AERODYNAMICAL EXPERIMENTS UPON A YACHT'S MAINSAIL. 

 The original observations are given in the first part of Table I. 

 Table I. — Principal Data and Results. 



= Angle of boom to wind. 



f, = Net cross-wind readings for a ^ 30.45 inches, 



fa= Net cross-wind readings for a = 24.05 inches. 



£),== Net drift readings for a = 30.45 inches. 



Dj= Net drift readings for o ^= 24.05 inches. 



M= Moment in inch-pounds. 



f = Cross-wind components of forces in pounds. 



d = Drift components of forces in pounds. 



X = Coordinate of center of pressure along wind in inches. 



y = Coordinate of center of pressure across wind in inches. 



X = Height of center of pressure above bottom of boom at mast in inches. 



Note. — For relative positions of center of figure of the sail and the centers of pressure see sail (Plate I ) 



The solution of the equations (see Plate 4) gave x and y, which are plotted 

 as faired curves on Plate 7, Figs. 4 and 5, and the square root of the sum of their 

 squares gave the distance along the boom at which the resultant pressure may be 

 considered as acting. The location of this point along the boom is shown by Fig. 6, 

 Plate 7, and the height above the boom by Fig. 7, Plate 7. The results from the 

 faired curves are given in the second part of Table I. 



The determination of s was perhaps the least precise of any of the character- 

 istics, as its derivation involved the difference between the readings obtained with 

 the arm at its original length and when shortened (see Plate 4, equation 4). In 

 some cases this resulted in a small difference of two large quantities. The loca- 

 tion of 2 as determined is plotted on Fig. 7, Plate 7, and a dotted curve is drawn 

 above and below it to indicate the limits of accuracy which are attributable to 

 the individual points. It is interesting to note that at about 0° and 100° the 

 method became indeterminate because the difference became zero. 



