The team previously studied live kestrels in the RMIT industrial wind tunnel. Credit: RMIT University.
A bio-inspired robotic bird that mimics kestrels is helping to unravel the mysteries behind the species’ exceptional hovering capabilities.
With atmospheric turbulence expected to worsen due to climate change, understanding how birds naturally cope with rough air could help engineers design small unmanned aerial vehicles (sUAVs) that are safer, more efficient and fly more smoothly.
sUAVs are commonly used for applications including aerial photography, search and rescue, agricultural monitoring and package delivery but are often grounded in turbulent conditions.
The research is part of a multi-year collaboration between RMIT University and the University of Bristol, and has delivered significant outcomes in the field of bio-inspired flight and turbulence mitigation.
Learning from the best
Among the most stable fliers in the avian world is the nankeen kestrel, whose movements in gusty and turbulent conditions were tracked by researchers using motion capture technology in RMIT’s Industrial Wind Tunnel facility – one of the largest of its kind in Australia.
RMIT researcher Matt Penn, who led part of the research into how birds handle turbulence, said birds have a range of strategies for enduring rough air, allowing them to fly in complex conditions that would typically ground sUAVs.
He stated: “Birds don’t rely on a single response to wind gusts; they constantly adjust their wings and tails to stay balanced, while the natural flexibility of their feathers and joints helps absorb sudden changes in airflow.
“They can also sense disruptions very quickly, which allows them to respond almost instantly and maintain control.”
The robotic kestrel in RMIT’s industrial wind tunnel. Credit: RMIT University.
The robotic replica
A robotic replica capable of imitating the movements most crucial to kestrels’ remarkably stable flight, has enabled further investigation into the subtle wing and body adjustments that contribute to this ability.
Dr Mario Martinez Groves-Raines, who completed the research during his studies at RMIT and the University of Bristol, said the robotic bird allowed the team to more precisely measure the forces involved.
Groves-Raines, who is now at the Royal Veterinary College in London, said: “By creating a robot replica, we were able to measure how specific movements were contributing to steadiness in flight.
“We uncovered several unique techniques behind the kestrel’s impressive stability.
“Many of these techniques have the potential to improve manoeuvrability of small aircraft, which encounter similar challenges to kestrels.”
RMIT senior researcher Associate Professor Abdulghani Mohamed said the research highlights the benefits of cross-institution collaboration and holds significant promise for the future of aviation design: “This research shows what’s possible when engineers look to nature for solutions.
“Our findings open new pathways for designing aircraft that can better handle turbulence.”
Next steps
While sUAVs already use a range of mitigation techniques similar to those seen in birds, few have been implemented effectively in operational aircraft due to complexity and efficiency trade-offs.
The team plans to build on its understanding of kestrels’ exceptional flight abilities by examining their capacity to sense their environment, including small amounts of turbulence encountered in environments where sUAVs operate.
While initially focused on smaller aerial vehicles, the researchers hope to simplify the data collected so it can be adapted for larger-scale aircraft.
The research is published in two papers in the Journal of the Royal Society Interface, Bridging the Gap: A Review of Gust Mitigation in Birds and Small UAVsand Stability and control benefits of coupled wing and tail morphing in kestrel wind-hovering flight explored using a robot replica.
