Biomimicry Tests of Bird Lift

Much of the work on mimicking the flight of birds is based on trial and error. However, a new technology that assesses the lift and aerodynamics of bird flight could change all of that. The device, produced by Stanford, can precisely measure the forces generated by a bird’s wing in a humane fashion using sensors, lasers and tiny protective “bird goggles.”

The device is based on Newton’s third law of motion, “For every action there is an opposite and equal reaction.” As the bird flies between perches in a small box the wings will create air fluctuations that in turn push on the bottom and top of the box. Sensors attached to the bottom of the box measure the force created by each stroke of the wings.

The sensors take measurements every 10 milliseconds to assess the wing beat. The system is sensitive enough to read the lab ventilation system. David Lentink, Lead researcher and Professor of Mechanical Engineering joked, "We have to turn off the air conditioning to conduct experiments, but we get very clean, precise data, so it's worth it."

Lentink noted that the ability to determine the lift generated by birds in free flight is a biomechanical “Holy Grail” – and that until now previous techniques produced results that were inconclusive.

"We've developed a way for the bird to just freely fly in a nice environment. It's a very animal-friendly method, and very precise, too … We reward the birds with seed for their flight. We have happy birds and happy researchers afterward," said Lentink.

In the end, it was found that two trained Pacific parrotlets were able to produce a lift twice the weight of their bodies on the down stroke. More interesting is the fact they generated almost no lift in the wing upstroke. The Stanford team suggests that this new information answers a number of questions in the research field.

Bird Lift Research to Advance Drone Technology

The Stanford team is also producing a new device that will be able to test more complex flight maneuvers. One goal is to test the hovering flight of hummingbirds and the membranous wings of bats. According to Lentink, studying these movements could help improve the designs of drones.

The Stanford team had built a wing-flapping robot before, but they were unable to measure the aerodynamics of the system until now. With the new lift-measuring device, they should be able to test and improve the aerodynamics of their bird-like drone.

Stanford’s not alone either. Other schools and industry experts have produced bird-like drones, and the applications to both research and the military are astonishing.

In 2011, Markus Fischer’s Festo team produced an ultralight glider bird modeled after the herring gull. This drone had one motor and the controllability to safely fly around an auditorium full of people.

Using accelerometers and Hall Effect sensors in the wings, Festo engineers were able to identify and control the drone’s position with a 32-bit microcontroller. In the end, the 450-gram drone was able to take off with 25 Watts and fly using only 16-18 Watts.

Also in 2011, École polytechnique fédérale de Lausanne (EPFL) presented their experiments on the flocking of fixed winged robots. Their drones were able to communicate via Wi-Fi and flock in formations similar to birds.

Even more impressive is the University of Maryland’s (U of M’s) Robo Raven. What sets Professors S.K. Gupta and Hugh Bruck’s drone apart is that it uses two motors. By using these motors, the research team is able to individually control each drone wing. In doing so, they are able to better mimic the flight of real birds. The robot can be seen performing impressive aerial maneuvers that would be impossible if the wings were not individually controlled.

In fact, U of M’s team was able to mimic the maneuvers of birds so precisely that their drone fell prey to a wild hawk. Professor Gupta said, "We can now program any desired motion patterns for the wings … This allows us to try new in-flight aerobatics—like diving and rolling—that would have not been possible before, and brings us a big step closer to faithfully reproducing the way real birds fly."

Using the aerodynamic lift testing device made by Lentink’s team at Stanford, all of these teams could gain invaluable feedback on the flight of their robots. In particular, U of M could use the information to program their drone to surpass its bird counterparts.

At the same time, combining these wing-flapping, biomimicry robots with EPFL’s flocking technology would offer a particularly impressive result, where the casual eye could have a hard time telling a flock of birds from a camouflaged flock of drones. Quite a scary concept for warzones, spies and military personnel.

With files from Bjorn Carey | Stanford News.