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