Qinetiq and Ultra Electronics set to ground-test system in Challenger business jet

Qinetiq and Ultra Electronics are designing a combined active/passive aircraft cabin noise-reduction system that they believe will reduce broadband cabin noise by 10dBA.

The two UK companies have developed AIRAT [Active Isolator Research for Aircraft Trim panels] cabin sidewall panel mounts that reduce vibration, and hence noise, passed from the aircraft's skin into the panel and passenger cabin.

The project is the result of a seven-year UK Department of Trade and Industry-funded study, and Qinetiq and Ultra are proceeding with help from Bombardier.

Ground-based testing will use a Challenger business jet cabin, and next year the team will test the system in flight. If successful, it could be commercially available by 2005.

Dr Robert Coppard, Qinetiq business group manager structural design, says 75% of noise transmitted from skin to cabin is conducted structurally. "In initial two-panel testing we saw noise reductions of up to 30dB, so we're very confident of achieving 10dB in flight," says Coppard.

Passive isolation such as traditional rubber mounts and foams are effective at blocking frequencies above 1kHz only. At high cruise speeds the turbulent boundary layer surrounding the aircraft fuselage generates broadband noise, so low frequencies must also be suppressed.

The AIRAT mounts combine both characteristics and even passively can suppress high-frequency vibrations better than traditional mounts. Active suppression, required for frequencies below about 500Hz, is achieved by the electrically actuated mounts detecting vibration coming through the aircraft structure and vibrating themselves to cancel it out.

Coppard says that, depending on panel sizes, each would use up to 12 mounts, with a Boeing 777-size aircraft needing "several hundred" mounts and associated wiring. He says the system could probably cope with individual mounts failing, as they would still provide passive suppression. "The system could even save weight as the need for other acoustic insulation would be reduced," he says.

The team estimates a market of $250-550 million for the devices if successful, based on a 10-25% uptake on large aircraft and even greater use on regional and business aircraft. System costs would be in the order of tens of thousands of dollars per airframe.

Ultra already supplies noise- reduction systems to corporate and regional aircraft such as the Beech King Air 350, Saab turboprops and Bombardier Dash 8 Q Series.

Source: Flight International