Abstract:
Methods and systems for automatically controlling aircraft takeoff rolls are disclosed. A method in accordance with one embodiment of the invention includes receiving an indication of a target takeoff roll path for an aircraft, and automatically controlling a direction of an aircraft, while the aircraft is on a takeoff roll, to at least approximately follow the target takeoff roll path. The method can further include providing an input to a rudder of the aircraft and, upon receiving an indication of an engine failure, can transfer the input from the rudder to a rudder trim element. In still further embodiments, the method can include commanding a ground track angle when an airspeed of the aircraft reaches a threshold value, and maintaining the ground track angle as the airspeed of the aircraft exceeds the threshold value.

Description:
TECHNICAL FIELD  
       [0001]     The present invention is directed generally to methods and systems for automatically controlling aircraft takeoff rolls.  
       BACKGROUND  
       [0002]     Conventional commercial transport aircraft include a multitude of automated systems for controlling the aircraft during flight. These systems include an aircraft autopilot, which can be activated by the flight crew after the aircraft has reached 200 feet in altitude for automatically guiding the aircraft along a target track. These systems also include flight directors and other visual cues that do not actually control the motion of the aircraft, but provide a moving target at the flight deck which the pilot “captures” when flying along the target track. Such visual guide cues can also be activated during takeoff.  
         [0003]     One drawback with the visual systems that provide guidance cues during aircraft takeoff is that while they adequately perform their intended functions, they may have limited utility in some conditions. These conditions may include low runway visibility, wet or icy runways, strong crosswinds, engine-out takeoffs, and/or engine-out refused takeoffs. Accordingly, it may be desirable to have automatic systems that provide an increased level of performance under these conditions.  
       SUMMARY  
       [0004]     The following summary is provided for the benefit of the reader and does not limit the invention as set forth in the claims. The present invention is directed generally toward methods and systems for automatically controlling aircraft takeoff rolls. A method in accordance with one aspect of the invention includes receiving an indication of a target takeoff roll path for an aircraft, and automatically controlling a direction of the aircraft while the aircraft is on a takeoff roll, so as to at least approximately follow the target takeoff roll path. In further particular aspects of the invention, the method can further include providing an input to a rudder of the aircraft, and in response to receiving an indication of an engine failure, transferring the input from the rudder to a rudder trim element. In still further particular aspects, the method can include gradually reducing the automatic control of the aircraft once the aircraft exceeds a threshold pitch angle.  
         [0005]     Aspects of the invention are also directed toward systems for controlling an aircraft. One such system includes a receiver configured to receive an indication of a target takeoff roll path for an aircraft, and a controller coupled to the receiver to receive the indication of the target roll path. The controller can further be coupled to a steering system of the aircraft to automatically control a direction of the aircraft while the aircraft is on a takeoff roll, so as to at least approximately follow the target takeoff roll path.  
         [0006]     A method in accordance with still another aspect of the invention includes determining a lateral deviation distance from a target path, determining a lateral acceleration, and filtering the lateral deviation with the lateral acceleration to produce a filtered lateral deviation. The method can further include filtering the lateral acceleration with the lateral deviation to produce a filtered lateral deviation rate. The method can then also include determining a commanded lateral position and commanded lateral position rate based on the complementary filtered lateral deviation and complementary filtered lateral deviation rates. Based on the commanded position, the filtered lateral deviation, the commanded lateral position rate and the filtered lateral deviation rate, the method can include determining a first commanded angular position. Based on the first commanded angular position, a sensed yaw rate, and a commanded lateral acceleration, the method can include determining a second commanded angular position. The method can further include directing a rudder and landing gear of the aircraft to move in a manner that directs the aircraft to the second commanded angular position. The foregoing arrangements can provide for a robust, automated system for controlling aircraft takeoff rolls. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a partially schematic illustration of an aircraft positioned on a runway for takeoff.  
         [0008]      FIG. 2A  is a partially schematic illustration of an aircraft and a system for controlling the aircraft during a takeoff roll, in accordance with an embodiment of the invention.  
         [0009]      FIG. 2B  is a schematic illustration of an aircraft flight deck that can house portions of the system shown in  FIG. 2A .  
