Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 97

Aerodynamic force (AF) is the resultant of all static pressures acting on an airfoil in an airflow multiplied by the planform area that is affected by the pressure. The line of action of the AF passes through the chord line at a point called the center of pressure (CP). It is convenient to consider that the forces acting on an aircraft, or on an airfoil, do so in some rectangular coordinate system. One such system could be defined by the longitudinal and vertical axes of an aircraft. Another could be defined by axes parallel to and perpendicular to the earth’s surface. A third rectangular coordinate system is defined by the relative wind direction and an axis perpendicular to it. This last system is chosen to define lift and drag forces. Aerodynamic force (AF) is resolved into two components: one parallel to the relative wind, called drag (D), and the other perpendicular to the relative wind, called lift (L). Figure 3.21 shows the resolution of AF into its components L and D.

Figure 3.21 Components of aerodynamic force.

Figure 3.22 Pressure forces on (a) nonrotating cylinder and (b) rotating cylinder.