The defense and the commercial sectors in US have been undergoing severe energy issues, with the prices and demand of fuel increasing over the years. Thus investigations into advanced fuel efficient designs have become inevitable. With increase in air traffic, environmental concerns of noise and emissions have also been brought to the forefront. This has resulted in NASA's ambitious N+3 vision, as exemplified in the Subsonic Fixed Wing projects's four corners of the design trade space. Also, the burgeoning interest in UAS platforms promises significant departures from traditional aircraft designs. To enable introduction of new aircraft into the inventory, the conceptual design of advanced concepts is critical. However, the aircraft design community realizes a need for introducing physics based analysis early in the design space. In particular weight estimates based on statistical relations are inadequate for new concepts, and there is a need for improved weight estimation. For this purpose, Intelligent Automation proposes VaC-CADO, a variable complexity conceptual aircraft design tool for the design of advanced airplanes by combining multi-fidelity optimization and MDO with FEM-based weight estimation. This is a novel technique leveraging on state-of-the-art in aircraft design and enhancing it using our extensive experience in this field.