         [0010]      FIG. 3  is an overall flow diagram of a process by which a system controls an aircraft during takeoff, in accordance with an embodiment of the invention.  
         [0011]      FIG. 4  is a schematic illustration of a takeoff command processor configured in accordance with an embodiment of the invention.  
         [0012]      FIGS. 5A-5C  are flow diagrams illustrating processes for computing runway tracking parameters in accordance with embodiments of the invention.  
         [0013]      FIG. 6  is a flow diagram illustrating a method for computing an outer loop command in accordance with an embodiment of the invention.  
         [0014]      FIG. 7  is a flow diagram illustrating a process for computing a rudder command, based on the outer loop command.  
         [0015]      FIG. 8  is a flow diagram illustrating a process for affecting rudder trim during an engine-out condition.  
         [0016]      FIGS. 9A-9C  illustrate simulated lateral deviations from a runway centerline using systems in accordance with embodiments of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]     The present disclosure describes systems and methods for automatically controlling aircraft takeoff rolls. Certain specific details are set forth in the following description and in  FIGS. 1-9C  to provide a thorough understanding of various embodiments of the invention. Well-known structures, systems and methods often associated with these systems have not been shown or described in detail to avoid unnecessarily obscuring the description of the various embodiments of the invention. In addition, those of ordinary skill in the relevant art will understand that additional embodiments of the invention may be practiced without several of the details described below.  
         [0018]     Many embodiments of the invention described below may take the form of computer-executable instructions, including routines executed by a programmable computer. Those skilled in the relevant art will appreciate that the invention can be practiced on computer systems other than those shown and described below. The invention can be embodied in a special-purpose computer or data processor that is specifically programmed, configured or constructed to perform one or more of the computer-executable instructions described below. Accordingly, the term “computer” as generally used herein refers to any data processor and can include Internet appliances, hand-held devices (including palm top computers, wearable computers, cellular or mobile phones, multi-processor systems, processor-based or programmable consumer electronics, network computers, minicomputers and the like). Information presented by these computers can be presented at any suitable display medium, including a CRT display or LCD.  
         [0019]     The invention can also be practiced in distributed computing environments, where tasks or modules are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules or subroutines may be located in local and remote memory storage devices. Aspects of the invention described below may be stored or distributed on computer-readable media, including magnetic or optically-readable or removable computer disks, as well as distributed electronically over networks. Data structures and transmissions of data particular to aspects of the invention are also encompassed within the scope of the invention.  
         [0020]      FIG. 1  illustrates an aircraft  100  positioned on a runway  111  of an airport  110 . The runway  111  includes a runway centerline  112  extending between ends of the runway  111 . Information obtained from localizer beacons  113  positioned at the ends of the runway  111  can be used to identify a target track (e.g., the runway centerline  112 ) along which the aircraft  100  is guided during takeoff. In other embodiments, this information can be obtained from other sources (e.g., satellite-based sources). Certain embodiments of the methods and systems described below are directed to automatically keeping the aircraft  100  on or very near the runway centerline  112  during a takeoff roll.  
         [0021]      FIG. 2A  illustrates the aircraft  100  along with a system  220  for controlling the lateral direction of the aircraft  100  during a takeoff roll. The aircraft  100  can include a flight deck  240  at which flight instruments are housed, a nose gear  202  which steers the aircraft  100  while the aircraft is on the ground, and a vertical stabilizer  204  that provides directional control both on the ground and in the air. The vertical stabilizer  204  can include a pivotable rudder  203  that yaws the aircraft  100 , and a rudder trim tab  205  that can be adjusted to place a fixed yawing moment on the aircraft  100 . In another embodiment, the trim tab  205  can be eliminated, and the rudder  203  can be coupled to a primary motor and a separate trim motor that holds a bias on the rudder  203 . The system  220  can automatically direct the motion of the rudder  203 , the (optional) rudder trim tab  205 , and the nose gear  202 .  
         [0022]     In one aspect of this embodiment, the system  220  includes a computer  221  having a processor  227  and a memory  228 . The computer  221  can also include a receiver portion  225  that receives input signals, and a controller  222  that directs control signals to the aircraft  100 , based on the input signals received by the receiver portion  225 . Accordingly, the receiver portion  225  can receive target information  229  corresponding to the target path along which the aircraft  100  is to be guided. The system  220  can also include sensors  223  that provide information about the velocities and accelerations of the aircraft  100  as it proceeds down the runway. Information corresponding to the operation of the system  220  can be presented at one or more displays  224 , which may in turn be located at the flight deck  240 .  
