Sikorsky Innovations has completed wind-tunnel testing of an active rotor system equipped with “high-authority” flaps, thus paving the way for improvements in noise, vibration–and, marginally, efficiency–on future rotorcraft.
The program started in 2008 and culminated with the trials, last year, at NASA’s Ames Research Center at Moffett Field in California. It is part of a broader program that encompasses leading-edge rotor blade 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. The electromechanical actuators were designed by Hamilton Sundstrand, and 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. In addition, the flap can move up to five times for every rotation of a blade.
A challenge was the centrifugal forces–700 gs–that the flaps have to withstand. “We tested the system on a spin rig and redesigned it several times,” Lorber said. The third iteration of the flap actuators went into the wind tunnel. There, the system performed extremely well over a variety of forward flight conditions up to 140 knots, according to Sikorsky. Goals were met in reduction of noise (minus 6 dB) and vibration (minus 20 percent). Performance was improved, too, with higher maximum load and better efficiency. “Our active flap rotor is more effective on noise and vibration than on cruise efficiency,” explained Russ Gray, chief engineer for advanced programs.
This particular rotor will not be tested in flight, Sikorsky said. However, it does plan to test fly the design. Anticipating future applications, Gray indicated one challenge will be ensuring it has low maintenance requirements.
The effort, jointly funded by Sikorsky and the U.S. Army Aviation Applied Technology Directorate, was part of Darpa’s Mission Adaptive Rotor program. Sikorsky officials said the technology is suitable for both civil and military helicopters, although the design goals would not be the same for the two.
In the near term, said Mark Scott, an engineer in Sikorsky’s Advanced Programs group, “we expect to complete large subscale wind-tunnel testing in the next phase of the program. We are awaiting a broad area announcement [a notice from the government requesting scientific or research proposals from private firms that may lead to contracts] to be released by the Army regarding future reconfigurable rotor research.” Sikorsky plans to respond to the announcement, he said.