Behaviour of a Ground Effect Machine 



the behaviour considerably. Although it is expected that the dynamical unstabil- 

 ity is caused by non-linear damping this could not be established with certainty. 

 The weight of the model was such that the base pressure during the experiments 

 was higher than in the actual design condition. 



The resistance over smooth water showed a maximum in the speed range 

 between 9 and 14 knots depending on the water depth. The highest resistance 

 hump in shallow water was about 50% higher than on deep water. 



The pitch and heave motions of the model proceeding in regular waves 

 showed the character of well damped systems. The behaviour was apparently 

 worst in bow seas of about vehicle length or somewhat longer. 



With increased cushion power and resulting larger rise heights the motions 

 and resistance showed a tendency to decrease. 



At high speeds the resistance could be reduced considerably by trimming 

 the vehicle by stern. In this condition the motions decreased as well. A side 

 wind seemed to have only a minor effect on the behaviour of the vehicle. 



The measured data did not show many unexplainable trends and in general 

 the results could be reproduced within reasonable limits. An exception must be 

 made for the yawing moment and sway amplitudes which records were rather 

 blurred by high frequency noise. 



REFERENCES 



1. Fuller, F. L., "Gravity Wave Drag Theory for the Waterborne Ground Effect 

 Vehicle," Grumman Aircraft Engineering Corp., Research Note RN-111, 

 June 1959. 



2. Hirsch, A. E., "The Hovering Performance of a Two Dimensional Ground 

 Effect Machine Over Water," Symposium on Ground Effect Phenomena, 

 Princeton University, Princeton, 1959. 



3. Mack, L. R., "Theoretical and Experimental Research on Annular Jets Over 

 Land and Over Water," Symposium on Ground Effect Phenomena, Princeton 

 University, Princeton, 1959. 



4. Tulin, M. P., "On the Vertical Motions of Edge Jet Vehicles," Symposium 

 on Ground Effect Phenomena, Princeton University, Princeton, 1959. 



5. Kuhn, R. E., Carter, A. W. and Schade, R. O., "Over Water Aspects of 

 Ground Effect Vehicles," Institute of Aeronautical Sciences, paper no. 60-14, 

 New York, 1960. 



6. Lin, J. D., "Dynamic Behaviour of Ground Effect Machines Over Waves," 

 Journal of Ship Research, Vol. 6, number 4, April 1963. 



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