GUY NORRIS / LOS ANGELES
Electrical energy from a fuel-cell based system set to drive flying wing for at least 40h
NASA is to attempt a record-breaking 40h flight of its Helios prototype flying wing powered by a newly developed fuel cell-based electrical energy system.
The flight of the NASA/AeroVironment-developed vehicle, targeted for 11 or 12 July, will be from the US Navy's Pacific Missile Range on Kaua'i, Hawaii, where the reconfigured Helios had its first flight this month. That was cut short to 15h after a glitch in the fuel-cell system plumbing prevented the alternative power source being switched on.
Unlike previous endurance flights powered by solar cell-powered electric motors, the attempt will be the first to fly both by day with the solar-powered system and at night using the fuel cell.
The fuel-cell system combines atmospheric oxygen with gaseous hydrogen from two pressurised tanks mounted on Helios's outboard wing sections. Helios, an unmanned air vehicle with a span of 75.3m (247ft), uses a series of proton-exchange membrane fuel cell stacks in the central landing gear pod.
The system will produce more than 15kW DC to power the aircraft's 10 propellers and systems. Up to 7kg (15lb) of hydrogen is contained in each tank, providing a specific energy density of around 500Wh/kg. Total weight of the development system is around 360kg (790lb), bringing take-off weight to around 1,090kg.
"We'd like to get the weight down to around 180kg," says NASA, which, with AeroVironment, plans to develop a fully regenerative system that would be capable of sustaining flights of six months or more. This would require an energy density of around 400Wh/kg, or roughly double the best current battery technology. The fuel-cell system is environmentally friendly, consuming no fossil fuels and emitting no atmospheric pollutants.
NASA says despite the long-term aim of a fully regenerative system, the flight tests of the new hydrogen-based fuel cell technology are relevant because of the limitations of flying a solar-powered UAV at higher latitudes.
NASA says a production version of Helios with a regenerative fuel- cell system could be used for environmental science missions, military surveillance and in stratospheric telecommunications.
Target altitude is 50,000- 60,000ft, requiring 10 propellers. Higher previous flights needed 14.
Source: Flight International
