Tested and working in 1.9 (I did not test it facing in both directions, but it likely works facing either direction).

These are some infinitely expandable 2 way flying machines that don't require replacing blocks. I made 2 designs. A 4x14x4 design (24 blocks), and a 5x16x4 design (33 blocks). The 4x14x4 design was designed for peyj n's 2 way flying machine expansion concept. The 5x16x4 design was designed for Redstone Jazz's 2 way flying machine expansion concept. Unlike Dico & RedstoneSpire's designs, these designs work facing any direction. Unlike my prevous designs, these designs need to be stopped in a specific way. I also made some stations for these flying machines.