The spar has {HEAD ~ an I beam or C beam cross section} in {TAIL ~ the region} not bonded to the blades so that the spar is twistable for pitch control 
The spar has { HEAD ~ an I beam or C beam cross section } in { TAIL ~ the region } not bonded to the blades so that the spar is twistable for pitch control
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD 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