Tag: wings and fins

Bat Flight Inspired Flapping Wing Robots Design

You might be familiar with fixed-wing drones, which are popular for filming and photographing. But have you thought about the bio-inspired flapping-wing robots? Researchers who study how bats fly are trying to apply the knowledge to the development of next-gen flying robots. 

Continue reading “Bat Flight Inspired Flapping Wing Robots Design”

You might be familiar with fixed-wing drones, which are popular for filming and photographing. But have you thought about the bio-inspired flapping-wing robots? Researchers who study how bats fly are trying to apply the knowledge to the development of next-gen flying robots. 

Continue reading “Bat Flight Inspired Flapping Wing Robots Design”

Staying airborne: How bird wings are built for aerodynamic and efficient flight

Flight is a concept that has, until relatively recently in history, eluded humanity. However, birds have been successfully flying for approximately 130 million years, proving themselves to be a physical marvel of the natural world. And while our means of flight have historically been crude in design and performance, nature provides an elegant, efficient solution to get creatures off of the ground. Rüppell’s griffon vultures have been recorded flying as high as 37,000 ft, while some species of shorebirds have been recorded flying as far as from Alaska to New Zealand over eight days without stopping. But how exactly do birds seem to effortlessly overcome gravity so effectively? And perhaps more importantly, how might we apply these answers to improve manmade aircraft?

Morphology

Obviously, the exact aerodynamics and physical characteristics of birds will vary from species to species, but there are still underlying similarities that enable birds to fly. A bird’s wing consists of a shoulder, elbow, and wrist joint which establish the wing’s basic shape and allow a range of motion. Covering the wing are structures called primary, secondary, and coverts, which are all groups of feathers that provide lift and stabilize flight. Feathers consist of flexible fibers attached to a center shaft, called the rachis. Overtime, the rachis will become damaged from fatigue and large instances of stress. As a result, birds will molt and regrow their feathers on a regular basis. 

A diagram of the structure of a bird wing
Picture by marcosbseguren on Wikimedia Commons

Generally, a bird’s body will be adapted to either gliding flight, in which the wings flap very infrequently, or active flight, in which the wings flap nearly constantly. For gliding birds, such as the ocean dwelling albatross, the wings will extend far away from the body, and prioritize both wing and feather surface area over flexibility. Additionally, these wings will have a thick leading edge, and will be much straighter. However for fast, agile birds, such as falcons, the opposite is true. Consequently, agility is sacrificed for energy efficiency. In both cases, the rachis will change shape and rigidity, becoming larger and stiffer for gliding flight and smaller and more flexible for agile flight. 

Aerodynamics

One of the most unique aerodynamic characteristics of birds is that nearly all of their lift and thrust is exclusively generated by their wings, as opposed to aircraft that implement both wings and engines. This provides, among other things, near instantaneous control of both flight direction and speed. In other words, this gives birds an advantage when hunting, escaping from predators, and maneuvering through a landscape. 

To aid in the generation of thrust and lift during flight, birds will change their wing shape through a process called active morphing. During flight, the wing will be bent inwards and twisted up during the upstroke, and extended and straightened during the downstroke. As a result, this minimizes drag while maximizing thrust and, consequently, energy efficiency. This can aid in anything from traveling farther distances to hunting prey.

An osprey folding its wings in while catching a fish
Photo by Paul VanDerWerf on Wikimedia Commons

Applications

Initially, these principles may seem difficult to realistically utilize in aircraft. After all, we are limited by the materials available and the size that aircraft must reach. However, small steps could be taken to improve the energy efficiency and responsiveness of aircraft. For example, wing shape, material flexibility, surface finish, and moving joints could all be explored. In fact, research at MIT is currently being conducted on flexible wings made of scale-like modular structures. If experiments like this are successful, it could show that aircraft designs inspired by nature may be the future of the world of aeronautics.

Which is more stable, washing machines or birds? The answer might surprise you

What do birds and washing machines have in common? Shockingly, it’s not the ability to wash clothes. Rather, most birds and washing machines are great examples of vibration isolation systems.

Now that’s cool and all – but what is a vibration isolation system?

Better known as a mass-spring-damper system, vibration isolators are generally a mechanical or industrial mechanism that can reduce the amount of vibrational energy produced by a system. Vibration isolators are incredibly important; studies show “undesirable vibrations” can shorten a machine’s service life and even permanently damage the machine and those using it. Considering this, engineers are constantly improving upon current vibration control systems, and are now looking to birds for inspiration.

But why birds? Well, to understand this, let’s consider a bird as a simple mass-spring-damper system.

Avian vibration isolation system represented as mass-spring-damper-system
Simple approximation of avian vibration isolation system as mass-spring-damper system. Taken from the 2015 study: ‘The role of passive avian head stabilization in flapping flight.”

