© 1995, by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Unsteady aerodynamic interference effects and thrust generation on a flapping/stationary airfoil combination in tandem are studied parametrically. A zonal Navier-Stokes solver is employed to compute the unsteady flowfield. The computational domain is discretized with overlapping uniform grids generated around each airfoil. The thrust generation and the propulsive efficiency of the flapping/stationary airfoil combination is found to be a strong function of reduced frequency and the amplitude of the flapping motion of the leading airfoil. The maximum propulsive efficiency of a NACA0012 airfoil combination has been computed to be 70% at a reduced frequency of 0.75 and a flapping amplitude of 0.20 chord lengths when the airfoils are separated by about two chord lengths.