Roberston says sensors on the Atlas show Reichert put out a peak of 1.1 kW of power, decreasing to 600 watts at the end. “The flight took almost everything I had,” Reichert admits. “He put out a hell of a lot of power,” acknowledges Leishman, noting a more typical figure is well below a kilowatt and that Gamera used both leg and arm power to increase its pilot's output.
UMD's biggest challenge, says Gamera team leader Will Staruk, was controlling drift. At very low disk loadings it does not take much to enter vortex ring state, the rotor equivalent of wing stall, Leishman says, and the HPHs drifted on descent. UMD added an rpm-varying electronic control system, “but did not have time to practice at altitude,” says Staruk.
AeroVelo, meanwhile, “changed its control strategy completely,” says Robertson, which had the effect of simplifying the machine and reducing weight—the opposite of what happed with Gamera. Originally, the Atlas had canard control surfaces at the tips of the blades, but these proved “untrimmable for stability and unpredictable to actuate,” he says.
While testing, they noticed how flexible the structure was and how easy it was to tilt the rotors, “like thrust vectoring,” Roberston says. With lightweight control lines connecting the bottom of the bike frame to the bottoms of the rotors, Reichert could lean the bike to pull on a line, bend the structure and tilt a rotor. This fast-reacting system overcame the problem of controlling drift.
Mark Miller, Sikorsky vice president of research and engineering, cites the “very creative way” AeroVelo took advantage of the flexible structure as an example of the “passion, drive and ingenuity” brought out by the competition. “AeroVelo used advanced materials and an inventive structural approach that was all about power-to-weight,” he says.
“Open competitions like this are just another mechanism we have used to ignite innovation in this industry and create an environment that has people taking on really tough problems,” says Chris Van Buiten, director of Sikorsky Innovations. “We've hired great talent directly out of these teams. We like this model for innovation.”
Tap the icon in the digital edition of AW&ST to watch a video of the prize-winning flight, or go to AviationWeek.com/video
Read more about the competition on our ThingsWithWings blog at ow.ly/mROKZ