Hidden Oscillations In The Closed-Loop Aircraft-Pilot System And Their Prevention*

The paper is devoted to studying and prevention of a special kind of oscillations-the Pilot Involved Oscillations (PIOs) which may appear in man-machine closed-loop dynamical systems. The PIO of categories II and III are defined as essentially non-linear unintended steady fluctuations of the piloted aircraft, generated due to pilot efforts to control the aircraft with a high precision. The main non-linear factor leading to the PIO is, generally, rate limitations of the aircraft control surfaces, resulting in a delay in the response of the aircraft to pilot commands. In many cases, these oscillations indicate presence of hidden, rather than self-excited attractors in the aircraft-pilot state space model. Detection of such a kind of attractors is a difficult problem since basin of attraction is not connected with unstable equilibrium. In the paper existence of the hidden attractor in pitch motion of the piloted aircraft is demonstrated and the nonlinear phase shift compensator is designed. The results obtained demonstrate that the proposed method in several times increases the admissible gain of the "airplane-pilot" loop as compared with non-corrected system.