Experiments were performed using simplified flapping wing kinematics that is representative of a low Reynolds number flyer. Measurements were made at half-span in order to avoid three-dimensional effects. A Pegasus laser was used to illuminate a chordwise slice of the wing at half-span. Leading-edge vortices (LEV) circulation is approximately equal and opposite to TEV circulation in the first chord and a half of travel after an impulsive start. This suggests that the aerofoil's bound circulation is negligible shortly after an impulsive start when an LEV is formed. An absence of bound circulation is consistent with previous observations of the net force acting normal to the wing chord. The large lift observed immediately after an impulsive start must therefore be caused by a combination of noncirculatory effects and the circulatory lift generated by the LEV-TEV pair, rather than by bound circulation
