This paper presents some results of an experimental investigation on the noise generated by model target-type thrust reversers. The experimental data are normalized and scaled up to sizes suitable for reversing the core jets of a four-engine STOL airplane, yielding perceived noise levels well above the 95-PNdB design goal for both sideline and flyover at 152 m. V-gutter and semicylindrical reversers were tested with a 5.24-cni-diam circular nozzle, and a semicylindrical reverser was also tested with a 7.78-cm-diam circular nozzle. The ratio of reverser frontal area to nozzle exit area ranged from 2.4 to 7.0. Other tests variables were the spacing between nozzle and reverser, reverser orientation, and nozzle jet velocity. The thrust reversers, in addition to being noisier than the nozzle alone, also had a more uniform directivity. The maximum over-all sound pressure level and the effective sound power level both varied with the 6th power* of the nozzle jet velocity. Nomenclature Af = reverser frontal area, m2 An = nozzle area, m2 Ci,C2,Cs = first, second, and third frequency bands exhibiting ground-reflection cancellations, assuming a point source ca = ambient speed of sound, m/sec Dn = nozzle-exit diameter, m fc = i/s-octave-band center frequency, Hz /M = the Vs-octave-band frequency exhibiting the highest sound pressure level, Hz K = empirical coefficient in sound power correlation, dB K± = empirical coefficient in acoustic efficiency correlation, dimensionless OAPWL = over-all sound power level, dB re 10~13 W OASPL = over-all sound pressure level, dB re 20 fj.N/m2 PNL = perceived noise level, PNdB PWL = ^/a-octave-ban d sound power level, dB re 10 ~13 W Ri,R2,Rs - first, second, and third frequency bands exhibiting ground-reflection reinforcements , assuming a point source Sn — nozzle Strouhal number, fcDn/Uj SPL = sound pressure level, dB re 20 /L/V/m2 Uj = isentropic nozzle velocity, m/sec W = sound power, W X = spacing between reverser and nozzle, m Y = reverser height, m Z = reverser width, m a = angle of reverser to horizontal, deg n - effective acoustic efficiency, W/(paAnUj3)f dimensionless 8 = microphone angle from nozzle upstream axis, deg QM — angle from nozzle axis at which maximum OASPL occurs, deg Pa = ambient density, kg/m3