Patent Publication Number: US-10787253-B2

Title: Variable directional thrust for helicopter tail anti-torque system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/172,811 filed on Jun. 3, 2016, now U.S. Pat. No. 10,377,479. The entire contents of which is hereby incorporated by reference for all purposes. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention is generally in the field of flight control, and relates specifically to an anti-torque system and control for helicopters. 
     STATEMENT OF FEDERALLY FUNDED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the invention, its background is described in connection with anti-torque systems. 
     Counter-torque tail rotors are often used in helicopters and are generally mounted adjacent to vertical fins that provide for aircraft stability. In such a configuration, the helicopter rotor produces a transverse airflow. Tail rotors can be driven at high angular velocities to provide adequate aerodynamic responses. Sometimes, vortices produced by a main helicopter rotor and the tail rotor can interact to reduce the efficiency of the thrust created by the rotors. The interference of the vortices may also cause an increase in noise. 
     To address these issues, the vertical fin can be replaced by an annular airfoil (sometimes called a ring wing) having an inner diameter greater than the diameter of the tail rotor and which can be mounted around the tail rotor. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention includes an anti-torque assembly for a helicopter comprising: a plurality of fixed blade pitch motors mounted on one or more pivots on the tail boom of the helicopter, wherein the plurality of fixed blade pitch motors on the one or more pivots are adapted to be oriented substantially in-plane with a tail boom of a helicopter during a first mode of operation that comprises a hover mode and wherein the fixed blade pitch motors are adapted to be oriented substantially off-plane from the tail boom of the helicopter during a second mode of helicopter operation that is different from the first mode. In one aspect, the plurality of fixed blade pitch motors can operate: in a different direction from the other motors to provide opposing thrust; with the thrust in the same direction; with different speeds; or with different directions and speeds. In another aspect, the anti-torque assembly comprises 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or more fixed blade pitch motors, and each motor can be: turned on or off independently or as a group; is a variable speed motor; or each motor can independently direct thrust in a different direction. In another aspect, the anti-torque assembly is defined as further comprising a ring or cowling that surrounds one or more individual motors of the anti-torque assembly that each ring or cowling being attached to a separate pivot, or the anti-torque assembly is surrounded by a single ring or cowling that is attached to the pivot. In another aspect, the anti-torque assembly is substantially co-planar with the tail boom during the hover mode. In another aspect, the second mode of helicopter operation is a flight mode, and wherein the anti-torque assembly is substantially perpendicular with the tail boom during the flight mode. In another aspect, the motors are electric. In another aspect, the module further comprises a logic in a flight control computer for calculating the anti-torque assembly system during transition to and from the first to the second mode of operation and for independently controlling fan direction and speeds for the fixed blade pitch motors to position the anti-torque assembly system for optimum thrust angle, as well as optimum thrust magnitude. 
     Another embodiment of the present invention includes an anti-torque assembly system for a helicopter, the system comprising: a plurality of fixed blade pitch electrically-driven, variable-speed motors mounted on one or more pivots; and one or more drive mechanisms to orient the fixed blade pitch electrically-driven, variable-speed motors to be substantially in-plane with a tail boom of a helicopter during a first mode of helicopter operation that comprises a hover mode and that orients the fixed blade pitch electrically-driven, variable-speed motors substantially off-plane with the tail boom of the helicopter during a second mode of helicopter operation that is different from the first mode, wherein the second mode of helicopter operation is a flight mode. In one aspect, the system further comprises a logic in a flight control computer for calculating the direction and thrust from the anti-torque assembly system during transition to and from the first to the second mode of operation and for independently controlling fan direction and speeds of the fixed blade pitch electrically-driven, variable-speed motors, and to position the anti-torque assembly system for optimum thrust angle, as well as optimum thrust magnitude. 
     In yet another embodiment, the present invention includes a method of operating a helicopter, the method comprising: orienting an anti-torque assembly comprising two or more fixed blade pitch electrically-driven, variable-speed motors on a pivot at the end of a tail boom of the helicopter, wherein the fixed blade pitch electrically-driven, variable-speed motors are substantially in-plane with the tail boom of the helicopter during a first mode of helicopter operation that comprises a hover mode and wherein the two or more fixed blade pitch electrically-driven, variable-speed motors are substantially off-plane with the tail boom of the helicopter during a second mode of helicopter operation that is different from the first mode, wherein the second mode of helicopter operation is a flight mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which: 
         FIG. 1  is a side-view schematic diagram of a helicopter showing an anti-torque assembly shown with fixed blade pitch motors. 
         FIGS. 2A and 2B  show schematic diagrams of a helicopter showing in  FIG. 2A  the position and overall thrust of the anti-torque assembly during hover mode with the direction of thrust to oppose the rotational motion of the main rotor during, e.g., hover.  FIG. 2B  also shows a top-view of the anti-torque assembly, but the anti-torque assembly is rotated about an axis with the direction of thrust shown toward the rear of the helicopter, in this case adding to the forward thrust which is generally used during high airspeed cruise. 