         [0023]      FIG. 2B  is a partially schematic illustration of the flight deck  240 , which can include windshields  241 , a glare shield  248  below the windshield, a mode control panel  244  housed in the glare shield  248 , and seats  242   a ,  242   b  from which the flight crew can access the mode control panel  244 . The flight crew can also access a primary flight display  243 , navigation displays  245 , and control and display units (CDUs)  246  positioned on a control pedestal  247 . The primary flight display  243  can include a flight director or other visual cue that can be automatically moved to provide guidance cues for the flight crew as they manually direct the aircraft. As discussed in greater detail below with reference to  FIGS. 3-9C , the system  220  can also automatically control the motion of the aircraft  100 , in addition to or in lieu of providing visual cues at the primary flight display  243 .  
         [0024]      FIG. 3  is a flow diagram of a process by which the system  220  can control the rudder, rudder trim tab, and nose gear described above with reference to  FIG. 2A . The system  220  can include a takeoff command processor  350  that receives instructions corresponding to deviations from the runway centerline, and produces commands to direct the aircraft toward the runway centerline. An outer loop control portion  351  receives the commands from the takeoff command processor  350  and combines them with information received from a sensor processor  352 , which in turn receives information corresponding to the velocity and acceleration of the aircraft from the sensors  223 . The outer loop control portion  351  produces an outer loop command that is combined with feedback signals.at an inner loop control portion  353  to produce a rudder surface command  354 . The rudder surface command  354  can automatically control the position of the aircraft rudder. A rudder trim system  355  can produce a rudder trim command  356  (which can provide additional directional stability during situations that include an engine-out takeoff). A nose wheel steering control portion  357  takes the rudder surface command  354  as input and produces a nose wheel steering command  358  (tailored for the nose gear) as output. The system  220  can also move the rudder input control device(s) (e.g., rudder pedals) in a corresponding manner to provide appropriate feedback to the pilot. Further details on the processes shown in  FIG. 3  are described below.  
         [0025]      FIG. 4  schematically illustrates a process carried out by the takeoff command processor  350  in accordance with an embodiment of the invention. The takeoff command processor  350  can receive filter constants that determine the manner in which information is filtered by the takeoff command processor  350 . The filter constants can include a filter frequency  459  (represented as WN-TKOFF in  FIG. 4 ), a lateral acceleration time constant command  463  (represented as YDDTAU in  FIG. 4 ) and a lateral acceleration limit (represented as YDDLIM in  FIG. 4 ). The takeoff command processor  350  can also receive a signal corresponding to a flight crew instruction to engage the automatic takeoff function (block  460 ), along with lateral deviation data. The lateral deviation data can include a complementary filtered lateral deviation rate  461  and a complementary filtered lateral deviation  462 . Further details regarding these data are provided later with reference to  FIG. 5C . The takeoff command processor  350  can perform a series of integrations within a filtering arrangement to produce a commanded lateral position  464 , a commanded lateral position rate  465 , and a commanded lateral acceleration  466 . These values correspond to, respectively, a target lateral position, a target rate at which the position is to be achieved, and a target acceleration via which the target position is to be achieved.  
         [0026]      FIGS. 5A-5C  illustrate processes that can be performed by the sensor processor  352  shown in  FIG. 3  in accordance with several embodiments of the invention. Each of these processes can include, but need not be limited to filtering the sensor data (e.g., via a complementary filter that reduces low frequency noise without compromising high frequency sensor signal content). For example,  FIG. 5A  illustrates a process for producing an adjusted track value  576 , based upon an input track value. The input track value can include a magnetic track  573 , or a true track  574 , and can be selected via a true track selection input  575 . The magnetic track  573  refers to the angular orientation of the aircraft relative to magnetic north, and the true track signal  574  refers to the angular orientation of the aircraft relative to true north. The system can also receive a signal corresponding to ground speed (block  567 ) and, if the ground speed is less than a threshold speed (e.g., 40 knots) then the adjusted track angle can be equal to the magnetic track angle or the true track angle, whichever is selected via the selector  575 . Once the aircraft&#39;s ground speed exceeds the threshold speed, the adjusted track angle can be corrected by an amount that depends upon the cross track acceleration  570 . The cross track acceleration  570  corresponds to the component of the aircraft acceleration that is normal to the track along which the aircraft is directed.  
