(FORTUNE Small Business) – I want to fly. That is why I'm zipped into a flight suit hurtling down a grass airstrip in a flimsy metal mosquito. My legs are wrapped around a man I met only moments ago and upon whom my life now depends: my flight instructor. Despite some whining from the 80-horsepower engine about the pudgy payload, takeoff is fast and so is the climb. In only six seconds we are airborne and soaring in an ultralight aircraft over the shimmering lakes and woodlands of eastern Minnesota. At 1,500 feet, with my feet dangling in midair, I'm wind-whipped, cold, and completely smitten. Mortgage the house, honey. This Harley of the sky is coming home with me.

Clearly I am having a midlife crisis. And why not? I'm a middle-aged suburban mother of three whose biggest thrill these days is drag racing my neighbor on our riding mowers. So no more knitting clubs or tennis doubles for me. I'm looking for some reckless adventure. I want to slip the surly bonds of earth and party in the clouds.

Ultralights are flying machines for the daredevil fringe of the aviation world. As defined by the Federal Aviation Administration, an ultralight is an aircraft that weighs no more than 254 pounds (without fuel or pilot) and hits a top speed of 63 miles an hour. Most have one seat; training versions have two. Powered by a tiny two-cycle engine, ultralights fly at about the same altitude as migrating birds: 500 to 2,000 feet. Some pilots go without instruments, though the model I'm in has an altimeter and airspeed indicator.

The Experimental Aircraft Association, an advocacy group in Oshkosh, Wis., estimates that the number of ultralight enthusiasts in the U.S. has grown from a handful two decades ago, when the contraptions were first invented, to more than 30,000 today. Many fly aircraft that are built from kits, such as the popular $25,000 Quicksilver Sport. This July many ultralight owners—along with about one million other barnstorming aviators—will flock to a field in central Wisconsin for the Oshkosh Air Show, a mecca for recreational aviation, featuring a five-mile flight line that includes everything from vintage warbirds to spacecraft.

Part of the appeal of ultralights is their low cost. Home-built kits start at about $10,000, and used models can be bought for as little as $5,000. "You really feel a part of the sky," says Dave Ahlberg, Midwestern representative of the U.S. Ultralight Association. "It's the closest thing to spreading your arms and flying away." No license is required, and lessons are affordable. My hourlong flight will set me back $120. To be proficient, I would need about 20 hours of instruction, which would cost some $2,400. In contrast, I'd have to spend about $7,000 to get a private pilot's license and fly a Cessna.

The FAA has some regulations, though. Ultralights should stay above 500 feet and are barred from flying over cities, towns, or livestock, which effectively restricts them to the wide-open spaces of the prairie, desert, mountains, and water. Flying at night or in the clouds is prohibited. Busy airports are off limits, which is why we are here in rural Minnesota at a private airstrip in Lino Lakes, about an hour north of Minneapolis. Still, this is a rebel's pastime. Out in the open spaces, far from civilization, the rules don't get enforced too zealously, and sometimes they don't get enforced at all. The Internet is brimming with accounts of what's known as "contour flying," in which a pilot surfs the ground, skimming cornfields low enough to touch the tassels, skipping up over fences and barns, and buzzing around silos in tight circles.

For my first flight, however, my instructor has promised to go strictly by the book: no loops, no rolls, no wing-wagging at the occasional curious onlooker below—just straight and level flight. Eric Rasmussen, 49, first took to the skies in a hang glider back in 1981. Before long he was leading tour groups on excursions in the mountains outside Valle de Bravo in central Mexico, teaching hang-gliding fans how to ride rising thermals of warm air with the migrating blizzard of monarch butterflies that breed in the forests surrounding the city. He now runs an ultralight dealership and flight school in nearby Osceola, Wis.

Once I'm suited up with helmet and headset and strapped into a small seat behind him on the training trike, we're ready. Several thousand feet of grassy runway lie before us, and the sky is a cavern of vivid blue. Not a soul is nearby, yet before starting the engine, Rasmussen shouts the traditional airman's warning: "Clear prop!" Then, a moment later, we are climbing into the yonder. Twenty or so miles away the skyscrapers of Minneapolis and St. Paul glimmer and flash in the orange sunset.

We enjoy a smooth climb, saying little, but savoring the feeling of flight. Besides, it's too noisy to talk. Ultralights not only feel like Harleys but sound like them. And the wind has me pinned against my seat. I glance over my right shoulder at the dark mass of pines below, and I feel a bit weak in the stomach. That's when Rasmussen merrily plunges into a tight pirouette, circling down several hundred feet to demonstrate the aircraft's versatility. "Everything okay back there?" he calls. "Unghhh," I moan into the microphone.

After leveling off, Rasmussen lets me take over. Ultralights are similar to gliders in that a pilot maneuvers with a control bar. There's no rudder: You turn right by shifting the bar to the left and vice versa to turn left. With the slightest pressure I can soar or dive, and that's when I fall in love with flight. A Cessna never felt this free.

How safe is this kind of flying? My husband, an airline pilot and a skeptic about the sport, puts it this way: "One stray duck and you're dead." The FAA says there were 51 fatalities in the two-seat training-model ultralights between 1995 and 2001, but the agency doesn't track accidents in single-seaters. Still, the anecdotal evidence is less than reassuring. Several prominent pilots have been killed in accidents recently, including the executive vice president of the U.S. Ultralight Association and Mike Jacober, one of the inventors of the sport, who died along with a student during a lesson in Alaska.

Jon Thornburgh is A 767 Captain for Delta Air Lines in Los Angeles and an advisor for the Experimental Aircraft Association. He says, "Ultralights are as safe as the pilot," meaning human mistakes are more dangerous than bird strikes. John Denver is the unfortunate poster child of pilot error: He was killed in 1997 when his new ultralight crashed off the coast of California. Federal investigators blamed Denver, suggesting that in his eagerness to fly he apparently neglected to check the fuel onboard. He may have simply run out of gas.

In any case, Rasmussen has never had a close encounter with a bird, nor has he ever run out of fuel. But he prefers to take precautions. His $40,000 two-seat training trike is equipped with a $3,500 ballistic parachute fitted with an explosive charge that will fire the chute in as little as two seconds in an emergency. Parachutes can cushion a fall even when deployed just 200 feet above the ground. Which is important because the landing is the most dangerous part of any flight.

That's what I'm thinking as Rasmussen gently nudges the wing forward, allowing the trike to descend slowly. Landing is the art of the controlled fall, a graceful ballet of subtle movements. On final approach, about a quarter-mile from the airstrip, he cuts the power to idle. Now the machine is truly gliding. In a graceful series of subtle movements, Rasmussen brings the trike down, flaring it ever so slightly just before touching ground. Then, without so much as a bounce, we are rolling across the grass, slower and slower until the ultralight comes to a halt.

I've found the answer to my midlife crisis. I want my wings.