Prokhorov 3 Treshchevsky ,and Volkov 



I t is seen that practically in all the cases the increase in the flow 

 air rate results in a decrease of resistance; in this case the supply 

 of air into the forward part of the air cushion, is the most favoura- 

 ble. 



The curve of figure 9 serves as an example of plotting the regions of 

 stable motion. The relationships shown are the result of processing 

 the model N° 2 test data according to the evaluation of the limiting 

 regimes when plough-in is developing with the consequent loss in sta- 

 bility. The curve shows the favourable influence of increase in the 

 air flow rate at the bow centering, making it possible to delay the set- 

 ting of the critical regimes. 



The definition of the non- steady hydrodynamic characteristics 

 which are necessary specifically for carrying out the calculations of 

 ACV heaving and pitching is based on the same methods used in a si- 

 milar case for displacement vessels. The linear character of the 



restoring forces Y = -r* - and moments M^z -^-^ defined experi- 



. 3 h * o vf c 



mentally in the working range of the flying heights h and trim angle 



Y for ACV with a flexible skirt gives grounds as a first approxima- 

 tion to proceed from the linear theory premises while defining the 

 non-steady characteristics. The tests are carried out on a plant 

 which makes is possible to perform in calm water the forced heaving 

 and pitching motions of the model; the plant is equipped with strain 

 gauges and provides the recording of kinematics of motion. To define, 

 for example, the coefficients of inertia and damping forces by the 

 test results, the equation of the forced heaving motions is written in 

 the following way : 



(M + Y h ) y + Y h y + — y = C (t Cos G k t-y), 



a h 



where M = model mass, 



C = rigidity of spring, 



1 - amplitude of disturbances, 



C^ = frequency of disturbing force 



Having experimentally defined the parameters of the forced motions 

 of the model in the form 



y = A I i(G * t " Sy) 

 where A = amplitude of oscillations of the model centre of gravity ^ 



6 = phase shift between the translation of the model and the 

 y 



disturbing force, 



?68 



