An EKF Based Method for Path Following in Turbulent Air

An innovative use of the Extended Kalman Filter (EKF) is proposed to perform both accurate path following and adequate disturbance rejection in turbulent air. The tuned up procedure employs simultaneously two different EKF: the first one estimates gust disturbances, the second one estimates modified aircraft parameters. The first filter, by using measurements gathered in turbulent air, estimates both aircraft states and wind components. The second one, by using the estimated disturbances, obtains command laws that are able to reject disturbances. The predictor of the second EKF uses the estimated wind components to solve motion equations in turbulent air. Besides a set of unknown stability and control parameters (containing displacements of the controls) is introduced into the predictor. This set contains modified aerodynamic coefficients. These ones are obtained by adding entirely new derivatives or synthetic increments to basic ones. Therefore, the above aforementioned unknown values of aircraft parameters augment the aircraft’s state. The filter estimates the augmented state by using a set of measurements formed by the desired flight path variables. In this way, it is possible to obtain the command laws by using the postulated unknown stability and control derivatives, which contain the control displacements. Therefore, the obtained control laws, related to either the characteristics of the disturbance or the desired flight path, are adaptive.