3D-printed insect wings provide new insights into energy-efficient gliding concepts

A joint research project by engineers from Princeton University and entomologists from University of Illinois Urbana-Champaign demonstrates how principles from biology can be technically investigated using 3D printing. The starting point of the work was the observation of American migratory locusts, which are able to cover remarkably long gliding distances with minimal energy expenditure. The focus was on the membranous hind wings of the species Schistocerca americana.

The results were published in the Journal of the Royal Society Interface. Project lead Aimy Wissa describes gliding as a particularly energy-efficient mode of flight in which the wings are fully extended without actively generating lift through flapping. A striking feature is the wavy, so-called corrugated structure of the hind wings, which are not flat when deployed.

“Grasshoppers have two pairs of wings,” she said. “The forewings are very leathery and are mostly used to protect the hindwings, which can fold. It is the membranous hindwings that are large and can flap and help with gliding.”

“Gliding is a mode of cheap flight,” Wissa said. “When we want to produce thrust, we flap. When we want to conserve energy, we fully deploy the wings and glide.”

To investigate the aerodynamic influence of this geometry, the researchers combined biological analysis with additive manufacturing. First, the wings were digitized using computed tomography in order to precisely capture their three-dimensional structure. Based on these data, several 3D-printed wing models were produced, in which individual parameters such as surface curvature, airfoil shape, and corrugation were selectively varied. These models enabled reproducible tests that would not be possible with real insects.

“As an entomologist, I was mostly interested in what the benefits of this corrugation might be,” Alleyne said. “I was wondering if corrugation is a disadvantage, or if it might be a neutral trait that came about to allow them to fold their wings. Corrugation also could be beneficial. We didn’t know.”

The printed gliders were tested both in a water flow chamber and in flight experiments in Princeton’s robotics laboratory. The results showed that while corrugation does contribute to lift, the best gliding performance was achieved by smooth wing models. The researchers see this not as a contradiction, but as an indication of a biological trade-off between aerodynamic efficiency and the ability to fold the wings compactly.

“As an entomologist, I am now interested in using the different prototypes and launch pad that the engineers developed to delve further into insect wing morphology,” Alleyne said. “While my lab often collaborates with engineers to do biology-inspired engineering, this can also go in the other direction, where we use engineering models and experimental tools to answer key biological questions.”

For entomologist Marianne Alleyne, the use of 3D-printed models opens up new ways to systematically analyze biological structures. At the same time, the findings provide points of connection for technical applications, such as the development of passive gliding vehicles or small, energy-efficient flying robots.