Boeing has provided a more revealing artist's concept of the SolarEagle ultra-endurance unmanned aircraft it is to build under DARPA's Vulture II program.Concept: Boeing
The solar-powered UAV will have a 400ft wingspan, and weigh in at 3,000lb including a 200lb payload. SolarEagle is being designed for at least a three-month endurance, and Boeing has signed up to demonstrate a minimum one-month flight through the winter solstice in late 2013/early 2014, when sunlight will be at its scarcest.
Boeing says the SolarEagle demonstrator will be close in size to an operational Vulture vehicle, which DARPA envisions orbiting in the stratosphere for its five-year lifetime - never returning to land and never being refueled or repaired.
The SolarEagle uses photovoltaic cells to collect energy during the day, storing it in fuel cells to power the vehicle through the night. In addition to solar cells over the entire upper surface of the wing and tailplanes, they cover the undersides of the outer wing panels, which are canted upwards to capture energy at low sun angles. The sides of the tailbooms are also covered in solar cells to catch the low-angle rays. The odd surfaces at the wingtips are for flight control.
Rival designs proposed launching several smaller UAVs that would link up in flight, or carrying the complete vehice aloft under a balloon. Boeing plans a conventional takeoff for the massive, but lightweight SolarEagle, picking a quiet day to launch the UAV so as to avoid any aeroelastic coupling with atmospheric turbulence during its day-long ascent to cruise altitude.