A new approach in conceptual aircraft design at Cassidian is presented which supports the initial assessment of mass data for a new configuration. It is based on the fast creation of a multidisciplinary analytical model for the description of the complete vehicle and the application of mathematical optimization methods to determine the mass of its structural components, subject to external loading conditions and requirements for the structural stiffness to meet the essential performance constraints. In the first place, this process serves as a tool that helps to find the optimum overall design for the top level requirements like range and payload by a direct coupling of the structural lay out with the vehicle's conceptual design topology and sizing process. Mass data from this process help to confirm and adjust the classic mass estimation process which is based on statistic and semi-empirical data for the individual components of the vehicle but also for the global mass properties like center of gravity location and mass moments of inertia, which are also important during the initial sizing process. In addition, the method help to find optimum solutions for the integration of heavy equipment by directly including the impacts from the attachment loads of these equipment items to the structure, as well as the related interactions with the vehicle's flutter stability. The basic analysis and optimization tool for this process is the Cassidian in-house program LAGRANGE. Its development started 30 years ago, based on the needs to assess and include all relevant design requirements for the stiffness and strength of an aircraft structure into the design process from the very beginning, and at the same time explore and exploit the new possibilities of "tailoring" the strength and stiffness properties of carbon composites. Whereas initial structural analysis and optimization application started by setting up rather simple structural analysis models from "scratch", recent years showed a trend towards first creating computer aided design models and then derive the analysis models from these already rather complex designs. The approach which is described in this paper is different from similar efforts because it starts with the creation of the analytical models by simple input data only. Its results can then be used to create or update the design model. The time to set up the complete model for a new configuration is less than one day, and it takes only minutes or few hours to modify the model for a different geometry, different requirements, or different options for the optimization process. Especially for new configurations, where no or only very limited statistical data exist from comparable projects, this new approach is very useful to support the generation and tracking of mass data, and it helps to minimize these masses by using analytical sensitivities for the essential design variables as functions from a set of complex design requirements from different disciplines. An example is presented for a generic medium-altitude-long endurance (MALE) UAV.
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