The Fundamental Problem of Aerodynamics

The basic problem addressed in this book is the accurate determination of the aero­dynamic force system acting on a body moving through the air. Figure 1.13 shows a typical force system on an airplane in flight; only the resultant forces are shown. An important task is to relate these resultant effects to the distributions of pressure and frictional forces that create them. We focus only on the part of the force system related to the interaction of the airflow with the vehicle—that is, on the creation of lift (L) and drag (D), the aerodynamic forces normal and parallel to the vehicle velo­city vector, as defined in the figure. However, much aerodynamic influence also is implied in the creation of thrust, as depicted by the vector T in Fig. 1.13. Interaction of the vehicle flow field with propellers, engine exhaust stream, cooling air inlets and outlets, and airbreathing propulsion system ducting must be accounted for. These important related aspects of applied aerodynamics are used at several points in the book to emphasize their strong dependence on knowledge of the vehicle flow field.