TABLE OF CONTENTS This chapter will focus on the first step in the system-identification process of Fig. 2.1, which is the collection of a well-suited time-history database. The ultimate quality of the identification results is highly dependent on 1) properly designed and executed flight tests of the aircraft being studied and 2) properly selected and well-documented characteristics of the instrumentation system. The recommended input for frequency-domain identification is a frequency sweep because it provides a fairly uniform spectral excitation over the frequency range of interest for good frequency-response identification and is robust to uncertainties in a priori knowledge of the system dynamics.
The key points covered in this chapter include the following: 1) general aspects of data requirements for system identification, 2) instrumentation system requirements, 3) optimal inputs, 4) frequency-sweep input, 5) flight-testing considerations, and 6) computer-generated sweeps. Excellent resource material on flight-data collection for system identification is included in the publications by Hamel and Aiken,66 Hamel,10 Williams et al.,67 and Klein and Morelli.6
An overarching principle of system identification is that the flight-test records must include the information content of the dynamic characteristics that you wish to capture in the model. Succinctly stated, "For particular dynamic characteristics to be identified in the model, they must be apparent in the data." Conversely, "If it's in not in the data, don't expect to be able to identify it in the model!" This basic principle impacts all aspects of flight-test preparation...
