Cruising and Hovering Response of a Tail-Stabilized Submersible 



TEST D«VT*V (RCF 3) 

 FROt^ EQ. { 9> 



Fig. 1 - Comparison with test results to determine 

 validity of theoretical representation of pitch mo- 

 ment in motion equations 



given in Eq. (lb) has this property. The turning test results (3) are used for 

 comparison with the representation given by Eq. (11). The expression for the 

 side force which is analogous to Eq. (11) is 



- f au^y; 



sin /S , 



or in dimensionless form 



Y' 



(12) 



As before, the coefficient data (3) are converted to the A basis and least square 

 fitted to Eq. (12), giving the result 



Y' = 4.53 sin /? . 



(13) 



Figure 2 shows the comparison of Eq. (13) with the experimental data. Although 

 the standard deviation of the test data from the theoretical curve is greater than 

 the standard deviation of the data among themselves (i.e., 0.25 vs 0.091), part of 

 this discrepancy arises because the tests were made at subcritical Reynolds 

 numbers (Re) at the high sideslip angles (i.e., 45° < /3 < 90°). This causes the 

 cross flow drag coefficient (which is equal to Y' at /? = 90°) to be larger than 

 would be the case if Re were higher than the critical value. If the data at /3 = 90° 

 had been obtained at Re ~ 1.0 xlO^ rather than at Re ~ 4,4x10^, it is expected 

 that much better correlation would have resulted. This conjecture plus the rea- 

 sonably good representation by Eq. (12) of the Y-force data in the range 

 -15° ^ /3 < 90° (even in the case of large variations in Reynolds number) 

 accounts for the retention of the simple expression for the Z-force in the mo- 

 tion equations. Additional test data over the whole range of attack angle and a 

 series of Reynolds numbers are needed for clarification. 



283 



