NO. 2 HYDROMECHANIC EXPERIMENTS RICHARDSON 5 



pontoon. It will be seen that a straight line on the logarithmic plots 

 very closely represents the locus of the observed points and thus 

 indicate that the resistances of the models closely approximate the 

 law of the square of the speed. As is well known, any equation of 

 the form Y = a x" wall plot as a straight line on a logarithmic plot, 

 and the slope of the curve transferred to the origin passes through 

 the margin at the upper end at a point corresponding to the exponent 

 n. The exponents are given in line 12 of Table i, wdiich shows the 

 value of the exponent n in the equation of the lines plotted on Plate 

 3 from the equation Rcc\'" the points being taken direct from the 

 straight line plots. 



TABLE I 

 Table i shows the computation of the head resistance in water for 

 each of these models, in detail, the final results appearing in lines 19, 

 20 and 21, giving results by three ditlerent niethods of computation. 



TABLE II 



Line 22 gives the head resistance computed by analysis of the total 

 resistance of the model into frictional resistance and residual resist- 

 ance, and then augmenting these values to the " full size " values in 

 accordance with Froude's method. 



Line 2;^ gives the head resistance in the same manner as line 22, 

 except the residual resistance is determined on the basis of relative 

 areas and relative speeds, being proportioned to the latter in accord- 

 ance with the exponent determined for the variation of residual 

 resistance of the model, instead of using the law of the square. 



Line 24 is an approx'unation, assuming the resistance to be directly 

 proportional to the cube of the linear ratio at " corresponding- 

 speeds." 



Line 25 is computed on the basis of the Lord Rayleigh method, 

 which' has been found reasonably satisfactory for the comparison of 

 dirigible models in England. In England ebonite models i inch in 

 diameter were used in water, and in air gold beater's skin models 

 3 feet in diameter. 



The National Physical Laboratory formula, which is based on the 

 Lord Rayleigh method, is 



in which « is a constant of form to be derived by experiment, p is the 

 density of the medium in which the experiment is carried on, v is the 

 kinetic viscosity, L is the length in feet, and V is the velocity in feet 

 per second. 



This method has been introduced at the suggestion of Naval Con- 



