问答题 Walk along the River Warnow, in northern Germany, and you may be lucky enough to spot a SeaFalcon, a sleek, white machine with two propellers, two wings and a distinctly unbirdlike tail. It looks like an aircraft. Which is what it is. Except, it isn't. It is a ship—at least in the eyes of the International Marine Organisation, which regulates such things. That matters, because ships are much more lightly regulated than aircraft.
The SeaFalcon is really a ground-effect vehicle. It flies only over water and only two metres above that water. This means the air beneath its wings is compressed, giving it additional lift. In effect, it is floating on a cushion of air. That makes it far cheaper to run than a plane of equivalent size, while the fact that it is flying means it is far faster—at 80-100 knots—than a ship of any size. Its designer, Dieter Puls, thus hopes it will fill a niche for the rapid transport of people and light goods in parts of the world where land and sea exist in similar proportions.
The theory of ground-effect vehicles goes back to the 1920s, when Carl Wieselsberger, a German physicist, described how the ground effect works. There was then a period of silence, followed by a false start. In the 1960s the Soviet armed forces thought that ground-effect vehicles would be ideal for shifting heavy kit around places like the Black Sea. Their prototypes did fly, but were never deployed in earnest and their jet engines consumed huge amounts of fuel.
This did, however, prove that the idea worked. And two German engineers, Mr. Puls and Hanno Fischer (whose version is called Airfish 8), have taken it up and made it work by using modern, composite materials for the airframes, and propellers rather than jets for propulsion. One reason the Soviet design was so thirsty is that the power needed to lift a ground-effect vehicle is far greater than that needed to sustain it in level flight. The Soviet design used heavy jet engines to deliver the power needed for take-off. But the SeaFalcon uses a hydrofoil to lift itself out of the water, and Airfish 8 uses what Mr. Fischer calls a hoverwing—a system of pipes that takes air which has passed through the propeller and blasts it out under the craft during take-off.
The next stage, of course, is to begin production in earnest—and that seems to be about to happen. Mr. Puls says he has signed a deal with an Indonesian firm for an initial order of ten, while both he and Mr. Fischer are in discussions with Wigetworks, a Singaporean company, with a view to starting production next year. South-East Asia, with its plethora of islands and high rate of economic growth is just the sort of place where ground-effect vehicles should do well.
All of which sounds optimistic. But a note of caution is needed. For another sort of ground-effect vehicle was also expected to do well and ended up going nowhere. The hovercraft differed from the vehicles designed by Messrs Puls and Fischer in that it relied on creating its own cushion of air, rather than having one provided naturally. That meant it could go on land as well as sea—which was thought at the time (the 1950s) to be a winning combination. Sadly, it was not. Hovercraft have almost disappeared. But then, in the eyes of the regulators, they counted as aircraft.