With the focus on the reduction of fossil fuel emissions, aircraft are continuously growing towards higher fuel efficiency. The traditional limits of aircraft performance can be surpassed through the use of composite materials which offer a reduction in aircraft weight. Due to the multidisciplinary nature of aircraft design, integration of different disciplinary analyses is required to arrive at a feasible design. The inclusion of composite design in the preliminary design process, however has become a challenge. This is due to the high computational cost associated with the composite aeroelastic tailoring tools used in the design process. A possible solution is available in the form of surrogate models which can reduce the computational costs. The current work focuses on the development of a methodology that allows the inclusion of surrogate-based model in the optimization for a computationally expensive aeroelastic tool (PROTEUS) developed at TU Delft. The resulting methodology can be expanded to a generic, computationally expensive tool in a multidisciplinary optimization setting. Wing design optimization is carried out based on surrogate modeling methodology and metal based design method. Comparison is made of the final optimized designs based on structural and performance parameters.