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