Solar-powered airplane wings its way to endurance record

A solar-powered, unmanned, high-altitude aircraft set a flight endurance record last month by staying aloft for 82 hours and 37 minutes.

The British QinetiQ Zephyr beat the 30 hours 24 minutes set by a Northrop Global Hawk in 2001 and Zephyr's own record of 54 hours set last year.

Launched by hand, Zephyr is an ultra-lightweight carbon-fiber aircraft. By day the 70lb Zephyr flies on solar power generated by silicon solar arrays no thicker than sheets of paper that cover the aircraft's wings. By night it is powered by rechargeable lithium-sulphur batteries, supplied by SION Power, which are recharged during the day using solar power, the company said.

The flight took place at the US Army's Yuma Proving Ground in Arizona between 28 and 31 July in the harsh conditions of the Sonoran Desert with temperatures up to 113°. Zephyr was flown on autopilot and via satellite communications to a maximum altitude of more than 60,000ft. The trial included a military assessment of a 5lb communications payload.

The Zephyr is under development as part of the Defense Advanced Research Projects Agency's (DARPA) Vulture program that ultimately looks to build an unmanned aircraft capable of carrying a 1,000-pound payload on five kilowatts of power and can stay airborne for an uninterrupted period of at least five years while remaining in the required mission airspace 99% of the time. The goals are to develop systems capable of offering persistent surveillance and communications capabilities.

DARPA recently picked Aurora Flight Sciences, Boeing and Lockheed Martin as contractors for the first phase of the Vulture program.

During the first phase of Vulture the three contractor teams will conduct studies to determine the design concept that best satisfies the operational tasks and optimizes design capability. They will also explore various vehicle configurations while concentrating on reliability and mission assurance design aspects. The phase will conclude with a concept design review of sub-scale and full-scale demonstration vehicles and the supporting technology development plan to reduce risk on key technologies, DARPA stated.

Vulture will use space satellite operations and design, in which long life and extreme reliability are routine, and bring this concept to the realm of aircraft operations in order to provide a level of flight previously unknown in aircraft operations, DARAP said. Vulture will provide pseudo-satellite benefits such as increased aircraft availability and consistent and persistent coverage, and allow smaller fleet sizes.

DARPA said the Vulture program will focus on developing innovative technologies and approaches for in-flight energy collection or refueling and ultra-reliable systems or systems able to be repaired in-flight. Other new technologies that will be developed and that are key to the ability of the Vulture system to provide the desired reliability include photovoltaic cells, high specific energy fuel cells, extremely efficient propulsion systems, in-flight precision autonomous materiel transfer and docking, extremely efficient vehicle structural design, mitigation of environmentally induced loads, and innovative vehicle control concepts.

Fixed wing aircraft aren't the only ultra-endurance aircraft on the flight line however. The Army's unmanned Boeing A160T Hummingbird helicopter in May successfully completed all planned phase I flight test demonstrations which included an 18.7-hour endurance flight on May 14-15 that will be claimed as a world endurance record for unmanned aerial vehicles in the weight class of 1,102 to 5,511 pounds. The A160 achieved an important demonstration milestone by hovering out of ground effect at 16,700 feet density altitude for over seven minutes. The gas-turbine-powered A160 flew the demonstrations autonomously.

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