Loss-of-control prevention and recovery flight controller

1. A control system for a fixed-wing aircraft, the control system comprising:

one or more processors; and

a memory coupled to the one or more processors and including program code that, when executed by the one or more processors, causes the control system to:

monitor a plurality of flight conditions of the aircraft, the flight conditions including a wind velocity vector;

in response to the flight conditions being within a first threshold box defined by a first plurality of flight condition thresholds, activate a first multi-loop flight control mode including a plurality of control loops each having a respective nominal bandwidth;

in response to one or more of the flight conditions exceeding one or more of the first plurality of flight condition thresholds, activate a second multi-loop flight control mode including the control loops in which each of the nominal bandwidths is multiplied by a bandwidth adaptation gain that decreases in response to an increase in a component of the wind velocity vector, and increases in response to a decrease in the component of the wind velocity vector; and

control the aircraft using the activated flight control mode.

2. The control system of claim 1 wherein the first multi-loop flight control mode is a nominal flight control mode, the second multi-loop flight control mode is a loss-of-control prevention control mode, the first threshold box is a protection box, and the program code further causes the control system to:

in response to the one or more of the flight conditions exceeding one or more of a second plurality of flight condition thresholds defining a safety box, activate a loss-of-control arrest control mode, and

in response to the one or more of the fight conditions being within a third plurality of flight condition thresholds defining an operation box while either the loss-of-control prevention control mode or the loss-of-control arrest control mode is active, activate a nominal flight restoration control mode.

3. The control system of claim 2 , wherein the nominal flight control mode implements a six degree-of-freedom trajectory tracking controller.

4. The control system of claim 2 , wherein the loss-of-control arrest control mode includes a full throttle control during an arrest phase.

5. The control system of claim 2 , wherein the loss-of-control arrest control mode includes a commanded aerodynamic attitude determined by a level and straight flight trim value of angle-of-attack and zero sideslip and bank angles.

6. The control system of claim 5 , wherein the loss-of-control arrest control mode tracks the commanded aerodynamic attitude via inner and outer aerodynamic attitude loops.

7. The control system of claim 2 , wherein the nominal flight restoration control mode includes a close-in sub-mode for guiding the aircraft to catch up with a target position dictated by a mission trajectory and a home-in sub-mode for restoring the mission trajectory of the aircraft.

8. The control system of claim 7 , wherein the close-in sub-mode is defined by a guidance approach wherein a velocity vector of the aircraft is aligned to a line-of-sight vector of the aircraft using proportional-integral-derivative linear regulation in an Earth reference frame.

9. The control system of claim 7 , wherein the home-in sub-mode includes a bandwidth adaptation for gradually regaining tracking performance of the aircraft and restoring the mission trajectory of the aircraft.

10. The control system of claim 1 , wherein the second multi-loop flight control mode employs time-varying parallel differential eigenvalues to sacrifice tracking performance to increase a tolerance for severe wind in real-time.

11. The control system of claim 1 wherein the program code further causes the control system to:

set a value of a supervisory control logic variable according to the flight conditions of the aircraft; and

determine which flight control mode to activate based at least in part on the supervisory control logic variable.

12. The control system of claim 11 , wherein the supervisory control logic variable is set to the value corresponding to a respective control mode in response to each flight condition of a set of flight conditions corresponding to the respective control mode being within a respective threshold of a set of thresholds corresponding to the respective control mode.

13. The control system of claim 12 , wherein:

the supervisory control logic variable is set to the value corresponding to a nominal flight control mode in response to each flight condition of a corresponding set of flight conditions being within the respective threshold of a set of operation thresholds corresponding to the nominal flight control mode;

the supervisory control logic variable is set to the value corresponding to a loss-of-control prevention control mode in response to each flight condition of the corresponding set of flight conditions being within the respective threshold of a set of protection thresholds corresponding to the loss-of-control prevention control mode;

the supervisory control logic variable is set to the value corresponding to a loss-of-control arrest control mode in response to each flight condition of the corresponding set of flight conditions being within a respective safety threshold of a set of safety thresholds corresponding to the loss-of-control arrest control mode; and

the supervisory control logic variable is set to the value corresponding to a nominal flight restoration control mode in response to each flight condition of the corresponding set of flight conditions being within a respective operation threshold of the set of operation thresholds corresponding to the nominal flight restoration control mode.

14. The control system of claim 13 , wherein the supervisory control logic variable is set to the value corresponding to the nominal flight restoration control mode when a predetermined set of flight conditions are each within a predetermined set of operation thresholds and a position error between the aircraft and a target position exceeds a range threshold.

15. A method of controlling a fixed-wing aircraft having an automatic a control system, the method comprising:

monitoring a plurality of flight conditions of the aircraft, the flight conditions including a wind velocity vector;

in response to the flight conditions being within a first threshold box defined by a first plurality of flight condition thresholds, activating a first multi-loop flight control mode including a plurality of control loops each having a respective nominal bandwidth;

in response to one or more of the flight conditions exceeding one or more of the first plurality of flight condition thresholds, activating a second multi-loop flight control mode including the control loops in which each of the nominal bandwidths is multiplied by a bandwidth adaptation gain that decreases in response to an increase in a component of the wind velocity vector, and increases in response to a decrease in the component of the wind velocity vector; and

controlling the aircraft using the activated flight control mode.

16. The method of claim 15 wherein the first multi-loop flight control mode is a nominal flight control mode, the second multi-loop flight control mode is a loss-of-control prevention control mode, the first threshold box is a protection box, and method further comprises:

in response to the one or more of the flight conditions exceeding one or more of a second plurality of flight condition thresholds defining a safety box, activating a loss-of-control arrest control mode, and

in response to the one or more of the fight conditions being within a third plurality of flight condition thresholds defining an operation box while either the loss-of-control prevention control mode or the loss-of-control arrest control mode is active, activating a nominal flight restoration control mode.

17. A computer program product for controlling a fixed-wing aircraft, the computer program product comprising:

a non-transitory computer-readable storage medium; and

program code stored on the non-transitory computer-readable storage medium that, when executed by one or more processors, causes the one or more processors to:

monitor a plurality of flight conditions of the aircraft, the flight conditions including a wind velocity vector;

in response to the flight conditions being within a first threshold box defined by a first plurality of flight condition thresholds, activate a first multi-loop flight control mode including a plurality of control loops each having a respective nominal bandwidth;

in response to one or more of the flight conditions exceeding one or more of the first plurality of flight condition thresholds, activate a second multi-loop flight control mode including the control loops in which each of the nominal bandwidths is multiplied by a bandwidth adaptation gain that decreases in response to an increase in a component of the wind velocity vector, and increases in response to a decrease in the component of the wind velocity vector; and

control the aircraft using the activated flight control mode.