Directivity and psychoacoustics focused multi-objective detectability optimisation for low noise rotorcraft trajectories

Abstract

This paper considers an advanced optimisation procedure for helicopter detectability as part of a typical approach trajectory. The objectives of the optimisation problem are formulated on the basis of two parameters: noise detectability threshold, and noticeability. Two key studies are undertaken, one purely looking at the optimisation of noise detectability – whether the noise is audible or not, and the other optimising between objective audibility and psychoacoustic noise perception. The detectability of the rotorcraft is then analysed for both cases and measured using a variety of microphone array configurations to investigate helicopter detection range and noise directivity control. These microphone points are the focus points of the optimisation procedure; the optimisation procedure utilises the strong changeability of helicopter noise directivity with trim condition to alter the flight path of the aircraft according to the placement of the microphones. Results within this paper have shown positive evidence that it is possible to optimise helicopter trim condition in flight to reduce helicopter detection and control noise directivity. Results also showed that for initial analyses, SEL and EPNL can be accurate and powerful tools for optimisation procedures to gauge annoyance in the absence of more sophisticated SQ metrics. The weightings given to the objectives within the objective function, and the calculation procedure for the costs associated with each objective were shown to strongly affect the optimal on-ground noise footprints. The relationships between the quantitative metrics used to encapsulate detectability were also found to strongly affect the results – and further study of the relationship between optimised values needs to be investigated in future work.