damping does decrease somewhat at the lower coefficients of tension. Again, these 

 results probably are adversely affected by the less than ideal control flap response. 



Following the evaluation, an attempt was made to improve flap response (Figure 

 16) . Figure 16a shows the flap response as measured in the laboratory prior to any 

 adjustments to the electronics. The response after adjustments were made is shown 

 in Figure 16b. The adjustments consisted of reducing the servo amplifier gain and 

 increasing the input current from 1.3 A to 1.6 A. These adjustments reduced the 

 steps in the flap response from approximately 4 deg to a value somewhat less than 

 2 deg. 



CONCLUSIONS AND RECOMMENDATIONS 

 The following is concluded: 



1. Based on limited evaluation data, the depressor will meet or exceed all 

 performance specifications except at the higher cyclic frequencies (near 0.2 Hz), 

 where the magnitude of the depth excursion is substantially attenuated. 



2. Although not necessarily recommended, a cycle amplitude, at lower frequen- 

 ies, which exceeds the specified value by a factor of two is achievable. 



3. The control response is not ideal. Some reworking of the control electro- 

 nics to improve response probably would improve the overall towing performance of 

 the depressor. 



4. Depressor dynamic stability is not excessive at coefficients of tension 



C below 0.6. This situation is aggravated by the lack of a smooth control response. 

 Consequently if the depressor is operated at the lower coefficients of tension, depth 

 excursions will increase. However, unless a very shallow towing depth is required, 

 operation of the depressor in this tension region normally should not be required. 



5. The design towcable breaking strength factor of safety is marginal. It 

 will be adequate only if the towcable is properly maintained and the remote sensor 

 cable drag does not cause undue localized stresses. 



The following is recommended: 



1. Operate the depressor at the highest coefficient of tension condition pos- 

 sible consistent with achieving the required magnitude of cyclic depth control. 

 This will minimize the variations in the relative vertical separations of the remote 

 sensors during cycle excursions (Appendix A). This also will operate the depressor 

 in the region of greatest stability. 



42 



