assembly 114 and downward along the aft-facing side of the mast assembly) to tilt the respective swash plate assemblies aft or aft and pitch the upper rotor blades 178 and lower rotor blades 188 accordingly. Thus, the upper swash plate actuator 144 affecting the aft- or aft-facing side of the upper swash plate assembly 148 can be retracted to move the aft- or aft-facing side of the upper swash plate assembly 148 downward toward the mounting platform 196, and the upper swash plate actuator 144 affecting the forward-facing side of the upper swash plate assembly 148 can be extended to move the forward-facing side of the upper swash plate assembly 148 upward from the mounting platform 196. The lower swash plate actuator 146 affecting the aft or aft facing side of the lower swash plate assembly 162 can be extended to move the aft or aft facing side of the lower swash plate assembly 162 downwardly away from the mounting platform 196, and the lower swash plate actuator 146 affecting the forward facing side of the lower swash plate assembly 162 can be retracted to move the forward facing side of the lower swash plate assembly 162 upwardly towards the mounting platform 196. In FIG. 10, the downward and upward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to FIG. 4. As shown in the figure, the swash plate assemblies are uniformly tilted aft or aft relative to the mast assembly (i.e., moved downward in the aft or aft direction along the mast assembly 114, and moved upward in the forward direction along the mast assembly) to allow for cyclical blade pitch.

[0062] When the rotor blades are adjusted from the default state shown in Figure 4 to the maximum positive differential collective position shown in Figure 11, the upper swash plate assembly 148 and the lower swash plate assembly 162 move in opposite directions along the mast assembly 114 to collectively pitch the upper rotor blades 178 upward and collectively pitch the lower rotor blades 188 downward. That is, the upper swash plate assembly 148 moves downward along the mast assembly 114 and the lower swash plate assembly 162 moves upward along the mast assembly 114 in Figure 11. Thus, the upper swash plate actuators 144 can be collectively retracted to move the upper swash plate assembly 148 downward toward the mounting platform 196 and the lower swash plate actuators 146 can collectively retract to move the lower swash plate assembly 162 upward toward the mounting platform 196. In Figure 11, the upward and downward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to Figure 4. As shown in the figure, the swash plate assemblies are uniformly moved along the mast assembly 114 toward each other and toward the mounting platform 196 to collectively pitch the upper rotor blades upward and collectively pitch the lower rotor blades downward.

[0063] When the rotor blades are adjusted from the default state shown in Figure 4 to the maximum negative differential collective position shown in Figure 12, the upper swash plate assembly 148 and the lower swash plate assembly 162 move in opposite directions along the mast assembly 114 to collectively pitch the upper rotor blades 178 down and collectively pitch the lower rotor blades 188 up. That is, the upper swash plate assembly 148 moves upward along the mast assembly 114 and the lower swash plate assembly 162 moves downward along the mast assembly 114 in Figure 12. Thus, the upper swash plate actuators 144 can be collectively extended to move the upper swash plate assembly 148 upward from the mounting platform 196 and the lower swash plate actuators 146 can collectively extended to move the lower swash plate assembly 162 downward from the mounting platform 196. In Figure 12, the upward and downward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to Figure 4. As shown, the swash plate assemblies move uniformly away from each other and away from the mounting platform 196 along the mast assembly 114 to collectively pitch the upper rotor blades downward and collectively pitch the lower rotor blades upward.

[0064] As shown in FIG. 13 , the control system 142 is also operable to adjust the rotor blades to various differential rotational positions where the pitch of the upper rotor blades 178 can differ from the pitch of the lower rotor blades 188 in both rotational phase and magnitude. For example, the upper swash plate assembly 148 can be tilted aft to enable a cycling blade pitch where the upper rotor blades 178 are pitched upward when rotationally positioned toward the aft- or aft-facing side of the mast assembly 114 and pitched down when rotationally disposed toward the forward-facing side of the mast assembly. Meanwhile, the lower swash plate assembly 162 can be tilted forward to enable a cycling blade pitch where the lower rotor blades 188 are tilted downward when rotationally positioned toward the aft- or aft-facing side of the mast assembly 114 and pitched upward when rotationally positioned toward the forward-facing side of the mast assembly. Thus, both the magnitude and phase of the cycling pitch can be adjusted for either rotor relative to one another. That is, the swash plates can be tilted in different directions. The phase between the upper rotor sinusoidal periodic pitch and the lower rotor sinusoidal periodic pitch varies around the azimuth angle and may be of different magnitudes.

[0065] Thus, to adjust the rotor blades from the default state shown in FIG. 4 to the differential cyclic blade pitch position shown in FIG. 13, the upper rotor blade 178 is pitched upward when rotated and positioned on the first or aft-facing side of the mast assembly 114 (right side in FIG. 13), and the upper rotor blade 178 is pitched downward when rotated and positioned on the second or forward-facing side of the mast assembly 114 (left side in FIG. 13). Meanwhile, the lower rotor blade 188 is pitched downward when rotated and positioned on the first or aft-facing side of the mast assembly 114, and the lower rotor blade 188 is pitched upward when rotated and positioned on the second or forward-facing side of the mast assembly 114. Thus, the pitch of the upper and lower rotor blades varies sinusoidally and periodically as the blades move around the azimuth angle and according to different phases. It should be understood that any variation of the differential cyclic blade pitch position may be possible. In other words, when the upper rotor blade 178 is rotated around the axis of rotation A, the upper rotor blade 178 is pitched upward. R When the lower rotor blades 188 rotate about the axis of rotation A, the pitch of the upper rotor blades 178 changes from being pitched upward when rotated and positioned on the aft-facing side of the mast assembly 114 to being pitched downward when rotated and positioned on the forward-facing side of the mast assembly 114. R As the lower rotor blades 188 rotate about their respective axes, the pitch of the lower rotor blades 188 changes from being pitched downward when rotated and positioned on the aft-facing side of the mast assembly 114 to being pitched upward when rotated and positioned on the forward-facing side of the mast assembly 114.

[0066] 13 , the upper swash plate assembly 148 and the lower swash plate assembly 162 are pitched in opposite directions to pitch the upper rotor blades 178 and the lower rotor blades 188 accordingly. Thus, the upper swash plate actuator 144 affecting the aft- or aft-facing side of the upper swash plate assembly 148 can be retracted to move the aft- or aft-facing side of the upper swash plate assembly 148 downward toward the mounting platform 196, and the upper swash plate actuator 144 affecting the forward-facing side of the upper swash plate assembly 148 can be extended to move the forward-facing side of the upper swash plate assembly 148 upward from the mounting platform 196. The lower swash plate actuator 146 affecting the aft or aft facing side of the lower swash plate assembly 162 can be retracted to move the aft or aft facing side of the lower swash plate assembly 162 upward toward the mounting platform 196, and the lower swash plate actuator 146 affecting the forward facing side of the lower swash plate assembly 162 can be extended to move the forward facing side of the lower swash plate assembly 162 downward from the mounting platform 196. In FIG. 13 , the downward and upward arrows represent the movement of the upper swash plate assembly 148 and the lower swash plate assembly 162 along the mast assembly 114, as compared to FIG. 4 .

[0067] Thus, the coaxial rotor system provides a location where non-rotating items can be easily attached between the rotors. For example, with a control system located between the upper and lower rotors, the pitch of the upper and lower rotor blades can be controlled independently of each other using separate upper and lower actuators, allowing the blades to be more precisely adjusted in flight. The stationary mast between the rotors also allows the use of any suitable type of actuator (e.g., electromechanical actuators, hydraulic actuators, electrohydraulic actuators, etc.), and the routing through the gearbox and three mast configuration allows the necessary wiring or hydraulic lines to be routed to power and control the actuators between the rotors. Optionally, the actuators may be electrohydraulic actuators and may include a local hydraulic reservoir, and electrical wiring may be routed along the mast assembly and through the gearbox.

[0068] Independent control of the upper and lower rotor blades allows for easy phase lag adjustments through flight control programming. Because each swash plate is independently controlled, the direction of the swash plate tilt angle can be adjusted electronically so that maximum blade pitch angle occurs at the correct azimuth position without requiring the fabrication of new hardware. Additionally, independent control of the upper and lower rotor blades allows for easy differential set application, since independent control of the swash plates allows the collective settings of each rotor to be set independently.

[0069] The upper and lower swash plates rotate only with the respective upper or lower rotor blades, thus reducing swash plate bearing weight, increasing swash plate bearing life, and also reducing swash plate assembly size and weight. Both swash plates rotate at the same speed as the respective upper or lower rotor blades, which is within the speed capability of the cross contact bearings, thus reducing the bearing count to one per swash plate. Thus, the weight and height of the swash plate assembly itself can be reduced, and the reduction in the overall height of the upper swash plate helps meet packaging constraints to fit both the upper and lower swash plates between the upper and lower rotor blades.

[0070] Additionally, locating the control system between the upper and lower rotor blades reduces the overall rotor system height. The rotor spacing may be determined by performance requirements and rotor blade deflection. In other words, the space between the rotors exists whether it is fully utilized or not. Because both the swash plate and all associated actuators and linkages are located between the rotors, the overall height of the rotor system above the aircraft is determined only by the desired rotor spacing and clearance between the rotor blades and the fuselage, and there are no additional linkages or actuators between the lower rotor and the gearbox or below the gearbox, resulting in a lower aircraft height. Additionally, the overall height of the rotor system within the fuselage is reduced, creating more space for other components to be located closer to the rotor centerline and / or allowing for increased cabin space.

[0071] Thus, a coaxial rotor system for a helicopter includes a central mast non-rotatably arranged on the helicopter, an inner mast arranged inside the central mast and rotatable about a rotation axis relative to the central mast in a first direction, and an outer mast arranged outside the central mast and rotatable about a rotation axis relative to the central mast in a second direction opposite to the first direction, the inner mast extending above an upper end of the central mast and the central mast extending above an upper end of the outer mast. An upper rotor blade is coupled to an upper portion of the inner mast and a lower rotor blade is coupled to the outer mast. The system is operable to independently adjust the pitch of the upper rotor blade and to adjust the pitch of the lower rotor blade.

[0072] For example, one aspect of the disclosure provides a coaxial rotor system for a helicopter. The coaxial rotor system includes a central mast non-rotatably disposed on a helicopter equipped with the coaxial rotor system. The central mast extends from the helicopter, and a rotation axis of the coaxial rotor system extends along a longitudinal axis of the central mast. The inner mast is disposed inside the central mast and is rotatable in a first direction about the rotation axis relative to the central mast. An upper portion of the inner mast extends above an upper end of the central mast. The outer mast is disposed outside the central mast and is rotatable in a second direction opposite to the first direction about the rotation axis relative to the central mast. The central mast extends above an upper end of the outer mast. An upper rotor blade assembly includes a plurality of upper rotor blades, and the upper rotor blade assembly is coupled to an upper portion of the inner mast. The plurality of upper rotor blades is rotatable in a first direction about the rotation axis via rotation of the inner mast. A lower rotor blade assembly includes a plurality of lower rotor blades, and the lower rotor blade assembly is coupled to the outer mast. The plurality of lower rotor blades are rotatable in a second direction about the axis of rotation via rotation of the outer mast. A control system is coupled to the central mast between the upper rotor blade assembly and the lower rotor blade assembly. The control system includes (i) an upper swash plate mechanically connected to the upper rotor blade assembly and (ii) a lower swash plate mechanically connected to the lower rotor blade assembly. The control system is operable to adjust the upper swash plate relative to the central mast to adjust the pitch of the plurality of upper rotor blades relative to the axis of rotation. The control system is operable to adjust the lower swash plate relative to the central mast to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation.

[0073] This aspect of the disclosure may include features of one or more of the following optional embodiments. In some embodiments, the upper swash plate and the lower swash plate each include (i) a non-rotatable ring disposed along the central mast and configured to be adjusted relative to the central mast when the control system operates to adjust the position and / or pitch of the respective swash plate to adjust the pitch of the respective rotor blades, and (ii) a rotating ring disposed rotatably along the central mast and connected to the respective rotor blade assemblies to adjust the pitch of the respective rotor blades when the position and / or pitch of the respective swash plate is adjusted. In further embodiments, the respective rotating rings of the upper swash plate and the lower swash plate rotate about a rotation axis in response to rotation of the corresponding upper or lower rotor blade assembly, and the respective rotating rings rotate at a rotation speed equal to the rotation speed of the corresponding plurality of upper or lower rotor blades. In other further embodiments, the respective rotating rings are rotatably attached to the respective non-rotating rings via respective cross-contact bearings. In yet another embodiment, the respective pitch links connect the respective rotating rings of the upper and lower swash plates to the respective upper and lower rotor blade assemblies. In yet another embodiment, the upper and lower swash plates are each disposed at a respective gimbal ball along the central mast. The respective non-rotating rings of the upper and lower swash plates translate together along the central mast and in conjunction with the respective gimbal balls when the control system operates to adjust the position of the respective swash plates. The respective non-rotating rings of the upper and lower swash plates pivot about their respective gimbal balls relative to the central mast when the control system operates to adjust the pitch of the respective swash plates.

