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As the time between different development projects of new aircraft (a/c) extends, experienced personnel in the field of basic a/c system design are difficult to employ when being on the onset of a new design. Further on basic a/c system design is a field neglected in literature and in the educational system. A text is under development that summarizes the Saab experience of the complete fuel system design with respect to the fighter a/c Viggen and Gripen, the commuter a/c 340 and 2000, the trainer a/c SK60 and also the conceptual a/c B3LA. This paper is an extract of this text and describe early considerations that have to be made when designing a fuel transfer system. Emphasis is put on the top requirements on a/c level.

There is an ongoing trend in the European Military a/c industry towards cooperation between nations when purchasing and between manufacturers when developing and producing a/c. Different manufacturers at different locations develop different parts or sub-systems. When using this approach a vital part of a fast and precise system evaluation is the use of simulation models. In order to stay competitive it is not only sufficient to be able to build large simulation models but also to do it fast. This paper describes the conclusions regarding a modeling strategy of large fluid systems drawn from the building of a simulation model of the JAS 39 Gripen fuel system. An overall process is suggested into which the activities of building a model are fitted. This is however not the main objective; it is more important to identify the different issues and activities at the engineering level.

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.