Sliding on Air

Even before the University of Hawaii's season-opening football game with Texas A. & I. last week, there had been a show of another kind of power and agility at the state's new $30 million Aloha Stadium in Honolulu. Two weeks ago, four of the stadium's six huge, 147-ft.-high grandstand sections were swung closer to the playing field. That maneuver marked the final successful test of the revolutionary 50,000-seat stadium, which uses advanced technology to change its shape and purpose by literally sliding on a cushion of air.

When sports-happy Hawaiians began planning a new stadium in Honolulu eight years ago, they wanted an all-purpose arena that would serve equally well for football and baseball, a neat trick never satisfactorily performed. For example, when stadiums basically designed for football are also used for baseball, the outfield is likely to be so shallow that even weak hitters tend to turn into Hank Aarons. Charles Luckman Associates, the big Los Angeles architectural firm, decided on a novel approach: they designed a stadium that called for two large grandstand sections in fixed positions at the north and south ends of the field; the four other sections, paired on the east and west sides, were to be moved around as events required. The two pairs of east-west stands would be pulled in close to the playing field to frame the classic football grid, or pushed back and angled away to form a baseball diamond. The stands would also be reconfigured for concerts or other events.

But how to move the massive structures, each of which would be as high as a 14-story building and weigh 1,750 tons? After looking at a variety of techniques, the Luckman designers, collaborating with Rolair Systems, Inc. of Santa Barbara, Calif, found the answer in air-film technology. Already used by Boeing to move heavy airframes about and by San Francisco's Bay Area Rapid Transit system to swing subway cars around at terminals, this new technology allows large, bulky objects to be maneuvered on so-called air bearings--thin (.031 in.), porous plastic disks. When air is forced through the disks from above at high pressure, it builds up underneath them in a thin film that acts as a bearing. In the Rolair-designed system at the Aloha Stadium, 416 such air bearings are positioned under the four movable stands. They are linked by pipe to three large compressors. When the compressors are turned on, the bearings lift the stands up about .004 in. above a smooth concrete surface. That is enough to reduce friction sufficiently so that the stands can be moved along by hydraulic jacks a distance of 180 ft. in only 20 or 25 minutes.

In fact, says Luckman's project chief, Samuel M. Burnett Jr., the stands can be maneuvered by muscle power alone. All it could take to prepare the stadium for baseball next spring is some season-end shoving by the football team.

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