In the simplest of terms, engineering is the art of creating a device to solve a problem. The device could be a structure like a bridge to get people from one place to another or a car to drive across that bridge. Nothing about the design of a bridge or a car is simple though. Engineers have to apply scientific principles to every element of a design to make sure that whatever is being engineered does in fact solve the problem at hand. Often engineers turn to nature for inspiration in their designs. Animals and plants are perfectly engineered to adapt for survival, something that has long been emulated in tools created for human use. Leonardo da Vinci was an artist and engineer who became particularly obsessed with the possible mechanics of flight. His more than 5,000 pages of notes reflected technical drawings on how he believed flight could be engineered. Leonardo was greatly influenced by how natural creatures like birds, bats, and insects flew as was reflected in the precise details of his drawings and notes.

Manned and unmanned flying vehicles are now common sights. And just as Leonardo da Vinci’s flying machines were inspired by animals, today’s engineers are still looking to the animal kingdom to solve engineering problems in devices like drones. In October of 2020, a team of engineers from the Swiss Federal Institute of Technology in Lausanne released a paper on a drone that they built after being inspired by a goshawk, a bird of prey common to Switzerland. The lead author on the paper, doctoral robotics student Enrico Ajanic, explained why he and his team chose the goshawk to be the model of the drone they built. “This bird hunts in forests, so it’s super agile,” he said. The hawk is also extremely fast and powerful. Enrico and his team looked at the specific characteristics that give goshawks such power and agility and applied this to a drone.

The goshawk has two flight stages, an aggressive and a cruising flight. In aggressive flight, the bird has its wings fully extended. The wing and tail feathers are also fanned out. This gives the hawk the agility to navigate difficult terrain. In cruise flight, a goshawk’s wings are slightly tucked in while the tail and feathers are folded in tightly. By making its body more streamlined, the hawk can conserve energy while reaching increased speeds. Using biomimicry, the team engineered a drone that could fly using the same aggressive and cruise flight modes of the goshawk.

The drone they designed is called the LisHawk, named in recognition of its’ animal inspiration and the Laboratory of Intelligent Systems where the team built it. The LisHawk is made from lightweight plastic and carbon fiber. The drone’s body is narrow with a pointed nose much like a beak. It has a wingspan of about 105 cm with a 30 cm wing chord, and a 24 cm long tail. These measurements nearly parallel a medium sized goshawk. At the nose of the drone is a propeller to give the drone power and lift. “The propeller is quite efficient,” Enrico explained, “and from a mechanical engineer point of view, it’s a simple system.” Mechanically, having the LisHawk flap its wings like a goshawk would be ineffective.

The wings can fully extend or hinge in at the wing chord. The wings also have thin feather flaps that can fold in or out. The tail can flap up or down, side to side, and also has feathers on it that can be fanned out or drawn in tight. When the wings and tail are tucked in, the streamlined shape of the drone allows it to reach a minimum speed of 17mph. When the wings and tail are in their extended position the drone’s speed decreases to 9mph while its ability to maneuver with agility increases. What makes LisHawk’s wing and tail mechanical ability particularly unique for a drone is that it can change its configuration while in flight.

Enrico and his team have been testing LisHawk in the lab, a wind tunnel, and in open outdoor spaces. The mechanics of the drone’s wings and tail have been very successful. What hasn’t been so smooth is actually flying the drone. Unlike most drones available today, the LisHawk takes a lot of skill to fly. This is an issue that the team is already working to rectify. The question is, in the ever growing field of drones, where does a fixed-wing, hawk inspired drone fit in? “Big cities require a drone which can fly long distances, so you have to be very efficient,” Enrico said. “But at the same time, you also need to avoid obstacles, because these cities are cluttered.” The way that a goshawk can fly through crowded forests can mirror how a drone will need to be flown through a cityscape. In the future, drones will be in mass use in such environments. Being able to sense and avoid obstacles is one major facet in enabling the safe integration of drones in cluttered spaces. Just as important will be a drone’s ability to navigate with agility like a hawk.

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