It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Friday, August 09, 2024
Steady flight of kestrels could help aerial safety soar
A new joint study by RMIT and the University of Bristol has revealed secrets to the remarkably steady flight of kestrels and could inform future drone designs and flight control strategies.
A new joint study by RMIT and the University of Bristol has revealed secrets to the remarkably steady flight of kestrels and could inform future drone designs and flight control strategies.
Making drones safer and more stable in turbulent conditions, or in cities where wind gusts from tall buildings make flying more difficult, makes applications like parcel delivery, food delivery and environmental monitoring more feasible, more often.
The study conducted in RMIT’s Industrial Wind Tunnel facility – one of the largest of its kind in Australia – is the first to precisely measure the stability of a Nankeen Kestrel’s head during hovering flight, finding movement of less than 5mm during hunting behaviour.
“Typically, aircraft use flap movements for stabilisation to achieve stability during flight,” said RMIT lead researcher Dr Abdulghani Mohamed.
“Our results acquired over several years, show birds of prey rely more on changes in surface area, which is crucial as it may be a more efficient way of achieving stable flight in fixed wing aircraft too.”
Anatomy of steady flight
Kestrels and other birds of prey are capable of keeping their heads and bodies extremely still during hunting. This specialised flight behaviour, called wind hovering, allows the birds to ‘hang’ in place under the right wind conditions without flapping. By making small adjustments to the shape of their wings and tail, they can achieve incredible steadiness.
Thanks to advancements in camera and motion capture technology, the research team was able to observe two Nankeen Kestrels, trained by Leigh Valley Hawk and Owl Sanctuary, at high resolution.
Fitted with reflective markers, the birds’ precise movements and flight control techniques during non-flapping flight were tracked in detail for the first-time.
“Previous studies involved birds casually flying through turbulence and gusts within wind tunnels; in our study we tracked a unique wind hovering flight behaviour whereby the birds are actively maintaining extreme steadiness, enabling us to study the pure control response without flapping,” said Mohamed.
By mapping these movements, the researchers gained insights that could be utilised to achieve steadier flight for fixed wing aircrafts.
“The wind hovering behaviour we observed in kestrels is the closest representation in the avian world to fixed wing aircraft,” said Mohamed.
“Our findings surrounding the changes in wing surface area could be applied to the design of morphing wings in drones, enhancing their stability and making them safer in adverse weather.”
The issue with current drones
Associate Professor of Bio-Inspired Aerodynamics at Bristol University and joint last author, Dr Shane Windsor, said the usefulness of current fixed wing unmanned aerial vehicles (UAV’s) was significantly decreased by their inability to operate in gusty wind conditions.
“UAV’s are being used in the UK to deliver post to remote islands, but their operation time is limited because of regular gusty conditions.
“Current commercial fixed wing aircraft have to be designed with one fixed geometry and optimised to operate at one flight condition.
“The advantage of morphing wings is that they could be continually optimised throughout a flight for a variety of conditions, making the aircraft much more manoeuvrable and efficient.”
Next steps
The team now aims to further their research by examining the birds under gusty and turbulent conditions, which would see further learnings in stable flight with the goal of allowing UAVs to operate more safely and more often.
While initially focused on smaller aerial vehicles, the team hopes to simplify the data collected so that it can be adapted for larger scale aircraft.
‘Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights’ published in the Journal of Experimental Biology (https://doi.org/10.1242/jeb.247305) is a collaboration between Mario Martinez Groves-Raines, George Yi, Matthew Penn, Simon Watkins, Shane Windsor and Abdulghani Mohamed.
The team acknowledges Mr Martin Scuffins from the Leigh Valley Hawk and Owl Sanctuary, for supporting the project and sharing expertise and knowledge critical to the project’s success.
Hovering in a wind tunnel
A Nankeen Kestrel hovering in the RMIT University wind tunnel
Fitting sensors
Martin Scuffins from the Leigh Valley Hawk and Owl Sanctuary and RMIT's Dr Abdulghani Mohamed fitting sensors to the kestrel in RMIT's wind tunnel facility.
New research from the University of Adelaide has shown that glossy black-cockatoos prefer to feed from trees growing in acidic soils.
Glossy black-cockatoos are seed-eating birds that feed almost exclusively on the cones of drooping sheoak trees. However, counterintuitively, they select trees that grow on the poorest soils found on ancient sedimentary rocks.
“Sheoak trees are three times more likely to be used as feeding trees if they are growing on non-limestone sedimentary rocks,” says Dr Gay Crowley, from the University of Adelaide’s School of Social Sciences.
Dr Crowley compared 6,543 feeding records with 23,484 sheoak records from New South Wales to make this discovery. She found that soil type has a direct influence on the way glossy black-cockatoos use the environment by comparing glossy black-cockatoo feeding records with soils and rocks on Kangaroo Island.
