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