         FIG. 3A  is an isometric schematic diagram of the tail portion of a helicopter that shows the anti-torque assembly in hover mode. 
         FIG. 3B  is a side-view schematic diagram of the tail portion of a helicopter that shows the anti-torque assembly in hover mode. 
         FIG. 3C  is an isometric schematic diagram of the tail portion of a helicopter that shows the anti-torque assembly in thrust mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims. 
     Most helicopters with a single, main rotor system require a separate rotor to overcome torque. This is traditionally accomplished on helicopters using a variable pitch, anti-torque rotor or tail rotor receiving power from the engine(s) through shafts and gearboxes. The present inventors have previously disclosed an anti torque control using a matrix of fixed blade pitch motor modules that uses a matrix of small fixed blade pitch electric motor modules in place of a traditional tail rotor. 
     With this configuration in mind (multiple electrically-driven, variable-speed motors driving fans), the anti-torque assembly of the present invention can be hinged at its center and free to rotate about an axis, e.g., a vertical or a horizontal axis. Logic contained in the flight control computer could independently control individual fan speeds to position the assembly for optimum thrust angle, as well as optimum thrust magnitude. This ability to modulate the direction and magnitude of tail rotor thrust can allow optimization of overall aircraft performance. 
     The present invention has certain advantages over prior tail-rotor configurations. One such advantage is the low rotational inertia of the individual fixed blade pitch motors (e.g., electrically, hydraulically, or pneumatically driven motors) that together form the anti-torque assembly, wherein the individual motors can be individually controlled to have their speed and direction changed rapidly. The present invention also eliminates the complexity of a variable blade pitch system. Another advantage of the present invention is that the use of a large number of fixed blade pitch electrically-driven, variable-speed motors provides safety and reliability from component failures through a high level of redundancy without excessive weight. Further, the wide distribution of fixed blade pitch electrically-driven, variable-speed motors provides for increased safety from external threats such as collision and lightening. 
     The present invention has further advantages. For example, when on the ground and with main rotor turning, the lower inertia of the fixed blade pitch electrically-driven, variable-speed motors allows for their motion to stop, which is further supported by the ability to shut down the motors which reduces the injury risk from blade contact to personnel. Further, as shown in one embodiment herein, the present invention allows for increased cruise efficiency through directional optimization of thrust angle of the anti-torque assembly. Additional advantages of the present invention include reduced passenger noise and vibration by operating only a subset of the plurality of fixed blade pitch electrically-driven, variable-speed motors at optimum speeds and directions and from the distributed noise profile they produce. Yet another advantage provided by the fixed blade pitch electrically-driven, variable-speed motors is a reduction in objectionable ground noise in hover by operating the motors at optimum speeds and directions. 
     The fixed blade pitch electrically-driven, variable-speed motors of the present invention provide integration of yaw stability augmentation capability through Fly-by-Wire control. Finally, the speed of the fixed blade pitch electrically-driven, variable-speed motors can be increased when operating at higher altitudes to compensate for decrease in thrust. 
     The present invention includes a convertible helicopter anti-torque assembly that uses fixed blade pitch electrically-driven, variable-speed motors for ground and low speed forward flight. The anti-torque assembly can have a surrounding ring or cowling that acts in place of a traditional tail rotor of a helicopter and that is connected to the helicopter via a pivot that can be used to direct the thrust of one or more motors of the anti-torque assembly. Alternatively, individual fixed blade pitch electrically-driven, variable-speed motors can each have a surrounding ring or cowling that is connected to a pivot. The combined blades of the various tail rotor motors that form the module can each provide separate thrust. The anti-torque assembly fixed can include two, three, four, five, six, seven, eight, nine, ten or more individual fixed blade pitch variable-speed motors, which can operate alone or in one or more combinations and in one or more directions. 
     When provided within a cowling, the various vortices can be captured to form a circulating air pattern, which can act as a pump to draw additional air through the center of the fixed blade pitch electrically-driven, variable-speed motors from the region adjacent the upstream surface of motors. The circulating air pattern and eduction can increase the diameter of the wake and the volume of air transported by the anti-torque assembly. The wake of the anti-torque assembly can be transported at a slow rate while including a greater mass of air by the operation of the combined fixed blade pitch electrically-driven, variable-speed motors, thus resulting in increased efficiency in the operation of the overall anti-torque assembly that acts as a tail rotor. 
     By using smaller individual electric motors, each having their own fixed pitch propeller, the overall rotational energy of each propeller is much smaller and can even use softer or even frangible materials that will protect any ground crews when coming into contact during a hover or slow flight, while still providing the additive aerodynamic forces to control aircraft yaw, roll or pitch in forward flight. 
