Flapping Flight: High Thrust and Propulsive Efficiency due to Forward Gliding Oscillations

Abstract

T HE flapping flight mechanism can provide revolutionary operation capabilities for tomorrow’s micro air vehicles (MAV) [1]. The unsteady aerodynamics of the flapping flight is vastly different from traditional fixed-wing flyers and allows for high maneuverability in cluttered environments [2]. To provide this maneuverability, high rates of thrust and propulsive efficiency beyond normal cruise flight conditions are necessary. Observations of flying birds in nature [3] revealed that birds are not only using the classic combined pitch/plunge motion for flapping flight but also incorporate an additional gliding motion of their wings in the direction of the free-stream velocity U1. The present note demonstrates that these gliding motions increase significantly both thrust and efficiency of flapping flight. For this purpose, unsteady Reynoldsaveraged Navier–Stokes (URANS) computations are used to estimate the flow around a flapping, birdlike airfoil SG04 [4] at a Reynolds number of 10 with fixed transition.