High-fidelity Aerostructural Optimization of a High Aspect Ratio Tow-steered Composite Wing

In the last 30 years since their introduction into aerospace applications, composites have become increasingly used, making up as much as 50% of modern aircraft by weight. Considering this fact, it is surprising that most aircraft today are only scratching the surface of the true potential of composite technology with traditional uniaxial fibers. With the introduction of Automated Fiber Placement machines (AFP), the tow direction in laminae is now allowed to be steered spatially throughout each layer. This process is known as composite tow steering and has been shown to have improved performance over its uniaxial fiber counterpart with no additional weight penalty. With modern aircraft wings moving toward higher aspect ratios, which inevitably leads to larger deflections, it is reasonable to assume that a tow-steered composite structure can be tailored to outperform its unsteered counterpart. However, given the highly coupled nature of the aerodynamics and structural response of the problem it is not obvious nor intuitive to find the composite fiber pattern that would yield an optimum result. To address this issue, we develop a framework for the simultaneous design of aerodynamic shape, structural sizing, and tow steering angles, while considering the wing flexibility. The aerodynamics are modeled using RANS CFD, while the structure is analyzed using a detailed finite-element model. Using this framework we perform two fuel burn optimization problems are performed for a high aspect ratio (AR = 13.5) baseline wing: one using a tow-steered structure and another with no steering, unsteered. The optimization was performed with respect to tow-steering design variables, wing airfoil shapes and twist, as well as structural thicknesses. Along with including design variables which controlled the tow-steering parameterization, geometric shape variables were also included to vary the shape of the wing. The tow-steered wing was able to decrease the wing mass by 13% relative to the baseline unsteered wing.