Browse Publications Technical Papers 2007-01-3817
2007-09-17

Implementation of Automatic Airspace Avoidance in an Advanced Flight Control System 2007-01-3817

An algorithm is developed and validated for automatic avoidance of restricted airspaces. This method is devised specifically for implementation with an advanced flight control system designed for general aviation application. The algorithm presented here implements two inputs to the aircraft; the bank angle, and the airspeed, while the control system always ensures coordinated maneuvers. Unlike collision avoidance systems, the current method is not designed to serve in an advisory role, but to assume complete control of the aircraft if necessary.
It is demonstrated that in order to implement this technique, the aircraft must be assigned an immediate domain whose size would have to depend on the aircraft performance and flight conditions. The strategy is designed such that as the domain surrounding the aircraft approaches that of the restricted airspace, aircraft control would switch gradually away from the pilot and to the controller, which would initiate an evasive maneuver. The degree of relative control is made dependent on the level of the threat defined by the steepness of trajectory and the extent of the overlap between the aircraft domain and the restricted space. While the algorithm is formulated primarily for avoiding a single zone, its application to multiple zones is also explored.
Application of the method on a light single-engine general aviation aircraft is demonstrated. Simulations are made using a six-degree of freedom model that includes the effects of wind. Results are presented for four cases involving single zones and one case involving multiple zones. The aircraft is made to approach the restricted zones with various airspeeds and attitudes with and without crosswind. It is shown that the controller can effectively prevent the aircraft from penetrating the prohibited area, while leaving the pilot some level of control. Recommendations are made to refine the strategy by employing a more sophisticated switching strategy and by implementing a multi-variable optimization of the control inputs.

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