Inside Unmanned Systems

AUG-SEP 2018

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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73 unmanned systems inside ENGINEERING. PRACTICE. POLICY. August/September 2018 "A previous study found the albatross spends more energy when it's walking around its nest than when it's f lying thousands of kilometers in the wind," said Peter Traykovski, an associate sci- entist at Woods Hole Oceanographic Institution in Massachusetts. "If you could duplicate that, that could have huge implications for our ability to monitor the oceans." VERY LITTLE WIND NEEDED Albatrosses can only f ly at about 25 percent of wind speed, which means they require good winds to soar. In contrast, sailboats can basically travel at 100 percent of wind speed, and so can travel even with low winds, but strong winds can generate waves that are too much for small sailboats the size of UNAv to handle. UNAv is de- signed to sail when the winds are too weak for f light and to f ly when the winds are strong enough to generate waves that would overwhelm a sail- boat, Bousquet said. The design for UNAv involves a long, slender glider-like airframe with a 3.4-meter wingspan, with a thin one- meter-tall triangular sail rising from its center and a narrow half-meter wing-like keel extending below its core. Altogether, the craft would only weigh three kilograms. The UNAv is designed to f ly with its body 40 centimeters above the water's surface, immersing 10 centimeters of its keel in the water. The research team's calculations suggest their de- sign could stay airborne in relatively calm winds as low as roughly 6.5 miles per hour—about a third of the wind speed that albatrosses require for soar- ing—and travel at speeds of about 23 miles per hour given such winds. With a light breeze of about 11.5 miles per hour, they predicted their design could travel at about 40 miles per hour, or about three to 10 times faster than a traditional sailboat. To move into the wind, the UNAv can, in principle, tack just like sail- boats. "Tacking means zigzagging in a succession of lines to move generally upwind or downwind," Bousquet said. ONE OF A KIND Autonomous vehicles known as ocean gliders do currently exist, and are similarly designed for long-range, long-term missions across the seas. However, ocean gliders travel under- water, instead of over or at the water's surface as the UNAv is designed to do. Ocean gliders adjust their buoyancy to go up and down in the water, and have "wings" that allow them to transform this up-and-down motion into forward motion. "Ocean gliders are ty pically bat- ter y-powered, so they have a f i- nite range—a f inite budget of up and dow n moves," Bousquet said. "Underwater gliders and the UNAv are somewhat complimentary—un- derwater gliders monitor what is at the surface and below, and the UNAv is designed to monitor what is at the surface and above. Of course, travel- ing in air is faster than traveling in water, and the UNAv does have its aspect of infinite range." A number of autonomous surface vehicles—robots that move across the water's surface—also have been developed. For example, Saildrone in A lameda, California, has devel- oped an autonomous carbon-f iber sailboat, while Liquid Robotics in Sunnyvale, California, a subsidiary of Boeing, has developed Wave Glider, an unmanned ocean robot that har- vests both solar and wave energy to help propel itself. "Saildrone and Wave Glider are ca- pable of long-duration missions, but they are extremely slow—a few knots at best," Bousquet said. "Conversely, the UNAv is able to travel at 20-plus knots—that is, an order of magnitude faster. Because the UNAv can also f ly for short period of times, it can gather atmospheric data and/or long-range visual data that the Saildrone or Wave Glider can't." Other autonomous gliding aircraft do exist, but they rely on thermal soaring, where they are carried aloft by warm updrafts much like eagles. "Of course, the issue with thermal soaring is that it is limited to regions where there are significant updrafts," Bousquet said. "Even when there are updrafts, it may be hard to find them." As far as Bousquet knows, the UNAv is the only design capable of dynamic soaring like albatrosses, where up- drafts are not necessary. Bousquet believes UNAv is the only autonomous unmanned vehicle capa- ble of both f light and traveling on the water. He did note there were a num- A robotic albatross could survey and study the oceans for weeks or months at a time, traveling tens of thousands of kilometers in a single mission." Gabriel Bousquet, postdoctoral associate, Massachusetts Institute of Technology "

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