The big doors opened on the new Minnesota Vikings stadium for the first time Friday. The process took about five minutes, accompanied by a loud beeping sound.

For three years, they've been called a signature design element of the new $1.1 billion U.S. Bank Stadium in downtown Minneapolis, but they've not all been open at the same time for a public event. (They've been tested by Mortenson Construction and, reportedly, they all work.)

Even Vikings executives haven't seen all five doors open, so they can't yet say how the air will flow through them and whether it will affect play on the field. Will the wind whip? Swirl?

"It could be all five doors are open and there's no effect," Vikings general manager Rick Spielman said. "There's a lot of things we don't know about."

Spielman said he expects kickers and punters to be most affected by air currents from open doors. The field is sunken — thus protected from winds — so only the high-flying footballs are likely to catch wind.

Staff members have been able to track elements, such as how the sun moves across the field through the seasons, but wind tests have been limited.

"We're trying to do everything we can to prepare ourselves or at least have an understanding, but until you get in there and get going, you won't know," Spielman said.

The team's first practice on the field is Friday. That's not open to the public. The first home game — a preseason contest against the San Diego Chargers — is at noon Sunday.

No decision has been made on whether the doors will be open Sunday, although team vice president Lester Bagley said, "We'd like to see them open."

The massive doors open onto the stadium's plaza and face downtown, providing a view of the city skyline.

The pivoting doors and a translucent plastic roof were selected as a cheaper alternative to a fully retractable roof. The aim with the doors and the roof was to give the indoor stadium an outdoor feel.

"We would like to have the doors open as deep into the season as possible," Bagley said.

Fan comfort is also important, so the doors were shut through two concerts last weekend and for a soccer match on Aug. 3, an extremely steamy night. The building did well in those conditions; the air inside was cool and fresh.

Like opposing teams, fans will get advance warning on the status of the doors. Per National Football League rules, the home team must announce the position of the doors no less than 90 minutes before a game.

An hour before the game starts, the doors must be in the position they will be in for the game's start.

"We can't open or close the doors when Blair Walsh is kicking a field goal," Bagley said. "Once you make a decision, you stick with it."

There are exceptions. The doors can be closed up until the final five minutes of the game in cases of precipitation.

The NFL also allows doors to be closed during a game for threatening hazardous weather, such as high winds or lightning, after consultation with the game's referee and the highest-ranking NFL official working at the game.

After Friday's practice, the team plays a day game Sunday, then a second home preseason game on Thursday night, giving them a sense of conditions at different times of the day.

The Vikings' era at their new home will officially begin on Sept. 18, when the Green Bay Packers come to town.

Spielman believes the players will be prepared for their new home, saying, "What it comes down to is playing football between white lines."

Rochelle Olson • 612-673-1747

Twitter: @rochelleolson