Abstract:
A method and system for controlling maneuverability of an aircraft includes receiving one or more signals indicative of commanded peak rotary acceleration at a first timeperiod; determining a signal indicative of an actual peak rotary acceleration for the first timeperiod in response to the receiving of the one or more signals for commanded pilot acceleration; and determining signals indicative of actual rotary acceleration for a second timeperiod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 61/987,112, filed May 1, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The subject matter disclosed herein relates generally to the field of rotary-wing aircraft and, more particularly, to a system and method for control of the aircraft by modifying commanded peak acceleration in order to reduce design and fatigue loads on the rotorcraft while maintaining agility and maneuverability. 
       DESCRIPTION OF RELATED ART 
       [0003]    In a typical rotorcraft, pilot commanded rotary acceleration (i.e., commands in yaw, pitch and roll) is shaped by a model following control system for rate and attitude displacement commands. Rotary acceleration on a rotorcraft imposes proportional design and fatigue loads on the aircraft during flight as Acceleration=Force (load)/Mass. Transient design maneuvers impose high spikes in acceleration during initiation and termination of the maneuver. These spikes result in high spikes in loads. Design and fatigue loads in a rotorcraft determine the required strength and structural weight. So, a significant reduction in peak acceleration provides significant load reduction. A system to modify the pilot commanded acceleration while producing similar agility in the rotorcraft would be well received in the art. 
       BRIEF SUMMARY 
       [0004]    According to one aspect of the invention, a method for controlling maneuverability of an aircraft, includes receiving, with a processor, one or more signals indicative of commanded peak rotary acceleration at a first timeperiod; determining, with the processor, a signal indicative of an actual peak rotary acceleration for the first timeperiod in response to the receiving of the one or more signals for commanded pilot acceleration; and determining, with the processor, signals indicative of actual rotary acceleration for a second timeperiod. 
         [0005]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an actual peak rotary acceleration that comprises control limiting the commanded peak rotary acceleration at a predetermined percentage. 
         [0006]    In addition to one or more of the features described above, or as an alternative, further embodiments could include maintaining the actual rotary acceleration for a greater duration than a commanded rotary acceleration. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments could include holding overall kinetic energy the same for the commanded rotary acceleration and the actual rotary acceleration. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments could include outputting a slower rate of change of the actual rotary acceleration than the commanded rotary acceleration for a longer duration. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining the actual rotary acceleration as a function of overall kinetic energy of the aircraft. 
         [0010]    According to one aspect of the invention, a system for controlling maneuverability of an aircraft includes one or more sensors configured to determine an aircraft attitude and rate; one or more controllers configured to issue displacement commands during a flight maneuver; a computer operably connected to the one or more controllers and configured to: receive one or more signals indicative of commanded peak rotary acceleration at a first timeperiod; determine a signal indicative of an actual peak rotary acceleration for the first timeperiod in response to the receiving of the one or more signals for commanded pilot acceleration; and determine signals indicative of actual rotary acceleration for a second timeperiod. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments could include wherein the processor is configured to control limit the commanded peak rotary acceleration at a predetermined percentage. 
         [0012]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to maintain the actual rotary acceleration for a greater duration than a commanded rotary acceleration. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to hold overall kinetic energy the same for the commanded rotary acceleration and the actual rotary acceleration. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to output a slower rate of change of the actual rotary acceleration than the commanded rotary acceleration for a longer duration. 
         [0015]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to determine the actual rotary acceleration as a function of overall kinetic energy of the aircraft. 
         [0016]    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 SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    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 like elements are numbered alike in the several FIGURES: 
           [0018]      FIG. 1  is a perspective view of an exemplary rotary wing aircraft for use with embodiments of the invention; 
           [0019]      FIG. 2  is a schematic view of an exemplary system for implementing an acceleration smoothing algorithm according to an embodiment of the invention; 
           [0020]      FIG. 3  is a graph showing acceleration control according to an embodiment of the invention; and 
           [0021]      FIG. 4  is a graph showing acceleration control according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to the drawings,  FIG. 1  illustrates a general perspective view of an exemplary vehicle in the form of a vertical takeoff and landing (VTOL) rotary-wing aircraft  100  for use with embodiments of the invention. As illustrated, the rotary-wing aircraft  100  includes an airframe  102  having a main rotor assembly  104  and an extending tail  106  which mounts an anti-torque system, such as a tail rotor assembly  108 . In embodiments, the anti-torque system may include a translational thrust system, a pusher propeller, a rotor propulsion system or the like. The main rotor assembly  104  includes a plurality of rotor blades  110  mounted to a rotor hub  112  that rotates about axis A. Also, tail rotor assembly  108  includes a plurality of rotor blades  116 . The main rotor assembly  104  and the tail rotor assembly  108  are driven to rotate by one or more engines  114  through one or more gearboxes (not shown). Although a particular helicopter configuration is illustrated and described in the disclosed embodiment, other configurations and/or machines, such as high speed compound rotary wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, tilt-rotors and tilt-wing aircraft, and fixed wing aircraft, will also benefit from embodiments of the invention. 
