Birds fly in a meticulous manner not yet replicable by human-made machines, though two new studies in Science Robotics and Science - by uncovering more about what gives birds this unparalleled control - pave the way to flying robots that can maneuver the air as nimbly as birds. Roboticists have tried to replicate feathery fliers for almost two decades, but these efforts have been hindered by use of rigid feather-like panels and a lack of understanding of the skeletal and muscular mechanics behind birds' highly morphable wings. In Science Robotics, Eric Chang et al. measured the kinematics of wing flexion and extension in cadavers of common pigeons. They applied their findings to a robot with wings made of 40 pigeon feathers, dubbed "PigeonBot." The pigeon feathers were connected to artificial wrists and fingers via synthetic elastic ligaments. By placing pigeon wings in a wind tunnel, the researchers determined that wrist and finger action provided fine control over feather placement, wing span, area and aspect ratio. In flight tests with the PigeonBot, asymmetric wrist and finger motion initiated stable turn maneuvers at sharp angles--some of the first evidence that birds primarily use their fingers to steer in flight. In Science, Laura Matloff, her team members from Chang et al., and additional colleagues investigated interactions between individual feathers of various bird species and found two primary mechanics underlying wing morphing: the passive redistribution of feathers and the fastening of adjacent overlapping feathers via hook-shaped microstructures protruding from each "branch" of the feather. Acting like Velcro, these structures locked during extension and unlocked automatically during flexion. In their PigeonBot, the researchers found that without this "directional Velcro," the resulting gaps between feathers led to loss of coherent feather coordination necessary for dynamic wing morphing under different environmental conditions. Interestingly, the rather noisy detachment mechanism was not found on silent fliers like the barn owl. The finding of "directional Velcro" between flight feathers informs the evolution of modern birds and their winged ancestors, and could be explored for fashion, medical and aerospace applications, the authors say.
###
Journal
Science