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