339 



TABLE 340.— FORCES ON THIN FLAT PLATES AT ANGLES TO THE WIND 



(FIG. 6) 



For plates at angles to the wind (angle of attack, o) the force is usually resolved into 

 components at right angles and parallel to the direction of the relative wind. The compo- 

 nents, termed the lift and drag, respectively, are expressed in the form of coefficients, the 

 forces being divided by the product of the dynamic pressure and the area of the plate (not 

 the projected area on a plane normal to the wind). The ratio of the distance between the 

 leading edge and the center of pressure to the chord length is called the center of pressure 

 coefficient, CP. The center of pressure is defined as the intersection of the line of action 

 of the resultant force, F, with the plate. The forces on a plate vary with "aspect ratio," a 

 term defined for a rectangular plate as the ratio of the span to the chord length. 



The lift (ClJ, drag (Cd), and center of pressure coefficients (CP) are given as functions 

 of angle of attack a for thin plates of aspect ratio 1, 3, and 6. 



CP 



CP 



CP 



10 20 30 40 50 60 70 80 

 ANGLE OF ATTACK, a, DEGREES 



90 



Fig. 6. — The lift coefficient (Ci), the drag coefficient (Cd), and the center of pressure 

 (CP) for thin plates for aspect ratios 1, 3, and 6, as a function of the angle a with the wind. 

 (See small figure in upper center.) D = CoAq, L = CiAq, X = CP X c. 



(continued) 



SMITHSONIAN PHYSICAL TABLES 



