Mimicking birds' flight could be the next step in drone design

Stanford University researchers are taking a closer look at the way animals fly, more specifically at the circular patterns of rotating air or vortices created by birds. The results of this study, it is hoped, will lead researchers and engineers to design drones that can better navigate in obstacle-filled areas.

The Office of Naval Research (ONR) is sponsoring the Stanford research project, with additional funding from the KACST-Stanford Center of Excellence for Aeronautics and Astronautics, a National Defense Science and Engineering Graduate Fellowship, and a Stanford Graduate Fellowship under ONR’s Multidisciplinary University Research Initiative (MURI).

The goal of a program like MURI is to investigate Department of Defense (DoD) topics that will one day help the military.

The flight-focused study with Stanford University focuses on unmanned and autonomous flight. Dr. David Lentink, Stanford assistant professor of mechanical engineering, is leading a team that found inaccuracies in the current ways of measuring vortices that birds create when they fly. Accurate measurements in this area is important for drone design because studying the way in which birds produce enough lift to fly will enable researchers to learn how to better create robotic wings, ultimately giving a drone more flexibility.

In an ONR release, Lentink explains: “For a long time, engineers have looked to animal flight literature to see how robotic wings could be designed better. But that knowledge was based on inaccurate models for lift. We now know we need new studies and methods to inform this design process better. I believe our method, which measures lift force directly, can contribute to such improvements.”

The results – published in the December 2016 issue of Bioinspiration & Biomimetics titled “Lift calculations based on accepted wake models for animal flight are inconsistent and sensitive to vortex dynamics” by Eric Gutierrez, Daniel B. Quinn, Diana D. Chin, and David Lentink – showed that much more research is still needed.

Lentink and his team trained a Pacific parrotlet named Obie to fly from perch to perch through a laser field infused with microparticles (see Figure 1). No animals were harmed in the experiment, as Obie wore laser safety goggles during each flight.

Figure 1: Obie the parrotlet wearing goggles before flight through a laser field. Image courtesy of Stanford University/Eric Gutierrez.

The team used three methods for calculating the lift. They found, however, “The three models predict different aerodynamic force values mid-downstroke compared to independent direct measurements with an aerodynamic force platform that we had available for the same species flying over a similar distance,” as Lentink points out in his paper. In scientific research, the same repeated outcome is what really matters to prove a theory. “The researchers then applied each of the three prevailing models to these new measurements multiple times. In each case, the existing models failed to forecast the actual lift of the parrotlets.”

Obie and several other parrotlet friends flew several times through the laser minefield, with nontoxic aerosol particles lighting up their path. Marc Steinberg, ONR program manager, says of the experiment, “One of the most exciting recent advances in understanding flying animals has been the use of new technologies like this to collect all kinds of data in free-flight conditions.” Steinberg, who oversees the ONR/Stanford research, states in the release: “We can learn what’s really happening – the biology and physics – and apply it to create UAVs [unmanned aerial vehicles] capable of navigating challenging environments like under a thick forest canopy or through urban canyons.”

High-speed cameras captured the birds’ wing tips and thus created a picture of the vortices. The data was combined with an aerodynamic force platform (a Lentink Lab instrument that was created with ONR’s support).

“The platform is basically an ultrasensitive weight scale that measures the force generated when a bird takes off in a specially designed flight chamber,” says Lentink. This measurement technique was developed by Lentink and his team; direct force measurements are used with flow measurements to create a more accurate model of aerodynamic phenomena in animal flight.

Going forward, Stanford University and ONR will continue the flight study. Their goal: Applying the information they have obtained toward how drones and UAVs can complete missions in hard-to-navigate areas. In such situations, the much-needed flexibility of Mother Nature’s wings could be especially useful.