Goggles for birds? Scientists too full?

In nature, no birds wear goggles. They do not need any additional equipment to protect themselves from wind and sand during flight because they have an organ called the nictitating membrane on their eyes, which is simply the "third eyelid" and protects the eyeballs during high-speed flight.

The translucent layer is the nictitating membrane. Image source: pinterest

But today, we are not going to introduce you to the bird's nictitating membrane, but to introduce a bird that actually wears goggles. Of course, the goggles are not worn by the bird itself, but by scientists.

Why do scientists put goggles on birds? Birds have nictitating membranes, so isn't putting goggles on birds a disrespect for their own abilities? If you want to know the truth, keep reading!

How to tame a bird to wear goggles?

The bird that scientists put goggles on is named Obi, a Pacific parrot (Forpus coelestis) from Stanford University.

Pacific parrot wearing goggles Photo credit: Eric Gutierrez

Scientists put on a pair of 3D-printed custom goggles, the lens material is very common - polycarbonate, can protect against direct laser light. Before this, no one had ever made goggles specifically for birds, so the production process was a process of trial and error. After a lot of attempts, scientists finally made the thickness and weight of the lens reach the most appropriate situation.

Specially customized goggles Source: Document 1

The scientists originally recruited three Pacific parrots to wear the goggles, but only one, Obi, adapted. It took them several months of feeding him fresh broccoli and seeds every day to get him to wear the goggles.

Image credit: Eric Gutierrez

The scientists must have gone to such great lengths to see how the birds would react when flying with goggles on. If the purpose of the experiment was really that simple, the scientists probably wouldn't have gotten the funding they applied for. So what's the real reason? Let's keep reading.

Obi flying with goggles. Image credit: Eric Gutierrez

The truth about wearing goggles for birds

As mentioned earlier, goggles have an important function for Obi - laser protection. Too bright light can cause damage to the eyes, not to mention the extremely high energy density of the aurora. When the laser hits the eyeball with a very small irradiation area, the high energy will cause the temperature of the eyeball tissue to rise sharply, causing the eyeball to be burned. Even birds with nictitating membranes cannot avoid damage to the eyes from lasers directly hitting them.

Training process source: Eric Gutierrez

Why use lasers? Because the experiment the scientists wanted to do required the use of lasers, so they put goggles on the experimental subject Obi. The experimental study was about the problem of vortices and lift generated by birds flapping their wings in flight.

Research principle diagram source: Reference 1

For a fixed-wing aircraft, the pressure on the lower wing is higher than that on the upper wing. Under the pressure difference between the upper and lower wing surfaces, the airflow on the lower wing bypasses the wing tip and flows to the upper wing surface. Since the airflow on the upper and lower wing surfaces has different flow directions at the trailing edge, a vortex is formed. The more lift generated on the wing, the stronger the vortex. This is vortex lift.

Generally speaking, when studying fluid mechanics, one has to observe and record the changes in the fluid. To record the changes in the fluid of air, one has to use a laser.

Obi flying in lasers. Image credit: Eric Gutierrez

But lasers alone are not enough, and some aerosol liquid must be sprayed in the air during Obi's flight to simulate a layer of mist in the air, so that the flow of air can be shown.

If there is no aerosol, the laser will directly penetrate the air without any refraction or reflection. Naturally, it cannot show the changes in air flow, and the laser irradiation will be in vain.

Obi flying in the mist, the changes in the fluid can be seen through the laser

Image credit: Eric Gutierrez

You can see that when Obi flaps his wings, vortices are created, similar to the vortices created by airplanes.

However, the difference between the vortices generated by fixed-wing aircraft and those generated by fixed-wing aircraft is that the vortices generated by the former are more unstable than those generated by fixed-wing aircraft and break up immediately. The vortices generated by aircraft break up only after the aircraft flies far away, while those generated by birds break up within three flaps of their wings after they fly out.

Obviously, the vortices generated by a bird's wingbeat are much more complex than those generated by an airplane.

The vortex generated during wing flapping Source: Reference 1

Knowing the changes in vortices generated by a bird's wing flapping, we can build a model through the wing kinematic equation, aerodynamic model, attitude kinematic equation, and center of mass dynamic equation, and then analyze the lift and drag at different moments during the flight process, and finally understand how the bird flaps its wings to fly stably...

Of course, this is just an ideal situation, because the scientist still didn't understand the changing rules of the vortex in the end (it couldn't be that simple), he just proposed an idea to solve the problem, and tried to study it by putting goggles on the bird...

However, with the maturity of science and technology, perhaps in the near future we will be able to design large-scale flapping-wing aircraft.

By the way, in order to solve the problem of fogging goggles, scientists applied a thin layer of shaving cream on the inside of the lens. It is very useful. Maybe you can try it on your glasses.

(Useful knowledge obtained√

References:

Gutierrez E, Quinn DB, Chin DD, et al. Lift calculations based on accepted wake models for animal flight are inconsistent and sensitive to vortex dynamics[J]. Bioinspiration & biomimetics, 2016, 12(1): 016004.

https://qa.1r1g.cn/aviation/ask/1474861/

https://zh.wikipedia.org/wiki/%E7%BF%BC%E5%B0%96%E6%B8%A6%E6%B5%81

Author: Su Chengyu

Produced by: Science Popularization China

Producer: Computer Network Information Center, Chinese Academy of Sciences