Prospective means for the aircraft pilot induced oscillation suppression

Aeronautical and Space-Rocket Engineering


DOI: 10.34759/vst-2022-1-201-210

Аuthors

Efremov A. V.*, Shcherbakov A. I.**, Korzun F. A.***, Prodanik V. A.****

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: pvl@mai.ru
**e-mail: mvcom@inbox.ru
***e-mail: korzunf@yandex.ru
****e-mail: vprodanik@mail.ru

Abstract

The article presents a brief overview of the accidents occurred in the past due to the aircraft pilot induced oscillation (PIO). It proposes the alternative algorithm for the nonlinear pre-filter (oscillation suppressor). Compared to the other pre-filter versions, the proposed filter is being installed inside the flight control system contour, and its output serves as an input signal for the actuator. According to its algorithm, this signal does not decline when its output signal (δ) is equal or less than rate limiting(δmax). However, when δ exceeds δmax, δ decreases according to the developed algorithm.

Effectiveness of the proposed pre-filter is being compared with the other two pre-filters versions. One of them is the traditional nonlinear pre-filter, which algorithm corresponds to the simplified actuator model. Its input signal is proportional to the control stick deflection. Another nonlinear pre-filter is so-called “rate limiter with feedback and bypass” developed by the SAAB Company for the JAS-39 aircraft.

The following two types of experiments were conducted:

– PIO suppression effectiveness comparison by various nonlinear pre-filters and of error reduction in the tracking task in case of precise knowledge of the actuator model parameters;

– Robustness evaluation of the proposed pre-filters.

All experiments were being conducted at one of the MAI flight-simulators. The piloting task consisted in pitch tracking task with the tracking error-minimizing goal. The dynamic configuration corresponded to the statically neutral aircraft with feedbacks ensuring the HP2.1 dynamic configuration from the Have PIO database with no nonlinear effects impact. The actuator simplified model parameters corresponded to ±15 deg/s and gain coefficient K = 10.

The experiments revealed that in case of piloting without pre-filters, the unstable PIO process occurs. Installation of whatever pre-filter allows suppressing the diverging oscillation. However the proposed nonlinear pre-filter ensures the of the of error variance decrease by2.35 and 1.95 times and higher bandwidth of closed-loop system compared to the conventional pre-filter and so-called “rate limiter with feedback and bypass”.

The experiments on robustness studying demonstrated that the inaccurate knowledge of the actuator model employed in all pre-filters algorithms does not affect practically on the results of experiments in the case of the proposed pre-filter. As for the other pre-filters, the inaccurate knowledge of actuator model parameters considerably affects the error variances and other pilot-aircraft system characteristics.

Keywords:

pilot induced oscillation, nonlinear prefilter, flight safety, aircraft-pilot system

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