A Non Conventional UAV In Ground Effect: Synthesis of a Robust Flight Control System

This paper discusses the synthesis of an Extended Kalman Filter (EKF) to perform both wind velocities and state estimation for a non conventional UAV flying in ground effect. Since, in IGE flight, motions into the symmetry plane are of primary concern, the study focuses on the longitudinal aircraft dynamics. The proposed estimator requires measurement of few flight variables, easily obtainable by means of conventional sensors; besides, it does not use Inertial Measurement Unit (IMU). To simulate a low cost sensing equipment, the model outputs are corrupted by white noise of relatively high standard deviation. Furthermore, to cope with the low rate of the GPS with respect to the other sensors, the EKF algorithm is modified to allow for a dual rate measurement model. State propagation is obtained by means of an accurate, highly non-linear mathematical model of the UAV dynamics which allows to cope with both the non conventional configuration and ground effect. Combined estimation of the UAV state and wind velocity is obtained by augmenting the system state vector with the wind velocity components. Numerical simulations show the effectiveness of the proposed method in widely different maneuvering conditions mixing IGE and OGE flight stages and in presence of largely dissimilar wind disturbance characteristics. The performance advantages with respect to a classical, computationally simpler estimation scheme are also highlighted. Closed loop simulations have shown the suitability of the obtained state estimates for control purposes.