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A team of MIT engineers has come up with an economical UAV design that can hover for long durations to provide wide-ranging communications support in case of a natural disaster. The researchers designed, built, and tested a UAV resembling a thin glider with a 7-meter wingspan. The device can carry 4 to 9 kilograms of communications equipment while flying at an altitude of 4,500 meters. The vehicle is powered by a 5-horsepower gasoline engine and can keep itself aloft for more than five days, longer than any gasoline-powered autonomous aircraft has remained in flight
The team was led by John Hansman, Professor of Aeronautics and Astronautics and Warren Hoburg, the Boeing Assistant Professor of Aeronautics and Astronautics. Hansman and Hoburg are also co-instructors at MIT. The two worked with students to design a long-duration UAV. In the spring of 2016, the U.S. Air Force approached the project with an idea for designing a long-duration UAV powered by solar energy. The thought at the time was that an aircraft, fueled by the sun, could potentially remain in flight indefinitely. Others, including Google, have experimented with this concept, designing solar-powered, high-altitude aircraft to deliver continuous internet access to rural and remote parts of Africa.
The team found that solar power — at least for long-duration emergency response — was not the way to go. “A solar vehicle would work fine in the summer season, but in winter, particularly if you’re far from the equator, nights are longer, and there’s not as much sunlight during the day. So you have to carry more batteries, which adds weight and makes the plane bigger,” Hansman said. The researchers came to their conclusions after modeling the problem using GPkit, a software tool developed by Hoburg, that allows engineers to determine the optimal design decisions or dimensions for a vehicle, given certain constraints or mission requirements.
This method is not unique among initial aircraft design tools, but unlike these tools, which take into account only several main constraints, Hoburg’s method allowed the team to consider multiple physical models simultaneously, and to fit them all together to create an optimal aircraft design. “This gives you all the information you need to draw up the airplane,” Hansman told MIT’s website. “It also says that for every one of these hundreds of parameters, if you changed one of them, how much would that influence the plane’s performance?”.
After determining, through their software estimations, that a solar-powered UAV would not be feasible, at least for long-duration use in any part of the world, the team performed the same modeling for a gasoline-powered aircraft. They came up with a design that was predicted to stay in flight for more than five days, at altitudes of 4500 kilometers in up to 94th-percentile winds. In fall 2016, the team built a prototype UAV, following the dimensions determined by students using Hoburg’s software tool. To keep the vehicle lightweight, they used materials such as carbon fiber for its wings and fuselage. The researchers designed the UAV to be easily taken apart and stored in a FedEx box, to be shipped to any disaster region and quickly reassembled.
This spring, the students refined the prototype and developed a launch system to fit on a typical car roof rack. The UAV sits atop the system as a driver accelerates and at a certain speed the remote pilot would angle the UAV toward the sky, automatically releasing a fastener and allowing the UAV to lift off.
In early May, the team put the UAV to the test. The UAV successfully took off, flew around, and landed safely. “There are a few aspects to flying for five straight days,” Hoburg says. “But we’re pretty confident that we have the right fuel burn rate and right engine that we could fly it for five days.”