Acoustic Predictions of the Moog S-250 in Hover

Acoustic predictions were performed for the Moog S-250 vehicle to assess a NASA mid-fidelity prediction toolchain for Urban Air Mobility vehicles. Experimental data from a 60-foot hover test is used for comparison. The S-250 is an RPM-controlled vehicle in a quadcopter-type configuration with four sets of contra-rotating rotors and powered by eight independently controlled electric motors. A rotor blade identical to those used on the S-250 was 3D laser scanned. The resulting point cloud enabled the development of custom airfoil tables using OVERFLOW which led to accurate blade loading calculations. Seven observer locations are chosen to evaluate and compare with the measured hover data, which was mapped to a hemisphere with a radius of 12.5 feet, half of the largest rotor tip-to-tip distance between two separate rotors on different pylon arms. Noise predictions at observer locations near the hemisphere horizon capture the measured trends and power spectral density amplitudes within 6 dB for the first few harmonics. Observer locations under the vehicle predict lower levels than the experimental data relative to the observer locations near the horizon, but overpredict measured levels at the first blade passage frequency.