The present disclosure relates, in general, to vibration isolation systems and, in particular, to vibration isolation systems for use on advancing blade concept rotorcraft.
Conventional, single rotor helicopters have a limited top speed due to the problem of retreating blade stall, in which the rotor blade on the retreating side of the rotor disc in forward flight experiences loss of lift due to the rotorcraft's linear forward flight velocity exceeding the rotor blade's minimum angular velocity for lift production. Attempts have been made to overcome retreating blade stall by utilizing an “advancing blade concept,” in which one or more rotor blades advance on both sides of the rotorcraft during flight, allowing for a faster forward airspeed. In one implementation, advancing blade concept rotorcraft include two counter rotating rotors that provide advancing blades on both sides of the rotorcraft during flight. It has been found, however, that advancing blade concept rotorcraft are particularly susceptible to high amounts of vibration. For example, counter rotating rotors may combine harmonics in the wakes of one another, thereby creating excessive vibration in the fuselage of such rotorcraft. Fuselage vibration may be further exacerbated by the use of stiff high hinge offset rigid rotors, which may be present on some advancing blade concept rotorcraft.
The excessive vibration associated with advancing blade concept rotorcraft contributes to crew fatigue, increased maintenance, increased operating costs and structural instability. Attempts have been made to use active force generators to reduce fuselage vibration on advancing blade concept rotorcraft. It has been found, however, that active force generators add significant weight, have reliability and maintenance problems, generate high loads that contribute to structural fatigue, consume large amounts of power and have undesirable failure mode characteristics. Accordingly, a need has arisen for a vibration system that effectively prevents the transmission of vibration throughout an advancing blade concept rotorcraft while avoiding the negative characteristics of active force generators.
In a first aspect, the present disclosure is directed to an advancing blade concept rotorcraft including an airframe and a pylon assembly subject to vibration. The pylon assembly includes a dual rotor system having coaxially disposed top and bottom rotor assemblies that counter rotate relative to one another. The advancing blade concept rotorcraft includes a vibration isolation system including at least one pylon link coupled to the airframe and the pylon assembly. The pylon link includes a Liquid Inertia Vibration Eliminator unit operable to reduce transmission of the pylon assembly vibration to the airframe. The advancing blade concept rotorcraft includes a plurality of active force generators adjacent to the pylon assembly. The active force generators include a first active force generator producing a force in a first direction and a second active force generator producing a force in a second direction different from the first direction to counteract multidirectional oscillations of the pylon assembly, thereby reducing vibration of the advancing blade concept rotorcraft.
In some embodiments, the counter rotating rotor assemblies may combine harmonics in the wakes of one another to emit a dual rotor system vibration frequency and the Liquid Inertia Vibration Eliminator unit may be tuned to cancel the dual rotor system vibration frequency originating from the dual rotor system. In certain embodiments, the pylon assembly may include a transmission and the pylon link may be coupled to the transmission. In some embodiments, the Liquid Inertia Vibration Eliminator unit may be a passive or active Liquid Inertia Vibration Eliminator unit. In certain embodiments, the Liquid Inertia Vibration Eliminator unit may include first and second fluid chambers, a tuning passage providing fluid communication between the first and second fluid chambers, a tuning fluid moveable between the first and second fluid chambers via the tuning passage to isolate the vibration of the pylon assembly, a housing and a piston disposed within the housing, the piston forming the tuning passage. In some embodiments, the piston may be operable to move within the housing such that the tuning fluid moves between the first and second fluid chambers via the tuning passage in response to the vibration of the pylon assembly.
In certain embodiments, the pylon link may include a first portion including a first end and a second portion including a second end, the first portion of the pylon link coupled to one of the housing or the piston and the second portion of the pylon link coupled to the other of the housing or the piston. In some embodiments, the pylon link may include at least one substantially horizontal pylon link and at least one substantially vertical pylon link. In certain embodiments, the pylon link may be a plurality of pylon links each including a respective Liquid Inertia Vibration Eliminator unit. In such embodiments, the pylon assembly may be subject to vibration in a plurality of degrees of freedom including first and second degrees of freedom, and the pylon links may include first and second pylon links, the first pylon link oriented to isolate vibration of the pylon assembly in the first degree of freedom, the second pylon link oriented to isolate vibration of the pylon assembly in the second degree of freedom. In some embodiments, the pylon links may include a plurality of substantially horizontal pylon links circumferentially disposed around the pylon assembly and a plurality of substantially vertical pylon links circumferentially disposed around the pylon assembly. In certain embodiments, the vertical pylon links may be circumferentially equidistant from one another. In some embodiments, the pylon links may include pairs of substantially horizontal pylon links and substantially vertical pylon links, each pair of horizontal and vertical pylon links forming an angle between 70 and 110 degrees. In certain embodiments, at least one of the horizontal pylon links may be angularly offset from a horizontal plane.
In some embodiments, the pylon link may include a torque restraint and fore/aft vibration isolation subsystem. In certain embodiments, the active force generators may be coupled to the airframe. In some embodiments, the active force generators may include at least one rotary active force generator. In certain embodiments, the first active force generator may produce a force in a vertical direction, the second active force generator may produce a force in a longitudinal direction and a third active force generator may produce a force in a lateral direction to produce forces to counteract the multidirectional oscillations of the pylon assembly, thereby reducing vibration of the advancing blade concept rotorcraft. In some embodiments, the advancing blade concept rotorcraft may include a pusher propeller having variable pitch blades configured to propel the advancing blade concept rotorcraft in a forward direction and a flight control system having a fly-by-wire architecture. In such embodiments, the top and bottom rotor assemblies may be rigid and/or variable speed rotor assemblies and the top and bottom rotor assemblies may each include four rotor blades. In certain embodiments, the advancing blade concept rotorcraft may include a tailboom including a downward fin and a horizontal stabilizer.
For a more complete understanding of the features and advantages of the present disclosure, reference is now made to the detailed description along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:
While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not delimit the scope of the present disclosure. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would 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 the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, and the like described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the devices described herein may be oriented in any desired direction.
Referring to
Top rotor assembly 28 includes top rotor hub assembly 38 from which a plurality of rotor blade assemblies 40 radially project outward. Similarly, bottom rotor assembly 30 includes bottom rotor hub assembly 42 from which a plurality of rotor blade assemblies 44 radially project outward. Top and bottom rotor assemblies 28, 30 may each include any number of rotor blade assemblies 40, 44. Top and bottom rotor assemblies 28 and 30 are also coaxial. In particular, top rotor hub assembly 38 is mounted to an upper rotor shaft 46. Upper rotor shaft 46 counter rotates within a lower rotor shaft 48, to which bottom rotor hub assembly 42 is mounted. Top and bottom rotor assemblies 28, 30 may be rigid, hingeless and/or stiff in plane. Rotor blade assemblies 40, 44 may be capable of collective and/or cyclic pitching is. It should be understood that various blade attachments may be utilized by advancing blade concept rotorcraft 10. Top and bottom rotor assemblies 28, 30 may be static or variable speed. In some embodiments, top and bottom rotor assemblies 28, 30 may be capable of tilting together in the same direction, or may tilt at different angles relative to one another.
Advancing blade concept rotorcraft 10 is a compound helicopter that includes translational thrust system 50 located at aft end 52 of tailboom 16. Translational thrust system 50 includes a pusher propeller 54 that propels advancing blade concept rotorcraft 10 in a forward direction. Assisted by pusher propeller 54, advancing blade concept rotorcraft 10 may be capable of high forward airspeed. By providing for propulsion for advancing blade concept rotorcraft 10, pusher propeller 54 may reduce the drag burden on dual rotor system 20. Pusher propeller 54 may be a variable pitch pusher propeller and may be clutchable. Pusher propeller 54 may be powered by engine 24 via a gearbox, such as transmission 22. While shown in the context of a pusher propeller configuration, it will be understood by one of ordinary skill that pusher propeller 54 may also be a more conventional puller propeller or could be variably facing so as to provide yaw control in addition to or instead of translational thrust.
Because pylon assembly 18 is subject to vibration, advancing blade concept rotorcraft 10 includes a vibration isolation system 56. Transmission 22 of pylon assembly 18 is mounted to airframe 14 by one or more pylon links 58. In particular, first end 60 of pylon link 58 is coupled to transmission 22 and second end 62 of pylon link 58 is coupled to airframe 14. As used herein, the term “coupled” may include direct or indirect coupling by any means, including moving and/or non-moving mechanical connections. Pylon link 58 includes a vibration isolator 64 such that vibration isolator 64 is interposed between pylon assembly 18 and airframe 14. Vibration isolator 64 intercepts vibrations between pylon assembly 18 and airframe 14 so as to reduce or prevent the transmission of pylon assembly vibration to airframe 14, thus preventing undesirable shaking, vibration or instability of fuselage 12.
Advancing blade concept rotorcraft 10 may utilize some or all aspects of X2 Technology™ by Sikorsky®, which may have a fly-by-wire architecture and include coaxial and counter rotating dual rotor system 20. It should be appreciated that advancing blade concept rotorcraft 10 is merely illustrative of a variety of aircraft that can implement the embodiments disclosed herein. Indeed, vibration isolation system 56 may be utilized on any aircraft that experiences vibration. Other aircraft implementations can include single rotor helicopters, hybrid aircraft, tiltrotor aircraft, tiltwing aircraft, quad tiltrotor aircraft, unmanned aircraft, gyrocopters, airplanes, jets and the like. As such, those skilled in the art will recognize that vibration isolation system 56 can be integrated into a variety of aircraft configurations. In addition, vibration isolation system 56 is not limited to controlling vibration between only pylon assembly 18 and airframe 14, and may be interposed between any two or more aircraft components to limit the transmission of vibration therebetween. It should be appreciated that even though aircraft are particularly well-suited to implement the embodiments of the present disclosure, non-aircraft vehicles and devices can also implement the embodiments.
Referring to
Attempts to control vibration on advancing blade concept rotorcraft using active force generators, such as those in active generation system 100, has led to a number of problems. Because active force generators 110a-1101 emit amplitudes that are opposite those of pylon assembly 108, the force amplitudes experienced by the advancing blade concept rotorcraft may be doubled, thereby increasing the fatigue on airframe 104 and other structures of the advancing blade concept rotorcraft. Active force generators 110a-1101 contribute a significant weight penalty to the advancing blade concept rotorcraft due to the presence of an active damping mass as well as support structure, power generation components and controlling devices necessary for the operation of active force generators 110a-1101. The airframe substantiation required to structurally mount active force generators 110a-1101 within the fuselage also contributes to the overall weight of active force generation system 100. Because active force generators 110a-1101 are active electronically-controlled devices, they require an electronic feedback loop that may produce a delayed response when maneuvering through transient flight envelopes. Active force generators 110a-1101 are also complex, expensive and have undesirable failure mode characteristics. For example, active force generation system 100 would cease to function if power to active force generators 110a-1101 were compromised. These and other disadvantages of active force generation system 100 have brought about a need for an improved system for controlling the vibration in an advancing blade concept rotorcraft.
