Modern drones and unmanned aerial vehicles (UAVs) struggle with safe and precise near-ground maneuvers – but birds can perform these movements effortlessly.
With that notion in mind, Associate Professor Samik Bhattacharya is studying how birds sweep their wings and use their tails during critical moments of takeoff and landing to improve the agility of drones. This research is supported through a three-year $400,000 grant from the U.S. National Science Foundation.
Bhattacharya and his team in the Experimental Fluid Mechanics Laboratory will use 3D-printed pigeons and magpies to observe both their movements and the subsequent flow of water around their wings and tails in a water-towing tank. The aerospace engineering researcher says he specifically chose pigeons and black-billed magpies because of the similarities between their wing size and shape as well as the differences in the size of their tails.
“The magpie's tail is almost twice the size of the pigeon's tail,” Bhattacharya says. “This lets the study isolate the effect of wing-to-tail area ratio on the aerodynamics so that the differences measured between the two species can be attributed largely to the tail rather than to differences in wing geometry.”
One phenomenon that Bhattacharya is particularly interested in studying is called a dipole jet. This occurs when a bird rapidly pitches its wings during landing or takeoff. The airflow can separate near the leading edge and form a leading-edge vortex while the airflow from the trailing edge creates its own vortex. The counter-rotating pair of vortices creates a jet of fluid between them known as a dipole jet.
“This jet effectively delivers a burst of extra lift or thrust that compensates for the fact that a bird's forward speed, and the lift from its bound circulation, is too low at the start or end of flight to keep it airborne on its own,” Bhattacharya says. “The strength and direction of this jet can be tuned through wing sweep and pitch timing, directly govern the forces a bird or a future UAV experiences during the most delicate, low-speed phase of landing or takeoff.”
Dipole jets are also the reason Bhattacharya and his team are conducting their experiments in a water tank. This environment supports the high resolution optical diagnostics needed to visualize dipole jets in action. It also makes airflow much easier to measure.
The end goal of these observations is to develop concrete guidance for designers and manufacturers to create quieter and more agile drones. The findings will be shared with the robotics and aerospace industries to improve package delivery, emergency operations and urban air mobility.
“Bird-inspired fixed- or flapping-wing drones could land almost anywhere quietly and safely – think rooftop deliveries, medical supply drops in disaster zones or inspection drones that perch like birds instead of hovering,” Bhattacharya says. “Beyond aviation, the research reveals fundamental secrets of how animals move through fluids – knowledge that could improve everything from wind turbines to underwater robots.”