Design and Structural Optimization of a Flying Wing of Low Aspect Ratio Based on Flight Loads

Abstract

The design process for new aircraft configurations is complex, very costly and many disciplines are involved, like aerodynamics, structure, loads analysis, aeroelasticity, flight mechanics and weights. Their task is to substantiate the selected design, based on physically meaningful simulations and analyses. Modifications are much more costly at a later stage of the design process. Thus, the preliminary design should be as good as possible to avoid any “surprises” at a later stage. Therefore, it is very useful to include load requirements from the certification specifications already in the preliminary design. In addition, flying wings have some unique characteristics that need to be considered. These are a differentiating factor with respect to classical, wing-fuselage-empennage configurations. The aim is to include these requirements as good and as early as possible. This is a trade-off, because the corresponding analyses require a detailed knowledge and models, which become available only later during the design process. New methodologies in the form of a comprehensive, algorithmic design process and a parametric aeroelastic modeling are developed. The first aspect of this work concentrates on the gust encounter of flying wings. Next to external disturbance, a controller for the pitching motion of marginally stable or unstable flying wings has an influence. The combination of both presumably increases loads. The gust encounter of flying wings is studied first for the open loop, then for the closed loop system and for variable longitudinal stability. The second focus is the comparison of low fidelity panel methods with higher fidelity aerodynamics. Similarities and differences between VLM and CFD based maneuver loads are shown. Then, all maneuver load cases are calculated using high fidelity aerodynamics within the preliminary design process. Application of parametric modeling and an algorithmic design process result in a final aeroelastic model, optimized for minimum structural weight.