Aeroelastic Tailoring of High Aspect Ratio Wings Using Novel Structural Layouts and Advanced Composite Materials

Abstract

Increasing demand in commercial aviation requires continuous improvement in aircraft efficiency. More efficient aircraft are required to reduce operating costs, increase efficiency, reduce emissions for environmental impact, and reduce fuel burn. To cope with this, novel aircraft designs need to be considered for potential benefits. High aspect ratio wings have been receiving increased attention due to their increased aerodynamic efficiency. However, the increased flexibility of the high aspect ratio wing makes it susceptible to aeroelastic instabilities. Thus, aeroelastic tailoring is required to optimize aeroelastic performance, improving the overall efficiency without significant weight and stability penalties. This thesis will utilize two main methods of tailoring: Use of novel structural layout by means of a strut and modification of internal wing structure, and advanced composite materials. Strut-bracing has been used in aircraft in the past, but use declined and the conventional low-wing cantilever wing became popular in commercial aircraft. Boeing SUGAR Volt concept, which Boeing aims to produce by 2035 uses a high aspect-ratio strut braced wing. Composite material is becoming more common in aircraft, as some have about 50% of the structure made of composite material. Analysis was done numerically using MSC Nastran, utilizing its aeroelasticity analysis tools. Initial study was conducted on a high aspect ratio (AR = 16) AL-2024 flat-plate to study general trends in structural performance and critical speed. A strut with no sweep, clamped at the root and the wing was chosen. Strut location at midspan near the leading edge of plate provided most favorable bending-twist coupling. Carbon fiber reinforced plastic (CFRP) with a sequence of [0,45]s (forward swept plies) provided even more favorable bending-twist coupling due to D16 term. This result was used as a starting point for high aspect ratio (AR = 19.35) wingbox analysis. Analysis of the strut location confirmed the optimal location near the leading edge, mid span of the wingbox. A ply orientation of [45,78.75]s was optimal and provided favorable bending-twist coupling due to D16 term as well. Rib orientation of 15 increased the coupling and further reduced structural parameters and increased the critical speed. Gust analysis of varying gust gradients showed great reductions of the strut-braced CFRP wing when compared to the AL-2024 wing with and without a strut. Overall, aeroelastic tailoring of the high-aspect ratio wing reduced the weight by 16.5%, maximum shear force by 66.1%, and bending moment by 85.1%. Moreover, the critical speed increased by 132.33%. The gust response benefitted greatly, as the composite wingbox with a strut showed a decrease between 46.04% and 57.28% for a gust margin between 1.5m and 3m in maximum shear force, and a decrease between 72.79% and 80.01% for a gust margin between 1.5m and 3m in maximum bending moment when compared to the no strut aluminum case. Overall, aeroelastic tailoring was capable of improving the efficiency of the wingbox.

Date of Award	7 May 2024
Original language	American English
Supervisor	Rafic Ajaj (Supervisor)