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