[0074] In some embodiments, the control system includes at least one upper swash plate actuator operable to adjust the upper swash plate relative to the central mast to adjust the pitch of the plurality of upper rotor blades relative to the axis of rotation, and the control system includes at least one lower swash plate actuator operable to adjust the lower swash plate relative to the central mast to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation. In further embodiments, each upper swash plate actuator of the at least one upper swash plate actuator and each lower swash plate actuator of the at least one lower swash plate actuator are independently operable to adjust the pitch of a respective plurality of upper or lower rotor blades. In other further embodiments, the at least one upper swash plate actuator includes a plurality of upper swash plate actuators, and the at least one lower swash plate actuator includes a plurality of lower swash plate actuators. In yet further embodiments, the plurality of upper swash plate actuators includes three upper swash plate actuators, and the plurality of lower swash plate actuators includes three lower swash plate actuators. In other further embodiments, the upper swash plate actuators are independently operable to adjust the plane of the upper swash plate relative to the longitudinal axis of the central mast, and the lower swash plate actuators are independently operable to adjust the plane of the lower swash plate relative to the longitudinal axis of the central mast. In other further embodiments, at least one upper swash plate actuator and at least one lower swash plate actuator are coupled to the central mast between the top end of the central mast and the top end of the outer mast. In some still other further embodiments, a fairing is coupled to the central mast above the outer mast to cover at least a portion of the control system for protection and aerodynamic drag reduction purposes.In some other yet further embodiments, the at least one upper swash plate actuator and the at least one lower swash plate actuator each include an electric actuator. In still further embodiments, wiring for the electric actuators is routed from the helicopter's power source along the central mast to the respective upper and lower swash plate actuators without damaging or colliding with the rotating components and systems. The wiring may pass through a gearbox of the coaxial rotor system. Optionally, the electric actuator includes an electromechanical actuator. Optionally, the at least one upper swash plate actuator and the at least one lower swash plate actuator each include a hydraulic actuator.

[0075] In some examples, the control system is coupled to the central mast between a top end of the central mast and a top end of the outer masts. Optionally, the outer masts circumscribe at least a portion of the central mast.

[0076] Another aspect of the disclosure provides a coaxial rotor system for a helicopter including a gearbox disposed on the helicopter and a mast assembly extending from the gearbox. The gearbox is operable to provide rotation of at least a portion of the mast assembly about an axis of rotation of the coaxial rotor system. The mast assembly includes a lower portion rotating in a first direction about the axis of rotation, an upper portion extending above the lower portion and rotating about the axis of rotation in a second direction opposite the first direction, and a central portion extending between the lower portion and the upper portion and not rotatable relative to the gearbox. A plurality of lower rotor blades are rotatable in a first direction via rotation of the lower portion of the mast assembly. A plurality of upper rotor blades are rotatable in a second direction via rotation of the upper portion of the mast assembly. The system is operable to adjust the pitch of the plurality of lower rotor blades and adjust the pitch of the upper rotor blades independently of one another.

[0077] In some examples, the coaxial rotor system includes a gearbox disposed on a helicopter equipped with the coaxial rotor system. The coaxial rotor system includes a mast assembly. The mast assembly extends from the gearbox when disposed on the helicopter, and a rotation axis of the coaxial rotor system extends along a longitudinal axis of the mast assembly. At least a portion of the mast assembly is rotatably coupled to the gearbox, and the gearbox is operable to provide rotation of at least a portion of the mast assembly about the rotation axis. The mast assembly includes: (i) a lower portion extending from and rotatably coupled to the gearbox when the mast assembly is disposed on the helicopter; (ii) an upper portion extending above the first portion and rotatably coupled to the gearbox when the mast assembly is disposed on the helicopter; and (iii) a middle portion extending between the lower portion and the upper portion and not rotatable relative to the gearbox when the mast assembly is disposed on the helicopter. The lower portion of the mast assembly rotates in a first direction about the rotation axis when the gearbox is operated to provide rotation of the lower portion. The upper part of the mast assembly rotates in a second direction about the axis of rotation when the gearbox operates to impart rotation of the upper part, the second direction being opposite to the first direction. The lower rotor blade assembly includes a plurality of lower rotor blades, the lower rotor blade assembly coupled to the lower part of the mast assembly. The plurality of lower rotor blades are rotatable in a first direction about the axis of rotation via rotation of the lower part of the mast assembly. The upper rotor blade assembly includes a plurality of upper rotor blades, the upper rotor blade assembly coupled to the upper part of the mast assembly. The plurality of upper rotor blades are rotatable in a second direction about the axis of rotation via rotation of the upper part of the mast assembly. A control system is coupled to a central part of the mast assembly between the lower rotor blade assembly and the upper rotor blade assembly. The control system includes (i) a lower swash plate mechanically connected to the lower rotor blade assembly, and (ii) an upper swash plate mechanically connected to the upper rotor blade assembly.The control system is operable to adjust the lower swash plate relative to a central portion of the mast assembly to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation. The control system is operable to adjust the upper swash plate relative to a central portion of the mast assembly to adjust the pitch of the plurality of upper rotor blades relative to the axis of rotation.

