University of Maryland team hovers near Sikorsky Prize

A team of students from the University of Maryland is close to a milestone for human-powered rotorcraft flight.

In 1980, the American Helicopter Society (Alexandria, Va.) announced the Igor I. Sikorsky Human Powered Helicopter Competition to encourage just that, development of the world’s first human-powered rotorcraft. In the years since, no one has yet fulfilled the competition’s requirements: controlled flight of at least 60 seconds, reaching an altitude of 3m/9.8 ft and remaining within a 10m/32.8 ft square. But in 2012 a team from the University of Maryland showed signs that the day is near.

On June 21, 2012, in the Reckord Armory on the campus of the University of Maryland in College Park, the university’s Gamera team flew its Gamera II rotorcraft. Piloted by mechanical engineering doctoral candidate Kyle Gluesenkamp, the craft set a new official U.S. record for human-powered rotorcraft flight duration at 49.9 seconds. A refined version of its earlier Gamera I vehicle, designed and built by students in the Clark School of Engineering, Gamera II is 30 percent lighter than the original and is designed for flights of more than 60 seconds — much longer than the 11.4-second world record set by Gamera I and enough to meet the Sikorsky Prize requirement. Gamera II features enhanced rotor design, an improved transmission and a redesigned cockpit. The June 21 flight was verified by the National Aeronautic Assn. (Washington, D.C.) on Aug. 9, 2012, and has been submitted to the Fédération Aéronautique Internationale (Lausanne, Switzerland) for world-record review.

Gamera II features four substantial rotors at the ends of an X-shaped frame made of carbon fiber trusses. The configuration increases vehicle stability yet puts the rotors as close to the ground as possible, increasing ground effect, a “free” increase in lift experienced by wings and rotor blades operating near the ground. The team spent more than a year designing and building a ground-effect test rig and developing empirical models to optimize Gamera II’s rotor design to exploit ground effect. The trusses are a novel concept, with a truss-of-trusses design wherein the most critically loaded members in the airframe truss have been replaced with “micro trusses” that provide unmatched buckling resistance with significant weight savings, says the team.

In August and September the team flew a further refined version of Gamera II. One flight surpassed the Sikorsky competition’s duration requirement, at 65 seconds, and stayed within a 10m/32.8 ft square area, but it did not reach the required altitude. That flight is under review for world-record consideration. Subsequent flights of shorter duration came close to the height requirement; one flight reached 8 ft/2.44m and the other was just short, at 9.4 ft/2.87m.

Although modifications increased its weight by about 6 lb/2.72 kg, the refined airframe’s rotor blades are longer by 700 mm/27.56 inches (with structural arms longer by 1m/3.28 ft). The blades and outboard sections are now made of semisolid foam shell to help maintain airfoil shape during flight. Further, the cockpit now allows more pilot arm flexion to increase the available power. The powertrain has a stiffer chain and modified tensioners that smooth power transfer.