Inventor and physicist Thomas Senkel created an Internet sensation with the October 2011 video of his maiden—and only—test flight of a spidery proof-of-concept 16-rotor helicopter dubbed Multicopter 1. Now the maker of the experimental personal aviation craft, the European start-up e-volo, is back with a revised "volocopter" design that adds two more rotors, a serial hybrid drive and long-term plans for going to 100 percent battery power. The new design calls for 1.8-meter, 0.5-kilogram carbon-fiber blades, each paired with a motor. They are arrayed around a hub in two concentric circles over a boxy one- or two-person cockpit. After awarding the volocopter concept a Lindbergh Prize for Innovation in April, Yolanka Wulff, executive director of The Charles A. and Anne Morrow Lindbergh Foundation, admitted the idea of the multi-blade chopper at first seems "nutty." Looking beyond the novel appearance, however, she says, e-volo's concept excels in safety, energy efficiency and simplicity, which were the bases of the prize. All three attributes arrive thanks largely to evolo's removal of classic helicopter elements. First, the energy-robbing high-mass main rotor, transmission, tail boom and tail rotor are gone. The enormous blades over a normal chopper's cabin create lift, but their mass creates a high degree of stress and wear on the craft. And the small tail rotor, perched vertically out on a boom behind the cabin, keeps the helicopter's body from spinning in the opposite direction as the main blades, but it also eats up about 30 percent of a helicopter's power. The volocopter's multiple rotor blades individually would not create the torque that a single large rotor produces, and they offer redundancy for safety. Hypothetically, the volocopter could fly with a few as 12 functioning rotors, as long as those rotors were not all clustered together on one side, says Senkel, the aircraft's co-inventor and e-volo's lead construction engineer. Without the iconic two-prop configuration, the craft would be lighter, making it more fuel efficient and reducing the physical complexity of delivering power to the top and rear blades from a single engine. Nor would the volocopter need an energy-hungry transmission. In fact, "there will be no mechanical connection between the gas engine and the blades," Senkel says. That means fewer points of energy loss and more redundancy for safety. E-volo's design eliminates the dependence on a single source of power to the blades. As a serial-hybrid vehicle, the volocopter would have a gas-fueled engine, in this case an engine capable of generating 50- to 75 kilowatts, typical of ultralight aircraft. Rather than mechanically drive the rotors, the engine would generate power for electric motors as well as charge onboard lithium batteries. Should it fail, the batteries are expected to provide enough backup power so the craft could make a controlled landing. Whereas helicopters navigate by changing the pitch of the main and tail rotor blades, the volocopter's maneuverability will depend on changing the speed of individual rotors. Although more complex, it is more precise in principle to control a craft using three to six redundant microcontrollers (in case one or more fails) interpreting instructions from a pilot using a game console–like joystick—instead of rudder pedals, a control stick and a throttle. Wulff's first impression about the volocopter's design is not uncommon. E-volo's computer-animated promotional videos of a gleaming white, carbon-fiber and fiberglass craft beneath a thatch of blades recall the many-winged would-be flying machines of the late 19th century. This point is not lost on Senkel. "I understand these skeptical opinions," he says. "The design concept looks like a blender. But we really are making a safe flying machine." That would be progress in itself. Multicopter 1 looked like something from an especially iffy episode of MacGyver, complete with landing gear that involved a silver yoga ball. Senkel rode seated amid all those rotors powered only by lithium batteries. Multicopter 1 generated an average of 20 kilowatts for hovering and was aloft for just a few minutes. There's a reason why the experimental craft flew briefly and only once.Senkel describes that first craft as "glued and screwed together." Seated on the same platform as the spinning blades, he says, "I was aware of the fact that I will be dead, maybe. Besides, we showed that the concept works. What do we win if we fly it twice?" he asks rhetorically. Other than putting the pilot safely below the blades, the revised volocopter design would operate largely the same as the initial prototype. The design calls for three to six redundant accelerometers and gyroscopes to measure the volocopter's position and orientation, creating a feedback loop that gives the craft stability and makes it easier to fly, Senkel says. The volocopter's revised prototype under construction could debut as soon as next spring. The first production models, available in perhaps three years, are expected to fly for at least an hour at speeds exceeding 100 kilometers per hour and a minimum altitude of about 2,000 meters, still far shy of standard helicopter's normal operating altitude of about 3,000 meters. "This could change our lives, but I don't expect anything like that for 10 years," Senkel adds. Given that most of the technology needed to build the volocopter is already available, "this idea is fairly easy to realize," says Carl Kühn, managing director of e-volo partner Smoto GmbH, a company that integrates electric drive systems and related components. Like Senkel, Kühn has modest short-term expectations despite his repeated emphasis on the standard nature of the technology involved. "I guess that e-volo will have [a prototype] aircraft in three years that can do the job—that it will lift one or two persons from one point to another," he says. The biggest immediate limitations appear to be regulatory. For instance, European aviation regulators consider any electrical system greater than 60 volts to be high voltage and regulate such systems more aggressively, Kühn says. As a result, the volocopter will operate below that threshold. The craft will also need to weigh no more than 450 kilograms to remain in the ultralight category, which is likewise subject to fewer government aviation regulations, according to Senkel. The Lindbergh Foundation's Wulff says the organization's judges felt e-volo had "a greater than 50 percent chance of succeeding, or they wouldn't have given them the innovation award." Asked if she would line up to fly one someday, she says, "I sure would. It looks very compelling to me." Follow Scientific American on Twitter @SciAm and @SciamBlogs. Visit ScientificAmerican.com for the latest in science, health and technology news. © 2012 ScientificAmerican.com. All rights reserved.