[0078] This aspect of the disclosure may include features of one or more of the following optional embodiments: In some embodiments, a central portion of the mast assembly extends from the gearbox, a lower portion of the mast assembly extends along and is disposed outside of the central portion of the mast assembly, and the central portion of the mast assembly extends above an upper end of the lower portion of the mast assembly.

[0079] In some examples, the top of the mast assembly extends along and is disposed inside the central portion of the mast assembly, and the upper end of the top of the mast assembly extends above the upper end of the central portion of the mast assembly.

[0080] In some embodiments, the upper swash plate and the lower swash plate each include (i) a non-rotating ring non-rotatably disposed along a central portion of the mast assembly and configured to be adjusted relative to the central portion of the mast assembly when the control system operates to adjust the position and / or pitch of the respective swash plate to adjust the pitch of the respective rotor blades, and (ii) a rotating ring rotatably disposed along a central portion of the mast assembly and connected to the respective rotor blade assemblies to adjust the pitch of the respective rotor blades when the position and / or pitch of the respective swash plate is adjusted. In further embodiments, the respective rotating rings of the upper swash plate and the lower swash plate rotate about a rotation axis in response to a rotation of the corresponding upper or lower portion of the mast assembly, and the respective rotating rings rotate at a rotation speed equal to the rotation speed of the corresponding upper or lower portion of the mast assembly. In other further embodiments, the respective rotating rings are rotatably attached to the respective non-rotating rings via respective cross-contact bearings. In other further embodiments, respective pitch links connect the respective rotating rings of the upper and lower swash plates to the respective upper and lower rotor blade assemblies. In yet another further embodiment, the upper and lower swash plates are each disposed at a respective gimbal ball along a central portion of the mast assembly, the respective anti-rotating rings of the upper and lower swash plates translate together along the central portion of the mast assembly and in conjunction with the respective gimbal balls when the control system operates to adjust the position of the respective swash plates, and the respective anti-rotating rings of the upper and lower swash plates pivot about the respective gimbal balls relative to the central portion of the mast assembly when the control system operates to adjust the pitch of the respective swash plates.

[0081] In some embodiments, the control system includes at least one upper swash plate actuator operable to adjust the upper swash plate relative to a central portion of the mast assembly to adjust the pitch of the plurality of upper rotor blades relative to the axis of rotation, and the control system includes at least one lower swash plate actuator operable to adjust the lower swash plate relative to a central portion of the mast assembly to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation. In further embodiments, each upper swash plate actuator of the at least one upper swash plate actuator and each lower swash plate actuator of the at least one lower swash plate actuator are independently operable to adjust the pitch of a respective plurality of upper or lower rotor blades. In other further embodiments, the at least one upper swash plate actuator includes a plurality of upper swash plate actuators, and the at least one lower swash plate actuator includes a plurality of lower swash plate actuators. In yet further embodiments, the plurality of upper swash plate actuators includes three upper swash plate actuators, and the plurality of lower swash plate actuators includes three lower swash plate actuators. In yet another embodiment, the upper swash plate actuators are independently operable to adjust the plane of the upper swash plate relative to a longitudinal axis of the mast assembly, and the lower swash plate actuators are independently operable to adjust the plane of the lower swash plate relative to a longitudinal axis of the mast assembly. In yet another embodiment, the at least one upper swash plate actuator and the at least one lower swash plate actuator are coupled to the central portion of the mast assembly between an upper end of the central portion of the mast assembly and an upper end of the lower portion of the mast assembly. In yet another embodiment, a fairing is coupled to the central portion of the mast assembly above the lower portion of the mast assembly to cover at least a portion of the control system for protection and aerodynamic drag reduction purposes.In yet another yet further embodiment, the at least one upper swash plate actuator and the at least one lower swash plate actuator each include an electric actuator. In yet a further embodiment, wiring for the electric actuators is routed from the helicopter's power source along a central portion of the mast assembly to the respective upper and lower swash plate actuators without damaging or colliding with the rotating components and systems. Optionally, the wiring passes through a gearbox. Optionally, the electric actuator includes an electromechanical actuator. Optionally, the at least one upper swash plate actuator and the at least one lower swash plate actuator each include a hydraulic actuator.

[0082] Optionally, the control system is coupled to the central section of the mast assembly between an upper end of the central section and an upper end of the lower section of the mast assembly. Optionally, at least a portion of the upper section of the mast assembly is disposed along an inner cavity of the central section of the mast assembly. Optionally, the inner section of the mast assembly circumscribes at least a portion of the central section of the mast assembly.