         [0027]      FIG. 5B  illustrates a process for determining a cross runway acceleration  572  based on the cross track acceleration  570  described above with reference to  FIG. 5A . The cross runway acceleration  572  corresponds to the acceleration generally normal to the major axis of the runway  111  shown in  FIG. 1 . The cross-runway acceleration will differ from the cross track acceleration when the aircraft track deviates from the runway centerline  112  ( FIG. 1 ). In an embodiment shown in  FIG. 5B , the cross runway acceleration can be effectively zero when the aircraft ground speed  567  is less than a threshold value (e.g., 42 knots). When the aircraft exceeds the threshold speed, the cross runway acceleration  572  can be computed based on the along-track acceleration  568 , the cross track acceleration  570 , and trigonometric functions  569 ,  571  based upon the difference between the adjusted track value  576  described above with reference to  FIG. 5A , and the runway heading.  
         [0028]      FIG. 5C  illustrates a process for determining the complementary filtered lateral deviation  462  (e.g., a deviation from the runway centerline), and the complementary filtered lateral deviation rate  461  (e.g., a deviation rate from the runway centerline). Both quantities are then used to determine the commanded lateral position, rate, and acceleration, as discussed above with reference to  FIG. 4 . The complementary filtered lateral deviation value  462  is obtained by filtering a lateral deviation from runway centerline value  578  with a body lateral acceleration value  579 . The lateral deviation value  578  can be obtained from an ILS system, unless a value for an estimated distance to the relevant localizer  577  is less than a threshold value (e.g., 600 ft.). In this latter case, the last lateral deviation value  578  before passing the threshold value can be used.  
         [0029]     The complementary filtered lateral deviation rate value  461  is obtained by filtering the body lateral acceleration value  579  with the lateral deviation value  578 . The body lateral acceleration value  579  can be calculated from sensor data, and can revert to the sensed cross-runway acceleration  572  when the ground speed  567  is less than a threshold value (e.g., 44 feet/second). Sensed values for the body yaw rate  580  and runway heading  581  are also used to obtain the filtered values  461  and  462 . One advantage of filtering the lateral deviation and lateral deviation rates is that it provides a high gain, stable feedback control loop, based primarily on position at low frequency values and rate at high frequency values. This arrangement is also expected to be less susceptible to signal noise.  
         [0030]      FIG. 6  illustrates a process for computing an outer loop command  684  corresponding to a relatively slowly changing command signal for changing the position of the aircraft rudder. In one aspect of this embodiment, the outer loop command  684  results from a proportional integral control scheme. When the track mode function is not engaged, the outer loop command  684  corresponds to the lateral position  464  commanded by the pilot, filtered via the complementary filtered lateral deviation value  462 . This value is combined with the commanded rate value  465  which is combined with the complementary filtered lateral deviation rate  461 . When the track mode function is engaged, the outer loop command corresponds to the immediate past value for adjusted track  576 .  
         [0031]      FIG. 7  is a flow diagram illustrating the inner loop control, configured in accordance with an embodiment of the invention. In one aspect of this embodiment, the outer loop command  684  is summed with a sensed yaw rate value  785  and a difference between the commanded acceleration  466  and a cross runway acceleration value  786  corrected for yaw acceleration. The result is the rudder command  354 .  
         [0032]      FIG. 8  is a flow diagram illustrating a method for trimming the aircraft rudder in accordance with an embodiment of the invention. In one aspect of this embodiment, the rudder surface command  354  has no effect on the rudder trim command unless the system receives an engine-out signal  891 . Instead, manual rudder trim commands  892  are used to determine the rudder trim command  356 . However, when the takeoff engage function  460  is active and the system receives an engine-out signal  891 , then the last rudder surface command  354  received after the aircraft has passed through a pitch attitude threshold is converted to a rudder trim command. Accordingly, the rudder trim is set to maintain the rudder position as the aircraft goes above the pitch attitude threshold. The aircraft may use this system in conjunction with other systems to further account for the yaw moment created by the engine-out condition.  
