Geometric Analysis Reveals How Birds Mastered Flight

Four Harris' hawks flew back and forth between grass-covered perches while scientists recorded their every move. The researchers were interested in watching birds land, but not as much as they would have liked.

In more than 1,500 flights between the perches, the four hawks almost always took the same path that allowed them to perch most safely and with the most control. As Graham Taylor, a professor of mathematical biology at the University of Oxford, and his colleagues described recently in Nature, the hawks flew in a U-shaped arcs, rapidly flapping their wings to accelerate into a dive.

Lydia France is a data scientist at the Alan Turing Institute and a researcher at the University of Oxford. The ability of hawks to land in the air is better than mechanical ones.

Samik Bhattacharya is an assistant professor in the experimental fluid mechanics lab at the University of Central Florida. The reasons why aircraft can't match birds aren't just a matter of engineering Although birds have been observed throughout history and have inspired designs for flying machines by Leonardo da Vinci and others through the centuries, the biomechanics that make birds' ability to fly a mystery.

A study published in Nature last March has begun to change that. During her PhD research at the University of Michigan, Christina Harvey discovered that most birds can change their wings mid-flight to fly like a passenger plane and fly acrobatically like a fighter jet. Their work shows that birds can completely change the aerodynamic characteristics that govern how air moves over their wings and how they tumble through the air to complete fast maneuvers, even if they don't have wings.

Some of the evolutionary pressures that made birds so proficient at flying were discovered by these discoveries. They are helping to redraft the blueprints that future engineers might follow when attempting to design aircraft as maneuverable and adaptable as birds, seemingly with effortless grace but still using formidably fast physical and mental resources.

She describes her studies of bird flight as "quantifying something that, to me, looks like magic." She never thought she would be the one looking for the birds' secrets.

The Geometry of Birds

Harvey didn't like birds when he was younger. She sat on a rocky ledge in a park near the University of British Columbia, resting after a short hike and thinking about what project to pursue as a newly appointed master's student. She thought that if you ignore how annoying they are, they will fly.

She gave up avoiding them in favor of trying to understand more about their power of flight after the gull became what she called her "spark" bird. There were gaps in our knowledge of how birds fly.

Taylor co-authored a 2001 study that inspired her. The first paper to lay out a theory for how birds and other flying animals achieve stability was written by Taylor.

Taylor said that stability comes from a combination of inherent stability and innate resistance. Control is a fifth- generation fighter plane's forte and inherent stability is what a paper airplane has. The 2001 research shows that inherent stability is more important in the flight of birds than was thought.

Harvey was interested in developing the first dynamic equations of stability in bird flight after reading Taylor's paper. She said they have all the equations for aircraft. I wanted them to fly.

To understand the stability and instability of bird flight and the challenges that birds face in controlling them, Harvey and her team needed to map out all the inertial properties of birds. The aerodynamic properties that act on a bird in motion are not related to the bird's mass and distribution.

The Beaty Biodiversity Museum at the University of British Columbia has a collection of frozen bird corpses. They took length, weight and wingspan, and extended the wings to figure out the range of motion of the birds.

They created a program that represented different types of wings, bones, muscles, skin and feathers in hundreds of shapes. They were able to calculate the center of gravity and the neutral point of the bird's flight with the help of the software. The properties were determined for each bird based on the shape of its wings.

The static margin is the distance between the center of gravity and the neutral point of the wing. If a bird's neutral point was behind its center of gravity, they would consider the bird to be inherently stable, meaning that it would return to its original flight path if pushed off balance. If the neutral point was in front of the center of gravity, the bird wouldn't be stable and would be pushed further from the position it was in.

Aeronautical engineers set the static margins to achieve their goals. Birds can change their body postures by moving their wings. Harvey and her team looked at how each bird's inherent stability changed.

Aimy Wissa, who wrote a commentary on the work for Nature, said that Harvey and her colleagues adapted a framework that is similar to what we do for aircraft.

Flexible Flight

About 160 million years ago, the therapods were limited flyers, only flying over short distances or in small spurts. More than 10,000 species of birds descended from the dinosaurs have evolved into amazing flight machines. It takes control of instability to pull out of it.

Birds are so maneuverable that biologists assumed they had evolved to be more unstable. Birds, like fighter jets, just kind of lean into these instabilities to perform these really fast maneuvers. That is the reason birds fly in this way.

The pheasant was the only species that was completely unstable. Four species were completely stable and 17 species were able to switch between stable and unstable flight by morphing their wings. The birds are being able to change between a more fighter-jet-like style and a more passenger-jet-like style.

According to further mathematical modeling by her team, evolution has preserved their potential for both stability and instability. Birds have the ability to change their flight properties as needed.

Modern aircraft can't do that because they need two very different control strategies. Stable flight requires constantly making changes to avoid crashes. The director of the avian ecology program at Archbold Biological Station in Florida said that birds have to do something similar.

The complexity of flight and our inability to deconstruct it have been obstacles to understanding the origin of birds.

The pheasant seems to not have the ability to shift between stable and unstable modes of flight. He wonders if those species never evolved or if they lost the ability at some point, like modern flightless birds.

Many of the somersaulting, spinning and plummeting maneuvers that birds have mastered aren't things that anyone would want to experience in a passenger aircraft Uncrewed aerial vehicles, also known as drones, are freer to make drastic maneuvers, and their increasing popularity is creating more opportunities for them to do so.

He immediately sent the study to his engineering group after seeing Harvey's study. Fixed-wing aircraft are great for agriculture because they can fly for hours and travel thousands of kilometers. They don't have the agility of the drones popular with beginners. Some of the amazing maneuvering talents of birds could be mimicked by novel designs for winged aircraft.

Taylor and his team are trying to figure out how birds learn to fly. Engineers might one day include artificial intelligence in the design of new flyers to allow them to mimic biology and learn flight behaviors.

Harvey is still deciding where her future research will lie on the spectrum from basic research into bird flight to designing and manufacturing drones and planes. She wants to build a team of engineering and biology students who are just as passionate about their studies as she is.

Harvey said that he didn't think he was fully blossomed in engineering. She thought she could be more inventive when she started working at the edge of biology. She spends a lot of time working on bird figures. She said that she draws half her time. I think it has changed my perspective.