A global team of research organizations is quietly working on an active rotor blade in which distributed piezo-electric actuators can change blade twist almost continuously over the course of one blade revolution. Partners can be found in the U.S., Europe and Asia. A full test campaign is scheduled for next year.
Joining forces are the U.S. Army, NASA, France’s Onera, Germany’s DLR, Korea’s Konkuk University and Aerospace research institute (Kari) and Japan’s Jaxa. The effort began in 2010, Blanche Demaret, Onera’s delegate director for rotorcraft, told AIN. It is known by the acronym Star, standing for smart twisting active rotor. It exploits a concept of actuator distribution over the blade originally conceived by DLR.
“A helicopter blade works as an airfoil in airflow running from the leading edge to the trailing edge for only a quarter of each revolution,” Demarets told AIN. For the remaining 75 percent of the revolution, it is subject to vortices and stalls, generating both noise and drag, respectively. In addition, the blade undergoes vibration transmitted from the main gearbox or created by the airflow.
“We are trying to act on these negative phenomena,” Demaret said. Piezo-electric actuators can be distributed over the surface of the blade to change twist. Other technologies, such as the one Eurocopter has dubbed Blue Pulse, use only trailing-edge flaps. In the Star project, Onera has been in charge of the closed-loop control. “Without any pilot input, the system will send actuating orders at a rate of 64 per second,” Demaret explained.
So what is this going to change for the crew? Nothing, in terms of piloting; the system should be “transparent.” The difference will be found elsewhere. “Any improvement to the main rotor has an impact on the helicopter’s entire performance,” Demaret said. Depending on the tradeoff the designers choose, they can make the helicopter faster or more fuel-efficient. Or they can reduce vibration and noise, or elect for a mix of all these.
Such an active rotor will run on a test rig next year. It will be installed at the large low-speed facility wind tunnel in Marknesse, Netherlands.
Even though this will be a major step in technology demonstration, Demaret remains conservative in making predictions about possible applications. “Sometimes it takes 10 years before a helicopter manufacturer is convinced and turns a technology into a product,” she said.
In an even more distant future, active blades might replace the swashplate, saving weight and complexity. The actuators could use plasma, vortex generators or pulsed air.