A New Distributed Electric Propulsion Aircraft Simulation Tool for Coupled Flight Dynamics, Free Wake, and Acoustic Predictions

A major barrier to certification and public acceptance of emerging distributed electric propulsion (DEP) aircraft is their noise. Like conventional helicopters, accurate noise prediction of DEP aircraft requires accurate modeling of realistic flight dynamics and controls. Furthermore, aspects unique to DEP aircraft must be modeled, such as variable rotor speed for thrust control, and unsteady aerodynamics arising from rotor thrust control and aerodynamic interactions between rotors and the airframe. To address these needs, this paper describes the development and software coupling of a noise prediction system for DEP aircraft. This system is demonstrated for maneuvering flight simulations consisting of a roll attitude doublet in low speed forward flight, for two rotor thrust control schemes: variable rotor speed and variable collective pitch. Loading noise levels for this configuration generally exceeded thickness noise levels. For a single rotor, loading noise modulated with thrust, regardless of the cause of the time variation of loading (variable rotor speed or collective pitch). However, the range of modulation was greater for the variable rotor speed case than for variable pitch. Less modulation is observed in the total noise for all rotors, because the rotor thrusts must vary to balance the aircraft. Interference patterns are observed for the constant speed case due to coherent phase relations between the rotors, whereas the noise of the variable speed rotors does not add coherently.