Tag Archives: flight

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.

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.