Book Description

Aircraft noise in the frequency range above 600 cps which produces the greatest interference with speech communication, can be controlled by practical amounts of sound insulation and can be estimated from the indicated airspeed in most jet propelled or multi-engine propeller driven aircraft. Since interference with speech communication is the most serious effect of aircraft noise, the methods contained in this report for estimation of the insulation required enable the aircraft designers to provide for necessary sound insulation in the earliest design stages. The principal source responsible for noise above 600 cps in the aforementioned aircraft types is the airflow over the fuselage and this noise is found to depend approximately upon the 2.75 power of the indicated air speed. Sound reduction afforded by the insulation is also found to be simply related to the surface density of the batting plus that of any non-porous septa included in the blanket.