Mechanical intelligence for artificial wings: A philosophy for multifold high-degree morphing with its mechanisms analogous to biology

Birds and fish have morphing propulsors and mechanical intelligence, which are the primary biomimetic inspirations. Myliobatid pectoral fins, which are morphologically similar to bird wings, are of particular interest. Artificial wings are expected to achieve multifold high-degree morphing, a substantial challenge and long-standing desire that current design philosophies have yet to effectively solve. Derived mathematically and inspired by the alignments of the skeletal joints of myliobatid fins, we propose a morphing philosophy for artificial wings: cross-section invariance. This philosophy facilitates simultaneous out-of-plane and planform morphing, simplifies proprioception, sensing, and control (the important aspects of mechanical intelligence), and features the intrinsic mechanisms analogous to the biological ones across morphing types and species. We mathematically characterize, verify, and validate the morphing philosophy and its intrinsic mechanisms. We present the mechanical implementations of the intrinsic mechanisms; each implementation mechanism is exquisitely designed to fulfill multifold roles to collaboratively enable multifold high-degree morphing. We demonstrate prototypes with a larger range of morphing performance that is currently unavailable in artificial wings and the biological counterparts. Our results suggest the potential of the philosophy for multimodal propulsion of biomimetic vehicles.