Unsteady Aerodynamics study of Plunging Airfoils at various frequencies and amplitude at low Reynolds Numbers of the order of Insect/Birds flight is of importance to the design and flying of Micro Aerial Vehicle to meet the requirement of Para-military forces, Border Security forces and other homeland service forces. A new methodology has been developed for the analysis of plunging airfoil based on CFD tool 'OpenFoam'. Since the experimental data available for NACA 0012 Airfoil is in plunging motion, conditions relevant to the experiment are chosen for the analysis. As plunging velocity increases there is an increase in thrust coefficient. Similar trends are observed from experiment and commercial CFD code, Fluent. However, OpenFoam agreement with experiment is better and comparable with commercial CFD code. Also from the analysis of NACA 4412 airfoil, it has been found that Cl, Cd behavior is unimodal at low frequency and multimodal at high frequency plunging motions.