Several such helicoid structures are combined with {HEAD ~ their radii overlapping}, for {TAIL ~ the most effective interception} of a certain cross sectional area of the fluid flow 
Several such helicoid structures are combined with { HEAD ~ their radii overlapping } , for { TAIL ~ the most effective interception } of a certain cross sectional area of the fluid flow
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH