Behaviour of a Ground Effect Machine 



revolutions given in the diagrams are average values of the four motors, scaled 

 up for the actual vehicle. 



Finally the model was tested flying over beam seas with a 15 knots wind 

 coming from the same direction as the waves. This wind was generated by some 

 fans mounted on the towing carriage. The number of revolutions and the direc- 

 tion of these fans were adjusted in such a way that at 28 knots the resultant wind 

 speed and direction had the correct values. 



The speed range in which the vehicle was investigated was limited by the 

 maximum speed of the towing carriages of the Seakeeping Laboratory and of the 

 Shallow Water Laboratory. They enabled measurements up to speeds corre- 

 sponding to 35 and 22 knots respectively. Unfortunately these are considerably 

 lower than the maximum speed of the actual vehicle. 



THE RECORDED DATA 



The Figs. 4 through 14 are graphical representations of the most charac- 

 teristic data recorded. The given values apply to the actual vehicle. 



Motions, forces and moments are in general characterized by a mean value 

 and a periodic oscillation round that mean. The periodic oscillations are shown 

 as double amplitudes. The mean values are given as the difference with respect 

 to the stationary condition with the cushion fans off. 



In Fig. 5 the number of points determined during the hovering tests did not 

 justify the fairing of curves. Therefore the actual test results are indicated. 

 The curves in the other figures are the result of fairing or cross fairing. The 

 number of points available for fairing depended on the investigated speed range. 

 Over a speed range from to 35 knots generally about 12 runs at various speeds 

 were made. For a speed range from 20 to 35 knots about 6 points were con- 

 sidered to be sufficient. 



In general the test results appeared to be reproducible in a satisfactory 

 manner. However, the lateral force and yawing moment showed a rather large 

 scatter. This was caused by torsional vibration in the towing apparatus. The 

 natural frequencies of this instrument combined with the model were in effect 

 not high enough for the wave experiments, especially at higher speeds. 



The vertical motion of the centre of gravity is designated as heave. The 

 mean value (rise height) over land is the distance between the ground and the 

 flat bottom. Over water it is just the difference in height with respect to the 

 floating condition in still water. 



The mean pitch angle (trim) is considered positive with the bow down. Roll 

 is positive when starboard side is down. 



The wave direction was defined as the angle between the velocity vectors of 

 the vehicle and the waves, positive when counterclockwise. 



The motions are shown in degrees and inches. The forces are given in 

 metric tons (2205 lbs) which are about equal to long tons (2240 lbs). 



697 



