Behaviour of a Ground Effect Machine 



Fig. Z - Model and towing apparatus 



In the first instance the static and dynamic properties were investigated on 

 the model hovering over smooth water and over land. For this purpose the 

 static stability, the reactions of the model to an impulse and the relation between 

 the rise height and the number of revolutions of the cushion fans were deter- 

 mined. These tests were performed both on the model with flexible trunks and 

 with rigid jet exits. Over the water the model appeared to be liable to self- 

 induced roll pitch and heave oscillations when fitted with rigid jet exits. 



It was felt that the tendency to self-induced rolling would be inconvenient in 

 an operational GEM. 



Moreover this phenomenon could obscure the effect of oblique waves on the 

 motions. Therefore it was tried to improve the over water hovering behaviour 

 of the model with rigid jet exits by minor structural changes in the bottom con- 

 figuration by modifying the central jet effectiveness and the directions of the 

 side jets. The model was tested also with varied radii of gyration. None of 

 these modifications improved the roll behaviour very much. The increment of 

 the radius of gyration, needed for a substantial reduction of the roll amplitude, 

 was beyond the possibilities of practical application. 



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