Tree-dwelling animals were the first to fly, new research suggests

The flapping wings increased the speed of the running robot by 90%, going from 0.68 m/s to 1.29 m/s, and also enabled it to climb steeper gradients, increasing from a 5.6° ascent to a 16.9° ascent, which would be important in the development of a hybrid running and flying robot that could have several civilian and military applications.

The researchers, from the University of California, Berkley and the Smithsonian Tropical Research Institute, proposed that testing the wings on robots could provide an insight into how they evolved in early birds.

Fossils of animals closely related to dinosaurs, dating back further than when birds actually emerged, show that feathers were present on all four limbs, suggesting that the original function of wings was to help animals glide when dropping from a height, much like a paper aeroplane.

An alternative theory is that the first wings may have appeared in land-based animals, functioning as a mechanism to increase running speeds and then leading to take-offs and flying thereafter. The aim of this research was to gauge how much of an advantage flapping wings give a running animal.

"By using our robot we can directly determine the performance effects of flapping wings on a running platform as well as gaining a much greater mechanical insight into how the wings are actually working on the robot. We are thus able to look at the performance of the wings directly rather than attempting to build theoretical aerodynamic models based on fossil morphologies that may be overly sensitive to various assumptions," said Kevin Peterson, lead author of the study.

The researchers concluded that flapping wings do provide an advantage to running robots but not to the level that is needed to allow it to take off.

"We believe that this result lends indirect support to the theory that avian flight evolved from tree-dwelling animals, and not from land animals that required ground-based running take offs," continued Peterson.

The potential to use such a winged robot in a multitude of applications, from reconnaissance, exploration of hazardous areas and search and rescue, was also highlighted.

Peterson said: "On the current robot, the wings allow for a stable descent, meaning it can jump from high areas and stably land on its legs at the bottom. The wings also increase running stability as well as the range of inclines the robot can traverse, further increasing the likelihood of a successful mission."