Boeing in August filed a patent that states the company believes an unmanned liquid hydrogen powered aircraft might be designed to fly for up to 10 days at 60,000 feet carrying loads of up to 2,000 pounds. Liquid hydrogen’s physical properties would help both dictate and optimize the aircraft’s design. To create the same energy, liquid hydrogen must occupy more than four times the volume of jet fuel, while, at the same time, it takes about 2.9 times more jet fuel (by weight) to produce the same energy. That being the case, Boeing’s proposed design would use a higher volume fuselage for fuel storage and highly efficient, very high-aspect ratio low-camber wings not aerodynamically compromised by internal fuel-carrying requirements. The wings particularly could be optimized for load carrying and high-altitude, long-endurance performance. To make power, the aircraft would “use one or more internal combustion engines adapted for hydrogen combustion” to drive propellers, not jet engines. The resultant aircraft, according to Boeing, would be useful for loitering on station as an airborne observation platform or flying cell tower. It would theoretically be more capable than an airship in negotiating winds and could increase its endurance toward 30 days if operated near sea level.
