Abstract
In this paper, the conditions for periodic modes formation in the closed-loop pilot-vehicle system in the compensatory control mode are established. The case of high gain pilot task is considered under the conditions of a sudden disturbance, as well as under the influence of the system nonlinearities, such as actuator position and rate limit. Sinusoidal input describing function method and parametric resonance equation were used to determine the onset conditions for self-oscillations and forced oscillations. The case when this methods lead to erroneous results is established. The numerical limits of permissible pilot gain, time delay and reference signal at which unstable periodic modes do not arise are calculated.
Highlights
Modern flight control systems have a complex configuration, a variety of targets and must meet the requirements of high reliability and safety
Effective aircraft dynamics with a high gain task is a necessary conditions for pilot-induced oscillations (PIO). appearance is the presence of effective aircraft dynamics with a high gain task
It was found that in this system, it is possible to calculate the conditions for periodic modes formation using the sinusoidal input describing function (SIDF) method and parametric resonance equations for such nonlinearities as position limitation, backlash
Summary
Modern flight control systems have a complex configuration, a variety of targets and must meet the requirements of high reliability and safety. When controlling in a closed loop, the so-called pilot-induced oscillations (PIO) are isolated They are characterized by a sudden appearance of aircraft oscillations in the longitudinal and/or lateral direction with a small or jump-resonant amplitude. SIDF method for a rate limited actuator and an inverse describing function method were used to predict limit cycle oscillations [Ashkenas et al, 1964; Klyde et al, 1995] It was examined the effects of the simultaneous presence of position and rate saturation in the control loop and the value of the input signal causing the limit cycles have been established [Amato et al, 2000]. A more detailed consideration of the case with actuator rate limit in the frequency domain is presented finding reasons why the SIDF method gives incorrect results in the study of pilot-aircraft systems
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