LOES Derivation of Non-Linear Actuation System for Flight Control Synthesis Purpose

Abstract

This paper presents methodology to extract Low Order Equivalent System (LOES) model from non-linear model of flight control actuation system. Synthesis of flight control law in conceptual phase only need simple model of flight control actuation system but can represents real conditions that might happen in operation such as reduced supply pressure, broken piston seal, active-standby actuator condition, etc. Simple model of flight control actuation system is represented by LOES model which is a transfer function for one specific operation condition. This work is started by get actuation responses from non-linear model for sinusoidal input with variation in frequency. With variation of input frequency, actuation response gain and phase for each frequency can be obtained and used to reconstruct frequency response of nonlinear model. Frequency response of non-linear model is used to estimate frequency response of approximate linear model. By obtaining frequency response of approximate linear model, transfer function of approximate linear model can be derived. The methodology that is presented in this work might be applied to any modern aircraft from fighter aircraft, trainer aircraft, cargo & military transport aircraft and civilian transport aircraft. This work is performed for hypothetical aircraft that has two elevators, two ailerons and one rudder. All the control surfaces have active-standby actuation configuration to ensure availability of control. At the end of this paper, transfer function of all control surfaces of hypothetical regional aircraft are obtained for some considered real condition and will be used for flight control law synthesis. Keywords: Non-linear, Actuation, LOES.