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 through aircraft fuselage structures and to develop prediction and control technology for application to power‐lift STOL aircraft. This paper describes the interior noise estimation procedure, compares the estimated levels with levels on existing jets and other transportation modes, and describes the recently initiated research program.

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Interior noise considerations for powered-lift STOL aircraft

The far field noise from subsonic jet impingement on a wing-flap with a 45 deg bend was experimentally investigated. The test parameters are jet Mach number and flap length. For long flaps, the primary source mechanisms are found to be turbulent mixing and flow impingement. For short flaps, the interaction of turbulent flow with the flap trailing edge appears to strongly influence the radiated noise.

Radiated noise from an externally blown flap

This document contains reference lists of published Langley Research Center papers in various areas of acoustics and noise control for the period 1940-1974 The research work was performed either in-house by the center staff or by other personnel supported entirely or in part by grants or contracts The references are listed chronologically and are grouped under the following general headings: (1) Duct acoustics, (2) Propagation and operations, (3) Rotating blade noise, (4) Jet noise, (5) Sonic boom, (6) Flow-surface interaction noise, (7) Human response, and (8) Structural response

Publications in acoustics and noise control from the NASA Langley Research Center during 1940 - 1974

Propulsive-Lift Noise of an Upper-Surface-Blown Flap Configuration

Progress report on the problem of community noise control for jet-powered STOL aircraft. Noise goals are discussed, along with noise control approaches for meeting these goals. Such significant noise control factors as the basic engine cycle, engine-airframe integration varieties, and certain details of the lift augmentation system are given special attention.

D. J. Maglieri

Papers

Noise control technology for jet-powered STOL vehicles.