Sikorsky Innovations has completed wind-tunnel testing of an active rotor system equipped with “high-authority” flaps, paving the way for what it says will be improvements in noise, vibration–and, marginally, efficiency–on future rotorcraft.

The effort started in 2008 and culminated with the trials, in January and February this year, at NASA’s Ames research center at Moffett Field in California. It is part of a broader program that also encompasses leading-edge devices. The tested system involved trailing-edge flaps and a closed-loop control.

In the wind tunnel, a production, 28-foot-diameter S-434 main rotor was fitted with the flaps. Hamilton Sundstrand designed the electromechanical actuators; United Technologies’ Research Center (part of the same corporation as Hamilton Sundstrand and Sikorsky) helped design the modified blades.

Sikorsky claims to have a much higher authority system than the one Eurocopter test flew in 2005. “We have plus or minus 10-degree deflections and are not limited to low frequencies,” Peter Lorber, Sikorsky’s manager of flight sciences, told AIN. Moreover, the flap can move up to five times for every rotation of a blade.

The centrifugal forces–700g–the flaps have to withstand posed a challenge for Sikorsky engineers. “We tested the system on a spin rig and redesigned it several times,” Lorber said. The third iteration of the flap actuators was the one that went into the wind tunnel.

There, the system performed “extremely well over a variety of forward flight conditions up to 140 knots.” It met Sikorsky’s goals for noise (minus 6dB) and vibration (minus 20 percent). Performance was improved, too, with an increase in maximum load and efficiency. “Our active flap rotor is more effective on noise and vibration than on cruise efficiency,” said Russ Gray, chief engineer for advanced programs.

This particular rotor will not be tested in flight. Nevertheless, Sikorsky does anticipate flying the system. The research effort was funded jointly by Sikorsky and the U.S. Army Aviation Applied Technology Directorate. The active rotor technology is suitable for both civil and military helicopters, but the two would have separate design goals, said Sikorsky officials.