Patent Application
20180290739
This disclosure relates generally to a teetering tail rotor yoke, and more particularly, though not exclusively, to a teetering tail rotor yoke with three or more bearings.
One way of accommodating blade pitch (or feathering) motion in teetering tail rotors is via a spherical bearing affixed to a yoke. The primary force reacted by these bearings is the centrifugal force (CF), which proportionally affects the bearings' load rating for given sizing constraints.
According to one aspect of the present disclosure, a tail rotor assembly can include a yoke arm; a rotor blade; and at least three spherical bearings, each of the three spherical bearings carried by the yoke arm and configured to pivotally secure the rotor blade to the yoke arm and to allow feathering movement of the rotor blade relative to the yoke arm during flight.
In some embodiments, the three spherical bearings are evenly spaced from each other on the yoke arm.
In some embodiments, each of the three spherical bearings can include a race; a spherical ball rotatably carried within the housing; and a passage extending through the spherical ball and configured to couple with a first attachment means associated with the rotor blade for securing the rotor blade to the yoke arm.
In some embodiments, the yoke arm has a longitudinal axis, each of the three spherical bearings can include a center line; and wherein the each of the centerlines is aligned with the longitudinal axis of the yoke arm.
In some embodiments, the at least three bearings are configured to allow feathering movement of the rotor blade relative to the longitudinal axis, while restricting transverse and longitudinal movement of the rotor blade relative to the longitudinal axis.
In some embodiments, the yoke arm can include a thickness in the range of 0.75 inches to 1.0 inches.
In some embodiments, the yoke can include a length in the range of 27.5 inches and 28.5 inches.
In some embodiments, the yoke arm comprises a width in a range of 3.0 inches to 3.5 inches.
In one embodiments, a rotorcraft can include a tail rotor assembly, the tail rotor assembly can include a yoke arm; a rotor blade; and at least three spherical bearings, each of the three spherical bearings carried by the yoke arm and configured to pivotally secure the rotor blade to the yoke arm and to allow feathering movement of the rotor blade relative to the yoke arm during flight.
In some embodiments, the three spherical bearings are even spaced from each other on the yoke arm.
In some embodiments, each of the three spherical bearings can include a housing; a spherical ball rotatably carried within the housing; and a passage extending through the spherical ball and configured to couple with a first attachment means associated with the rotor blade for securing the rotor blade to the yoke arm.
In some embodiments, the yoke arm has a longitudinal axis, each of the three spherical bearings can include a center line; and wherein the each of the centerlines is aligned with the longitudinal axis of the yoke arm.
In some embodiments, the at least three bearings are configured to allow feathering movement of the rotor blade relative to the longitudinal axis, while restricting transverse and longitudinal movement of the rotor blade relative to the longitudinal axis.
In some embodiments, the yoke arm can include a thickness in the range of 0.75 inches to 1.0 inches.
In some embodiments, the yoke can include a length in the range of 27.5 inches and 28.5 inches.
In some embodiments, the yoke arm can include a width in a range of 3.0 inches to 3.5 inches.
In one embodiments, a tail rotor yoke for a rotorcraft with a teetering tail rotor can include an elliptically shaped center portion that can receive a tail rotor gearbox; a first yoke arm extending from the center portion, the first yoke arm comprising at least three spherical bearing receiving sections; and a second yoke arm extending from the center portion, the first yoke arm comprising at least three spherical bearing receiving sections.
In some embodiments, the at least three spherical bearing receiving sections are evenly spaced apart.
In some embodiments, the first and second yoke arm can include a thickness in the range of 0.75 inches to 1.0 inches.
In some embodiments, the tail rotor yoke comprises a length in the range of 27.5 inches and 28.5 inches.
