Abstract:
A method of controlling a helicopter having a rotor with blades is provided. The method includes receiving, by a computing device comprising a processor, at least one input associated with the helicopter; generating, by the computing device, control signals configured to counteract blade bending associated with the rotors based on the received at least one input; measuring, by the computing device, blade signals using sensors for the blades; extracting, by the computing device, harmonic loads from the measured blade signals; adapting, by the computing device, the control signals based on the harmonic loads; and controlling, by the computing device, servos connected to the blades to adjust the blades according to the adapted control signals to reduce vibratory loads on the blades.

Description:
BACKGROUND 
       [0001]    Total vehicle height is an important design parameter for fitting on existing ship hangers and elevators, as well as fitting inside transport aircraft. As shown in FIGS.  1  and  2 A- 2 B, conventional coaxial helicopters are typically taller than other helicopters of similar performance due to the existence of an additional rotor and the flapping motion of the rotor blades necessitating a minimum vertical hub spacing (rotor separation ratio). In particular,  FIG. 1  shows an upper rotor  102  coupled to an upper rotor swashplate  104  and a lower rotor  106  coupled to a lower rotor swashplate  108 . A rotor hub separation  110  may generally separate the upper rotor  102  and lower rotor  106 .  FIG. 2A  illustrates a single axis/rotor helicopter  202 , whereas  FIG. 2B  illustrates a coaxial/dual rotor helicopter  204 . As shown in  FIGS. 2A-2B , the height of the helicopter  204  may be appreciably greater than the height of the helicopter  202 . 
         [0002]    Some helicopters, such as the Sikorsky X2 Technology™ Demonstrator, may have a reduced rotor separation ratio relative to other helicopters. The reduced rotor separation ratio may be facilitated by the use of hingeless, rigid rotors which may bend rather than flap like articulated rotors do. The high blade rigidity may imply large blade moments and approximately 20% 2/rev blade bending that may increase vibratory (peak to peak) blade stresses beyond 1/rev loads alone. Though 2/rev blade bending may cancel at a hub, the 2/rev blade bending may: (1) decrease minimum blade tip clearance between the two rotors (e.g., rotors  102  and  106 ), (2) increase peak blade stresses, and (3) increase rotor blade and hub design weight. 2/rev blade control typically cannot be accomplished using an ordinary swashplate, at least for rotors with two blades or more than three blades. In some instances, it may be desirable to utilize a configuration that does not include a swashplate. 
       BRIEF SUMMARY 
       [0003]    An embodiment is directed to a method of controlling a helicopter having a rotor with blades. The method includes receiving, by a computing device comprising a processor, at least one input associated with the helicopter; generating, by the computing device, control signals configured to counteract blade bending associated with the rotors based on the received at least one input; measuring, by the computing device, blade signals using sensors for the blades; extracting, by the computing device, harmonic loads from the measured blade signals; adapting, by the computing device, the control signals based on the harmonic loads; and controlling, by the computing device, servos connected to the blades to adjust the blades according to the adapted control signals to reduce vibratory loads on the blades. 
         [0004]    Another embodiment is directed to an apparatus for use in a helicopter having at least one rotor with blades, the apparatus includes at least one processor and a memory having instructions stored thereon that, when executed by the at least one processor, cause the apparatus to receive, with the at least one processor, at least one input associated with the helicopter; generate, with the at least one processor, control signals configured to counteract blade bending associated with at least one rotor based on the received at least one input; measure, with the at least one processor, blade signals using sensors for the blades; extract, with the at least one processor, harmonic loads from the measured blade signals; adapt, with the at least one processor, the control signals based on the harmonic loads; and control, with the at least one processor, servos connected to the blades to adjust the blades according to the adapted control signals to reduce vibratory loads on the blades. 
         [0005]    Another embodiment is directed to an aircraft having rotors, with each rotor having a plurality of blades. Each of the plurality of blades is associated with a sensor included in a plurality of sensors. The aircraft also includes a servo connected to at least one of the blades and a control computer. The control computer is configured to receive blade signals from the plurality of sensors; extract 2/rev loads from the blade signals; receive control signals for controlling the aircraft; adapt the received control signals based on the loads; and control the servo to adjust the blades to reduce a vibratory load on the blades. 
