Two years, several crashes and $700,000 in the making, a lifelike model of a pterosaur has its debut flight at Andrews Air Force Base on Saturday, and the scientists and engineers who built it want you to know this: Nature did it better.

The gawky-looking flying reptile owned the sky during the Age of the Dinosaurs, disappearing about 65 million years ago. And although the human species has since been to the moon and back, getting a 44-pound, radio-controlled replica into the air proved a humbling experience for the world-famous aeronautical engineers and paleontologists who collaborated on the project.

"To make this thing fly was like trying to shoot an arrow with the feathers in front," says Paul MacCready, the project's supervisor, who is best known for his prize-winning exploits with pedal- and solar-powered aircraft.

The giant pterosaur (the p is silent; the word means winged lizard) had an almost flight-defiant shape: long neck, large head and no tail, according to rare fossil remains. Still, it did fly -- for millions of years -- and the Smithsonian Institution's Air and Space Museum thought recreating the biggest beast that ever flew would be a wonderful centerpiece for "On the Wing," its new film about natural and mechanical flight.

The film premieres at the museum next month. And barring rain or too much wind, its $700,000 star is scheduled to make two brief, five-minute flights at Andrews on Saturday -- 9 a.m. and 9:30 a.m. -- to coincide with the Department of Defense Joint Services Open House at the base. Gates open to the public at 8:30 a.m. Sunday is the rain date for the pterosaur's flight.

What the public will see, however, is a crude substitute for the real thing. The contraption flies the way a bird would fly, propelling itself through the air by moving its wings back and forth and up and down and by adjusting to air currents. But with an 18-foot wingspan, MacCready's pterosaur is half the size of the full-scale model his team had hoped to build -- before a filming deadline and technical problems forced them to think smaller. It can't take off by itself and can only descend, not climb. Also, a planned flight on the Mall was scrapped because it needs more runway space and might be knocked off course by competing radio signals.

Even so, without the scientific progress of the past six years there might not have been any mechanical pterosaur. It took the latest developments in light-weight materials, wing-flapping propulsion and robotic control systems to keep the "creature," as it was playfully nicknamed, in the air.

Those who worked on the project say they regard the experience as one of the most exciting and intellectually challenging of their lives. Yet they note respectfully that it took humans years of technological advances just to duplicate a smaller, inferior version of what nature did.

"I think of it as a temperamental, adolescent, overweight actor that can really act," says MacCready, who hopes to build a life-size, 36-foot wingspan model. "It did its job perfectly and deserves an Academy Award -- but it's still a temperamental, adolescent, overweight actor."

The mechanical pterosaur is modeled after the Quetzalcoatlus northropi, the largest flying animal in the planet's history, whose fossils were found in Texas in 1972. Though the term pterosaur is often used interchangeably with another word, pterodactyl, paleantologists gruffly point out that the pterodactyl was another type of pterosaur and just a close relative of the Quetzalcoatlus northropi or QN for short.

By whatever name, however, this newest pterosaur comes nearly full circle from the earliest of human experiments with flight.

Before the Wright brothers successfully applied an engine to a fixed-wing airplane, revolutionizing man-made flight in the process, inventors who envied the birds thought they also had to imitate them. Leonardo Da Vinci was sketching designs for a moveable wing flying machine as early as 1490. Others, furiously flapping their home-made wings, later jumped off towers or attached feathery contraptions to their bicycles in a desperate bid to become airborne.

The scientists who developed the pterosaur "feel a real kinship with Leonardo and the Wright brothers and with the poor slob who jumped off the barn thinking he was going to fly," said Brian Duff, the museum's associate director.

And, like those earlier scientists, the QN team had its embarrassing setbacks.

AeroVironment Inc., the California-based MacCready firm that built the replica, gathered about 30 of the nation's top scientists together two summers ago for a weekend planning session. They agreed the project was feasible. They also, by all accounts, had a ball, engaging in spirited debates about how the creature looked and flew, experimenting with paper and model planes, flapping their arms in serious demonstrations of aeronautical principles.

But when MacCready's staff later moved the QN from the drawing board to the air, keeping it stable turned out to be a bigger problem than anyone had anticipated. There were countless crashes during testing, and the QN had one unfortunate encounter with power lines, resulting in a miniblackout in Simi Valley.

"Our only concern was to get it good enough to film," said Alec Brooks, the project's director. Yet on Dec. 13, with the camera crew due the next month, the MacCready team tried to fly the contraption for the first time after dropping a tail boom used to stabilize the QN on takeoff.

"It went into a rapid climb, then flopped over sideways and started falling like a dead bird," Brooks recalled.

Panic set in, and the team worked over the Christmas holidays. On Jan. 7, "it worked the way it was supposed to," Brooks said. The movie sequences were filmed in Death Valley later that month.

The final version is launched into the air using a tow line. At 500 feet, the launching trolley is disconnected. The QN's autopilot operates the flight, moving the head from side to side like a rudder and twisting and flapping the wings to keep it stable and propel it through the air. Battery-powered motors and an on-board computer take the place of the brain, muscles and ligaments.

Museum officials and MacCready said they will be happy if the QN project gives people even a rough idea of what it must have looked like when one of these creatures flew overhead 70 to 80 million years ago. In this age of confidence in technology, they say, there is much to appreciate about nature.

And if Leonardo gets another plug in the process, so much the better. For as MacCready is fond of saying: "There was nothing wrong with his math, he just didn't have the right materials."