Researchers from RMIT University in Australia have developed an autonomous fixed-wing micro air-vehicle (MAV) inspired by the way kestrels hover above their prey.
According to Alex Fisher, lead author of the paper, these birds take advantage of upward air currents to save energy while they’re flying. When they’re hunting, they hover over a location without flapping their wings which allows them to keep their heads still and spot prey on the ground. This technique led the team to try this out on its MAV. “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,” says Fisher.
The RMIT team envisions that, in the future, MAVs will be used to carry out tasks in urban environments, such as deliveries, surveillance, and search and rescue. The team is now applying the updraft tactic to the vehicles to increase their efficiency and extend work range.
The researchers used a commercially available polystyrene foam sailplane as their test platform. “We were lucky in a sense that these were lightweight, as it allowed us to test the MAV easily in the field,” says Fisher. “This MAV we chose had a number of advantages, including the ability to fly well in light winds, and large control surfaces making it more nimble in the air.”
The team created a control algorithm and installed it onto a 36 x 26 mm control board interfaced with a GPS and magnetometer. The MAV was then flown at two test locations, near a hill and close to a building. At the hillside location, the MAV was able to gain approximately 360 ft. in height, and could fly autonomously until the control batteries lost power. The test closer to the building proved to be more challenging, as the MAV was only capable of sustaining flight for about 20 seconds.
“The MAV has a relatively narrow range of wind speeds at which it can soar without power,” adds Fisher. “Birds are able to overcome this problem to some extent by changing the shape of their wings or moving their feathers.
The most challenging aspects of the tests were the long-lasting gusts and lulls of wind. Fisher and the team are now working on ways to mimic the changing arrangement of the wing and feathers on hovering birds to improve the soaring performance of their MAV.