Actively Twistable Rotor Blades Reduce Noise And Vibrations

Actively Twistable Rotor Actively Twistable Rotor Blades Reduce Noise And Vibrations

2026-02-04 Source: DLR | Translated by AI 2 min Reading Time

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Helicopters are indispensable, but loud and energy-hungry. Researchers have now confirmed in wind tunnel tests that actively twistable rotor blades with integrated piezoceramic actuators increase efficiency and significantly reduce noise and vibration.

The rotor with actively twistable rotor blades in the wind tunnel: The open measuring section and sound-absorbing wall and model fuselage cladding enable high-quality acoustic measurements.(Image: DLR) — The rotor with actively twistable rotor blades in the wind tunnel: The open measuring section and sound-absorbing wall and model fuselage cladding enable high-quality acoustic measurements.
(Image: DLR)

In hovering flight and at maximum speed, helicopters require a lot of power and have a high vibration level, especially in slow, fast and maneuvering flight. This could be significantly improved if the rotor blades could adapt statically and, above all, dynamically to the respective aerodynamic flight conditions. In the STAR (Smart Twisting Active Rotor) project, the German Aerospace Center (DLR) is working with other project participants from the USA, France, the Netherlands, Japan and South Korea to increase the performance of rotor blades and at the same time reduce their noise emissions and the vibrations they generate.

Tension Deforms Rotor Blades Like An Artificial Muscle

In the project, the researchers are investigating actively twistable rotor blades with piezoceramic actuators integrated into the blade skin, which deform when an electrical voltage is applied. In this way, the rotor blade is twisted—statically with DC voltage and dynamically with AC voltage—as if an artificial muscle were working in the blade.

The special feature of this approach is that the active twisting of rotor blades does not require any mechanical elements and is only influenced to a small extent by the centrifugal forces acting on the rotor blades.

Prof. Dr. Berend Gerdes van der Wall, Project Manager at the Institute of Flight Systems Engineering

Successful Tests in the Low-Speed Wind Tunnel

Noise source identification is made possible with microphones outside the flow (on the red square), while a "noise carpet" is measured using the microphones mounted in the flow on a wing and a traversing device.(Image: DLR) — Noise source identification is made possible with microphones outside the flow (on the red square), while a "noise carpet" is measured using the microphones mounted in the flow on a wing and a traversing device.
(Image: DLR)

After a long period of preparation, a four-blade rotor equipped with active twisting and a rotor size of four meters in diameter was tested for the first time worldwide in the large low-speed wind tunnel of the German-Dutch Wind Tunnels (DNW) in the Netherlands. The three-week measurement campaign took place at the end of 2025 under the leadership of DLR in close cooperation with all project participants from NASA, the US Army, ONERA, DNW, JAXA, KARI and Konkuk University.

Increased Efficiency, Reduced Noise And Vibration

During the tests, noise reductions of up to seven decibels were measured on approach, which corresponds to more than halving the perceived noise. Vibrations were also reduced by more than half, while the efficiency of the rotor was increased under high loads. In addition to the rotor forces, torques and its performance, the data obtained also includes the blade movements, their deformations and loads, surface pressures, acoustic measurements as well as flow field and boundary layer measurements. This information enables comprehensive validation of calculation programs. In addition, the results can be applied to various scenarios, from conventional helicopters to high-speed configurations and urban air mobility concepts.

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