     The fixed blade pitch electrically-driven, variable-speed motors can provide longitudinal pitch trim and lateral yaw trim. In cruise mode, the flow axis of the fixed blade pitch electrically-driven, variable-speed motors is aligned generally with or along the long axis of the fuselage to serve as a horizontal stabilizer. In hover mode, the arrangement of the fixed blade pitch electrically-driven, variable-speed motors eliminates the down load of a horizontal tail surface that may arise due to interference with the down wash from the main rotor. The fixed blade pitch electrically-driven, variable-speed motors can also off-load the anti-torque assembly in forward flight by positioning itself with a yaw-direction incidence angle via a pilot trim control, thereby reducing power consumption. The anti-torque assembly presents a surface area in sideward flight, and can thereby serve in a passive roll as a yaw damper. The anti-torque assembly can also help reduce the size of a horizontal stabilizer. Alternatively or in addition, application of the anti-torque assembly can allow for the elimination of both vertical and horizontal surfaces normally utilized on conventional helicopters. This can allow a reduction in weight, download for a horizontal stabilizer in the rotor wake and reduced projected side area and drag in lateral (side) flight. 
     The invention takes advantage of the unique performance capabilities of electric motors for use in helicopter anti torque control. Using this distributed electric propulsion design and today&#39;s flight control technology, each motor can be controlled independently to vary individual motor thrust, and thereby position the anti-torque assembly (hinged at the center and free to rotate about the vertical axis) for optimum overall thrust (direction and magnitude). In hover mode, a helicopter requires anti-torque thrust perpendicular to the airframe&#39;s centerline. As the helicopter increases its forward airspeed, this perpendicular thrust requirement reduces. As the anti-torque thrust requirement reduces, this thrust can now be directed more aft to optimize power utilization and overall aircraft performance. At maximum airspeed, this thrust could be directly almost entirely aft. 
       FIG. 1  is a side-view schematic diagram of a helicopter  100  having the anti-torque assembly  110 , depicted in this version with seven fixed blade pitch motors  112   a - g , which can be fixed blade pitch electrically-driven and/or variable-speed motors. The helicopter  100  includes a rotary system  102  carried by a fuselage  104 . Rotor blades  106  connected to the rotary system  102  provide flight for the helicopter  100 . The rotor blades  106  are controlled by multiple controllers within the fuselage  104 . For example, during flight, a pilot can manipulate cyclic controllers (not shown) for changing a pitch angle of the rotor blades  106  and/or manipulate pedals (not shown) to provide vertical, horizontal and yaw flight control. The helicopter  100  has a tail boom  108 , which supports the anti-torque assembly  110  at the aft end. The fixed blade pitch motors  112   a - g  provide counter-torque force for transversely stabilizing the helicopter  100 . Each of the fixed blade pitch motors  112   a - g  is mounted as part of the anti-torque assembly  110  on the tail boom  108 . The anti-torque assembly  110  is centered on a hub such that a leading edge of the anti-torque assembly  110  is presented to the side of the helicopter  100  toward the tail boom  108 . For example, when a single main rotor the helicopter  100  is rotating counter-clockwise when viewed from above, the leading edge of anti-torque assembly  110  is to the right (starboard) side of the helicopter  100 . 
     In  FIG. 2A  a top-view schematic diagram of a helicopter  100  shows the anti-torque assembly  110  on the tail boom  108  during hover mode with the direction of thrust to oppose the rotational motion of the main rotor during, e.g., hover. 
       FIG. 2B  shows a top-view of a helicopter  100  but the anti-torque assembly  110  on the tail boom  108  has been rotated about a single pivot or axis  114  with the direction of thrust shown toward the rear of the helicopter  100 , in this case adding to the forward thrust which is generally used during high airspeed cruise. In this embodiment, the pivot  114  is shown offset from the longitudinal axis of the tail boom  108 , however, the pivot  114  and the anti-torque assembly  110  can also be centered along the longitudinal axis of the tail boom  108 . 
     In operation, the anti-torque assembly  110  is oriented substantially in-plane with the tail boom  108  of the helicopter  100  during a first mode of helicopter operation. For example, the first mode of helicopter operation is a hover mode, which is typically a mode in which the helicopter  100  is sitting on or about the ground with the anti-torque assembly  110  provides thrust from the one or more fixed blade pitch motors  112   a - g  when the helicopter  100  is operating in slow speed flight. In this orientation, the anti-torque assembly  110  can provide maneuverability and trim to the helicopter operation. During hover, the direction of thrust of the one or more fixed blade pitch motors  112   a - g  of the anti-torque assembly  110  can be in opposing directions, for example, one subset of motors can direct their thrust in one direction, while another subset can be directed in the opposite direction to provide finer rotational control to the helicopter  100 . Of course, the speed of the individual motors can also be varied, under control of a logic in a flight control computer that calculates the position of the anti-torque assembly  110  during transition to and from the first to the second mode of operation and for independently controlling individual fan speeds to position the assembly for optimum thrust angle, as well as optimum thrust magnitude. 
