TORONTO—Ever since the Wright brothers took flight in 1903, feats of aviation have come fast and furious—from Charles Lindbergh's trans-Atlantic flight in 1927 to the first, round-the-world, nonstop balloon voyage in 1999.

But there is at least one big milestone still out there: In 1980, the American Helicopter Society International created a $25,000 prize for the first aviator to stay airborne for 60 seconds, reach an altitude of more than 10 feet, and hover without drifting more than 1,076 square feet—all in a machine powered by nothing other than the human body.


The prize grew to $250,000 after Sikorsky Aircraft Corp., a helicopter division of United Technologies Corp. , took it under its corporate wings. Now, two teams, one American and one Canadian, are getting tantalizingly close, after battling it out for years.

This weekend, engineering students from the University of Maryland will conduct flight trials for their Gamera II XR aircraft—a contraption with four giant blades that twirl just below a recumbent-style pedal bike. In past sessions, it hovered airborne for 65.5 seconds. But it got only about 9 feet off the ground, falling short of the prize.

Meanwhile, archrivals in Canada—a pair of former engineering students from the University of Toronto—are nipping at the Americans' heels. They have built their own machine, the "Atlas," that has made it as high as about 10 feet and stayed airborne 47 seconds.

A History of Helicopters

The idea of vertical flight can be traced back to China in approximately 400 B.C., when feathers attached to the end of a stick were rapidly spun between hands and cast into the air. See how much has changed since then.

A series of recent crashes have them sidelined for the next month. But they believe the Maryland team's bird has reached its physical limits. Their own device, they say, has engineering advantages that will eventually get it into the record books.

The Canadian inventors built their pedal system more like a conventional bike, which a pilot can pedal standing up, for more power. They are also counting on another advantage: their pilot currently holds a land-speed title for biking.

The Maryland team points to its own engineering innovation to boost power. It built in a crank that the pilot spins by hand, as he pedals furiously with his feet.

"Maryland says their secret weapon is the hand crank, but the math that we've done finds that doesn't overcome the advantage of an upright bike," says Cameron Robertson, vice president of structural design for Aerovelo Inc., the company he and his partner, Todd Reichert, set up to win the prize. The two have recruited 25 family, friends and interns to build the copter.

Italian artist and inventor Leonardo da Vinci first suggested human-powered helicopter flight with his doodles of an "aerial screw" in 1483.

Mike Hirschberg, executive director of the American Helicopter Society, a nonprofit group aimed at advancing vertical flight technology, said the organization was inspired by the Kremer Prize, promised to the first human-powered airplane that could navigate a figure eight between two markers a half-mile apart. Paul MacCready, an inventor from New Haven, Conn., won that in 1977 with a 70-pound craft put together with Mylar, piano wire, aluminum tubing and lots of tape.

Da Vinci's aerial screw.

"It's sort of like climbing Mount Everest," says Mr. Hirschberg. "It's to prove it can be done."

The Sikorsky Prize has drawn inventors from Brazil to Nigeria over the years, with more than 30 known attempts. Most didn't get off the ground because of design issues, fabrication problems or a lack of funding.

The first team to make real progress was a group of students from California Polytechnic State University, whose "Da Vinci III" whirlybird flew for about eight seconds in December 1989. Shortly afterward, the "Yuri I," constructed by students at Nihon University in Japan, made a crucial discovery: They found they could stay aloft for longer if the helicopter's blades were as close to the ground as possible. They managed to fly for nearly 20 seconds in December 1993, a world record that stood for years.

Without a further breakthrough, the Sikorsky Prize started to look unwinnable. That was until a University of Maryland professor challenged his engineering students to work out whether winning the prize was even theoretically possible.

They determined that it was and began to kick around the idea of actually building a copter to prove it. The university ponied up funding, and the group grew to about 50 undergrads and graduate students over the years. They recruit pilots on campus, at one point with a flier that asked, "Are you small but mighty?"

The team has built a few versions of their helicopter, named after the Gamera, a fire-breathing flying turtle and monster contemporary of Godzilla. It is also a nod to the school's mascot, the Terrapin.

Gamera I's first flight in May 2011 lifted off the ground for about four seconds. Two months later, it was flying 11 seconds. Last July, the Gamera II smashed the Yuri I's record for a human-powered helicopter—staying airborne for nearly 50 seconds.

"Someone bought us a round of drinks during happy hour at the bar that day," says Will Staruk, a graduate student and the team's project manager.

When Messrs. Robertson and Reichert, classmates at the University of Toronto, first heard about the Gamera's initial attempts back in 2011, they decided they would give the Sikorsky Prize a shot as well.

As part of a graduate project a year earlier, the two built the world's first human-powered ornithopter—a plane that flaps its wings—and flew it nearly 500 feet. The pair raised enough money to fund their own rapid successes, nearly matching the Gamera's flights inside an indoor soccer field near Toronto, Mr. Robertson says. The team believes its pedal system—essentially a modified road bike—and its speedy pilot give it an advantage.

One of the biggest challenges is the requirement to keep from drifting more than 1,076 square feet. Both sides are keeping secret the technology they say will help them do that.

Toronto's team isn't allowing outsiders to watch test flights. The University of Maryland, however, is inviting the public to watch its latest attempt this weekend. They have been testing the Gamera II XR—its rotors are slightly bigger than its predecessor—for weeks in a sports complex in Landover, Md.

"The Toronto team is very impressive," said Mr. Staruk. "But we'll see who crosses the finish line first."

Write to David George-Cosh at