Abstract:
A rotor blade assembly includes a rotor blade and a movable trim tab located along a span of the rotor blade. A linear positioner is located inside the rotor blade and operably connected to the trim tab to move the trim tab thereby reducing rotor blade vibration. A method for reducing vibration of a rotor assembly includes energizing a linear positioner located inside a rotor blade of the rotor assembly and moving an output piston of the linear positioner. A trim tab located at the rotor blade is moved to a selected trim tab angle relative to the rotor blade by the output piston, and the linear positioner is deenergized thereby locking the trim tab at the selected trim tab angle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to rotary-winged aircraft. More specifically, the subject matter disclosed herein relates to actuation of control surfaces of rotary-winged aircraft rotor blades. 
         [0002]    Manufacturing and assembly tolerances of rotors for, for example, rotary-winged aircraft such as helicopters, are often such that the resulting rotor is not balanced either in terms of weight, or lift produced by the rotor blades. The imbalance manifests itself in undesirable vibration and/or noise under certain flight conditions. Such issues also occur in other rotor applications, such as those for wind turbines. To mitigate the vibration issues, typically rotor blades are selectively weighted or trim tabs located at a trailing edge of the rotor blades are adjusted to balance the rotor. Trim tabs are bendable or movable portions of the rotor blade trailing edge and are typically bent upwards or downwards by ground maintenance personnel utilizing gages and tools to adjust position of the trim tab to reduce or eliminate the vibration. Such methods of adjustment are time consuming and cumbersome, and as stated, are only performed on the ground by maintenance personnel. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In one embodiment, a rotor blade assembly includes a rotor blade and a movable trim tab located along a span of the rotor blade. A linear positioner is located inside the rotor blade and operably connected to the trim tab to move the trim tab thereby reducing rotor blade vibration. 
         [0004]    In another embodiment, a rotary-winged aircraft includes an airframe and a main rotor assembly operably connected to the airframe. The main rotor assembly includes a plurality of rotor blade assemblies rotatable about a rotor assembly axis, at least one rotor blade assembly of the plurality of rotor blade assemblies including a rotor blade and a movable trim tab located along a span of the rotor blade. A linear positioner is located inside the rotor blade and operably connected to the trim tab to move the trim tab thereby reducing rotor blade vibration. 
         [0005]    In yet another embodiment, a method for reducing vibration of a rotor assembly includes energizing a linear positioner located inside a rotor blade of the rotor assembly and moving an output piston of the linear positioner. A trim tab located at the rotor blade is moved to a selected trim tab angle relative to the rotor blade by the output piston, and the linear positioner is deenergized thereby locking the trim tab at the selected trim tab angle. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a schematic illustration of an embodiment of a rotary-winged aircraft; 
           [0009]      FIG. 2  is a schematic illustration of an embodiment of a rotor blade assembly for a rotary-winged aircraft; 
           [0010]      FIG. 3  is a schematic illustration of an embodiment of a trim tab and linear positioner arrangement of rotor blade assembly for a rotary-winged aircraft; 
           [0011]      FIG. 4  is a plan view of an embodiment of a linear positioner of a rotor blade assembly; 
           [0012]      FIG. 5  is a cross-sectional view A-A of the embodiment of a linear positioner of  FIG. 4 ; and 
           [0013]      FIG. 6  is a cross-sectional view B-B of the embodiment of a linear positioner of  FIG. 4 . 
       
    
    
       [0014]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawing. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Shown in  FIG. 1  is a schematic of a rotary wing aircraft, in this embodiment, a helicopter  10 . The helicopter  10  includes a main rotor assembly  12 , and an airframe  14  having an extending tail  16  at which is mounted an anti-torque rotor  18 . Although the aircraft illustrated is a helicopter  10 , it is to be appreciated that other machines, such as turbo props or tilt-rotor aircraft or coaxial or tandem rotor helicopters or other structures such as wind turbine blades may also benefit from the system of the present disclosure. The main rotor assembly  12  includes a plurality of rotor blades  20  located about a rotor axis  22  via a rotor hub assembly  24 . Further, it is to be appreciated that the rotor blade  20  configurations described herein may be applied to other rotor assemblies, such as those for wind turbines. 
         [0016]    Referring now to  FIG. 2 , each rotor blade  20  extends from a blade cuff  26 , at which the rotor blade  20  is secured to the hub assembly  24  (best shown in  FIG. 1 ). The rotor blade  20  includes a root section  28  nearest the blade cuff  26  and a tip section  30  at a most radially outboard portion of the rotor blade  20 . A midspan section  32  is located between the root section  28  and the tip section  30 . Each rotor blade  20  section may be further defined by particular airfoil shapes or geometries to result in desired aerodynamic properties and performance of each section, and the rotor blade  20  as a whole. When the rotor blade  20  is rotated about the rotor axis  22 , a centrifugal force acting outwardly toward the rotor blade tip section  30  is imparted on the rotor blade and its components. 
