In considering aircraft design, it is very important to effectively size the tail configuration for stability and control. Multidisciplinary design optimization (MDO) focuses on the use of numerical optimization in the design of systems with multiple subsystems or disciplines of consideration. However, MDO uses deterministic calculations, and does not consider the uncertainties that arise from the employed analyses, including errors due to linearization and simplification. For problems with inadequate input data, the possibility-based design optimization (PBDO) scheme can be implemented in its stead to achieve reliable designs using membership functions for epistemic uncertainties. A multidisciplinary, possibilistic approach is presented to define the sizing of the empennage configuration of a twin-engine propeller-driven aircraft by changing shape parameters while satisfying the design requirements given the tailless aircraft configuration, the flight conditions, and various uncertainties. The corresponding disciplines are aerodynamics, stability and control, propulsion and weight and balance. Herein, different design requirements are considered including longitudinal/lateral/directional trim and stability characteristics, manufacturing and controllability criteria, handling qualities, operational requirements, airworthiness and survivability. The resulting aerodynamic characteristics and flight dynamic stability outcomes show that the optimized tail configuration for the proposed aircraft fully complied with airworthiness requirements and predefined constraints while considering several uncertainties due to the use of early-stage statistical estimations. The proposed approach can be used to enhance the preliminary design of multi-engine propeller-driven light aircraft where only low-fidelity, statistical estimations are available. The resulting output is not only an optimized aircraft configuration, but one where the stability of the design has been ensured. In this work, the aerodynamic characteristics have been determined using a validated semi-empirical program called MAPLA, developed for light aircraft designs and development in the preliminary design phase. Furthermore, the optimization framework consists of a deterministic optimizer that runs sequentially with a possibility assessment algorithm.
Recent development in Electric Vertical Take-off and Landing (eVTOL) aircraft makes it a popular design approach for urban air mobility (UAM). When designing these configurations, due to the uncertainty present in semi-empirical estimations, often used for aerodynamic characteristics during the conceptual design phase, results can only be trusted to approximately 80% accuracy. Accordingly, an optimized aircraft using semi-empirical estimations and deterministic multi-disciplinary design optimization (MDO) approaches can be at risk of not being certifiable in the detailed design phase of the life cycle. The focus of this study was to implement a robust and efficient possibility-based design optimization (PBDO) method for the MDO of an eVTOL tilt-wing aircraft in the conceptual design phase, using existing conventional designs as an initial configuration. As implemented, the optimization framework utilizes a deterministic gradient-based optimizer, run sequentially with a possibility assessment algorithm, to select an optimal design. To achieve this, the uncertainties which arise from multi-fidelity calculations, such as semi-empirical methods, are considered and used to modify the final design such that its viability is guaranteed in the detailed design phase. With respect to various requirements, including trim, stability, and control behaviors, the optimized eVTOL tilt-wing aircraft design offers the preferred results which ensure that airworthiness criteria are met whilst complying with predefined constraints. The proposed approach may be used to revise currently available light aircraft and develop eVTOL versions from the original light aircraft. The resulting aircraft is not only an optimized layout but one where the stability of the eVTOL tilt-wing aircraft has been guaranteed.
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