A new study by a UK university and an Australian research institution has examined the flight and hovering abilities of wild birds and said the discoveries could inform future aircraft design. 

The work by the University of Bristol and the Royal Melbourne Institute of Technology (RMIT) studied the flight of kestrels, and the bird of prey’s head movements specifically. 

The researchers said their findings could be used in future designs of unmanned aerial vehicles (UAVs) or even larger fixed-wing aircraft. 

“Typically, aircraft use flap movements for stabilisation 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 are among a select few species of birds that can utilise a skill known as “wind hovering”, which enables them to remain steady while hunting, without flapping their wings. In favourable conditions, they only need to slightly adjust the shape of their wings and tail to remain hovering above their target. 

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By using new high-speed cameras and motion-capture technology, the teams in Australia and the UK could more accurately assess kestrels at a sanctuary, rather than having to make the birds fly through wind tunnels or other unnatural environments. 

The findings could be used to inform aircraft designs, especially with the growth of the eVTOL sector. 

“The wind hovering behaviour we observed in kestrels is the closest representation in the avian world to fixed-wing aircraft,” Mohamed added.  “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.”

Although the research is new and it may take years before it is used in passenger-carrying aircraft, a more immediate use case could be the package-carrying drone market. 

Associate professor of bio-inspired aerodynamics at Bristol University and report joint author, Shane Windsor, explained how delivery drones could extend their flying capabilities. 

“UAV’s are being used in the UK to deliver post to remote islands, but their operation time is limited because of regular gusty conditions,” he said. 

“Current commercially available fixed-wing aircraft use conventional control methods to achieve stable flight, meaning the entire craft needs to be designed for one flying 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 manoeuvrable and efficient,” Windsor added. 

“Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights” was published in the Journal of Experimental Biology.