Finite-Time Attitude Control for Fixed-Wing UAVs With Constrained Velocities and IMRS

This paper investigates the practical finite-time (FT) attitude control problem of six-degree-of-freedom fixed-wing unmanned aerial vehicles considering input magnitude and rate saturation (IMRS), constraints on airspeed and angular velocity, and external disturbances. First, to handle IMRS constraints acting on both inputs of the translational and rotational subsystems, we propose a smooth first-order IMRS model to capture the magnitude and rate saturation nonlinearities. Second, by introducing asymmetric and symmetric nonlinear transformation functions, the magnitudes of the constrained velocities including airspeed and angular velocity are mapped onto the set of real numbers, yielding a velocity-unconstrained system. Then, by using the backstepping method and the robust adaptive control technique, the practical FT control laws for both subsystems are designed such that the actual flight direction and airspeed of the aircraft can be regulated. Using Lyapunov theory, the practical FT convergence of both tracking errors is ensured. Finally, the validity and superior characteristics of the devised control law are demonstrated through numerical simulations.