Patent Publication Number: US-2020292410-A1

Title: Method and system for determining rotor states

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to and incorporates by reference the entire disclosure of U.S. Provisional Patent Application No. 62/816,382 filed on Mar. 11, 2019. 
    
    
     BACKGROUND 
     This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
     Rotor aircraft, such as helicopters and tiltrotor aircraft, include one or more rotor systems. Each rotor system includes a mast driven by a power source (e.g., an engine or motor) and a yoke connected to the mast. A plurality of rotor blades are generally indirectly connected to the yoke with bearings. The bearings may be, for example, elastomeric bearings constructed from a rubber type material that absorb vibration. The bearings accommodate forces acting on the rotor blades allowing each rotor blade to flex with respect to the yoke/mast and other rotor blades. The weight of the rotor blades and the lift of the rotor blades generated by action of the rotor blades may result in transverse forces on the yoke and other components. 
     During operation of the rotor system, the rotor blades experience different rotor states. Rotor states include flapping, coning, axial, feathering, and lead-lag. Flapping can refer to an up-and-down movement of a rotor blade positioned at a right angle to the plane of rotation or can refer to a gimballing of the hub or a teetering rotor. Coning generally refers to an upward flexing of a rotor blade due to lift forces acting on the rotor blade. Axial forces generally refer to a centrifugal force on the rotor blades resulting from rotation of the rotor blades. Lead-lag forces generally refer to forces resulting from a horizontal movement of the rotor blades about a vertical pin that occur if, for example, the rotor blades do not rotate at the same rate as the yoke. Feathering forces generally refer to forces resulting from twisting motions that cause a rotor blade to change pitch. 
     In some applications, it is desirable to quantify the various rotor states during operation of the rotor aircraft. Conventionally, the determination of the various rotor states has been done via mechanical linkages and sensors. While using mechanical linkages has proven successful, adding mechanical linkages to the rotor system adds complexity and weight to the rotor system. 
     SUMMARY 
     An example of a rotor-state determining system for a rotor system includes a hub attached to a mast, a rotor blade coupled to the hub, a first sensor positioned on a first component of the rotor system, wherein the first sensor is isolated from movement of the rotor blade, and a second sensor positioned on a second component of the rotor system, wherein the second sensor detects movement of the rotor blade. 
     An example of a rotor-state determining method for a rotorcraft includes, by a flight control computer, collecting data from a first sensor positioned on a first component of the rotorcraft, wherein the first sensor is isolated from movement of a rotor blade, collecting data from a second sensor positioned on a second component of the rotorcraft, wherein the second sensor detects movement of the rotor blade, filtering the data collected by the first sensor to remove noise from the data collected by the first sensor, filtering the data collected by the second sensor to remove noise from the data collected by the second sensor, calculating a difference between the filtered first data and the filtered second data to determine a parameter of the rotor blade, and responsive to a determination that the parameter of the rotor blade exceeds a threshold value, taking a corrective action. 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  illustrates a rotorcraft in accordance with aspects of the disclosure; 
         FIGS. 2A and 2B  illustrate prior art systems for determining blade flapping angle; 
         FIG. 3  is an illustrative schematic of a system for determining blade flapping angle according to aspects of the disclosure; 
         FIG. 4  is an illustrative schematic of a system for determining blade flapping angle according to aspects of the disclosure; 
         FIG. 5  is an illustrative process flow for determining flapping according to aspects of the disclosure; 
         FIG. 6  is an illustrative process flow for determining flapping according to aspects of the disclosure; 
         FIG. 7  is an illustrative schematic of a system for determining various rotor states according to aspects of the disclosure; 
         FIG. 8  is an illustrative schematic of a system for determining various rotor states according to aspects of the disclosure; 
         FIG. 9  is an illustrative schematic of a system for determining various rotor states according to aspects of the disclosure; and 
         FIG. 10  is a schematic diagram of a general-purpose processor (e.g. electronic controller or computer) system suitable for implementing aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure provides many different aspects, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the 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. 
     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, etc. 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 device described herein may be oriented in any desired direction. 
