Structuraldesign of a variable span morphing wing: analysis, optimisation and study of the effect of design parameters on its mass

• Main Author: Sousa, Diogo Bento
• Publication Date: 2017
• Format: Master thesis
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10400.6/7957
• topic: Aerodynamic Analysis; Aerofoiloffset; Aircraft Design; Apdl-Ansys; Catia V5; Data Fitting; Fembased Structural Optimization; Matlab; Morphing Technologies; Parametric Study; Rpas; Variable-Span Wing (Vsw); Wing Mass Function; Xfoil.

A continuing search for design methods pointing towards optimising flight overall efficiency renewed interests in unconventional design solutions for aircraft future demands. In line with several other unconventional designs, the development of morphing wing technologies for in-flight shape adaptation is one of the richest and most challenging interdisciplinary fields researchers have focused in recent years. A detailed guide on a telescopic wing design and sizing is presented, effects of design parameters on wing structural mass are investigated and a full mass predicting function is developed to be applied on future telescopic wing designs. AtelescopicwingisdesignedforthenewOlharapoIII RPASoperatingintherangeofspeedsfrom about the stall speed of 11 m/s to 40 m/s. This wing is a high mounted, straight telescopic wing, without ailerons. The current version has a wingspan of 3.554 mfor a RPAS of 150 N. Its design makes use of aerodynamically optimised aerofoils and winglets, a minimum-mass optimised structure and actuation system and also, comprises morphing high-lift surfaces. The established actuation system has a mass of 0.325 kg. Proper aerofoil design to ensure geometric compatibility and good aerodynamic performance is performed. Trends on geometric and aerodynamic characteristics of resulting inward and outward offset aerofoils are discussed. Further wing characteristics are defined and CAD technical drawings are performed. Physics-based structural analysis and minimum mass optimisation, constrained by strength and stiffness limits, are built in APDL and solved in ANSYS. FEM associated errors are analysed and a mesh convergence study is carried. The resulting VSW is sized to 1.0 kg. Wing skin converged for a thickness of 2.24 mm. IFW and OMW spar caps are sized to a width of 21.7 mm and 0.8 mm, respectively. Morphing concepts typically present mass penalties due to their inherent complexity both in the load carrying structure and in systems that perform morphing. Simple yet suitably accurate mass predicting methods to aid design telescopic wings at early design phases, as well as to assess their benefits over conventional wings, are non-existent in the scientific community. A parametric study, which encloses an optimisation loop performing FEA, is implemented to obtain wing structural mass databases. The considered design parameters are maximum wingspan, wing chord, span variation ratio, aircraft take-off weight and flap's chord ratio. Mass functions are created by fitting multivariable high order polynomials to the obtained data. A MATLAB® script is developed to compute the regression models, obtain the polynomial coefficients and performpost-processing calculations. Fromthe latter, a screening to the significant terms and a goodness-of-fit assessment are conducted. A nonlinear ERR-Causality regression method is employed and a high fitting accuracy is accomplished. Conclusions on the effects of design parameters on wing structural mass are taken from ensuing partial derivatives and 3D plots. Moreover, a preliminary VSW full mass predicting function is developed from adding mass contributions of secondary structural components, actuation system and non-optimum effects to the structural mass function.