Patent Application
20180305006
The present disclosure relates to a rotary-wing aircraft, and more particularly, a pitch bearing assembly for a rotor system of a rotary-wing aircraft.
Compound helicopters generally include a main rotor assembly with coaxial, counter-rotating main rotors and a propulsor. The main rotor assembly is disposed at an upper portion of the helicopter airframe and the propulsor is disposed at a tail of the helicopter. The main rotor assembly generates lift, thrust and yaw control while the propulsor generally assists with generation of thrust for forward flight. Pitch change of rotor blades may be accommodated by an elastomeric bearing. But for large pitch ranges where elastomeric bearings would exceed packaging constraints, such as for a propulsor, inboard and outboard pitch change bearings can be employed.
While such arrangements have generally satisfied the requirements for traditional rotor systems, the art would be receptive to improved methods and systems for rotor systems.
According to an embodiment, a pitch bearing assembly includes an inboard pitch bearing including an inner race and an outer race, the outer race including a radially outwardly protruding tab, and an outboard end of the inboard pitch bearing including a plurality of rotation transmitting features. An outboard pitch bearing of the pitch bearing assembly includes an inner race and an outer race, an inboard end of the outer race of the outboard pitch bearing including a plurality of rotation transmitting features. A coupler of the pitch bearing assembly has an inboard end and an outboard end, the inboard end of the coupler having a plurality of rotation transmitting features engageable with the rotation transmitting features of the inboard pitch bearing, the outboard end of the coupler having a plurality of rotation transmitting features engageable with the rotation transmitting features of the outboard pitch bearing.
In addition to one or more of the features described above, or as an alternative, in further embodiments the rotation transmitting features of the inboard end and outboard end of the coupler and the rotation transmitting features of the outer races of the inboard and outboard pitch bearings include castellations.
In addition to one or more of the features described above, or as an alternative, in further embodiments the outer race of the outboard pitch bearing does not include a radially outwardly protruding tab.
In addition to one or more of the features described above, or as an alternative, in further embodiments the pitch bearing assembly is disposable between a hub arm and a rotor blade of a rotor system, the inner races are rotationally fixable to the hub arm, and the outer races are rotationally fixable to the rotor blade.
According to an embodiment, a rotor system includes a hub arm, a blade extending in a longitudinal direction over the hub arm; and, a pitch bearing assembly disposed between the hub arm and the blade, the pitch bearing assembly including an interior portion rotationally locked to the hub arm, an exterior portion rotationally locked to the blade, the exterior portion rotatably movable with respect to the interior portion; wherein the blade is axially translatable in the longitudinal direction with respect to the pitch bearing assembly.
In addition to one or more of the features described above, or as an alternative, in further embodiments the pitch bearing assembly includes an inboard pitch bearing having an outer race at the exterior portion of the pitch bearing assembly; an outboard pitch bearing having an outer race; and, a coupler rotationally fixing the outer race of the outboard pitch bearing to the outer race of the inboard pitch bearing.
In addition to one or more of the features described above, or as an alternative, in further embodiments the outer race of the inboard pitch bearing is rotationally fixed to the blade.
In addition to one or more of the features described above, or as an alternative, in further embodiments the blade includes a tab-receiving area and the outer race of the inboard pitch bearing includes a radially protruding tab seated with the tab-receiving area, the tab rotationally fixing the outer race of the inboard pitch bearing to the blade, and the tab-receiving area permitting axial translation of the blade relative to the pitch bearing assembly.
In addition to one or more of the features described above, or as an alternative, in further embodiments the tab-receiving area is a notch that extends from an inboard end of the blade.
In addition to one or more of the features described above, or as an alternative, in further embodiments the coupler includes an inboard end having a rotation transmitting feature in engagement with a rotation transmitting feature on the outer race of the inboard pitch bearing, and an outboard end having a rotation transmitting feature in engagement with a rotation transmitting feature on the outer race of the outboard pitch bearing.
In addition to one or more of the features described above, or as an alternative, in further embodiments the rotation transmitting features of the inboard end and outboard end of the coupler and the rotation transmitting features of the outer races of the inboard and outboard pitch bearings include castellations.
In addition to one or more of the features described above, or as an alternative, in further embodiments the pitch bearing assembly further includes an inspection path that extends from an exterior of the coupler to an interior of the coupler, the inspection path permitting inspection of at least one of the inboard pitch bearing and the outboard pitch bearing through the coupler.
