Theme DURING the past decade airplane propulsion systems have become louder, sprawling cities have moved closer to their airports and the general awareness of noise has made the public particularly sensitive to aircraft noise. A possible solution to the conventional, short, and reduced takeoff and landing (CTOL, STOL, and RTOL, respectively) noise problems is to place the engine over the wing. With such a configuration, the wing shields the ground from some of the engine noise and redirects it above the aircraft. Engine-over-the-wing (EOW) acoustic tests made with small models1-5 achieved good noise shielding by the wing for both powered (STOL, RTOL) and conventional (CTOL) lift applications. Based on these favorable results with small models, an EOW configuration consisting of a circular nozzle and wing section was scaled up to a large model from which: 1) noise levels and directivity patterns were measured; 2) acoustic scaling laws were checked; and 3) more accurate noise predictions can be made for full-sized aircraft. Contents Air supplied to a convergent nozzle placed over a wing section simulated the EOW configuration for conventional lift. The nozzle exit diameter was 13 in. and the wing chord was 7 ft. For powered lift, a nozzle-flow deflector was used to obtain flow attachment to the upper surface of the wing and flaps for lift augmentation. Acoustic measurements of the vertically mounted model were taken on a 50 ft radius with flap positions assumed to be typical of takeoff and approach for a jet exhaust velocity range of 550 to 1000 fps. Noise directivity patterns for an EOW configuration with powered lift are shown in Fig. 1. The directivity patterns are fairly uniform in the region in front of and under the wing (20° to 130°), and the corresponding noise levels are considerably less than above the wing (180° to 330°). Below the wing (20° to 130°), the decrease in over-all sound pressure level (OASPL) is up to 10 db for powered lift. It is this shielding of the noise by the wing that makes the EOW concept attractive. Similar results were obtained for a configuration with conventional lift. Shielding of jet noise by the wing for the EOW concept is shown in Fig. 2. The noise was measured at angular locations corresponding to the maximum under-the-wing (or flyover) noise, and at velocities assumed to be representative for powered and conventional lift systems, respectively. For powered lift applications, the three spectra
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