Abstract:
A rotary wing aircraft includes a rotor assembly includes a rotor sensor generating a rotor sensor time domain signal; a rotor transform module converting the rotor sensor time domain signal to a rotor sensor frequency domain signal; and a rotor transceiver for transmitting the rotor sensor frequency domain signal over a transfer medium; an airframe assembly including: an airframe transceiver receiving the rotor sensor frequency domain signal; and an airframe transform module converting the rotor sensor frequency domain signal to the rotor sensor time domain signal. Signals from the airframe assembly may also be converted to the frequency domain prior to transfer over the transfer medium to the rotor assembly.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates generally to rotary wing aircraft, and in particular to harmonic data transfer in a rotary wing aircraft. 
         [0002]    In a rotary wing aircraft, signals are often transferred between a stationary component (e.g., the airframe) and a rotating component (e.g., rotor system). For example, rotary wing aircraft having active rotors transfer rotor sensor signals from sensors on the rotor blades to a control system in the airframe. Control signals from an airframe control system are also transferred from the airframe to the rotor system. Transferring a time domain signal between the airframe system and rotor system requires significant bandwidth. Delays in signal transfer can impede certain control techniques due to a lack of consistent and timely data transfer between system components. Signal dimension and capacity limitations in transfer media results can preclude certain control techniques, altogether. 
       SUMMARY 
       [0003]    One embodiment includes a rotary wing aircraft includes a rotor assembly includes a rotor sensor generating a rotor sensor time domain signal; a rotor transform module converting the rotor sensor time domain signal to a rotor sensor frequency domain signal; and a rotor transceiver for transmitting the rotor sensor frequency domain signal over a transfer medium; an airframe assembly including: an airframe transceiver receiving the rotor sensor frequency domain signal; and an airframe transform module converting the rotor sensor frequency domain signal to the rotor sensor time domain signal. 
         [0004]    Another embodiment includes a method for transferring signals in a rotary wing aircraft, the method including in a rotor system, generating a rotor sensor time domain signal; converting the rotor sensor time domain signal to a rotor sensor frequency domain signal; and transmitting the rotor sensor frequency domain signal over a transfer medium; in an airframe system, receiving the rotor sensor frequency domain signal; and converting the rotor sensor frequency domain signal to the rotor sensor time domain signal. 
         [0005]    Another embodiment includes a rotary wing aircraft including an airframe assembly including: an airframe controller generating an airframe time domain signal; an airframe transform module converting the airframe time domain signal to an airframe frequency domain signal; and an airframe transceiver for transmitting the airframe frequency domain signal over a transfer medium; a rotor assembly including: a rotor transceiver receiving the airframe frequency domain signal; and a rotor transform module converting the airframe frequency domain signal to the airframe time domain signal. 
         [0006]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Referring now to the drawings wherein like elements are numbered alike in the several FIGURES, in which: 
           [0008]      FIG. 1  depicts a rotary wing aircraft in an exemplary embodiment; 
           [0009]      FIG. 2  depicts a block diagram of a system for transferring data between a rotor assembly and airframe assembly in an exemplary embodiment; and 
           [0010]      FIG. 3  depicts transmission and transformation of signals between airframe assembly and rotor assembly in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  illustrates a rotary wing aircraft  10  having a main rotor system  12  in an exemplary embodiment. The aircraft  10  includes an airframe  14  having an extending tail  16  which mounts a tail rotor system  18 , such as an anti-torque system, a translational thrust system, a pusher propeller, a rotor propulsion system, and the like. The main rotor system  12  is driven about an axis of rotation R through a main gearbox (illustrated schematically at  20 ) by one or more engines  22 . The main rotor system  12  includes a plurality of rotor blades  24  mounted to a rotor hub  26 . Although a particular rotary wing aircraft configuration is illustrated, other configurations and/or machines, such as high speed compound rotary wing aircraft with supplemental translational thrust systems, swashplateless rotor configurations, dual contra-rotating aircraft, coaxial rotor system aircraft, turbo-props, tilt-rotors and tilt-wing aircraft, will also benefit from embodiments of the invention. 