In addition to one or more of the features described above, or as an alternative, in further embodiments the coupler includes an aperture providing the inspection path.
In addition to one or more of the features described above, or as an alternative, in further embodiments the coupler includes castellations engageable with castellations on the inboard and outboard pitch bearings, and a longitudinal gap is disposed between at least one of the castellations and one of the coupler, the inboard pitch bearing, and the outboard pitch bearing to provide the inspection path.
In addition to one or more of the features described above, or as an alternative, in further embodiments the inboard pitch bearing includes a spherical bearing and the outboard pitch bearing includes a cylindrical bearing.
In addition to one or more of the features described above, or as an alternative, in further embodiments the rotor system further includes a tension torsion strap disposed within the hub arm, the blade axially translatable with the tension torsion strap due to centrifugal force.
In addition to one or more of the features described above, or as an alternative, in further embodiments a method of inspecting the rotor system, where the pitch bearing assembly of the rotor system includes an inboard pitch bearing and an outboard pitch bearing rotationally fixed by a coupler, includes: after the pitch bearing assembly is assembled on the hub arm, employing an inspection path that extends from an exterior of the coupler to an interior of the coupler and at least one of an inboard side of the outboard pitch bearing and an outboard side of the inboard pitch bearing; and inspecting a seal of at least one of the outboard pitch bearing and the inboard pitch bearing using the inspection path.
According to an embodiment, a rotary-wing aircraft includes an airframe; a rotor extending from the airframe and defining an axis of rotation; a rotor hub surrounding the rotor, the rotor hub having a plurality of hub arms; a plurality of rotor blades respectively engaged with the plurality of hub arms; and, each blade extending in a longitudinal direction over a respective hub arm; and, a pitch bearing assembly disposed between each hub arm and rotor blade, each pitch bearing assembly including an interior portion rotationally fixed to the hub arm and an exterior portion rotationally fixed to the blade, the exterior portion rotatably movable with respect to the interior portion; wherein the plurality of rotor blades is axially translatable in the longitudinal direction with respect to each pitch bearing assembly.
In addition to one or more of the features described above, or as an alternative, in further embodiments the pitch bearing assembly includes: an inboard pitch bearing having an outer race; an outboard pitch bearing having an outer race; and, a coupler rotationally fixing the outboard pitch bearing to the inboard pitch bearing.
In addition to one or more of the features described above, or as an alternative, in further embodiments the rotary-wing aircraft further includes a tension torsion strap disposed within the hub arm, the blade axially translatable with the tension torsion strap due to centrifugal force.
The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. However, it should be understood that the following description and drawings are intended to be exemplary in nature and non-limiting.
Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiments. The drawings that accompany the detailed description can be briefly described as follows:
As will be further described below, embodiments of a rotor system include a blade held to a rotor hub by means of a tension torsion strap and supported by a plurality of roller element pitch bearings. The blade is allowed to translate axially as the centrifugal forces increase with rotor speed while the radial position of the pitch bearing outer races is held constant with respect to blade. A tabbed feature on the outer race of the inboard pitch bearing at the inboard end of the blade nests in an open slot in the inboard end of the blade to link them together. The tab and notch feature constrain the outer race of the inboard pitch bearing to the blade in the radial direction while allowing axial translation of the blade relative to the outer race. The outer races of the outer pitch bearings inside the blade further outboard of the inboard pitch bearing also need to be constrained in the radial direction so the outboard pitch bearings are linked to the tabbed outer race of the inboard pitch bearing by way of a coupler with castellations which is designed to mate up with castellations on the outer races of both inboard and outboard pitch bearings.
In accordance with an exemplary embodiment, upper rotor assembly 22 includes a first plurality of rotor blades 15 supported by a first or upper rotor hub 20. Lower rotor assembly 24 includes a second plurality of rotor blades 16 supported by a second, or lower rotor hub 21. Each of the upper rotor blades 15 and each of the lower rotor blades 16 can be pivoted about a respective longitudinal axis thereof by way of collective and cyclic commands to execute flight control (e.g., lift, pitch, roll and yaw control) of the aircraft 10. In some embodiments, aircraft 10 may include a translational thrust system or propulsor 26 having a rotor system 100 located at extending tail 13 to provide translational thrust (forward or rearward) for aircraft 10. Rotor system 100 includes a plurality of blades 104 extending from rotor hub 101.
