The unsteady aerodynamic characteristics of a flapping wing are studied. The computational model for the unsteady aerodynamics of flapping wing using strip theory approach has been developed and clarified. The proposed method is used to solve the mechanical flying ornithopter (SlowHawk 2) of flexible wing membrane. In doing so, the model is verified through the computations performed on a mechanical flying Pterosaur replica as well as smaller biological species including the Corvus monedula and Larus canus. The effect of aerodynamic parameters on the performance of these biological flight vehicles is studied. The results are compared with those available in the literature, the overall agreement is excellent. The effect of Reduced frequency is studied defining an optimal design points for sustainable flight conditions ( L > W). A manual optimization is performed on the developed code for the SlowHawk 2 in order to get predicted values to be used as an input data for calculating the optimum aerodynamic characteristics of it.