The following disclosure describes various illustrative embodiments and examples for implementing the features and functionality of the present disclosure. While particular components, arrangements, and/or features are described below in connection with various example embodiments, these are merely examples used to simplify the present disclosure and are not intended to be limiting. It will of course be appreciated that in the development of any actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, including compliance with system, business, and/or legal constraints, which may vary from one implementation to another. Moreover, it will be appreciated that, while such a development effort might be complex and time-consuming, it would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, components, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other similar terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components, should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the components described herein may be oriented in any desired direction.
Further, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Example embodiments that may be used to implement the features and functionality of this disclosure will now be described with more particular reference to the attached figures.
It should be appreciated that rotorcraft 100 of
This disclosure describes a teetering yoke design that includes three spherical bearings. In embodiments, the three spherical bearings can be equally spaced apart, so that each bearing can react to 33+/−2% of the CF. Compared to yokes with two spherical bearings with a 50-50% split CF reaction, the multiple-bearing yoke described herein improves bearing and yoke life, facilitates weight reduction, improves kinematic clearances, and provides design redundancy in case of single bearing failure.
Example embodiments that may be used to implement the multiple bearing teetering yoke design are described below with more particular reference to the remaining figures.
The main rotor system 204 is a rotating part of a helicopter that generates lift. The main rotor system 204 consists of a mast, hub, and rotor blades. The mast is a hollow cylindrical metal shaft which extends upwards from and is driven and sometimes supported by the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. The rotor blades are then attached to the hub by any number of different methods.
The aircraft also includes a tail rotor (or antitorque system) 300 that counter acts torque produced by the rotating main rotor. Helicopters with a single, main rotor system 204 use a separate antitorque system 300. The tail rotor assembly 300 can include a variable pitch, antitorque rotor or tail rotor. Pilots can vary the thrust of the antitorque system to maintain directional control whenever the main rotor torque changes, or to make heading changes while hovering. Most helicopters drive the tail rotor shaft from the transmission to ensure tail rotor rotation (and hence control) in the event that the engine quits. Usually, negative antitorque thrust is needed in autorotations to overcome transmission friction.
In the exemplary embodiment, tail rotor assembly 300 includes four rotor blades 302a-d; however, it will be appreciated that tail rotor assembly 300 is adaptable for use with more or fewer blades in an alternative embodiment.
Tail rotor assembly 300 can include a tail rotor hub 306 that can secure one or more tail rotor yokes 400. Each tail rotor yoke 400 can secure two tail rotor blades.
The tail rotor assembly 300 can include a tail rotor drive system 304. The tail rotor drive system 304 can include an antitorque drive shaft and an antitorque transmission mounted at the end of a tail boom. The drive shaft may consist of one long shaft or a series of shorter shafts connected at both ends with flexible couplings. This allows the drive shaft to flex with the tail boom. The tail rotor transmission provides a right angle drive for the tail rotor and may also include gearing to adjust the output to optimum tail rotor rpm. Tail rotors may also have an intermediate gearbox to turn the power up a pylon or vertical fin.
The tail rotor assembly 300 can include a plurality of yoke arms, such as yoke arm 401. Two tail rotor blades e.g., 302a-302c can be secured to each yoke 401. Each yoke can include six spherical bearings, three on each yoke arm of the yoke. Each of the three spherical bearings carried by the yoke arm and configured to pivotally secure the rotor blade to the yoke arm and to allow feathering movement of the rotor blade relative to the yoke arm during flight. The three spherical bearings are evenly spaced from each other on the yoke arm. For example, the bearings can be spaced 3 inches apart.
Each of the three spherical bearings can include a race or housing, a spherical ball rotatably carried within the housing; and a passage extending through the spherical ball and configured to couple with a first attachment means associated with the tail rotor blade for securing the rotor blade to the yoke arm. The passage extending through the spherical ball can permit the attachment means for securing the tail rotor blade to the yoke arm. The attachment means can be a bolt or other attachment means.
The three bearing yoke 401 has a center section 402 and two arms 404a and 404b. The center section 402 accommodates a flapping bearing which engages with a tail rotor mast, thereby attaching the teetering rotor to the drive system. The center section 402 can have an elliptical shape, which can reduce the weight of the yoke 400, while enabling optimization of localized stresses and strains.
