Far field noise data were taken for convergent nozzles of various shapes and sizes at subsonic velocities exceeding 400 feet per second. For a circular nozzle, the nozzle inlet shape and lip thickness had no effect on the noise level, directivity, or spectra when compared at the same nozzle exit diameter and peak exhaust velocity. A sharp edged orifice was one exception to this statement. Coannular nozzles can produce additional high frequency noise. Blunt ended centerbodies, where there is significant base drag, also generate significant additional noise.The total noise power generation was essentially the same for cirpular, slot, and plug nozzles of good aerodynamic shape. The noise radiation patterns were essentially the same for these nozzle shapes except°° near the nozzle exhaust axis. These patterns were well described by "7 '(1 -M C cos 9j)~3, except near the nozzle exhaust axis. w

Acoustic measurements for large model engineover-the-wing (EOW) research configurations having both conventional and powered lift applications were taken for flap positions typical of takeoff and approach and at locations simulating flyover and sideline. The results indicate that the noise ,is shielded by the wing and redirected above it, making the EOW concept a prime contender for quiet aircraft. The large-scale noise data are in agreement with earlier small-model results. Below the wing, the EOW configuration is about 10 PNdB quieter than the engine-under-the-wing externally-blownflap for powered lift, and up to 10 dB quieter than the nozzle alone at high frequencies for conventional lift applications.

Noise data were obtained with a large externally blown flap model. A fan-jet engine exhaust was simulated by a 1/2-scale bypass nozzle supplied by pressurized air. The nozzle was pylon mounted on a wing section having a double-slotted flap for lift augmentation. Noise radiation patterns and spectra were obtained for nozzle exhaust velocities between 400 and 1150 ft/sec. The blown flap noise data are in good agreement with previous small model results extrapolated to test conditions by Strouhal scaling. The results indicate that blown flap noise must be suppressed to meet STOL aircraft noise goals.

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f l a p noise t o the t o t a l a i r c r a f t noise 1s assessed.Noise data were obtained with models of both internally and externally blown jet-flaps of the type currently being developed f o r STOL a i r c r a f t . The principal t e s t s were conducted with an augmentor-wing model and with an externally-blown double-slotted-flap model. Secondary t e s t s were 'D