The study, conducted in RMIT’s wind tunnel, is the first to accurately measure the stability of a kestrel’s head during hovering flight, finding movement of less than 5mm during hunting behaviour. The team’s findings are detailed below. Journal of Experimental Biology.
Using camera and motion capture technology, the research team observed two Nankeen kestrels trained by the Leigh Valley Hawk and Owl Sanctuary in high resolution. Equipped with reflective markings, the birds’ precise movements and flight control techniques were tracked in detail during non-flapping flight.
“In previous studies, birds flew leisurely through turbulence and gusts in wind tunnels. In our study, we tracked a unique hovering behavior in the wind, where the birds actively maintained extreme stability. This allowed us to investigate the pure control response without wing flapping,” said Dr. Mohamed.
By mapping these movements, the researchers gained insights that could be used to achieve more stable flight of fixed-wing aircraft.
“The wind hovering behavior we observed in kestrels is the most comparable behavior in the bird world to fixed-wing aircraft,” said Dr. Mohamed. “Our findings on wing surface changes could be applied to the design of morphing wings in drones to improve their stability and make them safer in bad weather.”
Dr Shane Windsor, Associate Professor of Bio-Inspired Aerodynamics at the University of Bristol and co-author, said the usefulness of current fixed-wing unmanned aerial vehicles (UAVs) is significantly limited by their inability to operate in gusty winds.
“In the UK, drones are being used to deliver mail to remote islands, but their operational time is limited due to regular gusts. Current commercial fixed-wing aircraft must be designed with a fixed geometry and optimised to operate in specific flight conditions.”
Dr Windsor continued: “The advantage of morphing wings is that they can be continuously optimized to suit different conditions during a flight, making the aircraft much more maneuverable and efficient.”
The team now plans to continue their research by studying the birds in gusty and turbulent conditions to gain further insight into stable flight, with the goal of making UAVs safer and more widely used.
Looking to the future, the team hopes to simplify the data collected so that it can be adapted for larger-scale aircraft.
