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