Chapter 6: stability and control
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Aerodynamic Center The advantage of using M.A.C. for  is that it not only is used in defining moment coefficient, but it also can be used to approximate the location of the wing’s aerodynamic center. Just as the aerodynamic center of airfoils is normally located at about 0.25 c, for wings the aerodynamic center is located approximately at the quarter chord point of the M.A.C. for Mach numbers below Mcrit. At supersonic speeds, the aerodynamic center shifts to approximately 0.50 M.A.C. For swept wings, the spanwise location of the M.A.C. is important because it must be known in order to locate the wing aerodynamic center. For untapered or linearly tapered wings, the spanwise location of the M.A.C.,  , is given by:
 (6.13)
where is the wing taper ratio defined in Figure 4.1. The aerodynamic center of swept wings is then approximately located at: xac = yM.A.C. tan LE + 0.25 M.A.C. (subsonic) (6.14)
xac = yM.A.C. tan LE + 0.50 M.A.C. (supersonic) Where the leading edge of the wing root chord is taken as x = 0. Figure 6.13 illustrates this location and also demonstrates a simple graphical method for locating the M.A.C. and aerodynamic center on linearly tapered wings. As shown in Figure 6.13, the graphical method for locating the M.A.C. involves drawing the 50% chord line of the wing, then laying out lines with lengths equal to croot and ctip at opposite ends and alternate sides of the wing. A line is drawn connecting the endpoints of these two new lines. This third line intersects the 50% chord line of the wing at the mid-chord point of the M.A.C. The checkerboard bar, pointed at both ends, is a commonly used symbol for the M.A.C. Directory: ~jps7 -> Aircraft%20Design%20Resources Aircraft%20Design%20Resources -> Systems in Transportation: The case of the Airline Industry Download 2.68 Mb. Share with your friends:
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