First, visualize vibrations as an oscillating force stemming from the bird’s body moving back-and-forth. Vibrational forces can be generated by the flapping of wings, unexpected gusts, and/or movement of legs. Now, if we continue up from the body to the neck, we can see where avian skeletal and muscular structure really begins to “show off its feathers.”

Characterized as a multi-layered structure, the avian neck contains many sections of “hollow” bones, connected by surrounding muscles. The structural units (muscles and bones) of the avian neck have properties of both springs and dampers, optimizing them for vibration isolation.

Simplified representation of multi-layered neck as spring-damper structure

For starters, we see the muscles largely act as springs. Springs have the unique ability to move a body with its vibrations. This behavior is present in the muscles connected to the bone segments, in that they are capable of instantaneously compressing, elongating and twisting in response to rapid changes in the body’s movement. This elastic response prevents not only the head, but the whole bird, from shaking when bombarded when vibrations from any form of movement.

Simplified visualization of multi-layered spring-damper structure. The transparent grey portion represents the hollow bone, which is connected by the black lines, or strong spring-like muscles. The empty space between each unit would consist of the softer, damper-like muscle. Taken from the 2021 study: “A novel dynamics stabilization and vibration isolation structure inspired by the role of avian neck.”

Alternatively, the muscles, primarily those not connected to bone, can act as dampers. Effective dampers are similarly identified by the ability to move with vibrations; however, they can dissipate some of the vibrational energy as heat, or store energy until relaxed. The interior muscles are capable of slowly deforming (changing shape) if exposed to steady vibrations, allowing for dissipation of excessive vibrational energy.

But hey, what about those bones?

The avian neck has nearly three times the number of bone sections than most mammals, on top of muscles entirely surrounding the neck. This drastically increases the bird’s flexibility, helping it maneuver through sharp positional changes, thereby further limiting the effect of vibrational forces.

Finally, what makes the avian vibration isolator truly superior is its passive activation. As engineers at Shanghai Jiao Tong University point out, manmade passive vibration isolators fall short because they require sensors and input energy to adjust for “shocks and random vibrations.” As previously explained, the multi-layered neck is well equipped to handle random oscillations, yet, more importantly, the bird’s neck muscles can passively change position to brace for incoming vibrations.

A recent study from Stanford University proved this concept by recording a whooper swan’s reaction to different strength gusts. They found that swan’s neck adjusted to protect the head, and that even when the flapping doubled, the movement of the head reduced by a quarter. Finally, it is important to note that passive activation is not limited to the sky; researchers have found that mainly terrestrial birds like chickens and pigeons have a similar neck structure and system for maintaining stability and clear vision.

Overall, continuing to study the avian vibration isolation system could prove very beneficial for many different applications. For a more in-depth look at the current work out, check-out the studies referenced throughout the article. Otherwise, enjoy watching this chicken work its body control magic!

Mercedes-Benz “Chicken” Magic Body Control Advertisement, highlighting the chicken’s amazing head stabilization ability.

Swimming Fast and Slow: What We Know About the Sailfish’s Iconic Fin

Indo-Pacific Sailfish
Indo-Pacific Sailfish. Credit: D. Corson/Shostal Associates

Sailfish, or Istiophorus platypterus, are one of the most recognizable fishes in the ocean due to their large sail-like dorsal fin. But, did you know that they are also iconic because they are one of the fastest swimmers in the ocean? Sailfish top speeds have been recorded to be up to 30 m/s, which roughly translates to 67 miles per hour. When researchers examined the sailfish swimming out in the ocean, they discovered that they have the unique ability to retract and deploy their sail and other fins. Furthermore, they saw that when swimming at top speeds, swordfish retract their sail, and when the fish are hunting prey, they deploy it. How does retracting the sail help them swim fast, and how does deploying the sail help them hunt? 

Sailfish swimming with both the sail retracted (0:24) and extended (0:40). Disregard the silliness of the video. Credit: Pew

Speeding Up

When it comes to swimming fast, the answer may have to do with drag. Due to their hydrodynamic characteristics, sailfish have a very low drag coefficient, which is the quantity used to describe the resistance of an object moving through fluid. Sailfish have a drag coefficient of 0.0075, which is similar to smaller fish such as pike, dogfish, and small trout. Additionally, due to their size, sailfish are able a generate much more force with each swimming motion than their smaller peers. The combination of these two factors allows them to move at such high speeds. The thing that truly sets sailfish apart, though, is this ability to retract their sail and pectoral fins. Studies show that when the sail and other fins were retracted, sailfish are able to reduce their drag by about 18%. With less drag to worry about, the fish can be more efficient in generating thrust from its swimming motion, which allows it to speed ahead of the competition. To get a sense of just how fast these fish move, watch the end of the video above, where they only get up to 40 mph!

Slowing Down

Sailfish usually feed on smaller fish that swim in schools, like sardines. These small fish “exhibit higher performance than large fish in unsteady swimming,” which is to say making quick lateral movements. So, if a sardine senses a sailfish coming at it at full speed, it will likely have no problems avoiding it. With the sail dorsal-fin raised, the increase in drag slows the fish down dramatically and steadies its swimming path.

