A propulsor system is an assembly of individual propulsors that act in concert to form {HEAD ~ a substantially continuous control surface} that undulates in {TAIL ~ a working fluid} 
undulates in
A propulsor system is an assembly of individual propulsors that act in concert to form { HEAD ~ a substantially continuous control surface } that undulates in { TAIL ~ a working fluid }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL