The prototypes, which cost the US Government up to $US500,000 each, form a tightly packed row of imposing concrete and metal panels.
One has sharp metal edges on top, while another has a surface resembling an expensive brick driveway.
The models, spaced around 9 metres apart, stand in the dirt just a few steps from homes in Tijuana, Mexico.
QF73 was forced to return 90 minutes into the flight and is now back on the ground in Sydney, a Qantas spokeswoman said.
Engineers are inspecting the aircraft.
“We understand delays can be frustrating for our passengers but we’ll always put safety ahead of schedule and our teams are doing everything they can to get passengers back on their way,” she said.