Abstract:
A flight control system having a control law, the control law operable to generate a modified pitch command, the modified pitch command representing a greater amount of collective pitch compared to an amount of collective pitch generated by a first pitch command, the modified pitch command being generated because a vertical descent speed of the rotorcraft at a given forward airspeed is greater than a threshold. A method of avoiding entry into an undesired vertical descent speed region during operation of a rotorcraft, including measuring a forward airspeed; evaluating a vertical descent of the rotorcraft; and generating a modified collective pitch command in respond to a first collective pitch command having a collective pitch value that would cause the rotorcraft to experience a vertical descent rate greater than a threshold value at the forward airspeed of the rotorcraft.

Description:
BACKGROUND 
     Technical Field 
     The embodiments of the present disclosure relate to flight control systems for rotorcraft, such as helicopters. 
     Description of Related Art 
     There is potential for rotorcraft to get into a dangerous area of the flight envelope where vertical performance is compromised if excessive vertical velocities are maintained at low airspeeds. Traditionally, aircraft flight manuals have warned aircrew of this potential and pilot training has taught them to avoid entering such situations. One disadvantage of the conventional procedure is that it is not always obvious to the aircrew that this situation has occurred, especially in poor visibility, at times of high workload (such as approach to landing) or if auxiliary systems such as autopilots are mishandled and cause inadvertent changes in forward or vertical speed. This can result in control limitations and restricted ability to arrest the high descent rates. 
     There is a need for an improved flight control system. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the system and method of the present disclosure are set forth in the appended claims. However, the system and method itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of an rotorcraft, according to one example embodiment; 
         FIG. 2  is a schematic view of a system, according to one example embodiment; 
         FIG. 3  is a schematic view of a system, according to one example embodiment; 
         FIG. 4  is a graphical representation of a threshold, according to one example embodiment; 
         FIG. 5  is a schematic view of a computer system, according to one example embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the system and method of the present disclosure are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     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. 
     Referring now to  FIG. 1  in the drawings, a rotorcraft  101  is illustrated. Rotorcraft  101  can include a rotor system  103  with a plurality of rotor blades  105 . The pitch of each rotor blade  105  can be managed in order to selectively control direction, thrust, and lift of rotorcraft  101 . For example, a swashplate mechanism  123  can be used to collectively and/or cyclically change the pitch of rotor blades  105 . It should be appreciated that swashplate mechanism  123  is merely exemplary of one possible system for selectively controlling the pitch of rotor blades  105 ; for example, an independent blade control system is another exemplary system for selectively controlling the pitch of rotor blades  105 . Rotorcraft  101  can include an airframe  107 , anti-torque system  109 , and an empennage  111 . Torque can be supplied to rotor system  103  and anti-torque system  109  with at least one engine  113 . A main rotor gearbox  115  is operably associated with an engine main output driveshaft  121  and the main rotor mast. 
     Rotorcraft  101  can include a collective stick  131  that is configured to allow a pilot to make a collective input to collectively change the pitch of the rotor blades  105 . The collective stick  131  can take on any variety of implementation specific configurations. In one embodiment, collective stick  131  is a lever and a collective input is made by lifting up or pushing down the collective stick  131 . In such an embodiment, lifting up the collective stick  131  can cause an increase a vertical lift of the rotorcraft  101  by increasing the pitch of each rotor blade  105  in unison. Similarly, pushing down the collective stick  131  can cause a decrease in vertical lift by decreasing the pitch of each rotor blade  105  in unison. It should be appreciated that collective stick  131  can take on other implementation specific embodiments and collective pitch inputs can be made by other mechanisms and movements. 
     Rotorcraft  101  is merely illustrative of the wide variety of aircraft and vehicles that are particularly well suited to take advantage of the method and system of the present disclosure. It should be appreciated that other aircraft can also utilize the method and system of the present disclosure. 
     Referring now also to  FIG. 2  in the drawings, a system  201  is illustrated in conjunction with rotorcraft  101 . It should be appreciated that though system  201  is illustrated with regard to rotorcraft  101 , system  201  is also implementable on other aircraft as well. Further, it should be appreciated that system  201  can be implemented in a wide variety of configurations, depending in part on the flight control configuration of the aircraft. 
