Abstract:
A method for directing formation flying of an aircraft includes sensing a relative position of a leader to a follower aircraft by one or more sensors disposed at the follower aircraft. The relative position is compared to a selected relative position, and a follower velocity of the follower aircraft necessary to move the follower aircraft to the selective relative position is determined via a flight control computer of the follower aircraft. The follower velocity is transformed into flight control inputs and the follower aircraft is moved to the selected relative position via the flight control inputs.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/360,761 filed Jul. 1, 2010, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The subject matter disclosed herein relates to flight control. More specifically, the subject disclosure relates to systems and methods for control of formation flying of aircraft. 
         [0003]    Formation flying of aircraft is a high pilot-workload activity where one or more follower aircraft attempt to maintain a desired position relative to a designated lead aircraft. Systems have been developed in an attempt to ease workload on the pilot, including systems in which there is communication between the lead aircraft and the follower aircraft. For example, the lead aircraft may be modified to emit a signal that is tracked and followed by the follower aircraft. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a method for directing formation flying of an aircraft includes sensing a relative position of a leader to a follower aircraft by one or more sensors disposed at the follower aircraft. The relative position is compared to a selected relative position, and a follower velocity of the follower aircraft necessary to move the follower aircraft to the selective relative position is determined via a flight control computer of the follower aircraft. The follower velocity is transformed into flight control inputs and the follower aircraft is moved to the selected relative position via the flight control inputs. 
         [0005]    According to another aspect of the invention, a system for directing formation flying of aircraft includes one or more sensors located at a follower aircraft, the one or more sensors configured to detect data regarding a position of the follower aircraft relative to a position of a leader. A flight control computer is located at the follower aircraft and is in operable communication with the one or more sensors. The flight control computer is configured to determine a relative position between the follower aircraft and the leader, compare the relative position to a selected relative position, determine a follower velocity of the follower aircraft necessary to move the follower aircraft to the selected relative position, transform the follower velocity into flight control inputs, and direct movement of the follower aircraft to the selected relative position via the flight control inputs. These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    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: 
           [0007]      FIG. 1  is a schematic view of an embodiment of formation flying of aircraft; 
           [0008]      FIG. 2  is a schematic view of another embodiment of formation flying of aircraft; and 
           [0009]      FIG. 3  is a schematic view of an embodiment of a method and system for controlling formation flying of aircraft. 
       
    
    
       [0010]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Shown in  FIG. 1  is schematic representation of a self-contained, autonomous formation flying system  10 . Referring to  FIG. 1 , the system  10  controls a position of a follower aircraft  12 , for example, a helicopter, to a leader. In the embodiment shown in  FIG. 1 , the leader is a lead aircraft  14 , but in other embodiments the leader may be another moving object, for example, a ground vehicle, a sea vehicle, or a refueling drogue. 
         [0012]    The follower aircraft  12  includes one or more passive sensors  16 . The sensors  16  of  FIG. 1  are imaging sensors, specifically cameras. In other embodiments, the sensors  16  may be infared sensors, radar, sonar, lidar, global positioning sensors, or the like, or a combination of different types of sensors  16 . Further, the sensors  16  may be sensors  16  already present at the follower aircraft  12  and not specifically utilized solely for the purposes described herein. For example, sensors  16  utilized may include: sandblaster sensors utilized to aide navigation through airborne particles such as sand and dust, missile detection sensors which in some cases are thermal-sensitive sensors, small arms fire sensors which in some cases are acoustic sensors, wire detection sensors, collision avoidance sensors, auto-land sensors, terrain following sensors, waypoint following sensors, or external load detection and pickup sensors. 
         [0013]    The sensors  16  at the follower aircraft  12  obtain a relative position of the lead aircraft  14 . To obtain an accurate relative position, in some embodiments it is advantageous to obtain information from more than one sensor  16  at the follower aircraft  12 . Further, as shown in  FIG. 2 , to increase the accuracy of triangulation, it is advantageous to position the sensors  16  at points as far apart as possible at the follower aircraft  12 , for example, a sensor  16  at or near a nose of the follower aircraft  12  and another sensor  16  at or near a tail of the follower aircraft  12 . This arrangement is particularly advantageous with certain types of sensors  16 , for example, cameras. It increases a ratio of distance between the cameras to the distance between the aircraft  12 ,  14 , thus resulting in a more accurate determination of a distance between the aircraft  12 ,  14 . 
