The Aerodynamics of Sails 

 Table 3 (Continued) 



(Prandtl, 1919; Glauert, 1943). Although experimental data is in abundance for 

 sections of moderate camber and thickness, very little data is available for very 

 thin, highly cambered sections. The small amount of such data that is available 

 indicates that the lift predicted by the thin airfoil theory is in poor agreement 

 with experiment. Figure 4 shows data obtained by Wallis (1961) and by the 

 author for thin, circular-arc sections with camber ratios of 0.10. The differ- 

 ence between experimental results and the theoretical solution for potential flow 

 about the section lies in the effect of the boundary layer. Under the assumption 

 of the boundary layer theory (Schlichting, 1955) that the pressure associated with 

 flow outside the boundary layer is conducted across the layer to the body, the 

 correct pressure should be obtained by calculating the potential flow about the 

 shape formed by the airfoil and the displacement thickness of the boundary layer. 

 The displacement thickness of the boundary layer and the external pressure are 

 interdependent, so that an iterative scheme must be used to determine the 

 solution. 



The Use of Semi-Empirical Boundary Layer Theories 



An exact solution to the boundary layer equations is impossible for the turbu- 

 lent boundary layer, so that a semi-empirical theory must be used to determine 

 the boundary layer parameters. There are a large number of these semi- 

 empirical theories in existence and of these, four have been investigated by the 



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