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