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