The Rotor-Nacelle Assembly comprises the nacelle and all its components (gearbox, generator, brakes, yaw actuators, etc) and the rotor (hub, blades, pitch actuators, etc). In practice, the RNA consists of everything that is mounted on top of the tower. In certain cases (for example when studying the eigenfrequencies of the tower), it is common to model the RNA as a point mass on top of the tower.