Based on flow visualization experiment and particle image velocimetry (PIV) measurement

the shedding vortex of flapping wing model with single degree of freedom was studied experimentally and several conclusions were obtained as follow. (1) A horn-shape shedding vortex with a wingspan-direction movement is generated around the leading edge as well as the trailing edge during flapping. (2) The shedding vortex leads to alternative pressure differences with unequal scalar on both sides of the flapping wing. (3) Both attack angle and inflow speed are not zero

which are essential factors to the lift generation of study object. (4) The maximum circulation of the shedding vortex appears at about 3/5 of the upward flapping journey

as well as the downward flapping journey. (5) The circulation of the shedding vortex is proportional to the flapping speed. (6) The flapping wing generates more work during the downward flapping journey

as compared with the upward flapping journey

resulting in the generation of lift within a whole flapping cycle.