Aerodynamic Nonlinearity Effects on Flight Dynamics of a Very Flexible Flying Wing

High-aspect-ratio (AR) wings are the prominent feature of very flexible aircraft, and greater AR designs are being explored for enhanced flight efficiency in civil aviation. However, the impact of higher flexibility on the aeroelastic behavior of fixed-wing aircraft still needs to be fully understood. This paper assesses the effects of aerodynamic nonlinearities from flow separation on the maneuvering and gust response of a high-aspect-ratio flying wing using low-order models. Three aerodynamic formulations are evaluated: a linear model without stall effects, a piecewise linear model with steady-stall characteristics, and a nonlinear model accounting for dynamic-stall phenomena. All models perform similarly during maneuvering oscillations near stall conditions, but the dynamic-stall model foresees flight dynamic instabilities poststall, which are not seen in other models given the same maneuver input. Under a limited number of discrete and continuous gust disturbances, the model without stall effects behaves nonconservatively, whereas the steady-stall model is more conservative compared to the dynamic-stall model, with respect to the prediction of flight instabilities. These outcomes highlight the importance of accounting for aerodynamic nonlinearities in understanding the flight dynamics of very flexible aircraft under moderate-to-high angle-of-attack excitations.