Non-linear aircraft flight path reconstruction review and new advances

Aircraft parameter identification techniques have become accepted as indisp ensable tools in the evaluation of prototype- and derivative aircraft in fl ight. Applications include estimation of stability- and control derivatives in the linearized equations of motion, synthesis of nonlinear aerodynamic and propulsion models in the context of performance certification and incor poration of information from dynamic flight test manoeuvres in a priori non linear flight simulation models. A variety of techniques in the time- as we ll as the frequency domain have been applied in the past. One of the succes sful techniques is the so-called two-step method (TSM) in which the origina l state-parameter estimation problem is decomposed into a nonlinear state/p arameter estimation or reconstruction problem and a subsequent linear param eter identification problem. In the literature, the first step of the TSM i s often referred to as 'flight path reconstruction'. The present paper focu ses on the first step of the TSM. After a derivation of the system models d escribing the flight path relative to a flat earth as well as a spherical a nd rotating earth, and observation models for air data and GPS, the flight path reconstruction problem is introduced. Requirements with respect to typ e and quality of flight test transducers are discussed. Next follows an ove rview of different approaches to the solution of the flight path reconstruc tion problem with emphasis on Kalman filter/smoother and Maximum Likelihood methods. A new adaptive algorithm is presented, the Modified Recursive Max imum Likelihood Adaptive Filter (MRML) which is shown to be significantly m ore robust with respect to initialisation errors than earlier methods. A re constructibility analysis is presented for different transducer combination s. Numerical examples are presented based on simulated as well as actual fl ight test data. Flight results are given of the flight path reconstruction part of an on-line pseudo real-time application of the TSM. The paper ends with concluding remarks. (C) 1999 Elsevier Science Ltd. All rights reserved .