Robust Detection of Oscillatory Failure Case in Aircraft Control Surface Servo-Loops

Abstract

This chapter deals with model-based Fault Detection and Diagnosis (FDD) methods which have been recently applied to Oscillatory Failure Case (OFC) in aircraft control surface servo-loops. This failure case, related to the Electrical Flight Control System (EFCS), could have an influence on structural loads and aircraft controllability. Two methods will be presented and, in order to improve FDD performance and robustness, the tuning of their free design parameters are discussed. The presented methods are nonlinear observer design and fault reconstruction via sliding-mode differentiation. The efficiency of the above techniques will be illustrated through their application to highly representative aircraft benchmarks, real flight data, and real-time implementation on Airbus test facilities. In addition to thrust control, the principal means of controlling an aircraft is through aerodynamic forces generated by control surfaces which are generally movable flaps located on the fuselage, wing, and tail. The primary purpose of certain control surfaces (e.g., elevator, rudder, and ailerons) is to generate control moments; hence, their resultant forces act at some distance from the aircraft center of mass. In this section the main control surfaces and their functions are briefly recalled (see Fig. 3.1).