09:40   Aeroelastic design 2 Chair: Thomas Wilson 09:40 30 mins Assessment of aeroelastic stability of high aspect wing aircraft during the preliminary design Sunpeth Cumnuantip, Matthias Schulze, Wolf R. Krueger Abstract: One concept to reduce an aircraft's fuel consumption is to increase wing aspect ratio. Although such slender wings have low induced drag, a number of aeroelastic issues arise. As an example, high aspect ratio wings are relatively soft in bending and torsion when compared to conventional designs. These structural dynamic properties can lead to a reduction of the flutter speed. In the current research projects VirEnfREI [1] and UP Wing [2], the Institute of Aeroelasticity of the German Aerospace Center performs the aeroelastic stability assessment of transport aircraft configurations equipped with high aspect ratio wings during the preliminary design phase. This paper will compare results of preliminary stability assessments and discuss influences from the structural design on the dynamic behavior of the wings. The in-house simulation-based tool cpacs-MONA [3] is used for the flutter assessment. The aerodynamic and structural simulation models used for the analysis are created by the in-house model generator ModGen [4]. Thus, preliminary but representative models are available which allow a detailed analysis of aeroelastic questions early on in the design process. Both the VirEnfREI and the UP Wing aircraft have the same wing aspect ratio of more than 15, however, they differ in the internal structure of the wing, resulting from different aerodynamic profiles. The dominant structural eigenforms for both configurations are the engine pitching mode (Figure 1, left), coupling with the wing bending mode and the wing torsional mode (Figure 1, right). Figure 1: Engine pitching eigenmode, left, and 1st symmetric wing torsion eigenmode, right, of the VirEnfREI aircraft The initial comparison of the result has shown that the flutter velocity of the UP Wing configuration is higher compared to the VirEnfREI configuration. An important factor for the difference in flutter speed is the increased spar height of the UP Wing configuration, resulting in a stiffer wing in bending and torsion. The engine pitching mode also has found to play a dominant role in those high aspect ratio wing designs, making pylon layout another critical design aspect. In the full paper, a short description of the design and analysis process will be given, followed by a discussion of the influence of the preliminary wing aerodynamic and wing structural designs on the aeroelastic characteristics of the aircraft. References 1. https://www.dlr.de/as/en/desktopdefault.aspx/tabid-18287/29084_read-76559/ 2. https://www.dlr.de/ae/en/desktopdefault.aspx/tabid-19296/31885_read-86706/ 3. M. Schulze, J. Neumann, and T. Klimmek, “Parametric Modeling of a Long-Range Aircraft under Consideration of Engine-Wing Integration” in Aerospace, 8 (1), Page 1-20. Multidisciplinary Digital Publishing Institute (MDPI). ISSN 2226-4310, 2021. 4. T. Klimmek, "Parametrization of Topology and Geometry for the Multidisciplinary Optimization of Wing Structures" in European Air and Space Conference, 2009. 10:10 30 mins On the aeroelasticity of high aspect ratio strut-braced wings: A parametric study Hamad Almarzooqi, Rafic Ajaj, Wesley Cantwell Abstract: The aviation industry is increasingly adopting high aspect ratio (AR) wings to meet the demands for more efficient and emission-friendly aircraft. High AR wings increase aerodynamic efficiency but come at the cost of structural and aeroelastic issues [1]. A candidate solution for these aeroelastic issues is strut-bracing. For example, the Boeing Sugar VOLT (AR = 19.55 [1]) utilizes strut-bracing at approximately 50% of the span and 15% of the chord[2]. This paper conducts a comprehensive parametric study on a high aspect-ratio (AR = 16) strut-braced flat plate (shown in figure 1) to identify the influence of material and geometric parameters on structural performance and aeroelastic stability. The finite element method is used for structural modelling, the doublet lattice method for aerodynamic modelling, and an infinite plate spline for aero-structural coupling. The analysis is conducted using MSC Nastran and MATLAB. The geometric variables include the location of the strut on the plate, the location of the strut on the fuselage, and boundary conditions on strut ends. The material of the plate is then changed from Aluminum-2024 to Carbon Fibre Reinforced Plastic composite, and the ply orientation and layup are also varied. The location of the strut on the plate is varied chordwise and spanwise, while the location of the strut on the fuselage is either fixed at mid-chord or variable with the location of the strut on the wing. The boundary conditions on the strut end (fuselage-wing) are varied between clamped and pinned (4 combinations). The optimum geometric parameters for the metal plate are found to be clamped-integral boundary conditions, with the variable location on the fuselage. The optimum geometric parameters are applied to the composite plate, and the ply orientation and strut location on the plate are studied. The optimum has a ply layup of [0, −45◦]s, and a strut location at 20-30% of the span, and 30-50% of the chord. This results in a 37% increase in the critical speed, a 71.5% decrease in the max bending moment and 21.35% decrease in shear forces.

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