         [0017]    Referring to  FIGS. 2 and 3 , the rotor blade  20  includes one or more trim tabs  34  located at a trailing edge  36  of the rotor blade  20 . The trim tabs  34  extend at least partially along the rotor blade  20  in a spanwise direction  38  and at least partially into the rotor blade  20  in a chordwise direction  40 . The trim tabs  34  are movable about a pivot axis  42  that extends along the spanwise direction  38 . To position the trim tab  34  at a selected trim tab angle  44 , a linear positioner  46  is operably connected to the trim tab  34  and located between a pressure side  48  and a suction side  50  of the rotor blade  20 . Such a linear positioner is suitable for use in high “g” environments, in some embodiments up to about 750 g. The linear positioner  46  includes an output piston  52  that translates in the chordwise direction  40  and, via connection to trim tab  34 , urges rotation of the trim tab  34  about the pivot axis  42 . Alternatively, the output piston  52  may translate in the spanwise direction  38  and is connected to the trim tab  34  via a bell crank or other linkage arrangement. To alter the position of the trim tab  34  to reduce vibration caused by, for example, rotor imbalance or certain flight conditions, the linear positioner  46  is energized. The output piston  52  translates chordwise, either toward the trailing edge  36  or toward a leading edge  54  of the rotor blade  20 . This results in the trim tab  34  pivoting about the pivot axis  42  to the selected trim tab angle  44 . When the selected trim tab angle  44  is achieved, the linear positioner  46  may be de-powered, thus locking position of the trim tab  34 . As will be described in more detail below, such adjustment of the trim tab  34  position may be accomplished via pilot input during flight, not only during ground maintenance operations as with prior art systems. 
         [0018]    Referring now to  FIG. 4-6 , the linear positioner  46  is shown in more detail. The linear positioner  46  includes an electric motor  56 , in some embodiments, a high power density brushless DC motor. The motor  56  is operably connected to, and drives a gear assembly  58 , which is, in turn, connected to a planetary roller screw nut  70 , which drives the output piston  52 . As shown, the motor  56  is oriented transverse to the output piston  52 , or in the spanwise direction  38 . Referring to  FIG. 5 , a cross-sectional view through a portion of the linear positioner  46  is shown. The motor  56  includes a motor shaft  60  extending therethrough. The motor shaft  60  includes a plurality of motor shaft gear teeth  62  that mesh with a reduction gear  64  of the gear assembly  58 . In some embodiments, as shown, the reduction gear  64  is a high single reduction spiral drive, worm gear or bevel gear  64 . It provides continuously meshing teeth resulting in smooth power transfer and efficient transmission of load from the motor shaft  60 , with a gear ratio sufficient to prevent back drive of the output piston  52 . Referring to  FIG. 6 , the reduction gear  64  drives a planetary roller nut  70 . Threaded rollers  72  between a screw shaft  68  and the planetary roller nut  70  comprise the load bearing elements of a rollerscrew  66  assembly. The use of the threaded rollers  72  result in an increased number of contact points enabling the rollerscrew  66  assembly to support high loads. To increase wear resistance of the threaded rollers  72 , a lubricant such as oil, grease, or dry lubricant may be utilized. Further, the rollers  72  may be constructed of one or more self-lubricating materials. The rollers  72  contact the planetary roller nut  70  and screw shaft  68  threads, thus transferring lubricant thereto. 
         [0019]    The planetary roller nut  70  and the reduction gear  64  are supported by a set of bearings  74 . In some embodiments, the bearings  74  are deep groove ball bearings. A first bearing  74   a  is located axially along the planetary roller nut  70  to carry actuator thrust loads and radial loads, while a second bearing  74   b  is free to move axially along the housing bore and carries radial loads. The screw shaft  68  is fitted with an anti-rotation device so as the planetary roller nut  70  is rotated by operation of the motor  56 , the rotation is translated into linear motion of the screw shaft  68  and the output piston  52 . Referring again to  FIG. 5 , the motor  56  includes motor bearings  76  to support the motor shaft  60 . The motor bearings are also deep groove ball bearings, in some embodiments. In some embodiments, the bearings  74  and motor bearings  76  are constructed using ceramic or steel balls or rollers, and solid lubricant impregnated separators. It is to be appreciated, however, that in other embodiments other materials may be utilized for construction of the bearings  74  and motor bearings  76 . 
         [0020]    Referring again to  FIG. 6 , the screw shaft  68  is connected to the output piston  52  including a shaft eye  78  that moves linearly when driven by linear motion of the screw shaft  68 . In some embodiments, the output piston  52  is coated with a hard facing matrix impregnated with appropriate dry lubricant. The output piston  52  is supported by two dry lubricated linear bearings  92 . In some embodiments, the shaft eye  78  includes a spherical bearing  80  to connect to the trim tab  34  while accommodating misalignment between the trim tab  34  and the linear positioner  46 . The output piston  52  includes a magnet  82  for determining a travel limit and end stops of the shaft eye  78  movement. The magnet  82  operates Hall effect switches or other proximity switches (not shown) that are connected to an electronic controller  86  (shown best in  FIG. 4 ) controlling operation of the linear positioner  46  via control of the electric motor  56 . 
         [0021]    Referring to  FIG. 4 , the controller  86  includes serial connection  88  to an aircraft control system (not shown) and/or wireless connectivity thereto. Connection to the aircraft control system allows for adjustment of the trim tab  34  by the pilot or operator, even during flight. In some embodiments, the adjustment of the trim tab  34  position may occur automatically, triggered by, for example, a vibration sensor (not shown). 
         [0022]    Referring again to  FIGS. 5 and 6 , to adjust the trim tab  34 , the electric motor  56  is energized by a power connection to the airframe  14 , or by a battery  90  located at, for example, the controller  86 . Power to the electric motor  56  drives rotation of the motor shaft  60 , which in turn drives the screw shaft  68  linearly via the reduction gear  64 . Rotation of the planetary roller nut  70  translates into linear motion of the screw shaft  68 , output shaft  52  and the shaft eye  78 . The linear motion drives rotation of the trim tab  34  about the pivot axis  42  to the selected trim tab angle  44 . When the selected trim tab angle  44  is achieved, the controller  86  is deenergized, and the position of the trim tab  34  is locked via the gear mesh between the motor shaft  60  and the reduction gear  64 . In high vibration environments, other locking mechanisms may be utilized, such as magnetic devices, brakes or clutches. 
         [0023]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.