Hovering kestrel inspires drone that gains altitude without using power
A near-future where the skies are filled with drones carrying out deliveries and surveillance might be hard to imagine, but it is something aerospace experts are already giving careful consideration to. Improving the efficiency of these vehicles, even at the margins, could mean huge energy savings and more reliable services across the board. To this end, Australian researchers have developed a fixed-wing aircraft that uses natural updrafts to climb higher, inspired by the ability of the kestrel falcon to hover while searching for prey on the ground.
The UAS (Unmanned Aircraft Aystem) Research Team at Melbourne's RMIT University has been studying nature as a means of improving aircraft performance for some time. It examines how birds like the kestrel use sensory information gathered through its feathers to make small adjustments to its wings and tail, allowing it to lock its head into position and keep its eyes stable while its scans the ground for prey, all without flapping its wings.
In its earlier work, the team has explored the kestrel's ability to detect and make use of surrounding wind currents as a means of countering turbulence. Its latest advance, however, has enabled a gliding aircraft that can not only maintain its altitude, but climb even higher without drawing on extra power.
"It's long been known the birds take advantage of upward air currents to save energy when flying," explains Alex Fisher, lead author of the research paper. "This 'boost' of upward-moving air can be found when the wind hits a large obstacle, like a cliff or mountain range, and to a smaller extent close to man-made obstacles like buildings."
The researchers fitted a commercially available polystyrene sail-plane with GPS, a magnetometer and a control board with a purpose-built control algorithm. They then turned to the field in search of natural upward drafts, choosing a hillside and a space alongside a building as their two test sites.
At the hillside, the researchers found the aircraft was able to gain around 360 ft (120 m) in altitude unpowered, flying autonomously until its control batteries lost power. The tests at a building site were less fruitful, with the aircraft only able to sustain flight for around 20 seconds due to long-lasting gusts and lulls in wind.
The researchers say there are lessons to be learnt from this second exercise, however. As birds are able to accomodate such fluctuations in wind patterns by changing the arrangement of their feathers and adjusting their wings, the researchers are now looking to mimic this process in pursuit of an aircraft with similar capabilities.
The research was published this month in the journal Bioinspiration & Biomimetics.