Referring to
In some embodiments, vibration isolators 228, 230 may be passive vibration isolators, and therefore not require a power source to be operational. With specific reference to
A top portion 248 of pylon link 210 may be attached to piston 236 via bracket 250, and a bottom portion 252 of pylon link 210 may be attached to housing 234. In other embodiments, top portion 248 of pylon link 210 may be attached to housing 234, and bottom portion 252 of pylon link 210 may be attached to piston 236. In operation, vibration of pylon assembly 202 at a particular frequency displaces piston 236 relative to housing 234 along double arrow 244. Because the force and displacement is oscillatory over time, piston 236 similarly oscillates relative to housing 234. A displacement of piston 236 causes a displacement of tuning fluid through tuning passage 246 in the opposite direction of the displacement of piston 236. The displacement of piston 236 causes an oscillatory reaction force due to strain and elastomeric seal and spring members 238a, 238b. At the same time, the volumes of tuning fluid in first and second fluid chambers 240, 242 are alternately increased and decreased such that the tuning fluid is pumped back and forth through tuning passage 246. The inertial force created by acceleration of the mass of the tuning fluid is out of phase with the pylon assembly vibration introduced to piston 236 via bracket 250. At an isolation frequency, the force of the mass of the tuning fluid cancels the force introduced to piston 236 via bracket 250, thereby isolating the vibration of pylon assembly 202.
LIVE™ unit 232 is a passive vibration isolator. Passive LIVE™ units are effective at or near a single vibration frequency. In contrast, an active vibration isolation system can be effective over a range of frequencies to accommodate more than just a single isolation frequency, such as when a rotorcraft operates at different rotor speeds or when attempting to reduce the transmission of pylon assembly vibration occurring at multiple frequencies. In some embodiments, LIVE′ unit 232 may be an active LIVE′ unit, such as by introducing a pump or other technique for actively oscillating or moving the tuning fluid through tuning passage 246. The dynamic response characteristics of an active LIVE™ unit can be altered as desired. An active LIVE™ unit may include active adjustment of the isolation frequency and the frequency response characteristics of the LIVE™ unit. For example, a pressure differential in a LIVE™ unit can be actively adjusted to affect the isolation frequency and frequency response characteristics of the LIVE™ unit. In some embodiments, active pumper devices may use piezoelectric or electromagnetic actuation within the LIVE′ unit to oscillate tuning fluid through tuning passage 246 by mechanically activating piston 236. In addition, an electromagnetic pump device, which uses an electric motor to oscillate piston 236 and dynamically displace the tuning fluid, may be used to generate a sinusoidal displacement of tuning fluid. The electric motor speed and sinusoidal displacement amplitude may be controlled to produce the desired quantity of pumped fluid and the frequency of fluid oscillations. Oscillating pumps external to the LIVE™ unit may also be used to introduce oscillating fluid flow to tuning passage 246 of piston 236.
In contrast to the active force generation system described in
Referring to
Pylon links 312, 314, 316, 318 are angled pylon links in that each pylon link 312, 314, 316, 318 is neither horizontal nor vertical relative to advancing blade concept rotorcraft 302, but is oriented at some angle therebetween. For example, pylon link 314 may form an angle 328 of between about 20 degrees and 70 degrees with vertical axis 330, which intersects the joint between pylon link 314 and airframe 306. Pylon links 312, 316, 318 may also form such angles with their respective vertical axes. Left forward pylon link 312 and right forward pylon link 314 are oriented such that axes 312a, 314a are non-parallel and converge at a forward focal point 332, thus forming a converging pair of pylon links. Left rear pylon link 316 and right rear pylon link 318 are oriented such that axes 316a and 318a are non-parallel and converge at an aft focal point 334, thus also forming a converging pair of pylon links. Both converging pairs of pylon links 312, 314 and 316, 318 are circumferentially disposed around pylon assembly 304 and, as best seen in
Aft focal point 334 is located at a higher waterline than forward focal point 332. The distance between forward focal point 332 and aft focal point 334 form a virtual roll axis 336 therebetween. In the illustrated embodiment, both forward focal point 332 and aft focal point 334 lie on a centerline (e.g. zero buttline) of advancing blade concept rotorcraft 302. One advantage of vibration isolation system 300 over conventional mount systems is that by locating forward focal point 332 and aft focal point 334 on different aircraft waterlines, the rolling tendency is substantially decreased. Transmission 310 may have a virtual swing arm between its center of gravity and virtual roll axis 336 with which transmission 310 will have a natural propensity to swing about. However, vibration isolation system 300 is configured such that virtual roll axis 336 is substantially inclined by orienting aft focal point 334 with a substantially higher waterline as compared to forward focal point 332. The inclination of virtual roll axis 336 impedes the swinging of transmission 310, which decreases the loads associated with the swinging of transmission 310.
