COLOGNE, Germany - Researchers at the German Aerospace Center (DLR) are studying methods to reduce helicopter noise and vibration through changes in rotor blade design as part of the Smart Twisting Active Rotor (STAR) project.
DLR notes that helicopters are widely used for civil and emergency operations but generate significant noise, particularly during landing descent. Rotorcraft operating in hover, high-speed flight, and maneuvering conditions require substantial power and can experience elevated vibration levels. According to the researchers, allowing rotor blades to adapt statically and dynamically to aerodynamic conditions could reduce vibration and improve efficiency.
Collaborative effort
The STAR project is being conducted by the German Aerospace Center Institute of Flight Systems and the Institute of Lightweight Systems, in collaboration with partners in the United States, France, the Netherlands, Japan, and South Korea. The research focuses on rotor blades equipped with piezoceramic actuators embedded in the blade surface. When electrical voltage is applied, the actuators induce a twisting motion in the blade, either statically using direct current or dynamically using alternating current. The approach does not rely on mechanical components.
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"The special thing about this approach is that the active twisting of a rotor blade requires no mechanical components and is only minimally affected by the centrifugal forces acting on the rotor blades," said Berend Gerdes van der Wall, project manager at the German Aerospace Center Institute of Flight Systems.
Following preparatory work, researchers tested a four-bladed active twist rotor with a diameter of four meters in the large low-speed wind tunnel operated by German-Dutch Wind Tunnels in the Netherlands. According to the German Aerospace Center, the test marked the first wind tunnel evaluation of a rotor system of this type at that scale.
The three-week measurement campaign took place in late 2025 under the leadership of the German Aerospace Center, with participation from the National Aeronautics and Space Administration (NASA), the U.S. Army, ONERA in France, German-Dutch Wind Tunnels, the Japan Aerospace Exploration Agency, the Korea Aerospace Research Institute, and Konkuk University. Test results indicated noise reductions of up to seven decibels during landing descent. The researchers also reported reduced vibration levels and increased rotor efficiency under high-load conditions.
"During the measurement campaign, we were able to successfully test our concept in a realistic environment," van der Wall said. "The results show that efficiency increased while noise and vibration were significantly reduced."
Data collected during the tests included rotor forces, moments, and power, as well as blade motion, deformation, and loads. Additional measurements covered surface pressure, acoustics, flow fields, and boundary layers. According to the researchers, the data will be used to validate computational models and assess potential applications for conventional helicopters, high-speed rotorcraft configurations, and emerging urban air mobility designs.