Although a particular aircraft configuration is illustrated in this non-limiting embodiment, other rotary wing aircraft may also benefit from embodiments of the invention. Although the dual rotor system is depicted as coaxial, other embodiments may include dual rotor aircraft having non-coaxial rotors. Further, while a particular aircraft configuration is illustrated in this non-limiting embodiment, other rotary wing aircraft will also benefit from embodiments of the invention. Moreover, aspects may be used in non-rotary wing aircraft, including fixed wing aircraft and tilt wing aircraft using rotor blades and/or propellers, and may be used in maritime propulsion systems, wind turbines and the like.
Propulsor 26, may be connected to, and rotatably driven by, an engine via a gearbox. Rotor system 100 may be mounted to the tail 13 with a translational thrust axis T, oriented substantially horizontal and parallel to a longitudinal axis of the aircraft 10 (including tail 13), to provide thrust for high-speed flight. The term “parallel” should be understood to include a translational thrust axis that is coincident with the longitudinal axis. While the propulsor rotational axis T is shown generally in parallel with a longitudinal axis of the tail portion 13, it is understood that the axis T can also be non-parallel with the longitudinal axis of the tail portion 13 in other aspects. Translational thrust axis T corresponds to the axis of rotation of rotor system 100, and corresponds to a longitudinal axis of a rotor shaft of the rotor system 100. While shown in the context of a pusher-prop configuration, it is understood that the rotor system 100 could also be a more conventional puller prop or could be variably facing so as to provide yaw control in addition to, or instead of, translational thrust. It should be further understood that any such system or other translational thrust systems may alternatively or additionally be utilized.
In accordance with an aspect of an exemplary embodiment, rotor system 100 may include propeller blades 104 having a variable pitch. More specifically, the pitch of propeller blades 104 may be altered with respect to the rotor hub 101, such as to change the direction of thrust (e.g., forward or rearward). Each of the rotor blades 104 can be pivoted about a respective longitudinal axis 128 (see
With further reference to
The rotor system 100 includes, in part, a rotor shaft and a rotor hub 101 (
The TT strap 110 restrains the centrifugal forces of the blade 104 as it rotates about the propulsor rotational axis T and roller pitch bearings 106, 108 to restrain blade bending moments. The TT strap 110 may be fixedly attached to the blade 104 at a location outboard of the hub arm 102, such as by using a fastener (not shown) that passes through an opening in a coupling 111 (
In an embodiment, the inboard and outboard pitch bearings 106, 108 are angular contact bearings respectively inserted over each hub arm 102 such that an interior portion of the pitch bearing assembly 105 is rotationally fixed to the hub arm 102. The blade 104 is inserted over the outer races 122, 124 of the pitch bearings 106, 108 such that an exterior portion of the pitch bearing assembly 105 is rotationally fixed to the blade 104. Also, outer surfaces of the outer races 122, 124 and an inner surface of the blade 104 are frictionally engaged. In an embodiment where the pitch bearings 106, 108 are angular contact bearings, centrifugal force maintains the bearings 106, 108 at proper working condition. Due to the inboard and outboard pitch bearings 106, 108, the rotor system 100 is able to accommodate a large range of pitch motion, such as may be required in prop rotors, however other rotor systems, such as, but not limited to a main rotor system or other propellers may incorporate the pitch bearing assembly 105. The bearings 106, 108 are pressed over the hub arm 102 and fixed longitudinally with respect to the hub arm 102. A liner 126 may be pressed between the bearing 106 and the hub arm 102. The inner races of the pitch bearings 106, 108 do not move axially with the blade 104 during axial translation of the blade 104 when the blades 104 move axially in direction 120 due to centrifugal force. The outer races 122, 124 of the pitch bearings 106, 108 rotate with the blade 104 radially about the hub arm 102. Thus, the blade 104 is able to pitch relative to the hub arm 102. In other words, the blade 104 may partially rotate about the axis 128, in either rotational direction 130 (
Each pitch bearing 106, 108 includes a plurality of roller elements 132 radially dispersed about the pitch bearing 106, 108 between an inner race 134, 136 and the outer race 122, 124. Each pitch bearing 106, 108 further includes an inboard seal 138 and an outboard seal 140 on the respective longitudinal ends of the pitch bearings 106, 108. The bearings 106, 108 are pre-greased so the seals 138, 140 hold grease within the bearings 106, 108 under the extremely high centrifugal forces they experience when the rotor system 100 is spinning. The pitch bearings 106, 108 may further include an inboard retaining ring 142 and an outboard retaining ring 144 on respective outer sides of the seals 138, 140. The outboard retaining ring 144 is there to arrest any centrifugal force trying to push the outboard seal 140 out and the inboard retaining ring 142 assists in locating and securing the inboard seal 138 during installation. In one embodiment, due to loads experienced during rotation such as bending loads that transmit through the blade 104, the inboard pitch bearing 106 may be a spherical bearing as shown, and thus includes two roller elements 132 within a longitudinal dimension of the inboard pitch bearing 106. Also in the illustrated embodiment, the outboard pitch bearing 108 is a cylindrical roller bearing which employs one cylinder riding on the outside of another cylinder, since the outboard pitch bearing 108 may see primarily radial load rather than axial load.
