“If this innovative design reaches the commercial market it will dramatically change the way we move about the planet.”
Multiple-overhead-rotor flying machines, which seemingly offered safety in redundancy, were common early on in helicopter development. Louis-Charles and Jacques Breguet’s Gyroplane No. 1 and George de Bothezat’s “Flying Octopus” were notable examples. Once engineers determined that the torque generated by the rotors needed a precise counterbalancing force, however, the more traditional single-rotor-with-tail-rotor design prevailed. Early inventors did discover that pilots could control helicopters by changing the speed of the rotors with a throttle, but the technology to do so wasn’t there. Ratcheting up or cutting back on the throttle acted too slowly to offer good control because the rotor had too much momentum. Furthermore, safety was an issue. As James Chiles explains in his history of the helicopter, The God Machine, “If any lifting rotor fails in flight, a multiple-rotor helicopter will go fatally out of balance unless it has so many main rotors that losing one or two won’t make a difference….No helicopter has flown with so many rotors.”
Until now. The German company e-volo debuted its radical new multicopter design, the VC1, in October 2011 at Karlsrühe, Germany, lifting 10 feet off the ground for 90 seconds. That flight garnered e-volo the Lindbergh Foundation’s Lindbergh Prize for advancements in green aviation. And in July 2012 at EAA AirVenture in Oshkosh the company unveiled its second-generation prototype, the VC2, with 18 rotors, compared to 16 on the VC1. Both prototypes use small battery-powered, fixed-pitch props whose rotational speed is controlled via a joystick. According to e-volo, the VC1 can fly for 20 minutes on current battery technology. Besides being the first electric-powered multicopters to achieve sustained flight without ground assistance, the VC1 and VC2 are noteworthy for the simplicity of their fly-by-wire control system. They do not require the cyclic control, collective control and anti-torque pedals common to most helicopters.
E-volo is touting its multicopter as safer than traditional single-rotor or coaxial helicopters. According to the company, the VC1 can perform a controlled landing even after four of its 16 battery-powered rotors have failed. The planned production version will have a pusher propeller for stable forward flight and a serial hybrid power system to provide sustained flight times of more than one hour, as well as additional batteries in case the range extender fails.
The VC2 has relocated the rotors above the fuselage for improved stability (due to a lower center of gravity), and has added three inflatable balls for landing gear. The company plans to begin an intensive two-year flight test program on the advanced prototype in September, which it hopes will yield a two-seat multicopter with a top speed of 62 mph, ceiling of 6,500 feet, takeoff weight of 1,000 pounds and flight time of one hour. E-volo is also working with the Fédération Aéronautique Internationale to obtain the classification for its new craft, which it calls a “volocopter.” Erik Lindbergh of the Lindbergh Foundation predicts, “If this innovative design reaches the commercial market it will dramatically change the way we move about the planet.”