Too little load-bearing, too much twisting
This is the reference design.
The segment ends are not coupled to the transport rails yet, and the only reason for using the same hardware in the center is to reduce the number of different hardware needed. The design need to be updated with a fully printed center piece to stabilize the plane (from bending under rated load, and from twisting).
Not much to look at, but the segment is good enough to clean up the OpenSCAD code, and render the model.