generated by movement of the individ- 

 ual blades. Blade pitch is varied as 

 the blade moves around its orbit so 

 that the sum thrust of all blades is in 

 the desired direction. This pitch is 

 varied for the pi-pitch propeller by- 

 rotating the blade at one-half the disc 

 rotational speed. Thrust direction is 

 varied by changing the relative phas- 

 ing of the blades with respect to the 

 disc. 



By placing the two thrusters at 45 

 degrees to the fore/aft vertical plane, 

 4 degrees of dynamic control (forelaft, 

 up/down, transverse, and yaw) are 

 available (Fig. 8.6). This is arrived at 

 by summing the thrust vectors. The 

 coordination of the vectors is con- 

 trolled by the pilot^s hand controller 



which directs the thrust in the direc- 

 tion his hand is moved. The farther 

 the hand is moved in a particular 

 direction, the greater the thrust mag- 

 nitude and vehicle speed will be." 



Cycloidal propellers offer several advan- 

 tages: Superior steering and maneuverabil- 

 ity, no need for rudders or external shafting 

 and elimination of the resistance produced 

 by such appendages. On the debit side, cy- 

 cloidal propellers are far less efficient than 

 screw-type propellers, they do not represent 

 any size or weight savings and there are 

 sealing problems (7). It would also seem that 

 protection against damage to the propellers 

 and underwater entanglement would be dif- 

 ficult to achieve without substantial loss of 

 efficiency. 



FORWARD 



V STARBOARD 

 \ CONTROL 



Fig. 8.6 MAKAKAI's thrusters' positions. [After Ref. (8)] 



374 



