This paper presents the development of a full turbine model and subsequent aero-servo-elastic simulation of the IEA 15MW Reference Wind Turbine, such that aerodynamic loads can be obtained and then applied to a simplified drivetrain in Finite-Element Analysis. This approach facilitates the quantification, through a computationally efficient method, of airgap deflections within the direct-drive generator caused by the shaft eccentricity that arises from aerodynamic loads. Shaft deflections were found to be higher under rated wind speeds than higher operating speeds, and the aero-servo-elastic model presented here performs favourably compared to later-published models.