Should be on your FC Workshop's Schematic Board under the Aetherial Wheel Projects tab as "Wheel Stand Prototype II".

Airship/Submarine doesn't need to be a specific level, but unlocking the schematic requires 6 x Empty Cluster, 3 x Synthetic Resin, and 8 x Red Clay. Can either trade with other FCs for these materials or send your vessels out hunting for them.