       FIG. 1  illustrates an example of a rotorcraft  10 . Rotorcraft  10  includes a fuselage  12 , a main rotor system  14  with rotor blades  16 , and a tail rotor system  18  with tail rotor blades  20 . An engine within fuselage  12  supplies main rotor system  14  and tail rotor system  18  with torque to rotate rotor blades  16  and tail rotor blades  20 . As illustrated in  FIG. 1 , rotorcraft  10  includes four rotor blades  16 . In other aspects, rotorcraft  10  could include as few as one, two, or three rotor blades  16  or more than four rotor blades  16  (e.g., five, six, etc.). Landing gear  22  extend from fuselage  12  and support rotorcraft  10  when rotorcraft  10  is landing or when rotorcraft  10  is at rest on the ground. Rotorcraft  10  includes a flight control computer  30  configured monitor and control aspects of rotorcraft  10 . Rotorcraft  10  is not meant to be limiting. Aspects of the disclosure apply to other rotorcraft as well. 
     Referring now to  FIGS. 2A-2B , prior art systems for determining blade flapping angle of a rotor blade are illustrated.  FIG. 2A  illustrates a system  200  for use with a teetering hub. System  200  includes a sensor  202  that is secured to a mast  204 . Sensor  202  is coupled to a rotor blade  206  via an arm  208  and a linkage  210 . Arm  208  is coupled to sensor  202  at one end and to a first end of linkage  210  at an opposite end. An opposite end of linkage  210  is coupled to a hub  212 . Rotor blade  206  is connected to hub  212  in a manner that allows for a teetering motion of rotor blade  206  about hub  212  (out of plane motion, such as blade flapping). System  200  also includes a feathering hinge  214  that permits a longitudinal rotation (e.g., feathering) of rotor blade  206  relative to hub  212  Out of plane motion of rotor blade  206  displaces linkage  210 , which causes arm  208  to rotate. The rotation of arm  208  is measured by sensor  202  to determine an amount of blade flapping. 
       FIG. 2B  illustrates a system  250  for use with an offset hinge rotor. System  250  includes a sensor  252  that is secured to a hub  254  of the offset hinge rotor. Hub  254  is coupled to a mast  256 . Sensor  252  is coupled to a rotor blade  258  via an arm  260  and a linkage  262 . Arm  260  is coupled to sensor  252  at one end and to a first end of linkage  262  at an opposite end. An opposite end of linkage  262  is coupled to a rotor blade  258  outboard of a flapping hinge  264 . Flapping hinge  264  allows rotor blade  258  to move out of plane to permit at least some amount of blade flapping. Out of plane motion of rotor blade  258  displaces linkage  262 , which causes arm  260  to rotate. The rotation of arm  260  is measured by sensor  252  to determine an amount of blade flapping. 
     While systems  200  and  250  are capable of determining blade flapping angle, they require the use of several mechanical components (e.g., arms and linkages) that add complexity and weight to the rotor system. Reducing the weight and complexity of these systems would be beneficial. 
     Referring now to  FIG. 3 , an illustrative schematic of a rotor system  300  is shown according to aspects of the disclosure. Rotor system  300  may incorporated into rotorcraft  10  or another aircraft. In other aspects, rotor system  300  may be incorporated into other machines that include rotors, such as a wind turbine and the like. Rotor system  300  is a teetering two-bladed rotor system and includes a teetering teetering hub  302  secured to a mast  304  about a flapping hinge  306 . Rotor system  300  includes a pair of rotor blades  308 ( 1 ),  308 ( 2 ), each of which is secured to teetering hub  302  via feathering hinges  310 ( 1 ),  310 ( 2 ). Feathering hinges  310 ( 1 ),  310 ( 2 ) allow rotor blades  308 ( 1 ),  308 ( 2 ) to feather about a longitudinal axis of rotor blades  308 ( 1 ),  308 ( 2 ). Flapping hinge  306  allows rotor blades  308 ( 1 ),  308 ( 2 ) to pivot relative to mast  304 . Only rotor blade  308 ( 1 ) is illustrated in  FIG. 3 . It should be understood that rotor system  300  is generally symmetric and that rotor blade  308 ( 2 ) is located opposite of rotor blade  308 ( 1 ). 
