Strumpf 



MOO feOO 



Fig. 15 - Effect of maximum 

 vertical MPD force on hover- 

 ing heave nnaneuver for other- 

 wise standard run conditions 



izo 



feO 

 30 



9, 



R«kO. 



-30 



- to 



< 



^. 



LR/Sf C 



^^ 



Fig. 16 - Effect of maxinnum 

 MPD vertical force rate on 

 hovering heave maneuver for 

 otherwise standard run 

 conditions 



It is noteworthy that reducing the rate of application Z^ of the vertical 

 thrust force does not have the same mitigating effects on hovering heave maneu- 

 ver response as does reducing z^. Figure 16 shows that reducing z increases 

 the coupling effects as well as the time of response and depth overshoot. How- 

 ever, any improvement in performance to be gained by increasing l^ will be 

 small for z^ > 100 lb/sec. 



The only other method found to improve the vertical plane, hovering limit 

 maneuver response of the tail-stabilized submersible is to increase the meta- 

 centric height Zq . Figure 17 shows this for otherwise standard conditions with 

 Up = 0. Increasing z^ from 0.01 to 0.10 ft decreases x^ from 79.5 to 21.5 ft, 

 e^ from -0.57 to -0.33 rad, t2 from 78 to 61 sec, and z^^ from 44.9 to 38.2 ft. 

 Further increase in z^ has little effect on response time and depth overshoot, 

 but continues to reduce the pitch and surge coupling effects. 



VI. CONCLUDING REMARKS 



Analyses of inherent dynamic stability and limit maneuver response have 

 shown that the tail-stabilized submersible can perform adequately in cruising 

 flight, but is subject to highly coupled, unstable hovering motions, especially in 

 stern-to-bow ocean currents. Two methods have been suggested for improving 

 its performance, but these are restricted in applicability. The first is to reduce 

 pitch and surge coupling effects by limiting vertical velocity through application 

 of only small unbalanced vertical control forces and the use of corrective pitch 

 control moments. This method will be difficult to apply in the vertical plane 



302 



