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