I. Introduction

The process of performing experiments, and recording system inputs and outputs, constitutes data gathering. Besides the ability to efficiently extract unknown system parameters applying advanced estimation techniques, which we will cover in the following chapters, data gathering is the other crucial aspect of flight vehicle system identification, because the basic rule If it is not in the data, it cannot be modeled applies to all exercises that attempt parameter estimation from experimental data. This is true irrespective of the type of flight vehicle we may attempt to model. Gathered data basically limits, both in terms of scope and accuracy, the model development and parameter estimation. Although data acquisition-related aspects like parameters (aircraft motion variables and control surface deflections) to be recorded, quality of sensors in terms of accuracy and noise, sampling rate, signal conditioners, and data recording equipment play a role in the overall process of data analysis, the most important aspects of data gathering are to 1) define the scope of the flight testing, 2) define a suitable sequence of flight maneuvers to be performed at each test point, and 3) choose an adequate form of the inputs to excite the aircraft motion in some optimum sense. The last topic is commonly called in the literature optimal input design.

The accuracy and reliability of parameter estimates, obtained by applying either the recent modern methods like maximum likelihood or past methods, elaborated in Chapter 1, Secs. VII and VI, respectively, depend heavily on the amount of information available...