A Conceptual Design and Optimization Method for Blended-Wing-Body Aircraft

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This paper details a new software tool to aid in the conceptual design of blended-wingbody aircraft. The tool consists of four main modules. In the preliminary sizing model a class I estimate of the maximum take-off weight, wing loading, and thrust-to-weight ratio is calculated. This information is used together with an initial guess of the 30 design variables that to form a geometric model of the aircraft. From this geometric model four disciplinary models are derived: an aerodynamic model, a model of the wing box structure, a model for the cabin, and a model for the fuel tank. In the subsequent analysis module refined weight estimation for the operating-empty weight is being calculated, as well as the center-of-gravity shift during loading, the static margin, the main stability and control derivatives, and the harmonic range. In the last module, these analysis results are compared to 27 nonlinear constraints stemming from the top-level requirements and the aviation regulations. A gradient-based optimization routine is employed to find a combination of the design variables that satisfies all constraints while optimizing for harmonic range at constant maximum take-off weight. Between 20 and 60 iterations are required to achieve convergence. The tool has been set up to allow for maximum configurational flexibility such as forward-swept outer wings, under-the-wing engines, and twin vertical tails.