In the example embodiment, each end of pylon links 312, 314, 316, 318 is coupled to transmission 310 and airframe 306 with spherical bearings to prevent pylon links 312, 314, 316, 318 from reacting to loads in unintended directions. For example, fore/aft loads and torsional loads are not reacted by pylon links 312, 314, 316, 318, but rather by torque restraint and fore/aft vibration isolation subsystem 322. Further, lateral loads are not reacted by pylon links 312, 314, 316, 318, but rather by lateral pylon link 320. Mounting pylon links 312, 314, 316, 318 with spherical bearings helps ensure that each pylon link 312, 314, 316, 318 will only react to loads along its respective axis 312a, 314a, 316a, 318a. Further, prevention of load reaction outside of axes 312a, 314a, 316a, 318a in combination with the freedom to adjust the waterline and fuselage station of forward focal point 332 and aft focal point 334 provide tunability to optimize vibration reduction and reduce the rolling tendency of transmission 310 about virtual roll axis 336.
Pylon links 312, 314, 316, 318, lateral pylon link 320, left fore/aft pylon link 324 and right fore/aft pylon link 326 may each include a vibration isolator. For example, pylon links 312, 314, 316, 318, lateral pylon link 320, left fore/aft pylon link 324 and right fore/aft pylon link 326 may each be “soft” (i.e. not rigid) in that each pylon link may include internal components, such as fluid, orifices, springs, elastomeric members and the like, to isolate vibrations between transmission 310 and airframe 306. Pylon links 312, 314, 316, 318, lateral pylon link 320, left fore/aft pylon link 324 and right fore/aft pylon link 326 may each include a LIVE′ unit that is either passive or active.
With specific reference to
Left fore/aft pylon link 324 has a piston 338 resiliently coupled to a housing 340 with an elastomeric member 342. Piston 338 and elastomeric member 342 divide housing 340 into a first chamber 344 and a second chamber 346. Similarly, right fore/aft pylon link 326 has a piston 348 resiliently coupled to a housing 350 with an elastomeric member 352. Piston 348 and elastomeric member 352 divide housing 350 into a first chamber 354 and a second chamber 356. Second chamber 346, first chamber 354 and a fluid line 358 are filled with a fluid 360. First chamber 344 and second chamber 356 do not require fluid 360 and thus can be open or vented rather than being enclosed chambers. For example, first chamber 344 and second chamber 356 can be filled with air, or open/vented to atmosphere.
In operation, torque restraint and fore/aft vibration isolation subsystem 322 is configured to resist or react to torque loads and measure torque loads, as well as attenuate vibration in the fore/aft direction. Referring in particular to
With specific reference to
Referring to
Vibration isolation system 400 may be used in conjunction with one or more active force generators 432, 434, 436. Active force generators 432, 434, 436 are operable to produce a force that counteracts the vibration of pylon assembly 410, thereby reducing vibration of the advancing blade concept rotorcraft. Active force generators 432, 434, 436 may be linear force generators, circular or rotary force generators or other suitable force generators. For example, active force generators 432, 434, 436 may be spring masses or shakers, including rotary hub-mounted shakers. It will be understood by one of ordinary skill in the art that the types of active force generators that may be implemented in vibration isolation system 400 are numerous, and that each of these types of active force generators may be implemented, in any combination, simultaneously with the illustrative embodiments.
