When Aerospace giants like Boeing and Airbus reveal some ambitious concept for the future of urban aerial transport, most showcase electrically powered variations on multicopters and hybrid aircraft, sketched out with familiar components like rotors and wings.
But the Russian engineers have another idea entirely. Known as a cyclogiro, cyclorotor, cyclocopter, or as some have called it an “egg-beater wing,” this aerial machine is the most exotic and ambitious vision yet.
A cyclocopter is driven by cylindrical, rotating wings, each with many small paddles or winglets. The direction of thrust can be changed rapidly by altering the angle of the winglets. The cyclocopter combines vertical take-off and landing with efficient forward flight and good maneuverability. At least, in theory.
Russia says its exotic air vehicle will beat anything the West, but many of the nation’s military boasts turn out to be vaporware, so could this crazy-looking contraption actually fly?
Russia’s Advanced Research Foundation, a military research organization analogous to the U.S. defense research firm DARPA, carried out a year-long project to find the best configuration to carry 220 to 2,200 pounds, including passengers. They concluded a cyclocopter gives the best aerodynamic performance, so now they’re building one—and they’re not alone.
It’s an idea that traces back more than a century into aviation history and is finding a second life with engineers around the world.
A Troubled Past
The first cyclocopter was built by Russian engineer E. P. Sverchkov in 1909. The challenge is getting airflow over the wing. Birds do it by moving the whole wing , and so does a cyclocopter, but the movement is in a circular pattern, which is mechanically simpler than flapping up and down.
As with many designs in those heady days of homemade flying machines, it failed to get off the ground. Other attempts at cyclocopters in the 1920s also remained earthbound, mainly because the difficulty of building the paddle arrangement.
“There is a large rotating structure which has to be carefully designed to be strong enough to handle the large centrifugal loads, and light enough to be used on a flying vehicle,” says aerospace engineer Moble Benedict of Texas A&M.
When liftoff was achieved in the 1930s, another problem emerged: The design is not stable. A real cyclocopter requires automatic flight controls that did not exist at the time, and so these machines remained on the drawing board as airplanes, autogyros, and helicopters soared high. By the 2000s though, Benedict and his colleagues were taking another look at “cycloidal propulsion”—not for manned flying machines but for something on a much smaller scale.
A helicopter’s rotor blades work well for lifting something big enough to carry humans. But if you were to scale them down to an insect’s size, Benedict says, they’re much less efficient because at this scale, more lift is gained from stirring air into vortices than from the flow over the airfoil, and cyclocopters are better at this.
Small helicopter at certainly feasible, like the palm-sized PD-100 Black Hornet recently acquired by U.S. forces, but “at small scale, cyclocopters can take advantage of unsteady aerodynamics and leading-edge vortices similar to what is produced on insect wings,” Benedict says.
To demonstrate, in 2016 his team flew the smallest cyclocopter ever, weighing just one ounce.
Cyclocopters possess other advantages, he says, such as better maneuverability than helicopters and a better ability to handle gusts, an essential quality for tiny aircraft buffeted by the wind. They are significantly quieter than multicopters, too. Once the technology matures, he says, cyclocopter drones are likely to be faster, more agile, and stealthier than their cousins.
They may also work on larger scales. Benedict’s team has a five-year grant under a project sponsored by the Army, Navy, and NASA’s Revolutionary Vertical Lift program to scale up cyclocopters. They recently demonstrated a 17-pound cyclocopter and are looking at larger vehicles, but two big challenges remain.
“One fundamental issue to overcome is keeping the weight of the cycloidal rotors down because weight grows very quickly with size,” Benedict says. “The other issue is designing blades with high bending and torsional stiffness-to-weight ratio at larger scales.”
The Flight of D-Dalus
David Wills was well aware of the problem of material strength. He describes a film of a 1930s cyclocopter made of wood and canvas which thrashed itself to pieces before it reached takeoff speed. However, modern carbon fiber laminates offered a solution
Wills was CEO of IAT21, an Austrian start-up developing a passenger-carrying cyclocopter called D-Dalus in the early 2000s. IAT21 conquered several technical issues, including patenting extremely low friction bearings and a manufacturing technique to make the blades light and strong. Wills has retired from IAT21 and no longer speaks for the company, but he believes that passenger cyclocopters will one day become commonplace—if they can get some investment attention.
Thrust-to-weight ratio and flight control were major issues for D-Dalus. Carbon fiber laminated materials helped bring the weight down, but finding a suitable engine was not easy.
“We were aware of ideal engines that would have offered excellent power to weight, but these were either prohibitively expensive or under exclusive control of classified defense projects,” says Wills.
As with early cyclocopters, when takeoff was achieved, maintaining stability was virtually impossible. “For the initial launch phase of the craft when it escapes ground-effects, the response to myriad thrusts, gusts and reflections places exceptional demands upon the flight control software," says Wills.
Willis says a modern version could have flight control built around a neural network, which could be trained to handle the complex flight conditions. Building such a system would be a big project for a small company, but fairly routine for any of the large aerospace players. Or, perhaps, the Russian military.
Russia Cyclocopter Redux
The Advanced Research Foundation is proud to be following in the footsteps of Sverchkov, a Russian pioneer—but they are motivated by more than patriotism. Project manager Jan Chibisov insists the design is fundamentally better than helicopters or multicopters.
“As shown by mathematical modeling, the cyclocopter is superior in a number of key parameters to multicopters,” says Chibisov in a press release. “In particular, with the same dimensions and take-off mass, the cyclocopter requires a much smaller engine power and almost twice the mass of the payload.”
Chibisov notes the cyclocopter’s lack of exposed blades, which can prove a hazard in a cluttered environment where any with power lines or other obstacles is likely to be catastrophic.
Wills agrees, noting another reason to expect better safety from this type of vehicle: “I personally have been in three helicopter crashes of varying grades during my military career. The cyclo-gyro aircraft design that we had could glide on engine failure. None of the helicopters I crashed in seemed to want to do that.”
The power plant, control system, and other components for the Russian cyclocopter have all been built and tested separately. The team are now integrating them and assembling the finished vehicle. Unmanned flight tests are scheduled for in 2020 and test flights with actual passengers will follow at a later stage.
A small, agile flying machine able to transport troops and cargo in an urban environment, flying down the canyons between buildings, and coping easily with gusty conditions has obvious appeal. The design would also come with commercial appeal, chasing the ever-elusive flying car market.
The cyclocopter looks strange, but it’s a flying machine with a century-old past and an increasingly optimistic future.