Dynamics of hinged wings in strong upward gusts
A birds wings are articulated to its body via highly mobile shoulder joints. The wings possess an impressive range of motion, which allows for movements that can modulate the production of aerodynamic load in flight. This is crucial for stability and control--particularly in gusty or turbulent environments. In this study, we develop a dynamics model to examine how a bird-scale gliding aircraft can use wing-root hinges (analogous to avian shoulder joints) to reject the initial impact of a strong upward gust. Our idea requires that the spanwise centre of pressure and the centre of percussion of the hinging wing start, and stay, in good initial alignment (the centre of percussion here is related to the idea of a sweet spot on a bat, as in cricket or baseball). We propose a method for achieving this rejection passively, for which the essential ingredients are: (i) well-considered lift and mass distributions; (ii) constant-torque hinges; and (iii) a wing whose sections stall softly. When configured correctly, the gusted wings will first pivot on their hinges without disturbing the fuselage of the aircraft, affording time for other corrective actions to engage. We expect this system to enhance the control of aircraft that fly in gusty conditions.