Prokhorov s Treshchevsky ,and Volkov 



where Q = air flow rate corresponding to the parameters 



3 



h , a> (m /sec) 



o x o ' ' 



g = acceleration of gravity (m/sec ) 



The value Sh^= j °- should be adopted as the dimensionless crite- 

 rion of similarity which is similar to the known Strouhal number 

 (UJ = angular frequency of oscillations). Then the dimensionless va- 

 lues of parameters h* , vp , K* , *? in equations (4) are the products 

 of the dimensionless amplitude of vertical and angular oscillations 

 and Strouhal number Sh^ or Sh*. 



Using the procedure described the tests were carried out for 

 three schematized models of ACV s with built-in fans. The scheme of 

 the sectional flexible skirt mounted on the models is shown in the 

 sketch (figure 3). The geometric characteristics of models are gi- 

 ven in Table 2. Figures 4-5 show some of the results obtained. The 

 curves in figure 4 illustrate the character of changing the factors 

 Q! i m j. » rn ^ > versus the dimensionless parameter Sh„at different 

 values of pressure factor Kp = p p (Pp , Pn = pressures in the re- 

 ceiver and air-cushion, respectively) and air flow rate Q. It is typi- 

 cal that the external air velocity effect on the non-steady characteris- 

 tics is practically absent in the range of the examined actual relation, 

 ships of the contrary velocity head and the cushion pressure ( Fig. 5). 

 The curve in Figure 5 shows the influence of the bow form at the 

 fixed values of frequency and pressure factor upon the same charac- 

 teristics. It is obvious that the bow form influences mainly the mo- 

 ment characteristics. 



The non-steady aerodynamic characteristics necessary for 

 the study of the ACV maneuvering in the horizontal plane are also de- 

 fined in the wind tunnel by the method of harmonic oscillations of the 

 model around its vertical axis and measuring the yaw damping moment 

 influencing the model. In this case the procedure of measurements 

 is similar to that described above. The experiments show that the 

 principal role in generating the damping moment belongs to the ver- 

 tical stabilizers and the hull effect on this moment is not significant. 

 It is observed that in some cases the damping moment on the hull- 

 stabilizer system decreases due to the adverse effect of the hull on 

 the stabilizers. 



II . DETERMINATION OF HYDRODYNAMIC CHARACTERISTICS 



In the towing tanks the tests are carried out to determine 



266 



