ProkhoroVj Treshchevsky ,and Volkov 



were carried out for the finite number of discrete vortices spaced 

 equally from the control points where the boundary condition is sa- 

 tisfied. The density of all vortices is defined from the system of 

 equations characterizing the boundary condition on the body surface 

 at control points. For the proper choice of the value of circulation 

 around the body, as with the known Joukowski condition in the wing 

 theory, a supplementary condition is introduced, viz. the density of 

 the trace vortices in all the points of the vortex sheet is the same 

 and equals to the density of the vortex shedding from the contour of 

 separation at the stern. Then the system of equations for defining 



the densities n,.r\ ,r\ ... r takes the form : 



V 2 ' 3 n 



n 



E 



Tk 

 k=l 



E Fi(Si, Sj) + E FjSp, Sj)~| = F(Sj,0,« y ) (1) 



P P 



where F. and F = induced velocities corresponding to transverse 

 and longitudinal vortices, 

 F = normal component of the free stream velocity, 



co = angular velocity of yaw. 



Figure 2 shows the pressure distribution over the contour 

 of intersection of the model and the basic plane obtained by the calcu- 

 lation method for model 2 with the angle jQ =10°. The test results 

 on defining the pressure distribution at the same section of the model 

 are also plotted in the same figure. As is seen, there is a fairly good 

 agreement between the theory and experiment. 



As noted above, the aerohydrodynamic forces due to the air 

 cushion are the decisive factors for the longitudinal motion of the 

 ACV. One of the methods used for defining the steady and non-steady 

 aerodynamic forces is based on the measurement of forces acting 

 upon the model which performs the harmonic oscillations. When car- 

 rying out these tests in a wind tunnel the forces are evaluated which 

 are connected with the qualities of an air cushion and deformation of 

 flexible skirts above the ground board simulating the water surface. 

 In some cases the results of such tests can be used, for the calcula- 

 tions of the ACV movement above the ice surface. 



Non- steady aerodynamic characteristics of ACV models 

 with built-in fans and flexible skirts are determined by using the ex- 

 perimental plant shown in figure 3. The principle of operation of this 

 plant consists in generating the definite harmonic oscillations for 

 the model and measuring the loads acting on this model with the con- 

 sequent determination of the lift and lateral moment derivatives ac- 

 cording to the kinematic parameters of motion. The plant is equipped 



264 



