Hang Time

Designers of spy planes have come up with any number of ways to increase dwell time over a target, from long-lasting UAVs to slow-moving airships to this hydrogen-powered craft called Phantom Eye, which was unveiled last week by Boeing Phantom Works.
According to Boeing, Phantom Eye will be shipped to NASA’s Dryden Flight Research Center in California later this summer, and will make its first flight (lasting four to eight hours) next year. The goal is to be able to stay aloft for four days.
My favorite detail: The engines are borrowed from a Ford Ranger pickup truck.