[0083] Variations and modifications of the specifically described embodiments can be made without departing from the principles of the invention, which are intended to be limited only by the scope of the appended claims, as interpreted under the principles of patent law.

Claims

1. 1. A coaxial rotor system for a helicopter, comprising: a central mast arranged non-rotatably on a helicopter equipped with the coaxial rotor system, the central mast extending from the helicopter, the rotation axis of the coaxial rotor system extending along a longitudinal axis of the central mast; an inner mast disposed inside the central mast and rotatable relative to the central mast about the axis of rotation in a first direction, an upper portion of the inner mast extending above an upper end of the central mast; an outer mast disposed outside the central mast and rotatable relative to the central mast about the axis of rotation in a second direction opposite to the first direction, the outer mast extending above an upper end of the outer mast; an upper rotor blade assembly comprising a plurality of upper rotor blades, the upper rotor blade assembly being coupled to the upper portion of the inner mast, the plurality of upper rotor blades being rotatable in the first direction about the axis of rotation via rotation of the inner mast; a lower rotor blade assembly comprising a plurality of lower rotor blades, the lower rotor blade assembly coupled to the outer mast, the plurality of lower rotor blades being rotatable in the second direction about the axis of rotation via rotation of the outer mast; a control system coupled to the central mast between the upper rotor blade assembly and the lower rotor blade assembly, the control system comprising: (i) an upper swash plate mechanically connected to the upper rotor blade assembly; and (ii) a lower swash plate mechanically connected to the lower rotor blade assembly; the control system is operable to adjust the upper swash plate relative to the central mast to adjust the pitch of the upper rotor blades relative to the axis of rotation; a control system operable to adjust the lower swash plate relative to the central mast to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation.

2. 2. The coaxial rotor system of claim 1, wherein the upper swash plate and the lower swash plate each comprise: (i) a non-rotating ring non-rotatably disposed along the central mast and configured to be adjusted relative to the central mast when the control system operates to adjust a position and / or pitch of each of the swash plates to adjust the pitch of each of the rotor blades; and (ii) a rotating ring rotatably disposed along the central mast and connected to a respective one of the rotor blade assemblies to adjust the pitch of each of the rotor blades when the position and / or pitch of each of the swash plates is adjusted.

3. 3. The coaxial rotor system of claim 2, wherein the rotating ring of each of the upper swash plate and the lower swash plate rotates about the axis of rotation in response to rotation of the corresponding upper or lower rotor blade assembly, and each rotating ring rotates at a rotational speed equal to a rotational speed of the corresponding plurality of upper or lower rotor blades.

4. The coaxial rotor system of claim 2 , wherein each said rotating ring is rotatably mounted to a respective said non-rotating ring via a respective cross-contact bearing.

5. The coaxial rotor system of claim 2 , wherein a respective pitch link connects the rotating ring of each of the upper and lower swash plates to the respective upper and lower rotor blade assemblies.

6. 3. The coaxial rotor system of claim 2, wherein the upper and lower swash plates are each disposed at a respective gimbal ball along the central mast, the non-rotating rings of the upper and lower swash plates translate together along the central mast and in conjunction with the respective gimbal balls when the control system operates to adjust a position of the respective swash plates, and the non-rotating rings of the upper and lower swash plates pivot about the respective gimbal balls relative to the central mast when the control system operates to adjust a pitch of the respective swash plates.

7. 2. The coaxial rotor system of claim 1, wherein the control system includes at least one upper swash plate actuator operable to adjust the upper swash plate relative to the central mast to adjust the pitch of the upper rotor blades relative to the axis of rotation, and wherein the control system includes at least one lower swash plate actuator operable to adjust the lower swash plate relative to the central mast to adjust the pitch of the lower rotor blades relative to the axis of rotation.

8. 8. The coaxial rotor system of claim 7, wherein each upper swash plate actuator of the at least one upper swash plate actuator and each lower swash plate actuator of the at least one lower swash plate actuator are independently operable to adjust the pitch of a respective one of the plurality of upper or lower rotor blades.

9. The coaxial rotor system of claim 7 , wherein the at least one upper swash plate actuator comprises a plurality of upper swash plate actuators and the at least one lower swash plate actuator comprises a plurality of lower swash plate actuators.

10. The coaxial rotor system of claim 9 , wherein the plurality of upper swash plate actuators includes three upper swash plate actuators and the plurality of lower swash plate actuators includes three lower swash plate actuators.

