Use of smart materials to reduce helicopter rotor noise is to be studied by Lucent Technologies and Sikorsky Aircraft, under a three-year, $13 million contract sponsored by the US Defence Advanced Research Projects Agency (DARPA). Lucent is a new subsidiary of US telecommunications giant AT&T, and its Bell Laboratories research-and-development arm has been working with DARPA on active structural-control since 1988.

Programme manager Larry Behrendt says the programme will look at the use of smart-material actuation devices on rotors to reduce blade-vortex-interaction (BVI) and high-speed impulsive (HSI) noise. BVI noise results when a blade "slices" through the tip vortex shed by the preceding blade. HSI noise is caused by the blade's passage through the air, and can be reduced by slowing the rotor. Behrendt says smart materials could be used to increase blade lift, and so slowing the rotor.

In a parallel effort, Lucent and Sikorsky will investigate the use of active structural-control to reduce cabin noise and vibration. Reducing noise requires high-frequency smart-material actuators, while vibration reduction requires low-frequency active structural-control, Behrendt says.

The rotor-noise effort will involve bench tests and wind tunnel tests of a sub-scale rotor, according to Behrendt.

Source: Flight International