The aim of this thesis is to explore methods to reduce the noise impact of unmanned aerial vehicles operating within acoustically sensitive environments by flight control system augmentation. Two methods are investigated and include: (i) reduction of sound generated by vehicle speed control while flying along a nominal path and (ii) reduction of acoustic exposure by vehicle path control while flying at a nominal speed. Both methods require incorporation of an acoustic model into the flight control system as an additional control objective and an acoustic metric to characterize primary noise sources dependent on vehicle state. An acoustic model was developed based on Gutin’s work to estimate propeller noise, both to estimate source noise and observer noise using two separate acoustic metrics. These methods can potentially mitigate the noise impact of unmanned aerial systems operating near residential communities.
The baseline flight control system of a representative aircraft was augmented with a control law to reduce propeller noise using feedback control of the commanded flight speed until an acoustic target was met, based on the propeller noise model. This control approach focuses on modifying flight speed only, with no perturbation to the trajectory. Multiple flight simulations were performed and the results showed that integrating an acoustic metric into the flight control system of an unmanned aerial system is possible and useful. A second method to mitigate the effects of noise on an observer was also pursued to optimize a trajectory in order to avoid an acoustically sensitive region during the path planning process. After the propeller noise model was incorporated into the vehicle system, simulations showed that it is possible to reduce the noise impact on an observer through an optimization of the trajectory with no perturbation to the flight speed
