Inspired by the northern goshawk (Accipiter gentilis), a team of researchers at the Swiss Federal Institute of Technology Lausanne, led by Enrico Ajanic, have built a 284-gram drone with a maximum wingspan of 1.05 metres.
According to Ajanic, “multicopter drones can hover and move well, but can’t fly long distance”, whereas “winged drones can fly long distances, but aren’t very agile”. The robo-hawk is the result of the team’s efforts to bring the benefits of different UAVs into a single unit.
“These results shed light on the avian use of wings and tails and offer an alternative design principle for drones with adaptive flight capabilities,” wrote the authors in a paper for the journal Science Robotics.
To mimic the flight behaviour of birds, Ajanic and his colleagues equipped the robot with motors that allow its wings to fold in or out, and its tail to contract or to fan out. After completing the design stage, the team performed a number of wind tunnel tests, optimisation studies, and outdoor flight tests.
When gaining height, the bio-inspired robot spreads both its wings and tail, and then, upon reaching top speed, the feather-like plates – 9 on each wing and a further 9 on the tail – are tucked in, thereby enhancing aerodynamics and providing for a more realistic flight simulation.
For more rapid altitude adjustment, the tail can also be moved in all four directions. Furthermore, each wing can be expanded and retracted independently to increase drag. This, according to the team, allows the robot to use 55.4% less power when travelling at its optimal speed (about 9.6 m/s) than it otherwise would with both wings and tail fully open.
“The morphing wing and tail structures of this design are insightful and novel,” said Jonathan Aitken at the University of Sheffield, UK, who was impressed by the robot’s ability to adjust its manoeuvrability mid-flight. “It offers the potential for unconventional flight manoeuvres, such as slow but controlled flight at high angles of attack”.
In the future, Ajanic plans to increase the robot’s level of autonomy by adding artificial intelligence that would allow it to fly without human control or supervision.