Abstract: The unsteady aerodynamic loads on wings with lending edge separation in inviscid incompressible flow are calculated using vortex-lattice method. The calculated results of delta and double delta wings with oscillating L.E. flaps not only show influence upon aerodynamic response as a result of different oscillatory frequencies and hinge line swept-back angles, but also reveal the phenomena of aerodynamic lag and nonlinear interaction associated with unsteady vortex flows.