IN-FLIGHT SOURCE NOISE OF AN ADVANCED LARGE-SCALE SINGLE-ROTATION PROPELLER

A large-scale advanced single-rotation turboprop engine was installed on the left wing of a Gulfstream II aircraft for in-night aeroacoustic tests. This program, designated propfan test assessment (PTA), involv ed aeroacoustic tests of the propeller over a range of flight conditio ns. Data was taken both near the source propeller at flight conditions and on the ground, resulting in a unique set of data which is valuabl e for evaluating acoustic propagation models for cruise noise ground m easurements. The in-flight data reported herein was taken for seven te st cases. An acoustically instrumented Learjet was flown in formation with the Gulfstream II to acquire noise measurements, and acoustic dat a was also acquired on the Gulfstream II aircraft. These acoustic meas urements defined source levels and directivities for input into long-d istance propagation models to predict en route noise. The sideline ton e directivities measured by the Learjet showed maximum levels near 105 deg from the propeller upstream axis. Azimuthal directivities based o n the maximum observed sideline tone levels showed highest levels belo w the aircraft (with a + 3-deg propeller axis angle of attack). An inv estigation of the effect of propeller tip speed (with other engine par ameters, such as thrust, shaft power, flight speed, and altitude, held constant) showed that the tone level reduction associated with reduct ions in propeller tip speed is more significant in the horizontal plan e than below the aircraft.