Boeing has won a US Defense Advanced Research Projects Agency (DARPA) contract to study a fuel cell-based propulsion system for an ultra-long endurance unmanned air vehicle (UAV).

Designated under the project name Ultra LEAP (long endurance aircraft programme), the work is aimed initially at designing, developing and testing the fuel cell-based power system. The second phase, scheduled for next year, involves building and demonstrating a complete propulsion system as well as an ultra-long endurance UAV that will use the power system in a projected third phase.

Unlike other long endurance UAV concepts, such as Aero-Vironment Helios and Pathfinder Plus lightweight flying wing developments being pursued in partnership with NASA, the Boeing/DARPA project is based on a "more significant air vehicle" that could be produced "with current [propulsion] technology", says Charlie Guthrie, Boeing Unmanned Systems director of rapid prototyping and advanced concepts. It would use fuel cells powered by stored on-board hydrogen, rather than externally collected power from systems such as solar panels.

The Boeing system is expected to build on automotive fuel cell research, and lead to development of an electrically-powered vehicle capable of sustained flights lasting several weeks. The most likely power source is expected to be a cell consisting of a carbon anode and cathode immersed in an electrolyte. Both electrodes would contain platinum, which acts as acatalyst, breaking down oxygen molecules into atoms as the gas bubbles pass the cathode. Oxygen absorbs electrons while combining with water to form hydroxide ions. At the same time hydrogen gives up electrons at the anode as it combines with hydroxide ions to form water. The current flowing between the electrodes drives a motor which powers propellers or propulsors.

The Ultra LEAP family of vehicles is expected to join Boeing's portfolio of UAVs ranging from micro and mini vehicles to the X-45 unmanned combat air vehicle. The Ultra LEAP platform is designed for commercial and military roles ranging from a communication relay station and remote sensing pseudo-satellite, to surveillance and early warning platforms.

Source: Flight International