         [0006]    Additional embodiments are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements. 
           [0008]      FIG. 1  illustrates a coaxial, dual rotor helicopter; 
           [0009]      FIG. 2A  illustrates a single axis/rotor helicopter; 
           [0010]      FIG. 2B  illustrates a dual rotor helicopter; 
           [0011]      FIG. 3  illustrates a control system for a coaxial, dual-rotor helicopter according to an embodiment of the invention; 
           [0012]      FIG. 4  illustrates a control algorithm and process flow according to an embodiment of the invention; 
           [0013]      FIG. 5  is a schematic block diagram illustrating an exemplary computing system according to an embodiment of the invention; and 
           [0014]      FIG. 6  is a flow chart of an exemplary method according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    It is noted that various connections are set forth between elements in the following description and in the drawings (the contents of which are included in this disclosure by way of reference). It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. In this respect, a coupling between entities may refer to either a direct or an indirect connection. 
         [0016]    Exemplary embodiments of apparatuses, systems, and methods are described for using 2/rev individual blade control (IBC) feedback to reduce 2/rev blade deflections and loads. In some embodiments, one or more blade sensors may detect 2/rev bending signals. The signals may be processed and actions may be taken to null or mitigate the impact of the 2/rev loads. In some embodiments, a controller may convert from commands for lateral, longitudinal, and/or collective blade cyclic pitch (A1s, B1s, Theta) to position commands for blade actuators using a sine and cosine calculation based on a sensed angular position of a rotor. 
         [0017]    Referring to  FIG. 3 , a control environment or system  300  for a helicopter  340  is shown according to an embodiment of the invention. As illustrated, helicopter  340  includes a fuselage  342  and a rotor assembly  344 . In an embodiment, the rotor assembly  344  includes an upper rotor assembly  346  and a lower rotor assembly  348  that are co-axial and rotate in an opposite direction to each other. The upper rotor assembly  346  may include upper rotor blades  302  while the lower rotor assembly  348  may include lower rotor blades  306 . The upper and lower rotor blades  302 ,  306  may turn or rotate based on IBC servos or rotary actuators. Specifically, upper rotor blades  302  may be rotated by IBC servos  308   a,    308   b  which receive control signals from an upper servo controller  350 . Also, lower rotor blades  306  may be rotated by IBC servos  309   a,    309   b  which receive control signals from a lower servo controller  352 . The IBC servos  308   a - 308   b,    309   a - 309   b  allow for precise control of, e.g., angular position, respective upper and lower rotor blades  302 ,  306  which may be facilitated by a transmission  310 . 
         [0018]    One or more strain gages or sensors  316   a - 316   b  and  317   a - 317   b  may be incorporated into the one or more blades. Particularly, sensors  316   a - 316   b  may be incorporated into upper rotor blades  302  and sensors  317   a - 317   b  may be incorporated into lower rotor blades  306 . The sensors  316   a - 316   b,    317   a - 317   b  may detect a rotor blade flatwise bending moment in the one or more of the blades  302 ,  306 . The flatwise bending moment is converted to raw bending signals  322  which may be conveyed, potentially via the transmission  310  and using a slip ring (e.g., an optical slip ring), to a control computer  326 . 
         [0019]    The control computer  326  may analyze the raw bending signals  322  and extract the 2/rev sinusoidal components from the raw bending signals  322 . Such extraction may be facilitated using a harmonic estimation algorithm, which may correspond to or be similar to a Fast Fourier Transform (FFT). The control computer  326  may generate and transmit servo control signals  334  to upper and lower servo controllers  350 ,  352 , which may be transmitted to the respective IBC servos  308   a - 308   b,    309   a - 309   b  via the transmission  310 . The control computer  326  may transmit to the upper and lower rotor assemblies  346 ,  348  via the servo controllers  350 ,  351  2/rev sine and cosine signals, also known as phase and amplitude, which may be based on aircraft flight states (e.g., airspeed). 
         [0020]    The servo control signals  334  may adjust 2/rev actuation signals to achieve a specified 2/rev blade bending load. While a zero-valued 2/rev blade bending load may be desirable from a blade fatigue load standpoint, applying varying loads to the upper and lower rotor assemblies  346  and  348  may be beneficial to tip clearance during one or more helicopter maneuvers. Optimization of rotor lift to drag ratio (L/D) may require different input from that needed for minimizing loads. A control system  300  may reduce 2/rev loads to zero, improve efficiency based on a pilot-selectable mode for level flight, and/or maintain tip clearance during maneuvers. 
