The U.S. Naval Research Laboratory's (NRL) Ion Tiger, a hydrogen-powered fuel cell unmanned air vehicle (UAV), has flown 23 hours and 17 minutes, setting an unofficial flight endurance record for a fuel cell-powered flight. The test flight took place on Oct. 9-10 at Aberdeen Proving Ground. The Ion Tiger fuel cell system development team is led by NRL and includes Protonex Technology Corporation, the University of Hawaii, and HyperComp Engineering. The program is sponsored by the Office of Naval Research (ONR).

The electric fuel cell propulsion system onboard the Ion Tiger has the low noise and signature of a battery-powered UAV, while taking advantage of hydrogen, a high-energy fuel. Fuel cells create an electrical current when they convert hydrogen and oxygen into water, with only water and heat as byproducts. The 550W (0.75 horsepower) fuel cell onboard the Ion Tiger has about four times the efficiency of a comparable internal combustion engine and the system provides seven times the energy in the equivalent weight of batteries. The Ion Tiger weighs approximately 37 lb and carries a 4- to 5-lb payload.

Small UAVs are growing in importance for naval missions, as they provide capabilities ranging from surveillance collection to communication links. Electric UAVs have the additional feature of being nearly undetectable from the ground. Due to the high energy in the fuel cell system onboard the Ion Tiger, it is now possible to do long endurance missions with an electric UAV, thus allowing a larger cruise range and reducing the number of daily launches and landings. This provides more capability while saving time and effort for the crew.

In 2005, NRL backed initial research in fuel cell technologies for UAVs. Today, says NRL's Karen Swider-Lyons, "the long endurance flight was made possible by the team's research on high power, efficient fuel cell systems, lightweight hydrogen-gas storage tanks, improved thermal management, and the effective integration of these systems."

Fuel cell technology is being developed to impact the operational spectrum of technologies including ground, air and undersea vehicles and man-portable power for Marine expeditionary missions. "The Ion Tiger successfully demonstrates ONR's vision to show how efficient, clean technology can be used to improve the warfighter's capabilities," comments ONR's Michele Anderson.

The composite pressure vessel that stores hydrogen for the fuel cell stacks is manufactured by HyPerComp Engineering (Brigham City, Utah, USA). The vessel is carbon fiber filament wound, has a capacity of 22L, and measures 22 inches/559 mm long and 9 inches/229 mm in diameter. Service pressure is 5,000 psi.