Centurion solar-powered high-altitude aircraft in flight

Since 1980 AeroVironment, Inc. (founded in 1971 by the ultra-light airplane innovator--Dr. Paul MacCready) has been experimenting with solar-powered aircraft, often in conjunction with the NASA Dryden Flight Research Center, Edwards, California. Thus far, AeroVironment, now headquartered in Monrovia, California, has achieved several altitude records with its Solar Challenger, Pathfinder, and Pathfinder-Plus aircraft. It expects to exceed these records with the newer and larger solar-powered Centurion and its successors the Centelios and Helios vehicles, in the NASA Environmental Research Aircraft and Sensor Technology (ERAST) program.

The Centurion is a lightweight, solar-powered, remotely piloted flying wing aircraft that is demonstrating the technology of applying solar power for long-duration, high-altitude flight. It is considered to be a prototype technology demonstrator for a future fleet of solar-powered aircraft that could stay airborne for weeks or months on scientific sampling and imaging missions or while serving as telecommunications relay platforms. Although it shares many of the design concepts of the Pathfinder, the Centurion has a wingspan of 206 feet, more than twice the 98-foot span of the original Pathfinder and 70-percent longer than the Pathfinder-Plus' 121-foot span. At the same time, Centurion maintains the 8-foot chord (front to rear distance) of the Pathfinder wing, giving the wing an aspect ratio (length-to-chord) of 26 to 1.

Other visible changes from its predecessor include a modified wing airfoil designed for flight at extreme altitude and four underwing pods to support its landing gear and electronic systems (compared with two such pods on the Pathfinder). The flexible wing is primarily fabricated from carbon fiber, graphite epoxy composites, and kevlar. It is built in five sections, a 44-foot-long center section and middle and outer sections just over 40 feet long. All five sections have an identical thickness--12 percent of the chord, or about 11.5 inches, with no taper or sweep.

Solar arrays that will cover most of the upper wing surface will provide up to 31 kilowatts of power at high noon on a summer day to power the aircraft's 14 electric motors, avionics, communications and other electronic systems. Centurion also has a backup lithium battery system that can provide power for between two and five hours to allow limited-duration flight after dark. Initial low-altitude test flights at Dryden in 1998 were conducted on battery power alone, prior to installation of the solar cell arrays.

Centurion flies at an airspeed of only 17 to 21 mph, or about 15 to 18 knots. Although pitch control is maintained by the use of a full-span 60-segment elevator on the trailing edge of the wing, turns and yaw control are accomplished by applying differential power -- slowing down or speeding up the motors -- on the outboard sections of the wing.

The video clip depicts the aircraft on the lakebed prior to and during its first low-altitude check flight under battery power on November 10, 1998.

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