In the figure below, sub-figures C and D show how much the tail oscillates (in grey) and the direction in which the fish is moving (in black) when the sail is retracted and deployed, respectively. Zero on the Y-axis represents the tail being directly in line with the rest of the body and the fish is moving straight forward. While the sail is up, the tail moves far less aggressively and the fish more consistently moves in a straight line.

Side by Side comparison of Sailfish swimming with and without sail
Affect of Sail on stability while swimming. Credit: Stefano Marras

This allows the sailfish to become more controlled in its movements and help pursue a sardine performing evasive maneuvers. When it gets within striking distance, the sail helps counterbalance the fish’s swift lunge at its prey, which provides much-needed accuracy. Biologists have also theorized that the large size of the sail helps herd the school closer together, but no official research has been done on this.

Take-Aways

The sailfish’s ability to retract and deploy its sail dorsal-fin gives it unique advantages in both long-distance swimming and hunting. Minimizing drag is one of the most important concepts for travel through any fluid (air or water), so understanding how the sailfish is able to reduce drag could provide a new perspective on things. The sail’s ability to provide stability at lower speeds has potential use in any sort of water travel, whether it be with cargo ships (like the Evergreen in the Suez), boats, or submarines.  

If you are interested in another unique feature of the Sailfish, its bill has been a popular topic as of late, especially with its feeding habits. The bill is often used like a sword, either spearing or stunning prey, and also has been thought to have helpful drag-reducing qualities. Click here for more information.

Sources

Woong Sagong, “Hydrodynamic Characteristics of the Sailfish (Istiophorus platypterus) and Swordfish (Xiphias gladius) in Gliding Postures at Their Cruise Speeds,” Plos One, https://doi.org/10.1371/journal.pone.0081323

Stefano Marras, “Not So Fast: Swimming Behavior of Sailfish during Predator–Prey Interactions using High-Speed Video and Accelerometry,” Integrative and Comparative Biology,” https://doi.org/10.1093/icb/icv017

P. Domenici, “How sailfish use their bills to capture schooling prey,” The Royal Society Publishing, https://doi.org/10.1098/rspb.2014.0444


How do Hummingbirds and Nectar Bats Hover?

What do hummingbirds and nectar bats have in common?

Bat feeding. Photo from Pixabay.

Hummingbird feeding. Photograph from Shutterfly.

Nectar!

Due to their dietary needs, evolution played an important role in the flight mechanisms of these species. In order for them to collect nectar, they developed the ability to hover over flowers.

Understanding hovering capabilities of these animals has been unclear for a long time. Hence, researchers, Ingersoll, Haizmann, and Lentink, set on discovering how exactly these species do it in this research paper.

 

 

The researchers headed to the tropics, Costa Rica, for 10 weeks to conduct the study. This destination was chosen, because it is home to 10% and 15% of the worlds’ respective bat and hummingbird populations. In the neotropical environment, they studied 17 hummingbird species and 3 bat species. They chose popular species that were representative of the environment.

The researchers captured living birds and bats to measure forces exerted from their wings. They also digitized their wing kinematics to see similarities and differences between them. They placed the species into a 0.125 cubic meter box as seen in figure 1. On the walls of the box, they installed force sensors and plates to measure the forces exerted by their wings. They recorded the species with a high resolution camera. After they collected the data, they released the animals back into the wild.

Figure 1: The experimental setup. Modified from Ingersoll, Haizmann, and Lentink, Science Advances 2018. 

After running a convergence study, they found that hummingbirds and nectar bats have different wingbeats. Hummingbirds create a quarter of vertical aerodynamic forcing during the upstroke of their wingbeat—meaning that when their wings go up, they create a force that is 1/4 of their body weight. Hummingbirds’ wingbeats are more horizontal than generalist birds and bats, which helps generate this lift. On the other hand, nectar bats generate elevated weight supporting during the downstroke, by inverting their wings more than hummingbirds with a greater angle of attack. Theoretically, this takes up more power than hummingbirds’ wingstroke. However, due to the fact that bats have a large wingspan, energy costs are made up and power used becomes similar to the hummingbird per unit body mass.

The researchers also decided to look into interspecies differences to see if different hover poses, due to different diets, produced different upstroke support. In both hummingbirds and bats, there was no remarkable difference. 

Therefore, the study concluded that hummingbirds are more efficient, due to symmetry in beating back and forth, which creates a lift force upward to reduce drag and power required. However, bats are able to compensate for the lack of vertical force during upstroke, with large wingspan and a higher angle of attack to maximize aerodynamic force to combat gravity, by combining lift and drag forces on the downstroke. 

These findings will largely help engineers understand design tradeoffs, like the ones discussed, with aerodynamic power to help aerial robots, like the Nano Hummingbird and Bat Bot seen in these videos:

For more information check out this!

 

Find out more about Bat Bot here.