         [0012]    FIG,  2  is a block diagram of a system for transferring data between a rotor assembly  30  and airframe assembly  40  in an exemplary embodiment. Airframe assembly  40  is located in the airframe  14  and includes an airframe controller  42 . Airframe controller  42  may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, airframe controller  42  may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. Airframe controller  42  may also be part of a flight control system that is part of the rotary wing aircraft  10 . 
         [0013]    Airframe controller  42  includes an airframe transform module  44  that converts signals from one domain to another domain, and vice versa. In exemplary embodiments, the airframe transform module  44  is a fast Fourier transform (FFT) module to convert signals from the time domain to the frequency domain. Airframe transform module  44  also performs an inverse transform, from the frequency domain to the time domain. An airframe transceiver module  46  is used to send and receive signals over a transfer medium  50  that communicates signals between the airframe assembly  40  and rotor assembly  30 . 
         [0014]    Airframe sensors  48  detect conditions of the airframe  14  and provide airframe sensor signals to airframe controller  42 . Airframe sensors  48  may detect a variety of conditions, such as position of airframe elements, speed, acceleration, etc. Airframe sensors  48  produce airframe sensor signals in a first domain, for example, the time domain. 
         [0015]    Rotor assembly  30  is located in the rotor system  12 . Portions of the rotor assembly may be mounted in the rotor hub  26  and other portions in rotor blades  24 . A rotor controller  32  is positioned, for example, in rotor hub  26 . Rotor controller  32  may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, rotor controller  32  may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. 
         [0016]    Rotor controller  32  includes a rotor transform module  34  that converts signals from one domain to another domain, and vice versa. In exemplary embodiments, the rotor transform module  34  is a fast Fourier transform (FFT) module to convert signals from the time domain to the frequency domain. Rotor transform module  34  also performs an inverse transform, from the frequency domain to the time domain. A rotor transceiver module  36  is used to send and receive signals over a transfer medium  50  that communicates signals between the airframe assembly  40  and rotor assembly  30 . 
         [0017]    Rotor sensors  38  detect conditions of the rotor system  12  and provide rotor sensor signals to rotor controller  32 . Rotor sensors  38  may detect a variety of conditions, such as position of rotor elements, speed, acceleration, etc. Rotor sensors  38  produce rotor sensor signals in a first domain, for example, the time domain. Rotor sensor signals from rotor sensors  38  are provided to rotor controller  32 . Rotor controller  32  may generate control signals for rotor actuators  39  in response to the rotor sensor signals. Rotor controller  32  may also transmit the rotor sensor signals to airframe controller  42  as described in further detail herein. 
         [0018]    Rotor actuators  39  may interface with a variety of components on the rotor system  12 . For example, rotor actuators  39  may be included in rotor hub  26  to control individual blade pitch, lead-lag, flap, etc. Rotor actuators  39  may also be positioned in rotor blades  24  to control flight characteristics of the rotor blades  24 . For example, rotor blades  24  may be active rotor blades having control surfaces positioned by rotor actuators  39 . Rotor actuators  39  may be electrically controlled actuators that impart physical movement to components of the rotor system  12  in response to control signals from rotor controller  32 . 
         [0019]    Transfer medium  50  may be a wired link, such as a slip ring. Alternatively, transfer medium may be a wireless link, such as a UHF, WIFI broadband, rotary transformer, optical communication, etc. In this embodiment, airframe transceiver  46  and rotor transceiver  36  use wireless communications protocols (e.g., 802.11x, Bluetooth, NFC) to send signals wirelessly, if using UHF or WIFI broadband, and other appropriate digital protocols for the other types of transfer medium  50 . 
         [0020]      FIG. 3  depicts transmission and transformation of signals between airframe assembly  40  and rotor assembly  30 .  FIG. 3  depicts a scenario where a rotor sensor time domain signal is generated at rotor sensor  38  and then transformed to a rotor sensor frequency domain signal by rotor transform module  34 . Rotor transceiver  36  transmits the rotor sensor frequency domain signal to airframe transceiver  46  over the transfer medium  50 . Airframe transform module  44  performs an inverse frequency transform to provide the rotor sensor time domain signal to airframe controller  42 . It is understood that the output of the airframe transform module  44  may not exactly match the original rotor sensor time domain signal, due to errors (e.g., roundoff) in the particular transform/inverse transform used. References to the rotor sensor time domain signal after transform/inverse transform includes such errors, along with errorless versions. 
