Aircraft pitch control via second-order sliding technique

Control of high-performance low-cost uncrewed air vehicles involves the pro blems of incomplete measurements, external disturbances, and modeling uncer tainties. Sliding mode control combines high precision with robustness to t he 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. Howe ver, standard sliding modes are characterized by a high-frequency switching of control, which causes problems in practical applications (so-called cha ttering effect). The implemented second order sliding controller features b ounded continuously time-dependent control and provides higher accuracy tha n the standard sliding mode, while preserving precise constraint fulfillmen t 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.