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Noise Reduction Efforts for Special Operations C-130 Aircraft Using Active Synchrophaser Control

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Research paper

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Aircraft noise often inhibits mission effectiveness. As a result, flight crews, ground maintenance personnel, and passengers suffer degraded voice communication, impaired performance, increased fatigue, and hearing loss. In an effort to reduce the level of noise both inside and outside of the aircraft, techniques have been developed that attempt to quiet the environment. The simplest approach uses passive noise reduction methods, including installing acoustic insulation and exhaust modifications, but these only provide limited success. A more complicated approach uses an active noise cancellation ANC system, which offers improved performance that can augment passive methods to significantly reduce both internal and external aircraft noise. ANC achieves noise reduction by creating an anti-noise, which is an equal and opposite acoustic wave that cancels the unwanted noise. This type of cancellation works well in smaller volumes, like headset ear cups. For larger volumes or environments, arrays of loudspeakers are needed, but are often ineffective due to their size and weight. Since the primary noise on multi-engine turboprop aircraft, such as the C-130, originates from the engine-propeller system, the noise from one engine-propeller can be tuned to provide a canceling acoustic wave to reduce the noise generated from another engine-propeller on the same aircraft. Because the levels of noise generated from each engine-propeller combination are similar under normal operating conditions, a means to adjust the propeller phasing to create a noise canceling effect is needed. For multi-engine propeller-driven aircraft, engine-propeller phase control is accomplished using an electromechanical device called a synchrophaser. To optimally control the phase angle relationships among the four engine propellers, a controllable or active synchrophaser system is needed. The synchrophaser system described in this paper is a joint effort between AFRL and AFSOC.

Subject Categories:

  • Transport Aircraft
  • Non-electrical Energy Conversion
  • Acoustics
  • Noise Pollution and Control

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