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