July 2004 
Volume 03, Issue 3 
Special Features

Fuel cells to keep UAVs aloft

U.S. military forces and government agencies today need unmanned aerial vehicles (UAVs) with long endurances aloft to conduct extended surveillance and reconnaissance missions. However, this capability does not yet exist, and surveillance satellites cannot make up the shortfall because their continuing orbits do not allow constant focus on an area of interest.

To meet this emerging requirement, engineers at the Advanced Unmanned Systems unit of Phantom Works' Integrated Defense Advanced Systems (IDeAS) organization are currently integrating fuel cells into Boeing UAV designs. This approach uses cryogenically stored liquid hydrogen to power the aircraft's onboard fuel cell.

The resulting UAVs will have powered endurances aloft of more than seven days. By comparison, the current world record holder for high-altitude, unmanned flight endurance is the Boeing-built Condor UAV, which flew nearly 60 hours and cruised above 55,000 feet in 1989.

But creative thinking at Boeing is setting the stage for vastly longer flight endurances in the near future. Phantom Works engineers are now investigating a hybrid power system that combines a fuel cell with highly efficient solar panels manufactured by Boeing Spectrolab. The electricity generated by these solar panels performs onboard electrolysis to break down the water produced by the fuel cell. This regenerative process creates more hydrogen that is automatically stored in pressurized tanks to provide the fuel cell with a replenished fuel supply.

Under this self-sustaining system, the solar panels power the electrolyzer as well as the UAV's electrically driven propeller during daylight hours. After dark, the fuel cell takes over powering the propulsion system. The result is a high-altitude Boeing surveillance UAV capable of durations aloft easily measured in months, not days.

"The result will be long-loiter UAVs that provide the same capabilities as geosynchronous satellites but at a small fraction of the cost," said Leland "Lee" Wight, senior manager for Long Endurance Geostationary Systems, Advanced Unmanned Systems, Boeing Phantom Works. "This is just one example of the innovative applications we're pursuing for fuel cells. It's cutting-edge stuff outside our normal approaches to airplane design, and the excitement here is unbelievable."

-Jay Spenser


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