Overview

Aircraft system identification is mainly concerned with providing a mathematical description for the aerodynamic forces and moments in terms of relevant measureable quantities such as control surface deflections, aircraft angular velocities, airspeed or Mach number, and the orientation of the aircraft to the relative wind. Aerodynamic parameters quantify the functional dependence of the aerodynamic forces and moments on measureable quantities, when the mathematical model is parametric.

Estimation of aerodynamic parameters from flight-test data requires that a mathematical model of the aircraft be postulated. The mathematical model includes both the aircraft equations of motion and the equations for aerodynamic forces and moments, known as the aerodynamic model equations. In this chapter, the equations of motion will be formulated as ordinary differential equations for the aircraft states, with algebraic equations for the measured outputs. The aerodynamic model equations will be developed first using linear terms, polynomials, and polynomial splines with time-invariant parameters, then generalized to include time-dependent terms representing unsteady aerodynamic effects.

Continuous-time differential equations are used almost exclusively for aircraft system identification. The main reasons are used the form of the aircraft equations of motion (which will be derived in this chapter) is known, and the parameters appearing in the continuous-time differential equations have physical significance for aircraft stability and control. It is therefore of interest to estimate the values of these parameters and their associated uncertainties. Furthermore, results from wind-tunnel tests and analytic computations are typically given as values of the physical parameters, and these values are often used...