Digital particle image velocimetry (DPIV) is employed to quantify instantaneous flow around the wings and deduce corresponding aerodynamic properties such as lift and drag coefficients.
Underactuated flapping wings
Achieving the desired kinematics with the minimum weight and complexity of wings and actuating structures has led to a strong interest in adopting passively pitching flapping wings for small-scaled flying vehicles. The pitching angle of this kind of flapping wing can be passively modulated by an elastic hinge acting as a torsional spring which balances the moments resulting from fluid mechanic and inertial forces. The successful implementation of such underactuated flapping wings strongly depends on their ability to operate efficiently in wind disturbances. This raises important questions of how the time-history of the wing pitching motion, and consequently unsteady aerodynamic effects are altered by freestream disturbances compared to quiescent hovering.
The passive-pitching flapping wing in quiescent hovering.