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