A comprehensive linearized aerodynamic approach is elaborated to summarize the author and coworkers effort to model flapping bi-and quad-wing ornithopter in producing lift and thrust for forward flight. The objective of the modeling is to assess the extent of linearized aerodynamic approach in mimicking mid-sized flapping Biosystems like bats and birds. Viscous effect and leading-edge suction is utilized in the basic Unsteady Aerodynamic Approach. Analysis is carried out by differentiating the pitching and flapping motion phase-lag and studying its respective contributions to the flight forces. Observation based heuristic modeling of Leading Edge Vortex is developed to study its influence on Lift and Thrust. The influence of the Strouhal number on the propulsion generation is also simulated and studied. Encouraging results are discussed in comparison with existing models in the literature, with a view to gain insight in developing a practical ornithopter model. The objectives and contributions of this work are to present and asses the merit of a simple approach based on first principles in revealing particular characteristics, and to investigate some critical and relevant characteristics that could be tackled with a simple approach.