     Rotor system  300  also includes a first sensor  312  positioned on mast  304  and a second sensor  314  positioned on teetering hub  302 . First sensor  312  is an inertial sensor, such as an angular rate sensor, that senses out-of-plane angular velocity of the non-flapping portion of rotor system  300 . Inertial sensors measure motions relative to an inertial reference frame as opposed to sensors which measure motion relative to another body (e.g., sensor  202 ). Because first sensor  312  is isolated from teetering hub  302 , first sensor  312  only detects rigid body and elastic motions of rotorcraft  10 . In some embodiments, first sensor  312  could be located somewhere else on fuselage  12  or another part of the aircraft that is isolated from the motion of teetering hub  302 . Second sensor  314  is an inertial sensor, such as an angular rate sensor, that senses out-of-plane angular velocity of teetering hub  302  to detect flapping motions of rotor blade  308 ( 1 ). Teetering hub  302  is coupled to mast  304 , which is coupled to the airframe of rotorcraft  10 . As a result, second sensor  314  also detects the rigid body and elastic motions of rotorcraft  10 , in addition to the flapping motions of rotor blade  308 ( 1 ). The difference in the angular velocity measured by sensors  312 ,  314  provides the instantaneous relative velocity of teetering hub  302 , which can be used to estimate the flapping displacement of rotor blade  308 ( 1 ) using a variety of techniques that are discussed in more detail relative to  FIGS. 5 and 6  below. This concept can be extended to measure other rotor states (e.g., lead-lag, feathering, coning) and to other rotor system configurations (e.g., fully articulated or flexured rotors). 
     Referring now to  FIG. 4 , an illustrative schematic of a rotor system  400  is shown. Rotor system  400  illustrates an offset-hinge rotor and includes a hub  402  and a first sensor  412  secured to a mast  404 . Rotor system  400  also includes a pair of rotor blades  408 ( 1 ),  408 ( 2 ), each of which is secured to hub  402  via flapping hinges  406 ( 1 ),  406 ( 2 ), respectively. Flapping hinges  406 ( 1 ),  406 ( 2 ) allow rotor blades  408 ( 1 ),  408 ( 2 ) to pivot relative to mast  404  to allow flapping. Only rotor blade  408 ( 1 ) is illustrated in  FIG. 4 . It should be understood that rotor system  400  is generally symmetric and that rotor blade  408 ( 2 ) is located opposite of rotor blade  408 ( 1 ). 
     Rotor system  400  includes first sensor  412  that is positioned on hub  402  and a second sensor  414  that is positioned outboard of flapping hinge  406 ( 1 ). First sensor  412  is an inertial sensor, such as angular rate sensor that senses out-of-plane angular velocity of a non-flapping portion of hub  402 . First sensor  412  detects rigid body and elastic motions of the aircraft. Second sensor  414  is an inertial sensor that senses out-of-plane angular velocity of the portion of hub  402  and/or rotor blade  408 ( 1 ) outboard of flapping hinge  406 ( 1 ). Second sensor  414  detects flapping motions and rigid body and elastic motions of the aircraft. The difference in the angular velocity between sensors  412 ,  414  is the angular velocity of the flapping motion, which can be used to estimate flapping displacement using a variety of techniques that are discussed in more detail relative to  FIGS. 5 and 6  below. Off-axis motions are a source of error, though the errors are small if the motions are small. The amount of off-axis motion depends on hub configuration (e.g., gimballed, teetering, flexured, bearingless) and location of the sensors relative to real or virtual hinges. 
       FIG. 5  is an illustrative method  500  for determining flapping using the rotor domain.  FIG. 5  is discussed relative to  FIG. 4  above. Those of skill in the art will recognize that aspects of method  500  may be applied to other rotor systems as well. In a typical aspect, flight control computer  30  carries out method  500 . In other aspects, a separate computer module may carry out method  500 . The separate computer module may be coupled to flight control computer  30 . Method  500  begins with step  502 . In step  502 , movement of rotor blade  408 ( 1 ) is monitored. Monitoring movement of rotor blade  408 ( 1 ) includes collecting angular-rate data from sensors  412 ,  414 . Method  500  then proceeds to step  504 . 
     In step  504 , the data from one or both of sensors  412 ,  414  is filtered. For example, out-of-band content is removed from the data to improve a signal to noise ratio (SNR) of the data. For example, step  504  can include filtering data received from first sensor  412  to remove high-frequency and low-frequency noise from data output by first sensor  412 . Data from second sensor  414  may be similarly filtered in step  504 . Method  500  then proceeds to step  506 . 
