Spin Recovery of High-Angle-of-Attack Aircraft With Altitude Gain Reduction in the Presence of Aerodynamic Uncertainty: A MIMO Super-Twisting Sliding Mode Approach

To recover steady, straight-level flight of a high-angle-of-attack aircraft from its oscillatory spin, a MIMO super-twisting sliding control approach is proposed in this study. Since at high angles of attack, the aerodynamics governing the aircraft is highly nonlinear, tabulated data are utilised to ensure the validity of the results up to an angle of attack of 90°. Regarding uncertain aerodynamic coefficients, the robustness of the control approach is necessary. It is shown that the first-order classical sliding control and power rate reaching law methods are successful approaches to recover an aircraft from its state of spin in the absence of aerodynamic parameter uncertainties. However, in the presence of these uncertainties, chattering affects their performance and the altitude required to perform the recovery manoeuvre, referred to as altitude gain, significantly increases. To overcome these issues, a second-order sliding control algorithm is proposed in this study. The system outputs are considered as roll, pitch, rate of yaw change to attain level flight, and rate of change of altitude to assure straight flight. Thus, a 4 × 4 super-twisting SMC scheme is developed. Finite-time convergence of sliding variables, which guarantees asymptotic stability of the aircraft control system, is proven via the Lyapunov direct method. Simulation results illustrate that the proposed control algorithm serves not only as a reliable approach to perform the recovery manoeuvre but also as a highly effective method to overcome aerodynamic uncertainties without inducing chattering in control inputs. In addition, it enables the recovery manoeuvre to be performed with lower altitude gain.