Application of Aero-Structural Wing Design under Hi-Fi-Based Longitudinal Static Stability Constraints

Abstract

Over the past decade, growing attention was given to exploring the benefits of engaging numerical multidisciplinary design optimization (MDO) in aircraft design. MDO uses optimization methods to solve design problems incorporating a number of disciplines. The expected benefit of MDO lies in accelerating the aircraft development process and reducing its costs. Like any other optimization problem, a MDO task in aircraft design aims at improving a specific objective function while maintaining thousands of aircraft performance and geometrical constraints. Typical examples of geometrical constraints are the sizes of the landing gear or the fuel tank. The structural integrity constraints or the landing and take-off constraints, such as approach speed and take-off field length are examples on performance constraints. One vital performance constraint, that is inevitable to consider while designing a new aircraft configuration, is the longitudinal static stability constraint. It refers to the aircraft’s stability about its lateral axis. At DLR, the cross-institute gradient-based MDO chain [1,2] employs RANS-based methods to predict the aeroelastic cruise performance. Moreover, mid-fidelity methods are employed to predict the loads and structure sizing process and some empirical equations govern the overall aircraft design constraints. One of the targets of this highly cooperative effort is to increase the predictability of the multidisciplinary design analysis (MDA) tools that are used in the MDO chains. This target plays a great role in bringing MDO closer to the hands of practitioners. The aim of this study is to investigate the newly implemented RANS-based prediction of the longitudinal stability constraint within MDO. At DLR, this constraint was until recently predicted via low-fidelity empirical methods which are sensitive only to the global shape of the wing planform, the size of the tail, and their positions along the fuselage. The RANS-based prediction of this constraint was implemented for the gradient-based MDO chain, using the adjoint approachi [3] and was tested on a matured research aircraft, while varying the wing profiles and two planform parameters; its sweep and aspect ratio. This study will investigate the engagement of this constraint on a newly developed aircraft [4] while performing aerostructural optimization of the wing profiles and planform and will show the effects towards engaging the size of the horizontal tail plane as a design parameter in MDO.