Physics: Principles and Problems


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For use with Chapter 13
States of Matter

Robofly
Posted October 1st, 2001

Many animals – such as birds and bats – can fly, but insects were the first to develop this ability millions of years ago. However, for many years, the exact physics of insect flight has baffled scientists. The subject has even reached an Internet chain letter that claims that a scientist once proved that a bumblebee cannot fly – but that the bumblebee doesn’t realize this fact.

The bumblebee example is an urban legend, dating back to a 1934 book by entomologist Atoine Magnan. In his book, Magnan recounts a story from his engineer assistant who studied a bumblebee’s flight pattern based on the same physics that aircraft used. His calculations showed that the bumblebee cannot achieve the proper lift with wings of such small size. However, we all know that an insect’s wing path and movement is very different from the long wings on an airplane or glider.

Physicists haven’t been able to fully explain insect flight mainly because insect wings flap so fast (as much as 600 times a second.) They haven’t been able to model and observe the wing motion in controlled conditions – until now. Michael Dickinson, a biology professor at the University of California, Berkeley, has developed a way to model insect wing behavior and slow it down to a manageable speed.

Dickinson’s model, which he affectionately calls "Robofly," is a 2-foot robotic insect immersed in a mineral oil. Robofly’s wings are controlled by six computerized motors that can be programmed to mimic several different insects – from the fruit fly to the dragonfly.

Oil is used as Robofly’s medium because it is much thicker and viscous than air. The thicker the fluid, the slower the movement, but otherwise, the wings will basically behave the same way. By increasing wing size and using this thicker fluid – in this case mineral oil – Dickinson was able to slow down Robofly’s flapping to once every five seconds.

Traditional airplane and bird wings achieve lift with a process known as the Bernoulli’s Principle: air flowing over the wing moves faster than that flowing under the wing. This builds up higher air pressure under the wing, which results in a force pushing the wing upwards. When the angle of the wing becomes too steep, the pressure systems above and below the wing separate and the plane will suddenly lose lift. This is known as a "stall."

Insects generally create a stall with every wing flap, but because this motion happens so fast (in a fraction of a second), they achieve too great amount of lift before the pressure systems are able to separate and cause the stall.

By studying insect flights, scientists may soon one day replicate it for practical use. Miniature Roboflies can be made to fly through the air and be used for search and rescue, environmental monitoring, surveillance, mine detection, and even planetary exploration.

Activity
Use the Internet to research how insects fly. Use this information to build a 3-D model of an insect’s wings.

References

 


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Physics: Principles and Problems