Flying insects defy aerodynamic laws of airplanes, researchers find

July 11, 2016

The maneuvers of flying insects are unmatched by even the best pilots, and this might be due to the fact that these critters don't obey the same aerodynamic laws as airplanes, a team of New York University researchers has found.

"We've known for quite a while that the aerodynamic theory for airplanes doesn't work so well in predicting the force of lift for flapping wings," says Leif Ristroph, an assistant professor at NYU's Courant Institute of Mathematical Sciences who directed the study. "We found that the or wind resistance also behaves very differently, and we put together a new law that could help explain how move through the air."

"To double its , an airplane must increase its thrust four-fold to counter the stronger wind resistance," Ristroph explains in outlining the law. "In contrast, we found that flapping wings have a drag that is in direct proportion to its flight speed - to go twice as fast, an insect simply needs to double its thrust."

The study, which appears in the journal Physical Review Fluids, also included: Natalie Agre, the lead author and an undergraduate in NYU's College of Arts and Science; Stephen Childress, an emeritus professor at the Courant Institute; and Jun Zhang, a professor at the Courant Institute and NYU Shanghai.

The significance of and its strong increase with speed has been known since before the Wright brothers took flight. This fact is summarized by a mathematical law that posits increases as the square of speed; hence, moving twice as fast requires four times the thrust to overcome the higher drag.

Previous studies of flying insects, which beat their wings hundreds of times a second, suggested that these creatures do not obey this same relationship.

To make this sense of this discrepancy, the researchers in Courant's Applied Math Lab built a robotic wing apparatus for measuring the motions, flows, and forces. The apparatus allowed the team to compare steady motions of a wing, as would occur for airplane flight, to the maneuvers of insects, in which their wings flap as they move through air.

The team's results showed that the back-and-forth motions cause the drag to resist the movement in some instances; however, at other times the drag is actually directed forward, more like a thrust. The net force that results depends on the flight speed as well as the flapping motions, all of which the authors include in a new drag law.

This law may not be news to insects, which have been flying with for hundreds of millions of years. But the authors think that their findings could help guide the design of tiny flying robots that mimic the wing motions of insects.

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8 comments

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tblakely1357
1.8 / 5 (5) Jul 11, 2016
I read somewhere that airflow over wings changes as you scale up/down. That's why scale RC models of real aircraft often have out of scale wing dimensions to make them fly better. I assume the effect is even more pronounced with insects, necessitating them to use a much different approach to fly than aircraft.
Mimath224
5 / 5 (8) Jul 11, 2016
I'm not too sure there is really something new here. Over half a century ago when at a physics/biology lecture this was one of the topics mentioned. Can't remember the details now but there was also a very loose comparison between shark and dolphin. If memory serves the main idea was stroke flexibility. Obviously aircraft are more or less rigid while insect flight will depend on just how flexible the wings are. As with shark and dolphin there is, I think, a flexibility component depending on the amount of muscle and nerve in tail regions.
Whydening Gyre
4.6 / 5 (9) Jul 11, 2016
Don't think there's really a new "law" of aerodynamics involved here. just a new understanding of the mechanism as used in a different manner.
katesisco
1.3 / 5 (8) Jul 12, 2016
Which of course the aerodynamic laws are wrong. As has been discussed before. Miles Mathis has the latest point of discussion: http://milesmathi...lift.pdf
BigusDickus
Jul 13, 2016
This comment has been removed by a moderator.
Da Schneib
5 / 5 (3) Jul 13, 2016
Major anti-science talking point demolished here: "Teh sciensetis can't tell how a bee flies!!!111!!oneone!"

Now they can. That's how science works.
Steelwolf
not rated yet Jul 16, 2016
Well, once they have the laws Completely Figured Out, and how to do it in a mechanical fashion, I want my own Ornithopter as soon as they hit the market (heck, I would even take a usable, working prototype), Thank You!
Da Schneib
not rated yet Jul 16, 2016
I want my own Ornithopter
Never happen, at least not in Earth gravity. Surface area- and therefore lift- increase as the square of linear size; but volume- and therefore mass- increase as the cube.

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