Aircraft pitch control via second-order sliding technique

Control of high-performance low-cost uncrewed air vehicles involves the problems of incomplete measurements, external disturbances, and modeling uncertainties. Sliding mode control combines high precision with robustness to the aforementioned factors. The idea behind this approach is the choice of a particular constraint that, when maintained, will provide the process with the required features and remove, therefore, the plant's uncertainty. However, standard sliding modes are characterized by a high-frequency switching of control, which causes problems in practical applications (so-called chattering effect). The implemented second-order sliding controller features bounded continuously time-dependent control and provides higher accuracy than the standard sliding mode, while preserving precise constraint fulfillment within a finite time. It possesses, also, significant adaptive properties. The general approach is demonstrated by solving a real-life pitch control problem. Results of a computer simulation and flight tests are presented.