- Andy Davis
Monarch butterflies are being studied by aerospace engineers to design better flying machines
Yes, you read that title correctly - there are some very exciting things happening these days with monarchs, that relates to the growing engineering field of "bioinspiration"! This is a scientific field where researchers use lessons from nature to improve on human technology, and for designing new machines. I've been reading about some new research that has focused on monarchs in the last couple of years, and I've even started collaborating with some of these folks too. It seems that engineers have begun to take notice of the monarchs' amazing migration in North America, and are asking how can we learn from it to design better flying machines! Today I'm going to explain some of this new research (in layperson terms), and provide links to some of the latest papers and stories about them.
As we know, monarchs in eastern North America undertake one of the longest insect migrations in the world, travelling each fall from breeding sites as far north as Canada, to arrive at overwintering sites in central Mexico. This journey is ~3000miles, or ~40000km depending on your country's measurement system. Of course, a lot of monarchs never succeed in reaching their destination, but the important thing is that the monarch is designed ("built" if you will) for this journey! Its body and wings are the product of a thousand+ years of evolution, and in theory, it is perfectly suited for this long-distance journey. Here is why the engineers are so interested in the monarch. They want to know what are the design features of the wings that allow for such a tremendous journey, for such a tiny animal. They want to know how the wings flap, and how frequently. They want to know what is the angle of the wings during flapping, and so on. In other words, they want to learn everything about how the monarchs are able to make this journey, so they can apply this knowledge to designing better drones, and flying robots!
One of the leading engineering labs that is tackling these questions is at the University of Alabama, in Huntsville, which is a national hub of aerospace research. Huntsville is also the home of the U.S. Space and Rocket Center. Fun fact - I've actually taken my kid to space camp here (gratuitous photo below...).
Anyway, from what I can tell, there are actually a number of engineers and different labs at Alabama who are currently devoting time to studying monarchs. They all seem to have a similar approach, where they bring live monarchs into their labs and perform a series of tests using very high-tech gadgetry and equipment. The majority of work seems to be testing and watching the monarchs in free flight, though some work is done to test flapping behavior by monarchs on a tether. I've also seen researchers studying flexibility of monarch wings!
One lab recently published the following paper in an engineering journal - Effects of flight altitude on the lift generation of monarch butterflies: from sea level to overwintering mountain. Here is the link. It may be downloadable, but be warned, these engineering papers are not easy reads. From my read of this paper, these researchers wanted to know how the monarch flight behavior changed as it goes from low to high elevations. As we know, the monarchs travel the 3000-mile journey by flying in sections each day. On some days, they can fly close to the ground, but on others they can be seen soaring way up in the sky - so high you need binoculars to see them. The air density is quite different between ground level and high in the atmosphere, which can affect flight aerodynamics. So the researchers wanted to know how monarchs compensate for these changes.
They performed a series of flight tests using live monarchs placed in a giant sealed container (pictured below), which is designed to simulate high-altitude conditions. In other words, the researchers can remove some of the air from the chamber to create a partial vacuum.
This is a picture from the supplemental files of the paper. Crazy right? It sounds like they allowed the monarchs to freely fly in the chamber, and there were a series of lights and high-speed cameras inside that recorded the flight. Then, the researchers played the videos back and recorded the data they needed on the flight behavior. They did these flight tests with the air pressure at sea-level, and then at high-elevation.
Their results showed that monarch wings can generate more lift when they are at higher elevations, meaning that the flight is more energetically efficient when the monarch is flying very high. They had expected that monarchs might compensate for the low air pressure by simply flapping more frequently, but actually, this was not the case. It seems that the monarchs compensated by a simple change in the angle of their flaps, which apparently augmented their flap effectiveness. They also tended to fly slightly slower at the high altitude environment, which was also surprising. Anyway, these findings provide insights into how to design better flying machines that would work at high altitudes.
An earlier project from this same university was aimed at studying the undulating flight behavior of monarchs. There is a link here to an abstract of that project in a meeting symposium. This paper appeared to win an award and was also highlighted by a university press release (link here) which is much more user-friendly. From my read of this study, it seems that the researchers watched monarchs in flight in another special chamber which recorded fine-scale details of the wing flapping and flight trajectory. The monarchs had tiny stickers on their wings that were tracked by special infra-red cameras. There was also a hefty amount of computer simulations and statistical modelling too. In the end the researchers determined that the bobbing up and down behavior of monarchs in flight actually saves energy. This too seems like useful information for inspiring flying machines.
Let me also put in a link here to a really cool video piece on this study, which was done by a local news channel. This 3-minute video shows footage of the engineering lab where the study was done, and you can see all of the high-tech gear!
Next, there was an even earlier study done a number of years ago from this university, but from a different lab. I recall hearing about it at the time, but I'm not sure if it was published. Here is a link to a press release from the time of that study. It sounds like these researchers were interested in understanding how the wing scales of monarchs helps their aerodynamic efficiency. In their investigation, they measured the flying ability of monarchs twice - once with their scales, and once with all of their wing scales removed! I've never tried this, but it sounds like you can use a special solution to "wash" off the scales, and the monarch is unharmed (but naked!). Anyway, their tests showed that monarchs flew better with their scales on versus off, meaning that the scales provide a benefit during flapping flight. Somehow, the scales affect the flow of air over the wing surface, which improves the flight. The researchers said that this could be used to inspire some sort of scale-like coating over flying surfaces. Cool!
Finally, let me briefly tell you about some exciting new "bioinspiration" research that I'm involved in too. I recently began a collaboration with some engineers at New Mexico Tech, in their Department of Mechanical Engineering! This department also has people who are keen to study monarchs for their remarkable migration ability. However, one difference here is that these researchers are most excited about how the wing color of monarchs is involved in their migratory success! Yes, wing color is important for the flight of animals. In particular, my collaborator, Mostafa Hassanalian, has found in prior work that some flying animals (seabirds) appear to be uniquely colored to provide aerodynamic benefits. Here is a link to one of his (very technical) papers on this. Believe it or not, he has found that animals with black surfaces on their wings are more aerodynamic, because the black surface warms the pocket of air above it, which creates a smoother ride! It's much more complicated than that, but anyway, we are actually testing if this is true with monarchs right now! This involves tracking monarch flight in a lab, using thermal imaging cameras, high-speed cameras, and other high-tech gear. Stay tuned for updates on this!
OK, I'm winding down now. There is actually a lot more up and coming research that I didn't cover here, but hopefully this blog post gives you a bit of a taste of this new and growing field, and how the monarch is becoming an engineering superstar. As if it needed more fame, right?
That's all for now.
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