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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74 unmanned systems inside   August/September 2018 MARINE INNOVATION ber of designs for unmanned aircraft that could also travel underwater, f ly- ing either through rotors, fixed wings or f lapping wings. However, "traveling underwater is difficult, because motors are at their peak efficiency in a relatively narrow range of rotation speeds," Bousquet said. "Air-water vehicles with propel- lers have their propellers spin very fast in air and very slow underwater. Accordingly, they are probably very inefficient underwater." In contrast, he said, UNAv is designed for both ef- ficiency and long-range travel. PROTOTYPE TESTED The researchers built a prototype to test their design's critical maneuver— transitioning between f lying in the air and dipping its keel down to sail in the water. Accomplishing this move does not necessarily require a sail, so Bousquet and his colleagues Michael Triantafyllou and Jean-Jacques Slotine decided not to include a sail in their prototype to simplify their preliminary experiments. The scientists tested their prototype on the Charles River. They equipped it with auto-pilot instrumentation, GPS, inertial measurement sensors and ul- trasound to help control the craft and track its height above the water. Because the prototy pe lacked a sail or any other mechanism to get it moving, the researchers hung it from a fishing rod attached to a boat and towed the robot down the river. "The towing line generates a force ver y similar to that of a sail, hence it can be thought of as a simulated sail," Bousquet said. The researchers used a lightweight off-the-shelf competition glider air- frame so it could f ly at relatively low speeds. "The f lip side of being opti- mized for lightweightness was that the airframe was not very robust, so we could not afford many crashes and everything had to work just right from the start," Bousquet recalled. "This made testing quite stressful." All in all, when the prototype reached a speed of about 20 miles per hour, the robot autonomously f lew, successfully riding the wind on its own. A remote microcomputer could then send the robot orders to dip low enough to sub- merge its keel in the river, steer away from the tow boat, and then fly back up, lifting its keel out of the water. FUTURE DESIGNS Bousquet envisions the UNAv will have auxiliary solar cells on its wings and a foldable propeller driven by solar power. "Every now and then—say, 5 percent of the time—we envision that the UNAv will use its solar-charged propeller to zoom to higher altitudes to gather data of interest," he said. He also noted this design is geared toward small vehicles. "It w ill not work for airliner-sized systems," he said. "Larger systems have a heavi- er mass per amount of w ing area, so they require more w ind to stay aloft." Still, "at the upper end of pos- sible weight and sizes, a recreational one-seater 'f lying sailboat' is physi- cally plausible, which would be really cool," he noted. Traykovski, who investigates how storms interact with coasts, envi- sions one day dropping a few of these robots into hurricanes. "Right now NOA A [the National Oceanic and Atmospheric Administration] moni- tors hurricanes with hurricane hunter airplanes, which carry out overf lights to drop a few instruments into the storms to measure their pressure and other properties at a given time," he said. "With robotic albatrosses, you can imagine them staying with a hur- ricane as it goes up the coast for weeks at a time." Future research not only needs to test how UNAv performs with a sail added to it, but to explore how well it performs against waves. Still, with low winds, waves are relatively small, "so touching the water is a manageable challenge," Bousquet said. In contrast, with high winds and waves, "there is enough wind to be f lying like an alba- tross, and no need to dip the keel in the water, so in principle, the waves are less of a problem." To help UNAv deal with any large waves that it cannot avoid, there is technolog y "for drones to autono- mously navigate through forests us- ing machine-vision and path-plan- ning algorithms," Bousquet noted. "We want to use these technologies to teach the UNAv how to f ly in strong weather with large waves." Future research should explore what the UNAv should do in case of a crash. Bousquet noted there are prototypes of small UAS that are able to crash land A previous study found the albatross spends more energy when it's walking around its nest than when it's flying thousands of kilometers in the wind." Peter Traykovski, associate scientist, Woods Hole Oceanographic Institution "

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