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Unformatted text preview: AA 311 Lecture 5: Airfoil Nomenclature; Lift and Drag Reading:  Chapter 5. Consider the wing of an airplane as depicted in Figure 1. The cross-sectional shape obtained as the intersection of the airplane’s wing with a vertical plane perpendicular to the wing is called an airfoil . An airfoil is a planar object, while a wing is a finite three-dimensional shape. Such an airfoil shape is shown in Figure 2. Figure 1: Wing and airfoil. Figure 2: Airfoil nomenclature. The locus of points halfway between the upper and lower surfaces is called the mean camber line . The most forward point of the mean camber line is the leading edge . The most rearward point of the mean camber line is the trailing edge . The line connecting the leading edge and the trailing edge is called the chord line . The distance between the leading and trailing edges (the length of the chord line) is called the chord of the airfoil, denoted with the symbol, c . The camber is the maximum distance between the mean camber line and the chord line, measured perpendicular to the chord line. The thickness of the airfoil is the maximum distance between the upper and lower surfaces, measured perpendicular to the chord line. Figure 3 shows an airfoil exposed to the airflow. The free-stream velocity of the ambient flow is denoted with V ∞ . The direction of the free-stream velocity is called the relative wind . The angle between the relative wind and the chord line is called the angle of attack , α . As discussed earlier, all aerodynamic 1 Figure 3: Airfoil nomenclature. forces can be grouped into two fundamental sources: 1) pressure forces; 2) shear forces. The resultant of all aerodynamic forces acting on the airfoil is denoted with R . This resultant aerodynamic force can be decomposed into components parallel and perpendicular to the relative wind. The component parallel to the relative wind is called drag , and the component perpendicular to the relative wind is called lift ....
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- Fall '09
- Aerodynamics, Lift, Airfoil