Abstract:
A system and method for controlling a deceleration profile of an aircraft, includes a processor and memory that receives a signal indicative of a deceleration command; receives signals indicative of a sensed velocity and a commanded heading rate; determines a commanded velocity in response to the receiving of the deceleration command and the commanded heading rate; determines an estimated deceleration command as a function of the commanded velocity; and determines an actual deceleration command in response to the determining of the estimated deceleration command.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with Government support with the United States Navy under Contract No. N00019-06-C-0081. The Government therefore has certain rights in this invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject matter disclosed herein relates generally to the field of control systems in rotorcraft and, in particular, to an advanced control law that utilizes a fly-by-wire system to augment a preprogrammed deceleration profile for a rotorcraft. 
       DESCRIPTION OF RELATED ART 
       [0003]    Many vehicles, including helicopters, use an onboard fly-by-wire (FBW) system to control vehicle operation. Emerging FBW helicopters provide high levels of augmentation. These FBW systems greatly reduce pilot workload and enhance safety. Part of the safety enhancements includes control inputs that allow pilots to aggressively maneuver within the airframe structural limits and not exceed these limits. Within these flight control systems, it is possible for the pilot to engage a deceleration mode whereby the flight control system follows an automated deceleration profile in order to automatically decelerate to a specific location. However, in typical aircraft, a pilot may not be able to augment the automated deceleration profile once initiated. This often results in the helicopter overshooting the specific location by flying a very controlled approach to a wrong location. Improvements in providing an advanced control law that allows a pilot to augment the deceleration profile once engaged would be well received in the art. 
       BRIEF SUMMARY 
       [0004]    According to an embodiment of the invention, a method for controlling a deceleration profile of an aircraft, includes receiving, with a processor, a signal indicative of a deceleration command; receiving with the processor, signals indicative of a sensed velocity and a commanded heading rate; determining, with the processor, a commanded velocity in response to the receiving of the deceleration command and the commanded heading rate; determining, with the processor, an estimated deceleration command as a function of the commanded velocity; and determining, with the processor, an actual deceleration command in response to the determining of the estimated deceleration command. 
         [0005]    In addition to one or more of the features described above, or as an alternative, further embodiments could include receiving of the deceleration command further comprises receiving longitudinal and lateral deceleration commands. 
         [0006]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a commanded longitudinal velocity and a commanded lateral velocity. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a longitudinal velocity error signal indicative of a difference between the commanded longitudinal velocity and a sensed longitudinal velocity. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a lateral velocity error signal indicative of a difference between the commanded lateral velocity and a sensed lateral velocity. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a commanded acceleration in response to the receiving of the deceleration command. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a second error value indicative of a difference between the commanded acceleration and a sensed acceleration. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a longitudinal commanded gain ratio as a function of the longitudinal velocity error signal and a total velocity magnitude. 
         [0012]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a lateral commanded gain ratio as a function of the lateral velocity error signal and a total velocity magnitude. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining the estimated deceleration command as a function of the total velocity magnitude. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments could include determining a Translational Rate Command response wherein controller deflection correlates to steady state velocity. 
         [0015]    According to another embodiment of the invention, a system for controlling a deceleration profile of an aircraft includes a propeller comprising a plurality of blades, wherein the propeller is associated with a sensor; a processor; and memory having instructions stored thereon that, when executed by the processor, cause the system to: receive a signal indicative of a deceleration command; receive signals indicative of a sensed velocity and a commanded heading rate; determine a commanded velocity in response to the receiving of the deceleration command and the commanded heading rate; determine an estimated deceleration command as a function of the commanded velocity; and determine an actual deceleration command in response to the determining of the estimated deceleration command. 
         [0016]    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 receive longitudinal and lateral deceleration commands. 
         [0017]    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 a commanded longitudinal velocity and a commanded lateral velocity. 
         [0018]    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 a longitudinal velocity error signal indicative of a difference between the commanded longitudinal velocity and a sensed longitudinal velocity. 
         [0019]    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 a lateral velocity error signal indicative of a difference between the commanded lateral velocity and a sensed lateral velocity. 
         [0020]    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 a commanded acceleration in response to the receiving of the deceleration command. 
         [0021]    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 a second error value indicative of a difference between the commanded acceleration and a sensed acceleration. 
         [0022]    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 a longitudinal commanded gain ratio as a function of the longitudinal velocity error signal and a total velocity magnitude. 
         [0023]    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 a lateral commanded gain ratio as a function of the lateral velocity error signal and a total velocity magnitude. 
