Optimal Control Approach to Helicopter Noise Abatement Trajectories in Nonstandard Atmospheric Conditions

This paper discusses the development of a software suite that aims to optimize helicopter trajectories with respect to the noise impact on the ground. The software suite has been developed around an advanced gradient-based optimization algorithm based on optimal control theory. The helicopter trajectories are modeled using an eight-degree-of-freedom flight mechanics model. To determine the noise impact on the ground, a helicopter noise model developed in this work consists of three modules, namely, a helicopter source noise model, a propagation model, and a noise impact model. To determine the noise levels on the ground, the source noise levels are determined from a database of aeroacoustically determined noise levels for varying flight conditions and projected on a hemisphere centered at the main rotor hub. The noise propagation model included in the suite is capable of determining the propagation loss between the source and the receiver in nonstandard atmospheric conditions, and it yields the total noise level in individual receiver locations. Finally, these noise levels can be quantified into a single noise impact criterion, which can be used as an optimization criterion in the optimal control formulation. To exemplify the capabilities of the suite, a hypothetical city center approach procedure is optimized for the noise impact in communities surrounding the helispot.