         [0014]    The follower aircraft  12  further includes a control system  18 , shown schematically in  FIG. 3 . The control system  18  includes a sensor fusion computer  20  that collects data from the sensors  16  and converts sensor data obtained of the lead aircraft  14  into an estimate of a position of the lead aircraft  14  relative to the follower aircraft  12 . In embodiments where the sensors  16  are cameras, for example, the sensor fusion computer  20  is an image processor that converts video images of the lead aircraft  14  obtained by the cameras into the relative position. 
         [0015]    In other embodiments, as stated above, a combination of sensor  16  types may be used. For example, some embodiments utilize a combination of video sensors  22 , radar sensors  24  and global positioning sensors  26  located at the follower aircraft  12 . The sensor fusion computer  20  receives visual data from the video sensors  22  and runs a visual tracking algorithm  28  to process the visual data into an estimate of relative range  30 , azimuth  32 , and elevation  34  (shown in  FIG. 1 ) between the lead aircraft  14  and the follower aircraft  12 . Radar sensors  24  provide relative range  30  and azimuth  32  data to the sensor fusion computer  20 . Further, radar sensors  24  can track more than one target, for example, more than one lead aircraft  14 . Inclusion of multiple radar sensors  24  can provide elevation  34  aw well as range  30  and azimuth  32 . 
         [0016]    Relative global positioning data and sensor data, in the form of range  30 , azimuth  32  and elevation  34  is provided to the sensor fusion computer  20 . Relative global positioning requires an additional global positioning sensor  26  and a datalink device  36  at the lead aircraft  14 . Global positioning coordinates of the lead aircraft  14  are obtained and transmitted to the follower aircraft  12 , where the relative position of the follower aircraft  12  is determined by comparing the data from the lead aircraft  14  global positioning sensor  26  to the data from the follower aircraft  12  global positioning sensor  26 . A relative position  42  obtained via the various sensors is communicated through an avionics bus  38 , such as a MIL-STD-1553 bus, to a flight control computer  40  of the follower aircraft  12 . 
         [0017]    The relative position  42  is compared to a selected relative position  44  at the flight control computer  40 . A determination is made by the flight control computer of a magnitude of an error  46  between the relative position  42  and the selected relative position  44  and it is determined whether high gain corrective measures  48  or relatively low gain corrective measures  50  are necessary to move the follower aircraft  12  such that the relative position  44  is within an acceptable range. The necessary correction is determined and transformed into body-axis velocities v x , v y , and v z  relative to the three body axes of the follower aircraft  12 . 
         [0018]    To physically change the direction of the follower aircraft  12 , the flight control computer  40  converts the body and inertial axis velocities v x , v y , and v z  are converted into pilot path inputs. The flight control computer  40  communicates the body axis velocities to controls in the follower aircraft  12  which may include, but are not limited to, controls for the roll stick, pitch stick, pedals, and/or throttle or collective stick. Through these inputs, the flight control computer  40  directs the follower aircraft  12  into a desired position envelope  52 . 
         [0019]    The system  10  includes safety features to avoid overaggressive inputs to change the path of the follower aircraft  12  and also means for the pilot to disengage the system if necessary. For example, in cases where the relative position  44  is a great distance away from the selected relative position  46 , the flight control computer  40  might prescribe harsh corrections to the path of the follower aircraft  12  to return the follower aircraft  12  to the desired position envelope. Such harsh corrections, however, might endanger the aircraft, its crew and/or other aircraft and their crew, and/or exceed ride comfort limits of the follower aircraft  12 . For this reason, the intended corrections are compared to limits at a correction limiter  54 , which then limits the amount of correction available, limits specific commands such as roll, pitch, etc., and also limits the rate of such commands to preserve safety of the aircraft and nearby aircraft. 
         [0020]    Further, the system  10  includes means for the system  10  to be disengaged. Such means may include a pilot input to a control stick of the aircraft  12 , a button or switch which is activated by the pilot. Further, if the flight control system  40  determines that the path of the lead aircraft  14  is unsafe to follow, the flight control system  10  will engage the formation flying system  10 . 
         [0021]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while 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.