JUL 2018


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JULY 2018 38 CompositesWorld FEATURE / Composite UAVs Take Flight Jungle Hawk Owl and funded by the US Air Force (Gateways Branch, AFLCMC/HNAG, Hanscom Air Force Base, Bedford, MA. US), is a bit more modest than that for Facebook's Aquila. e goal is to build a drone capable of staying aloft for five or more days, in high and low geographical lati- tudes, in all seasons, at an altitude of approxi- mately 4,572m. Such a drone would be designed to perform as a communications hub, providing temporary Internet/phone connections over a large area in the event of a wide-scale power or service outage. e drone's design was modeled on a glider, with a typically thin aerodynamic profile. e first, full-scale version, test flown this past year at a maximum altitude of 122m, has a wing thick- ness of 42.4 mm tapering to 20.8 mm, and a total, empty weight of only 12.7 kg. After minor adjust- ments to the aircraft and its automotive rooftop launch system are complete, high-altitude flight tests are scheduled for this summer, with the drone carrying a full payload of communication equipment and fuel, weighing up to 45.4 kg. John Hansman, professor of aeronautics and astronautics at MIT and one of the staff supervising the student research, a collabora- tion between MIT and the MIT Lincoln Labora- tory (Lexington, MA, US), reports that the wings comprise a core sandwich molded in a two-step process. To achieve the necessary aerodynamic precision, the wing's upper surface skin was molded separately, via vacuum infusion, from one ply of unidirectional carbon fiber fabric oriented 90° to the length of the wingspan. To make the bottom wingskin, spar caps of varying thick- ness were molded from unidirectional fabric and placed in the mold. Styrofoam was then placed Developed at the Massachusetts Institute of Technology (MIT, Cambridge, MA, US), the Jungle Hawk Owl unmanned aerial vehicle (UAV), funded by the US Air Force in an effort to develop a way to provide a drone-based alternative method of WiFi access, relies significantly on composites for its lightweight construction. One reason was the hope that the aircraft could be kept aloft for extended periods, exclusively by solar power. Using a new modeling software tool called geometric programming optimization, however, researchers discovered that the goal of powering the drone with solar energy was infeasible. The program, called GPkit for short, was developed at MIT by Warren Hoburg, professor of aeronautics and astronautics and a member of the project team that is designing the Jungle Hawk Owl drone. The GPkit program reportedly facilitates consideration of about 200 factors and physical models simultaneously, and then integrates them to create an optimal aircraft design. In the case of the solar-powered drone, the model determined it would work during the summer season in either hemisphere, but not in the winter. Further, it indicated that adding more batteries would make the drone too heavy. Alternatively, the same modeling predicted that a 5-hp gasoline engine would be sufficient to keep the drone in flight for more than five days at an altitude of 4,572m in up to 94 th -percentile winds at any latitude. Hansman says the GPkit tool provided a "state-of-the-art" design optimization technique. "In terms of its structural aerodynamics," he adds, "this plane is exquisitely proportioned." SIDE STORY Drones: MIT software casts doubt on solar-powered UAVs FIG. 3 Drone incorporated into robotic workcell A "collaborative" fiber-winding process recently demonstrated by researchers at the University of Stuttgart consists of two, six-axis KUKA robots and a lightweight, custom-built drone or UAV "go-between." The robots precisely place wet-or pre-impregnated fiber on the winding frame, while the drone shuttles the fiber between each of the robotic arms. The project demonstrated the capability of the drone-aided fiber winding to fabricated long- parts normally exceeding the reach of a single, stationary robot. Source | University of Stuttgart Fight Controller (Pixhawk) RGB Camera Electronic Speed Control (ESC) Lipo Battery Onboard Computer (Odroid XU4) Radio Receiver Flow Sensor Electromagnet Controller (Arduino Nano) Electromagnet Effector (male) Electromagnet Effector (female) Motor & Propeller

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