“Sheoaks gain their nutrition through fungal associations, rather than from the soil, and their associated fungi thrive on poor soils,” says Dr Crowley, whose research was published in the journal PLOS ONE.
“Many iconic Australian animals, such as bilbies, potoroos, bettongs and bandicoots, feed directly on soil fungi – including native truffles. The same pathways are likely to be responsible for their distribution in the environment.”
Glossy black-cockatoos are one of Australia’s five species of black-cockatoos and can be found across eastern Australia as well as on Kangaroo Island in South Australia. The species is listed as endangered in South Australia, and as vulnerable throughout the rest of its distribution.
To ensure the long-term survival of species that depend on soil fungi, especially the glossy black-cockatoo, Dr Crowley says conservation efforts need to consider the value of habitats on poor soils.
“Conservation efforts often prioritise the richest, most fertile parts of the landscape. This is because many rare animals, such as greater gliders and powerful owls, are most abundant in forests growing on rich soils derived from basalt or limestone,” says Dr Crowley.
“However, many other animals, such as potoroos, bandicoots, and glossy black-cockatoos may be best protected by preserving habitats on infertile soils.”
Credit: Material provided by the author of the paper, Julien Tailleur
A crowd or a flock of birds have different characteristics from those of atoms in a material, but when it comes to collective movement, the differences matter less than we might think. We can try to predict the behavior of humans, birds, or cells based on the same principles we use for particles. This is the finding of a new study published in the Journal of Statistical Mechanics: Theory and Experiment, JSTAT, conducted by an international team that includes the collaboration of MIT in Boston and CNRS in France. The study, based on the physics of materials, simulated the conditions that cause a sudden shift from a disordered state to a coordinated one in "self-propelled agents" (like biological ones).
“In a way, birds are flying atoms,” explains Julien Tailleur, from MIT Biophysics, one of the authors of the research. “It may sound strange, but indeed, one of our main findings was that the way a walking crowd moves, or a flock of birds in flight, shares many similarities with the physical systems of particles.”
As Tailleur explains, in the field of collective movement studies, it has been assumed that there is a qualitative difference between particles (atoms and molecules) and biological elements (cells, but also entire organisms in groups). It was especially believed that the transition from one type of movement to another (for example, from chaos to an orderly flow, known as a phase transition) was completely different.
The crucial difference for physicists in this case has to do with the concept of distance. Particles moving in a space with many other particles influence each other primarily based on their mutual distance. For biological elements, however, the absolute distance is less important. “Take a pigeon flying in a flock: what matters to it are not so much all the closest pigeons, but those it can see.” In fact, according to the literature, among those it can see, it can only keep track of a finite number, due to its cognitive limits. The pigeon, in the physicists' jargon, is in a “topological relationship” with other pigeons: two birds could be at quite a large physical distance, but if they are in the same visible space, they are in mutual contact and influence each other.
It was long believed that this type of difference led to a completely different scenario for the emergence of collective motion “Our study, however, suggests that this is not a crucial difference,” continues Tailleur.
“Obviously, if we wanted to analyze the behavior of a real bird, there are tons of other complexities that are not included in our model. Our field follows an advice attributed to Einstein, namely that if you want to understand a phenomenon, you have to make it ‘as simple as possible, but not simpler’. Not the simplest possible, but the one that removes all complexity that is not relevant to the problem. In the specific case of our study, this means that the difference that is real and exists - between physical distance and topological relationship - does not alter the nature of the transition to collective motion.”
The model used by Tailleur and colleagues is inspired by the behavior of ferromagnetic materials. These materials have - as the name suggests - magnetic properties. At high temperature or low density, the spins (simplifying: the direction of the magnetic moment associated with electrons) are oriented randomly due to the large thermal fluctuations and are therefore disorderly. However, at low temperatures and high density, the interactions between the spins dominate the fluctuations and a global orientation of the spins emerges (imagining them as many aligned small compass needles).
Another finding is that in the model used, stratified flows form within the larger group, which is akin to what we also observe in reality: it is rare for a mass of people to move all together in one direction; rather, we see within it the motion of finite groups, distinguishable flows that follow slightly different trajectories.
These statistical models, based on the physics of particles, can therefore also help us understand biological collective movement, concludes Tailleur. “The road towards understanding collective motion as we see it in biology—and using it to design new materials—is still long, but we are making progress!”
In a model of self-propelled particles aligning with their topological neighbors, one observes the formation of traveling bands (in green), typical of discontinuous transitions. The particle colors encode their orientations.
Credit
Material provided by the author of the paper, Julien Tailleur
Distance Vs Topological relations + traveling bands
Credit
Material provided by the author of the paper, Julien Tailleur
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