The paper discusses the development of a novel linearization algorithm to obtain high-order linear time-invariant (LTI) models of the coupled rotorcraft flight dynamics, vibrations, and acoustics. To demonstrate the methodology, the study makes use a nonlinear simulation model of a generic utility helicopter (PSU-HeloSim) that is coupled with an aeroacoustic solver based on a marching cubes algorithm. First, a revisited harmonic balance algorithm based on harmonic decomposition is applied to find the periodic equilibrium and approximate high-order LTI dynamics at 80 kts level flight. Next, the proposed output linearization scheme is applied to derive time-invariant, linearized equations of the main rotor forces and moments, and acoustics. Simulations are used to validate the response of the linearized models against that from nonlinear simulations. Additionally, the cost of linearization and potential performance benefits of employing linear models versus nonlinear simulations are assessed. The high-order LTI models thus obtained are shown to provide similar acoustic predictions compared to those of nonlinear simulations for small amplitude maneuvers, but at a fraction of the computational cost. These linear simulations are shown to run in the order of thousands of times faster than real time, and four orders of magnitude faster than nonlinear acoustic predictions based on a marching cubes algorithm.