Aeroelastic Design and Analysis of a Bioinspired Flexible Airfoil

Low-altitude fliers like birds and small unmanned aerial vehicles are prone to large flight disturbances as a result of chaotic and unpredictable flow conditions in the atmospheric boundary layer. Unlike birds, which mitigate undesirable changes in aerodynamics through active unloading of their wings and passive compliant properties of feathers, low-altitude UAVs are at the mercy of the environment which can result in unstable flight. The current state-of-the-art for aircraft aerodynamic alleviation or unloading typically uses control surfaces to mitigate unwanted effects and retain stability. However, this requires a series of sensors, controllers, and actuators to monitor and adapt to these changes and as a result, may not warrant an instantaneous response. Inspired by the flexibility of bird wings, flexible airfoils have been shown to delay separation, enhance lift-to-drag ratio, and modulate free stream fluctuations. The results presented here assess the structural response of a bioinspired flexible airfoil under aerodynamic loading and demonstrate that the trailing edge displacement is largely a function of the Reynolds number and is relatively independent of the angle of attack. These results strongly support the hypothesis that biological wings passively unload aerodynamic forces under increased wind gusts, while largely remaining stable with variations in inclination. However, the displacement undergoes a predictable snap-through-like phenomenon as the angle of attack transitions from positive to negative values, and some consistent decrease in displacement is observed at the onset of stall. These results motivate existing and future research into tailorable stiffness airfoils.