Determination of Aerohydro dynamic Performance of ACVs 



one can find the coefficients Y h and Y h and similarly the moment coef_ 

 ficients characterizing the pure pitching motions M JV and M ^ . The 

 definition of factors characterizing the influence of pitching upon hea- 

 ving is possible provided that the vertical translations of the center 

 of gravity are recorded. 



The experimental plant scheme and some of the results ob- 

 tained are given in figures 10-11. Depending upon the type of rope- 

 and-block connections provision is made for the translational verti- 

 cal ( var. 1 ) or angular ( var. 2 ) motions of the model and for re- 

 cording kinematic parameters on the oscillograph tape. In figure 11 

 the coefficients of inertia forces obtained by the above method are 

 plotted against frequency. 



It is necessary to note that the aerodynamic characteristics 

 corresponding to flight over the water surface are different from si- 

 milar characteristics of the model over the ground board. The diffe- 

 rence is obviously due to the influence of the water surface deforma- 

 tions and mass forces; it minimizes as the Froude number increases. 



The experimental plant described was also used for the defi- 

 nition of damping and inertia characteristics which manifest themsel- 

 ves at non-steady motion of the model along the longitudinal axis; the 

 plant is switched on according to variant 3. As the test results show, 

 the forces determining the above loads are negligible for ACV models. 



In the cases when during the tests in a towing tank the aero- 

 dynamic components are so important ( in comparison to hydrody- 

 namic forces) that they cannot be neglected, it is necessary to 

 consider that the aerodynamic effect upon the model tested is not 

 fully simulated. This introduces some infinity in the results ob- 

 tained due to both the distorbed aerodynamic action and the effect 

 of this action upon the position of the freely towed model and 

 consequently upon its hydrodynamic characteristics in the total 

 forces and moments measured. In such cases the aerodynamic 

 components are excluded from tests in the towing tank and are de- 

 termined in a wind tunnel. The procedure of carrying out the ex- 

 periments of such kind is as follows : the model is rigidly fasten- 

 ed to the dynamometer which measures the lift, drag and longi- 

 tudinal moment of the model at the fixed values of height and trim 

 of the model. During the tests the measurements are carried out 

 in a prescribed regime. Then according to the same program the 

 tests are conducted on a model equipped with a working fan over 

 the ground board fixed under the model in a close vicinity to water 



269 



