Robot glider can fly like an albatross, cruise like sailboats

MIT scientists have designed a robotic glider that can skim along the water's surface, riding the wind like an albatross while also surfing the waves like a sailboat.

In regions of high wind, the robot is designed to stay aloft, much like its avian counterpart. Where there are calmer winds, the robot can dip a keel into the water to ride like a highly efficient sailboat instead.

The robotic system, which borrows from both nautical and biological designs, can cover a given distance using one-third as much wind as an albatross and travelling 10 times faster than a typical sailboat.

The glider is also relatively lightweight, weighing about 6 pounds. The researchers hope that in the near future, such compact, speedy robotic water-skimmers may be deployed in teams to survey large swaths of the ocean.

"The oceans remain vastly undermonitored," said Gabriel Bousquet, a former postdoctoral fellow at Massachusetts Institute of Technology (MIT) in the US.

In a previous study, researchers decoded the dynamics of albatross flight and identified the mechanics that enable the tireless traveller to cover vast distances while expending minimal energy.

The key to the bird's marathon voyages is its ability to ride in and out of high- and low-speed layers of air.

Researchers found the bird is able to perform a mechanical process called a "transfer of momentum," in which it takes momentum from higher, faster layers of air, and by diving down transfers that momentum to lower, slower layers, propelling itself without having to continuously flap its wings.

They observed that the physics of albatross flight is very similar to that of sailboat travel. Both the albatross and the sailboat transfer momentum in order to keep moving.

The team drafted a design for such a hybrid vehicle, which ultimately resembled an autonomous glider with a three-metre wingspan, similar to that of a typical albatross.

They added a tall, triangular sail, as well as a slender, wing-like keel. They then performed some mathematical modelling to predict how such a design would travel.

"We found that in light winds you can travel about three to 10 times faster than a traditional sailboat, and you need about half as much wind as an albatross, to reach 20 knots," Bousquet said.

The team built a prototype of their design, using a glider airframe designed by Mark Drela, professor at MIT.

To the bottom of the glider they added a keel, along with various instruments, such as GPS, inertial measurement sensors, auto-pilot instrumentation, and ultrasound, to track the height of the glider above the water.

"The goal here was to show we can control very precisely how high we are above the water, and that we can have the robot fly above the water, then down to where the keel can go under the water to generate a force, and the plane can still fly," Bousquet said.

Experiments prove that the team's conceptual device can travel successfully, powered by the wind and the water. Eventually, he envisions fleets of such vehicles autonomously and efficiently monitoring large expanses of the ocean.

"Imagine you could fly like an albatross when it's really windy, and then when there's not enough wind, the keel allows you to sail like a sailboat," Bousquet said.

"This dramatically expands the kinds of regions where you can go," he said.