A rotor system for tilt rotor aircraft comprises an engine disposed at a first fixed location on a wing member; a prop-rotor pylon mechanically coupled to the engine along a drive path, and a gearbox disposed in the drive path. The prop-rotor pylon is rotatably mounted on a spindle, and the prop-rotor pylon is configured to selectively rotate about a rotational axis of the spindle between a vertical position and a horizontal position. The gearbox comprises a rotational axis aligned with the rotational axis of the spindle.