If one considers the problem of converting an aircraft mission profile into an airframe design from an optimization theory perspective, it becomes obvious that the search problem comes with all the trimmings. The design space is large and multidimensional, there are multiple and often highly multimodal objectives and constraints, these depending not only on the design variables, but often on each other as well. Multidisciplinary Design Optimization studies can be conducted at different levels of detail, depending on the chosen trade-off between the size of the design space and the fidelity of the analysis. In this paper we discuss some of the challenges arising at the conceptual level, where simple, but versatile models and low cost analysis tools are used to guide the designer through the first, fundamental decisions of the design process. At the centre of our proposed design workflow lies a parametric geometry, residing in an off-the-shelf Computer-Aided Design (CAD) tool - this provides the models required by the multidisciplinary analyses. We also touch on some of the issues specific to the design of our chosen class of aircraft - Unmanned Air Vehicles (UAVs). To summarize: a CAD-based UAV conceptual design framework is proposed and demonstrated.