The sound-track baritones take off as a young man in a clown suit, red Nerf-ball nose and aviator glasses stands with arms outflung on a biplane above the Grand Canyon. As the plane soars over a precipice, the audience wishes for seat belts. Now, we're told, they're ready to try the stunt.. With no parachute, he's going to attempt the forbidden headstand! It becomes an endless wing-walk that brings sweat to every palm.

"Flyers," guaranteed to become another long-run hit, opens Friday on the Air and Space Museum's five- by seven-story screen.

Unlike the museum's two previous film spectacles, with which it will alternate, the half-hour "Flyers" incorporates a story line about Tim, a would-be stunt pilot, and his mentor, Kyle Murphy, a World War II ace now flying for the movies. They simulate sweeps over WWI trenches, snatch a clothesline, buzz the camera tower. Meanwhile, they're rebuilding a Corsair fighter to reenact Kyle's wartime crash-landing.

Wasn't Kyle scared when his landing gear failed in the South Pacific? "I was too young and dumb to know better," the ace confesses. It's a dirty job, but somebody's gotta be the hero.

While "To Fly" was a balloon ride above the amber waves and "Living Planet" went sightseeing on five continents, this IMAX feature, produced by MacGillivray/Freeman Films (which also produced "To Fly") and Dennis Earl Moore Productions, is less scenic but more truthful. It's dangerous up there, but what the hell: Why do you suppose they call it a joystick? "FLYERS" -- At the Air & Space Museum daily; admission $1, children 50 cents.