In the embodiments disclosed herein, which include the inboard and outboard pitch bearings 106, 108 as well as the tension torsion strap 110, the blade 104 is able to move axially in direction 120 with respect to the hub arm 102 and the pitch bearings 106, 108 due to centrifugal force (and are able to move axially in a direction opposite to direction 120 when the centrifugal force is reduced or removed). However, in any longitudinal location of the blades 104 with respect to the hub arm 102 and pitch bearing assembly 105, it is important that the outer races 122, 124 of the pitch bearings 106, 108 remain rotationally locked to the blade 104. Thus, in one embodiment, the rotor system 100 further includes the coupler 112 such that the bearings 106, 108 are locked to each other, and the inboard pitch bearing 106 is rotationally locked to the blade 104. As shown in
In the illustrated embodiments, because the tabs 146 are only disposed on the inboard pitch bearing 106, and because the outboard pitch bearing 108 needs to be driven as well, the coupler 112 ties in the two bearing outer races 122, 124 to each other so that they rotate together in the rotor system 100. The tabs 146 and coupler 112 are provided to mechanically and positively transfer the rotation between the bearings 106, 108 and blade 104 rather than just relying on friction between the outer races 122, 124 and the blade 104. As best shown in
As shown in
In another embodiment, as shown in
Thus, an aspect of the embodiments described herein includes a method of inspecting the outboard pitch bearing 108 (and/or inboard pitch bearing 106) after the rotor system 100 is assembled, or at least after the pitch bearing assembly 105 is assembled onto the hub arm 102, including a method of inspecting the seal 138 of the outboard pitch bearing 108 (and/or seal 140 of the inboard pitch bearing 106). The method includes accessing the pitch bearing 106 and/or 108 to be inspected via the inspection path 166 which begins exteriorly of the coupler 112 and ends interiorly of the coupler 112 and inboard of the outboard pitch bearing 108 (or outboard of the inboard pitch bearing 106). In embodiments of the pitch bearing assembly 105, the inspection path 166 may extend through one of an opening 164 in the coupler 112, through the longitudinal gap 264, or through a hole in one of the castellations 254. Then, the method may further include pushing a borescope 168 towards the pitch bearing 106 or 108 to be inspected, or shining a light 168 towards the pitch bearing 106 or 108 which will enable an operator to better inspect the inboard or outboard pitch bearing 106, 108, such as the seal 140 of the inboard pitch bearing 106 or the seal 138 of the outboard pitch bearing 108. While, in one embodiment, the borescope can visualize and the light can shine through the opening 164, gap 264, or castellation hole, in a further embodiment the borescope or a light (such as a flexible light) can further be inserted through the opening 164, the gap 264, or castellation hole to check the seal or other portions of the inboard or outboard pitch bearing 106, 108. Thus inspection is enabled without having to remove the whole pitch bearing assembly 105.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be further noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another.
While the present disclosure is described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the present disclosure. In addition, various modifications may be applied to adapt the teachings of the present disclosure to particular situations, applications, and/or materials, without departing from the essential scope thereof. The present disclosure is thus not limited to the particular examples disclosed herein, but includes all embodiments falling within the scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 62/489,550 filed on Apr. 25, 2017. The entire contents of U.S. Provisional Patent Application No. 62/489,550 are incorporated herein by reference.
This invention was made with Government support under Agreement No. W911W6-13-2-0003 for the Joint Multi-Role Technology Demonstrator Phase I— Air Vehicle Development program. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62489550 | Apr 2017 | US |