     System  201  is particularly well suited for implementation in aircraft having a fly-by-wire flight control computer, such as flight control computer  125 ; however, a partial authority fly-by-wire aircraft can also utilize system  201 . For example, system  201  can be utilized with a flight control system having collective actuators  124   a ,  124   b , and  124   c  that can receive commands from a trim motor, autopilot system, or any other system that allows collective commands to be realized by collective actuators  124   a ,  124   b , and  124   c . A trim motor  127  is schematically illustrated in conjunction with collective stick  131 . Trim motor  127  can be any mechanism(s), device(s), system(s), etc., that can receive and commands from collective stick  131  and communicate those commands, via flight control computer  125 , to one or more collective actuators, such as collective actuators  124   a ,  124   b , and  124   c . Further, Trim motor  127  can be any mechanism(s), device(s), system(s), etc., that can selectively impart forces, resistance, movements, etc. to collective stick  131 . 
     Referring now also to  FIG. 3 , the system  201  of the present disclosure relates to a collective axis stability augmentation system for of rotorcraft  101 , the augmentation system can include forward airspeed sensing and vertical speed sensing, and be at least partially integrated with a flight control computer  125 . In one embodiment, system  201  is incorporated into a fly by wire control system of rotorcraft  101 . An attempted flight maneuver into a dangerous part of the flight envelope can result in system  201  automatically raising the collective pitch of rotor blades  105  to avoid the potentially dangerous situation, but can be overridden by the pilot if desired. 
     System  201  can include controls laws, which are illustrated as vertical loops  203 . Vertical loops  203  can include vertical axis control laws configured to make control commands so that the rotorcraft  101  can achieve a desired vertical axis state, such as vertical speed or vertical altitude, for example. Furthermore, the vertical loops  203  can adjust for differences between a commanded vertical state and an actual vertical state. One example can be if the rotorcraft  101  is directed to hold the rotorcraft  101  at a commanded altitude, but the rotorcraft experiences a sudden downward gust of wind, then the vertical loops  203  will generate commands to collective actuators  124   a - 124   c  in order to increase pitch (therefore thrust) in order to maintain the commanded altitude. 
     A vertical speed hold command  205  is a command that can be generated by a pilot or an autopilot system. In one embodiment, a pilot vertical speed hold command can be a physical positioning of the collective stick  131  by the pilot that produces a descent rate. In another embodiment, the vertical speed hold command  205  can be an autopilot system that is automatically flying the aircraft. For example, an autopilot system can attempt to create an approach to a landing site and as a result make a vertical speed hold command  205 . One example quantification of the descent rate can be a feet per minute (fpm) descent rate. For example, a −2500 fpm is a greater vertical axis descent rate than a −800 fpm descent rate. 
     A forward airspeed data  207  is data pertaining to the forward airspeed of the rotorcraft  101 . In one embodiment, forward airspeed data  207  is real time data measured from a sensor  211 , such as a pitot probe which can convert ram air into a forward airspeed measurement. In another example embodiment, forward airspeed data  207  can be derived from GPS satellite data, for example. 
     A selector  209  is configured to analyze the vertical speed hold command  205  and the forward airspeed data  207  and either allow the vertical speed hold command  205  to proceed to the vertical loops  203  and further as a pitch command to the collective actuators  124   a - 124   c , or alternatively modify the vertical speed hold command in way that increases collective pitch so that the rotorcraft  101  does not experience a vertical axis descent rate beyond a threshold. Referring now also to  FIG. 4 , an example threshold  401  is illustrated. Threshold  401  is a function of a vertical speed and forward airspeed. The threshold  401  is a maximum allowable descent in the vertical axis for a given forward airspeed. In the example embodiment, when the rotorcraft  101  has a forward airspeed of 40 knots (kts) or less, then system  201  will impede a collective pitch position that would otherwise result in a vertical axis descent greater than 800 fpm. As the forward speed of rotorcraft  101  increases, the threshold  401  of the vertical speed descent also increases. Once the forward speed of rotorcraft  101  obtains 75 knots, the threshold  401  of the vertical speed descent is capped at 2500 fpm. It should be appreciated that the illustrated threshold  401  is merely an example of an implementation specific threshold curve. 
