Rotorcraft External Far-Field Noise Measurement Using a Hot Air Balloon

A novel and new method of measuring the far-field noise of a helicopter is proposed by the Delta Group International/University of Maryland team that uses a hot-air-balloon as the measurement platform. The method meets the Army STTR objectives of being capable of measuring helicopter noise above and near the tip-path-plane of the helicopter without measurable ground reflections. The new method is direct (data measuring and reduction procedures are similar to ground based systems) and has many advantages including the ability to take acoustic data at almost any breathable altitude above the ground with almost no background noise. This facilitates acoustic measurements at almost all angular positions and multiple microphone-to-helicopter distances, enabling the development of full spherical representations of helicopter noise over a full range of helicopter flight conditions. The proposed Phase I work will concentrate on mitigating the risk of this approach by developing balloon testing flight procedures, performing a pilot test of this new concept, and designing improvements for a Phase II operational system. The DGI/UMD team believes that the hot air balloon acoustic measurement system will yield seminal acoustic data and, at the same time, minimize costs of acquiring the data.