     At step  506 , a difference between the fixed and flapping angular velocities is determined to reject rigid body and elastic motions of mast  404 . For example, flight control computer  30  may determine the difference by subtracting the magnitude of the data of first sensor  412  from the magnitude of the data of second sensor  414 . The difference between the two data sets describes a parameter of the rotor blade, which in this example is an amount of flapping of rotor blade  408 ( 1 ). In other aspects, the parameter may describe coning, feathering, lead/lag, or the like. In some aspects, method  500  proceeds to step  508  in which the data from step  506  may be filtered to further improve the SNR. In some aspects, step  508  is optional. Method  500  then proceeds to step  510 . 
     At step  510 , the 1/revolution sine and cosine components of the difference signals are extracted from the output of step  508 , which can be done using known techniques. An azimuth of mast  404  is used to provide a phase reference for demodulation of motion into its sine and cosine components and for RPM measurement. In some aspects, the value of the azimuth of mast  404  is a property known by flight control computer  30 . The extracted sine/cosine components of step  510  are used in step  512  to scale from velocity to displacement (e.g., via integration). In some aspects, bandwidth is low enough to assume quasi-sinusoidal steady state. At step  514 , non-ideal effects incurred due to filtering and delays can be directly accounted for using various known techniques. Step  514  outputs a determined flapping displacement. Method  500  then proceeds to step  516 . 
     At step  516 , flight control computer  30  compares the determined flapping displacement to a threshold value of flapping displacement. The threshold value of flapping displacement is a maximum amount of flapping that is desirable. Exceeding the maximum amount of flapping can lead to damage, loss of control, or other failures. If the value of the determined flapping displacement is less than the threshold value, rotorcraft  10  continues operation and method  500  returns to step  502 . If the value of the determined flapping displacement is greater than the threshold value of flapping displacement, method  500  proceeds to step  518  and flight control computer  30  takes a corrective action. The corrective action can be an automatic change to an operating parameter of rotorcraft  10  (e.g., change pitch of the rotor blades, change amount or direction of cyclic, change amount of collective, change rpm of the rotor blades, etc.) and/or an alert or alarm that is presented to a pilot (e.g., a flashing light, an audible warning, a vibrating seat, and the like). 
       FIG. 6  is an illustrative method  600  for determining flapping using the time domain.  FIG. 6  will be discussed relative to  FIG. 4  above. In a typical aspect, flight control computer  30  carries out method  600 . In other aspects, a separate computer module may carry out method  600 . The separate computer module may be coupled to flight control computer  30 . Steps  602 ,  604 ,  606 , and  608  are similar to steps  502 ,  504 ,  506 , and  508  discussed above relative to  FIG. 5 . At step  610 , flight control computer  30  determines an integral of the resulting flapping velocity signal of step  608  to produce displacement signals. For example, a lossy integration technique can be used. The integrator is configured to remove any steady-state or offset errors that build over time due to non-idealities in the source data or signal conditioning. Steps  612 - 616  are similar to steps  514 - 518  discussed above relative to  FIG. 5 . 
     Referring now to  FIG. 7 , an illustrative schematic of a rotor system  700  is shown. Rotor system  700  illustrates a discrete hinge example and includes a hub  702  secured to a mast  704 . Rotor system  700  also includes a pair of rotor blades  708 ( 1 ),  708 ( 2 ) secured to hub  702 . Rotor blades  708 ( 1 ),  708 ( 2 ) are secured to hub  702  via flapping hinges  706 ( 1 ),  706 ( 2 ), feathering hinges  710 ( 1 ),  710 ( 2 ), and lead-lag hinges  720 ( 1 ),  720 ( 2 ), respectively. In some aspects, hinges  706 ,  710 , and  720  may be connected in series as a part of an armature or linkage that is disposed between hub  702  and rotor blade  708 . Only rotor blade  708 ( 1 ) is illustrated in  FIG. 7 . It should be understood that rotor system  700  is generally symmetric and that rotor blade  708 ( 2 ) is located opposite of rotor blade  708 ( 1 ). 
