Science & Technology - Posted by James Devitt-NYU on Monday, February 13, 2012 12:20 - 1 Comment 
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(1 votes, average: 3.00 out of 5) Loading ...Top-heavy ‘bugs’ show how to hover
Structures that are top-heavy are better able to maintain flight stability than those that bear a lower center of gravity, a finding that may lead to new design principles for hovering aircraft and maneuverable flapping-wing robots. (Credit: NYU)
NYU (US) — Top-heavy structures are more likely to maintain their balance while hovering in the air than those that bear a lower center of gravity, new research shows.
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The text of this article by Futurity is licensed under a Creative Commons Attribution-No Derivatives License.
The findings, published in the Physical Review of Letters, run counter to common perceptions that flight stability can be achieved only through a relatively even distribution of weight—and may offer new design principles for hovering aircraft.
As the Wright brothers demonstrated 100 years ago, the key challenge of flight is maintaining balance. Yet, while insects took to the air 400 million years earlier, their flight stability remains a mystery because of the complex aerodynamics of their flapping wings.
Researchers from New York University approached this question by creating experimental conditions needed to achieve stable hovering in mechanical flyers.
To do so, they created a range of pyramid-shaped “bugs” constructed from paper that hover when placed in an oscillating column of air, mimicking the effect of flapping wings. They captured the experiment with high-speed videos in order to analyze the nature of the airflow around the bugs.
To gauge which types of structures best maintained their balance, they created paper bugs with various centers of mass. Top-heavy bugs were made by fixing a weight above the pyramid, and low center-of-mass bugs bore this weight below.
Surprisingly, the top-heavy bugs hovered stably while those with a lower center of mass could not maintain their balance. The team showed that when the top-heavy bug tilts, the swirls of air ejected from the far side of the body automatically adjust to keep it upright.
“It works somewhat like balancing a broomstick in your hand,” explains Jun Zhang, professor at the Courant Institute and one of the study’s co-authors. “If it begins to fall to one side, you need to apply a force in this same direction to keep it upright.”
For bugs, it is aerodynamical forces that provide this stability.The lessons learned from these studies could be put to use in designing stable and maneuverable flapping-wing robots, the researchers say.
The study was funded by grants from the National Science Foundation and the U.S. Department of Energy.
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1 Comment
jim jones
I might have been more willing to accept the findings of this study but for a couple of major flaws, at least IMO: First, the researchers–or the author of the article–did not cite one example of an insect or any other flying creature with its center of mass above the lifting forces. Bees, moths, birds, house flies, etc. all develop their lifting forces above their centers of mass. Second, I did a bit of research, and an article summarizing the study which identified the principles of bee flight pointed out the fact that aerodynamic forces are not linearly scaleable as a function of size. Further, the oscillating airstream flowing over the paper model used in the researchers’ experiments was highly unlikely to provide accurate dynamic similarity to flying creatures. Namely, the researchers could have gotten any answer they wanted by altering the model/air flow dynamics.
Of course, there would be no news in proving what nature proved millions of years ago–namely that almost all flying creatures evolved with their lifting forces situated above their centers of mass. And, why not? It’s all about energy efficiency–critical for survival in the natural world.