Free flight

PEPPERELL -- The cargo hold of the twin-prop aircraft is packed with goggle-wearing skydivers sitting hunched on steel benches, parachutes packed on their backs like camel humps. The plane climbs past 10,000 feet, 11,000 feet. Their chatter becomes louder, more boisterous.

Twelve thousand feet, 13,000 feet. The rear door opens. The cabin fills with a rush of cool air and the roar of the engines. The sky yawns across to the horizon. The ground is a distant patchwork below. Then, three, two, one, whoosh! The first skydiver jumps and recedes like a bottle rocket, a tiny dot against an enveloping blue sky. Eight more follow, sucked into invisibility in seconds.

Brian Caldwell waits. The plane is 4 miles from the drop zone when he finally waddles toward the door. With his goggles, helmet, and webbed black and blue jumpsuit, he looks like a cross between a superhero and a penguin. He smiles, rocks three times, and leaps out the door.

For a moment, with his hands across his torso, he plunges. Then he stretches out his arms like the wings of a giant bird and begins to rise.

Over the next four minutes, before he opens his parachute, Caldwell is in flight, carving giant parabolas across the sky. He descends as if he's surfing a wave headfirst. His arms and shoulders steer his course, the wind pushing into his body like a rushing river, a modern-day Icarus in flight.

``The sky is an invisible ski slope," he says. ``You can go wherever you want."

Welcome to the latest craze to hit the skydiving community. It's called wingsuit diving, and Caldwell is among the first in New England to master this distant edge of an already extreme sport.

For at least 1,500 years of recorded history, people have been leaping off tall objects with wooden wings and dreams of flight. Gravity has always won.

But now, suddenly, they are sliding to earth on the back of the wind, covering as much as 13 horizontal miles over four and five minutes of flight.

``It's complete joy, complete freedom," said Jari Kuosma, president and owner of Birdman Inc. and the creator of the modern wingsuit. ``There is absolutely nobody telling you what to do. It's like flying in your dreams, like Superman."

A giant leap forward in wingsuit technology made in the mid-1990s is drawing thousands into the sport, and most are living to tell about it.

In 1999 in Finland, Kuosma stitched together the prototype of what would be the first mass-manufactured wingsuit. He borrowed a car and drove around Europe selling his suits at skydiving jump sites. He was kicked out of more than a few and called crazy by skydiving purists. But eventually his suits began to find a niche.

Slowly, the sport has spread, and in the past few years it has found its way to Massachusetts. There are about 3,000 birdmen worldwide, Kuosma said, perhaps two dozen in New England, a fraction of the 35,000 active skydivers in the United States.

The sport is rapidly evolving. The launch Caldwell made from the plane over Pepperell last week, for instance, is something with which he is still experimenting. By leaping out the cargo door, then raising his arms and spreading his legs, he can elevate, rising 200 feet above the plane. With a video camera mounted on his helmet, Caldwell records each jump and later studies his flight to learn how to position his body to glide more efficiently.

He flies belly down, arms outstretched like Superman. By dipping his right shoulder, he accelerates forward and turns right. If he raises his right ankle he will slow and turn left. Bend at the knee, and his forward speed slows, while his angle of descent increases. To gain altitude, Caldwell tucks his arms into his body and dives, picking up speed as he plunges to earth. Then he spreads his wings and shoots back up, buoyed by the resistance.

``It feels like you're being gently lifted from your wrist and shoulders," Caldwell said of flight. ``The sound can be anything from the regular wind whistle of free fall to a gentle flapping breeze."

Most people fall at about 120 miles per hour when they skydive. With his arms spread, Caldwell has measured his rate of descent as slow as 44 miles per hour and his forward speed at more than 100 miles per hour. All the while he has tremendous control over his direction.

``It's the most peaceful, most exhilarating feeling in the world," he said.

``Nothing compares."

At 29, Caldwell is typical of birdmen, in that he has long been an adrenaline junkie. Born in Hudson, N.H., he is an industrial machine technician by trade and an adventurer by inclination. He has tried scuba diving, rock climbing, and snow boarding.

But the first time he saw a wingsuit, his interest in everything else drifted away. He was skydiving when he happened to share a plane with a birdman. They left the plane just a few moments apart. Caldwell fell like a stone. The birdman spread his wings and flew.

``From that moment on, I just knew," Caldwell said. ``I had to fly."

The urge is nothing new. In the sixth century , the Chinese were trying to fly with large kites attached to their bodies, said Michael Abrams, author of ``Birdmen, Batmen, and Skyflyers: Wingsuits and the Pioneers Who Flew in Them, Fell in Them, and Perfected Them ."

In the ninth century, Turkish adventurers were leaping off towers and mosques with cloaks and manmade feathered wings.

In the 16th century, Leonardo da Vinci fiddled with designs for flight in his studio in Italy.

``There have been attempts in pretty much every century," Abrams said.

``I think it's just something inside of people, and it's there from when we're little kids."

It wasn't until the 1930s, when these would-be fliers were able to leap from airplanes, that their risks were met with some success. Scores of Batmen began leaping from planes with parachutes and giant ribbed wings. The fatality rate was tremendous, but with the wings providing wind resistance, a few experienced something close to flight.

A turning point came in the 1970s, when parachutes evolved from the simple, round models of the World War II era to rectangular, double-layered airfoils. The design change enabled people to not just float down, but actually fly forward.

Then in the mid-1990s, in one of the great ``ah, ha" moments of birdman history, a Frenchman designed an airfoil into the webbing of his jumpsuit. The airfoil created lift, and the modern birdman was born.

``For hundreds of years, most of these people who tried to fly were just crazy," Abrams said. ``Then, suddenly, in the past five years there are thousands of people flying in wingsuits, and they're not dying very often.

``A new age of personal flight has really just begun."

In the seven years since Kuosma began manufacturing his birdman suits, about a dozen people have died, and several competitors have cropped up with slightly different designs. Wings have grown larger, the airfoils more efficient, material more aerodynamic. The result is that birdmen and women are flying farther and longer.

The next great challenge: the landing. The birdman's holy grail is to set down without a parachute.

At first glance, the idea seems impossible. While the wingsuit can slow down a descent to about 40 miles per hour, flying horizontally is possible only for brief moments.

To increase that ability, more speed is needed, so birdmen have begun strapping small jet engines to their legs to propel them forward.

Until that is perfected, daredevils have begun experimenting by trying to land on the downward slope of mountainsides. The spectacle is terrifying, but the goal, many say, is within reach.

``It will happen in the next five to seven years," Caldwell predicted.

And will he be among those to try it?

``Someday," he said. ``Why not?"

Douglas Belkin can be reached at dbelkin@globe.com.