HYDROCOPTER 



The final NBTS candidate is a system which depends on mechanical 

 thrust for lift. This concept has been discussed before by Beno and Clark and 

 in a study done under contract by the Bechtel Corporation. ^■^' ^^ Such 

 systems are usually thought of as having one or more vertical axis propellers 

 and are invariably labeled as underwater helicopters or "hydrocopters." 



After considering various propulsion and power systems, the authors 

 decided that an underwater helicopter had potential as a heavy-lift vehicle. 

 Any system dependent on mechanical means for generating 20 to 30 tons of 

 thrust will inevitably be a large power consumer. The only practical way of 

 supplying enough power would be through an electrical conductor from a 

 remote power source, either at the surface or in the ocean floor. This is 

 thought to be feasible. 



Conceptual Design 



Hull Configuration. A toroid hull was chosen since it appeared to 

 offer the most efficient shape for a hydrocopter vehicle. The artist's sketch 

 in Figure 19 shows a toroidal hull vehicle hovering above the sea floor. 

 Figure 20 is a more detailed plan drawing which illustrates most of the 

 principal vehicle design features. 



A personnel sphere is accommodated in the toroid center "hole." It 

 could be constructed from high-strength steel or titanium, or possibly manu- 

 factured from a titanium-glass composite, rigid titanium frame with large 

 glass units, thus affording excellent viewing for the vehicle pilots. The sphere 

 would be buoyant and detachable in the event an emergency prevents 

 recovery of the entire vehicle. 



Three, nearly cylindrical, ring-stiffened pressure hulls provide sufficient 

 permanent buoyancy to compensate for the deadweight of other vehicle 

 subsystems. In the event of power failure, the hydrocopter, which is near 

 neutrally buoyant, would ascend by jettisoning a small amount of expendable 

 ballast. 



Propulsion System. After a trade-off study of candidate propulsion 

 systems, it was decided that cycloidal propellers offered the greatest possible 

 efficiency and versatility. Cycloidal propellers consist of circular rotary 

 platforms to which are affixed several movable blades. The platform 

 generally rotates about a vertical axis. Once forward movement is initiated, 

 oscillating movement of each blade about its own axis, coupled with the 

 uniform platform rotation, produces a cycloidal blade path. 



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