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