HARRISBURG, PA. -- The plane is flying through the air like a big orange bug -- a dip, a roll, a loop -- and Karen Shelly is dangling from the wing by her ankles.

Upside down, she waves at the crowd below, at the tens of thousands of people attending the Pennsylvania International Air Show. Her husband of two weeks is down there, too, shifting nervously from foot to foot and thinking aloud, "I'll be glad when this is over."

"Now watch carefully, ladies and gentlemen," the announcer's voice booms over Harrisburg International Airport, "as Karen climbs very deliberately, very carefully, onto the top wing . . . because Ron Shelly does not want to lose one of the most beautiful daughters a man could have . . . . "

Ron Shelly is at the controls of the old Stearman biplane that is snapping and rolling through the skies with the tiny figure perched on the wing and the plume of air-show smoke trailing behind.

It's not a reassuring sight from below. But Ron Shelly, a retired Navy pilot, and Karen Shelly, a probation and parole officer in Fauquier County, don't let themselves dwell on the obvious dangers of their 15-minute act. Together, they form what probably is the world's only team of father-daughter barnstormers, performing at air shows from Norfolk to Kalamazoo.

Imagine soaring through the sky at 100 miles an hour, climbing in and out of the cockpit, walking on the wing, scrambling to stand at the top of the plane for a hammerhead roll and a straight-up ascent, while the runways and the cornfields and the spectators in neon-colored visors swirl below. Then imagine that the pilot of the World War II plane you're astride is the same man who used to caution you to be home by 11.

Although the Shellys acknowledge the built-in contradiction, they also agree that their brand of wing-walking is not so perilous as it looks.

"The way I see it, there's nobody better than having my dad fly the plane," said Karen Shelly, 28. "I'm very confident of his ability. I don't think he would ever let me do this if he didn't think it was safe."

Of course, some people might wonder why Karen Shelly would want to wing-walk under any circumstances, but the reasons seem clear enough to her.

Besides the financial gain -- she and her father receive several thousand dollars a weekend -- there is another benefit.

"You get down on the ground after it's over," she said, "and you feel like you can do anything."

Air shows are a warm-weather staple. From April to October, crowds converge on local airports to see daredevil stunts, clamber over military planes, eat ice cream on a baking-hot tarmac.

At the Harrisburg show last weekend, an estimated 300,000 spectators were entertained by a women's parachute team, the U.S. Navy's Blue Angels squadron, a beer-advertising micro-jet and Oscar Boesch, who pilots the "Wings of Man" sailplane to the strains of "Born Free."

As is their habit before a show, Ron Shelly, 57, busied himself by tinkering with the plane; Karen Shelly waited quietly with her husband, Powell Duggan, a Warrenton, Va., lawyer. ("He's my groupie.")

For breakfast, she said, she had eaten only a plain biscuit.

"She had her eyes closed the first time she ever wing-walked," Duggan said. "I don't know why she ever opens them."

Actually, walking on wings was not such a stretch for Karen Shelly. For years, she and her four brothers and sisters, and her mother, Joan, pitched in as Ron Shelly performed at "The Flying Circus," a weekly air show in Virginia.

Ron Shelly, a Navy pilot for 26 years, got involved in stunt flying after he retired from the military and bought the 1940 Stearman, a big World War II training plane that later was used for crop-dusting.

For 11 years, he and his partner, Bill Fitzsimmons, traveled the eastern half of the country, performing at large shows.

When Fitzsimmons decided to retire last year, Shelly was on the lookout for a new star. Karen Shelly, a tall, athletic woman with a degree in sociology, was game.

Practicing first on the ground at her parents' Midland, Va., home, she learned where to place her hands and feet for each step, how to climb onto the top wing, how to get back down. Although she wears a waist harness during the routine, it must be disconnected and refastened several times as she moves around the plane -- and those moments, as her husband pointed out, are the most dangerous.

Karen Shelly found the aerobatic ride to be "exhilarating," and the father-daughter act debuted last June at an air show in Greensboro, N.C.

"I was really scared the first time -- 'Am I sure I want to do this?' " Karen Shelly said. "Then Dad gave the signal and I couldn't chicken out. It was an incredible day, smooth and calm, and you could see forever."

Some things you can't predict up there: a kamikaze insect, a wayward bird, a sudden burst of wind. So far, in her second season of 15 shows, Karen Shelly has been lucky: No heart-stopping moments.

And yet, she and her father are jubilant, clearly pleased another weekend of performances is over.

The big orange plane taxis slowly down the runway, Karen Shelly is standing and waving at the crowds. She hops down when the plane stops and hugs her father, then her husband, whose relief shows plainly on his face. Now they all will go out and have a big celebratory dinner.

"Working with Karen," Ron Shelly said with a grin, "is the highlight of my career . . . . But usually people just want to know, 'What does her mother think about all of this?' "