         [0021]    Referring to  FIG. 4 , a flow chart of architecture  400  is shown. The architecture  400  may be used to generate the servo control signals  334  of  FIG. 3  for an aircraft. The architecture  400  may be implemented in connection with one or more devices or entities, such as the control computer  326  of  FIG. 3 . 
         [0022]    A pilot  402  may issue one or more directives regarding the operation or flight of an aircraft (e.g., helicopter). The directives may be received by a command model  404 . The command model  404  may estimate dynamics in a feed-forward fashion. For example, the command model  404  may generate an estimate of blade dynamics based on the pilot directives. The command model  404  may include models that may map inputs (e.g., pilot directives, flight measurements or parameters (e.g., airspeed, acceleration, attitude, etc.), etc.) to outputs (e.g., anticipated or estimated aircraft dynamic responses). The models may be established using simulations or wind tunnel data. The models may be refined based on system flight data. While described in terms of a pilot  402 , it is understood that the pilot can be a human pilot, or could be an autonomous or semi-autonomous pilot using one or more processors, and/or could be separate from the aircraft as in the case of an unmanned aerial vehicle. 
         [0023]    The command model  404  may generate (primary) flight control signals as well as 2/rev signals, which may be provided to a feedback block  406 . The command model  404  may also provide input to an inverse dynamics block  408 . The inverse dynamics block  408  may predict controls to implement desired aircraft dynamics. The command model  404  and the inverse plant  408  may function as follows: the pilot  402  makes a command with an inceptor (e.g. cyclic stick), the command model  404  converts that inceptor command to an aircraft dynamic command (e.g. pitch the nose down at X degrees per second), the inverse plant  408  ideally is the inverse of an aircraft dynamics block  414 , so it takes the commanded dynamics and converts them to blade angle commands (e.g., input X deg/s pitch rate, output Y deg rotor cyclic blade pitch). 
         [0024]    Outputs of the feedback block  406  and the inverse dynamics block  408  may be summed at a node  410 . The output of the node  410  may drive a servo control block  412 . The servo controls  412  may impact or drive the aircraft dynamic response  414 , which may be monitored or detected by blade sensors  416  and flight control sensors  418 . A 2/rev harmonic estimation block  420  may estimate 2/rev frequencies/vibrations based on the output of the blade sensors  416 . Together, the blade sensors  416  and the 2/rev harmonic estimation block  420  may be used to provide 2/rev load alleviation. The flight control sensors  418  and the 2/rev harmonic estimation block  420  may provide input to the feedback block  406 . 
         [0025]    Referring to  FIG. 5 , an exemplary computing system  500  is shown. The system  500  is shown as including a memory  502 . The memory  502  may store executable instructions as well as models used in the method described in  FIG. 6 . The executable instructions may be stored or organized in any manner and at any level of abstraction, such as in connection with one or more applications, processes, routines, methods, etc. As an example, at least a portion of the instructions are shown in  FIG. 5  as being associated with a first program  504   a  and a second program  504   b.    
         [0026]    The instructions stored in the memory  502  may be executed by one or more processors, such as a processor  506 . The processor  506  may be coupled to one or more input/output (I/O) devices  508 . In some embodiments, the I/O device(s)  508  may include one or more of a keyboard or keypad, a touchscreen or touch panel, a display screen, a microphone, a speaker, a mouse, a button, a remote control, a control stick, a joystick, a printer, etc. The I/O device(s)  508  may be configured to provide an interface to allow a user to interact with the system  500 . 
         [0027]    The system  500  is illustrative. In some embodiments, one or more of the entities may be optional. In some embodiments, additional entities not shown may be included. For example, in some embodiments the system  500  may be associated with one or more networks. In some embodiments, the entities may be arranged or organized in a manner different from what is shown in  FIG. 5 . One or more of the entities shown in  FIG. 5  may be associated with one or more of the devices or entities described herein (e.g., the control computer  326  of  FIG. 3 ). 
