Str^m-Tejsen and Chislett 



n 20 » 40 



RUXIER ANGLE, d(gi«t& 



» -» -W 



n 20 30 40 



RUDDER ANGLE, dtgrces. 



Fig. 31 - Results of static-rudder-angle tests made at different speeds 

 (a) dimensional plot of longitudinal force X, (b) dimensionless plot of 

 longitudinal force X 



the forces generated by a rudder situated within it, it can be seen that these 

 crosscoupling terms will vary with engine characteristics and control settings. 

 Values corresponding to a particular type of engine or control arrangement can 

 conveniently be obtained, however, by carrying out model tests at predeter- 

 mined revolution and speed values which have been obtained from calculations 

 of the type described in the foregoing section. 



The experimental results presented in Figs. 27 to 32 were measured with 

 the model free to sink and trim but restrained in roll. 



A distinction should be drawn between "speed -reduction" tests of the type 

 described above and tests at different speeds in which the propeller revolutions 

 correspond to the propulsion point for the speed in question. The nondimen- 

 sional results of such tests vary very little with speed, which may be explained 

 in a rough way by considering the flow geometry at different speeds to be simi- 

 lar in such tests, as the revolutions increase uniformly with ship speed. 



372 



