This paper discusses structure and functionalities of a knowledge-based engineering (KBE) application, called multimodel generator (MMG), developed to support aircraft multidisciplinary design, analysis, and optimization. Designers can use the MMG as an advanced modelling tool to swiftly generate geometrical models of many and diverse aircraft configurations and variants, by combining and adjusting a limited number of parametric objects, called high-level primitives. Besides capturing the geometric aspects of the design, the MMG also has the capabilities to automate a large part of the lengthy and non-creative pre-processing activities involved in the design verification process. The proposed KBE application has demonstrated to be a valuable solution for some of the critical needs indicated by the multidisciplinary design and optimization community, namely a flexible and robust generative tool to increase the level of automation in aircraft design, including the development of novel configurations; the exploitation of high-fidelity analytical tools already in the early design phase; the management of the design activities across distributed networks of disciplines specialists.