         [0023]      FIG. 2  illustrates a schematic block diagram of a fly-by-wire (FBW) flight control system  200  (also referred to as FBW system  200 ) for the rotary-wing aircraft  100  according to an exemplary embodiment. As illustrated, the FBW system  200  implements an acceleration smoothing algorithm  208  which shapes the pilot&#39;s controller and displacement commands and produces a desired stability response and flight augmentation. The FBW system  200  includes a model following control law which shapes controller displacement commands through an inverse vehicle model to produce the desired aircraft response. The FBW system  200  processes controller inputs  204  and sensor data and transmits the resultant signals to the aircraft  100  primary servos. In an embodiment, the FBW system  200  may provide modified angular rate and angular attitude commands in order to produce a desired rotary acceleration on the aircraft  100  for a longer duration while producing the same agility in the aircraft  100 . The FBW system  200  includes a computing system such as a flight control computer (FCC)  202 . The FCC  202  receives pilot command signals of the controller inputs  204  and sensed parameter signals from a plurality of sensors  206  including operating conditions such as lateral acceleration, angular attitude and angular rate as well as magnitude and direction of wind speed relative to the rotary-wing aircraft  100  in order to produce the desired stability response and flight augmentation. The controller inputs  204  may take various forms including sidearm controllers, a yaw pedal system or other such flight controllers. 
         [0024]    In an embodiment, the FCC  202  receives sensed information such as, for example, a magnitude of the wind relative to the rotary-wing aircraft  100 , a direction of the wind relative to rotary-wing aircraft  100 , lateral acceleration, aircraft attitude, and aircraft angular rate from sensors  206  and interprets displacement positions of the controller inputs  204  based on pilot commanded rotary acceleration in order to determine peak acceleration command signals in order to achieve similar peak velocity for implementation on aircraft  100 . Also shown in  FIG. 2 , the FCC  202  includes a memory  212 . The memory  212  stores the acceleration smoothing algorithm  208  as executable instructions that are executed by a processor  210 . The instructions may be stored or organized in any manner and at any level of abstraction, such as in connection with the execution of the acceleration smoothing algorithm  208 . The processor  210  may be any type of processor (CPU), including a general purpose processor, a digital signal processor, a microcontroller, an application specific integrated circuit, a field programmable gate array or the like. Also, in embodiments, memory  212  may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic or any other computer readable medium onto which is stored the acceleration smoothing algorithm described below. 
         [0025]    In an embodiment, the flight control computer  202  receives commanded peak rotary acceleration from controller inputs  204  and implements, through algorithm  208 , an acceleration limiting to reduce the peak acceleration by, e.g., 40 percent. The algorithm  208  also provides a modified rotary acceleration command that extends the rotary acceleration for a longer duration in order to reach similar peak velocity in approximately the same timeperiod, thereby maintaining maneuverability and agility. Another embodiment includes extending the duration of the rotary acceleration when the controller input  204  is not commanding rotary acceleration in order to hold overall kinetic energy the same and produce maneuverability in the aircraft  100 . 
         [0026]      FIG. 3  is a graph shown acceleration smoothing that is implemented by the flight control computer  202  ( FIG. 2 ) according to an embodiment of the invention. Initially, pilot commanded rotary acceleration input  300  is received at time period  302 . The commanded acceleration input  300  is associated with commanded peak acceleration  304 . The flight control computer  202  ( FIG. 2 ) determines an actual rotary acceleration command  306  that is associated with an actual peak rotary acceleration  308 . In an embodiment, the actual peak acceleration  308  is reduced by  40  percent although other percentage reductions are permissible. As the commanded acceleration follows the commanded rotary acceleration curve  310  towards steady-state acceleration  312 , the acceleration smoothing algorithm  212  receives the sensed acceleration of aircraft  100  from sensors  206  and determines the actual rotary acceleration moving forward in time. The algorithm  212  ( FIG. 2 ) outputs the actual rotary acceleration  314  for a longer duration than commanded rotary acceleration  310  which provides for a similar peak velocity for the aircraft  100  ( FIG. 1 ) in approximately the same timeperiod, similar angular rate  316  and a similar angular attitude  318 . 
         [0027]      FIG. 4  is a graph shown acceleration smoothing that is implemented by forward limiting the actual peak acceleration according to an embodiment of the invention. Initially, pilot commanded rotary acceleration inputs  400  are received at time period  402 . The commanded acceleration input  400  is associated with commanded peak acceleration  404 . The flight control computer  202  ( FIG. 2 ) determines an actual rotary acceleration command  406  that is associated with an actual peak rotary acceleration  408 . The acceleration smoothing algorithm  212  ( FIG. 2 ) provides control limiting for sudden/rapid maneuvers by limiting peak acceleration and the remainder of control input is allowed slowly. As the commanded acceleration follows the commanded rotary acceleration curve  410  towards steady-state acceleration  412 , the acceleration smoothing algorithm  212  ( FIG. 2 ) receives the sensed acceleration of aircraft  100  from sensors  206  ( FIG. 2 ) and determines the actual rotary acceleration moving forward in time in order to hold overall kinetic energy the same. The algorithm  212  ( FIG. 2 ) outputs a slower rate of change of actual commanded rotary acceleration following curve  414  than commanded rotary acceleration  410  for a longer duration which provides that the overall kinetic energy under the curve remains the same for curve  410  and curve  414 . Further, the result of the modifying the commanded acceleration is an area for commanded rotary acceleration  410  that is the same as the area for the actual rotary acceleration thereby holding overall kinetic energy the same, a similar angular rate  416  and a similar angular attitude  418 . 
         [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 the various embodiment 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.