Swaan and Wahab 



Fig. 3 - Model flying over shallow water 



The tests with the model flying over smooth water were conducted with the 

 rigid jet exits of original shape. 



The model fitted with flexible trunks was liable to self-induced roll oscilla- 

 tions only and the amplitudes were smaller compared with the model fitted with 

 rigid jet exits. For this reason the tests in waves were executed with flexible 

 trunks only. 



Flying over smooth water the resistance and the motions of the model were 

 investigated as a function of the water depth. 



The behaviour of the vehicle proceeding over waves was investigated on the 

 model flying in several directions over regular deep water waves of various 

 lengths and one height. The effect of variations in the wave height, rise height 

 and trim was investigated for wave directions and wave lengths which appeared 

 to be the worst for the model. 



Most of the tests were conducted on the model having zero trim at zero 

 speed, with the four cushion fans adjusted as to keep the differences between the 

 numbers of revolutions of the fans as small as possible. In the trimmed condi- 

 tion the numbers of revolutions of the fore and aft cushion fans differed in order 

 to give 1 ft difference in height between the bow and stern. The numbers of 



696 