     In a second mode of operation, the anti-torque assembly  110  is oriented substantially off-plane with the tail boom  108  of the helicopter  100  during a second mode of helicopter operations that is different from the first mode. For example, the second mode of helicopter operation is a flight mode (e.g., a low to high speed forward flight mode). In the flight mode, the orientation of the anti-torque assembly  110  is changed from being substantially co-planar with the tail boom  108  to being non-planar. For example, the anti-torque assembly  110  can be substantially perpendicular with the plane of the tail boom  108 , by pivoting about pivot  114 . Alternatively, the orientation of the anti-torque assembly  110  can be anywhere between co-planar and perpendicular relative to the tail boom  108 . 
       FIGS. 3A and 3B  show a schematic diagram of the anti-torque assembly  110  oriented in-plane with the tail boom  108  of the helicopter  100 . The anti-torque assembly  110  is mounted to the tail boom  108  of the helicopter  100  using pivot  114 . As shown in  FIG. 2 , the pivot  114  is offset from the tail boom  108  to allow the anti-torque assembly  110  to be rotated. In some implementations, a distance by which the anti-torque assembly  110  is offset from the tail boom  108  depends on the position of the pivot  114 . In this embodiment, the pivot  114  is connected a fork  116  attached to the tail boom  108 . The fork  116  includes an upper end  118  and a lower end  120 . The anti-torque assembly  110  is mounted to the fork  116  between the upper end  118  and the lower end  120 . For example, the anti-torque assembly  110  can include an upper pivot position  114   a  and a lower pivot position  114   b  attached to the upper end fork  116  and the lower end  120 , respectively. 
       FIG. 3B  is a schematic diagram of an elevation view of the anti-torque assembly  110  oriented in-plane with the tail boom  108  of the helicopter  100  on upper and lower pivots  114   a,b . The bottom portion of the fork  116 , which includes the lower end  120  can be thicker than the top portion of the fork  116  which includes the upper end  118 . When the helicopter  100  flares, e.g., during landing, the anti-torque assembly  110  is at its lowest point creating a risk of contact with the ground. If there is contact, the thicker bottom portion of the lower end  120  can provide greater strength to the fork  116  to take the force of contact and decrease (e.g., minimize or prevent) flexing, thereby protecting the anti-torque assembly  110 . In some implementations, a stinger (not depicted) can be connected to the fork  116  as an alternative or in addition to having a thicker bottom portion to take the force of contact and decrease flexing. 
       FIG. 3C  is a schematic diagram of the anti-torque assembly  110  oriented off-plane with the tail boom  108  of the helicopter  100 . In  FIG. 3C , the anti-torque assembly  110  has been rotated on a Z-axis that passes between the upper end axis  114   a  and the lower end axis  114   b  perpendicular from an in-plane orientation during a hover mode to an off-plane rotation during a flight mode in which the anti-torque assembly  110  is substantially perpendicular to a rotational plane of the tail boom  108 . In some implementations, the anti-torque assembly  110  can be pivoted on a horizontal X-axis to provide yaw control of the helicopter  100 . 
     A pivoting mechanism and the anti-torque assembly  110  can be included at the end of the tail boom  108  of the helicopter  100 . In some implementations, the pivoting mechanism can be electric, or can even be a bell crank system and can include a pulley cable system connected to the bell crank system. The pivoting mechanism can be controlled by an operator of the helicopter  100  to orient the anti-torque assembly  110  substantially in-plane with the tail boom  108  of the helicopter  100  during a first mode of helicopter operation, and to orient the anti-torque assembly  110  substantially off-plane with the tail boom  108  of the helicopter  100  during a second mode of helicopter operation that is different from the first mode. In a fly-by-wire configuration, the pivoting mechanism can be controlled by a logic in a flight control computer that calculates the position of the anti-torque assembly  110  during transition to and from the first to the second mode of operation and for independently controlling individual fan speeds to position the assembly for optimum thrust angle, as well as optimum thrust magnitude. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. In some implementations, the fixed blade pitch electric motor module can be controlled by pilot inputs in combination with the operating status of the air vehicle (e.g., hover, transition or forward flight). In implementations in which the rotorcraft is operated using some form of fly-by-wire or fly-by-light control systems, the fixed blade pitch electric motor module operation can be controlled by the computer system, which, in turn, can get cues from the pilot&#39;s inputs, etc. 
     All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects. 
     As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of” or “consisting of”. As used herein, the phrase “consisting essentially of” requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), propertie(s), method/process steps or limitation(s)) only. 
     The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context. 
     As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%. 
     All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.