.X 



A = ^sp.(v-a-,2-(|^^^, 



O 



or with (1) and (3) 



A = i p'c,(v - cr)^. (T . (14) 



2 



The dimensionless factor 



2 

 °d = STT^^^) = sir^«^ (15) 



corresponds to the resistance coefficient, (14) may be written again 



A = p'v^p.cTpT, 



with 



= 1 «^2.2, 



C(p) = J STr'S'd - p)" 

 in analogy to (13). Based on observations of waves in their initial 

 state, Jeffreys evaluated s = 0.30 (0,27). 



Another attempt for estimating the resistance coefficient was 

 made by H, Motzfeld [19]. The distribution of the pressure p over 

 wooden wave profiles of different form was determined by experiments 

 and measurements in a wind tunnel. For the width b = 1 of a given 

 profile, the pressure resistance 



p sina ds, 



••■/ 



where S is the "length of unrolling" of the wave, ds an element of 

 the wave profile, S, and a the angle between the direction x of 

 flow and ds. With dtj = ds»sina, the integral has the value 



r 



W^ = f p('7 )d'»^ . 



The pressTire resistance over a wave length A is given as the plane 

 area bounded by the curve piri). If we put 



58 



