a rotor blade rotated in synchronism with said second sprocket drum to actuate {HEAD ~ said hinged door panel} momentarily open on {TAIL ~ each half revolution} of said rotor blade 
momentarily open on
a rotor blade rotated in synchronism with said second sprocket drum to actuate { HEAD ~ said hinged door panel } momentarily open on { TAIL ~ each half revolution } of said rotor blade
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH