The Lockheed Martin C-130 Hercules has many fans, but even its most dedicated supporters would never claim that internal quietness is one of its virtues. This noise is not only annoying, it causes fatigue for crews and passengers.

UK company Ultra Electronics (Stand A1004) is now engaged on a test programme with the US Air National Guard to cut C-130 cockpit noise substantially .

Ultra's Controls Division's Active Noise Control (ANC) system uses microphones to 'sample' engine noise inside an aircraft then re-broadcast the same level of noise, but opposite in phase, to cancel it out. It is fitted to around 700 civil aircraft such as the Bombardier Q300 Dash 8 and Saab 2000.

Following interest from the US Air Force's Battlelab, which looks for off-the-shelf technology that can help the service fight more effectively, Ultra fitted a demonstration system in the cockpit of a C-130H of the 167th Airlift Wing, West Virginia Air National Guard.

Cockpit noise inside a four-bladed C-130 can reach 111.9 decibels (dB) around the co-pilot's seat. The ANC system, consisting of 28 microphones and 24 loudspeakers fitted behind trim panels, cuts noise at the co-pilot's seat to 96.2dB, equating to a reduction of 90% in noise power, says Ultra.


Crews flying the aircraft are undergoing regular measurement to try to quantify improvements resulting from the quieter working environment.

One benefit that can be quantified relates to the system's embedded propeller balance monitoring system (PBMS), which calculates where groundcrew should re-position counterbalances to provide a smoother ride. PBMS cuts the time for this task from a day to around 1h, says Rob McDonald, Ultra's marketing director.

The test aircraft has shown a 56% improvement in vibration, he says, resulting in longer life for avionics and less structural fatigue.


Source: Flight Daily News