Currently, Boeing is designing a 737-sized twin-propeller-driven UAV with a 150-foot wingspan. It looks like a giant glider with high-aspect-ratio wings. Carrying a 250-pound baseline payload, the lightweight UAV would cruise at 60,000 feet. The just-completed first phase of research included design of the fuel cell-based propulsion system and risk-reduction studies. In the second contract phase, scheduled to begin this year, Boeing will build and demonstrate a complete propulsion system. If all goes well, the firm will build and fly two all-composite prototypes of the Ultra-LEAP UAV in the third phase, with aircraft fabrication anticipated within the next two years.