     Selector  209  is configured to identify a vertical speed hold command  205  that would exceed the threshold  401 , and replace the vertical speed hold command  205  with the threshold value for the given forward airspeed. The threshold value command is received and processed by the vertical loops  203  control laws and further commanded to collective actuators  124   a - 124   c . Further, commands can be further sent from vertical loops  203  to trim motor  127  so that the collective stick  131  is impeded from decreasing collective pitch any further than the threshold value  401 . In one embodiment, the pilot can override system  201  and decrease collective pitch beyond threshold value  401  for a given forward airspeed by overcoming the impeding force on collective stick  131  by trim motor  127 . 
     System  201  is advantageously configured such that attempted flight into the prohibited part of the flight envelope will result in the vertical speed hold command being modified to the threshold  401 , which is a predetermined vertical speed limit at that particular forward airspeed. The system  201  is configured to not only modify the position of collective stick  131  to acquire the vertical speed threshold, but also to produce aural and/or visual alerts to the pilot. The pilot can override the vertical speed threshold  401  at anytime by apply force/displacement to the collective stick  131 . As a result, the system  201  automatically modulates collective input to preclude the rotorcraft from inadvertently entering dangerously high vertical speed conditions that could otherwise result in a crash. One advantage of the system  201  of the present disclosure is that it is autonomous and does not require pilot awareness of the situation, which is one of the inherent dangers, and also reduces pilot workload. 
     Referring now also to  FIG. 5 , a computer system  501  is schematically illustrated. Computer system  501  can be configured for performing one or more functions with regard to the operation of system and method further disclosed herein. Further, any processing and analysis can be partly or fully performed by computer system  501 . Computer system  501  can be partly or fully integrated with other aircraft computer systems. 
     The system  501  can include an input/output (I/O) interface  503 , an analysis engine  505 , and a database  507 . Alternative embodiments can combine or distribute the input/output (I/O) interface  503 , analysis engine  505 , and database  507 , as desired. Embodiments of the system  501  can include one or more computers that include one or more processors and memories configured for performing tasks described herein. This can include, for example, a computer having a central processing unit (CPU) and non-volatile memory that stores software instructions for instructing the CPU to perform at least some of the tasks described herein. This can also include, for example, two or more computers that are in communication via a computer network, where one or more of the computers include a CPU and non-volatile memory, and one or more of the computer&#39;s non-volatile memory stores software instructions for instructing any of the CPU(s) to perform any of the tasks described herein. Thus, while the exemplary embodiment is described in terms of a discrete machine, it should be appreciated that this description is non-limiting, and that the present description applies equally to numerous other arrangements involving one or more machines performing tasks distributed in any way among the one or more machines. It should also be appreciated that such machines need not be dedicated to performing tasks described herein, but instead can be multi-purpose machines, for example computer workstations, that are suitable for also performing other tasks. 
     The I/O interface  503  can provide a communication link between external users, systems, and data sources and components of the system  501 . The I/O interface  503  can be configured for allowing one or more users to input information to the system  501  via any known input device. Examples can include a keyboard, mouse, touch screen, and/or any other desired input device. The I/O interface  503  can be configured for allowing one or more users to receive information output from the system  501  via any known output device. Examples can include a display monitor, a printer, cockpit display, and/or any other desired output device. The I/O interface  503  can be configured for allowing other systems to communicate with the system  501 . For example, the I/O interface  503  can allow one or more remote computer(s) to access information, input information, and/or remotely instruct the system  501  to perform one or more of the tasks described herein. The I/O interface  503  can be configured for allowing communication with one or more remote data sources. For example, the I/O interface  503  can allow one or more remote data source(s) to access information, input information, and/or remotely instruct the system  501  to perform one or more of the tasks described herein. 
     The database  507  provides persistent data storage for system  501 . While the term “database” is primarily used, a memory or other suitable data storage arrangement may provide the functionality of the database  507 . In alternative embodiments, the database  507  can be integral to or separate from the system  501  and can operate on one or more computers. The database  507  preferably provides non-volatile data storage for any information suitable to support the operation of the system and method disclosed herein, including various types of data discussed further herein. The analysis engine  505  can include various combinations of one or more processors, memories, and software components. 
     The particular embodiments disclosed herein are illustrative only, as the system and method may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Modifications, additions, or omissions may be made to the system described herein without departing from the scope of the disclosure. The components of the system may be integrated or separated. Moreover, the operations of the system may be performed by more, fewer, or other components. 
     Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosure. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.