Noise Reduction System for General Aviation Aircraft

Noise generated by general aviation aircraft has a negative impact on the aviation community, and strict adherence to FAR Part 36 regulations requires noise reductions on the majority of these aircraft. Any new aircraft certified or any modification to an existing aircraft must show compliance with this regulation. The majority of these aircraft are owned by individuals and are used for recreational flying. Community airport noise standards are increasingly more strict as suburban areas spread toward small airports. The majority of noise in these airplanes, which use reciprocating engines, is derived from the engine and exhaust, and can be reduced or eliminated through the use of a properly designed exhaust/muffler system. In this Phase I program, Ultramet proposes to develop the design methodology and system characterization for add-on muffler systems requiring only slight modification to the exhaust system. A durable, high-temperature ceramic foam bulk adsorber/baffle material will be used to create 20-25 dB engine noise reduction at design exhaust system backpressures of less than 2" of mercury. The proposed program will include acoustic characterization of various high-temperature baffle/adsorber materials, providing a design methodology for a given airplane engine noise frequency spectrum and sound pressure level. Additionally, the design procedures and materials data will be verified by constructing and beginning FAR qualification of a quiet muffler system for a general aviation aircraft.