         [0024]    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 
         [0025]    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: 
           [0026]      FIG. 1  is a perspective view of an example rotary wing aircraft for use with embodiments of the invention; 
           [0027]      FIG. 2  is a schematic block diagram of an embodiment of a control system for a rotary wing aircraft; 
           [0028]      FIG. 3  is a schematic block diagram of a deceleration to hover strategy according to an embodiment of the invention; 
           [0029]      FIG. 4  is a schematic view of a loop closure control strategy according to an embodiment of the invention; and 
           [0030]      FIG. 5  is a schematic view of a control law according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Referring to the drawings,  FIG. 1  schematically illustrates a rotary wing aircraft  10  which includes an augmented flight control system according to an embodiment. The aircraft  10  includes an airframe  14  having a main rotor assembly  12  and 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 assembly  12  includes a plurality of rotor blades  20  mounted to a rotor hub  22 . The main rotor assembly  12  is driven about an axis of rotation A through a main rotor gearbox (not shown) by a powerplant system, here shown as two internal combustion engines  24   a - 24   b.  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, turbo-props, tilt-rotors and tilt-wing aircraft, will also benefit from embodiments of the invention. 
         [0032]      FIG. 2  illustrates an example of a flight control system  30  that utilizes a model following control system that receives, in an embodiment, a real-time deceleration-to-hover command via cyclic and/or collective sticks in order to adjust or augment a pre-programmed or stored deceleration profile. The pre-programmed deceleration profile facilitates deceleration of the aircraft  10  to a hover. The control system  30  may be, in embodiments, a full authority or a limited authority flight control system which provides feed-forward and feedback paths to achieve the desired response characteristics. The control system  30  implements a deceleration-to-hover control algorithm  42  that augments the pre-programmed deceleration profile and provides attitude commands for controlling the cyclic and/or collective pitch when the stick is moved out of detent. Moving the stick out of detent controls the swashplate angle and holds the swashplate in that position until the stick is released upon which the automated deceleration profile is re-initiated. The control system  30  provides an architecture that can be used to provide a useable Translational Rate Command (TRC) like response where controller deflection correlates to steady state velocity. In this instance, the deceleration-to-hover command is scheduled to grow as a function of total groundspeed speed. When the pilot makes a steady state input, the aircraft gains speed, the deceleration command grows until it equalizes with the Decel-to-Hover command and the aircraft holds velocity. While deceleration commands are being referenced throughout this disclosure, it is to be appreciated that reference to acceleration commands can include positive acceleration as well as negative acceleration (or deceleration). 
         [0033]    A schematic of a control system  30  to accomplish this is illustrated. Pilot commands/inputs  34  from pilot inceptors such as, for example, a cyclic stick and/or foot pedals are received by a flight control computer  32  as a commanded acceleration or deceleration for trim attitude changes. A number of sensors  36  are provided in order to sense flight conditions of aircraft  10  such as, in some non-limiting examples, longitudinal velocity, lateral velocity, airspeed, measured thrust, measured torque or the like. Data from sensors  36  is directed to flight control computer  32  operably connected to sensors  36  where they are compared to control laws  38  and a look-up table with notional estimated values of a relationship between attitude and acceleration. Flight control computer  32  communicates command signals as acceleration and deceleration command signals  40 , e.g., lateral and longitudinal deceleration commands for aircraft  10 . In embodiments, flight control commands  40  may be estimated from aircraft parameters or determined according to a schedule of attitude to acceleration as a function of sensed longitudinal velocity of aircraft  10 , sensed lateral velocity of aircraft  10  or the like. 
         [0034]    In an embodiment, flight control computer  32  includes a memory  46 . Memory  46  stores the deceleration-to-hover control algorithm  42  as executable instructions that is executed by a processor  44 . 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 deceleration-to-hover control algorithm  42 . Processor  44  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  46  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 deceleration-to-hover control algorithm  42  described below. 
         [0035]      FIG. 3  illustrates a schematic view of a high-level deceleration to hover strategy  50  as part of control algorithm  42  of Flight Control Computer  32 . Initially, signals  52  from a pilot inceptor such as, for example, a cyclic stick and/or a collective stick are received by an acceleration command model  54 . A pilot for aircraft  10  can perturb the system by commanding delta acceleration from a trim schedule. This allows the pilot to increase or decrease a scheduled deceleration through pilot sticks, giving them the ability to manipulate the final destination. As a non-limiting example, signals  52  are received by control system  30  that represent pilot stick inputs to aircraft  10 . Pilot stick inputs are interpreted by acceleration command model  54  as trim attitude changes and are converted into additive acceleration or deceleration command signals  56  which are subsequently integrated into reference velocities in integrator block  66 . Signal  56  represents a pilot commanded delta acceleration commands. Signal  59  represents reference velocities from the acceleration integrators  66  that are received by a deceleration look-up table  60 . Deceleration look-up table  60  outputs one or more signals  58  representing scheduled acceleration commands that are provided to a summation block  62 . A signal  64  for a total value between signal  56  and signal  58  is determined in Summation block  62 . Signal  64  is fed to an integrator block  66  that integrates the input over time for determination of reference velocity commands  68 . Reference velocity commands  68  represents commanded velocity commands that are also provided as feedback signals for command of rotor  12  ( FIG. 1 ) for, in an embodiment, modulating the automated deceleration profile and hand-flying the aircraft  10  to a hover at a desired final location. The benefits of strategy  50  is that the architecture is attitude independent with the output of the acceleration command model  54  and the deceleration to hover table  60  summing to total acceleration. The structure provides commanded accelerations and commanded velocities such that the quantities can be controlled via feedback loop closures to determine the appropriate pitch and roll trim attitudes. 