         [0028]    Turning to  FIG. 6 , a flow chart of a method  600  is shown. The method  600  may be executed in connection with one or more components, devices, or systems, such as those described herein. The method  600  may be used to control blade bending (e.g., 2/rev blade bending) in various flight states for an aircraft, such as a coaxial helicopter configured with individual blade control on each rotor, and can also be used to develop models in advance of flight or during flight. 
         [0029]    In block  602 , one or more models may be developed. The models may be used to provide a prediction or estimate regarding one or more dynamic responses. For example, the models may be used to estimate blade dynamics or loads based on pilot inputs. Block  602  can be developed outside of the aircraft being flown, and therefore can be stored on the aircraft and recalled as needed in later operation. For instance, the models can be created using test data (such as wind tunnel data), or simulation data. As such, block  602  can be optional in aspects and can be performed separately from other blocks of the method of  FIG. 6 . 
         [0030]    In block  604 , one or more controls or control signals may be generated. The control signals may be generated based on the estimation models of block  602  in conjunction with input signals from, for example, a pilot. The control signals may serve to counteract the estimated dynamic responses/loads. The control signals may attempt to control higher harmonic (e.g., 2/rev) blade bending in different flight states. 
         [0031]    In block  606 , blade signals may be measured, potentially using one or more sensors. 
         [0032]    In block  608 , an estimation or extraction of higher harmonic loads from the measured blade signals of block  606  may be performed. Based on an identification of the higher harmonic loads in block  608 , the control signals of block  604  may be adapted. For example, the control signals of block  604  may be adapted to minimize the higher harmonic loads by switching from one model to the next. 
         [0033]    In some embodiments, one or more of the blocks or operations (or a portion thereof) of the method  600  may be optional. In some embodiments, the blocks may execute in an order or sequence different from what is shown in  FIG. 6 . In some embodiments, one or more additional blocks or operations not shown may be included. 
         [0034]    Technical effects and benefits of aspects include, in aspects, a reduction in terms of the weight of components aboard an aircraft (e.g., a helicopter). For example, because 2/rev stresses may represent approximately 20% of the vibratory stress during level flight, 2/rev cyclic control can reduce the vibratory flatwise blade loads by approximately the same amount (20%), which may allow for a reduction in terms of a design weight of various rotor components (e.g., blades and hubs). 2/rev control may be used to improve the rotor L/D by approximately 5% relative to conventional aircraft configurations. 2/rev control may be used to improve tip clearance during maneuvers, allowing for a reduced rotor separation ratio and therefore a reduction in terms of total aircraft height. However, it is understood that aspects can have other advantages in addition to or instead of the above-noted advantages, benefits and effects. 
         [0035]    Embodiments of the disclosure have been described in connection with aircraft/rotorcraft. Aspects of the disclosure may be applied in other environments or contexts. For example, aspects of the disclosure may be used to provide for a reduction of stress in turbine applications based on higher harmonic controls. Further, while described in the context of a specific example (2/rev), it is understood that aspects can be used in other per revolution harmonics. Additionally, while described in the context of a coaxial aircraft, it is understood that aspects can be used in single rotor aircraft, wind turbines, and other like bodies. 
         [0036]    As described herein, in some embodiments various functions or acts may take place at a given location and/or in connection with the operation of one or more apparatuses, systems, or devices. For example, in some embodiments, a portion of a given function or act may be performed at a first device or location, and the remainder of the function or act may be performed at one or more additional devices or locations. 
         [0037]    Embodiments may be implemented using one or more technologies. In some embodiments, an apparatus or system may include one or more processors, and memory storing instructions that, when executed by the one or more processors, cause the apparatus or system to perform one or more methodological acts as described herein. Various mechanical components known to those of skill in the art may be used in some embodiments. 
         [0038]    Embodiments may be implemented as one or more apparatuses, systems, and/or methods. In some embodiments, instructions may be stored on one or more computer-readable media, such as a transitory and/or non-transitory computer-readable medium. The instructions, when executed, may cause an entity (e.g., an apparatus or system) to perform one or more methodological acts as described herein. 
         [0039]    Aspects of the disclosure have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps described in conjunction with the illustrative figures may be performed in other than the recited order, and that one or more steps illustrated may be optional.