But the Soviet Navy's commanders were never enthusiastic about the program. Though the Central Hydrofoil Design Bureau, which constructed the prototype, built two more large ekranoplans-a 140-ton amphibious landing craft and a 400-ton vehicle armed with six anti-ship missiles-the Navy was already building large hovercraft for amphibious assaults and had bombers to strike NATO warships. Plus, the ekranoplans lacked the range to be useful as transports. The Navy accepted five out of a planned fleet of 140 and used them for trials, but none ever became operational.
Aware of this long, painful history and the many inherent challenges of WIG aircraft, Boeing engineers have revived the concept, with a key twist. The craft they're designing is a cross between a land-based airplane and a Soviet WIG. It exploits the WIG effect, but it can fly like an airplane over terrain and land at an airport. It doesn't need the ekranoplan's thick, heavy boat hull, or extra power to haul itself out of the water. It has become the Pelican, sharing its broad, drooped wings with the birds that swoop over California's coastline.
The Pelican, as currently envisioned, will be capable of flying at the same speed and height-300 mph, up to 20,000 feet-as most other airplanes powered by turboprops (jet engines geared to propellers, which, at Pelican's speed, are more efficient than standard jet engines). The difference is that it will cover significantly greater ranges while hugging the water's surface and taking advantage of the ground effect. There are two elements to the phenomenon. A wing lifts an airplane because the pressure beneath it is higher than the pressure above it-a result of the wing's shape and forward movement. At the lateral tip of the wing, the high-pressure air underneath flows around to the upper surface. This creates a vortex, a rotating airflow that robs the wing of lift. But if the aircraft is flying very close to the surface, there is no room for the vortex to develop properly and it becomes weaker. The second element of ground effect is "ram pressure." The higher-pressure air under the wing cannot escape downward, as it could at higher altitudes, and a cushion of trapped air forms under the wing. An airplane in ground effect can fly on less power, using less fuel, than one at high altitude.
Two numbers define the strength of the ground effect: the airplane's wingspan and its flying height. The aerodynamic support generated-or benefit, in aviation jargon-is proportional to the span divided by the height. The increased aerodynamic support is one of the huge differences between the Pelican and the Russian ekranoplans. "It's a function of span," says Rawdon, "and that's why a very large WIG makes sense." With its 500-foot wingspan, the Pelican gets a "slight benefit" at 100 feet. "It goes up at 50 feet. At 20 feet, it's really good. If we could fly at 10 feet, we would."
If built, Boeing's Pelican will be powered by four pairs of 80,000-hp turbine engines, similar in size to the gas turbine engines used today in large ships. These will spin four pairs of 50-foot, eight-bladed, counter-rotating propellers-more than twice the size of any propeller in history. The cargo hold will be unpressurized, which will help make the airplane significantly easier to build-its vast size notwithstanding.