11. 10. The coaxial rotor system of claim 9, wherein the plurality of upper swashplate actuators are independently operable to adjust a plane of the upper swashplate relative to the longitudinal axis of the central mast, and the plurality of lower swashplate actuators are independently operable to adjust a plane of the lower swashplate relative to the longitudinal axis of the central mast.

12. 8. The coaxial rotor system of claim 7, wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator are coupled to the central mast between the upper end of the central mast and the upper ends of the outer masts.

13. 13. The coaxial rotor system of claim 12, wherein a fairing is coupled to the central mast above the outer masts to cover at least a portion of the control system for protection and aerodynamic drag reduction purposes.

14. The coaxial rotor system of claim 12 , wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator each comprise an electrically powered actuator.

15. 15. The coaxial rotor system of claim 14, wherein wiring for the electric actuators is routed from the helicopter power source, along the central mast, to the respective upper and lower swash plate actuators without damaging or striking the rotating components and systems.

16. The coaxial rotor system of claim 15 , wherein the wiring passes through a gearbox of the coaxial rotor system.

17. The coaxial rotor system of claim 15 , wherein the electrically powered actuator comprises an electromechanical actuator.

18. The coaxial rotor system of claim 12 , wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator each comprise a hydraulic actuator.

19. 2. The coaxial rotor system of claim 1, wherein the control system is coupled to the central mast between the upper end of the central mast and the upper ends of the outer masts.

20. The coaxial rotor system of claim 1 , wherein at least a portion of the inner mast is disposed along an inner cavity of the central mast.

21. The coaxial rotor system of claim 1 , wherein the outer masts circumscribe at least a portion of the central mast.

22. 1. A coaxial rotor system for a helicopter, comprising: a gearbox disposed in a helicopter equipped with the coaxial rotor system; a mast assembly, when installed on the helicopter, extending from the gearbox, wherein an axis of rotation of the coaxial rotor system extends along a longitudinal axis of the mast assembly; at least a portion of the mast assembly is rotatably coupled to the gearbox, the gearbox operable to impart rotation of at least the portion of the mast assembly about the axis of rotation; the mast assembly comprises: (i) a lower portion extending from and rotatably coupled to the gearbox when the mast assembly is disposed on the helicopter; (ii) an upper portion extending above the lower portion and rotatably coupled to the gearbox when the mast assembly is disposed on the helicopter; and (iii) a central portion extending between the lower portion and the upper portion and not rotatable relative to the gearbox when the mast assembly is disposed on the helicopter; the lower portion of the mast assembly rotates in a first direction about the axis of rotation when the gearbox is operated to impart rotation to the lower portion; a mast assembly, wherein the upper portion of the mast assembly rotates about the axis of rotation in a second direction when the gearbox is operated to impart rotation of the upper portion, the second direction being opposite to the first direction; a lower rotor blade assembly comprising a plurality of lower rotor blades, the lower rotor blade assembly coupled to the lower portion of the mast assembly, the plurality of lower rotor blades rotatable in the first direction about the axis of rotation via rotation of the lower portion of the mast assembly; an upper rotor blade assembly including a plurality of upper rotor blades, the upper rotor blade assembly coupled to the upper portion of the mast assembly, the plurality of upper rotor blades being rotatable in the second direction about the axis of rotation via rotation of the upper portion of the mast assembly; a control system coupled to the central portion of the mast assembly between the lower rotor blade assembly and the upper rotor blade assembly, the control system comprising: (i) a lower swash plate mechanically connected to the lower rotor blade assembly; and (ii) an upper swash plate mechanically connected to the upper rotor blade assembly; the control system is operable to adjust the lower swash plate relative to the central portion of the mast assembly to adjust the pitch of the plurality of lower rotor blades relative to the axis of rotation; the control system is operable to adjust the upper swash plate relative to the central portion of the mast assembly to adjust the pitch of the upper rotor blades relative to the axis of rotation.

23. 23. The coaxial rotor system of claim 22, wherein the central portion of the mast assembly extends from the gearbox, and the lower portion of the mast assembly extends along and is disposed outwardly of the central portion of the mast assembly, and the central portion of the mast assembly extends above an upper end of the lower portion of the mast assembly.

24. 23. The coaxial rotor system of claim 22, wherein the upper portion of the mast assembly extends along and is disposed inwardly of the central portion of the mast assembly, and an upper end of the upper portion of the mast assembly extends above an upper end of the central portion of the mast assembly.

