Engineers at Boeing are designing a cargo plane designed to skim just above the water like a large sea bird. It’s dubbed the Pelican, because it will use the same “wing-in-ground effect,” or WIG, that the awkward bird does to glide almost effortlessly above the water. When applied to man-made flying vehicles, WIG aerodynamics represent a critical exception to a long-held rule of aviation—altitude equals efficiency. The reason most long-range airplanes are high-altitude jets is that flying in thick air at lower altitudes normally takes significantly more fuel. But if you get extremely close to the surface—around 50 feet or below, as a WIG vehicle would—a cushion of air generated by the plane’s velocity helps support it in flight, so that the plane cruises even more efficiently than a high-altitude jet.