         [0036]      FIG. 4  illustrates a schematic view of a detail of a loop closure strategy  100  that is implemented by control algorithm  42  for augmenting pilot commands that are received according to an embodiment of the invention. In an embodiment, implementation of control algorithm  42  begins when flight control computer  32  ( FIG. 2 ) receives and stores pilot stick inputs such as, for example, longitudinal stick inputs  102  and lateral stick inputs  104 . Longitudinal stick inputs  102  and lateral stick inputs  104  represent commanded cyclic and/or collective attitude commands that are received from pilot inceptors. The longitudinal stick input  102  is interpreted by a longitudinal acceleration command model  106  and is converted into a signal  110  as additive commanded longitudinal acceleration. Similarly, lateral stick input  104  is interpreted by a lateral acceleration command model  108  and is converted into a signal  112  for an additive commanded lateral acceleration. Calculation block  134  provides signals representing estimated commanded longitudinal acceleration  118  and estimated commanded lateral acceleration  120  to respective summation blocks  114 ,  116  for determination of an error value through an additive determination. Error value  122  is a delta commanded longitudinal acceleration while error value  124  is a delta commanded lateral acceleration. Also, in order to close linear acceleration feedbacks, signals that represent a commanded longitudinal groundspeed  136  is fedback to a multiplier block  131  where it is multiplied with a signal that represents commanded heading rate  127 , which represents pedal inputs that command heading rate and provides an ability for the pilot to be able to change the ground track angle. The output of multiplier block  131  is sensed longitudinal acceleration  133 . Also, Sensor signal  138  representing commanded lateral groundspeed is fedback to a multiplier block  129  where it is multiplied with a signal that represents commanded heading rate  127  in order to output sensed lateral acceleration  135 . Additionally, commanded longitudinal and lateral velocities/groundspeeds  136 ,  138  are fedback to deceleration to hover calculation block  134  for determination of estimated commanded longitudinal acceleration  118  and estimated commanded lateral acceleration  120 , for processing as described above with respect to  FIG. 4 . 
         [0037]    Sensed lateral acceleration  135  and delta commanded longitudinal acceleration  122  are provided to summation block  130  which outputs error signal  141 . Similarly, sensed longitudinal acceleration  133  and delta commanded lateral acceleration  124  are provided to summation block  132  which outputs error signal  143 . Error signals  141 ,  143  are applied to respective integrators  126 ,  128  to output a value of an integral of its input signal with respect to time. Integrators  126 ,  128  output respective output signals that represent commanded longitudinal velocity/groundspeed  136  and commanded lateral velocity/groundspeed  138  for aircraft  10 . Also, in order to close linear velocity feedbacks, signals for sensed linear velocities such as, for example, sensed longitudinal velocity/groundspeed  140  and sensed lateral velocity/groundspeed  142  are received from one or more sensors  36  ( FIG. 2 ) and fed to respective summation blocks  144 ,  146  for comparison with commanded longitudinal velocity  148  and commanded lateral velocity  150 . Output signals  148 ,  150  represent error values of signals for commanded longitudinal and lateral velocities respectively. 
         [0038]    Referring to  FIG. 5 , the commanded longitudinal velocity  148  is applied to a square product block  150  while the commanded lateral velocity signal  150  is applied to square product block  152 . The output signals  154 ,  156  representing magnitudes of commanded velocities are added in a summation block  158  and fed to a square root block  160  for determination of a magnitude of the total commanded velocity  162 . The magnitude of the total commanded velocity  162  (as a “Y” input) and commanded longitudinal velocity signal  148  (as a “X” input) is applied to an advance ratio block  164  for dividing X by Y. Output value  168  represents a longitudinal commanded gain ratio signal  168 . The magnitude of the total commanded velocity  162  (as a “Y” input) and commanded lateral velocity signal  150  (as an “X” input) is applied to an advance ratio block  166  for dividing X by Y. Output value  170  represents a lateral commanded gain ratio signal  170 . 
         [0039]    Further, the magnitude of the total commanded velocity  162  is applied to a deceleration to hover look-up table  172  and signals  174 ,  176  representing respective estimated longitudinal acceleration commands and lateral acceleration commands are provided to respective product blocks  178 ,  180 . The estimated acceleration commands  174 ,  176  are multiplied by respective gain ratios in order to determine respective actual commanded longitudinal deceleration command signals  182  and actual commanded lateral deceleration command signals  184  for modulating the scheduled deceleration profile and hand-fly the aircraft  10  to the desired final location. 
         [0040]    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. For instance, aspects of the invention are not limited to rotorcraft, and can be used in wind turbines, engine turbines, and other systems with rotary elements. 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 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.