ProkhoroVj Tveshchevsky ,and Volkov 



environments. The difficulties in simulating the aerohydrodynamic 

 effect and the necessity of analysing the data obtained make one carry 

 out the experiments in the towing tanks and wind tunnels independent- 

 ly. In. the last few years the central place in such experiments belon- 

 ged to obtaining the steady and non-steady characteristics necessary 

 for the calculation of transient processes and estimating the ACV sea- 

 keeping qualities. 



This paper gives a brief description of the most typical, in 

 the authors' opinion, methods of defining the above characteristics. 

 The description of these methods is illustrated by the measurement 

 results concerned with schematized models of ACV s with different 

 bow form. 



I . DEFINITION OF AERODYNAMIC CHARACTERISTICS 



As is known, the character of ACV movement in the longitu- 

 dinal plane depends mainly on the air cushion parameters and also on 

 hydrodynamic interaction between the flexible skirt and water surface. 

 The ACV movement in the horizontal plane depends, to a great extend, 

 on aerodynamics of external flow around the vehicle 



There are two main problems relating to the study of exter- 

 nal flow around the ACV, viz. , the decrease in air resistance and the 

 achievement of predetermined maneuverability and stability. 

 The first problem can be solved only on the basis of the rational 

 choice of the hull form. The second one is usually solved by mounting 

 the system of stabilizers. For the ACV s with the length-to-breadth 

 ratio of 1. 5 to 2. 5 the resistance as well as side forces are determi- 

 ned by the distribution of normal pressure over the perimeter of the 

 hull; so the studies of both problems are closely connected with each 

 other. 



The experimental investigation of the aerodynamic forces 

 and moments which are due to the external flow is generally carried 

 out on rigid models because slight deformations of the flexible skirt 

 have little effect on its aerodynamic characteristics. A six-compo- 

 nent balance is used for this purpose Water surface is simulated by 

 a flat ground board. 



The nature of aerodynamic factors can be revealed from the 

 results of the experiment with schematized models carried out for 

 the study of the effect the hull form has the ACV s aerodynamic cha- 

 racteristics. Table 1 lists the values of geometric characteristics 

 of the models tested, their resitance factors and the derivatives of 



262 



