  With the characteristics of vertical take-off and landing and long endurance,
tiltrotor has attracted considerable attention in recent decades for its
potential applications in civil and scientific research. However, the problems
of strong couplings, nonlinear characteristics and mismatched disturbances
inevitably exist in the tiltrotor, which bring great challenges to the
controller design in transition mode. In this paper, we combined a
super-twisting extended state observer (STESO) with an adaptive recursive
sliding mode control (ARSMC) together to design a tiltrotor aircraft attitude
system controller in transition mode using STESO-ARSMC (SAC). Firstly, the six
degrees of freedom (DOF) nonlinear mathematical model of tiltrotor is
established. Secondly, the states and disturbances are estimated by the STES
observer. Thirdly, ARSM controller is designed to achieve finite time
convergence. The Lyapunov function is used to testify the convergence of the
tiltrotor UAV system. The new aspect is that the assessments of the states are
incorporated into the control rules to adjust for disruptions. When compared to
prior techniques, the control system proposed in this work can considerably
enhance anti-disturbance performance. Finally, simulation tests are used to
demonstrate the efficacy of the suggested technique.
