Interior noise considerations for powered-lift STOL aircraft

Several powered‐lift configurations which are currently under development for future use on STOL aircraft involve impingement of the jet engine exhaust onto wing and flap surfaces. Previous studies have suggested that the impinging jet produces higher noise levels at lower frequencies than does the jet alone. These higher levels, together with the closer proximity of the engine and flap noise sources to the fuselage sidewall than for present‐day jet aircraft, suggest that the noise levels in these aircraft may be high enough to interfere with passenger comfort. To investigate this possibility, interior noise levels were estimated for both “upper surface blown” (USB) and “externally blown flap” (EBF) configurations. The estimated levels were found to be very high, especially at low frequencies, compared with interior noise levels found on existing commercial jet aircraft. As a result of this finding, a research program has been initiated to develop better understanding of low‐frequency noise transmission t...