Nonlinear Phase Shift Compensator for Pilot-Induced Oscillations Prevention

The pilot-induced oscillation (PIO) is denoted as unintended steady fluctuation of the piloted aircraft, generated due to the efforts of the pilot to control the aircraft. 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. Due to the tight relationship between magnitude and phase frequency responses for linear systems, applicability of the linear compensator for mentioned aim is highly restricted. This leads to the idea of employing the nonlinear phase shift compensator. In the control theoretic literature, various nonlinear corrective devices (NCD) are elaborated, which make it possible to change the phase-frequency and amplitude-frequency responses independently on each other. In the paper, a novel phase shift compensator based on nonlinear correction technique is presented and numerical comparative study for two models of a pilot for PIO prevention during the flight is given. 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.

I. Introduction

The pilot-induced oscillation (PIO) is denoted as unintended steady fluctuation of the piloted aircraft generated due to the efforts of the pilot to control the aircraft. While PIOs can be easily determined from the analysis of the post-flight data, the pilots often do not recognize that PIO occurs: from their point of view, the plane seems faulty, having “a breakage” [1]—[3]. The PIO is one the topical problems from the very beginning of aviation, and the efforts of many scientists and designers for many years were aimed to their elimination, see [1], [4] for mentioning a few.