The trough has width substantially corresponding to that of the take off location and has {HEAD ~ a bottom} and sidewalls which preferably converge in {TAIL ~ the shape} of a funnel 
preferably converge in
The trough has width substantially corresponding to that of the take off location and has { HEAD ~ a bottom } and sidewalls which preferably converge in { TAIL ~ the shape } of a funnel
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH