GALLERY OF DESIGNS — click a thumbnail for a larger version    Stadiums
	This track is more conventional, an oval surrounding a football field and flanked by grandstands (in blue) on each side.  But I've designed a retractable dome to cover everything. Giant semi-circular frames (in yellow), nearly 400 feet in diameter, are stored in ditches outside the turns.  Using underground counterweights, they pivot up from their ditches, each pulling a quarter-sphere of clear plastic film behind them (hopefully there's no wind that day), to form two arches spanning the field at the 10-yard lines.  Then a 240-foot-long motorized spool rolls between the arches, deploying another three acres of plastic across the top of the structure.  Finally, the whole thing is pressurized so the plastic doesn't sag. (TEXT CONTINUED BELOW) I've also included a baseball diamond, but it's "only a possibility."  The outfielders would have trouble with the oddly-placed warning track.  They might stumble over the discus and shot-put circles.  Worse, they might sink into the long jump pit in short right field. It is unlikely that this design would be practical.  But has anyone else come up with a retractable air-supported dome?