How to advance drone technology? Mirror bird flight patterns.

According to industry experts, learning how birds navigate between stable and unstable flight can improve drone design.

Although drone deliveries have been popular for some time, there are still a few troublesome design challenges that must be solved. Drones need to know how to navigate buildings, electrical wires, trees and other aircraft more seamlessly if they’re going to succeed in the mainstream. In short, they need to be able to fly like a bird.

bird flying
Photo of a gull flying courtesy of Christina Harvey.

“Being able to maneuver in a cluttered environment—that’s really challenging for current drones,” says Christina Harvey, an aerospace engineer and zoologist who leads the Biologically Informed Research and Design (BIRD) lab at UC Davis.

Harvey studies the mechanics of how birds fly, then takes these insights and applies them to drones and other unmanned aerial vehicles (UAVs). Although drones were being sent up into the sky long before COVID-19, the pandemic spurred additional interest. During the COVID-19 pandemic, at least 18 countries deployed drones for delivery and transportation purposes of medical supplies, according to UNICEF. The Federal Aviation Administration reports there are more than 330,000 commercial drones registered in the United States and predicts this number will reach 858,000 by 2026.

When Harvey majored in mechanical engineering as an undergrad, avian flight wasn’t on her radar, but all that changed by the time she was in graduate school—gulls captured her attention and became the foundation for a large amount of the work she’s done to date.

“The thing I focus on is [birds’] ability to maneuver,” she says. Whether it’s foraging for food or evading a predator, birds can adapt with “really quick little shifts.” Drones can’t currently do this, but maybe one day they will.

We still don’t know everything about bird flight

While studying birds in flight helped the Wright brothers and others learn how to design and fly planes, Harvey says there’s still a lot that humans don’t understand about how birds actually fly. “We have come a lot farther in recent years,” she says, adding that “there’s lots of space for contribution.”

For example: What more is there to learn about a bird’s muscles? How does feather porosity affect how much air passes through a bird’s wings when flying? Or how much energy do birds expend when doing certain flying maneuvers?

“It’s not that no one’s looked at these attributes, but there’s just lots of room to actually understand some of those attributes better,” she says.

One attribute that piqued Harvey’s interest was learning more about how birds experience stable flight (a resistance that birds can execute, which keeps them from going in the wrong direction) and unstable flight, which allows birds to twirl and spin acrobatically, like a fighter jet. Harvey wanted to know if birds were evolving to become more unstable, given that it made them more maneuverable. Research on topics like these has important implications for drone development because learning more about how birds perform complex tasks could someday give researchers insight into applying these findings in drone design.

Avian research assists drone design

It’s long been thought that birds were considered “unstable” fliers, given their ability to execute complicated flying maneuvers, but research done by Harvey shows that birds perform both stable and unstable flight patterns by adjusting their wings.

bird flying
Photo of a gull flying courtesy of Christina Harvey.

Harvey and her fellow researchers arrived at this conclusion by examining 36 frozen bird cadavers across 22 different bird species. They recorded measurements on a bird’s length, weight and wingspan, then manually lengthened and contracted a bird’s wings to determine the range of motion of the bird’s wrists and elbows. Having this information helped them estimate the location of birds’ center of gravity.

“It sounds like an easy thing to do, but because they’re made of lots of little different components that move, it wasn’t actually well known where the center of gravity of a bird was,” Harvey says.

All of this information was entered into a modeling program that Harvey created, called AvInertia, a combination of the words avian and inertia (the latter used because the researchers were trying to estimate the inertial characteristics of a bird). Inertial characteristics relate to the body mass of a bird versus aerodynamic properties, which relate to what happens when a bird is in motion. Results showed that the range of wrist and elbow motion alone was sufficient enough to enable switching between stable and unstable flight in 17 out of 22 bird species.

Another study done by Harvey built on this work by using 3D-printed models and aerodynamic studies to describe how gulls can change the shape of their wings to maneuver successfully in bad weather. They were also able to predict a bird’s reaction time to a gust of wind, lessons that may one day be useful in drone design.

Designing drones to navigate wind, urban areas and storms

Harvey’s research has plenty of implications for drone design. UAVs, for example, are considered stable devices because they don’t perform wild maneuvers, but they could be engineered to have their wings change shape in the same way birds do, which could allow them to move more freely.

“I think the most useful part [of my research] is that birds likely have the capacity to shift between stable and unstable flight,” she says. “What I think we should do is start to look towards developing drones that have the capacity to do that. I think that’s where I view this work going next, trying to incorporate that shift within a physical UAV.”

Abdulghani Mohamed, a professor of engineering at the Royal Melbourne Institute of Technology in Australia who specializes in bird research and drone design, has already designed a patented sensor system to counteract turbulence based on the way kestrels are able to hover in the wind. He continues to do research in this area, which will be important “as drones start to fly around and buzz in cities,” he says. Because drones are so small and lightweight, “they don’t have enough mass and inertia to counteract relatively larger wind gusts.”

Mohamed and his fellow researchers are taking a cue from kestrels, who need to keep their heads steady in the air when hunting for prey—it’s thought that they are able to do this by using their feathers as sensors. “If you provide them with the right wind conditions, they won’t flap,” he says. “They can just stay there spreading their wings, and that’s amazing.” Mohamed’s sensor uses pressure-based measurements to basically replicate that function and allows researchers to predict how a bird or aircraft should react in a wind gust.

The most useful part [of my research] is that birds likely have the capacity to shift between stable and unstable flight. [We should start] developing drones [with] the capacity to do that.

—Christina Harvey, aerospace engineer and zoologist, UC Davis

Still, there’s much that remains to be figured out: how to fly drones quietly, how to camouflage them (for military purposes), and how to maximize in-flight time. Birds may help answer these questions, too.

“At the moment, the energy density of batteries is probably about 30 times lower than the fat/energy-based storage of birds,” Mohamed says. An average multi-rotor, four-propeller drone can only last about 20 minutes, while a higher-end model could last for an hour, for example, he says. “Everyone’s trying to push the endurance of that,” he says. “I think we’re probably only scratching the surface of things with respect to what we can get drones to do.”

Harvey believes that designing drones to navigate rural and urban environments will be crucial, as will ensuring that drones are able to “talk” to each other or a command center.

Bird flying
Photo of a gull flying courtesy of Christina Harvey.

“I think one of the biggest challenges is the communication between these flying objects because once you have lots of little things flying around your city, that’s going to need some really good policy in place and control towers and making sure everyone’s on the same grid,” she says.

Drones are also expected to help humans learn more about climate change as the need for storm monitoring increases.

“As we start to see more extreme weather, I do think that there’s going to be a bigger role for these vehicles and being able to adapt to extreme weather,” Harvey says, noting that some birds have learned to fly into the eye of a hurricane. “In general, flying in those conditions is extremely challenging for anything. As we want to better understand hurricanes and what’s happening—the science within them—we’re going to need these vehicles to be able to do that.”

In the future, technology will continue to play a crucial role in applying insights from birds to drone design. Harvey cited one study that combines motion capture data on bird flight with computer simulations to show how birds optimize their landings. One day, this may help engineers develop small aircraft that can perch like birds.

“They’ve developed some really amazing high-tech approaches to actually capture birds in flight so that we can start to understand what they’re doing,” she says. “Before, people would look at the birds and try and guess what they were doing. Now, they have cameras and can recreate the shape of birds as they fly through space. There’s a lot of really cool tech going on.”

Lead photo of a gull flying courtesy of Christina Harvey.