The Effect of Aerodynamic Braking on the Inertial Power Requirement of Flapping Flight: Case Study of a Gull

There has been an unresolved question of whether there is any significant degree of aerodynamic braking during wing deceleration in the flapping flight of birds, with direct analogies existing with flapping micro air vehicles. Some authors have assumed a complete conversion of kinetic energy into (useful) aerodynamic work during wing deceleration. Other authors have assumed no aerodynamic braking. The different assumptions have led to predictions of inertial power requirements in birds differing by a factor of 2. Our work is the first to model the aerodynamic braking forces on the wing during wing deceleration. A model has been developed that integrates the aerodynamic forces along the length of the wing and also throughout the wing beat cycle. A ring-billed gull was used in a case study and an adult specimen was used to gather morphometric data including a steady state measurement of the lift coefficient. The model estimates that there is a 50% conversion of kinetic energy into useful aerodynamic work during wing deceleration for minimum power speed. This aerodynamic braking reduces the inertial power requirement from 11.3% to 8.5% of the total power. The analysis shows that energy conversion is sensitive to wing inertia, amplitude of flapping, lift coefficient and wing length. The aerodynamic braking in flapping micro air vehicles can be maximised by maximising flap angle, maximising wing length (for a given inertia), minimising inertia and maximising lift coefficient.