Image Number 11 for United States Patent #8131405.
An adaptive guidance system (AGS) regulates the altitude and heading of a parasail to arrive at a target at a prescribed altitude. Since the altitude profile depends both on unknown wing loading, and wind magnitude and direction, the AGS estimates the glide slope and wind on the fly and provides a command to a stability augmentation system (SAS) that results in the desired glide slope and heading by performing a sequence of maneuvers and sensing the response. According to one embodiment, the SAS operates in the linear region and includes a PID controller that uses the difference between the actual heading and heading command to create an actuator output. The actuator output is limited by a position/rate limiter that imposes the physical limitations of the response time of the actuator/servos and position limits to prevent entering the nonlinear region. Alternatively, an adaptive SAS operates in both the linear and nonlinear region and includes a neural network (NN) that receives an error signal (difference between a reference model and actual heading) which is used to adapt the weights of the NN.