{HEAD ~ The collective control} for {TAIL ~ pitch change} employs a coil spring mounted between a pitch horn and a hub 
for
{ HEAD ~ The collective control } for { TAIL ~ pitch change } employs a coil spring mounted between a pitch horn and a hub
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH