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