         [0021]    Airframe controller  42  generates an airframe time domain control signal (e.g., adjust blade pitch) in response to the various sensor signals. An airframe sensor time domain signal from airframe sensor  48  may also be obtained by airframe controller  42 . The airframe time domain signals  41  (e.g., control signals and/or sensor signals) are transformed to airframe frequency domain signals by airframe transform module  44 . The airframe frequency domain signals are transmitted across transmission medium by airframe transceiver  46 . 
         [0022]    The rotor transceiver  36  receives the airframe frequency domain signals. The rotor transform module  34  converts the airframe frequency domain signals to airframe time domain signals by applying the inverse transform. It is understood that the output of the rotor transform module  34  may not exactly match the original airframe time domain signal, due to errors (e.g., roundoff) in the particular transform-inverse transform used. References to the airframe time domain signal after transform/inverse transform includes such errors, along with errorless versions. 
         [0023]    Rotor controller  32  processes the various airframe and rotor time domain signals to generate control signals for actuator  39 . It is understood that the types of signals generated and processed (e.g., sensor signal, control signals) are exemplary, and that other signal types may be processed. 
         [0024]      FIG. 3  also depicts the nature of the frequency domain signals. For a time domain signal of value u(t k ) at any given time t k , the transform modules  34  and  44  creates u o (t k ), representing the mean (also known as average or zero-th component) of the time domain signal and a pair of harmonic coefficients, u i   c (t k ) representing the amplitude of the cosine component at frequency w, of the time domain signal, u i   s (t k ), representing the amplitude of the sine component at frequency ω i  of the time domain signal. In another embodiment of the frequency domain signal, the transform modules  34  and  44  creates u o (t k ), representing the mean (also known as average or zero-th component) of the time domain signal and a pair of harmonic coefficients, u i   s (t k ) representing the amplitude of the sine component at frequency ω i  of the time domain signal, and φ i (t k ), representing the phase of the sine component at frequency ω i  of the time domain signal. The frequency domain signal is represented by choosing a finite number n of ω i , namely ω 1  to ω n  to adequately represent the time domain signal. Transforming the time domain signal prior to transmission over the transfer medium  50  reduces the amount of data for transmission. 
         [0025]    Further, the transform modules  34  and  44  may limit the transformation from the time domain to the frequency domain for a set of frequencies ω i  deemed relevant to the system. For example, in a rotary wing aircraft, the pair of coefficients (cosine component, and sine component) may be generated for a fundamental frequency (e.g., ω 1 =the rotor RPM) and multiples of the fundamental frequency (harmonics, e.g. ω n =n*ω 1 ). The mean or the average is also referred to as the 0 th  harmonic. As used herein, a frequency domain signal includes the average or 0 th  harmonic, and amplitudes of cosine and sine components in fundamental frequency (1 st  harmonic) and multiples of the fundamental frequency. 
         [0026]    The rotor transform module  34  may compute harmonics of a fundamental frequency (e.g., rotor fundamental frequency), and only generate coefficients for the harmonic components of the time domain signal. Limiting the coefficients to harmonic components of the time domain signal further reduces the amount of data. This also eliminates coefficients attributable to non-harmonic signals, which are often less relevant to measurement or control of the rotor system. Transferring coefficients of harmonic components of the time domain signal also allows the transceivers  34  and  44  to operate at a lower data rate, as the coefficients only need to capture variation in the harmonic coefficients and not the time domain signal itself. 
         [0027]    Embodiments provide for a reduction in data transferred between and airframe system and rotor system of a rotary wing aircraft. Reducing the amount of data allows the data to be repeated multiple times, which improves redundancy and fault-detection. The system may employ low cost, low power, low weight components and commercial off-the-shelf electronic components for on-rotor harmonic computation. 
         [0028]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit 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.