The aircraft design process has several phases, the first of which is conceptual design. In this phase, models describing an aircraft concept's properties are used to evaluate its function and identify designs that meet given requirements. Fighter aircraft are generally expected to be capable of communicating, delivering munitions and gathering data about their environment to gain situational awareness. The ability to avoid detection by hostile sensors can also be important, depending on the aircraft's role. The design process of the aircraft itself has usually focused on an aircraft's flight performance and ability to carry loads, e.g. munitions and extra fuel. While acceleration, rate of turn, maximum speed, and operational range are important parameters, the success of military missions also depends on sensor capabilities and signature levels. However, sensor installation and signature reduction measures can affect the aircraft and its flight performance. Whether an aircraft concept fulfills the requirements given is evaluated using simulations in appropriate scenarios. The concept's performance is assessed using models of aircraft properties, weapon properties, sensor capabilities and signature levels. Models of the aircraft properties are usually connected dynamically, and respond to changes in such things as the size of the concept. However, sensor and signature models are often the result of a separate optimization process and are only statically connected to the aircraft model. The complete aircraft model can be improved by introducing sensor and signature models that dynamically describe both their functions, and their impact on the aircraft. Concurrent design of all the aircraft properties may improve the quality of results from scenario simulations. When models used in simulations contain parameters coupled to each other, analysis of the resulting data is particularly important because that is what supports a decision maker's design choice. Sensor and signature models, in some cases combined with flight performance models, have been used to test methodologies intended for use in conceptual aircraft design. The results show that even seemingly simple models can produce results that can make a significant contribution to the aircraft design process. v vi Preface Five papers are included in the thesis. All papers are published or presented at conferences. I Military utility: A proposed concept to support decision-making