         [0033]      FIGS. 9A-9C  illustrate expected aircraft performance associated with systems in accordance with aspects of the embodiments described above. Each Figure illustrates a graph depicting lateral deviation from the runway centerline as a function of time. Accordingly, each graph tracks the lateral progress of the aircraft as it moves down the runway during a takeoff roll.  
         [0034]      FIG. 9A  illustrates the lateral deviation from the runway centerline for an aircraft taking off after initially being located 30 feet away from the runway centerline. As is evident from  FIG. 9A , the system can automatically and smoothly move the aircraft to the centerline before the aircraft takes off. Takeoff in this case occurs at about  30  seconds.  
         [0035]      FIG. 9B  illustrates the lateral deviation from the runway centerline in a situation in which the right engine of the aircraft fails when the aircraft has a velocity just below V 1 . As is shown in  FIG. 9B , the aircraft moves laterally when the engine fails, but only by a distance of about five feet, before the system returns the aircraft to the centerline while the aircraft successfully slows down and stops before the end of the runway.  
         [0036]      FIG. 9C  illustrates predicted aircraft performance in a situation in which the right engine fails at a threshold airspeed (e.g., V 1 ), and the aircraft continues to take off. As is shown in  FIG. 9C , the aircraft begins to deviate from the runway centerline when the engine fails, but successfully takes off and maintains the same track it was on when it reached the threshold airspeed. Accordingly, the system will not continue to try and correct lateral deviation once the aircraft achieves the threshold airspeed (e.g., V 1 ). Instead, the aircraft will continue along the track it was on just prior to reaching the threshold airspeed for a time after having achieved the threshold airspeed, including after the aircraft has left the ground.  
         [0037]     One feature of embodiments of the systems described above is that they can be configured to automatically guide the aircraft along a runway centerline (or other relevant path) during a takeoff roll. Accordingly, this automatic system can make takeoffs during difficult environmental conditions easier for the flight crew. Such environmental conditions can include icy or wet runways, strong crosswinds, low visibility, and/or engine out scenarios.  
         [0038]     Another feature of at least some of the foregoing embodiments is that the system can gradually reduce the degree to which it controls the aircraft lateral position and track angle. For example, in at least some embodiments, the system can cease controlling the aircraft to the runway centerline after the aircraft passes a threshold airspeed (e.g., V 1 ). The system can guide the aircraft to maintain whatever track angle it had just prior to reaching the threshold pitch angle. Furthermore, embodiments of the system can gradually reduce the yaw control provided by the system after the threshold pitch angle is achieved. In particular aspects of these embodiments, the system can disengage as the aircraft lifts off (e.g., 3-4 seconds after achieving the threshold pitch angle). After the system disengages, the flight crew has control over the lateral and directional position of the aircraft and can retain control of the aircraft until engaging the autopilot (typically at an altitude above 200 feet). An advantage of the foregoing arrangement is that it can reduce the tendency for the aircraft to undergo sudden changes in yaw as it lifts off the airport runway.  
         [0039]     Still another feature of systems in accordance with embodiments of the invention is that they can automatically respond to an engine out condition. For example, in particular embodiments, the system can automatically trim the rudder to account not only for the last commanded yaw input, but also to account for the yaw input resulting from the yaw moment created by the loss of an engine. This differs from existing systems, which compute a thrust differential based on the loss of an engine and provide a rudder input corresponding to the thrust differential, including a gain factor. A potential advantage of the arrangement described above with reference to  FIG. 8  is that it can more directly respond to the yawing moments created by the engine out condition, rather than predicting these effects based on a thrust differential. Accordingly, the system may more accurately, quickly and precisely reduce the yawing moment created by the loss of an engine.  
         [0040]     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, the control laws and sensor techniques described above are representative of particular embodiments of the invention, and may be different in other embodiments. In further embodiments, the aircraft can be controlled to follow a track that is different than a runway centerline. Aspects of the invention described in particular embodiments may be combined or eliminated in other embodiments. For example, some systems may include all the features described above with reference to  FIGS. 3-8 , and others may include subsets of these features. Although advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages. Additionally, not all of the foregoing embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.