Validated Design and Analysis Tool for Small Vertical-Lift Unmanned Air Vehicle Noise Prediction

A procedure and supporting computer code for the prediction of noise that radiates from small, vertical lift UAV aircraft is proposed. The resulting building block procedure is theoretically based but is verified experimentally at several output stages. Noise source models for rotors, lift-fans, engines etc. are developed and validated through specially designed experiments and stored in a component digital library. For a given small lifting UAV configuration, these noise source models are combined into a hemispheric representation of the total radiated noise. The total radiated field is governed by the operating state of the vehicle as described by the governing performance model for the chosen configuration. Standard propagation effects and subjective weightings are used to radiate hemispheric noise levels to ground observers. The resulting computer program can be mathematically flown along prescribed trajectories to estimate ground noise radiation of several small UAV aircraft.

The development of a validated external noise prediction code for small vertical lift UAVs will have a large impact on the potential commercial uses of these vehicles. Vehicles that are noisy are likely to have restricted operations because of their acoustic intrusiveness. Designing and operating small vertical lift UAVs so they operate quietly will help facilitate their application potential. When fully developed, the acoustic prediction tool can be used to help determine the best vehicle performance design within acoustic constraints and/or the quietest design within performance constraints. The prediction tool can also assess quiet methods of flying the small vertical lift UAV to minimize annoyance to surrounding communities. The tool will also be useful to the government in assessing how small UAV aircraft can quietly operate within the United States air transportation system.

The development of a validated external noise prediction code for small vertical lift UAVs will have a large impact on the potential military uses of these vehicles. Excessive and distinct small UAV noise radiation reduces the mission effectiveness by alerting the enemy that a UAV is in the area. In addition,the UAV's distinct acoustic signature presents the enemy with targeting opportunities – thus reducing the survival rate on each mission. When fully developed, the acoustic prediction tool can be used to help determine the best vehicle performance design within detection acoustic constraints and/or the quietest detection design within the performance constraints of the vehicle. The prediction tool can also assess quiet methods of flying the small vertical lift UAV to minimize the likelihood of acoustic detection. The tool will also be useful to the military in planning non-detectable UAV missions.

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