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Mean aerodynamic chord (MAC) is defined as:[3] \mbox{MAC} = \frac{2}{S}\int_{0}^{\frac{b}{2}}c(y)^2 dy,
where y is the coordinate along the wing span and c is the chord at the coordinate y. Other terms are as for SMC.Physically, MAC is the chord of a rectangular wing, which has the same area, aerodynamic force and position of the center of pressure at a given angle of attack as the given wing has. Simply stated, MAC is the width of an equivalent rectangular wing in given conditions. Therefore, not only the measure but also the position of MAC is often important. In particular, the position of center of mass (CoM) of an aircraft is usually measured relative to the MAC, as the percentage of the distance from the leading edge of MAC to CoM with respect to MAC itself.Note that the figure to the right implies that the MAC occurs at a point where leading or trailing edge sweep changes. In general, this is not the case. Any shape other than a simple trapezoid requires evaluation of the above integral.The ratio of the length (or span) of a wing to its chord is known as the aspect ratio, an important indicator of the lift-induced drag the wing will create. In general, planes with higher aspect ratios — long, skinny wings — will have less induced drag, which dominates at low airspeeds. This is why gliders have long wings.
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