Cabin noise mathematical modeling for single engine aircraft

Abstract

Previous in‐flight data [A. J. Campanella, J. Acoust. Soc. Am. Suppl. 1 69, S28 (1981)] indicated that the main source of cabin noise in single‐engine aircraft, often 88 to 93 dBA at the pilot's ear position during cruise flight, arises from the engine exhaust, with the propeller noise apparent only during takeoff and full power climb. Mathematical modeling of the exhaust and propeller noise propagation from their source to the pilot's ear position was devised to optimize exhaust silencing means within the constraints presented by aerospace structures. Through comparison with in‐flight data, it was found that the matching assumption should include that fact that the exhaust SPL harmonics have a velocity maximum at the exhaust outlet and a pressure maximum at the piston/cylinder source. It was further assumed that all harmonics had the same amplitude, representing an impulse source. Exhaust gas temperature, transport velocity, density, outside air temperature, cabin temperature, flight altitude, floor and window barrier (mass law), and intervening distances were included as model variables. Propeller noise was modeled after P. A. Franken and L. L. Beranek [Noise Reduction, edited by L. L. Beranek (Krieger, Huntington, NY, 1980), pp. 685–688]. This computerized mathematical model can be used to predict the effect of exhaust outlet location and a variety of exhaust silencer components on the A‐weighted sound level at the pilot's ear position.