No abstract

The design of aircraft has evolved over time from the classical design approach to the more modern computer based design method utilising multivariate design optimisation. In recent years aircraft concepts and configurations have become more diverse and complex thus pushing many synthesis packages beyond their capability. Furthermore, many examples of aircraft design software focus on the analysis of one particular concept thus requiring separate packages for each concept. This can lead to complications in comparing concepts and configurations as differences in performance may originate from different prediction toolsets being used. This paper presents the GENUS Aircraft Design Framework developed by Cranfield University's Aircraft Design Group to address these issues. The paper reviews available aircraft design methodologies and describes the challenges faced in their development and application. Following this, the GENUS aircraft design environment is introduced, along with the theoretical background and practical reasoning behind the program architecture. Particular attention is given to the programming, choice of methodology and optimization techniques involved. Subsequently, some applications of the developed methodology, implemented in the framework are presented to illustrate the diversity of the approach. Three special classes of aircraft design concept are presented briefly.

Background: In the interest of improving aircraft performance, studies have highlighted the benefits of Box wing configurations over conventional cantilever aircraft configuration. Generally, the greater an aircraft's average thickness to chord ratio (τ), the lower the structural weight as well as volumetric capacity for fuel. On the other hand, the lower the ., the greater the drag reduction. A review of patents related to the Box-wing aircraft was carried out. While methodologies for optimizing wing thickness of conventional aircrafts have been studied extensively, limited research work exist on the methodology for optimizing the wing thickness to chord ratio of the Box wing aircraft configurations. Methods: To address this gap, in this work, a two stage optimization methodology based on gradient search algorithm and regression analysis was implemented for the optimization of Box wing aircrafts wing thickness to chord ratio. The first stage involved optimizing the All Up Mass (AUM), Direct Operating Cost (DOC) and Zero Lift Drag Coefficients (CDO), with respect to the aft and fore sweep angle for some selected τ values. At the second stage, a suitability function (γ) was optimized with respect to the aft and fore sweep angle for some selected τ values. A comparative study was further carried out using the proposed methodology on similar size cantilever wing aircraft. Results: From the result, an optimal τ value was reached. Also the τ value for the cantilever aircraft found based on the proposed methodology was similar to the true τ value of the adopted aircraft, thereby validating the methodology. Conclusion: Based on the optimal τ value reached from this work, the Box wing aircraft are suitable for thin airfoils.

Background: Induced drag accounts for significant percentage of cruise and total aircraft drag. In agreement with Prandtl’s theorem, the ideal arrangement for minimum induced drag is a closed biplane design. Past studies have implemented fixed tip fins for closed biplane design, with the reduction of induced drag associated with fixed tip fin found to be less than optimal. A review of patents related to the box-wing aircraft was carried out. Methods: In an attempt to further reduce the induced drag for box wing aircraft, this study proposed the implementation of Active Tip Fins (ATF) for aircraft design. Athena Vortex Lattice (AVL) software was used to simulate the induced drag associated with AFT in comparison with that of a fixed tip fin. Results: From the result, the ATF design shows a superior induced drag reduction. Conclusion: ATF design is a novel concept that has the potential of improving box wing aircraft performance.