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Choosing between concepts is often the most critical part of the design process. Different concepts have different advantages and disadvantages. The concept that is the best choice is most often dependent on the top level requirements. Sometimes there may also be a trade off between concept choice and the top requirements. In aircraft (a/c) fuel system design it has often proved difficult to find the switching point where the superior concept is changed. This sometimes makes the designer conservative and leads to the selection of a concept with too high a penalty. There is also a risk for the opposite and perhaps worse scenario: That the designer strives to reduce weight and cost and therefore, accidentally, chooses an under achieving concept and thus induces large downstream cost if late redesign or retro modifications are necessary. This paper shows how optimization has been successfully used at Saab Aerospace as a tool that supports concept selection.

In this paper modern optimization techniques are applied to an aircraft sizing problem. The paper starts by discussing how optimization could support the design activity and thereafter different methods of formulating the design problem as an optimization problem is discussed. Finally the problem of aircraft sizing is addressed by combining the presented optimization strategy with a simulation model of an aircraft based on mathematical models gathered from the literature. The outcome of the optimization is for example the optimal layout in order to minimize fuel consumption for a specific mission or the trade-off between the number of passengers and the fuel consumption per passenger.