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Flapping wing propulsion offers unrivalled manoeuvrability and efficiency at low flight speeds and in hover. These advantages are attributed to the leading edge vortex developing on an unsteady wing, which induces additional lift. We propose and validate a manipulation hypothesis that allows prolongation of the leading edge vortex growth phase, by delaying its detachment with the aid of flow control. This approach targets an overall lift increase on unsteady airfoils. A dielectric barrier discharge plasma actuator is successfully used to compress secondary structures upstream of the main vortex on a pitching and plunging flat plate. To determine flow control timing and location, the tangential velocity on the airfoil surface is used, which is also used to quantify topological effects of flow control. This flow control is then tested for different motion kinematics and on a NACA 0012 airfoil. Significant increase of the peak circulation of the leading edge vortex of about 20% for all cases with flow control indicates that this approach is applicable for various kinematics, dynamics and airfoil types.