Incremental sliding-mode control and allocation for morphing-wing aircraft fast manoeuvring

This paper presents a novel robust controller for fast manoeuvring of a morphing aircraft to enhance the longitudinal manoeuvrability by combining a nonlinear disturbance observer (NDO) and incremental sliding-mode control (NDOISMC). Based on multi-body dynamics theory, a longitudinal nonlinear model of a symmetric variable sweep and variable span morphing aircraft is established. The NDO is introduced to estimate model uncertainties due to difficulties in precise dynamic modelling during fast morphing. In addition, the NDOISMC algorithm is proposed to generate virtual control inputs, which does not require an accurate model of the aircraft. The NDOISMC algorithm is proven semi-globally uniformly ultimately bounded (SGUUB) by using Lyapunov theory in the presence of uncertainties whose first derivatives are bounded. Furthermore, virtual control inputs are allocated to variable sweep, variable span, and aerodynamic control surfaces using second-order cone programming (SOCP). Finally, numerical simulations demonstrate the effectiveness of the proposed method. The results reveal that the control burden of the aerodynamic control surfaces is reduced with the help of a morphing wing in the manoeuvring flight. Moreover, superior control performance for fast manoeuvring of a morphing aircraft is achieved by using NDOISMC compared with existing methods under model uncertainties.