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This paper presents an investigation into the noise produced by an unmanned aerial vehicle (UAV). The platform used, 'Spotter', is a fixed-wing, light UAV comprising a 4-meter wingspan. Spotter was originally designed to perform long-endurance, all-weather patrol missions in coastal and maritime environments. This vehicle has been continuously upgraded and is now used in a broader range of applications. Increasing demand by research and industrial partners, as well as the UK Civil Certification Authority (CAA) has led to a survey of the Spotter's in-flight noise footprint. The CAA Operating Safety Case of this platform is currently being updated and the major findings are presented in the paper. Preliminary results were obtained in flight tests performed at the Draycot Aerodrome over two expeditions in the summer of 2021, in the UK. A series of flyovers, takeoff and landing operations were measured. Flyovers were performed at constant altitude at series of power settings, incrementing from low to maximum power output. These measurements are then used to generate Noise-Power-Distance curves for the Spotter UAV. Static directivity characteristics of the dual propeller setup were also measured, with intent of feeding into future airport exposure studies.

This paper extends the simplified airport noise model Rapid Aviation Noise Evaluator (RANE) [Torija et al., Journal of the Acoustical Society of America, Vol. 141, No. 2, 2017, pp. 981–995], adding capability of including fully nonisotropic noise sources. This extended tool, RANE v2, is developed as a part of multidisciplinary acoustic assessment of novel aircraft, in order to produce ground contours around airports and helipads. Version 2 extends the capability of RANE to accommodate predictions of future air vehicles implementing propulsion systems solution with inherent directional properties. The model uses three-dimensional noise emission surfaces around a series of discretized segments that represent the aircraft flightpath. The main inputs are the sources’ sound power level, the distance from the flightpath at which a level is observed, and the source three-dimensional directivity. The directivity function may take analytical or numerical form, allowing for experimental data inputs. This paper demonstrates the use of spherical harmonics as a form of directivity function with a closed-form analytical solution for calculating the noise exposure contours. Results and comparison against the Federal Aviation Administration’s Aviation Environmental Design Tool module for helicopter community noise indicate that exposure contour coordinates can be estimated for high and low noise exposure levels. The incorporation of source directivity allows for the assessment of lateral attenuation, engine installation effects, and transition operations (for vertical to horizontal flight and vice versa) via the assumption of individual source directivities and, therefore, complex noise surfaces. As a consequence of the analytical nature of the model, low computational requirements allow for fast exploration of the design space and parametric studies, with minimal input requirements. The capabilities of RANE v2 are demonstrated by predicting noise footprints for three helicopters, each of different size, performance, and directivity characteristics.

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