Build a lightweight helicopter

  • University of Maryland pilot Colin Gore pedals steadily as UMD's craft, Gamera, takes flight. Team member Elizabeth Weiner stands by to coach, her pants taped at 30 cm intervals to gauge the air-craft's height.
  • For a human-powered helicopter to create enough lift to fly, the blades have to be huge. Here, Reichert's team prep their machine, Atlas, for a flight attempt in a soccer center near Toronto.
  • Canadians Todd Reichert and Cameron Robertson launched their own human-powered helicopter team in 2012 to capture the elusive Sikorsky Prize. But an American crew might just nab the purse first.
Date:23 May 2013 Tags:, ,

Build a lightweight helicopter, pedal hard, and hover for 60 seconds. Sounds easy? Not so fast. No one’s claimed this prize in 32 years. But two teams are very, very close. By Jeff Wise.

A huge, spindly, spider-like contraption arches over the AstroTurf of an indoor soccer stadium near Toronto, its X-shaped trellis of carbon-fibre tubing so diaphanous that it’s hard to make out. The end of each truss arm terminates in a pair of shiny, fragile rotor blades made of foam, balsa and Mylar.

From the centre of this precarious assemblage, nearly 40 metres across, hangs a skein of slender cords that supports a dangling, wheel-less bicycle frame. If this all seems rickety, it becomes doubly so when wiry 31-year-old Todd Reichert clambers up and settles on to the bike seat: the double arch above him sags and sways like a hammock as it accepts his weight.

REICHERT SHOUTS: “Ready… go!” Four student volunteers who had been holding the rotor blades steady run towards the centre of the craft as Reichert starts pedalling, and the blades begin to spin in great slow arcs. His face is a mask of concentration, his mouth set in a grimace as his legs pump faster and faster. The only sound is the periodic squeak of a bearing.

The students clustered around him seem too rapt to breathe. The craft is so fragile it looks as if it could collapse at any moment. And that’s by design: the 54 kg flying machine, dubbed Atlas, contains just enough structure to lift Reichert’s 75 kilograms, and scarcely a gram more. As Reichert explains: “There’s a thousand joints in here, and if a single one fails, it all falls apart.”

Reichert continues to pedal, settling into a measured rhythm. As if by sheer force of will, one of the rotors shudders and begins to rise, then another. The aircraft subtly tilts, as though straining for the sky. Then a student notices that one rotor is swinging dangerously close to the ground. “Dead stop!” she calls.

As the long rotors spool down, you can almost hear the collective sigh of relief. The craft didn’t get airborne, but it didn’t break, either. Soon the students will have the trim perfect. Their dream is alive.

ATLAS is Reichert’s entry in the international battle for the $250 000 (about R2,3 million) Sikorsky Prize, which will go to the world’s first minimally capable human-powered helicopter. Established in 1980 and long dormant, the prize has become within the past year the most hotly contested challenge in the field of human-powered aircraft.

In an age when an ever-increasing share of aviation is being taken over by robots, excitement is brewing once more over that most ancient of fantastical dreams: to fly using nothing more than human ingenuity and muscle. That powerful urge may be deep-wired, but it wasn’t until recently that the first truly functional human-powered fixed-wing craft took to the air.

In 1977, pilot Bryan Allen flew the Gossamer Condor in a figure-eight pattern around pylons 800 m apart at a course in California, netting American aeronautical engineer Paul MacCready the £50 000 Kremer Prize. Two years later, MacCready upstaged himself with the Gossamer Albatross, which flew 35 km across the English Channel in three hours. Then, in 1988, a team from MIT set the world distance record by flying a craft, the Daedalus, 113 km between the Greek islands of Crete and Santorini in just four hours.

The requirements for the Sikorsky Prize are relatively modest. To win, a humanpowered rotary craft must rise clear of the ground for at least 60 seconds and achieve a height of 9,8 feet (about 3 m). The centre of the craft, meanwhile, has to remain within an area of 33 square feet (3,06 m²).

In the 32 years since the prize was established, only five human-powered helicopters have even left the ground. The first, in 1989, hovered for 8,6 seconds; the second, in 1994, managed to stay airborne for just shy of 20 seconds. Then, in 2011, students at the University of Maryland launched a project called Team Gamera that by 2012 regularly achieved flights of 50 seconds and more. These successes inspired Upturn, a project currently under development at the California Polytechnic State University, and Reichert’s Canadian bid.

Reichert has a knack for tackling seemingly impossible tasks. In 2010, as a doctoral candidate in aeronautical engineering at the University of Toronto, he built and piloted the world’s first continuously flying human-powered ornithopter, an aircraft that propels itself by flapping its wings. The following year, he broke the college land speed record by hitting 116,8 km/h in an enclosed bicycle he designed and built. Now, the newly minted PhD and his 26-year- old partner, structural engineer Cameron Robertson, are hoping that the Sikorsky Prize will help finance projects for their fledgling engineering company, AeroVelo.

A nationally ranked speed-skater, Reichert is intense, with pale blue eyes, a scrubby beard and close-cropped dark hair. He began sketching the Atlas helicopter in late 2011 and spent the winter drafting a detailed design. Last year, he used Kickstarter to raise R323 000 for the project. Later, student volunteers helped assemble the craft in an old barn.

What makes Atlas unique is that it has a mechanism that allows the pilot to steer the aircraft by changing the pitch of steerable winglets at the tip of each rotor blade. To keep the design secret, the Canadians have kept off Twitter and have allowed no photographs on the Internet. “No one’s ever built a control system for a human-powered helicopter before,” Reichert says.

On the first day of my visit, Reichert manages to get only part of his craft airborne. That’s no small feat, but time is running short. Right now, Reichert’s biggest obstacle isn’t physics. It’s the University of Maryland team, who are on the verge of taking the prize. They have more volunteers and more money, and they’ve been perfecting their craft for a lot longer. If they succeed – and at the moment it seems very possible they will – all of Reichert’s work will have been in vain. As the crew hurries to prepare Atlas for its next flight, the media co-ordinator paces up and down the AstroTurf, compulsively checking the University of Maryland team’s Twitter feed and muttering darkly.

 

At that exact moment, 650 km km south, on the outskirts of Washington, DC, William Staruk, student team leader for the University of Maryland, is putting his group through similar preparations in anindoor athletic facility – this one a wood-floored gymnasium with a rubberised track around its perimeter.

As the circulating stream of recreational walkers looks on, Staruk consults some of the dozen or so undergrads and graduate students who’ve assembled for today’s run at the record book. The most recent iteration of their craft, named Gamera II XR, looks in broad outline very much like Atlas: four carbon-fibre trusses connect four double-bladed rotors to a centrally suspended pilot’s seat. The craft’s one departure from severe utilitarianism is a stuffed turtle mascot strapped to the front of the pilot’s cage.

Slightly smaller than Atlas, Gamera is also lighter and much better tested. Maryland students have been working on versions of the craft since 2008 and have already logged flight times in excess of 70 seconds and altitudes of more than 2,1 metres.

Staruk is more subdued than Reichert – he’s an engineer, not an athlete. The 24-year-old Massachusetts native moves around the gymnasium with a methodical sense of purpose, checking this, consulting on that. He and his teammates are not after personal glory or wealth – the school will get any prize money. “This is a scholarly effort for us,” Staruk says.

As the dozen or so students in polo shirts move about their tasks, a pop song ooh-ooh-oohs over the PA. The pace is noticeably more measured than at the soccer field in Toronto. Since Gamera is an academic undertaking, the team members have been very open about their efforts, tweeting and posting videos of milestones.

They express reservations about the Atlas team’s secrecy but remain confident in their advantage. “They’ve got to figure out the kind of issues that we’ve been tweaking for the past two years,” says Darryll Pines, the school’s dean of engineering.

Most of these issues stem from the fundamental inefficiency of helicopters. “A helicopter has to generate thrust straight up, so you have to pull your entire weight,” Staruk says. “It takes three to four times more power to fly a human-powered helicopter than a human-powered airplane.”

The basic parameters of both projects are simple. When it comes to generating thrust, there are two options: move a little bit of air a lot, as a jet engine does, or move a lot of air a little bit, the way the long, thin wings of a glider do. The physics determine that the latter is much more efficient, which is why both Atlas and Gamera are so enormous: The only way they can get airborne with such a tiny amount of power is by pushing down on a very large volume of air.

The challenge is making such a huge system light enough to get airborne under the extremely low power that a human being can generate – about half a horsepower, or 0,37 kilowatts. The difficulty of this proposition is one reason the Sikorsky Prize has gone unclaimed for so long.

But scientific advances have made the challenge less daunting. “Materials and construction technology have come a long way,” says aeronautical engineering professor Inderjit Chopra, Gamera’s faculty adviser. Cheap, fast computing has made it possible to model complicated aerodynamic flows and to analyse on-the-fly data from wireless sensors. And carbon fibre and other materials allow structures to be much bigger, lighter and stronger than ever.

Three years ago, as Staruk and his UMD team began building their first iteration of Gamera, they quickly encountered the boundaries of current aerodynamic understanding. To rise off the ground, human-powered helicopters are helped by a phenomenon called ground effect, in which wings close to the surface of the earth experience a sharp reduction in drag. It’s very helpful in getting off the ground but difficult to model. “Ground effect is a very complex phenomenon; there are all sorts of vortices,” Chopra says. “You can only validate experimentally. There isn’t much theory.”

It turns out that even in an age of massive data crunching, then, there is no substitute for human ingenuity, patience and judgment. Atlas and Gamera bear the marks of their creators’ design decisions. Gamera is pedalled with feet and hands so the pilot can deliver power steadily, not just on the downstroke of the pedals. Atlas has only foot pedals, leaving the pilot free to control the steerable winglets.

That may ultimately give Atlas the edge. But Gamera has advantages, too. The University of Maryland has committed some R1,8 million to the project, Pines says. Then there is the vast pool of potential power sources in the university community. “We have five pilots now – four undergraduates and one grad student,” Staruk says. The Gamera team can pick or choose a powerplant based on the needs of the moment. Last year, the students increased the span of the rotors, which reduced the maximum pilot weight and forced them to bench two pilots.

“The coolest thing for me about taking part in this project,” Gamera pilot Colin Gore says, “is the knowledge that I was only the fourth person to lift off vertically from the surface of the Earth under my own power. So even on a bad day, you have to step back and get some perspective and say, hey, this is pretty cool!”

Back in Toronto, the Atlas team manage to finish tweaking and trimming the craft, and Reichert knocks off a pre-flight test, cranking the rotors for a minute to make sure that everything is in balance. A few more adjustments, and it’s time for a real flight – and not a moment too soon. Reichert rented the stadium until 5 pm, and time is slipping away.

At 4:30 pm, Reichert climbs into the Atlas frame. The eight blades begin to spin. The rotors rise briefly above the artificial grass, but the trim is still not right, and after a few seconds the machine settles back down. If the Canadians haven’t achieved victory, at least their fragile craft has once again escaped damage.

Meanwhile, down in Maryland, things are just getting started. The school year began the day before, and the undergraduate volunteers weren’t able to show up until after lunchtime. But as evening settles in, the athletic centre is abuzz with activity. At last, the Gamera is ready to fly. A single student stands next to the pilot to offer advice and provide feedback; four others hold each rotor tip.

A gong rings. “You’re clean; go!” Staruk calls out. The four students steadying the rotors let go and run to the periphery of the room to watch with the other students and faculty advisers. The blades spin, and within seconds Gamera rises to head height.

A succession of fresh pilots achieves a string of flights that edges the Marylanders closer to their goal. On hand is an observer from the National Aeronautic Association, the US body designated to certify the record attempt. For each flight, he eyeballs the craft’s height in comparison with a mark on the far wall set about 3 m above the floor. He’s also checking video footage taken from multiple angles and monitoring sonar altimeters mounted on each landing skid.

But there’s a problem. Each time the pilots gradually reduce their pedalling power to slowly bring Gamera in for a landing, the craft starts to slide sideways. “We’re not entirely sure what’s causing it,” Staruk says, “but it could have to do with the fact that it’s descending into the turbulence created by its rotor blades.”

When the students designed Gamera, staying within the 3,06 m² box had seemed such a trivial part of the challenge that they didn’t bother to include any steering mechanism. Now it looks as though that omission could derail their effort. At 7 pm, Gamera achieves a best-ever altitude of 2,59 m and manages to descend without leaving the prescribed box. The Sikorsky Prize seems poised to fall. And then, at 9 pm, disaster: a hard landing snaps a truss. Gamera is grounded. The next day, the team members furiously make repairs, and the day after that, a student pilot takes the copter to a height of 2,865 m, just centimetres away from the prize’s altitude requirement. But control remains problematic. On the way down, the machine slips sideways faster than ever before and lands hard, shattering another truss arm. No one is hurt, but the project is put on hold until the team can figure out how to control Gamera.

Up in Toronto, Reichert finally makes a free flight that lasts 15 seconds and then suspends testing. He and Robertson need to prepare for an upcoming human-powered speed trial in Nevada, followed by an ornithopter-building project with the MythBusters.

Neither team is disheartened by its failure to end the Sikorsky Prize’s 32-year drought. If anything, the excitement has been intensified by the unexpectedly prolonged drama. And so, in hours snatched from jobs and school and other projects, the teams struggle on, devising new solutions, scheduling flight tests, figuring out what works and what doesn’t.

They know that the others could snatch the prize at any moment and lay the decades-old quest to rest. For the victor, success will mean worldwide headlines; for the also-ran, the scrap heap. It’s all up for grabs.