In
In
The foregoing description of embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the present disclosure. Such modifications and combinations of the illustrative embodiments as well as other embodiments will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.
The present application is a continuation of co-pending application Ser. No. 15/459,781 filed Mar. 15, 2017.
Number | Name | Date | Kind |
---|---|---|---|
3514054 | Mard | May 1970 | A |
3635427 | Balke | Jan 1972 | A |
3698663 | Balke | Oct 1972 | A |
4236607 | Halwes et al. | Dec 1980 | A |
4720060 | Yana | Jan 1988 | A |
4974794 | Aubry et al. | Dec 1990 | A |
5310137 | Yoerkie, Jr. | May 1994 | A |
5316240 | Girard et al. | May 1994 | A |
5435531 | Smith et al. | Jul 1995 | A |
5439082 | McKeown et al. | Aug 1995 | A |
5788182 | Guimbal | Aug 1998 | A |
6009983 | Stamps et al. | Jan 2000 | A |
6431530 | Stamps et al. | Aug 2002 | B1 |
7648338 | Welsh | Jan 2010 | B1 |
7719416 | Arms | May 2010 | B2 |
7857255 | Pancotti et al. | Dec 2010 | B2 |
8328129 | Smith et al. | Dec 2012 | B2 |
8499907 | Smith et al. | Aug 2013 | B2 |
8840062 | Smith et al. | Sep 2014 | B2 |
9145946 | David et al. | Sep 2015 | B2 |
9249856 | Lee et al. | Feb 2016 | B1 |
9254914 | Hendricks et al. | Feb 2016 | B2 |
9365294 | Griffin | Jun 2016 | B2 |
9777788 | Lee | Oct 2017 | B2 |
10330166 | Lee | Jun 2019 | B2 |
20020128072 | Terpay | Sep 2002 | A1 |
20080036617 | Arms et al. | Feb 2008 | A1 |
20080142633 | McGuire et al. | Jun 2008 | A1 |
20090321556 | Pancotti et al. | Dec 2009 | A1 |
20100090055 | Smith et al. | Apr 2010 | A1 |
20130105621 | Smith et al. | May 2013 | A1 |
20130119591 | Lee et al. | May 2013 | A1 |
20130270415 | Lee et al. | Oct 2013 | A1 |
20140314563 | Mayrides et al. | Oct 2014 | A1 |
20150125299 | Baskin et al. | May 2015 | A1 |
20150136900 | Griffin et al. | May 2015 | A1 |
20150139800 | Hendricks et al. | May 2015 | A1 |
20150289056 | Storm | Oct 2015 | A1 |
20150308534 | Smith et al. | Oct 2015 | A1 |
20160200432 | Darrow, Jr. et al. | Jul 2016 | A1 |
20170225774 | Welsh et al. | Aug 2017 | A1 |
20180038439 | Lee | Feb 2018 | A1 |
Entry |
---|
Advancing Blade Concept (ABC) Technology Demonstrator, Applied Technology Laboratory—U.S. Army Research and Technology Laboratories, Apr. 1981. |
European Exam Report; Application No. EP 18155504.6; European Patent Office; dated May 31, 2018. |
European Search Report; Application No. EP 18155504.6; European Patent Office; dated May 14, 2018. |
Go et al., Performance and Vibration Analyses of Lift-Offset Helicopters, International Journal of Aerospace Engineering, vol. 2017, Jun. 15, 2017. |
Hager, The Need for High Speed in Next Generation Rotorcraft, U.S. Army War College, Mar. 2012. |
S-69 (XH-59A) Advancing Blade Concept Demonstrator, Sikorsky Archives, https://www.sikorskyarchives.com/S-69%20(XH-59A).php, Apr. 2012. |
Number | Date | Country | |
---|---|---|---|
20200262549 A1 | Aug 2020 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 15459781 | Mar 2017 | US |
Child | 16716264 | US |