Estimation of aircraft aerodynamic parameters from flight data

Several ways for obtaining aerodynamic parameters of an aircraft from flight data are presented with the emphasis on present problem areas. The paper starts with a brief description of data analysis from steady measurements. Then, a concept of system identification applied to aircraft is introduced with a discussion of various steps in this procedure. This is followed by a formulation of a mathematical model of an aircraft with aerodynamic forces and moments approximated either by polynomials or splines. The main part contains a rather detailed treatment of two more often used techniques for parameter estimation. The first method is based on linear regression which can be extended to a stepwise regression for model structure determination and to data handling procedure, known as data partitioning. The second technique applies the maximum likelihood principle to measured data. In this part, mainly the output error estimation method is considered. The problem of near linear relationship among measured time histories is mentioned in a separate section together with some diagnostic measures and two estimation techniques dealing with this problem. Because of a renewed interest in the frequency domain analysis, one section of the paper is devoted to this problem. All the methods explained in the paper are demonstrated in several examples using real flight data.