CompositesWorld

JUL 2018

CompositesWorld

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NEWS 37 CompositesWorld.com UAV Update unprecedented UAV flight durations with radically new designs, which, by necessity, hope to maximize the advantages of advanced composites. In development since 2014, Facebook's Aquila (Fig. 1, p. 36), an all-carbon-fiber composite, solar-powered, four-propeller drone, has been test flown twice. In 2016, it was aloft for 96 minutes below 305m, and this past year, it flew for about 106 minutes, reaching an altitude of 914.4m. e Aquila is intended for big things: Aquila's stated target customer base is the several billion people around the world without reliable online access. Given the enormous geographical scale, the drone must be capable of very long, uninterrupted flight, and that, in turn, has profound consequences for Aquila's flight performance and design param- eters. Facebook must build and launch pilotless aircraft capable of continuous flight for months and at very high altitudes — 60,000- 90,000 ft (18,290-27,430m). At this height, the drone can provide WiFi coverage over about 60 square miles. When the technology is perfected, Facebook CEO Mark Zuckerberg has stated he intends to build a fleet of the drones. Although this is potentially good news for the composites industry, Facebook has released little specific engineering detail about the Aquila or the carbon fiber materials and laminate used to construct it. CW has learned that the flight-tested version has a "wingspan wider than a Boeing 737," which puts it in the range of 110 ft (±34m). Foregoing the extra weight and drag of conventional landing gear, the Aquila also is equipped with a Kevlar "landing pad" bonded to the bottom of the motor pods, one reason it only weighs about 1,000 lb (454 kg), with roughly half of that mass accounted for by batteries. Zuckerberg, however, has made clear that the drone needs to be made even lighter. When traveling upwind, the drone flies, by design, at a land speed of only 10-15 mph, which keeps it centered over the target area intended to receive signal. e communications system will use lasers to transfer data, which is about 10 times faster than land-based fiber optics. On the drone's second, most recently flown version, an unspecified coating material applied to the wings created a "smoother finish" and is credited for doubling its climb rate to 54.9m/min, compared to the climb rate of the first drone. at said, it remains to be seen if Aquila's ambitious flight duration goals can be met using only solar power. e proj- ect's main challenges in the next phase, according to posts on the Aquila Facebook site, are solar panel efficiency, battery storage and achieving acceptable cost paradigms for operation. Facebook says it intends to expand the test program to include drones with different "form factors, sizes and weights," and fly to higher alti- tudes in the next round of test flights. Meanwhile, a team of MIT engineers has designed, built and tested a UAV with a 24 ft (7.32m) wingspan, fabricated entirely from composites reinforced with carbon fiber and Kevlar (Fig. 2, this page), e objective of the UAV development project, dubbed FIG. 2 Short-term, emergency communications drone This team of engineering students at the Massachusetts Institute of Technology (MIT, Cambridge, MA, US) designed, built and fight-tested, at low altitude, this UAV prototype with 24-ft (7.32m) wingspan, made entirely from carbon fiber and Kevlar. A product of the US Air Force's Jungle Hawk Owl project, the UAV's performance goal is to fly continuously up to five days at an altitude of 15,000 ft (4,572m), to provide temporary communications in the event of a disaster. Source | MIT

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