Artificial swallowtail butterfly reveals flight secrets

By Matt WALKER

In a bid to find out how a butterfly takes to the air, researchers have built their own artificial version.

They have created a model swallowtail butterfly that can fly just like the real thing.Swallowtails have large, slow-beating wings that means they fly unlike other butterflies.

Despite these limitations, the model insect proves that swallowtails still achieve forward flight with simple flapping motions, say the researchers.

Details of the artificial butterfly are presented in the journal Bioinspiration & Biomimetics, published by the Institute of Physics.

Undulating movements

Swallowtail butterflies have particularly large wings for their body size, and flap them relatively infrequently.

They are also unique among flying insects because their fore wings partly overlap their hind wings. Because their two sets of wings effectively flap as one, that in theory gives them little control over the aerodynamic forces on their body.

That means their wings are limited to a basic flapping flight, and their bodies are forced to undulate up and down as they fly, say researchers Dr Hiroto Tanaka from Harvard University in Cambridge, Massachusetts, US and Dr Isao Shimoyama from the University of Tokyo, Japan.But this has been impossible to check in real butterflies, because of the complexity of measuring the various forces acting on their wings and body.So Drs Tanaka and Shimoyama decided to build an artificial swallowtail, dubbed an "ornithopter".

The body is built from balsa wood, and the wings powered by a wire crank driven by a rubber band. The researchers made artificial wings from a thin film of polymer, fabricating them with plastic veins mimicking those of an actual swallowtail butterfly.That emulated the stiffness distribution of an actual wing.

Overall, the model is the same size and weight as a real swallowtail.

What is more, it can fly forwards just as a real butterfly.

Filming the robot butterfly in high speed helped the researchers calculate the forces acting on its wings and body.Just as a real swallowtail would, the robot's body undulated up and down in flight.

However, it also confirms that swallowtails need veins on their wings to achieve stable flight, and do not need to continually adjust them as many others insects do.