In this paper, we propose a sliding-mode controller for a mini unmanned aerial vehicle (UAV) with propellers to follow the predetermined attitude trajectory. First the vehicle attitude dynamic model is established for angular displacements and for angular velocities, respectively. Next a sliding-mode controller with a switching surface is designed to eliminate uncertainties and disturbances. Then the attitude tracking control of a mini-UAV using the proposed control strategy is illustrated while flight. Finally, we employ the Lyapunov stability theory to fulfill the stability analysis of the proposed controller for the overall nonlinear control system. Extensive simulation results are gained to validate the effectiveness of the proposed sliding-mode controller.

This paper describes the dynamic modeling and analysis of a fixed-wing micro air vehicle (MAV). A nonlinear model for the MAV motion with six degrees of freedom is formulated first. Next, an extended version of the linear-time-invariant model for the MAV is derived by applying small perturbation theory and linearizing around an equilibrium flight condition. This ad hoc extended model for the MAV retains more terms that are generally neglected in mathematic models of conventional airplanes. To explore the stability and control characteristics, the aerodynamic derivatives required by dynamic modeling are evaluated using low-Reynolds-number wind tunnel testing data and some theoretical/empirical formulas. A fixed-wing MAV with a 15-cm wingspan successfully flown in 2002 is used as a baseline prototype for dynamic modeling and analysis. The longitudinal and lateral dynamic responses of the MAV under various conditions are demonstrated. The performance of the present extended MAV model is investigated by comparing the flight dynamics for different models. The simulation results show that the proposed extended model is consistent with the nonlinear dynamics model for a wider range of flight conditions. The present analysis may aid a better understanding of flight characteristics as well as design and analysis of MAV systems.

This study presents a means of explicit guidance for ballistic entry using an improved method of matched asymptotic expansions. The trajectory of ballistic entry into a planetary atmosphere is still an important and often critical phase of a mission. In the paper, feedback control via drag modulation is used to guide the vehicle during the atmospheric entry, whereas a matched asymptotic solution for the entry trajectory is available to aim the target. The feedback control ensures the stability of a trajectory around the nominal trajectory by compensating for the non-linear terms in the motion of the vehicle. Using the improved method of matched asymptotic expansions, the control algorithms for the guidance law are derived explicitly and tested against the 1976 U.S. Standard Atmosphere. Simulation results indicate that the control algorithms can effectively control the trajectories in the lower atmosphere under the targeting dispersions of atmospheric variations.

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