Davis and English 



necessary to measure these wakes on a l/8th-scale mainfoil model in the towing 

 tank. This was done to determine the flow irregularity and also to obtain infor- 

 mation with which to design a wake simulator for the water -tunnel tests. As 

 will be seen later, it was found essential to conduct the water-tunnel tests in the 

 presence of the wake simulator. 



The rig for measuring the wakes is shown in Fig. 4, where it is seen that a 

 five -hole probe was mounted at the aft end of the port pod with a crank arm for 

 altering the angular setting. The experiments were conducted at a speed of 30 

 ft/sec, the probe having been calibrated at this speed previously. In the tests, 

 the attitude of the foil assembly was varied over a considerable range of pitch 

 and yaw to cover the ranges likely to be encountered by the ship in service con- 

 ditions. However, in order to conduct the tests within a reasonable time, the 

 wakes were measured at the 0.7 propeller radius only. 



Fig. 4 - Rig for wake measurement 



The wake measurements showed variations with pod attitude, but on the 

 whole these variations were not large and the results obtained at the zero yaw 

 and pitch setting, which are shown in Fig. 5, can be considered representative 

 of the complete tests. From these results the wake shadows cast by the pod at- 

 tachments are evident, the main foil wake being the greatest. The results are 



966 



