Muscle-Powered Helicopter Aims High

Gamera, the University of Maryland’s human-powered helicopter.

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The helicopter is notoriously difficult to fly. With the primary rotor trying to spin the fuselage one way and a tail rotor pushing the other, the pilot has a lot to control. But however tough a CH-53E Super Stallion may be to handle, its pilot doesn't haven't to sweat for power.

Not so for the pilot of a new aircraft out of the University of Maryland's Alfred Gessow Rotorcraft Center. Gamera, as the vehicle is called, flies on human power. In May of this year a student athlete, Judy Wexler, pumping legs and arms, powered the craft's four rotors and managed to raise it just off the ground for a good 4.2 seconds.

Judy Wexler in the cockpit of the Gamera, made the longest human-powered flight by a female U.S. pilot hovering for 11.4 seconds.

That's long enough to set a record for a human-powered helicopter flight, but not long enough to win the Sikorsky Prize. The prize is to be awarded to the first group to fly on human power for 60 seconds, at a height of three meters without leaving a 10-m square. It's been up for grabs for 30 years now. The Maryland group's May flight was only meant to be a step toward winning the prize. Their next flight, which could take place this spring, is aimed at getting the craft airborne for a full minute at an altitude of a good four or five feet. With the data from that flight, they may finally be ready to fly Gamera high enough to win the $250,000 prize.

The Weight Challenge

Gamera is built of four trusses, each with a rotor. Legs and arms both drive the rotors to keep vibrations down, not for the extra power. With arms free, too much force is applied to the structure to stabilize the pilot.

To increase height and airtime, research at the center proceeds on three fronts: reducing weight of the craft, increasing efficiency of the rotor design, and finding a human of just the right size and strength. Decreasing weight is simple enough. Already the entire craft is made of composites and foam. No extra weight is put into durability. "If we can do only one shot, that's fine," says Inderjit Chopra, director of the center. "We're not looking to reuse the same thing over and over again." But since the helicopter is what Chopra calls a "built up structure," there's plenty of fat to trim. And advancing rotor design is merely a matter of experimenting with airfoils, rpm, and length, as it would be on any helicopter, whatever its power.

Team working on the lightweight rotor mechanism.

The Human Factor

The real key to a human-powered helicopter is the human.

"The starting point is really the propulsion system," says Chopra. "You start with the person, and then build from there." Chopra had once assumed that pilots after Wexler would have to be similarly light and similarly powerful, and that winning the prize would be a mater of vehicle refinement. But when he consulted with the university's kinesiology department, he found otherwise. To increase flight time, the kinesiolgists said Chopra's power source would have to go up three-quarters of a horsepower for every 6 seconds of airtime.

The resulting human needs to weigh about 130 lbs. Chopra is training several at a time, after learning the hard way. "We were ready—we had this guy, and then he broke his finger. Out of action for 3 months," he says.

With human fragility properly managed, human engineering may get human power to fly a helicopter for a minute—as long as human fallibility doesn't get in the way. "We train them as undergraduates," Chopra says of his student engineers, all human. "Afterward they're gone. After exams they want to go home, enjoy themselves. If someone gave me all the money in the world, I'd hire full-time people."

The calculations for design, weight, and power, are, essentially, in the can. And, with extensive training on a leg and arm exercise machine, several of Chopra's potential pilots have brought their probable air times up from 40-odd seconds to 60-odd seconds. The primary cause for delay is location. Chopra could not find a hanger large enough to house the assembled structure, so he has to rely on campus gyms that serve other needs other than those of human-powered helicopter enthusiasts. When their time slot comes around, the Gamera team has only a few days to get the vehicle together and in the air.

If all stars align, Gamera may soon be a few feet—and a few hundred thousand dollars—closer to them.

Michael Abrams is an independent writer.

The starting point is really the propulsion system. You start with the person, and then build from there.

Inderjit Chopra, director, Alfred Gessow Rotorcraft Center, University of Maryland