{HEAD ~ The axis} of the structure about which the helicoid turns is making {TAIL ~ an angle} with the flow vector in the order of or slightly larger that the pitch angle 
is making
{ HEAD ~ The axis } of the structure about which the helicoid turns is making { TAIL ~ an angle } with the flow vector in the order of or slightly larger that the pitch angle
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH