Coupled flight dynamics and aeroelasticity research of flexible flying wing aircraft with folding wingtips

Abstract

In recent years, increasing attention has been paid to the application of folding wingtips on transport aircraft. However, there is a lack of research about folding wingtips on unmanned aerial vehicles (UAVs). This study investigates the effects of folding wingtips on the flight dynamics and aeroelastic stability of high-aspect-ratio (HAR) flying wing UAVs. A modeling method of coupled flight dynamics and aeroelasticity (CFA) in a mean-axis frame is established, integrating the doublet lattice method (DLM) and rational function approximation (RFA). Validated against published data, the method is used to analyze 11 aircraft configurations varying in wingtip folding angles. It was found that folding wingtips significantly alter modal characteristics, inducing frequency variation and mode reordering, which in turn modify flutter phenomena. It is also demonstrated that the body freedom flutter (BFF) speed increases as the folding angles increase, thereby enhancing flight safety. Furthermore, in longitudinal dynamics, large folding angles degrade static stability margins, and there is a positive correlation between the pitching damping ratio and folding angles. Finally, the comparison of the time responses of flight attitudes, with and without considering the structure elasticity, reveals that the coupling between flight dynamics and aeroelasticity yields pronounced oscillatory behavior with different convergence rates, posing greater challenges for flight control systems. The findings emphasize the necessity of considering the effects of folding wingtips and structural elasticity on the flight dynamics and aeroelastic stability in flight control strategies.