Each of the two arms 404a and 404b facilitate attachment to rotor blades that are underslung relative to the flapping hinge. The blades are attached to the yoke 400 via spherical bearings 406a-c and 406d-f, three on each arm, equally spaced apart and centered at the Pitch Change Axis (PCA). The flapping hinge is oriented at a desired angle relative to the Mean Aerodynamic Chord (MAC) of the blade to induce a Delta-3 hinge. Lastly, the center section has provisions to preload the flapping bearing at install as necessary.
The yoke 400 is shown with three bearings on each yoke arm. Yoke arm 404a includes a first bearing 406a, a second bearing 406b, and a third bearing 406c, each of the bearings being configured to allow feathering movement of the blade relative to the yoke arm 404a. Yoke arm 404b includes a first bearing 406d, a second bearing 406e, and a third bearing 406f, each of the bearings being configured to allow feathering movement of the blade relative to the yoke arm 404b. In the preferred embodiment, the bearings 406a-f are spherical bearings that sit flush with an upper surface and a lower surface of yoke arms; however, it will be appreciated that other types of bearings and devices could be used in lieu of the preferred embodiment. The spherical bearings allow for feathering motion of the rotor blades, which provides significant advantageous over conventional tail rotors, namely tail rotors having rotor blades rigidly attached to the yoke arm.
Turning to
The spherical bearings can be attached or affixed to the yoke arm (e.g., via swaging or staking). A rotor blade can be attached to a yoke through the three or more spherical bearings. Each of the three or more spherical bearings can restrict longitudinal and transverse movement of the rotor blade relative to the yoke. Feathering of the blade can be compensated for by the at least three spherical bearings that allow for pivoting movement of the rotor blade relative to the yoke.
More generally, the three bearing yoke can have dimensions being of 10% reduction in cross-sectional area for the most highly loaded bearing location, which translates into material and weight savings. The actual dimensions of the three bearing yoke can be based on application specificity, such as CF loads and/or design packaging.
The bearing gap Bo represents a diameter of the spherical bearing for the two bearing yoke. The two bearing yoke 501 would use a larger spherical bearing than the three bearing yoke 401, so that Bo>Bn. The use of smaller bearings include cost savings on the bearings and a more compact design packaging.
The flowcharts and diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of various embodiments of the present disclosure. It should also be noted that, in some alternative implementations, the function(s) associated with a particular block may occur out of the order specified in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order or alternative orders, depending upon the functionality involved.
Although several embodiments have been illustrated and described in detail, numerous other changes, substitutions, variations, alterations, and/or modifications are possible without departing from the spirit and scope of the present invention, as defined by the appended claims. The particular embodiments described herein are illustrative only, and may be modified and practiced in different but equivalent manners, as would be apparent to those of ordinary skill in the art having the benefit of the teachings herein. Those of ordinary skill in the art would appreciate that the present disclosure may be readily used as a basis for designing or modifying other embodiments for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. For example, certain embodiments may be implemented using more, less, and/or other components than those described herein. Moreover, in certain embodiments, some components may be implemented separately, consolidated into one or more integrated components, and/or omitted. Similarly, methods associated with certain embodiments may be implemented using more, less, and/or other steps than those described herein, and their steps may be performed in any suitable order.
Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained to one of ordinary skill in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims.
In order to assist the United States Patent and Trademark Office (USPTO), and any readers of any patent issued on this application, in interpreting the claims appended hereto, it is noted that: (a) Applicant does not intend any of the appended claims to invoke paragraph (f) of 35 U.S.C. § 112, as it exists on the date of the filing hereof, unless the words “means for” or “steps for” are explicitly used in the particular claims; and (b) Applicant does not intend, by any statement in the specification, to limit this disclosure in any way that is not otherwise expressly reflected in the appended claims.
