1. Introduction

Aerodynamics is a fundamental subject investigating the interaction of the (atmospheric) gases with objects moving in them. This is a basic science that explains how to develop flying objects (aircraft) with minimum drag, maximum lift, and acceptable and controllable side force and moments.

Aerodynamics [1–8] deals with the theory of aerodynamic force and moment generation and the description of force and moment components appearing on aerofoils, wings, rotating wings, circular bodies at low, moderate, subsonic, supersonic, and hypersonic speeds and

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

developing the models and methods of calculating the aerodynamic forces and moments. The theoretical and practical methods of evaluation and estimation of the aerodynamic forces and moments are synthetized in aircraft aerodynamic design, i.e., finding the best aerodynamic shape of the aircraft with maximum lift and minimum drag (ratio of which is called as aerodynamic goodness) and controllable other force moments. The aerodynamic characteristics are applied in aircraft motion description, namely for estimating the flight performance, determining the stability conditions and stability, flight dynamics and control.

Aerodynamics is a subfield of fluid and gas dynamics and uses their basic equations. However, there are no good and general methods for calculating the aerodynamic forces and moments that depend on shape and geometrical characteristics of the body, fluid properties, and motion dynamics. Therefore, a series of nondimensional aerodynamic coefficients were introduced, and with the use of results from theoretical and practical investigations (including the computation fluid dynamics and wind tunnel and flight tests), different models of aerodynamic coefficients were developed. The models depend on the real situations, objects, and goals of their application as shown in Figure 1, reflecting the aerodynamic mathematical modeling approach of Tobak [11] in the form of known Bisplinghoff's representation [12].

This chapter describes the goal- and object-oriented models of the aerodynamic coefficients and discusses their applicability. It contains 10 subchapters (10 points). The first is this introduction. The second one shortly explains the aerodynamic force and moment generation. The third point introduces the aerodynamic coefficients and defines their mathematical models. The fourth subchapter deals with the first, simple models based on several partial derivatives. The fifth point states improvement of the simple models and describes the so-called classic aerodynamic models. Generally, these models are most used by aerodynamics, flight performance, stability, flight dynamics, and control. The developed aerodynamic models described

Figure 1. Modeling approach to aerodynamic coefficients (affecting aspects) [9, 10].

by the next point are used for nonsteady aerodynamics, studying the very nonlinear and even chaotic motion of aircraft. The seventh point shows how the advanced aerodynamic coefficient might be created including the analytical models, special approximation of the measured data, using the soft computing to estimate the coefficient models. Applicability of the described models is discussed in the following eighth subchapter. Finally, the ninth point shows a use of an advanced aerodynamic model. The conclusion (tenth point) summarizes the materials introduced and described by this chapter.
