Micro flying robots can fly more effectively than flies

August 1, 2009
A fruit fly with a wingspan of 5 mm inspires the design of flying micro robots. Photo: Dickinson lab

There is a long held belief among engineers and biologists that micro flying robots that fly like airplanes and helicopters consume much more energy than micro robots that fly like flies. A new study now shows that a fly wing that spins like a helicopter blade generates the same amount of lift as a flapping fly wing while consuming only half the energy to move the wing. This finding can inspire the design of efficient micro flying robots with spinning fly-like wings.

Engineers have long been stymied in their attempts to fabricate micro aerial robots that can match the amazing flight capabilities of nature’s most advanced flying insects -- flies. Such flies -- if they could be made efficient enough for long missions -- could be used for a variety of tasks, from spying, to mine detection to search and rescue missions in collapsed buildings.

RoboFly a robot model of fruit fly wings that is 100 times larger than a fruit fly. It is submerged in oil to simulate the viscosity of the sticky air around the wing of a real fruit fly. Photo: Dickinson lab

There is a long held belief among engineers and biologists that micro flying robots that fly like airplanes and consume much more energy than micro robots that fly like advanced insects such as flies. The previous thinking was that basic flapping wings at the small scale of insects waste less energy while generating lift. This idea, which has become integral to the development of fly-sized flying robots, now has been tested rigorously by a Dutch aerospace engineer, David Lentink at Wageningen University (Netherlands), who joined forces with a leading expert on insect flight, biologist Michael Dickinson at the California Institute of Caltech.

Together they used a giant robot fly submerged in a tank of oil to test whether flies consume less energy to hover than a micro helicopter outfitted with a fly wing. To their surprise, they found that a spinning fly wing generated the same amount of lift as a flapping fly wing while consuming only half the energy to keep the wing moving. The study shows that robots that hover like flies can save up to 50% energy if they swing an insect wing around like a helicopter blade. This finding can result in new, more energy efficient micro flying robot designs inspired by both the effective wing shape of insects and the energy efficient spinning motion of helicopter blades.

Leading Edge Vortex on top of a fruit fly wing. Image: David Lentink & Michael Dickinson

Flapping wings waste a lot of energy accelerating the air back and forth,’ explains Lentink.  "That is why spinning insect wings consume less energy than flapping wings." So what does all this mean for engineers keen on designing micro fliers? "Engineers have been thinking that fly sized flying machines would have to fly like a fly to be energy efficient," says Lentink, but he now realizes that is not the case. The reason being that both spinning and flapping insect wings can generate much more lift than predicted by aerodynamic theory -- up to twice as much. The extra lift is generated by a stable ’tornado-like’ vortex that runs parallel to the leading edge of the wing. This vortex lowers the pressure over the wing and sucks it upward, lifting the insect's weight into the air. It was already known that both spinning and flapping insect wings can generate such a lift boosting vortex.

The new work shows which wing motion generates high lift most effectively -- the insect that spins around similar to a helicopter blade. Nevertheless, we still have much to learn from flies, says Dickinson. These tiny animals have evolved into some of nature’s best fliers and whereas the micro batteries of humans can keep their fly-sized robots aloft for mere seconds or minutes, flies can fly effortlessly for hours. ‘With such an effective form of energy storage and motors,  flies are much less dependent on energy efficiency than our best robot flies," says Dickinson> "We can still learn from nature how to improve our robot designs, but not without a better understanding of why flies fly so well."

More information:

Published on the 31th of July in two Research Articles in the Journal of Experimental Biology:

- Lentink, D. and Dickinson, M.H. (2009) Rotational accelerations stabilize leading edge vortices on revolving fly wings. J. Exp. biol. 16.
- Lentink, D. and Dickinson, M.H. (2009) Biofluidynamic scaling of flapping, spinning and translating fins and wings. J. Exp. biol. 16.

Provided by Wageningen University

Explore further: Deciphering the Mystery of Bee Flight

Related Stories

Deciphering the Mystery of Bee Flight

November 30, 2005

One of the most elusive questions in science has finally been answered: How do bees fly? Although the issue is not as profound as how the universe began or what kick-started life on earth, the physics of bee flight has perplexed ...

Bird sized airplane to fly like a swift

July 18, 2007

Nine Dutch Aerospace Engineering students at the Delft University of Technology, together with the Department of Experimental Zoology of Wageningen University, designed the RoboSwift.

Flies provide aerodynamic model for tiny flying vehicles

August 28, 2006

When it comes to flying, the fly reigns supreme. This two-winged insect’s sophisticated flying behavior enables it to make sharp turns, aim at targets and hover – traits which make the insect an ideal prototype for tiny ...

Cyclogyro Flying Robot Improves its Angles of Attack

January 22, 2009

(PhysOrg.com) -- In the past few decades, researchers have been investigating a variety of flying machines. Most studies have focused on improving the flying performance of standard flying mechanisms, rather than developing ...

Flapping wing vehicle improves on the a helicopter

December 11, 2008

(PhysOrg.com) -- Since the days of Leonardo da Vinci people have tried to build machines that fly with flapping wings like a bird or an insect. Even in the jet age the idea remains attractive because such machines could be ...

Recommended for you

Google braces for huge EU fine over Android

July 18, 2018

Google prepared Wednesday to be hit with huge EU fine for freezing out rivals of its Android mobile phone system in a ruling that could spark new tensions between Brussels and Washington.

EU set to fine Google billions over Android: sources

July 17, 2018

The EU is set to fine US internet giant Google several billion euros this week for freezing out rivals of its Android mobile phone system, sources said, in a ruling that risks fresh tensions with Washington.


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (3) Aug 02, 2009
have I missed something. what insects have spinning wings?
1 / 5 (1) Aug 02, 2009
You've obviously never been bit by a rotor- skeeter.
4.5 / 5 (2) Aug 03, 2009
TJ, what the article is saying is that sometimes mother nature is NOT the be-all, end-all master of engineering and that simple human inventions like the helicopter are more energy efficient.... However if you need the maneuverability of a fly then fly like a fly. Flies need to be able to zig and zag with reaction times in the millisecond range. However for simple hovering (hoovering as you cannucks say) spinning is indeed more efficient than flapping...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.