It is shown how various types of {HEAD ~ light} and thin but rigid helicoid surfaces can be constructed from sheet materials without requiring {TAIL ~ plastic deformation} because of the small pitch angles, as here employed 
It is shown how various types of { HEAD ~ light } and thin but rigid helicoid surfaces can be constructed from sheet materials without requiring { TAIL ~ plastic deformation } because of the small pitch angles , as here employed
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH