When Leonardo da Vinci first depicted a helicopter or aerial screw in a drawing dating from 1480, the imaginary flying machine was human-powered.
However, since Spanish engineer Juan de la Cierva made the first documented flight of an autogyro near Madrid in 1923, all functional rotorcraft have been powered by lightweight reciprocating (piston) or gas turbine engines, or by reaction drive propulsion systems (i.e. tip jets).
For pilots and passengers of conventional helicopters, the idea of the pilot also providing all the power required for a flight is a radical idea. That could soon change.
On Jan. 25, about 60 aviation enthusiasts, including Canadian Skies Magazine, gathered at an indoor soccer field north of Lester B. Pearson International Airport in Toronto, Ont. to observe the latest test flights of the Canadian AeroVelo team’s Atlas human-powered helicopter, a leading contender in the American Helicopter Society (AHS) International’s AHS Igor I. Sikorsky Human Powered Helicopter (HPH) Competition.
While a record attempt was delayed as the team reviewed control effectiveness, the flight envelope of the Atlas was significantly increased during nine test flights, including flights during which the Atlas remained aloft for about 30 seconds and reached a height of almost five feet (based on the lowest points of the four rotors), with very little lateral drift compared to preliminary flights in late August and early September 2012.
Leading the AeroVelo Atlas team are Todd Reichert and Cameron Robertson, two youthful engineering graduates of the University of Toronto Institute for Aerospace Studies (UTIAS). Reichert is also the lead pilot (and one of three people to have flown the Atlas, along with Calvin Moes and Trefor Evans). The Atlas is not Reichert and Robertson’s first joint aviation venture: the pair also designed, built and, in 2010, successfully flew a human-powered ornithopter, Snowbird, for which they became the youngest people to win Canada’s highest aviation award, the Trans-Canada (McKee) Trophy. (In 2011, this team also broke a college human-powered bicycle speed record, achieving 72.6 miles per hour, or 116.9 kilometres per hour, at a competition in Nevada.)
The Atlas has a maximum dimension of 47.8 metres (157 feet) on a diagonal. According to Robertson, that makes it the second-largest helicopter of any kind ever built (in maximum dimension), and the largest human-powered helicopter ever built (in wing area or max dimension). The truss structure of the Atlas is made of light carbon tube and Vectran liquid-crystal polymer line. In the middle is a Cervelo carbon bike frame, which provides the drive train used to power the four 20.4-metre (66.9-foot) diameter two blade rotors.
The Atlas’s rotor blades have a light tubular spar and a non-linear taper with canards at the blade tips that are linked to controls on the handlebars. The transmission is driven by polymer line that runs from four custom Kevlar wound spoked wheels at the center of each rotor to a take-up reel on the bicycle.
Impressively, the Atlas weighs only 121 pounds (55 kilograms), and requires less power to fly than is needed to operate a cordless drill, toaster or hairdryer!
Even so, the power required for a human-powered helicopter is above the aerobic threshold and can only be sustained for a minute or two. The endurance and altitude require a very large but very light aircraft, and a very powerful pilot, said Robertson. Track cyclists are most appropriate for this flight, as they produce much higher power than endurance cyclists. They can sometimes produce 1,500 Watts (2 horsepower) for less than five seconds. Todd has trained to produce 1,100 Watts for up to 10 seconds, and an average power of over 770 Watts for a minute. The pilot power/weight ratio must be extremely high, such that only a specially trained athlete can be successful.
Robertson added, The controllability issue is also one that must be accounted for from the start – it doesn’t lend itself to a simple add-on solution. Everything has to come together in the right package.
AHS executive director Mike Hirschberg, who observed the recent Atlas test flights near Toronto, explained, The AHS HPH Competition isn’t about creating a practical machine. It is an engineering challenge to the vertical flight technical community. This is a multi-disciplinary project that harnesses technical skills and teamwork to overcome what many have said for three decades was an impossible challenge.
Indeed, since the competition was introduced in 1980, the goal of achieving da Vinci’s original vision has proved elusive, with the prize still unclaimed. To win, a human-powered helicopter must fly for at least 60 seconds and reach an altitude of at least three metres in a hover, with the pilot remaining within the boundaries of a 10-by-10-metre square area.
The inspiration for the AHS prize was the flights of the Gossamer Condor (1977) and Gossamer Albatross (1979), two record-setting human-powered fixed-wing aircraft. However, the rotors of a human-powered helicopter need to overcome the weight of the helicopter, whereas the propellers of a human-powered airplane need to only overcome the drag of the aircraft. As Ben Berry, a team leader on the rival Gamera II XR helicopter being developed by students at the Alfred Gessow Rotorcraft Center at the University of Maryland, described the challenge: Rotorcraft require more power than fixed-wing and humans are poor powerplants.
In 1989, the Da Vinci III /IV developed by a team at the California State Polytechnic University (Cal Poly) became the first human-powered helicopter, flying for a record setting 8.6 seconds and to a height of 8 inches (20 centimetres). As recently as 2009, the unofficial world record for a human-powered helicopter was held by Professor Akira Naito of Nihon University in Japan, with the Yuri 1 achieving an altitude of 20 centimetres and a flight duration of 19.46 seconds.
The AHS contest became more attractive in 2009 when Sikorsky Aircraft made a generous pledge of $250,000 US to be awarded to the team that met the requirements of the competition. In 2011, the University of Maryland fielded the first human-powered helicopter to fly since the 1990s, the Gamera I, which set world records for flight duration at 11.4 seconds.
The University of Maryland team then developed the Gamera II and the Gamera II XR, which now weighs in at just 82 pounds (37 kilograms) and has four 47.2-foot (14.4-metre) diameter rotors. The Gamera II XR has flown for 65 seconds and reached an altitude of more than 9 feet (2.7 metres), but on separate flights in 2012.
Another contender for the prize is the NTS Works Upturn in California, which draws on the experience of the Da Vinci III/IV developed at Cal Poly. The aircraft has flown for 10 seconds and reached a height of about 2 feet (0.6. metre); Cal Poly students are continuing development of the human-powered helicopter as the Upturn II. Unlike the Atlas and Gamera XR, which are both quad rotor designs, the Upturn has a two-blade rotor system with an 85-foot (25.9-metre) diameter, plus two orthogonal 48-foot (14.6-metre) diameter blades with two tip-mounted 6-foot (1.8-metre) propellers.
Although all of the teams have had some success, it’s clear that they still have their work cut out for them. Said Hirschberg, It’s been a third of a century since the competition began. If it were easy, it would have been done by now.