Martin Scuffins from the Leigh Valley Hawk and Owl Sanctuary and RMIT’s Dr Abdulghani Mohamed fit sensors to the kestrel in RMIT’s wind tunnel facility. Picture: supplied by RMIT
A new joint study between the Royal Melbourne Institute of Technology (RMIT) and the University of Bristol in the UK is revealing the secrets of the ability of kestrels to fly steady.
This could inform future drone designs and flight control strategies, according to RMIT.
The Australian university says boosting the flight stability of drones in turbulent conditions, or in cities with wind gusts, makes uses like parcel delivery, food delivery and environmental monitoring more feasible more often.
The study, conducted in RMIT’s Industrial Wind Tunnel facility, is the first to precisely measure the stability of a Nankeen kestrel’s head during hovering flight; it found their head moved less than 5mm during hunting behaviour.
“Typically, aircraft use flap movements for stabilisation to achieve stability during flight,” says 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 can keep their heads and bodies extremely still during hunting. This specialised flight behaviour, called wind hovering, allows the birds to ‘hang’ in place under the right wind conditions without flapping.
They make small adjustments to the shape of their wings and tail to achieve incredible steadiness, according to RMIT.
Using advances in camera and motion capture technology, the research team observed two trained Nankeen kestrels at high resolution. The birds’ precise movements and control techniques during non-flapping flight were tracked in detail 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 behaviour whereby the birds are actively maintaining extreme steadiness, enabling us to study the pure control response without flapping,” Dr Mohamed explains.
“The wind hovering behaviour we observed in kestrels is the closest representation in the avian world to fixed wing aircraft,” he says.
“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.”
Associate Professor of Bio-Inspired Aerodynamics at Bristol University and joint last author, Dr Shane Windsor says the usefulness of current fixed-wing drones significantly decreased by their inability to operate in gusty conditions.
“UAVs are being used in the UK to deliver post to remote islands but their operation time is limited because of regular gusty conditions,” he explain.
“Current commercial fixed wing aircraft have to be designed with one fixed geometry and optimised to operate at one flight condition.
“The advantage of morphing wings is that they could be continually optimised throughout a flight for a variety of conditions, making the aircraft much more maneuverable and efficient.”
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