ABSTRACT
In this chapter, we examine the forces that are exerted on a body moving through a fluid. Consider, for example, a wing or airfoil moving at a velocity V through air. For convenience, and in keeping with the control volume approach, we impose a velocity on the system equal to –V, thus rendering the airfoil stationary while air moves past the wing. The air velocity is given the symbol U, or U1, to denote this transformation. The forces of interest are the drag force and the lift force. These forces act parallel and perpendicular to the principal airspeed direction, respectively. These concepts are illustrated in Figure 6.1.
