A groundbreaking collaborative study by RMIT and The University of Bristol has unveiled the secrets behind the exceptional flight stability of kestrels. These findings hold immense promise for revolutionizing future drone designs and flight control strategies.
By enhancing drone stability, particularly in turbulent urban environments with challenging wind conditions, this research has the potential to significantly advance critical applications such as parcel delivery, food delivery, and environmental monitoring.
The study, conducted in RMIT’s state-of-the-art Industrial Wind Tunnel facility, has provided the first precise measurements of a Nankeen Kestrel’s head stability during hovering flight, revealing astonishingly minimal movement of less than 5mm during hunting behavior.
“Typically, aircraft use flap movements for stabilization to achieve stability during flight,” said RMIT lead researcher Dr. Abdulghani Mohamed. “Our results acquired over several years show birds of prey rely more on changes in surface area, which is crucial as it may be a more efficient way of achieving stable flight in fixed-wing aircraft too.”
Kestrels and other birds of prey demonstrate remarkable skill in maintaining stillness during hunting. This specialized flight behavior, known as wind hovering, enables the birds to remain stationary under suitable wind conditions without flapping. Through subtle adjustments to their wings and tail, they achieve exceptional steadiness.
Thanks to advancements in camera and motion capture technology, the research team was able to closely observe two Nankeen Kestrels, trained by Leigh Valley Hawk and Owl Sanctuary, at high resolution.
Equipped with reflective markers, the birds’ precise movements and flight control techniques during non-flapping flight were meticulously tracked for the first time.
“Previous studies involved birds casually flying through turbulence and gusts within wind tunnels; in our study, we tracked a unique wind hovering flight behavior whereby the birds are actively maintaining extreme steadiness, enabling us to study the pure control response without flapping,” said Dr. Mohamed.
By analyzing these movements, the researchers discovered valuable insights that could be used to enhance the stability of fixed-wing aircraft during flight.
“The wind hovering behavior we observed in kestrels is the closest representation in the avian world to fixed-wing aircraft,” added Dr. Mohamed. “Our findings surrounding the changes in wing surface area could be applied to the design of morphing wings in drones, enhancing their stability and making them safer in adverse weather.”
Dr. Shane Windsor, Associate Professor of Bio-Inspired Aerodynamics at Bristol University and co-author of the study emphasized that the current limitations of fixed-wing unmanned aerial vehicles (UAVs) in gusty wind conditions significantly diminish their effectiveness.
“UAVs are being used in the UK to deliver post to remote islands, but their operation time is limited because of regular gusty conditions. Current commercial fixed-wing aircraft have to be designed with one fixed geometry and optimized to operate at one flight condition.
“The advantage of morphing wings is that they could be continually optimized throughout a flight for a variety of conditions, making the aircraft much more maneuverable and efficient.”
The team’s next step is to expand their research by studying the behavior of birds in gusty and turbulent conditions. They hope to gain a deeper understanding of stable flight, which could improve the safety and reliability of UAV operations.
Although their initial focus is on small aerial vehicles, they aim to streamline the collected data for potential adaptation to larger aircraft.
Journal reference:
- Mario Martinez Groves-Raines, George Yi, Matthew Penn, Simon Watkins, Shane Windsor, Abdulghani Mohamed. Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights. Journal of Experimental Biology, 2024; DOI: 10.1242/jeb.247305