25. 23. The coaxial rotor system of claim 22, wherein the upper swash plate and the lower swash plate each comprise: (i) a non-rotating ring non-rotatably disposed along the central portion of the mast assembly and configured to be adjusted relative to the central portion of the mast assembly when the control system operates to adjust a position and / or pitch of each of the swash plates to adjust the pitch of each of the rotor blades; and (ii) a rotating ring rotatably disposed along the central portion of the mast assembly and connected to each of the rotor blade assemblies to adjust the pitch of each of the rotor blades when the position and / or pitch of each of the swash plates is adjusted.

26. 26. The coaxial rotor system of claim 25, wherein the rotating rings of each of the upper and lower swash plates rotate about the axis of rotation in response to a rotation of the corresponding upper or lower portion of the mast assembly, each rotating ring rotating at a rotational speed equal to a rotational speed of the corresponding upper or lower portion of the mast assembly.

27. 26. The coaxial rotor system of claim 25, wherein each said rotating ring is rotatably mounted to a respective said non-rotating ring via a respective cross-contact bearing.

28. 26. The coaxial rotor system of claim 25, wherein a respective pitch link connects the rotating ring of each of the upper and lower swash plates to the respective upper and lower rotor blade assemblies.

29. 26. The coaxial rotor system of claim 25, wherein the upper and lower swash plates are each disposed at a respective gimbal ball along the central portion of the mast assembly, the anti-rotating rings of the upper and lower swash plates translate together along the central portion of the mast assembly and in conjunction with the respective gimbal balls when the control system operates to adjust a position of the respective swash plates, and the anti-rotating rings of the upper and lower swash plates pivot about the respective gimbal balls relative to the central portion of the mast assembly when the control system operates to adjust a pitch of the respective swash plates.

30. 23. The coaxial rotor system of claim 22, wherein the control system includes at least one upper swash plate actuator operable to adjust the upper swash plate relative to the central portion of the mast assembly to adjust the pitch of the upper rotor blades relative to the axis of rotation, and wherein the control system includes at least one lower swash plate actuator operable to adjust the lower swash plate relative to the central portion of the mast assembly to adjust the pitch of the lower rotor blades relative to the axis of rotation.

31. 31. The coaxial rotor system of claim 30, wherein each upper swash plate actuator of the at least one upper swash plate actuator and each lower swash plate actuator of the at least one lower swash plate actuator are independently operable to adjust the pitch of a respective one of the plurality of upper or lower rotor blades.

32. 31. The coaxial rotor system of claim 30, wherein the at least one upper swash plate actuator comprises a plurality of upper swash plate actuators and the at least one lower swash plate actuator comprises a plurality of lower swash plate actuators.

33. 33. The coaxial rotor system of claim 32, wherein the plurality of upper swash plate actuators includes three upper swash plate actuators and the plurality of lower swash plate actuators includes three lower swash plate actuators.

34. 33. The coaxial rotor system of claim 32, wherein the plurality of upper swash plate actuators are independently operable to adjust a plane of the upper swash plate relative to the longitudinal axis of the mast assembly, and the plurality of lower swash plate actuators are independently operable to adjust a plane of the lower swash plate relative to the longitudinal axis of the mast assembly.

35. 31. The coaxial rotor system of claim 30, wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator are coupled to the central portion of the mast assembly between an upper end of the central portion of the mast assembly and an upper end of the lower portion of the mast assembly.

36. 36. The coaxial rotor system of claim 35, wherein a fairing is coupled to the central portion of the mast assembly above the lower portion of the mast assembly to cover at least a portion of the control system for protection and aerodynamic drag reduction purposes.

37. 36. The coaxial rotor system of claim 35, wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator each comprise an electrically powered actuator.

38. 38. The coaxial rotor system of claim 37, wherein wiring for the electric actuators is routed from the helicopter power source, along the central portion of the mast assembly, to the respective upper and lower swash plate actuators without damaging or striking the rotating components and systems.

39. 39. The coaxial rotor system of claim 38, wherein the wiring passes through the gearbox.

40. The coaxial rotor system of claim 37 , wherein the electrically powered actuator comprises an electromechanical actuator.

41. 36. The coaxial rotor system of claim 35, wherein the at least one upper swash plate actuator and the at least one lower swash plate actuator each comprise a hydraulic actuator.

42. 23. The coaxial rotor system of claim 22, wherein the control system is coupled to the central portion of the mast assembly between an upper end of the central portion of the mast assembly and an upper end of the lower portion of the mast assembly.

43. 23. The coaxial rotor system of claim 22, wherein at least a portion of the upper portion of the mast assembly is disposed along an inner cavity of the central portion of the mast assembly.

44. 23. The coaxial rotor system of claim 22, wherein the inner portion of the mast assembly circumscribes at least a portion of the central portion of the mast assembly.

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