     Rotor system  700  also includes a first sensor  712  that is positioned on hub  702 , a second sensor  714  that is positioned between lead-lag hinge  720 ( 1 ) and flapping hinge  706 ( 1 ), a third sensor  716  positioned between flapping hinge  706 ( 1 ) and feathering hinge  710 ( 1 ), and a fourth sensor  718  positioned between feathering hinge  710 ( 1 ) and rotor blade  708 ( 1 ). Each of sensors  712 - 718  are inertial sensors that measure motions relative to inertial reference frames as illustrated by arrows in  FIG. 7 . 
     Including sensors  712 - 718  allows for lead-lag, coning, flapping, and feathering rotor states to be monitored. Lead-lag motion can be estimated from an angular velocity difference in local Z-axis rotation sensed by first sensor  712  and second sensor  714 . Coning can be measured as a quasi-steady angular velocity difference in local Z-axis rotation sensed by first sensor  712  and third sensor  716 . The difference in sensed rotational velocity varies with the cosine of the coning angle. Flapping motion appears as oscillatory content and is the second harmonic of actual flapping motion and also appears in the difference in sensed angular velocity as the first harmonic of rotor angular motion. Oscillatory feathering motion can be estimated from the difference in local X-axis rotation between third sensor  716  and fourth sensor  718 . The Z and Y axes of fourth sensor  718  contain flapping, coning, and lead-lag motion information. However, these measurements may have components of other motions in them due to off-axis effects. One of skill in the art will recognize that the concepts of methods  500  and  600  may be used in combination with rotor system  700  to determine various aspects of the rotor states thereof (e.g., lead-lag, coning, flapping, and feathering rotor states). 
     Referring now to  FIG. 8 , an illustrative schematic of a rotor system  800  is shown. Rotor system  800  illustrates a hingeless/bearingless rotor system and includes a hub  802  secured to a mast  804 . Rotor system  800  includes a pair of rotor blades  808 ( 1 ),  808 ( 2 ) that are coupled to hub  802  via flexures  806 ( 1 ),  806 ( 2 ), respectively. Only rotor blade  808 ( 1 ) is illustrated in  FIG. 8 . It should be understood that rotor system  800  is generally symmetric and that rotor blade  808 ( 2 ) is located opposite of rotor blade  808 ( 1 ). 
     Rotor system  800  also includes a first sensor  812  that is positioned on hub  802  and a second sensor  814  that is positioned outboard of flexure  806 ( 1 ). Each of sensors  812 ,  814  are inertial sensors, such as multi-axis angular rate sensors. Including sensors  812 - 814  allows for lead-lag, coning, flapping, and feathering rotor states to be monitored. Flapping and coning angle motion can be determined based upon an angle between the rotation vector indicated by first sensor  812  and the rotation vector indicted by a second sensor  814 , projected onto the rotating XZ plane. Lead-lag angular motion can be determined based upon the difference in magnitude of rotation vectors indicated by first sensor  812  and second sensor  814 . It is noted that flapping, feathering, and coning change a direction of the rotation vector sensed by second sensor  814 , but not the magnitude of an output of second sensor  814 . Feathering angle can be determined based upon a projection onto the rotating YZ plane of an angle between a rotation vector provided by first sensor  812  and second sensor  814 . Rotor speed can be determined based upon rotation indicated by first sensor  812  about the Z axis. One of skill in the art will recognize that the concepts of methods  500  and  600  may be used in combination with rotor system  800  to determine various aspects of the rotor states thereof (e.g., lead-lag, coning, flapping, and feathering rotor states). 
     Referring now to  FIG. 9 , an illustrative schematic of a rotor system  900  is shown. Rotor system  900  illustrates a hingeless/bearingless rotor system and includes a hub  902  secured to a mast  904 . Rotor system  900  includes a pair of rotor blades  908 ( 1 ),  908 ( 2 ) that are coupled to hub  902  via flexures  906 ( 1 ),  906 ( 2 ), respectively. Only rotor blade  908 ( 1 ) is illustrated in  FIG. 9 . It should be understood that rotor system  900  is generally symmetric and that rotor blade  908 ( 2 ) is located opposite of rotor blade  908 ( 1 ). 
     Rotor system  900  also includes a first sensor  912  that is positioned on hub  902  and coaxial with mast  904 , a second sensor  914  that is positioned on hub  902  but outboard of a centerline of mast  904 , and a third sensor  916  that is positioned on rotor blade  908 ( 1 ). First sensor  912  and third sensor  916  are three-axis accelerometers and second sensor  914  is an angular rate sensor. Including sensors  912 - 916 , each of which may be an inertial sensor, allows for lead-lag, coning, and flapping rotor states to be monitored. Flapping and coning angular motion can be determined based upon an out-of-plane (of rotor rotation) projection of an angle between a centrifugal force (CF) vector computed by second sensor  914  (about the Z axis; corrected by first sensor  912 ) and a CF vector indicted by third sensor  916 . Lead-lag angle can be determined by an in-plane (of rotor rotation) projection of an angle between a CF vector computed by second sensor  914  (about the Z axis; corrected by first sensor  912 ) and a CF vector indicted by third sensor  916 . RPM can be determined based upon second sensor  914  about the Z axis. One of skill in the art will recognize that the concepts of methods  500  and  600  may be used in combination with rotor system  900  to determine various aspects of the rotor states thereof (e.g., lead-lag, coning, and flapping rotor states). 
     Referring now to  FIG. 10 , a schematic diagram of a general-purpose processor (e.g. electronic controller or computer) system  31  suitable for implementing the aspects of this disclosure is shown. System  31  includes processing component and/or processor  32  suitable for implementing one or more aspects disclosed herein. In some aspects, flight control computer  30  and/or other electronic systems of rotorcraft  10  may include one or more systems  31 . In addition to processor  32  (which may be referred to as a central processor unit or CPU), system  31  might include network connectivity devices  33 , random access memory (RAM)  34 , read only memory (ROM)  35 , secondary storage  36 , and input/output (I/O) devices  37 . In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processor  32  might be taken by the processor  32  alone or by the processor  32  in conjunction with one or more components shown or not shown in the system  31 . It will be appreciated that the data described herein can be stored in memory and/or in one or more databases. 
     Processor  32  executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices  33 , RAM  34 , ROM  35 , or secondary storage  36  (which might include various disk-based systems such as hard disk, floppy disk, optical disk, or other drive). While only one processor  32  is shown, multiple processors  32  may be present. Thus, while instructions may be discussed as being executed by processor  32 , the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors  32 . The processor  32  may be implemented as one or more CPU chips and/or application specific integrated chips (ASIC s). 
     The network connectivity devices  33  may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices  33  may enable the processor  32  to communicate with the Internet or one or more telecommunications networks or other networks from which the processor  32  might receive information or to which the processor  32  might output information. 
     The network connectivity devices  33  might also include one or more transceiver components  38  capable of transmitting and/or receiving data wirelessly in the form of electromagnetic waves, such as radio frequency signals or microwave frequency signals. Alternatively, the data may propagate in or on the surface of electrical conductors, in coaxial cables, in waveguides, in optical media such as optical fiber, or in other media. The transceiver component  38  might include separate receiving and transmitting units or a single transceiver. Information transmitted or received by the transceiver component  38  may include data that has been processed by the processor  32  or instructions that are to be executed by processor  32 . Such information may be received from and outputted to a network in the form, for example, of a computer data baseband signal or signal embodied in a carrier wave. The data may be ordered according to different sequences as may be desirable for either processing or generating the data or transmitting or receiving the data. The baseband signal, the signal embedded in the carrier wave, or other types of signals currently used or hereafter developed may be referred to as the transmission medium and may be generated according to several methods well known to one skilled in the art. 
     RAM  34  might be used to store volatile data and perhaps to store instructions that are executed by the processor  32 . The ROM  35  is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage  36 . ROM  35  might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM  34  and ROM  35  is typically faster than to secondary storage  36 . The secondary storage  36  is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM  34  is not large enough to hold all working data. Secondary storage  36  may be used to store programs or instructions that are loaded into RAM  34  when such programs are selected for execution or information is needed. 
     The I/O devices  37  may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, transducers, sensors, or other well-known input or output devices. Also, transceiver component  38  might be considered to be a component of the I/O devices  360  instead of or in addition to being a component of the network connectivity devices  33 . Some or all of the I/O devices  37  may be substantially similar to various components disclosed herein and/or may be components of a flight control system and/or other electronic systems of rotorcraft  10 . 
     The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” “generally,” and “about” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. For example, the various rotor systems described herein may be incorporated into various devices/machines that include rotors such as wind turbines and the like. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.